Undercover
farming
ucf
JANUARY/FEBRUARY 2022
I VOLUME 19 NO 1 I I R45.00 PER ISSUE
MELONS IN A GREENHOUSE
AGRICULTURAL e-TRADE
COTTON IN GREENHOUSES?
GREENHOUSE MIXING TANKS
New hydroponics start-ups: Why its commercially viable Page 4
An Explanation of pH Management Page 11
Why water soluble fertilizers? Page 16
Remove unwante ions from water Page 18
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GREENHOUSES I SHADE NET I HYDROPONICS I AQUAPONICS PROPRIETOR I ADVERTISING SUZANNE OOSTHUIZEN 082 832 1604 suzanne@axxess.co.za EDITORIAL CONTENT & COMPILATION Johan Swiegers 082 882 7023 editors@axxess.co.za ADDRESS PO Box 759, Montana Park 0159 E-MAIL magazine@axxess.co.za FAX 086 518 3430 DESIGN Yolandé van Zyl FINANCE / NEW PROJECTS Marion Oosthuizen 071 639 9300 DISCLAIMER Undercover Farming accepts no responsibility for claims made in advertisements or for opinions and recommendations expressed by individuals or any other body or organisation in articles published in Undercover Farming. COPYRIGHT Copyright is reserved and the content may only be reproduced with the consent of the Editor.
Contents 4
New Hydroponics Start-ups: Why its Commercially Viable
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Pruning and Trellising of Tomato Plants for Higher Yields
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Rijk Zwaan Leads the Pack with Locally ProvenTomato Varieties
10 11 15
Tomato Leaf Miners Trapped with Novel Invention
16 17
Why Water Soluble Fertilizers?
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Remove Unwanted Ions from Water to Ensure Quality Water is Fed to Greenhouse Plants
FRONT PAGE: New Hydroponics Start-ups: Why its Commercially Viable. Read pp 4-5.
INSIDE ...
An Explanation of pH Management How Changes in Season Influence Greenhouse Plants The Advantages of Perlite in Greenhouse Production
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Beginning on the right foot
Psalm 37:23-24: “The Lord directs the steps of the godly. He delights in every detail of their lives. Though they stumble, they will never fall, for the Lord holds them by the hand.” Proverbs 16:9: “We can make our plans, but the Lord determines our steps.”
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ith Covid-related issues still hanging in the air and news of countries ‘opening up’ and even getting rid of masks, we all have learned certain disciplines over time. Since Undercover Farming is very much part and parcel of the food industry, it was in many instances also harmed during lock-down. But, when the pressure is on, the thinking caps come out of the cupboard and new ideas spring forth. Surely our consumers carry the burden of high prices and in most cases these are legally justified. South Africa’s major vegetable production areas were severely hit with excessive rains and floods and other areas with severe high temperatures and drought. This is South Africa for you; a country with extremes in climate patterns. We do not complain! It still is seen globally as a great destination! Studies in the world pointed out that a higher consummation of vegetable varieties on the plate enriches the body with a wide array of vitamins and iron. South Africans and South Americans will not agree as their braais or barbeques are the main object of filling the tummy daily. But Covid taught us a few things about eating habits and the younger set worldwide, are tuning in on food channels where the multitude of delicious vegetable varieties are dished up in mouth-watering ways. Having said this, anybody who wishes to start up a greenhouse to grow a vegetable or leafy greens product should first do their homework. This will entail looking at demands and supply in the markets, then sitting down with an experienced grower to work out the initial investment, obtain training and preferably team up with a mentor. Last but not least; your endeavours to grow foodstuffs for your local or public market must make money in order to have you grow your business! We look forward to see many new, young greenhouse producers come to the fore in South Africa to supply in the immense need of food for millions of people!!
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Plastic on the floor between plant rows keeps the greenhouse neat. Note the yellow sticker pest cards here and there to warn about the presence of pests.
NEW HYDROPONICS START-UPS: WHY ITS COMMERCIALLY VIABLE Many younger people become enthusiastic over entering the fresh produce market but in a nonformal manner. Their question is; “Will I be able to make ends meet and grow in order to become financially viable?
