Field Guide to Growing Forage Sorghums

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Growing

Value in the

Green Sorghum for Forage Field Guide

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Field

Notes

Advanta has earned a reputation as the industry leader in developing high-quality forage sorghums by breeding for both agronomic and nutritional traits. Most of our research focuses on developing Brown Midrib (BMR) 6 hybrids. Advanta’s genetics offer the highest nutritional value of any hybrids on the market.

Our research is continuing to provide more digestible forages for ruminant animals. Call us if you have questions or want more information about sorghums for forage.

Ricky Rice, Advanta US forage specialist 800-333-9048

Growing Value in the Green — Sorghum for Forage Field Guide was written and produced by AgriThority® agronomists Dr. Robert Lemon and Dr. Sandy Stewart in cooperation with Ricky Rice, Advanta US forage specialist.

Specific mention of a product is neither an endorsement nor a warranty of performance by AgriThority® or Advanta. Information in this publication related to crop protection chemicals is based on the best available information at the time of printing. In all cases, the actual product label takes precedence over any information contained within this publication. Pesticide labels can and do change. ALWAYS read and follow label instructions when using crop protection chemicals.

The Sorghum Advantage............... 2 Types of Sorghum.....10 Ruminant Nutrition......................... 18 Forage Quality............................... 26 Measuring Forage Quality...... 32 Versatility.......................44 Agronomic Management...... 58 Weed Management........ 72 Herbicide Resistance Management...............86 Insect and Disease Pests............... 90 Irrigation Management............96 Harvesting Forage Sorghums.... 106

Useful Information....................... 114 Sorghum Head Development.......121 Terminology...... 122

CONTENTS

References............... 112

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The Sorghum Advantage 2

Even under extreme drought conditions sorghums continue to provide grazing and exceptional nutrition

Sorghum offers many advantages over other forage crops including drought tolerance and greater water use efficiency; ability to plant later than corn and achieve similar biomass yields; outstanding forage nutritional quality attributes, especially with Brown Midrib 6 traits (BMR 6); and lower soil fertility requirements compared to corn.

WHY SORGHUM?

Sorghum has become a primary component feedstock for dairy and beef cattle operations in the Midwestern and Southwestern states and is rapidly expanding into other regions of the U.S..

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Sorghums with the BMR 6 trait have less lignin than conventional sorghums and are extremely palatable, have high digestibility that rivals corn silage as the choice for cattlemen and dairymen looking to improve animal performance.

WHY SORGHUM?

Sorghums are highly productive plants possessing the C4 photosynthetic pathway

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One of the great benefits of sorghum over corn is the excellent heat and drought tolerance. Sorghum will produce similar yields to corn, but will do so with 30% to 50% less water. With rising energy costs and water conservation concerns across the U.S., sorghum offers a viable economic alternative to corn. A recent study conducted by the Texas AgriLife Extension Service indicated that if producers in the Texas Panhandle converted irrigated corn silage acreage to a sorghum-based system, the region could save over 400,000 acre-inches of water annually. This would lower the cost of irrigation pumping by $2.8 million. Certainly these benefits are not unique to Texas – sorghum can help any producer in almost any region of the U.S. reduce production costs without sacrificing tonnage or forage nutritional quality.

Sorghums used for forage are generally classed as forage sorghum, sudangrass, and sorghum-sudangrass hybrids. Because characteristics differ both across and within these different types, each class offers a producer multiple-use opportunities.

Sorghum Characteristics Sorghums are warm season grasses native to Africa and are classified botanically as perennial plants, although they are typically produced as an annual crop. Their introduction into the U.S. can be linked to Benjamin Franklin who cultivated broomcorn in the late 1700’s and to Johnsongrass (Sorghum halapense), which was brought to South Carolina as a forage crop in 1830.

Sorghums are highly productive plants possessing the C4 photosynthetic pathway.

Plants with the C4 pathway are very efficient at assimilating carbon at high temperatures, which increases productivity in stressful and non-stressful environments alike. Sorghums also are very drought tolerant and have high water-use efficiency.

Growth Habits Sorghums are characterized as summer annual grasses with an upright growth habit; they can reach heights of 15 feet, producing very large amounts of high quality biomass tonnage.

Grain sorghums are much shorter and partition a large part of overall biomass into grain. Typically, grain types have compact panicles producing large amounts of seed, while forage types have more open panicles, produce less seed and much greater forage.

Some cultivars may tiller at early stages of growth, while others may not develop tillers until maturity is reached or until meristematic (growing point) tissue is removed

WHY SORGHUM?

Sorghum leaves are similar in conformation to corn but are generally somewhat smaller on an individual basis.

Most sorghum plants possess greater total leaf area than corn due to a greater number of nodes per plant (more nodes equal more leaves). Forage sorghums will have leaves very similar in size to corn, while sudangrass and sorghum-sudangrass will be smaller than corn.

Sorghums are highly productive, initiating a high number of tillers.

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through grazing or cutting. More tillers, larger leaf areas and greater biomass yields are obtained under long-day conditions (14-hour day-length) as opposed to shorter days (10-hour day-length). The size of the stalk is affected by plant population – lower plant densities will have plants with larger, thicker stalks, while higher plant densities will have plants with smaller, thinner stalks.

Stalks are solid and may be relatively dry at maturity or contain sweet juice. Root buds (primordia) occur at each stalk node and brace roots may grow from these buds. There is an additional bud at each node that supports tiller development. The earliest developing tillers will originate from the basal nodes closest to the soil surface.

Sorghums will yield 1.75 to 2.5 tons of biomass per one inch of irrigation water...

WHY SORGHUM?

Temperature

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Optimum temperatures for photosynthesis and growth occur between 77º F and 86º F; but, sorghums have earned the reputation for being extremely tolerant of very hot and dry conditions, while still producing optimal forage. Research indicates that sorghum maintains high levels of photosynthetic activity above 100º F, conferring the basis for high biomass yields even under the harshest environments. Primary production months will be March through September (depending upon geographic location), but growth will occur until maturity is reached or freezing temperatures/frost occurs. At low temperatures, growth and development will be slowed; minimal growth occurs below 60º F.

Sorghum Uses Water Efficiently Sorghum is extremely drought and heat tolerant and produces high yields and requires much less water than corn. Generally, sorghums will yield 1.75 to 2.5 tons of biomass per one inch of irrigation water, while corn produces less than one ton per inch of water applied (Table 1). The amount of yield produced (biomass, grain,

etc.) for a given amount of water is termed water use efficiency (WUE). With rising energy costs and water conservation concerns across the U.S., sorghum with its high WUE offers a viable economic and sustainable alternative to corn.

Production and Water Use Efficiency of Irrigated Forage Sorghum & Corn for Silage Type of Forage

Sorghum-sudangrass Photoperiod Sensitive Sorghum Brown Midrib 6 Sorghum Non-Brown Midrib 6 Sorghum Corn

Silage Yield

Silage Production

(tons/acre)

(tons/inch of irrigation water applied)

24.5 33.0

1.79 2.51

23.1 25.6

1.76 1.94

23.8

0.84

Bean, et al. 2001. Texas Cooperative Extension

Sorghums also have a very large and extensive root system capable of reaching soil profile depths of over five feet (Table 2). This large and efficient root system enables the sorghum plant to find water when other crops like corn cannot.

Table 1.

Production and Water Use Efficiency of Irrigated Forage Sorghum and Corn for Silage.

WHY SORGHUM?

Sorghums tolerate significant moisture stress and will resume vegetative growth after drought-induced dormancy. Leaves are generally smooth and covered with a waxy substance called “bloom� that reduces water loss. Additionally, sorghum leaves have a very high number of stomata (openings for uptake of carbon dioxide and release of oxygen and water). Under water stress, leaves will roll along the midrib reducing leaf surface area, keeping the plant from losing water and wilting.

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Amount of Water Used by a Grain Sorghum Crop During the Season Soil Profile Depth (feet) Water Uptake (inches) Percent of Total Water Used

0 1 2 3 4

to to to to to

1 2 3 4 5

8.9 6.6 4.0 2.8 1.3

35 26 16 11 5

USDA-ARS Report No. 29 Table 2.

Amount of Water Used by a Grain Sorghum Crop During the Season.

Even where irrigation is not limiting, sorghum remains a more economical choice over corn because similar biomass yields and forage quality can be produced using much less water, with reduced energy and labor costs. Thus, forage sorghum used for animal feedstocks provides an attractive alternative to corn-based systems from both a production and water conservation standpoint, in both dryland and irrigated production systems.

WHY SORGHUM?

Sorghum Adaptation

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Sorghums have wide adaptation. Once considered a southern forage and grain crop, improved genetics and hybrid development have expanded adaptation across the U.S., well into the Northeastern and UpperMidwestern states. Breeding advances addressing low temperature tolerance will further expand opportunities for utilizing sorghum-based forage production systems.

Advantages of Sorghum Sorghums offer several advantages over other forages and offer a diversity of management options, such as: • high water use efficiency • high tonnage yields • lower fertility requirement, especially nitrogen • excellent nutritional quality, especially with BMR 6 types • perfect for dryland, limited and full irrigation situations • supply livestock grazing during summer months • unsurpassed regrowth ability for multiple harvest and grazing operations • early maturity catch-crop following a primary crop loss • robust cover crop • outstanding rotational crop benefits • green-chop fresh forage • high yielding and excellent quality silage Regardless of the production system, sorghum’s adaptive nature, high production, and diverse use make it a valuable tool and the best choice for forage producers demanding high quality feedstocks.

Sorghum Attributes Excellent drought tolerance Uses 1/3 less nitrogen than corn High quality forage Highly productive and adaptable

WHY SORGHUM?

In many situations, very high tonnage can be expected from less than 120 lbs of nitrogen fertilizer

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Types of Sorghums Used for Forages 10

Dairy and beef cattle demonstrate excellent performance when grazing sorghums

Forage Sorghums Best Choice – Silage Operations.

Forage sorghums are generally taller, produce more leaves, and are later maturing than typical grain sorghum hybrids. Most forage sorghums produce small heads compared to grain types, but some recently developed forage sorghums support grain yields similar to traditional grain sorghums. Many forage sorghums have a sweet stalk making them very palatable to

SORGHUM TYPES

Sorghums used for forage are generally classed as forage sorghum, sudangrass, and sorghum-sudangrass hybrids. Because characteristics differ both across and within these different types, each class offers a producer multiple-use opportunities.

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livestock when used for grazing or hay production.

Forage sorghums can produce very high biomass yields, but have limited regrowth potential making them excellent choices for single-cut silage and standing green-chop production uses. The soft dough stage is considered the optimum time for harvesting.

SORGHUM TYPES

Sudangrass Best Choice – Grazing and Hay Operations.

Sudangrass is smaller in plant architecture, has finer stalks, produces more leaves than forage sorghum and develops multiple tillers. Compared to forage or grain sorghums, sudangrass looks more like a “grass” plant. It possesses excellent regrowth ability with very quick recovery following cutting or grazing, compared to forage sorghum or sorghumsudangrass hybrids.

Total biomass tonnage for a single harvest generally Very high will be less than yields of forage sorghum. Sudangrass biomass is primarily utilized for grazing and hay production and yields can be can serve as an excellent cover-crop. expected with sorghums Sorghum-sudangrass hybrids

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Best Choice – Grazing and Hay Production.

Sorghum-sudangrass hybrids are typically crosses between forage sorghums (female parent) and sudangrass types (male parent). They characteristically reach a height of six to eight feet, have smaller stalks than forage sorghum, strong tillering, and produce more tonnage than sudangrass. They have excellent regrowth potential compared to forage sorghums, but

less than sudangrass. As with sudangrass, the excellent regrowth ability of sorghum-sudangrass hybrids makes them well suited for multiple harvest systems. The term “haygrazer” is typically applied to these hybrid crosses.

Although, sorghum-sudangrass hybrids are primarily used for grazing and hay production, they can be used for silage. If used for silage, the crop should be allowed to wilt before chopping to insure proper moisture content.

Brown Midrib 6 Trait Best Choice – Grazing, Hay and Silage Production.

Lignin is the primary constituent that provides strength to the cell wall. It is very much like rebar used in concrete. Lignin is the primary non-digestible component of forages – the higher the lignin percentage the lower the digestibility and quality.

Brown Midrib 6 sorghums have 40% to 60% less lignin compared to conventional sorghums and BMR 6 sorghum silage has similar, and often times better nutritive value than corn silage.

BMR 6 Highly digestible; Superior to other BMR types.

BMR 6 forages are highly digestible and very palatable

SORGHUM TYPES

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SORGHUM TYPES

The midrib of most grass leaves (sorghums, corn, johnsongrass, etc.) is white to off-white in color.

Sorghums containing the BMR 6 gene have midrib and sometimes stalks that have a brown coloration, which is very distinct compared to non-BMR types. Brown Midrib 6 plants possess a very unique and valuable attribute – the stalk and leaves have a lower lignin content, which translates into a much higher percent digestibility The BMR 6 gene is highly superior to other and increased palatability, BMR types, which include BMR 12 and BMR 18 gene hybrids. supporting more cattle weight gain and increased milk production similar to corn silage.

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The BMR 6 gene is highly superior to other BMR types, which include BMR 12 gene and BMR 18 gene hybrids.

The nutritional value of BMR 6 sorghums over BMR 12 and BMR 18 hybrids has been demonstrated in many research trials. In fact, BMR 6 sorghums have been shown to be equal to or better than corn and alfalfa in numerous feeding studies. The BMR 6 gene is available in forage sorghum, sorghum-sudangrass hybrids, and photoperiod sensitive sorghums.

BMR-6 availability - Forage sorghums, Sudangrass, and Sorghum-sudangrass and Brachytic and Photoperiod Sensitive types of each.

Photoperiod Sensitive Sorghums Best Choice – Hay and Silage Production.

Photoperiod sensitive (PS) sorghums initiate flowering in response to day length. One of the most important factors affecting the flowering response in plants is light, and plants have differing photoperiod requirements for triggering their reproductive response (e.g. heading).

Plants can be separated into three categories in response to photoperiod – short-day, long-day and day-neutral plants. Actually it is the light and dark period acting together that controls the response. The PS sorghums will not initiate heading until the day length becomes less than about 12.5 hours. Consequently, PS sorghums will remain vegetative from mid-March through September. The advantage of this trait allows the plant to remain vegetative for most of the season, adding new leaves and maintaining very high quality forage. This allows flexibility in timing the harvest, eliminating issues associated with weather or availability of custom harvesters. Remember, forage quality starts to decline once the sorghum plant initiates heading and flowering. Photoperiod sensitive availability - Forage sorghums and Sorghumsudangrass.

Male Sterile

Male sterile sorghums maintain excellent forage quality and

SORGHUM TYPES

palatability.

Best Choice – Single Harvest or Silage Production.

Sorghum is normally a self-pollinated crop, but crosspollination can occur. Male sterile plants produce no anthers and thus no pollen for self-fertilization. If no pollen source is nearby to cross pollinate, then male sterile plants will produce no grain. The sugars and protein produced and stored in the vegetative portions of the plant will not be mobilized from the stalk and leaves because these nutrients are not needed for grain development. Thus, male sterile sorghums maintain excellent forage quality and palatability. When combined with the BMR 6 trait, male sterile forage sorghums will have higher energy content than other hybrids that produce grain.

Male sterile availability – Forage sorghums.

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Brachytic Dwarf Sorghums Best Choice – Grazing, Hay, and Silage Production.

There are four dwarfing genes in sorghum which control height. These genes produce a type of dwarfism known as “brachytic dwarfism”, which reduces the length of the internodes without affecting other agronomic plant characteristics, such as leaf number, leaf size, maturity or yield/biomass production. Brachytic Dwarf sorghums produce comparable tonnage to taller hybrids by producing more leaves and more tillers. Sorghums with this trait have very high leaf to stalk ratios, prolific tillering, superior standability, and comparable tonnage to normal height sorghums. Brachytic Dwarf availability - Forage sorghums and Sorghum-sudangrass.

Brachytic Dwarf sorghums produce comparable tonnage to taller hybrids...

SORGHUM TYPES

Brachytic dwarf types have very short internodes supporting superior standability and prolific tillering ability for high yields

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Ruminant Livestock — The Perfect Forage Consumer 18

RUMINANT NUTRITION

To fully appreciate the value of sorghums from a forage management and nutritional quality perspective, and to properly develop appropriate feedstock rations, one needs to have a basic understanding of the “milk and meat factory” that is being fed – the ruminant animal. Ruminants come in all shapes and sizes.

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Although we are most familiar with domestic animals, such as dairy and beef cattle, sheep and goats, there are many other ruminants in the animal kingdom, including buffalo, elk, moose, deer, pronghorn antelope, big-horn sheep, llamas, camels, giraffes, and others too numerous to mention.

The ruminant animal’s digestive system is fairly complex and consists of several parts (Figure 2). There are four compartments, including the rumen, reticulum, omasum and abomasum. The abomasum is a true stomach, while the other organs serve to break down feedstocks.

Basically, there are three steps involved in a ruminant obtaining energy and nutrients from forage:

RUMINANT NUTRITION

• First, the cow must ingest a feed source • Second, the feed source must be digested in the rumen • Third, the cow must absorb the nutrients produced via the digestive process The rumen is the “factory” where much of the “work” occurs enabling the animal to utilize feedstocks high in fiber. The rumen is commonly referred to

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Figure 2.

Cow’s Digestive System. University Minnesota, Cooperative Extension Service.

as a “fermentation vat.” In its natural environment the ruminant animal’s basic diet is composed of FORAGE, not grain.

