Irrigation Scheduling Options

Find a method that fits your needs and management style.

By Amanda Huber

Peanut growers have several options for scheduling irrigation. Any one of these methods is better than waiting for visible stress, says University of Georgia Extension irrigation specialist Wesley Porter.

“Based on the irrigation survey we conducted, we know that a lot of peanuts are still being irrigated based on visible stress and fewer are using more advanced scheduling methods,” he says.

Make The Most Of Your Dollar

Porter reminds growers that although they don’t pay for water, they do pay to move that water with energy costs.

“This year’s budget costs for pumping irrigation has the average irrigation cost at $8.50 per acre-inch of water applied. For 500 acres of irrigated land, if you put out 10 acre-inches of water, that’s $42,500.

There are many irrigation scheduling tools available to producers from the checkbook method to computer models and soil moisture sensors. Depending on your operation and irrigation capabilities, one of these methods may be a good fit.

The checkbook method is available for corn, cotton, peanuts and soybeans and is published in each respective production guide. It is free and requires minimal user input.

“This method is not advanced and is one step above irrigating a set amount of irrigation a certain number of times per week,” says Porter. “It also tends to be conservative, meaning that it can lead to over irrigating in wet years and under irrigating when it’s dry.”

The checkbook methods are all developed based on a historical average crop water use and evapotranspiration.

Computer Models

The next step up in irrigation methods, according to Porter, is one of the computer models. Producers have several options including smart irrigation apps, PeanutFARM and Irrigator Pro.

These methods are usually free and also require minimal user input. The real-time daily data used in computer models often comes from a local network of weather stations.

“These models use the checkbook as the backbone but rely on daily real-time data to make decisions. One benefit is they take soil type into consideration.

“A localized computer model can be a very good option for a producer new to scheduling irrigation. It can help them keep a track of how much irrigation they need and when to apply it based on current climatic conditions.”

Soil Moisture Sensors

The most accurate way of scheduling irrigation currently is with the use of soil moisture sensors. There are many types of sensors, and costs can range from $500 up to $2,500 per site.

Irrigation scheduling with the use of soil moisture sensors provides current data to be used to make hourly to daily irrigation decisions. User input is required for these methods and use of the data can be a challenge, but it is an accurate method when used correctly.

“It’s not readily adopted because of the investment and, like any electronic device, you are going to have problems because the sensors are placed into a harsh environment.

“Also, the data can sometimes be difficult to interpret or make accurate decisions from. Once you get this data, how will you use it? If you’re at this last stage and saying, ‘I’ve got this data but I’m not real sure how to use it,’ I would encourage you to use a hybrid systems.”

A Hybrid System

Irrigator Pro is considered a hybrid system that can be used multiple ways.

“It can be used for soil-water balance such as the computer models, and it has an option where soil temperature and/or soil metric potential data can be manually entered or automatically populated into the model using soil sensors,” says Porter.

Irrigation recommendations from Irrigator Pro are based on long-term, multi-crop irrigation management research performed by the USDA Agriculture Research Service’s National Peanut Research Laboratory in Dawson, Georgia.

Irrigator Pro, which is available for peanuts, corn and cotton, calculates the available water in the soil and the daily water needs of the crop based on its growth stage. If the water needs of the crop exceed the available water in the soil, irrigation is recommended. Irrigation recommendations are based on long-term, multi-crop irrigation management research performed by the Agriculture Research Service’s National Peanut Research Laboratory in Dawson, Georgia.

Rainfall and irrigation data can be manually entered into Irrigator Pro, or the data can come from another source, such as soil water potential sensor values from a UGA Probe and Bridge device or from the Trellis wireless soil moisture system.

Work on Irrigator Pro continues and in 2022, Porter says, it will include volumetric measures of water content using capacitance sensors.

Know The Critical Time

Once the peanut crop is in the ground, it’s time to start considering how to manage it and specifically how to manage irrigation.

Porter says to keep in mind that the water requirement for peanuts is irrigation plus rainfall, and the weekly water requirement recommendation was developed based on the historical average of evapotranspiration.

“Your actual water and irrigation requirement may vary slightly based on weather conditions and rainfall during the growing season.”

Peak water use for peanuts is at 70 to 100 days after planting. PG

Possible Causes of Poor Uniformity

Common Problems Measures

Clogged nozzles

Sprinklers not turning

Inadequate system pressure**

Towers containing leaky boots or stuck open drain plugs

Sprinkler in wrong order**

End-gun not adjusted properly

Wrong end-gun nozzle**

Worn nozzles** Remove and clean nozzles

Repair sprinklers and check for inadequate pressure

Increase pressure if possible

Replace gasket, boots or drain plugs

Obtain printout from manufacturer and install sprinklers correctly

Adjust part circle stops on end-gun

Place correct nozzle on end-gun

Replace sprinkler nozzles

Excessive wind* Check uniformity while wind velocity is low * Only conduct a uniformity test when wind velocities are less than 5 miles per hour to obtain representative results. **These items may need irrigation dealer input.

Why Is Uniformity Important?

Just as crop uniformity is important to reach maturity equally, so is the uniformity of water application.

University of Georgia Extension water educator David Hall says systems not properly checked and maintained can lead to significant losses in potential income.

“A farm’s return on investment is directly affected by the way water is applied to crops. The wrong end-gun settings can result in overwatering or underwatering large portions of field acres. Clogged or partially clogged nozzles lead to obvious water shortages that can be visually observed or measured using yield monitors.”

By request, UGA Extension’s mobile irrigation lab can perform a pivot test. Contact your local Extension office for assistance with this process.

Q&ACalcium Q & A Shortages, alternatives and targeted application— these are the key topics in 2021.

Editor’s Note: University of Georgia soil scientist Glen Harris answers gypsum-related questions.