V
egetable production provides a promising economic opportunity for reducing rural poverty and unemployment in developing countries and is a key component of farm diversification strategies. Vegetables are mankind›s most affordable source of vitamins and minerals needed for good health, according to Science Direct. It is for certain that hydroponics greenhouses are becoming more popular and frequently discussed as business ventures or just community fresh food supply entities. The technologies in hydroponics farming are advancing at a phenomenal pace and now even smaller greenhouses can become successful.
Reasons Producing in greenhouses with hydroponics systems is very profitable. They are more productive than soil farming, but require a higher start-up
4 Undercover farming I January/February 2022 I Volume 19 No 1
cost. However, against the much larger open land space, water usage, climate errs and pests, higher volumes of produce are produced with less water and often, less chemical usage. Highvalue fruits and vegetables produce the most revenue. Plants grown in hydroponics greenhouses can produce yields up to 11 times higher than those grown in soil farms. In hydroponics greenhouses, plants can be stacked vertically or horizontally and, since their roots don’t grow as much, they can be placed closer together. Hydroponics farms can grow three to ten times more produce than soil farming using the same amount of space. Furthermore, in a greenhouse you can produce 41 kg of produce per sq. meter each year. Compare that with the much lower 3.9kg in the case of open land farming and get going! However, the costs of hydroponics operations are a little different from those of soil farming. There are many things you can do to maximize the profits of your hydroponics greenhouse. Here are a few ideas to help you maintain a profitable greenhouse. High-Value produce Producing high-value vegetables and fruit is the best way to take advantage
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of the efficient but costly environment of a hydroponics farm. High-value fruits and vegetables can have an edge on the market and can even be sold as “luxury” food. Some of the most profitable crops you can grow in your hydroponic greenhouse are: • Leafy greens like spinach, celery, mint, or lettuce • Tomatoes • Sweet Peppers • Cucumbers • Strawberries and other berries • Melons Herbs and even cannabis (stringent laws protecting the market). Special greens are planted for specific use by high-end restaurants; therefore opportunities exist to obtain a steady market. Medicinal plants like cannabis, flower varieties and cultivating seedlings for other greenhouse operators are among money-making ideas for the newcomer. Lettuce and similar leafy vegetables are technically low-value crops, but their low maintenance and improved yielding in hydroponics farming make them most suitable for hydroponic greenhouses. Grow Year-round in a Greenhouse Hydroponics greenhouses produce yearlong harvests. The closed environment of a greenhouse allows you to precisely control the conditions for your plants, without having to worry about climate and season. A producer will be able to harvest at any time of the year, without any interruptions. A sure way to maximize revenue in a hydroponics farm is growing vegetables that are out of season on open land farms. Since seasons have no effect on the production of a hydroponics greenhouse, hydroponic produce will take a larger market share when it’s out of season. Large investment at first Starting a hydroponics farm comes with a high initial investment. The average cost of setting up a 30 by 10m hydroponics operation would be around R75 000. This entails the structure, cladding with plastic, your seedling bags filled with grow medium (as you do not grow in soil), the irrigation lines, pump or two, two tanks) water and soluble fertilizer and plastic under the plants (and walkways, if possible). You
Note the string which is used to train the plant towards a top wire. This keeps the plant upright, the leaves and fruit develop well and there is good airflow between plants. will also have measuring equipment like thermometers and pH sensors to manage your plants. See this as an investment in experience and as soon as you are ready and acquired a market for your produce, invest in another greenhouse. Still, thanks to its higher-yielding and efficiency, hydroponics greenhouses are very profitable in the long run. If this challenge can be overcome, hydroponic farmers can only expect their business to grow over the next decade. Quick Growth Cycles In open land farming, the soil must go through a period of restoration before the next crop can be grown. Meanwhile, in the hydroponics greenhouses, one can plant the next crop as soon as the previous one is harvested. Some farmers divide their greenhouses and
plant at intervals so the total crop does not yield at once. This technique you will experience as you grow for your market. Additionally, hydroponics plants have faster growth thanks to having all the nutrients readily available in the water. Minimal Pesticide use In greenhouse farming there is a muchreduced usage of pesticides. There is no weed without soil, so dealing with weed is out of the picture. By growing without soil you’re also dispensing of all the common pests that come with it. But a few pests in hydroponics systems can be a problem. It’s one of the challenges hydroponics farmers face. However, there are much fewer pests in hydroponics farming but are much
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NEW HYDROPONICS START-UPS:
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Plants need to be trained up regularly and water shoots (nonfruit bearing branches) clipped away to allow maximum food to reach the higher branches where fruit grows.