First Stages of Digestion - Chewing Before any digestion can occur, the feedstock must be chewed. This mechanical affect of chewing is called mastication and it is the initial action that breaks the forage into small pieces and increases the surface area of the feed as it enters the rumen for the digestion process.

The Rumen and Reticulum Where Forage is Turned into Energy

The microbes supply the cow with what it requires – capability to digest forage, a source of protein, and volatile fatty acids which provide the cow’s energy source.

There are billions of microbes in the rumen that are responsible for the fermentation or digestion of the fiber contained in forages. Microbes in the rumen include

RUMINANT NUTRITION

The rumen is the largest compartment in the digestive tract and has a capacity of 40 to 50 gallons. It is here that the cow’s “microbial partners” reside.

The relationship between the cow and the microbes living in the rumen is somewhat similar to the symbiotic relationship between a legume plant and its nitrogen fixing bacteria – one does not live well without the other.

The cow provides the microbes with what they need to flourish – water, warm temperature for activity, the forage source, and the anaerobic conditions (no oxygen) in the rumen. The microbes supply the cow with what it requires – capability to digest forage, a source of protein, and volatile fatty acids which provide the cow’s energy source.

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bacteria, protozoa and fungi. They digest the feed through the process of fermentation. Under normal conditions the temperature of the rumen is 102º F and the optimum pH range if from 5.8 to 6.2.

A single cow may move her jaw over 50,000 times in one day.

The reticulum has an internal structure that resembles a honeycomb pattern. After initial digestion the food may be subjected to additional mechanical activity during the process of rumination or cud chewing, where material is passed from the reticulum back up the esophagus to the mouth for more chewing. The time spent by the animal chewing-cud depends on the fiber content. The higher the fiber content, the more time required for rumination, which translates into less feed intake and less milk or beef production.

RUMINANT NUTRITION

Each regurgitation or bolus is chewed 40 to 50 times before it is swallowed again. Cows produce extremely large quantities of saliva, as much as 50 gallons per day. This saliva is very important because it provides fluid for the rumen and may help in maintaining the proper rumen pH. Saliva contains high amounts of bicarbonate which serves as a good buffer.

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The microbial population of the rumen is extremely important to the cow. Billions of these microscopic creatures are present in the rumen and each is very specific to its function. The primary products of the fermentation process are: •

•

•

Volatile fatty acids which are the cows primary energy source.

Ammonia which is used to manufacture microbial protein. Bacteria are 60% protein, making them the major source of protein for the cow as the bacteria move from the rumen and are digested in the abomasum.

Gases, which are sources of wasted energy as they are “burped” regularly by the animal.

When feed is ingested by the cow, the nutrients are initially in the form of carbohydrates, proteins and fats.

These are digested to products that can be used by the cow or by the microbial population in the rumen.

Rumen microbes ferment all carbohydrates but the soluble and storage forms are fermented more quickly than the structural forms. Sugars and starches are broken down fairly easily. By comparison, cell wall material is more difficult to digest. As plants mature, cell walls become lignified. Lignin reduces digestibility.

Soluble carbohydrates are digested 100 times faster than are storage carbohydrates, while storage carbohydrates (starch) are digested about five times faster than structural carbohydrates (cellulose, hemicellulose).

RUMINANT NUTRITION

Plant tissue is about 75 percent carbohydrates (different types). All sugars belong to the class of biochemicals known as carbohydrates (CH2O), so named because their chemical formula all include carbon as well as the elements hydrogen and oxygen in the same two-to-one ratio found in water. Microbial fermentation breaks carbohydrates into simple sugars. The microbes use these sugars as an energy source for their own growth and make end products which are used by the cow. The final products of carbohydrate fermentation are volatile fatty acids and gases.

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The Energy Source – Volatile Fatty Acids The product of carbohydrate digestion in the rumen is volatile fatty acids (VFA). Volatile fatty acids provide the major energy source for the animal. There are different types of VFA produced and the animal’s diet has influence on which VFA are generated. The three major VFA are acetic acid (acetate), propionic acid (propionate), and butyric acid (butyrate). These compounds are absorbed through the rumen wall and transported by the bloodstream to the liver where they are converted to other sources of energy – energy used for maintenance, milk production, growth, etc.

The three major VFA: Acetic acid Propionic acid

RUMINANT NUTRITION

Butyric acid

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•

•

•

Acetic acid is typically associated with high forage diets and milk fat production. Acetic acid is a two-carbon VFA and comprises about 50% to 70% of the total VFA produced in the rumen.

Propionic acid production is linked to a diet high in starch and sugars and yields energy for weight gain and lactose production. Propionic acid is a three-carbon VFA representing about 15% to 30% of rumen VFA production.

Butyric acid is metabolized in the liver and is a source of energy for development of skeletal muscles and other body tissues. Butyric acid is a four-carbon compound and makes up about 5% to 15% of the total VFA production.

Protein Cows can use protein contained in the feed they eat or from the high protein microbes that pass from the rumen. These rumen microbes are the primary source of protein for the cow. Microbes pass from the rumen into the omasum and then to the abomasum where they are absorbed by the cow.

Fats Fats are an energy source for cattle; an optimal feed ration should contain up to 5% fat. Cottonseed is an excellent source of fat and provides a good method to boost the energy content of a feed ration.

Omasum The omasum is positioned between the reticulum and abomasum. The combined contractions of the rumen and reticulum cause the finer particles of food to pass into the omasum. It is here that water is absorbed from partly digested food, before it enters the abomasum (true stomach). The entering feedstock is composed of over 90% water. The major function of the omasum is to remove the water and continue to digest the feed.

The abomasum is considered a true stomach, much like that of humans (monogastric). In the abomasum, acid digestion occurs rather than the anaerobic fermentation process occurring in the rumen. The abomasum produces gastric juices (acids and enzymes). The pH within this true stomach is very low, typically about 2.0. The low pH environment kills rumen microbes and the enzymes (pepsins) digest the protein in the microbes (bacteria are 60% protein) which are then absorbed into the bloodstream along with sugars and mineral nutrients.

RUMINANT NUTRITION

Abomasum

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Forage Quality — Understanding Plant Cell Structure 26

Forage sorghums are highly palatable

FORAGE QUALITY

To understand forage quality, it is important to understand plant cell structure. Plant cells differ from animals in that plant cells have a defined cell wall.

The cell wall brings rigidity and strength to the plant, much like the skeleton of an animal. The cell wall consists of three layers – middle lamella, primary wall and secondary wall (Figure 3).

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Primary Wall The middle lamella is the first layer formed Secondary Wall and makes up the outer wall of the cell.

Direction It is composed of Cell of Wall Lumen pectic compounds and Thickening protein. The primary Low cell wall is formed after the middle lamella and Lignin consists of cellulose, Concentration Gradient pectic compounds, hemicelluloses High and proteins. The secondary cell wall is Figure 3. formed after the cell has reached full size and is Diagram of composed of cellulose, hemicellulose, and lignin.

Plant Cell.

Fiber

FORAGE QUALITY

The term fiber defines the insoluble, complex carbohydrates of the plant cell. Thus, the primary components of fiber are cellulose, hemicellulose, and lignin.

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• Cellulose is a polysaccharide composed of glucose units connected with beta-1,4 linkages.

It is 50% to 90% digestible. • Hemicellulose is a polysaccharide composed of a variety of sugars including xylose, arabinose, and mannose. It is 20% to 80% digestible. • Lignin is the primary component of wood and is chemically resistant to breakdown. It is comprised of long chains of aromatic plant alcohols. It is non-digestible.

The soluble contents of plant cells are composed of sugars, starches, fat, proteins and pectins.

Starch is the primary plant storage carbohydrate. It is a polysaccharide composed of glucose units connected

with alpha-1,4 linkages (compared to cellulose that has a beta-1,4 linkage). This linkage makes a significant difference in how each compound can be utilized.

Starch is easily digested by most animals (e.g. humans, pigs, cows, etc.), but only microbes have the enzymes necessary for cellulose digestion. Ruminants rely on the microbes in the rumen for fiber digestion.

Cellulose forms the framework of both primary and secondary cell walls along with hemicellulose and pectin.

Lignin fills in and around the cellulose, hemicellulose and pectin and provides the structural support for the cell, forming the “plant skeleton.”

Conventional sorghums have higher lignin content than BMR 6 types

FORAGE QUALITY

• “Concrete slab” example. Metal rods called “rebar” are placed in the concrete to provide strength and reinforcement. The greater the surface area of the rebar that comes in contact with the concrete, the greater the strength of the slab. One can think of a cell similarly, with the cellulose, hemicellulose and pectin serving as the “concrete” foundation, while lignin acts as the “rebar.” The more rebar (lignin) that is used, the stronger and more rigid the foundation (cell).

As the plant matures, more and more lignin is deposited into the cell walls to provide rigidity and strength to resist lodging. Unfortunately, the plant’s mechanism for building strength leads to a lower nutritional quality

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plant. Lignin is virtually non-digestible, so as lignification occurs in older, more mature plants digestibility and quality decline. Therefore, harvesting at the proper time is critical to maintaining and supplying high quality forage.

What is forage quality?

Simply stated, forage quality is the ability of a forage source to meet an animal’s nutritional requirements.

Consequently, the science of forage quality is about identifying the factors that may be limiting the ability of a forage source to supply the necessary nutrients to meet livestock needs.

What affects the quantity of nutrients an animal can obtain from forage?

There are two primary factors involved:

FORAGE QUALITY

•

•

Highly digestible forage sorghums support greater feed intake

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Intake – because animals can only eat so much feed per day, bulky feeds with low nutrient densities can limit nutrient availability.

Digestibility – once the feedstock is consumed, the nutrients must be digested before they are available to provide energy and nutrients to the animal. Digestion is the process of mechanical, chemical and enzymatic breakdown of consumed feeds into smaller components for absorption.

What limits intake?

Fiber is the bulky, slowly digested portion of the forage that fills the rumen and causes the animal to stop eating. Until the fiber is digested or passes from the rumen, the animal will be unable to consume more feed.

For example, dairy cows fed high quality forage produce more milk than cows fed a lesser quality ration.

The nutrient and biochemical composition of forage is paramount in determining its quality. Along with quality, the overall potential feeding value of a forage is influenced by the form in which it is fed and the palatability of the forage. Several factors affect the quality of forage when used for grazing, hay and silage.

Forages with a lower lignin content are more digestible and higher quality.

FORAGE QUALITY

There are numerous forage quality indicators used in the dairy and beef industry and the science of forage quality analysis continues to change and improve.

However, there are several key forage quality indicators that provide the basis for forage quality analysis and utilization in determining nutritive value. The following sections will address key factors.

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Measuring Quality — Key Forage Quality Parameters 32

Animal performance is directly linked to energy and the potential energy of a feedstock is directly linked to digestibility.

Although there are numerous factors that should be evaluated in determining forage quality, digestibility is the key characteristic that determines forage nutritive value.

MEASURING QUALITY

BMR 6 sorghums supply high energy value

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For many years, acid detergent fiber (ADF) and neutral detergent fiber (NDF) were used to predict digestibility and intake. Acid detergent fiber and NDF provide relatively good estimates of fiber content in forage, but these measurements do not provide the best estimate of forage fiber digestibility and animal performance.

Acid Detergent Fiber (ADF) The ADF fraction is determined by boiling a sample in an acid detergent solution for one hour. The ADF components are primarily cellulose and lignin.

Traditionally, ADF has been used to predict digestibility.

Lower ADF content equates to better quality forage.

Neutral Detergent Fiber (NDF) The NDF fraction is determined by boiling a sample in a neutral detergent solution for one hour. The NDF components are primarily hemicellulose, cellulose, and lignin. Because these compounds are closely associated with bulkiness of forage, NDF is closely related to animal feed intake and rumen fill, thus NDF can be used to predict voluntary intake of a feedstock. Brown Midrib 6 sorghums have NDF values as low as 40%. The lower the NDF content, the better the forage (Figure 4).

MEASURING QUALITY

Lower ADF and NDF Content equals better quality forage

34

Determining Digestibility – A Better Method Digestibility refers to that portion of the feed that is absorbed as it passes through the animal’s digestive tract. In 1970, Goering and Van Soest developed an “in vitro” technique (performing a given procedure in a controlled environment outside of a living organism – in this case the cow) for determining dry matter digestibility. It was termed in vitro true dry matter digestibility (IVTD, IVDMD).

Forage Consumed (lbs./day)

50 45 40 35 30 25 30

35

40

45

50

NDF Percentage of Forage

Figure 4. Influence of NDF on intake.

In vitro true digestibility is an anaerobic fermentation performed in the laboratory to simulate digestion as it occurs in the rumen. Rumen fluid is collected from animals (e.g. dairy cows or steers) consuming a typical diet. Forage samples are incubated in rumen fluid and buffer for a specified period of time at 102 F. The original method used a 48-hour incubation. During this time, the microbial population in the rumen fluid digests the sample as it would occur in the rumen. The end result of the IVTD procedure is the undigested fibrous residue.

BMR 6 Digestibility As previously discussed, lignin is the primary non-digestible component of forages – the higher the lignin percentage the lower the digestibility and quality.

Brown Midrib 6 sorghums have 40% to 60% less lignin compared to conventional sorghums and BMR 6 sorghum silage has similar, and often times better

MEASURING QUALITY

The obvious factors affecting digestibility are type of crop and variety/hybrid characteristics and the maturity of the crop. As the crop matures, more lignin is deposited within cells reducing digestibility. Lignin and ligninbased compounds are not digestible.

35

Quality Characteristics of Different Forages Forage Quality Parameters Forage Type

CP%

ADF%

NDF%

Lignin%

IVTD%

Brown Midrib 6 Forage Sorghum

9.2

27.6

45.9

3.6

81.3

Conventional Forage Sorghum

8.3

29.9

49.1

4.4

75.5

Corn

9.0

23.9

41.2

3.5

82.7

Bean, et al. 2001. Texas Cooperative Extension

Table. 3. Quality Characteristics of Different Forages. nutritive value than corn silage and other BMR types such as BMR 12 and BMR 18. Studies have shown IVTD’s of over 80% for the BMR 6 sorghums (Table 3).

MEASURING QUALITY

Studies have also shown that feeding BMR 6 silage in place of corn silage at either 35% or 45% of dietary dry matter resulted in greater milk production efficiency

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Effects of Different Forage Sources on Dairy Cow Performance DMI lbs/day

NDF Intake lbs/day

Milk Production lbs/day

Milk Fat %

Milk Protein %

BMR 6 Sorghum

55.44

19.80

75.02

3.89

2.89

Corn

53.46

19.80

74.36

3.88

2.97

BMR 18 Sorghum

51.98

21.78

70.84

3.77

2.98

Conventional Sorghum

51.04

22.88

68.20

3.57

2.89

Forage Type

Oliver, et al. 2004. Journal of Dairy Science

Table. 4. Effects of Different Forage Sources on Dairy Cow Performance.

and higher milk fat percentage. The BMR 6 silage had greater NDF digestibility (NDFd) and cows fed the BMR 6 silage derived more energy from digestion of NDF compared with cows fed corn silage (Table 4). In addition, the BMR 6 sorghum outperformed a conventional forage sorghum and a BMR 18 sorghum, and was equal to corn silage in overall milk production.

Effects of Grazing Conventional and BMR 6 Sorghum-sudangrass on Performance of Stocker Calves.

Gain (lbs/day) Forage Type

1999

2000 2 Yr Avg.

Gain (lbs/acre) 1999

2000 2 Yr Avg.

BMR 6 Sorghumsudangrass

2.91 2.97 2.94

316

359

338

Conventional Sorghumsudangrass

2.74 2.51 2.63

305

295

300

McCollum, et al. 2003. Texas Cooperative Extension

Similar improvements in animal performance are also obtained by increasing the nutritional value of forages fed to beef cattle. Results from sorghum-sudangrass grazing trials demonstrate the superiority of the BMR 6 trait. Stocker calves grazing BMR 6 sorghumsudangrass had an average daily gain of 0.31 lbs more that the non-BMR 6 sorghum and 38 lbs more gain per acre (Table 5).

In addition to providing nutritional benefits to livestock, increased forage digestibility of BMR 6 sorghums also provides economic benefits to the producer in a couple of ways. First, more digestible forages can be

MEASURING QUALITY

Table 5. Effects of Grazing Conventional and BMR 6 Sorghum-sudangrass on Performance of Stocker Calves.

37

substituted directly for a standard forage and because of the greater nutrient availability, animal performance will increase. Second, the composition of the diet can be changed to reflect the additional nutritional value of the more digestible forage, which will reduce the need for costly energy concentrates and reduce overall production costs.

NDFd

NDF Digestibility (NDFd)

Forage testing laboratories now offer another digestibility determination called NDFd. This analysis excellent provides information that is extremely useful for assessing forage digestibility, potential energy and tool for animal performance. is an

evaluating Neutral Detergent Fiber represents the cell wall

MEASURING QUALITY

forages.

38

constituents of the plant. It contains hemicellulose, cellulose, and lignin that vary individually in quantity depending upon plant species, stage of maturity, and environment. So, even though forages may have similar ADF and NDF values, the fiber composition could be different. Consequently, the NDFd values could be very different and so could the performance of the animals fed these different forages.

Forage NDFd analysis are routinely conducted by commercial labs using the same method for determining IVTD. Forage samples are incubated in a simulated rumen environment using rumen fluid extracted from live animals, for specific time periods.

The calculation is based on the sample amount of NDF prior to rumen incubation compared to the amount of NDF remaining after a designated amount of time.

Research has

demonstrated that incubation times of 30 hours and 24 hours rather than 48 hours more closely approximates the digestion potential of NDF in dairy cows because feed is not retained in the rumen for 48 hours. The 30 hour NDFd is also referred to as Cell Wall Digestibility (CWD).