QWill there be a gypsum shortage as we have heard about?

AThe same rumors made the rounds last year, but gypsum was always available. According to my sources, there shouldn’t be a problem with the gypsum supply this year either. However, the logistics of moving the gypsum is more likely to be the primary problem. In his words, “You may not get it exactly the day you want it, but you should get it pretty soon thereafter.”

QIs there an alternative to gypsum that will provide the calcium needed by the crop?

AThe short answer is “not really.” Gypsum is the best. Lime is also recommended but needs to be done at or before planting and only when a pH adjustment is called for. Other products have been tried, such as 10 gallons of liquid calcium chloride applied through the pivot, but it does not provide as much soluble calcium as 1,000 pounds per acre of gypsum. Also, alternatives do not leave as much calcium in the soil as gypsum does.

QWhat can we do in case of a shortage or simply to reduce the tonnage needed?

AWe always need to put calcium where it is needed. One tool that I think is underutilized is the pegging zone calcium test. Sampling around the field directly from the pegging zone and learning how much is present will let you know both how much and where it is needed. In places where you already have the UGA recommended 500 pounds per acre and a calcium to potassium ration of at least 3:1, there will not be a yield or grade increase if you do not apply gypsum.

What I am interested in seeing more of is grid sampling and variable-rate gypsum application. Some farmers are starting to implement this strategy to put product out only where needed. One farmer said he now uses less than half of what he was before. If there is a shortage, grid sampling and variable-rate application will probably get more popular.

QWhat about foliar-applied calcium products? Is that a possible alternative to gypsum?

ANo. Foliar products do not provide the rate of calcium needed and, even if they did, calcium does not translocate through the plant from the leaves to the pods. Calcium has to be absorbed with water directly through the walls of the developing pods in the pegging zone (top 4 inches or so of soil) not through the roots or any other part of the peanut plant.

Foliar calcium products with a recommendation of 1 quart per acre and sprayed at a total spray volume of 10 to 20 gallons per acre do not provide enough calcium.

However, liquid calcium applied through a center-pivot irrigation system is different. This is considered a soil-applied application because the amount of water per acre is such that it runs off the leaves and onto the soil. For comparison, the foliar-fed system applies 10 gallons per acre, whereas applying 1 acre-inch of water through the pivot puts out approximately 27,000 gallons of water!

QWhich is better on dryland peanuts: lime or gypsum?

AIn most years, gypsum outperforms lime applied at planting for providing calcium to the pegging zone. The calcium in lime is less soluble than the calcium in gypsum under limited water situations. In dryland production, and without significant rains, the calcium in lime may not become available to the developing pods in the pegging zone as it would with the use of irrigation.

QShould I split my gypsum applications and put some on at planting and some at early bloom?

AResearch studies have not found this to be a benefit to providing calcium to the crop. In fact, if you get a big rain early, the calcium can leach or move downward out of the pegging zone. Plus, split applications would add an unnecessary trip across the field.

QHow late in the season is too late to put out gypsum?

AGypsum should be applied at early bloom or approximately 30 to 45 days after planting, depending on growing conditions.

Once you get past 100 days after planting, the majority of pods have absorbed what calcium there is in the soil solution. It is either enough for kernels to develop or not. After this, damage to the vines during application would not be desirable.

QWhat are the recommended calcium requirements in soil and gypsum application rate?

AThe current recommendation from the University of Georgia is you need both 500 pounds per acre and a calcium to potassium ratio of at least 3:1 in the pegging zone. If either of these levels is not met in a pegging zone soil test, then apply 1,000 pounds per acre of gypsum at early bloom to runner-type peanuts.

Peanuts to be saved for seed should automatically receive 1,000 pounds per acre of gypsum at early bloom even if these levels are met. PG Q&AVirginia-Market Type Calcium Q & A Editor’s Note: North Carolina State University Extension agronomist David Jordan talks about calcium use in Virginia-type varieties.

QLast year, I applied normal landplaster but still had a lot of pops. What do you think could have been the problem?

AExcessive rain after gypsum application or dry weather during pegging and fruit set can cause pops. Could one of these examples be the reason? All Virginia market-type peanuts should get adequate calcium in the pegging zone. This equates to 1,500 to 2,000 pounds per acre of gypsum at blooming. Calcium must be available in the pegging zone when the first pods begin to form.

QWhat is the proper timing for applying landplaster to meet the crops calcium needs?

ABest results are obtained when gypsum is applied in late June or early July. I think some gypsum is going out earlier than needed. If there’s a lot of rain, particularly an excessive amount, after application, it is possible we are running out of calcium later in the season.

Some moisture is needed to make gypsum soluble and calcium available to the peanut fruit. In unusually This picture shows a calcium deficient peanut kernel embryo versus a normal dry years, peanuts may show embryo. symptoms of calcium deficiency, even when recommended rates of gypsum are applied.

Overall, gypsum application is better early than late. Just not too early.

QWhat did you find in the potash application field trial you did on peanuts? I understand it was applied up to and after emergence in fairly high rates with little or no incidence of pops.

AWe did a series of studies many years ago applying 250 pounds of potash on the soil surface right after planting and observed no major issue. If soil test calls for it, you should apply it, but don’t cut back on gypsum. Of course, high rates of potash can cause issues with nutrient balance, but the rates we typically apply in fields with good fertility programs are not a major issue. We would recommend that potash be distributed throughout the soil profile to the root zone where it is needed.

QWhat is the relationship between soil pH and gypsum for peanuts?

AMany years ago, we did a study with a range of soil pH values and rates of gypsum. What we found was that getting your soil pH close to 6.0 will help get a positive return on your gypsum investment. In fact, when soil pH is too low there are times when you will get a negative response to gypsum. Getting the pH right continues to be critical. PG