simpler to deal with if you are awake and inspecting your pants daily. Having an enclosed and controlled system, it’s easy to identify the pests and to introduce biological measures (like early warning gummed pads that show any pests around) without resorting to strong chemicals. Water use Efficiency A hydroponics farm uses up to 90% less water than traditional soil farming. The water used for irrigation is recycled, filtrated and pumped back into the plants until it is consumed and absorbed by them. There are systems that will actually measure your over-fertigation so you can save on input costs. In short; greenhouse hydroponics is not for the feint hearted, but neither is open-land farming! Though, the economic feasibilities in greenhouse farming are by far a more acceptable investment in time, capital and thoughtful energy to play a meaningful role in food security. More countries are showing a high percentage of greens, veggies and fruit consumption than those with high meat consumption. JS
During the colder months, and especially if you are located in an area with longer cold climate, a coal burner heat system is essential. There are producers doing trials with solar panels, but that is still a high investment.
UNDERCOVER FARMING CONFERENCE – GAUTENG
2022
Don’t miss an opprtunity to learn from the professionals! 6 Undercover farming I January/February 2022 I Volume 19 No 1
GREENHOUSES I SHADE NET I HYDROPONICS I AQUAPONICS
PRUNING AND TRELLISING OF TOMATO PLANTS FOR HIGHER YIELDS
S
haping tomato plants can be done by pruning and trellising plants with indeterminate growth habit. This will enhance air circulation and ventilation, optimize space and sunlight, improve growth balance between roots, leaves and fruit, and optimize the working space. Advantages of shaping the tomato plant • Reduces the incidence of physiological disorders e.g. fruit cracking and the uneven ripening of fruit due to exposure to high solar radiation and high temperature • Reduces the incidence of fruit rot and soil-borne diseases • Maximizes the efficiency of photosynthesis • The upright plants have fewer disease problems with leaf spots and fruit rots because their leaves stay drier and are not in contact with pathogen laden soil Disadvantages of shaping the tomato plant • Requires expertise (good management and skilled workers) • Trellising and pruning need to be done regularly – labour intensive • Plants can be damaged during training and harvesting Pruning Pruning is simply the removal of the side shoots or suckers which develop between the main stem and the leaf. It helps to maintain a balance between vegetative and reproductive growth. Generally, if you do not prune or prune few side shoots, your plant will show excessive vegetative growth which may result in smaller fruit size. Care should be taken not to prune the growing point of the main stem otherwise your plant will stop growing and bearing fruit. Suckers can be removed with thumb and forefinger by pulling outwards. They
Growing-point
Sucker/side-shoot
Side-shoots
Removal of sucker/side-shoot with the thumb and forefinger are removed while they are young and succulent (2 to 5 cm long) when they heal faster. Large suckers are not easily removed and can create a larger wound, which takes time to heal and can be an entry point for pathogens. Experimental evidence has shown that there is a high reduction in yield when side shoots are allowed to develop 15-20 cm in length because they use nutrients which should go into fruit development. When working with big-suckers, it is important to remove the growing point of the sucker, causing less shock to the plant. Removing big suckers may necessitate using a knife, shears or scissors. It is important to disinfect the instrument after cutting to prevent diseases being spread from one plant to another. Pruning of suckers is known to increase the size of the fruit and promotes early harvesting. Determinate cultivars are not supposed to be pruned, but the leaves below the first truss can be removed to enhance air circulation. Pruning does not affect the fruit size or the vegetative growth of determinate cultivars if pruning is done below the first truss. Pruning of suckers above the first truss will result in lower yield. Trellising Trellising is done by tying twine from the bag to the stay wire above the plant.