Obviously, when developing feed rations the focus is on feeding the cow, but in actuality the development of a feed ration should focus on providing the proper nutrients for the rumen microflora. The microflora ferment the fiber and sugar for their energy needs and the by products are the VFA that the cow uses for energy.

Neutral Detergent Fiber digestibility is an excellent tool for evaluating feedstocks. Increased NDFd will result in higher energy values and, more importantly, better animal performance. It has been demonstrated that cows have greater feed intake and produce more milk when fed forages with higher NDFd values. A one unit increase in NDFd corresponds to a 0.37-lb-per-day increase in dry forage intake and a 0.55-lb-per-day increase in milk production.

Dry matter is the portion of any forage material which remains after all moisture has been removed. As plants mature, DM content increases. Forage yields, protein content, energy and digestibility are all expressed on a DM basis in order to make meaningful comparisons on nutritional value of different forages.

Crude Protein Although protein is a key component of a feedstock, it is generally over-rated as a primary indicator of forage quality. Neutral detergent fiber digestibility is a much more important quality parameter and should be viewed as a much better gauge of forage quality.

more milk when fed forages that have high NDFd.

MEASURING QUALITY

Dry matter (DM)

Cows produce

39

MEASURING QUALITY

Proteins are complex organic compounds found in all living cells. They contain nitrogen and are the main constituent of muscle. Protein content is typically expressed as crude protein (CP) on a dry matter basis.

Crude protein equals the percentage of nitrogen multiplied by 6.25. For example, if a feed analysis showed a nitrogen content of 3%, then the CP would be calculated as 3% X 6.25 = 18.75%.

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Another term often referred to in the context of proteins is amino acid. The building blocks of proteins are amino acids of which animals require 23 different types. Plants and many microorganisms are able to synthesize amino acids from simple nitrogenous compounds, such as nitrate and ammonium which plants obtain from the soil. Ruminants (e.g. cattle, sheep, goats, and deer) are capable of making these important amino acids.

Nonfibrous Carbohydrates (NFC) Nonfibrous carbohydrates is an estimate of the rapidly available carbohydrates in a forage. Primarily, this is an estimate of the starch, sugars and other compounds.

Total Nonstructural Carbohydrates (TNC) Total nonstructural carbohydrates is a measure of only the starch and sugar in a forage.

Energy Energy is derived from the digestion of carbohydrates, fat and protein. There are no laboratory procedures to measure energy. It is a product of the digestion process; therefore, it is a calculated value based on feed digestibility and is expressed as calories. A kilocalorie (Kcal) is a 1000 calories and a megacalorie (Mcal) is 1000 kilocalories.

Net Energy Lactation (NEl) Net Energy Lactation is the estimated energy value of a feed for milk production, expressed as megacalories (Mcal) per pound of feed. It is calculated from the ADF value. Different forages use different equations to determine NEl, therefore correctly identifying forages is important.

Energy is derived from digestion of carbohydrates, fat and protein.

Net Energy Gain is the estimated energy value of a feed for body weight gain above that required for maintenance. This is a calculated value.

Net Energy Maintenance (NEm) Net Energy Maintenance is the estimated energy value of a feed to maintain an animal at a stable weight. This is a calculated value.

Palatability Palatability describes the animal’s preference for a feedstock when offered a choice among different feeds.

MEASURING QUALITY

Net Energy Gain (NEg)

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It is a complex phenomenon determined by animal, plant and environmental variables. Palatability of a certain forage plant may be different for sheep, Livestock find BMR 6 sorghums very palatable. compared to cattle, or goats. Factors affecting palatability include type of crop and variety/hybrid, growth stage, chemical composition or toxic compounds that might be present in the forage, and the selection by the animal for different plant parts (leaves versus stems).

Brown midrib 6 forages are extremely palatable.

Ash Ash is an estimate of the total mineral content of a forage remaining after burning.

MEASURING QUALITY

Minerals

42

Minerals represent the primary elements including calcium, phosphorus, magnesium, potassium, sodium, sulfur and the trace minerals are iron, zinc, copper, manganese, and molybdenum. Mineral content of forages is dependent on maturity, forage species and soil fertility.

Phosphorus Digestibility High producing dairy cows require approximately 0.40% phosphorus in the dry matter diet for optimal milk production and reproductive function. Phosphorus is often fed in higher amounts than is necessary. Research has shown a direct correlation between phosphorus dietary intake and manure excretion. Phosphorus contamination of ground and surface water resources is

the single most important environmental issue facing the dairy industry. Reducing phosphorus levels in manure through dietary intake is an efficient and economical approach to reducing phosphorus loading rates on dairy farms.

Research has shown that phosphorus digestibility is very high in BMR 6 sorghum (Figure 5). Additional research had demonstrated that a BMR 6 sorghumsudangrass ration resulted in approximately 6 g per day less fecal phosphorus excretion per cow when compared to corn silage. This could result in approximately 4 lbs. less phosphorus excretion per cow per 305-day lactation period. This amount of reduction in phosphorus excretion is potentially important from an environmental and economical standpoint. Feeding BMR 6 sorghums could significantly lower phosphorus loading rates, reducing the potential for surface and ground water contamination and improving environmental quality. Additionally, lower phosphorus levels greatly benefit soil fertility relationships.

Feeding BMR 6 sorghums could significantly lower phosphorus loading rates and improve environmental quality.

70

64.6

50

49.4 40

40.9 33.2

30 20 10 0

Conventional

BMR 18

BMR 6

Corn

Figure 5. Phosphorus digestibility in different forages. Dann, et al. 2007.

Journal of Dairy Science.

MEASURING QUALITY

60

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Versatility for Hay,Silage and Fresh Forage 44

VERSATILITY

Forage sorghums offer several advantages over other types of forage crops and offer a diversity of management options. Sorghum is an excellent choice for dryland, limited and full irrigation situations and livestock operations needing grazing during summer months.

45

Sorghum is the perfect choice for hay production systems, and offers utility as a catch-crop following a primary crop loss, and can also serve as a very vigorous cover crop. In all those different situations the crop can be used for grazing, hay production, green-chop fresh forage, and silage. Some hybrids/ types possess high tillering and regrowth characteristics which are excellent choices for multiple-cut and grazing situations.

Additionally, sorghums are rapidly becoming a favorite choice for silage production in both beef and dairy cattle operations. Regardless of the production system, sorghum’s adaptive nature and diverse use make it a valuable tool for forage producers.

VERSATILITY

Hay Production and Factors Affecting Hay Quality

46

Variety/hybrid selection is the most important decision the grower will make. It has direct impact on the potential yield and forage quality achieved. Not all sorghums are created equal when it comes to hay production and quality. Sorghums used for hay operations need to be selected based upon yield potential, rapid regrowth ability, stalk size (smaller stalks promote rapid curing), and harvest-time flexibility.

Brown midrib 6 sorghum-sudangrass hybrids are an excellent choice for haying and grazing uses. The exceptional quality of the BMR 6 sorghums is unsurpassed and supports exceptional animal performance.

The growth stage is very important to forage quality.

Quality changes over time – as the crop progresses closer to maturity (heading and flowering), the quality will begin to decline and lignin content will increase.

Optimum growth stage for achieving maximum quality and tonnage is typically the boot stage, or just prior to the boot stage. As the crop heads and grain formation begins, nutrients from the stalk and leaves will be translocated to the developing grain, reducing forage quality. Another advantage to harvesting during the younger, vegetative stage is that stalks will be thinner, which means easier conditioning, smaller windrows and more rapid curing.

Optimum growth stage for harvest is boot stage.

VERSATILITY

The proper time of day for cutting is a debatable topic. In theory, plant sugars are lower in the morning due to nighttime respiration use and reach a peak in the afternoon after photosynthesis has been ongoing for several hours. Research indicates there is a quality and palatability advantage from cutting in the afternoon.

However, if the crop does not have sufficient drying time/heat to fully wilt before nightfall, it will continue to use sugars through respiration, until wilted the following day. This greatly minimizes the potential benefits of the afternoon harvest. Taking all factors into consideration, the best time to harvest is probably late morning after the dew has dissipated. Avoid cutting on cloudy days or during the night when sugar levels will be lower and drying time will be increased.

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Weather-damaged hay is primarily related to rainfall events that occur after cutting. Research shows fresh-cut hay with less than one inch of rain took a few more hours to dry, but had minimal quality and/or quantity loss. A light rain on hay that is almost dry and ready for baling caused significant losses. It has been determined that for every inch of rain, dry matter yield is reduced 5% and digestibility is reduced by 10%. Most nutrient losses occur from leaching of soluble carbohydrates and shattering of stems and leaves as it is raked multiple times attempting to hasten drying. The longer hay stays wet, the more energy value is lost and, to a lesser extent, the more protein content decreases.

Forage can be safely baled at 15% to 20% moisture

VERSATILITY

Moisture content of forage when baled directly affects hay quality. High moisture content can lead to bale overheating. Heat destroys protein, reduces quality and can be a fire hazard. Plant material continues to respire (produce oxygen) for a short time after it is baled. Plant respiration and bacterial action creates heat as the plant oxygen is consumed. Too much heat generates combustion. Conversely, extreme drying can result in loss of leaf material which is typically the most nutritious portion of the plant. Forage can be safely baled at a moisture content of 15% to 20%.

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Storage obviously affects hay quality. Protection from weather is best, but in many cases, may not be feasible or affordable. Australian research shows that in a 30-inch annual average rainfall area, a 5-ft. diameter bale stored for one year loses 8% of its weight under shed protection and loses 24% of its weight when stored uncovered on the ground. When stored uncovered, but off the ground the weight loss is 17%.

Making Silage – the Fermentation Process

VERSATILITY

The fermentation process that preserves forage as silage is biochemistry in action. Silage fermentation requires four basic elements to successfully complete the process – anaerobic conditions, proper moisture, adequate levels of plant sugars, and the proper bacteria to drive the anaerobic process.

Chopped forage is compressed as it is ensiled to remove air. Cells of the sorghum plant are still metabolically active, and in conjunction with microorganisms create carbon dioxide and heat. As the carbon dioxide levels increase, an anaerobic condition develops and desirable bacteria begin the fermentation process when respiration ceases. If too much air is present or if the carbon dioxide escapes, respiration will continue and plant cells will continue to consume sugar. For this reason it is important to pack and cover as quickly as possible. Oxygen is silage’s worst enemy. Once respiration is complete, acetic and lactic acids are produced by the bacteria feeding on available starch and sugars in the chopped sorghum forage. Fermentation will continue until the acid content limits bacterial activity.

The desired pH of about 4.2 should be attained in about three weeks.

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Factors Affecting Silage Quality Compaction. If the forage is not well compacted the remaining air will allow a different type of fermentation to occur, resulting in overheating. In the ensiling operation the crop should not be cut faster than it can be compacted.

When properly compacted, it should be difficult to dig material out with bare hands. Silage that has overheated will often be a much darker color and have a distinct caramel smell.

Nutritional value of overheated silage is very low.

Silage Quality Chop Length. The size of the chopped forage is Checklist important since it affects the packing process and

animal performance. Modern forage harvesters can cut material as small as 0.25 inches. Finely cut forage will Chop at 1.25� compact easier than larger cut pieces and should result in successful silage production. The fineness of cut also Moisture 60-70% affects animal intake. A shorter chop length results in higher intake and improved animal production. The Harvest at optimum chop length is about 1.25 inches.

Properly Compacted

correct stage

Moisture content required will depend on the storage method, but generally it falls within the range of 60% to if needed 70%. Ensiling material wetter than this may result in the loss of valuable nutrients as water and soluble nutrients accumulate at the bottom of the bunker or storage facility as silage effluent. Crops with moisture content above 70% can be ensiled by cutting and field wilting the crop prior to picking up and storing. Conversely, if the crop is too dry and has moisture content below 60%, compaction will be difficult.

VERSATILITY

Inoculate

50

Sufficient plant sugars are required for the necessary production of lactic acid. Generally there are no concerns with sugar levels in forage sorghums when cut at the correct growth stage.

Silage inoculants are not essential to the silage making process, but they are highly recommended. Typically, silage inoculants are bacterial cultures to aid the lactic acid fermentation process which is essential to a successful end product. These lactic acid bacteria occur naturally, but the ensiling process can be expedited with the use of appropriate inoculants.

The finished silage product is only as good as the quality of forage that was used to make it. The important quality parameters are digestibility, energy and protein.

In any crop these factors typically decline as the crop reaches maturity and grain begins to develop. It is best to harvest forage sorghums about two weeks after flowering. This ensures optimum tonnage and quality. The BMR 6 sorghums are superior in quality and animal performance compared to the BMR 12 and BMR 18 types, and equal in performance to corn silage. Brown midrib 6 forages demonstrate clear nutritional advantages over conventional sorghums and their excellent palatability and digestibility profile are equal to corn.

Best to harvest forage sorghums 2 weeks after flowering for optimum tonnage and quality.

Green chop forages are cut at younger stage of maturity up to heading and fed directly to livestock without any drying of the forage. Sudangrass and sorghum-sudangrass hybrids can be used to provide green chopped forage during the growing season. Green chopping can be initiated once the crop has reached18 inches tall and should be completed before the crop starts to show heads.

VERSATILITY

Green Chop

51

Grazing

Brachytic dwarf types should be grazed to a 2 inch height

VERSATILITY

to allow

Sudangrass and sorghum-sudangrasses are excellent for grazing systems because they have such strong regrowth ability and have less potential for prussic acid issues than forage sorghum types. As with any grazing operation the objective is to keep the crop in a high quality nutritive condition, which is directly related to growth stage. Livestock can begin grazing sudangrass once it has reached a height of 15 to 20 inches and sorghum-sudangrass when it has attained a height of 20 to 30 inches. Sudangrass can be grazed sooner due its lower prussic acid potential than sorghum-sudangrass.

for optimum Rotational grazing methods should be used to insure

52

regrowth.

proper utilization. Animals should be allowed to graze the crop to a 6 inch level (to allow rapid regrowth) and then rotated to the next pasture. Before returning cattle to the previously grazed pasture the crop should have grown to a height of at least 18 inches. With brachytic dwarf types, the crop should be grazed to a two inch height and still have sufficient nodes for regrowth.

Avoid Potentially Harmful Compounds There are two potentially harmful situations that can occur in sorghum that all producers must understand.

These potential problems are prussic acid poisoning and nitrate toxicity. By understanding the sorghum plant and growing conditions these problems can be successfully addressed and avoided.

Prussic acid poisoning Many different plant species, including sorghum contain varying amounts of cyanogenic glycosides. Glycosides are compounds containing a carbohydrate and a non-carbohydrate compound in the same molecule.

They break down into glucose (sugar) and the non-carbohydrate compound through a process called hydrolysis (addition of water) as a result of enzymatic activity. In cyanogenic plants this decomposition frees the cyanide from its chemical bond and it becomes the toxic compound hydrocyanic acid, commonly known as prussic acid. In sorghum the compound is also called dhurrin.

VERSATILITY

These cyanogenic compounds are located in epidermal cells of the plant (outer layer of cells); and, the enzymes responsible for mediating the formation of prussic acid are located in the mesophyll cells (leaf tissue). Any event that causes the plant cell to rupture allowing the cyanogenic compound and the enzyme to combine will produce prussic acid.

When plant tissue is damaged by chewing, chopping, trampling, or freezing the cyanogenic glycoside and the enzyme come in contact and prussic acid is formed.

53

Once plants containing prussic acid have been consumed the toxin rapidly enters the blood stream and is transported throughout the animal’s body.

Prussic acid inhibits oxygen utilization by animal cells.

High concentrations of prussic acid may be associated with rapid growth of a drought stressed crop following rainfall or irrigation, or warm temperatures following a cool temperature period. Under normal conditions, prussic acid can form in young, rapidly growing plants.

Do not Factors known to elevate prussic acid levels in forage graze crops sorghums include resumed growth following drought,

frost, high soil nitrogen fertility, low soil phosphorus levels, and 2,4-D herbicide applications. Potentially resumed harmful prussic acid poisoning can be eliminated by adopting the following management practices:

that have

growth following stressful

VERSATILITY

conditions.

54

•

•

Do not graze crops that have resumed growth following stressful conditions caused by drought or freezing/frost damage. It should be noted that the new growth that develops following the release of stress (rainfall following drought conditions) will be high in prussic acid. Avoid grazing young drought stressed fields.

Do not allow hungry stock into forage sorghum fields. Make sure animals have experienced alternate feed sources before moving to sorghum fields.

•

•

•

Do not plant forage sorghum in fields that have very high levels of nitrogen.

Do not graze the crop until it reaches about 18 to 24 inches in height. Young plants and regrowth will have higher prussic acid levels.

Select plant types that inherently have lower potential for prussic acid development.

Hay and Prussic Acid Concerns Generally it is considered that cutting and field drying is adequate to reduce prussic acid to safe levels. The prussic acid is converted to a gas and released as the hay cures in the field. However, making hay from a drought stressed crop still has the potential for prussic acid poisoning. When in doubt, hay samples can be analyzed at a certified laboratory prior to feeding livestock.

Silage and Prussic Acid Concerns The ensiling process does not diminish prussic acid concentrations in the forage. If the crop is cut with a forage harvester and moved directly to the storage facility, prussic acid will have insufficient time to volatilize. Crops cut and allowed to wilt (e.g. mower-conditioner) before chopping and ensiling will have greater opportunity for prussic acid to be released from the forage. As with a stressed hay crop, the best recommendation is to be cautious when making silage from a stressed sorghum crop.

Prussic acid is converted to a gas and released as hay cures.

Under normal growth conditions, plants absorb nitrate from the soil and the nitrate is then converted to amino acids. This assimilation of nitrate requires energy, water and favorable temperature for growth. When plants

VERSATILITY

Nitrate Toxicity

55

are stressed, the assimilation process is diminished and plants can accumulate nitrate. Typically nitrates will accumulate in the lower third of the plant stalk and leaves where the nitrate is stored and available for plant use when growth resumes. Many plant species are prone to nitrate accumulation, including corn, small grains, carelessweed (amaranthus species.), sunflower, and sorghum.

Sorghums can accumulate nitrates any time normal plant growth is disrupted.

VERSATILITY

Sorghums can accumulate nitrates during any environmental condition that disrupts normal plant growth, such as drought, prolonged cloudy conditions, frost, etc. Similar to prussic acid poisoning, drought is generally considered the most frequent cause of high nitrates in plants. However, even in the absence of stress if very high levels of nitrogen are present in the soil, plants can accumulate nitrates. This response is called “luxury consumption” and it can occur in sorghum. The following are common factors that associated with nitrate accumulation in plants:

56

•

•

•

Crop is produced in a very fertile soil or a soil that has had high levels of nitrogen fertilizer or manure applied.

An environmental stress factor that limits plant growth, such as drought, cloudy conditions, or cool conditions (frost/freeze).

Fields that have leaves removed but the plant (stalk and roots) remains intact. This could be due to weather damage (hail), grazing, or insect feeding (grasshoppers, worms).

Livestock Affects The term nitrate toxicity is the common terminology used, but the toxic compound to the livestock animal is nitrite. Nitrate is converted to nitrite in the rumen. Nitrite is then absorbed into the bloodstream directly from the

rumen wall where it converts hemoglobin (oxygen carrying molecule) to methhemoglobin. Methhemoglobin cannot transport oxygen to body tissues. The animal dies from oxygen insufficiency, or asphyxiation, with the blood turning a brown color rather than the normal bright red.

Hay and Nitrate Toxicity Concerns Nitrate does not dissipate from hay like prussic acid.

Once high nitrate levels are established in a plant, the nitrate will remain intact in the hay. High nitrate forage must be diluted with normal forage and/or grain before fed to livestock.

Silage and Nitrate Toxicity Concerns The fermentation phase of the ensilage process converts about 50 percent of the nitrates to a non-toxic form. High nitrate silages can be fed if proper precautions are taken. These include diluting the forage with other feeds, supplementation with grain and not feeding to hungry, pregnant, or stressed livestock.

Use caution when feeding high nitrate forage to livestock

Do not harvest drought stricken crops within one to from hay like three weeks following a good rainfall. Do not green chop a field within seven days of a killing frost. Cut at a higher prussic acid. stubble height because nitrates accumulate in the lower portion of stalk. If prussic acid is suspected, do not feed silage for one month to allow dissipation.

VERSATILITY

Do not over-apply nitrogen fertilizer. For sudangrass and Nitrate sorghum-sudangrasses, the seasonal needs for the crop will be between 1 to 1.25 lbs. nitrogen per growing day. does not Apply 45 to 60 lbs. of nitrogen for the first cutting. dissipate

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Agronomic Best Management Practices 58

Seedbed Preparation

Agronomic Management

As with most crops, good seedbed preparation is important to achieving optimum stand establishment.

A cloddy, rough seedbed will result in less than desirable plant populations and optimal plant density is crucial to reaching production and forage quality goals. Following similar soil preparation techniques for corn and grain sorghum, which promotes good seed-to-soil contact, is recommended for forage sorghums.

59

Tillage Systems Forage sorghums are well suited for reduced tillage management systems. As with all crops planted into reduced or no tillage situations, adequate seed-to-soil contact is critical. Planting equipment (planters and drills) should be outfitted with proper coulters, trash managers and press wheels to ensure optimum seed placement and soil coverage. Soils have a tendency to warm slower in reduced tillage systems due to higher levels of plant residue remaining on the soil surface.

Agronomic Management

Seed-to-soil contact is critical for proper germination

60

Some crop residues can reduce germination and seedling growth of sorghum through a process called allelopathy (toxic compounds are released from the decomposing residue). Cereal rye (secale cereale) has been identified as a crop that will reduce sorghum stand establishment. Therefore, sorghum should not be planted into reduced or no tillage conditions where rye was the previous crop.

If sorghum is planted into a field following a rye crop, then conventional tillage techniques should be used.

Planting Date Soil Temperature Sorghums are warm season grasses so warm soil temperatures are important for rapid germination and emergence. The ideal soil temperature for planting is Sorghums are well suited for reduced and no-tillage systems

68Âş F. However, forage sorghum can be planted at soil temperatures of 60Âş F when warm weather is forecast for the next several days. If at all possible avoid planting into cool soil conditions. Cool soils will delay germination and emergence and expose seed and seedlings to the soil borne disease complex. Early plantings often result in poor emergence and lower than desired plant populations. Sorghums are less tolerant of cool conditions than corn and are sensitive to low temperature stress. Monitoring soil temperature prior to planting is a good management practice, especially in reduced or no tillage situations.

Planting Depth The optimum planting depth for sorghums is about 1.0 to 1.5 inches. Planting depth may vary depending upon soil type and moisture conditions.

Row Spacing There is not an optimum row spacing for forage sorghums, although narrower row spacings tend to produce higher yields. The best row spacing is the one that is tailored to the producer’s production system, equipment needs and forage requirements for the livestock enterprise. One of the primary attributes of forage sorghums over corn is the optimum production flexibility that sorghum provides from both a row spacing and seeding rate perspective.

planting into cool soils which will delay germination.

Agronomic Management

Developmental research is underway addressing increased tolerance to cold temperatures during germination, emergence and early season growth.

Preliminary findings are very promising. In the near future, cold temperature traits in forage sorghums will expand adaptability to more northern regions and allow earlier planting opportunities in traditional regions.

Additionally, the ability to plant earlier in traditional southern geographies would coincide with early spring rainfall and more moderate spring temperatures, which would minimize potential risks from mid-summer heat stress.

Avoid

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Narrower

Effect of Row Spacing on Forage Sorghum Silage Production Planted generally at 8 lbs./acre and Harvested in the Dough Stage

row spacings

produce

Year

higher

Row Spacing (inches)

2001 (Tons/acre)

2002 (Tons/acre)

yields.

12

24.0 a

21.4 a

18

19.1 b

19.0 b

36

16.0 c

15.7 c

2001 - Irrigated 2002 - Non-irrigated, adequate seasonal rainfall Means followed by the same letter within a column are not significantly different.

Sanderson, et al. 1992. Texas Agricultural Experiment Station

AGRONOMIC MANAGEMENT

Table 6. Effect of Row Spacing on Forage Sorghum Silage Production Planted at 8 lbs./acre and Harvested in the Dough Stage.

62

Each forage sorghum type lends itself to differing row spacing and plant population requirements, depending upon the production situation (e.g. hay versus silage production, BMR 6 versus conventional types). Plant population is a more important factor than row spacing.

Forage sorghums for silage production are often planted in various row configurations from 6 to 30 inches to accommodate harvesting equipment. Narrower row spacings generally produce higher biomass yields (Table 6).

Sudangrass and sorghum-sudangrass are most often intended for grazing and haying operations.

Consequently, they are generally planted in narrow rows and in most cases they are planted with a grain drill.

Seeding Rates Planting rates for forage sorghums vary by type and the intended use of the forage (e.g. hay, green-chop, grazing, silage) and irrigated or dryland conditions.

Below are some general guidelines, but it is best to consult with your local seed provider for specific planting recommendations for your sorghum product.

Achieving the optimum plant population is the most important aspect of a successful forage sorghum production system and is a critical production practice.

Most forage sorghums are planted at high populations to reduce stalk diameter, which improves forage quality and palatability.

Small stalks also allow faster drying time following cutting.

Achieving the optimum plant population is the most important aspect of the production system.

Sudangrass, sorghum-sudangrass – hybrids are typically seeded at higher rates than forage sorghums.

Wider row spacings (greater than 20 inches) will require lower seeding rates, ranging from 10 to 15 lbs/acre. Use lower rates for dryland and higher rates for irrigated production. Narrower row spacings should be planted at 15 lbs/acre dryland, and 25 lbs/acre irrigated.

Agronomic Management

Forage sorghums – are normally planted in a range of 6 to 20 lbs/acre (16,000 seed/lbs.) Narrow row spacings (6 to 20 inches) will require higher seeding rates than wider row spacings (greater than 20 inches). Dryland seeding rates should be about half to two-thirds the irrigated rates. Although forage sorghums are not the best choice for hay operations, if they are used then higher seeding rates should be planted to reduce stalk size.

63

General Seeding Rate Guidelines for Conventional Sorghums Dryland

Irrigated

Row Spacing (inches) 6 to 20 Forage Type

> 20

6 to 20

> 20

Seeding Rate (lbs./acre)

Forage Sorghum

—

8

20

12

Sorghum-sudangrass

15

10

25

15

Photoperiod Sensitive

15

10

25

15

Table 7. General Seeding Rate Guidelines for Conventional Sorghums.

Do not plant BMR 6 hybrids

AGRONOMIC MANAGEMENT

at rates intended for conventional types, those

64

rates are too high.

Seeding Rate Guidelines for BMR 6 Types Most forage sorghums are recommended to be planted at the higher end of seeding rate guidelines to insure smaller stalk diameter, thereby reducing lignin content and improving quality and palatability. However, BMR 6 types possess very low lignin content (improved digestibility over conventional types by more than 40%) which demands a different management approach.

With the high level of digestibility of BMR 6 types it is unnecessary to establish high plant populations. The following guidelines provide for the best quality, production and standability for BMR 6 types. The lower seeding rates support larger stalk diameters which prevent lodging and maximize biomass tonnage. Do not plant BMR 6 hybrids at rates intended for conventional types – those rates are too high for BMR 6 types and increases lodging risk.

Planting BMR 6 types at high seeding rates increases lodging risk

General Seeding Rate Guidelines for BMR 6 Sorghum Types Dryland Drilled Sorghum Type

Irrigated

Rows

Drilled

Rows

Seeding Rate (lbs./acre)

Forage Sorghum BMR 6 (14,000 seed/lbs)

5 to 9

4 to 7

6 to 9

5 to 8

Forage Sorghum Brachytic Dwarf BMR 6 (16,000 seed/lbs)

3 to 5

3 to 5

5 to 7

5 to 7

10 to 30

—

12 to 35

—

Sorghumsudangrass BMR 6 (13,000 to 15,000 seed/lbs)

Sorghum-sudangrass Brachytic Dwarf BMR 6 10 to 25 (13,000 to 15,000 seed/lbs)

Forage production systems will

—

12 to 25

—

Table 8. General Seeding Rate Guidelines for BMR 6 Sorghum Types.

Although sorghums have a reputation for high production in less than optimum environments, like all crop plants forage sorghums will respond to fertility. Fertilizer applications should be based upon results obtained from a soil test for a given field and an appropriate yield goal. Obtaining soil tests annually or at a minimum every two years provides a good record of changing soil fertility status and helps in determining future fertility needs. There is no substitute for soil testing. As opposed to grain production systems where stover is returned to the soil, forage production systems will remove large amounts of nutrients, especially nitrogen and potassium that will need to be replenished through a sound soil fertility program. High yielding forage sorghums producing over 20 tons of biomass can remove over 120 lbs of nitrogen and 280 lbs of potash as K2O. Consequently, annual soil testing is extremely important to determining crop needs and for maintaining an accurate historical record of soil nutrient trends.

amounts of nutrients, so soil testing is critical to determining proper nutrient levels.

AGRONOMIC MANAGEMENT

Soil Fertility

remove large

65

pH Condition The optimum pH for sorghum is 6.0 to 7.0. At high pH conditions (7.5 and higher), sorghums can suffer from micronutrient deficiencies of iron, manganese, and zinc.

The primary symptom will be chlorosis (yellowing and bleaching of leaves). In high pH conditions, these micronutrients become insoluble and are not readily available to the plant.

Excessive

Nitrogen

nitrogen can Nitrogen is the most heavily applied nutrient used

for sorghum production, and is also the most difficult to

create potential properly manage because of its reactivity and mobility

in the soil environment. Inadequate nitrogen reduces

lodging and yield potential, whereas excessive nitrogen can create

potential lodging problems and nitrate toxicity issues.

Recommended nitrogen rates are based on the issues. nitrogen required to produce a crop at a realistic yield goal, and should be reduced by credits for residual nitrate nitrogen (NO3-N) in the soil, as well as by any NO3-N applied in irrigation water.

AGRONOMIC MANAGEMENT

nitrate toxicity

66

Nitrogen management is the second most critical aspect of a forage sorghum production system behind plant population, especially when growing BMR 6 types.

Estimated Nitrogen, Phosphorus, and Potassium Requirements for Sudangrass and Sorghum-sudangrass Hay Production Sudangrass and Sorghum-sudangrass types

Each Hay Harvest

Hay Production Nitrogen

Phosphorus P2O5

Potassium (K2O)

lbs. of Nutrient/acre

45 to 60

65

80

Table 9. Estimated Nitrogen, Phosphorus, and Potassium Requirements for Sudangrass and Sorghum-sudangrass Hay Production.

Due to the potential for nitrate accumulation, it is recommended that for haying/grazing operations no more than 45 to 60 lbs of nitrogen per acre be applied preplant, and 45 to 60 lbs of nitrogen per acre be applied at each harvest or grazing period. For sudangrass and sorghum-sudangrasses, the seasonal needs for the crop will be between 1.0 to 1.25 lbs of nitrogen per growing day. Do not over-apply nitrogen fertilizer due to potential lodging and nitrate toxicity issues.

Seasonal

Estimated Nitrogen, Phosphorus, and Potassium Requirements for Forage Sorghum Silage Production Forage Sorghum types 35% DM

Silage Production Nitrogen

Tons biomass/acre

Potassium (K2O)

lbs. of Nutrient/acre

50 75 100 125 150

45 65 75 75 75

sorghum-sudangrass are 1.0 to 1.25 lbs of nitrogen per

80 100 120 140 160

Table 10. Estimated Nitrogen, Phosphorus, and Potassium Requirements for Forage Sorghum Silage Production.

Soil testing and previous cropping and fertility history should be used to credit any nitrogen that might be present in the upper portions of the soil profile (down to a 24 inch depth). Split applications of nitrogen are more efficient than applying the total amount of nitrogen in a single preplant application. With center pivot irrigation systems, nitrogen can be metered through the irrigation system for very efficient delivery.

growing day.

AGRONOMIC MANAGEMENT

10 15 20 25 30

Phosphorus P2O5

needs for

67

If nitrogen is to be applied in a side-dress operation it should be made by 20 to 30 days after emergence to avoid root pruning. The sorghum root system is extensive and it is largely responsible for the crops unique drought tolerance and high productivity under hot and dry conditions, so the last thing a grower wants to do is damage this massive root system.

Good Rule: Apply no more than 60 lbs of nitrogen fertilizer per acre in a

Agronomic Management

preplant

68

operation.

Nitrogen Management Guidelines for BMR 6 Types Because BMR 6 types contain less lignin than conventional sorghums, it is extremely important to manage nitrogen rates to minimize the potential for lodging. High to excessive nitrogen levels promote very large plant development and the potential for lodging is greatly increased. A good rule to follow is to apply no more than 60 lbs of nitrogen fertilizer per acre in a preplant operation and follow each harvest or grazing period with 30 to 40 lbs of nitrogen per acre on hay and grazing types and 30 to 50 lbs of nitrogen per acre on grain type forage sorghum. This will minimize any potential lodging problems.

Credits for NO3-N from Irrigation Water In some regions (for example in the High Plains of Texas and certain areas in Nebraska), irrigation water contains moderate to high levels of NO3-N that should be credited toward sorghum nitrogen requirement. In order to determine if irrigation water contains significant NO3-N, a water sample must be collected and submitted to a testing laboratory. For every one ppm of NO3-N in irrigation water, 0.23 lbs per acre of nitrogen will be added to the soil with each inch of water applied.

Thus, one acre-foot (12 inches) of 10 ppm NO3-N irrigation water would supply about 27 pounds of nitrogen per acre. This can be calculated using the following: ppm of NO3-N in water x 0.23 x inches of water applied = lbs of nitrogen per acre added.

As an example, suppose 15 inches of irrigation water are applied and the water test indicates 10 ppm for NO3-N. Based on the above formula, an additional 34.5 lbs of nitrogen per acre will be applied during the growing season (10 ppm x 0.23 x 15 inches = 34.5 lbs N per acre). Table 11 provides a quick reference for other irrigation amounts and irrigation water NO3-N concentrations. The pounds of nitrogen added in irrigation water should be subtracted from the overall amount needed by the crop for a specific yield goal.

Plant Available Nitrogen in Irrigation Water NO3-N in Irrigation Water (ppm) Water Applied (inches)

20

30

40

lbs nitrogen added/acre

20 27 34

41 55 68

61 83 102

82 110 136

Table 11. Plant Available Nitrogen in Irrigation Water

Phosphorus and Potassium Phosphorus and potassium (potash) requirements for sorghum will be slightly lower than corn. Soil testing is the best means for determining seasonal needs. Depending upon soil test levels, phosphorus needs will be from 0 to 75 lbs P2O5 per acre and potassium requirements ranging from 0 to 160 lbs K2O per acre. These nutrients should be applied preplant and can be banded for most efficient use.