The stem is then twisted around the twine to give support. Trellising should be done two weeks after transplanting. If transplants are not trellised at early stage, they become crooked and trellising then will result in breaking or damaging the plant. Normally a tomato plant may grow approximately 5 – 6 m in a 6 month growing season. It is therefore important that the stay wires are strong enough to carry the mass of a whole row of plants with fruit. The total mass of the plants and fruit in a 45 m row is more than 1 ton. Therefore, considerable damage to plants will result if the stay wire breaks at the height of the production season. Caring of the leaves When the plant matures, especially when the first two trusses have been harvested, lower leaves turn yellow. Generally, remove yellow leaves below the ripening fruit clusters. These yellow leaves should be snapped off with fingers and removed as they are not actively photosynthesizing. In addition, this will enhance air circulation around the base of the plant, and will help to reduce fungal and bacterial disease build-up. This can be done by holding the main stem with one hand and snapping off the leaf where it is attached to the main stem using the other hand.
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RIJK ZWAAN LEADS THE PACK
with locally proven tomato varieties
R
ijk Zwaan South Africa (RZSA) is a local subsidiary of the international vegetable seeds company Rijk Zwaan Zaadteelt en Zaadhandel B.V. based in De Lier, the Netherlands. Established in 1924, this family-owned company has grown to become the fourth largest vegetable breeding company in the world. With the ‘Our Vision’ statement the company envisages contributing to a healthy future; not remaining a vision, but building upon an important cornerstone in company culture which is widely considered the way it approaches commercial decisions. RZSA is proud to offer vegetable varieties that are adapted to local conditions stemming from the rich heritage of experience in the protected cultivation of vegetable crops. Due to collaboration with its partner growers, RZSA is able to select varieties from Rijk Zwaan’s international portfolio that has significant local potential. It is through these partnerships that our team can increase the speed at which information exchange takes place, which in turn increases the quality and quantity of our R&D efforts. Various vegetable crops are being produced with protected cultivation techniques, but however, the favourites are still the majority of crops comprised of Cucumber, sweet pepper, tomato, and lettuce. The RZSA team has made some new additions to the tomato
product portfolio, and it now includes varieties suitable for various purposes. The local range of tomato varieties is segmented to fit with the different protected cultivation techniques of net houses, plastic tunnels, mid-tech multi-span greenhouses, and high-tech greenhouses, being used in South Africa. As the requirements of each segment differ, each variety is uniquely suited to provide a valuable solution to the growers’ requirements. DOUFU RZ F1 is a round-shaped tomato with a fruit weight of 160-240g. The fruit has thick fruit walls and long shelf life. This variety is particularly suited to short cycle (3-6 months harvest) crops in plastic tunnels and midtech multi-spans. LINDSAY RZ F1 is a round-shaped tomato variety that fits particularly well in the summer production slot in net houses. Its’ compact open plant type contributes to a healthy and high yielding variety with very firm fruits of great quality. SPARTUS RZ F1 is a versatile and multi-seasonal round tomato variety that has a combination of TYLCV, TSWV:0 and Fol:0-2 resistances. It performs well in short cycle crops in all types of greenhouses and has the ability to set fruit in hot and cold conditions. ADVENTURE RZ F1 and ENDEAVOUR RZ F1 are the two round tomato varieties suitable for long crop cycles (6-10 months
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harvest). And so these varieties have the ability to provide exceptionally high yields in mid-tech and high-tech greenhouses. These varieties also produce the best yields when combined with our tomato rootstocks SUZUKA RZ F1, EMPERADOR RZ F1 and EMBAJADOR RZ F1. These tomato rootstocks provide the plants with extra vigour and resistance against root diseases that support the needs of a tomato plant in a long production cycle or where disease pressure is high. TRONUS RZ F1 is the latest addition to the round tomato line-up. It has a strong and healthy plant with large round fruits suitable for cultivation in net houses and plastic tunnels during summer and winter. “Rijk Zwaan SA has a national footprint with technical representatives in all major production areas. Our motto of ‘Sharing a healthy future’ drives us to maintain transparent and long term relationships with our growers, in which we provide access to and share knowledge on various topics, said Gerhard Smit, Commercial Director; Rijk Zwaan South Africa. Growers who are keen to produce these excellent varieties should visit our website (www.rijkzwaan.co.za) or contact the office (061 120 3082) to obtain the contact details of their nearest local representative.
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Rijk Zwaan offers a wide range of high-quality vegetable varieties. We select and test them thoroughly to ensure their suitability for growing in South African conditions. In addition to the seeds themselves, we also provide reliable information about the performance of our varieties and expert cultivation advice from our crop specialists. This ensures the grower has the best start to a successful harvest.
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36 Steyn Road, Rietvallei Farm Krugersdorp 1739 South Africa | Postal address P.O. Box 2259, Ruimsig Krugersdorp 1732 South Africa Tel: +27 61 120 3082 / 116 9690 / 116 956 Undercover farming I November/December 2021 I Volume 18 No 6 9 Email: info@rijkzwaan.co.za | www.rijkzwaan.co.za
GREENHOUSES I SHADE NET I HYDROPONICS I AQUAPONICS
TOMATO LEAF MINERS TRAPPED WITH NOVEL INVENTION
F
requent infestation caused by tomato leaf miner flies (Liriomyza sativae) is a serious problem in the pesticide-independent cultivation of greenhouse tomatoes. This problem is caused by the persistent settlement of the flies in the greenhouse through larval movement between the phylloplane and rhizosphere soil of the host plants.
management strategy. Thus, the present work provides an experimental basis for an electric field-based method for the control of tomato leaf miner flies. (From a thesis by Teruo Nonomura and Hideyoshi Toyoda (2020, Laboratory of
Phytoprotection Science and Technology, Faculty of Agriculture and Agricultural Technology and Innovation Research Institute, Kindai University, Japan) Source: MDPI Insects, published 11 December 2020.
The present work was conducted to develop a new physical control method to disrupt this developmental relationship. A simple electrostatic cover (EC) was constructed to trap adult flies emerging from underground pupae. The EC consisted of insulated iron rods linked to a voltage generator, which supplied a negative charge to the insulated iron rods, and non-insulated iron rods linked to a grounded line. The electric field formed in the space between the negatively charged and grounded iron rods generated an attractive force that could trap the target insects entering the electric field. A practical assay to demonstrate the functionality of the EC in a greenhouse revealed that the EC was able to capture all adult flies emerging from pupae. The simple structure of the EC makes it easy to fabricate for farmers who wish to integrate it into their pest
PRUNING AND TRELLISING
Diagram of the structure of an electrostatic cover (EC) for capturing adult tomato leaf miner flies emerging from underground pupae (A). An electrostatic field formed between negatively charged insulated iron rods and grounded noninsulated iron rods (B). One EC was placed horizontally to capture insects that fly upward (C), and other ECs were placed vertically to capture insects blown towards the plants.
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It is important not to remove the green leaves since they function as a source of food supply to the fruits. The figure below shows how a plant should look after removing the old leaves. Old leaves should be removed far from the production area and destroyed to prevent the spreading or build up of diseases. Indeterminate cultivars grow very tall, and with time the yield and fruit size become progressively smaller. Removing the growing points of a plant will stop growth and enhance fruit ripening. With approaching low temperatures (frost), it is important to prune the growing points of all the plants. This is because tomato is sensitive to low temperatures, so by removing the growing points will stop fruit bearing and ripening of fruits will be enhanced. By: M. Maboko, ARC
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Removal of the older leaves results in trusses facing towards the walkway, which makes easy to harvest.