In field situations where phosphorus and/or potassium are at very high levels, sorghums have the ability to “mine� the soil. This could be especially important in

AGRONOMIC MANAGEMENT

9 12 15

10

69

Agronomic Management

70

Iron chlorosis symptomology – note interveinal chlorosis areas with high soil phosphorus and potassium levels due to repeated heavy manure applications.

High potassium levels in forage have the potential to cause health problems, specifically milk fever when fed during the latter stages of pregnancy; therefore, it is very important to soil test regularly to determine soil nutrient levels.

Other Nutrients Sorghum is sensitive to certain micronutrient deficiencies, specifically iron and zinc. In high pH soils (greater than pH 7.5), iron and zinc are less available to the plant. Although there may be ample supply of each

nutrient in the soil, the iron and zinc are bound by calcium compounds that are not soluble and thus the iron and zinc are unavailable for uptake.

Field history is the best indicator of whether iron chlorosis problems will occur. If the field has a history of producing iron chlorosis problems, then a foliar fertilizer product such as iron sulfate will need to be applied in one or multiple applications to maintain a healthy crop.

Sulfur is also an important nutrient because it can affect nitrogen metabolism in the plant. Deficiencies of sulfur reduce protein synthesis which can lead to increased nitrate levels in the plant. Sulfur should be applied according to soil test recommendations.

Agronomic Management

Iron chlorosis can be variable in the field, depending on soil conditions

71

Weed Management in Forage Sorghums 72

WEED MANAGEMENT

Effective weed control is essential in producing high yielding, high quality forage sorghum. However, weed control can be challenging because sorghum is a relatively small seeded plant that can emerge slowly, allowing weeds to compete for light, water, nutrients, and space. Weed control is complicated by the fact that relatively few herbicides are labeled for use in forage sorghum.

73

Therefore, a major component of any weed control program is establishing a good stand quickly, allowing sorghum to emerge and develop rapid growth without weed competition. A combination of cultural, chemical, and possibly mechanical weed control will be necessary for maximum production.

Start Clean

WEED MANAGEMENT

A clean weed-free seedbed is a key first step in forage sorghum production.

74

Because of the small number of herbicides registered for use in forage sorghum and a relatively high seeding rate, starting with a clean, weed-free seedbed is a key first step in forage sorghum production. Weeds can be removed from the seedbed through tillage or burndown herbicide applications. Burndown can be achieved economically with broad spectrum herbicides or tankmixes that have little or no residual activity. These are commonly Roundup, Touchdown and other glyphosate brands, Ignite (glufosinate), 2,4-D, or dicamba. Burndown applications should be made at least three weeks prior to planting and preferably six weeks.

Because of a lack of labeled herbicides, there are few chemical control options for managing weeds in sudangrass. Therefore, weed control must be achieved through cultural means such as starting with a clean seedbed, planting high quality seed into a moist seedbed for rapid germination and emergence, and achieving a good stand that will reach canopy closure quickly. Established stands of sudangrass and sorghum-sudangrass are very competitive with weeds.

Herbicides Labeled for Use in Forage Sorghums common name HerbicideA

Labeled Crops

Interval Prior To

SorghumSorghum sudan Sudangrass

Rainfast Timing (hrs)

Grazing

Feeding

YES

YES

NO

PP PRE POST

4

21

21

s-metolachlor Dual II Magnum

YES

YES

NO

PP PRE

—

NR

NR

atrazine + s-metolachlor Bicep II Magnum

YES

YES

NO

PRE PP

—

NR

NR

atrazine + s-metolachlor + glyphosate Expert

YES

YES

NO

PP PRE

2

60

60

glyphosate + dicamba Fallow Star

YES

YES

NO

PP PRE

6

56

56

atrazine + dicamba Marksman

YES

YES

NO

PP PRE POST

4

21

21

glyphosate + s-metolachlor Sequence

YES

YES

NO

PP PRE

4

NR

NR

dicamba Clarity

YES

YES

NO

PP POST

4

Mature GrainB

Mature GrainB

carfentrazone Aim

YES

YES

NO

POST

6

NR

NR

bromoxynil Buctril

YES

YES

YES

POST

1

45

45

bromoxynil + atrazine Brozine

YES

YES

NO

POST

4

45

45

2,4-D

YES

YES

NO

POST

4

7

7

bentazon Basagran

YES

YES

NO

POST

4

12

12

A B

Other brand names exist; for simplicity only one product is listed. NR = no restrictions See label for dairy restrictions.

WEED MANAGEMENT

atrazine Atrazine

75

Pre-emergence (PRE) Herbicide Use Effective use of PRE herbicides reduces early weed competition. Sorghum, however, is sensitive to some PRE herbicides. Most PRE herbicides provide effective control of small seeded broadleaf weeds. More importantly, however, a PRE application may be the only opportunity for effective control of annual grasses, especially seedling johnsongrass.

A PRE Atrazine is typically the PRE herbicide of choice and application provides effective control of most broadleaves and some may be the only opportunity for effective

WEED MANAGEMENT

grass control.

76

annual grasses. However, atrazine will not provide control of johnsongrass, fall panicum, foxtails, witchgrass and broadleaf signalgrass. If weeds are present at the time of application, atrazine can be applied in combination with a contact herbicide such as Gramoxone Inteon, Roundup, Touchdown, or other glyphosate brands. Atrazine should not be applied to sudangrass.

Dual Magnum (s-metolachlor) may be applied PRE to forage sorghum if seed is properly treated with Concep.

Failure to properly treat sorghum seed with Concep will result in crop injury. Metolachlor provides effective control of most small-seeded broadleaves and is effective on more grass species than atrazine.

Pre-plant and Pre-emergence Herbicides for Forage Sorghum Herbicide

atrazine AAtrex 4L or 90DF Atrazine 4L or 90F

Rate

Comments/Restrictions

1.6-2.0 qt 1.8-2.2 lb

PRE, PPI, or PPI. Do not use on sandy soils where organic matter is less than 1%. Do not apply to sudangrass. Broadleaves and some annual grasses.

1.0-1.67 pt

PRE, PP, or PPI. Seed must be treated with Concep.

Use higher rates on soils with higher clay content.

Apply no more than 14 days prior to planting on sandy soils. Small-seeded broadleaves and annual grasses. Do not apply to sudangrass.

1.6-2.1 qt

PRE, PP, or PPI. Seed must be treated with Concep.

Do not use on sandy soils where organic matter is less than 1%. Apply no more than 14 days prior to planting on sandy soils. Broadleaves and annual grasses. Do not apply to sudangrass.

s-metolachlor Dual II Magnum Charger Max Brawl II Cinch

s-metolachlor + atrazine Bicep II Magnum Charger Max ATZ Brawl II ATZ Cinch ATZ

PRE or PP. Apply up to 30 days prior to planting.

Seed must be treated with Concep. Do not apply to sudangrass. Broadleaves, annual grasses, and existing weeds.

glyphosate + dicamba

PRE for no-till or ridge plant. Apply at least 15 days prior to planting. Burndown of existing weeds.

Do not apply to sudangrass.

33-44 oz

Fallow Star

atrazine + dicamba Marksman

2 pts

PP. Apply at least 15 days before planting. 60 day PHI. Broadleaves and some annual grasses.

Do not apply to sudangrass.

Banvel K + Atrazine

s-metolachlor + glyphosate

2.5-4 pt

Sequence

dicamba Clarity Banvel Sterling Distinct

0.5 pt

PP or PRE. See notes for s-metolachlor. Seed must be treated with Concep. Burndown, small-seeded broadleaves, and annual grass preemergence.

Do not apply to sudangrass.

PP. Apply at least 15 days prior to planting.

Broadleaf burndown.

Do not apply to sudangrass.

WEED MANAGEMENT

s-metolachlor + 2.5-3.0 qt atrazine + (1-1.5% OM) glyphosate 3-3.75 qt Expert (1.5% OM)

77

Bicep II is a premix of metolachlor and atrazine and is an effective herbicide combination. However, seed must be treated with Concep and Bicep cannot be applied to sudangrass or sorghum-sudangrass hybrids. “Expert� is a premix of atrazine, metolachlor, and glyphosate and is labeled for PRE use in forage sorghum. Residual activity of Expert is similar to Bicep II and the addition of glyphosate to the premix will provide burndown control of existing grasses, allowing for a clean start.

In narrow rows canopy closure

Post-emergence (POST) Herbicide Use

WEED MANAGEMENT

Post-emergence weed control in forage sorghums will occur is usually a combination of cultural, chemical, and mechanical control. An actively growing, healthy stand quickly and of sorghum is very competitive with most weed species and provides very effective weed control, shade-out weeds. especially when broadcast seeded. Once sorghum is established, it can be very competitive with weeds.

78

Cultivation is an option when sorghum is planted in rows. Time cultivation to control weeds before they are large and prior to the point where crop injury from root pruning can occur (prior to 30 days after emergence of the crop). In narrow rows, canopy closure should occur quickly and shade-out emerging weeds.

Atrazine can be applied to actively growing weeds before sorghum reaches 12 inches in height for effective control. Best control is achieved if applications are made before broadleaves such as common lambsquarter and pigweed reach 6 inches in height.

Do not apply atrazine to sudangrass.

Specific mention of a product is neither an endorsement nor a warranty of performance by Agrithority or Advanta. Information in this publication related to crop protection chemicals is based on the best available information at the time of printing. In all cases, the actual product label takes precedence over any information contained within this publication.

Pesticide labels can and do change. ALWAYS, read and follow label instructions when using crop protection chemicals.

Some herbicide options do exist for POST control of broadleaf weeds in forage sorghum. Buctril, Basagran, Aim, and 2,4-D are options. Buctril and Basagran provide good control of broadleaves and are labeled for use in forage sorghum. Tankmixes of Basagran and atrazine can provide better broadleaf control than Basagran alone. 2,4-D can cause injury if the herbicide gets into the whorl of the plant; therefore, only directed applications that minimize contact with the crop are recommended. Combinations of Buctril with 2,4-D, dicamba, and atrazine are labeled for use. The addition of 2,4-D or dicamba to Buctril can improve control of pigweed and larger broadleaves; however, pay close attention to labeled weed sizes when using Buctril and Buctril tankmixes.

A healthy vigorous stand of sorghum is the most effective weed control measure.

WEED MANAGEMENT

Post-emergence annual grass control is difficult in forage sorghums. Currently there are no labeled herbicides for over-the-top applications that will control annual grasses, with the exception of the limited control that may be achieved with atrazine applied before sorghum reaches 12 inches in height. This underscores the critical need for starting with a weed-free seedbed, using a PRE herbicide at planting, and using early POST herbicides as needed. A healthy, vigorous stand of sorghum is the most effective weed control measure and will out-compete most grasses.

79

Post-emergence Herbicides for Use in Forage Sorghum Herbicide

carfentrazone Aim

atrazine

AAtrex 4L or 90DF Atrazine 4L or 90F

bromoxynil

Buctril Buctril 2EC Broclean2EC Brox 2EC Maestro 2EC

bromoxynil + atrazine Brozine

Rate

Apply up to 6-leaf growth stage. Use drop nozzles or hoods to limit deposition in the whorl, especially 0.5-0.8 oz + NIS under cool, cloudy conditions. Tank mixes with 2, 4-D (amine), Atrazine, can improve broadleaf and grass control. Broadleaves. Do not apply to sudangrass.

3.2-4.0 pt 1.8-2.2 lb

Apply from emergence through 12-inch crop height but before weeds exceed 1.5 inches. Season-use restrictions apply. Do not apply to sudangrass.

Broadleaves and some annual grasses.

0.5-0.75 pt for Buctril 4EC (Double for 2EC formulations)

POST. Use lower rate at 3-leaf stage and higher rate 4-leaf stage. Do not apply after pre-boot stage.

2 pt can be applied through chemigation. Refer to label for maximum weed sizes controlled. Most broadleaves.

1.5-3.0 pt

2,4-D

WEED MANAGEMENT

Various (consult labels for specific products)

80

0.33-0.66 pt

dicamba

Clarity Banvel Vision Sterling Blue

bentazon Basagran

Comments/Restrictions

8 oz

1-2 pts

POST. Use lower rate at 3-leaf stage and higher rate past 4-leaf stage. Do not apply after pre-boot stage.

Refer to label for maximum weed sizes controlled.

Most broadleaves and some annual grasses. Do not apply to sudangrass.

POST. Apply when sorghum is between 6 and 15 inches. Use drop nozzles to minimize crop contact on plants greater than 8 inches. Temporary crop injury can occur when applied under high soil moisture or temperature conditions. Sorghum hybrids exhibit varying levels of tolerance – contact your seed company rep for hybrid-specific recommendations. Do not graze within 30 days of application. Vapor drift from ester formulations can radily occur leading to potential damage to sensitive crops – consult state guidelines before use. Can be added to bromxynil for improved broadleaf control, especially pigweed. Broadleaves only.

Do not apply to sudangrass.

POST. Apply from emergence through 15 inches.

Use drop nozzles to minimize crop contact on plants greater than 8 inches. Do not graze or feed prior to mature grain stage. Can be added to bromxynil for mproved broadleaf control, especially pigweed.

Broadleaves. Do not apply to sudangrass.

POST. Do not exceed 2 pts per season. Do not apply to sorghum that is heading or blooming. Do not graze within 12 days of treatment. Do not use in California. May be tankmized with Atrazine or Clarity. Broadleaves. Do not apply to sudangrass.

Crabgrass

Fall panicum

Texas panicum

Goosegrass

Nutsedge, yellow

Shattercane

Witchgrass

P

G P

G

P

P

F

F

F

P

P

P

F

P

E G

E

E

F

E

E

E

F

P

E

F

P

E G

E

E

F

E

E

E

F

P

E

yellow foxtail

barnyardgrass

P

s-metolachlor

green/giant foxtail

Rhizome johnsongrass

atrazine (Atrazine)

common name (Herbiicide)A

Broadleaf signalgrass

Seedling johnsongrass

Herbicide Performance Ratings For Grass Control of Selected Species

(Dual II Magnum)

atrazine + s-metolachlor (Bicep II Magnum)

atrazine + s-metolachlor + glyphosate (Expert)

E1 E1 E1 E1 E1 E1 E1 E1 E1 E1 G1 E1 E1

glyphosate + dicamba (Fallow Star)

E

E

E E

E

E

E

E

E

E G

E

E

atrazine + dicamba

P

P

G P

G

P

P

F

F

F

P

P

(Marksman)

glyphosate + s-metolachlor (Sequence)

P

E2 E2 E2 E2 E2 E2 E2 E2 E2 E2 G2 E2 E2 P

P

P P

P

P

P

P

P

P

P

P

P

carfentrazone (Aim)

P

P

P P

P

P

P

P

P

P

P

P

P

P

P

P F

P

P

P

P

P

P

F

P

P

P

P

G F

G

P

P

F

F

F

F

P

P

bromoxynil (Buctril)

bromoxynil + atrazine (Brozine) 2,4-D

P

P

P P

P

P

P

P

P

P

P

P

P

bentazon (Basagran)

P

P

P P

P

P

P

P

P

P G

P

P

Other brand names exist; for simplicity only one product is listed.

Rating for POST weed emergence only. Residual control will be similar to Bicep II Magnum.

2 Rating for POST weed emergence only. Residual control will be similar to Dual II Magnum E = excellent control, 90% or better; G = good control, 80-90%; F = fair control, 50-80%; P = poor control, less than 50% A 1

WEED MANAGEMENT

dicamba (Clarity)

81

Hemp Sesbania

Canada thistle

Devilsclaw

Tropic croton

Sicklepod

Burcucumber

Mornigglory

Prickly sida

Velvetleaf

Smartweed

Ragweed (Giant)

Ragweed (Common)

E. Black nightshade

Waterhemp spp.

Pigweed spp.

Lambsquarters

Jimsonweed

common name (Herbiicide)A

Cocklebur

Herbicide Performance Ratings for Broadleaf Control of Selected Species

atrazine (Atrazine)

E E E E E E E F E G E G F G G G F F

s-metolachlor

P P F G G F F P P P P P P P P P P P

(Dual II Magnum)

atrazine + s-metolachlor

E E E E E E E G E E E G F G G G G F

(Bicep II Magnum)

atrazine + s-metolachlor + glyphosate (Expert)

E E E E E E E G E E E G E E G F G F

glyphosate + dicamba (Fallow Star)

E E E E E E E E E E E E E E G F G E

atrazine + dicamba

E E E E E E E E E G E E G G E G F G

(Marksman)

glyphosate + s-metolachlor

E E E E E G E G G E E G E E G F F F

WEED MANAGEMENT

(Sequence)

82

dicamba (Clarity)

E E E E E E E G E G G E F E E P G E

carfentrazone (Aim)

P P G G G G P P P E F E P P P P G P

bromoxynil

E E E F F G E E E G F G F P G G E G

(Buctril)

bromoxynil + atrazine (Brozine)

E E E E E E E E E G G G F G G G E G

2,4-D

E E E E G F E E F G G E P G G E G E

bentazon (Basagran)

E E G P P P G E E G G P P G F F P P

Other brand names exist; for simplicity only one product is listed.

Rating for POST weed emergence only. Residual control will be similar to Bicep II Magnum.