Trellising shows the stem twisted around the twine, which is attached to the stay wire.
GREENHOUSES I SHADE NET I HYDROPONICS I AQUAPONICS
Ph is most important in greenhouse farming (Pic: Hannah)
An Explanation of pH Management
I
mproper management of media pH commonly results in poor growth and reduced plant quality in greenhouses and nurseries. The pH or soil reaction has a primary influence on the solubility and availability of plant nutrients. Many crops have a narrow range of pH tolerance. If the pH of the soil medium falls above or below this tolerance zone, they may not grow properly due to nutrient deficiency or toxicity. For general greenhouse production a pH of 6.2-6.8 is considered ideal for mineral soils, and 5.8-6.2 is recommended for peat or bark media. Of course, this depends upon the crops grown. Poinsettias are tolerant of variable pH, while seed geraniums are very particular, since pH 5.7 or below can result in iron toxicity problems. Except for nitrates, potassium, and
total soluble salts, the availability of most fertilizer elements is affected to some extent by the media pH. Calcium and magnesium become more available as the pH increases, but the opposite is true for iron, manganese and phosphorus. A one unit pH drop can increase the solubility of manganese by as much as 100 times and the solubility of iron by as much as 1000 times. pH explained The pH measure is a relative concentration of hydrogen ions (H+) to hydroxide ions(OH-). The greater the number of H+ ions in relation to OH- the more acidic the solution becomes. The greater the ratio of OHions to H+, the more basic the solution becomes. PH is measured on a scale of 1-14. A pH of 7 indicates that the H+
and OH- ions are in balance. A reading below 7 means that there are more H+ ions and a reading above 7 indicates more OH- ions. pH H+ OHIn horticulture we have traditionally used a pH reading to make amendments to our growing media and irrigation water. But while pH is a good indicator of the availability of dissolved fertilizers in the root zone, it is not at all good at predicting the effect that a given irrigation source will have on the media pH. For that, you must also know the buffering capacity or alkalinity of the media and the irrigation source. Alkalinity levels indicate the relative
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AN EXPLANATION OF PH:
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ability of the media to resist or neutralize the effects of acids. The higher the alkalinity level, the greater the amount of acidification that will be required to produce a desired pH drop. pH Testing All commercial horticultural businesses, regardless of size, should have a reliable pH meter. Follow the instructions included to preserve the accuracy and life of your instrument. Solution samples can be read directly, or after a few hours of settling time. Dissolved CO2 in water supplies can cause slightly lower readings until the sample has come to equilibrium with the air. Freshly mixed samples of media should be watered and allowed to stand for 24 hours before a reading is taken to release some of the lime and fertilizers. The preferred method for testing media pH is to obtain several representative samples of a crop and to measure each separately. Multiple measurements will give greater accuracy in reading, and will show the degree of variability of pH from pot to pot. A saturated media extract or a 1:1 soil to distilled water ratio is fine for measuring pH. Why add Lime? Many horticultural soils require the addition of lime to correct pH and to supply calcium and magnesium. Lime directly affects the alkalinity of the soil medium. The amount of lime needed depends upon these factors: the type of lime, the fineness of the lime particles and the pH, acid content, and buffering capacity of the media. Most potting soils today are amended with dolomitic limestone to supply adequate calcium and magnesium and to buffer the acid content of peat, a prime constituent of many potting soils. Other types of limestone include calcium carbonate, which supplies only calcium, and hydrated lime, which reacts very fast, but is not as long lasting. Hydrated lime is seldom used alone since it is very quick acting and short lived. It is sometimes used in emergencies to raise pH after the plants have been potted, or as a partial component of the lime additives. For greenhouse and nursery soils, the
Using a pH meter.