2 Rating for POST weed emergence only. Residual control will be similar to Dual II Magnum E = excellent control, 90% or better; G = good control, 80-90%; F = fair control, 50-80%; P = poor control, less than 50% A 1

Replant and Rotational Crop Restrictions for Forage Sorghum Herbicides Wheat, Winter

0

0

0

0

0

2CS 2CS 2CS 2CS 2CS 2CS

atrazine + Sorghum1, s-metolachlor + Corn glyphosate (Expert)

0

0

2CS 2CS 2CS 2CS NCS NCS

glyphosate + dicamba (Fallow Star)

NR

3

Sorghum, Corn

0

0

Sorghum1, Corn, Soybean, Cotton, Peanut

0

0

(Dual II Magnum)

atrazine + s-metolachlor

Sorghum1, Corn

(Bicep II Magnum)

atrazine + dicamba (Marksman)

glyphosate + s-metolachlor (Sequence)

dicamba (Clarity)

Corn

Soybean

0

Sorghum1, Corn, Soybean, Cotton, Peanut

Cotton

Sorghum Corn

Clover

Sorghum

atrazine (Atrazine) s-metolachlor

common name (Herbiicide)A

Alfalfa

Replant Option

Corn

Wheat, Spring

Rotational Restrictions (months)

2CS 2CS 2CS 2CS 2CS 2CS 4

9

4.5 4.5

0

0

0.5 NCS NCS 0.5 0.5 NCS NCS 2CS 2CS 10

10 2CS 2CS

4

9

4.5 4.5

0

0

0-42 0.5-42 4

4

42

42

42

42

carfentrazone (Aim)

Sorghum , Corn, Soybean, Cotton, Peanut

0

0

12

12

0

0

0

0

bromoxynil

Sorghum, Corn, Soybean

0

0

1

1

1

1

1

1

Sorghum, Corn

0

0

24

24

15

15

24

12

bromoxynil + atrazine (Brozine) 2,4-D amine

See label for specifics

7-14 15-30 days days

2,4-D ester

See label for specifics

7-14 days

NR

NR

bentazon (Basagran)

1

NCS NCS 0.5 0.5 NCS NCS 1-3 1-3

1

NR NR NR NR

2CS = two cropping seasons NCS = next cropping season NR = no restrictions 1 Use only CONCEP-treated seed 2 See label for specific requirements A Other brand names exist; for simplicity only one product is listed.

1 NR

1-3

7-30 days

NR NR

WEED MANAGEMENT

(Buctril)

1

83

WEED MANAGEMENT

Glyphosate 1X (above) and drift rate injury (right).

Leaves will yellow and progress to necrotic on the leaf margins.

Distinguishable from nutrient problems by necrotic leaf margins.

84

ALS-inhibitor injury from a PRE application. The photo shows injury from a PRE application of nicosulfuron. Severe injury can occur with reddened leaves, especially in situations when sorghum is planted following a failed corn crop that has had an application of an ALS-inhibiting herbicide.

ALS-inhibitor injury symptoms from POST application. Note the reddening of the midrib which should be visible on the upper and lower leaf surface. Often accompanied by interveinal yellowing at higher rates.

Drift (left) 1X rate (below).

Photos courtesy of Dr. Daniel Stephenson, LSU AgCenter and Dr. Paul Baumann, Texas AgriLife Extension Service

WEED MANAGEMENT

Mesotrione injury symptoms. Note bleaching of leaves.

Mesotrione is a corn herbicide for which carryover to sorghum should be avoided when planting sorghum following a failed corn crop.

85

Herbicide Resistance Management — A Challenge for all of U.S. Agriculture 86

Glyphosate resistant johnsongrass. Photo courtesy of Dr. Daniel Stephenson, LSU AgCenter

Left — Glyphosate resistant waterhemp

HERBICIDE RESISTANCE

Herbicide resistance management is a critical issue facing U.S. agriculture.

The development of resistant weeds to several modes of action has prompted the agricultural community to become more mindful of the need to employ resistance management and resistance mitigation techniques in their overall weed management program. In particular, resistance development of certain pigweed species to glyphosate and ALS-inhibiting herbicides has the potential to significantly influence not only herbicide selection, but the overall cropping system across the farm landscape.

87

Preventing herbicide resistance is far more cost effective in the long term than having to mitigate a resistance problem after it develops. Rotating crops and herbicide modes of action are recognized as keys to preventing the onset of resistance to certain important herbicides. The repeated use of any herbicide mode of action, in the absence of alternatives, results in a monoculture for weed control and greatly increases the likelihood of resistance developing. Employing a diversity of weed control measures across the landscape over time greatly facilitates preventing herbicide resistance.

A diversity Relatively few herbicides are labeled for use in forage of weed control measures across the landscape greatly facilitates

HERBICIDE RESISTANCE

the prevention of herbicide

88

resistance.

sorghums. While herbicide resistance is not now considered a “hot topic� in forage sorghum production, there are characteristics of the production systems that could favor the onset of resistance to key classes herbicides. Foremost among these are the repeated use of only one mode of action, especially in a no-till or minimum-tillage system. Tillage can be considered a weed control mechanism which helps mitigate resistance. However, in conventional tillage systems, producers should strongly consider rotating their herbicide modes of action from year to year. Recent experience in other crops indicates that herbicide resistance in weeds can occur in a variety of crops and cropping systems and forage sorghum producers are therefore not immune to the problem.

The following table lists the herbicides labeled for use in forage sorghums, their mode of action, and the likely risk for resistance development with repeated use.

Producers should consider this information closely when planning their weed control programs from year to year.

This includes forage sorghum as well as previous and future crops. Currently, there are 331 herbicide resistant weed biotypes documented worldwide and the list grows longer each day.

Labeled Herbicides for Use in Forage Sorghums and Their Modes of Action WSSA Number of Likelihood of Mode of Documented developing Action Group Resistant resistance with NumberB Weeds in USC repeated use

common name HerbicideA

Mode of Action

atrazine Atrazine

Photosystem II

5

23

High

s-metolachlor Dual II Magnum

Inhibition of very long-chain fatty acids

15

1

Low

5 + 15

0

Low

5 + 15 + 9

0

Low

atrazine + Photosystem II + s-metolachlor Inhibition of very Bicep II Magnum long-chain fatty acids Photosystem II + Inhibition of very long -chain fatty acids + EPSP synthase inhibition

glyphosate + dicamba Fallow Star

Synthetic auxin + EPSP synthase inhibition

4+9

0

Low

atrazine + dicamba Marksman

Photosystem II + synthetic auxin

4+5

0

Low

glyphosate + s-metolachlor Sequence

Inhibition of very longchain fatty acids + EPSP synthase inhibition

15 + 9

0

Low

dicamba Clarity

Synthetic auxin

4

6

Low

carfentrazone Aim

PPO inhibition

14

2

Medium

bromoxynil Buctril

Photosystem II (different from group 5)

6

1

Low

bromoxynil + atrazine Brozine

Photosystem II with different binding behaviors

5+6

0

Low

2,4-D amine

Synthetic auxin

4

6

Low

2,4-D ester

Synthetic auxin

4

6

Low

bentazon Basagran

Photosystem II (different from group 5)

6

0

Low

A B C

Other brand names exist; for simplicity only one product is listed.

Numerical system to describe modes of action is taken from the Weed Science Society of America.

As of August 2009, according to WSSA.

HERBICIDE RESISTANCE

atrazine + smetolachlor + glyphosate Expert

89

Insect and Disease Pests of Sorghum 90

Worm damage.

INSECT AND DISEASE

Insects are generally not a serious management issue in forage sorghums.

However, numerous insect pests can occasionally become problematic, such as wireworms, cutworms, different aphid species, sorghum midge, chinch bugs, spider mites, armyworms and corn earworms. Approved seed treatment insecticides can provide protection from early season pests.

91

Disease Management Diseases are generally not a serious management concern for forage sorghums. However, soil borne diseases can affect any crop including forage sorghums. Consequently an approved fungicide seed treatment should be applied to seed to prevent seed and seedling damage.

Charcoal rot, which develops under hot, dry conditions after the plants have bloomed, occasionally causes lodging problems. Early harvest may be necessary in the most severe cases.

Problems caused by soil and foliar pathogens can be minimized by selecting resistant hybrids, avoid planting in cool and wet conditions, and maintaining a good crop rotation scheme. Selecting sorghums that have anthracnose and fusarium tolerance is highly recommended for the Eastern and Southeastern U.S. An approved fungicide seed

INSECT AND DISEASE

treatment should be applied to prevent seed and seedling

92

damage

Seedling Disease Complex

Rhizoctonia solani, Fusarium sp., Pythium sp.

Seedling diseases are more problematic when planting into cool and wet soil conditions. Because of the cool conditions, germination and emergence processes are slowed, providing pathogens with greater opportunity to attack the germinating seed and seedlings. Lack of crop rotation for an extended period also favors development of seedling disease. Growers should utilize high quality seed treated with approved fungicide protectants, and soil temperature should be at least 60ยบ F before planting.

Head Smut

Disease photos courtesy: Dr. Tom Isakeit, Texas AgriLife Extension Service

Sorghum Downy Mildew

Peronosclerospora sorghi Young plants infected with this fungus are pale yellow or have light-colored streaking on the leaves, often accompanied by a white fuzzy (downy) growth on the underside of the leaf. These symptoms indicate a systemic soil borne infection and these plants will not produce a head.

Germinating sorghum seed is more prone to infection early in the season, when soil temperatures are cooler. Leaves that emerge later have white parallel stripes of green and white tissue, which should not be confused with iron deficiency (chlorosis). Iron chlorosis symptomology will have a yellowing between the leaf veins. The white stripe symptomology of downy mildew is not limited to veins and will vary in width. Later in the season these striped areas turn brown and become necrotic, resulting in a shredded leaf. Management consists of using a ystemic fungicide seed treatment and planting resistant hybrids.

Fusarium Stalk Rot

Sorghum Downy Mildew

Plant disease resistant hybrids when possible.

Head Smut Sporisorium reilianum Symptomology of this fungal disease is characterized by the presence of dark-brown smut galls that emerge in place of the panicle. Plants become infected in the seedling stage but symptoms are not seen until heading.

Fusarium Stalk Rot

INSECT AND DISEASE

Fusarium moniliforme, and Fusarium thapsinum Stalk rot caused by Fusarium can affect both roots and stalks of sorghum. Fusarium stalk rot is typically associated with early season dry conditions, followed by cool, wet weather. Fusarium stalk rot is often associated with both high and low nitrogen fertility, high plant populations, and lack of crop rotation. Any conditions causing plant stress can support stalk rot development.

93

Anthracnose Colletotrichum graminicola Anthracnose fungus damages both foliage and stalks of sorghum. Leaf lesions are small, elliptical to circular, usually less than 3/8-inch in diameter. These spots develop small, circular, straw-colored centers with wide margins that may vary in color from reddish to tan to blackish purple. The spots may coalesce to form larger areas of infected tissue. Stalk and peduncle (stem that holds the panicle) infections can inhibit water flow (and mineral nutrients and sugars) to the developing grain causing poor development. The fungus also Anthracnose invades individual kernels and the small branches of the panicle. Management includes use of resistant hybrids, crop rotation, and burial of crop residue.

INSECT AND DISEASE

Rust

94

Puccinia purpurea The rust fungus appears on leaves as small raised pustules that rupture and release reddish-brown, rust colored spores. Pustules occur on both the upper and lower leaf surfaces. Rust is generally observed on older, mature plants and is found on the oldest leaves.

In severe infestations, forage sorghum yields can be reduced. The same fungus also infects Johnsongrass and can overwinter in southern production areas.

Charcoal Rot

Macrophomina phaseolina The charcoal rot fungus infects stalks and the symptomology is an internal shredding of tissue at and above the ground line. This can be observed by splitting the stalk with a knife and noting the deteriorated soft pith tissue leaving the tougher vascular strands. Fungal structures called sclerotia (resembling black pepper) can

be observed in the affected tissue. Another type of stalk rot (Pythium sp. and Fusarium sp.) may show the shredded condition but the black sclerotia will not be present.

Charcoal rot development is favored by hot and dry conditions during the postflowering period. Host plants are usually in the early-milk to late-dough stage when infection occurs. Charcoal rot is a very common fungus and is widely distributed. Management of crop residue, crop rotation, avoiding Charcoal Rot excessive plant populations, proper fertility, and selecting drought-tolerant, lodging-resistant hybrids are recommended to minimize the occurrence.

Sooty Stripe

Sooty Stripe

INSECT AND DISEASE

Ramulispora sorghi Sorghum is the only known host of this fungal pathogen.

Plants may be infected at any stage of growth but older leaves are infected first. Initial symptoms appear as small water soaked spots on leaf blades and sheathes.

Spots may be circular to elongated and reddish-brown to tan in color. The lesions have a reddish purple to tan border and are surrounded by a yellow area.

Crop rotation is the best management practice.

95

Irrigation Management 96

IRRIGATION MANAGEMENT

One of the great benefits of utilizing sorghum over corn is the excellent heat and drought tolerance that sorghum possesses. Sorghum will produce similar yields to corn and will do so with 30 percent to 50 percent less water.

Generally, sorghums will yield 1.75 to 2.5 tons of biomass per one inch of irrigation water applied, while corn will produce less than one ton per inch of water applied.

97

One of the keys to irrigation management of sorghum is not to over water the crop during later stages of development prior to harvest. Behind seeding rates and nitrogen management, this is a critical best management practice.

Peak Sorghum Similar to most crops, early season water use in Water Usage: sorghum is relatively low (less than 0.2 inches of water

per day). Between 30 and 60 days after planting, water use will increase as the plant begins to accumulate high plants use from levels of biomass. The peak water use period will be between 50 to 80 days after planting. During this peak 0.3 to 0.4 inches stage in water use the plant can use from 0.3 to 0.4 inches of water per day.

At 50 to 80 days,

IRRIGATION MANAGEMENT

of water daily.

98

For optimum production it is necessary to begin the season with a full soil water profile. If rainfall has not been adequate to sufficiently recharge the profile, then a preplant irrigation will be necessary. The initial irrigation should be applied at about 30 to 40 days after planting, with the second application about three weeks later.

Depending upon in-season rainfall, production of 20 tons per acre will require about eight to 16 inches of irrigation water.

Irrigation Effect on Yield, Water Use and Quality of Forage Sorghum Irrigation Level

Plant Height (ft.)

Yield (tons/acre)

Total WUE water used (tons/total (inches) water used)

Dryland

3.3

9.1

14.2

1 irrigation 4.5

11.6

2 irrigations 5.8 4 irrigations 7.6

% IVTD

% ADF

% CP

0.6

85.7

27.3

10.0

18.2

0.6

84.1

28.8

8.9

16.1

22.8

0.7

83.3

29.2

7.7

23.4

29.4

0.7

80.6

29.5

6.8

Bean, et al. 2003. Texas Cooperative Extension

Table. 12. Irrigation Effect on Yield, Water Use and Quality of Forage Sorghum.

Irrigation should be terminated at boot to the early heading stage. This will help prevent lodging and will peed the dry-down process, and ensure that the grain will be at the proper moisture in the milk to soft dough stage.

IRRIGATION MANAGEMENT

Table 12 demonstrates forage sorghum production potential across different irrigation regimes. In this study each furrow irrigation supplied about four inches of water.

99

Grazing Systems Irrigation Management For sudangrass and sorghum-sudangrass, irrigate after harvest and terminate watering two weeks prior to the next harvest. The initial harvest should be timed at the boot stage, which is typically 50 to 60 days after planting. Subsequent harvests should be on a 45-day schedule. If managing for dairy cattle, the initial harvest could be timed at about 45 days after planting and subsequent harvests on a 30-day schedule.

Irrigation Water Quality and Salinity

IRRIGATION MANAGEMENT

Salinity can be a problem in the west and southwestern states, primarily California, Arizona, New Mexico and Texas. Susceptibility to salt injury varies by crop and sorghum is much more tolerant of salinity than corn.

Sorghum is classified as a moderately salt tolerant crop, compared with corn that is classified as moderately sensitive.

100

Irrigation water quality is determined by the total amounts of salts and the types of salts present in the irrigation water. A salt is a combination of two elements

Poor stand, reduced growth and water stressed appearance caused by severe salinity

(ions). One has a positive charge (e.g. sodium) and one has a negative charge (e.g. chloride). Generally, water contains a variety of salts including sodium chloride (table salt), sodium sulfate, calcium chloride, calcium sulfate (gypsum), etc. The types and amounts of salts in the water and thus the salinity of the water depend on the source. Water dominated by salts other than sodium salts is often termed “gyppy water� and does not pose the soil structural problems associated with sodium laden water.

The quality of well water depends on the composition of underground formations from which the water is pumped. When these are marine formations, they usually have higher salt levels.

Marginal leaf burn and iron chlorosis problems associated with salinity

IRRIGATION MANAGEMENT

Saline irrigation water can cause two major problems in crop production – salinity hazard and sodium hazard. When irrigation water is used by plants or when it evaporates from the soil surface, salts contained in the water are left behind and can accumulate. These salts create a salinity hazard because they compete with the plant for water.

Elevated salts in irrigation water and soil solution cause a situation called high osmotic potential. As osmotic potential increases, the salts in the water compete with the plant for available water. So, in very severe salinity situations even if the soil is wet the plant can appear to be in a drought stressed condition because it cannot access the water in the soil. Also, certain salts can reduce the availability of certain micronutrients such as iron. Foliar applications of salty water often cause marginal leaf burn.

101

IRRIGATION MANAGEMENT

Sodium hazard is caused by high levels of sodium which can be toxic to plants and damage medium to fine textured soils. When the sodium level in a soil becomes high, the soil will lose its structure, become dense and form hard crusts on the surface. To determine if irrigation water may be a problem, a water sample should be analyzed for total soluble salts, sodium hazard, and toxic ions.

High levels of sodium cause soil crusting and plant damage

102

Sodium hazard is based on a calculation of the sodium adsorption ratio (SAR). The SAR is a measurement of the amount of sodium in the water. Toxic ions include elements such as chloride, sulfate, sodium and boron. In some cases, even though the salt level is not high, one or more of these elements may be at toxic levels to the crop.

Total soluble salts measures the salinity hazard by estimating the combined effects of all the different salts that may be in the water. It is measured as the electrical conductivity (EC) of the water. This may also be represented as total dissolved solids. Salty water carries an electrical current better than pure water, so the EC rises as the amount of salt increases.

Sorghum and corn differ in their ability to tolerate salinity. Critical levels for salinity, sodium hazard and toxic ions have been established for most crops and vegetables. These critical levels are not absolute – they provide an indicator of plant response and potential yield loss. These salinity factors can be expressed numerically in many different ways. The numbers have

Critical Values for Salts in Irrigation Water for Sorghum and Corn Measurement Electrical Conductivity (EC)

Units

Micromhos per centimeter umhos/cm Millimhos per centimeter mmhos/cm Decisiemens per meter dS/m Parts per million ppm Milligrams per liter mg/l Sodium Adsorption Ration (SAR)

No units

Sorghum

Corn

1,700 1.7 1.7 1,088 1,088

1,100 1.1 1.1 704 704

10

10

Toxic Ions (resulting in foliar damage)

ppm mg/l meq/l

3.0 3.0 0.3

2.0 2.0 0.2

ppm mg/l meq/l

710 710 20

533 533 15

ppm mg/l meq/l

710 710 31

533 533 23

McFarland, et al. 2002. Texas Cooperative Extension

Table 13. Critical Values for Salts in Irrigation Water for Sorghum and Corn.

IRRIGATION MANAGEMENT

Boron Parts per million Milligrams per liter Milliequivalents per liter Chloride Parts per million Milligrams per liter Milliequivalents per liter Sodium Parts per million Milligrams per liter Milliequivalents per liter

103

Note: the same relative meaning, but the units of

measurement used to express the values are different

Sorghum can (like saying 12 inches or 1 foot). Table 13 lists the

different factors and corresponding critical values for different units of measurement. These values represent levels of salinity the maximum salt level in irrigation water that can be used without reducing yield. Keep in mind that these than corn. values are estimates. Actual crop response may vary depending on soil type, rainfall, irrigation frequency, etc. tolerate higher

IRRIGATION MANAGEMENT

Irrigation water with a salt level near the critical value is referred to as marginal quality water. Marginal quality can be used, but it should be recognized that some production potential will be lost. Plants can grow in the presence of low levels of salts, but yield potential will be reduced.

104

Correcting poor irrigation water quality. Managing salt problems is not an easy task. The best solution for salt problems is fresh water recharge from rainfall which serves to leach salts below the root zone. Crop selection is an obvious management technique and sorghum is a fairly tolerant crop — much better than

corn. In situations where foliar damage is a concern, there are different methods and technologies available that minimize spray contacting the leaves. The Low Energy Precision Application (LEPA) and subsurface drip (SDI) systems are very effective at minimizing leaf contact and are also very water use efficient.

Increasing soil organic matter also provides benefit. Using manure as a fertilizer source and maintaining crop residue on the soil surface can improve water holding capacity and improve nutrient cation exchange capacity. Be aware that manures can contain high levels of salt so care should be taken to avoid over-application in salinity prone fields. A good management practice is to routinely have irrigation water tested by an accredited laboratory.

Crop selection is an obvious management technique and sorghum is a fairly tolerant crop...

IRRIGATION MANAGEMENT

Preliminary observations indicate that BMR 6 types are more tolerant to salinity than conventional sorghums. Advanta has an active research program addressing salinity tolerance.

105

Harvesting at Optimum Growth Stage 106

Harvesting sorghums at the optimum stage of growth is critical to balancing production and quality. Older, more mature crops will have lower forage quality, yielding a less nutritious feedstock than a crop harvested at the optimum time.

HARVESTING

Forage sorghum ready for harvest

107

Sugars manufactured through photosynthesis in leaves move in the phloem (which is part of the plumbing system of the plant) to other parts of the plant. This movement is much like an elevator system with cars moving in two directions – downward from leaves to roots and lower stalks, and upward from leaves to growing points and reproductive structures. The movement of sugars, nutrients and other plant substances is called translocation.

Sugar molecules move relatively quickly in the plant, from six to 15 inches per hour. Plant parts that supply sugars to other plant parts are called “sources.” The primary sources are leaves that have completed their initial phase of expansion growth. Regions of the plant that utilize translocated sugars are called “sinks.”

Plant parts that do not have high rates of photosynthesis such as growing points (buds), reproductive structures, stalks, and roots are strong sinks. Sugars for the sink come from leaves positioned near the sink.

Typically, a high percentage of the sugars in grain are derived from the last leaf on the plant – the flag leaf.

HARVESTING

Movement of sugars, nutrients and other plant substances is called translocation.

108

From a forage quality standpoint this physiological response is very important. Once a sorghum plant approaches heading, the plant initiates a process of translocating and reallocating carbohydrates from the leaves and to a lesser extent stalks to the developing grain. After pollination, the grain begins to develop and becomes the strongest physiological sink and sugars and amino acids are rapidly translocated to the developing grain where they are converted to starch and protein. Also at this time the lignin content in the plant is increasing, reducing quality and digestibility of the forage. Consequently, as the plant matures its forage

nutritive value is diminished, producing less metabolic energy for the animal and reducing animal performance.

The optimum stage of growth for maximizing both yield and quality has been determined for the different types of sorghums.

When to Harvest Forage Sorghum •

•

•

As the

Forage sorghum types – harvest when grain has plant matures attained the late milk to early soft dough stage its forage of development.

Sudangrass types – harvest when 50 percent of nutritive value the plants have reached the flag leaf stage. Set the harvester about 6 inches above ground surface. is diminished.

Cutting at this height will leave nodes to promote rapid regrowth.

Sorghum-sudangrass types – in the drier Southwest and Western regions of the U.S., drying down the harvested crop will be faster due to warmer and drier conditions. In the East and Southeastern regions, getting the crop to dry down adequately can be a challenge. Harvest when plants have reached the flag leaf stage. Set the harvester about 6 inches above ground surface. Cutting at this height will promote more rapid regrowth.

HARVESTING

109

•

•

•

Photoperiod sensitive forage sorghum types – harvest prior to head exertion from the boot.

Cutting height can be low to maximize yield.

Brachytic dwarf types – forage sorghums should be harvested when grain has attained the late milk to early soft dough stage of development.

Sorghum sudan grasses should be harvested when the crop has reached the flag leaf stage.

Brachytic dwarf types can be harvested at a lower height than conventional sorghums due to the compressed internode lengths. Mechanical harvesters should be set to a 2 inch height and cattle should be allowed to graze to the 2 inch height to promote rapid and adequate regrowth from the remaining basal nodes.

Male Sterile forage sorghum types – because this type produces no grain the plant will not be allocating sugars and amino acids from leaves and stalk. Therefore, the crop should be allowed to head and begin to dry down before harvest.

HARVESTING

Harvest Management in Slow Drying Environment

110

In environments that are not conducive to rapid drying (such as the Southeast, East, and Northeast) it is very important to utilize several key harvest management factors to dry the crop as quickly as possible. As the crop grows and increases biomass, the total moisture that must be removed after cutting is greatly increased (Figure 6). The crop should be at about 65 percent to 70 percent moisture at harvest to insure optimum conditions for ensiling.

The proper growth stage may not coincide with optimum plant moisture. At the proper growth stage for harvest the crop may be at 85 percent moisture.

The proper growth stage may not coincide with optimum plant moisture.

Tons of Water to Remove from Biomass

Figure 6. Estimated tons of water to remove per acre for 35 percent dry matter BMR 6 Sorghum-sudangrass intended for silage.

Kilcer, et al. 2007. Cornell University Cooperative Extension.

14 12 10 8 6 4 2 0

30

36

42

48

54

60

Alfalfa

BMR 6 Sorghum-Sudangrass Height (inches)

The following harvest management practices will assist in drying down the crop to adequate moisture levels:

HARVESTING

• Set mower-conditioner cutter height six inches above the ground surface.

• Harvest when the crop has attained a height of 36 to 48 inches.

• Use a full width swath, similar for hay cutting to support rapid moisture loss from plants. Do not use a narrow, tall windrow or drying will be insufficient.

111

Key References Used in Development of this Publication Bean, B., and T. McCollum III.

Fribourg, H.A.

2004. BMR forage sorghum – what’s all the fuss about. Texas Cooperative Extension. Amarillo.

1995. Summer annual grasses. p. 463472. In R.F. Barnes et al. (ed.) Forages.

Vol. 1. 5th ed. Iowa State Univ. Press, Ames.

Bean, B., F. T. McCollum III, M. Rowland, and K. McCuistion.

2003. Sorghum growth and development.

B-6137. Texas Cooperative Extension.

College Station.

Bean, B., T. McCollum III, D. Pietsch, M. Rowland, J. Banta, R. VanMeter, and J. Simmons.

Hoffman, P.C., R.D. Shaver, D.K. Combs, D.J. Undersander, L.M. Bauman, and T.K. Seeger.

2001. 2001 Texas Panhandle irrigated sorghum silage trial. AREC-02-44. Texas Cooperative Extension. Amarillo.

Butler, T., and B. Bean.

Forage sorghum production guide.

Texas Cooperative Extension. foragesoftexas.tamu.edu/pdf/ FORAGESorghum.pdf. Stephenville.

Dann, H.M., R.J. Grant, K.W. Cotanch, E.D. Thomas, C.S. Bullard, and R. Rice. 2007. Comparison of brown midrib sorghum-sudangrass with corn silage on lactational performance and nutrient digestibility. Journal of Dairy Science. 91:663-672.

Ferguson, R.B.

REFERENCES

Gerik, T., B. Bean, and R. Vanderlip.

2003. Forage sorghum response to irrigation level. Texas Cooperative Extension. Amarillo

2000. Grain and silage sorghum. p.

97-103. In R.B. Ferguson et al. (ed) Nutrient management for agronomic crops in Nebraska. Nebraska Cooperative Extension. EC155. Lincoln.

Frederiksen,R.A., ed.

1986. Compendium of sorghum diseases.

American Phytopathological Society. St. Paul, MN. 82 pp.

112

2001. Understanding NDF digestibility of forages. Focus on Forage. Vol. 3, No. 10.

University of Wisconsin - Madison.

Huffman, C.F. 1956. The mysteries of the rumen.

Journal of Dairy Science. 39:688-692.

Kilcer, T., G. Albrecht, P. Cerosaletti, P. Barney, Q. Ketterings, and J. Cherney.

2007. Brown midrib sorghum sudangrass, Part I: successfully growing a high energy grass for dairy cows. Fact Sheet 14.

Cornell University Cooperative Extension.

Livingston, S.D., C.G. Coffman, and L.G. Unruh.

1996. Correcting iron deficiencies in grain sorghum. L-5155. Texas Agricultural Extension Service. College Station.

Marsalis, M.A. 2006. Sorghum forage production in New Mexico. Guide A-332. New Mexico Cooperative Extension Service. Las Cruces.

McFarland, M.L., R.Lemon, and C. Stichler.

Sanderson, M.A., R.M. Jones, J. Ward, and R. Wolfe.

2002. Irrigation water quality: critical salt levels for peanuts, cotton, corn and grain sorghum. L-5417. Texas Cooperative Extension. College Station.

1992. Silage sorghum performance trial at Stephenville. Forage Research in Texas. Report PR-5018. Texas Agricultural Experiment Station. Stephenville.

McCollum III, F.T., K. McCuistion, and B. Bean.

Smith, C.W., and R.A. Frederiksen (ed.).

2003. Five year observations on grazing capacity and weight gains of stocker cattle grazing summer annuals. Texas Cooperative Extension and Texas Agricultural Experiment Station. Amarillo.

Stichler, C., and J.C. Reagor.

Moran, J. 2005. Tropical dairy farming: feeding management for small holder dairy farmers in the humid tropics. p. 312.

Landlinks Press.

2000. Sorghum: origin, history, technology, and production. 824 p.

John Wiley and Sons, Inc. 2001. Nitrate and prussic acid poisoning. L-5321. Texas Agricultural Extension Service. College Station.

Stichler, C., M.L. McFarland, and C. Coffman.

1997. Irrigated and dryland grain sorghum production in south and southwest Texas.

1999. Evaluation of the importance of the B-6048. Texas Agricultural Extension digestibility of neutral detergent fiber from Service. College Station. forage: effects on dry matter intake and Stuart, P. milk yield of dairy cows. Journal of Dairy 2002. The Forage Book. A comprehensive Science. 82:589-596. guide to forage management. 2nd Edition.

Oliver, A.L., R.J. Grant, J.F. Pedersen, Pacific Seeds. Toowoomba, Australia.

Oba, M., and M.S. Allen.

and J.O’Rear.

Provin, T.L., and J.L. Pitt.

2003. Nitrates and prussic acid in forages: sampling, testing and management strategies. L-5433.

Texas Cooperative Extension.

College Station.

Umphrey, J.E., and C.R. Staples.

1992. General anatomy of the ruminant digestive system. Factsheet DS 31 of the Dairy Production Guide.

Florida Cooperative Extension Service.

Gainesville.

REFERENCES

2004. Comparison of brown midrib 6 and 18 forage sorghum with conventional sorghum and corn silage in diets of lactating dairy cows. Journal of Dairy Science. 87:637-644.

113

Conversions and Useful Information Multiply by

To get:

If you know:

Multiply by

To get:

Acres

0.405

Hectares

Degrees F

(-32) x 0.5555

Degrees C

Acres

43,560

Square feet

Fathoms

6

Feet

Acres Acres

0.0015625

Square miles

Feet

30.48

Centimeters

160

Square rods

Feet

0.3048

Meters

Bushels

1.2472

Cubic feet

Feet/minute

0.01136

Miles/hour

Bushels

0.04606

Cubic yards

Furlongs

40

Rods

If you know:

4

Pecks

Gallons

3,785

Cubic cm

Bushels (corn)

0.0254

Metric tons

Gallons

3.785

Liters

Bushels (soybeans)

0.0272

Metric tons

Gallons

128

Fluid ounces

Bushels (sorghum)

0.0254

Metric tons

Gallons H2O

8.3453

Pounds H2O

Bushels (wheat)

0.0272

Metric tons

Grams

0.0353

Ounces

Grams

0.0022

Pounds

Grams/L

1,000

ppm

Hectares

2.471

Acres

USEFUL INFORMATION

Bushels

114

Bu/Acre (corn or sorghum)

62.74089

kg/hectare

Bu/Acre (soybean or wheat)

67.2224

kg/hectare

Inches

2.54

Centimeters

CaCO3

0.40

Calcium (Ca)

Inches

0.08333

Feet

Calcium (Ca)

2.5

CaCO3

Inches

0.0254

Meters

Centimeters

0.0328

Feet

27,154.28

Gallons H2O/Ac.

Centimeters

0.3937

Inches

K 2O

0.83

K (elemental)

Centimeters

0.01

Meters

Kilograms

2.205

Pounds

Cubic feet

0.80176

Bushels

Kilograms

0.01594

Tons

Cubic feet

0.0283

Cubic meters

Kg/hectare

0.015939

Cubic feet

7.4805

Gallons

Bu/Acre (corn or sorghum)

Cubic feet

28.32

Liters

Kg/hectare

0.014876

Cubic inches

0.554

Fluid ounces

Bu/Acre (soybean or wheat)

Cubic meters

35.31

Cubic feet

Kilometers

3,281

Feet

Cubic meters

1.308

Cubic yards

Kilometers

0.6214

Miles

Cubic yards

21.71

Bushels

Liters

0.0353

Cubic feet

8

Fluid ounces

Liters

0.2642

Gallons

(+17.98) x 1.8

Degrees F

Meters

3.281

Feet

Cups Degrees C

Inches H2O/Ac.

Conversions and Useful Information Multiply by

To get:

If you know:

1.094

Yards

Metric Tons

39.3683

Bushels (corn or sorghum)

Metric Tons

36.7437

Bushels (soybeans or wheat)

If you know: Meters

Multiply by

To get:

Pints

16

Ounces (fluid)

Pints

0.5

Quarts

K (elemental)

1.2

K2O

Pounds

16

Ounces (dry)

Pounds

0.0005

Tons

Pounds

0.45359

Kilograms

Metric Tons

2,204.62

Pounds

Metric Tons

1.1023

Short tons

Pounds H2O

0.1198

Gallons

Miles

5,280

Feet

Pounds/Acre

1.12

Kg/hectare

Miles

1.6093

Kilometers

Quarts

0.25

Gallons

Miles

320

Rods

Quarts

0.9463

Liters

Miles

Yards

Rods

16.5

Feet

88

Feet/minute

Rods

0.025

Furlongs

Milliliters

0.001

Liters

Rods

0.003125

Miles

Milliliters

0.034

Fluid ounces

Short tons

907

Kilograms

Milliliters

0.2

Teaspoons

Short tons

0.9072

Metric tons

Ounces (dry)

28.3495

Grams

Square feet

0.00002296

Acres

Ounces (fluid)

29.573

Cubic cm

0.001

Hectares

Ounces (fluid)

0.0078125

Gallons

Tablespoons

0.5

Fluid ounces

Ounces (fluid)

0.0625

Pints

Tablespoons

3

Teaspoons

Ounces (fluid)

0.03125

Quarts

Teaspoons

5

Milliliters

Ounces (fluid)

2

Tablespoons

Teaspoons

0.17

Fluid ounces

Tons

Ounces (fluid)

Square meters

6

Teaspoons

907.1849

Kilograms

P2O5

0.44

P (elemental)

Tons (short)

2,000

Pounds

Pecks

0.25

Bushels

Tons (long)

2,240

Pounds

Percent

10,000

ppm

Yards

0.9144

Meters

P (elemental)

Yards

0.000568

Miles

2.292

P2O5

Pints

2

Cups

Pints

473

Milliliters

Pints

0.125

Gallons

Pints

0.4732

Liters

USEFUL INFORMATION

1,760

Miles/hr

115

Bushel Weights of Various Crops and Forages ACCEPTED BUSHEL WEIGHT (pounds)

Standard Moisture (if applicable)

Sorghum

56

14.0%

Sudangrass

40

Corn

56

15.5%

Soybeans

60

13.0%

Wheat

60

13.5%

Rye

56

14.0%

Barley

48

14.5%

Oats

32

14.0%

Bermudagrass

40

Bluegrass

14

Orchardgrass

14

Ryegrass

24

Tall fescue

24

Timothy

45

Alfalfa

60

Clovers

60

CROP

USEFUL INFORMATION

Sprayer Calibration Example

116

Determine the following: GPM = Gallons Per Minute (Per Nozzle) GPA = Gallons Per Acre MPH = Miles Per Hour W = Nozzle spacing in inches for broadcast

applications = Spray width for banded applications = Row spacing (in inches) divided by number of nozzles per row for directed spraying MPH = (feet traveled x 60) / (seconds to travel x 88) GPA = (5,940 x GPM) / (MPH x W) GPM = (GPA x MPH x W) / 5,940 Acres Per Tank = (Size of tank in gallons) / (GPA) Amount of product to add to tank = (Rate of product per acre) x (Acres per tank)

Example: You want to apply 1 quart of Atrazine per acre broadcast. The sprayer is set up with nozzles spaced every 20 inches. Tank size is 100 gallons.