calcium carbonate or dolomite lime used should be rated as 65 mesh or better, which means that 65% of the particles are small enough to pass through a 100 mesh screen. This is often called pulverized lime. Calcium sulfate, or gypsum has a neutral effect upon pH and can be used as a calcium source when no pH effect is required. The amount of lime to use depends upon the peat source. If the peat is highly buffered (acidic), then more lime is needed to have the same effect. Perlite, vermiculite and most other aerating materials have little effect on pH, but since their addition decreases the volume of peat, proportionately less lime is needed. For example, if a cubic meter of pure peat required 7 kg. of lime to raise the pH to 6.0, then a 50% peat, 50% perlite mixture would require only half as much. Alkalinity Testing If you have regular solution analysis performed you can usually request an alkalinity or bicarbonate test also. Do-it-yourself alkalinity test kits are also available for low cost from scientific companies. The effects of both pH and alkalinity are important to the nutrition and root health of your crops. Understanding these principles will help
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to take some of the guesswork out of managing media and solution pH. How to Measure Alkalinity Unlike pH, alkalinity is a measure of a solution’s ability to neutralize acids. It is the alkalinity level that determines how your irrigation water will influence the pH of the growing media. Most people who are familiar with pH would expect that high pH irrigation water would tend to raise the media pH over time. However, if the water has very low alkalinity, it may not have a significant effect on media pH despite its high initial pH. By contrast, if we used irrigation water with a high alkalinity level, say 200 ppm bicarbonate a greater effect on media pH can be expected. The higher the alkalinity of the irrigation water, the faster the root media pH will change. Rain water sources of irrigation water normally contain little or no bicarbonate. Well water sources often range from 50-150ppm. Although some bicarbonate alkalinity is good, higher levels can be toxic to some plants and in these cases, well water must be mixed with rainwater to bring the bicarbonate into the desired range. If insufficient bicarbonate is available naturally, then
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AN EXPLANATION OF PH:
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potassium bicarbonate can be added. Both limestone and bicarbonate raise pH by the production of carbonate. Over time, high alkalinity water sources will tend to increase pH, while low alkalinity sources will decrease it, depending on the rate of leaching and fertilization and the nature of the fertilizers used. Growers with very low alkalinity levels have sometimes found it useful to provide a modest background level of bicarbonate of (60-100) ppm. By then adding small additions of acids to achieve the desired pH, they can dose nutrient solutions with sufficient buffering capacity to change or stabilize the pH of the root media.
to raise the pH too quickly due to the possibility of ammonia release. Lower rates of bicarbonate (60-180 ppm or 1-3 kg. per 1000 liters) with each watering are effective at raising pH over time.
Changing Media pH
Fine ground elemental sulfur at 5 g per 15 cm pot or 15 g per 2-3 gallon container is recommended by some sources as a gradual way of bringing down pH. It is the action of certain soil bacteria that create the change, usually in about 10-15 days. Acid additions are the most common method of reducing
Understanding the relationship of alkalinity to pH makes it easier to change the media pH when needed. Regular pH testing of the root media is necessary to monitor the condition of the root media and to identify the need for amendment. Several factors come into play when attempting pH alterations. Variables that can influence the rate of pH change and the amount of modifying action needed are: soil temperature, root volume, leaching fraction, the buffering capacity of both the soil medium, and the irrigation source.
Lowering pH Iron sulfate dissolved at 1-4 kg. per 100 liters has been used where pH is too high. The solution should be acidified enough to dissolve all the sulfate. Ammonium sulfate will lower pH slowly but very effectively due to the action of nitrifying bacteria. The crops treated should be ammonium tolerant, the pH should not be less than 6.2, and the temperature should be above 15oC.
pH. They work best if used as a regular component of the feed solution to prevent the media from becoming too basic. Reducing the feed solution to around pH 4, depending on the alkalinity, can be effective for producing a more rapid change, but some nutrients may be tied up. Most growers use a lab analysis or a trial and error method to calculate how much acid to add toa solution to get a desired pH. Residues Wherever chemicals are used to raise or lower pH in irrigation water they may leave deposits on leaves, particularly when used in misting systems. Precipitates caused by sulfuric and phosphoric acids are more of a problem than nitric acid, but nitric acid is more hazardous to handle and can elevate EC levels at high injection rates. By: M Southwood.