Step 1: Determine the sprayer speed (MPH) in field conditions. Mark 100 feet and time how long it takes to travel the 100 feet. If it took 10 seconds then: MPH = (100 feet x 60) / (10 seconds x 88) = 6.8 MPH Step 2: Determine the output of one nozzle at a constant pressure. Suppose you were able to catch 12 oz in 20 seconds. That would equal to 36 oz in one minute (28 x 3). Convert 36 oz to gallons.

36 oz / 128 = 0.28125 gallons. The output then from one nozzle is 0.28125 GPM.

Liquid Volume Calculation Vertical Tank Volume (gallons) = Diameter2 (ft) x 5.875 x Height of tank or liquid (ft)

Step 3: Now that you know MPH, GPM, and nozzle spacing, apply them to the following formula: GPA = (5,940 x GPM) / (MPH x W) = (5,940 x 0.28125) / (6.8 x 20) =12.3 GPA

Acres per tank = (size of tank in gallons) / GPA = (100) / (12.3) = 8.13 acres per tank.

Step 5: Determine the amount of Atrazine that needs to be added to each 100 gallon tank with the following formula: Amount of product to add to tank = (Rate of product per acre) x (Acres per tank) = (1 qt Atrazine) x (8.13 acres per tank) = 8.13 qt Atrazine = 2.03 gallons Atrazine.

USEFUL INFORMATION

Step 4: Determine the acres per tank according to the following formula:

117

Storage Bin Calculations Cylinder

Volume (cubic feet) = Diameter2 (ft) x 0.7854 x Height (ft) Volume (cubic feet) x 0.8 = Bushels Other Calculations

Cone of grain

Volume (cubic feet) = [Diameter2 (ft) x 0.7854 x Height (ft)] / 3 Volume (cubic feet) x 0.8 = Bushels

Area of a Circle = Radius2 x 3.1416 or Diameter2 x 0.7854 Area of a Rectangle = Length x Width Area of a Triangle = (Base x Height) / 2

Rectangle Bin

Volume = Length x Width x Height Tons = [Volume (cubic feet) x Weight (per cubic feet)] / 2,000

USEFUL INFORMATION

Trapezoid Storage

118

Volume (cubic ft) ={ [Height of longest side (ft) + Height of shortest side (ft)] / 2} x Length (ft) x Width (ft) Tons = [Volume (cubic feet) x Weight (per cubic feet)] / 2,000 Triangle Storage

Volume (cubic ft) = [Height (ft) x Length (ft) x Width (ft)] / 2 Tons = [Volume (cubic feet) x Weight (per cubic feet)] / 2,000

Length of Row Equal to 1/1000th of an Acre to Determine Plant Population An easy and accurate way to determine plant populations is by determining the number of plants in a row that is equal to 1/1000th of an acre.

To do this, count the number of live plants in a given row length based on the row spacing. For example, if your row spacing is 7 inches, and you counted an average of 80 plants in 74 feet, 8 inches of row, your plant population would be 80,000 plants per acre.

Row width (inches)

Length of one row equal to 1/1000th of an acre

6

87 feet, 1 inch

7

74 feet, 8 inches

8

65 feet, 4 inches

10

52 feet, 3 inches

15

34 feet, 10 inches

20

26 feet, 2 inches

28

18 feet, 8 inches

30

17 feet, 5 inches

32

16 feet, 4 inches

36

14 feet, 6 inches

38

13 feet, 9 inches

40

13 feet, 1 inch

To be most accurate, average your stand counts from at least 4 locations in a field.

USEFUL INFORMATION

To be most accurate, average your stand counts from at least 4 locations in a field.

Stand Count

119

Weights and Analysis of Common Fertilizers Dry Bulk Analysis

Approximate Weight (lbs/ft3)

34-0-0 21-0-0-24 46-0-0 13-0-44 16-0-0 15-0-0-34 11-52-0 18-46-0 0-46-0 0-0-60 0-0-50 0-0-22 0-0-22

58-62 60-64 48-52 NA NA NA 58-64 56-60 66-72 66-70 85-93 68-72 94-98

Material

Pounds fertilizer per gallon

Approximate Weight (lbs/ft3)

28-0-0 UAN 30-0-0 UAN 32-0-0 UAN 10-34-0 11-37-0 Anhydrous Ammonia (82-0-0)

2.98-0-0 3.26-0-0 3.54-0-0 1.16-3.96-0 1.32-4.4-0 4.23-0-0

10.66 10.85 11.06 11.65 12.00 5.15

Material

Ammonium Nitrate Ammonium Sulfate Urea Potassium Nitrate Sodium Nitrate Calcium Nitrate Monoammonium Phosphate Diammonium Phosphate Triple Superphosphate Muriate of Potash Sulfate of Potash K-Mag (prill) Sul-Po-Mag

USEFUL INFORMATION

Liquid Fertilizers

120

Sorghum Head Development

1) Boot Stage

4) Full Bloom 5) Milk/Soft Dough

6) Hard Dough

7) Physiological Maturity

SORGHUM HEAD DEVELOPMENT

3) First Bloom

2) Head Exertion

121

Agronomic Terminology Disease/Insect/Nematode Ratings

indicates plant reaction to a pest. Classes include resistant (R), moderately resistant (MR), moderate (M), moderately susceptible (MS), and susceptible (S).

Growth Habit

characteristic plant form such as upright, low-growing, prostrate, bushy, etc. Sorghums have an upright growth habit.

Maturity

number of days required to reach optimum time for harvest.

Nitrate Toxicity

nitrate can accumulate in sorghums when poor growth conditions prevent the nitrate from being assimilated into amino acids. This can occur under drought situations, prolonged cloudy conditions, and cool temperatures.

AGRONOMIC TERMINOLOGY

pH

122

measure of soil acidity/alkalinity. Optimum pH for sorghum growth is from 6.0 to 7.0. At high pH conditions (>7.5) sorghum is susceptible to micronutrient stress, especially iron.

Photoperiod

the initiation of the reproductive (heading) response to day length. Plants are characterized as sensitive or insensitive to day length changes. Photoperiod sensitive sorghums will not initiate heading until the day length is less than 12.5 hours.

Prussic acid poisoning

sorghums, sudangrass, and sorghum-sudangrass hybrids produce cyanide, which can poison livestock under certain conditions. High concentrations of prussic acid may be associated with rapid growth of a drought stressed crop following rainfall or irrigation, or warm temperatures following a cool temperature period.

Recovery After Cutting

ability of sorghum to regrow following mechanical harvest or grazing.

Saline Soils (white alkali)

soils that have water soluble salt levels at high concentrations that can reduce germination and plant growth. Sorghum is a fairly salt tolerant crop.

Saline-Sodic Soils (black alkali)

a saline soil, but the dominant cation is sodium which is toxic to plants and can damage medium to fine textured soils.

High sodium levels destroy soil structure causing dense, hard crusts.

Seedling vigor

characteristics that determine the potential for rapid, uniform emergence and development of healthy, normal seedlings under various field conditions. Strong vigor is recommended when planting under less than ideal soil and temperature conditions.

Soil Temperature

Tillers

side-shoots that develop from axillary buds at the lower nodes of the sorghum plant and are morphologically identical to the main stalk.

Uniformity

refers to the percentage of plants that possess similar characteristics. Plants with different characteristics are considered off-types.

Water Requirement

sorghum has excellent heat and drought tolerance, especially compared to corn. Sorghum will produce similar yields to corn, while requiring 30 to 50% less water.

AGRONOMIC TERMINOLOGY

warm soil temperatures are important for rapid germination and emergence. Forage sorghum can be planted at soil temperatures of 60ยบ F, but avoid planting into cool soil conditions. Cool soils will delay germination and emergence and expose seed and seedlings to the soil borne disease complex.

123

Agronomic Terminology Brachytic Dwarf Sorghums

have very short internodes and very high leaf to stalk ratios, prolific tillering, superior standability, and comparable tonnage to normal height sorghums.

Best Choice – Grazing, hay, and silage production.

Availability - Forage sorghums and Sorghum-sudangrass.

AGRONOMIC TERMINOLOGY

Brown Midrib Trait

124

the brown midrib (BMR) trait is associated with reduced lignin content. Plant mutations in sorghum were reported by Purdue researchers in 1978. Originally, 19 different BMR mutant lines were produced. Of the 19 lines, only three were considered to have acceptable agronomic characteristics, and they were defined as the BMR 6 gene, BMR 12 gene and BMR 18 gene. The enzymatic mechanisms responsible for reduced lignin synthesis are different between the BMR 6 and BMR 12 or BMR 18 gene (BMR 12 and 18 gene support the same mechanism). The BMR 6 gene has been proven in field and nutritional studies to be the superior gene from an agronomic and forage quality standpoint.

Brown Midrib 6 Trait

sorghums with the BMR 6 trait have less lignin than conventional sorghums, are extremely palatable and have high digestibility.

Forage Sorghum

produce very high biomass yields, but have limited regrowth potential making them excellent choices for single-cut silage and standing green-chop production uses. The soft dough stage is considered the optimum time for harvesting.

Best Choice – Silage production.

Male Sterile

produce no anthers and thus no pollen for self fertilization.

If no pollen source is nearby to cross pollinate, then male sterile plants will produce no grain maintaining excellent forage quality and palatablility. When combined with the BMR 6 trait, male sterile forage sorghums will have higher energy content than other hybrids that produce grain.

Best Choice – Single harvest or silage production.

Availability – Forage sorghums.

Photoperiod Sensitive Sorghums

initiate flowering in response to day length of less than about 12.5 hours. Will remain vegetative from mid-March through September maintaining very high quality forage, allowing flexibility in harvest timing eliminating issues associated with weather or availability of custom harvesters.

Best Choice – Hay and silage production.

Availability - Forage sorghums and Sorghum-sudangrass.

Photosynthetic Type

Plant Color

sorghum plant color is typically referred to as tan or purple.

Sorghum-sudangrass hybrids

typically crosses between forage sorghums (female parent) and sudangrass types (male parent). Reach heights of six to eight feet, have smaller stalks than forage sorghum, strong tillering, and produce more tonnage than sudangrass.

They have excellent regrowth potential.

Best Choice – Grazing, hay and silage production.

Sudangrass

smaller in plant architecture, has finer stalks, produces more leaves than forage sorghum and develops multiple tillers.

Has excellent regrowth ability with very quick recovery following cutting or grazing.

Best Choice – Grazing and hay production.

AGRONOMIC TERMINOLOGY

refers to warm or cool season plants. Sorghum is a warm season plant.

125

Forage Quality Terminology Acid Detergent Fiber (%ADF)

determined by boiling a sample in an acid detergent solution for one hour. The ADF components are primarily cellulose and lignin. ADF has been used to predict digestibility. Lower ADF content equates to better quality forage.

Brown Midrib 6 Digestibility

BMR 6 sorghums have 40 to 60% less lignin compared to conventional sorghums and much greater palatability and digestibility. Feeding BMR 6 sorghums to dairy and beef cattle produces outstanding animal performance, with higher milk production and greater weight gain.

FORAGE QUALITY TERMINOLOGY

Carbohydrates

126

all sugars belong to the class of biochemicals known as carbohydrates (CH2O), so named because their chemical formulas all include carbon as well as the elements hydrogen and oxygen in the same two-to-one ratio found in water (e.g. Glucose – C6H12O6 ).

Cell Wall Digestibility (%CWD) 30 hour Neutral Detergent Fiber digestibility.

Cellulose

fiber component forming the framework of both primary and secondary cell walls along with hemicellulose and pectin and is 50 to 90% digestible.

Crude Protein (CP)

percentage of nitrogen in forage multiplied by 6.25.

Digestibility

portion of the feed that is absorbed as it passes through the animal’s digestive tract once the feedstock is consumed.

Dry matter (DM)

the portion of any forage material which remains after all moisture has been removed. Forage yields, protein content, energy and digestibility are all expressed on a DM basis in order to make meaningful comparisons on nutritional value of different forages.

Energy

derived from the digestion of carbohydrates, complex carbohydrates, fat and protein. There are no laboratory procedures to measure energy. It is a product of the digestion process; therefore, it is a calculated value based on feed digestibility and is expressed as calories. A kilocalorie (Kcal) is a 1000 calories and a megacalorie (Mcal) is 1000 kilocalories.

Fiber

the insoluble, complex carbohydrates of the plant cell.

The primary components of fiber are cellulose, hemicellulose, and lignin.

Hemicellulose

fiber component consisting of a variety of sugars including xylose, arabinose, and mannose and is 20 to 80% digestible.

is an anaerobic fermentation performed in the laboratory to simulate digestion as it occurs in the rumen. Rumen fluid is collected from animals (e.g. dairy cows or steers) consuming a typical diet. Forage samples are incubated in rumen fluid and during this time the microbial population in the rumen fluid digests the sample as it would occur in the rumen. The end result of the IVTD procedure is the undigested fibrous residue.

The obvious factors affecting digestibility are type of crop and variety/hybrid characteristics and the maturity of the crop.

Lignin

comprised of long chains of aromatic plant alcohols.

Lignin provides the structural support for the cell and is non-digestible, so as lignification occurs in older, more mature plants digestibility and quality decline.

Net Energy Lactation (NEl)

an estimated energy value of a feed for milk production, expressed as megacalories (Mcal) per pound of feed.

It is calculated from the ADF value.

FORAGE QUALITY TERMINOLOGY

In Vitro True Dry Matter Digestibility (%IVTD, %IVDMD)

127

Neutral Detergent Fiber (%NDF)

determined by boiling a sample in a neutral detergent solution for one hour. The NDF components are primarily hemicellulose, cellulose, and lignin. Because these compounds are closely associated with bulkiness of forage, NDF is closely related to animal feed intake and rumen fill, thus NDF can be used to predict voluntary intake of a feedstock. The BMR 6 sorghums have NDF values as low as 40%. The lower the NDF content, the better the forage.

FORAGE QUALITY TERMINOLOGY

Neutral Detergent Fiber Digestibility (%NDFd)

128

provides extremely useful information for assessing forage digestibility, potential energy and animal performance.

Although forages may have similar ADF and NDF values, the fiber composition could be different. Consequently, the NDFd values could be very different and so could the performance of the animals fed these different forages. The IVTD procedure is used but the calculation is based on the sample amount of NDF prior to rumen incubation compared to the amount of NDF remaining after a designated amount of time. Higher NDFd will result in higher energy values and, more importantly, better animal performance.

Nonfibrous Carbohydrates (NFC)

estimate of the rapidly available carbohydrates available in a forage. Primarily, an estimate of the starch, sugars and other compounds.

Palatability

animal’s preference for a feedstock when offered a choice among different feeds. Factors affecting palatability include type of crop and variety/hybrid, growth stage, chemical composition or toxic compounds that might be present in the forage. Brown Midrib 6 types are extremely palatable.

Sugars

the most basic units of carbohydrates composed of carbon, hydrogen and oxygen. Examples include glucose, fructose, galactose, xylose and ribose.

Total Nonstructural Carbohydrates (TNC) measure of only the starch and sugar in a forage.

Undigested Neutral Detergent Fiber (%UNDF) the undigested NDF, primarily lignin fraction.

10 days

20 days

30 days

Three Leaf Five Leaf Growing Point Emergence Differentiation

Days After Emergence

50 days

Boot Stage

Flag Leaf

Half Bloom

60 days

Forage Sorghum Growth Stages

Soft Dough

70 days

Physiological Maturity

90 days

Growing Value in the Green — Sorghum for Forage Field Guide was written and produced by AgriThority® agronomists Dr. Robert Lemon and Dr. Sandy Stewart in cooperation with Ricky Rice, Advanta US forage specialist.

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Specific mention of a product is neither an endorsement nor a warranty of performance by AgriThority® or Advanta. Information in this publication related to crop protection chemicals is based on the best available information at the time of printing. In all cases, the actual product label takes precedence over any information contained within this publication. Pesticide labels can and do change. ALWAYS read and follow label instructions when using crop protection chemicals.

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