It is always best to catch pH problems early, before drastic steps are needed. When it becomes necessary to raise or lower the pH in the crop, it is wise to start conservatively to avoid overshooting the tolerance range in the other direction. Wild pH swings can be worse than the original problem. How to Raise pH Heavy leaching tends to reduce salts and raise pH provided the water pH is higher than the soil. This also will help to remove any pH-related toxic levels of minor elements such as manganese or iron. Hydrated lime has been used to raise pH in existing crops by dissolving 1 kg. per 100 liters fresh water. After leaving the mixture overnight, the clear solution is drenched onto the crop. This method does not work very well with hard water sources. Potassium bicarbonate dissolved at 1 kg. per 100 liters will add about 600 ppm bicarbonate to water plus 400 ppm potassium. However, it is best not
Testing water alkalinity is important before it is mixed with soluble fertilizers and transported to the plants – and you can do it on-farm.
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GREENHOUSES I SHADE NET I HYDROPONICS I AQUAPONICS
HOW CHANGES IN Season Influence Greenhouse Plants The plants’ water volume requirement will have to be upgraded daily due to the warmer weather as well as the expected rapid growth of young preharvest plants. This increasing need for water is echoed by the growing need for minerals as the plants need more and more nutrients to fuel the rapid growth. The relative nutrient balances must be maintained over the growth period, with careful attention for the need in Potassium during and after flowering – especially in fruiting vegetables like tomatoes. With high radiation conditions, excessive root EC or salt build-up is one of the main factors resulting in production losses. E.g. Tomato plants with thick stems, compacted internodes, deformed growth points and poor or no fruit set are examples of a too high salt load on the plant.
W
ith summer plants growing well and soon autumn sets in, growers must be ever-watchful to react smartly to all the changes taking place in the plant and climate over this transition period. During the winter - spring – summer transition, changes are often so subtle that they can catch the grower unawares. It can be generally stated that successful greenhouse growers are those who can “pro-actively” (vs. reactively) avoid potentially harmful conditions to counter potential plant stress and harvest reduction. The main players in the seasonal changes affecting the plants will be lengthened day length plus increasing day and night temperatures. These increases in climatic energy levels equate to increased water use by plants, mainly for evaporative cooling. In the case of indeterminate growers like tomatoes (that were transplanted for the summer), a further
complicating factor is the exponential plant development associated with the first rapid plant growth until roughly the onset of the harvest period. During winter, fertigation EC’s are maintained at a relatively high level in an attempt to “force” as much nutrition into the plants during these periods of lower water usage. Inversely, the EC should be gradually reduced as the warmer season progresses due to the higher water usage. If the Ec is not reduced in time, plants may reach a “salt saturation point” and “shut down” transpiration temporarily. This is to protect the cells from damage due to excessive salt build-up in the plant. Typical wilting during the midday period can be ascribed to this “shutdown”. Blossom end rot often results from this periodic wilting. At the same time as reducing EC, the water volume will have to be increased to match the transpiration of the plants.
In the broad, growers tend to overfertilize in an attempt to boost growth. Sometimes high root zone salinity can also be ascribed to a watering regime not suited to climate, or simply, inadequate water volume to facilitate sufficient flushing of the root zone (runoff % too low). EC levels should be as low as will maintain good growth and allow plants to continue transpiration throughout the day. Fertilizer mixtures containing significant levels of Chlorides (often in an attempt to lower the cost of fertigation) increase the relative EC of the mixture. Programs with no or very low Chloride levels, especially for summer, will help in reducing the ion load on the root system – allowing easier uptake of beneficial minerals and further aiding the prevention of salt build-up in the roots. Successful warm weather fertigation can only be done following a program which allows the plant to optimally utilize water for evaporative cooling, transport of sufficient and balanced nutrients plus enough oxygen for healthy root function and growth. Source: Advice from P de Vries
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GREENHOUSES I SHADE NET I HYDROPONICS I AQUAPONICS
WHY WATER SOLUBLE FERTILIZERS?
Tanks filled with different soluble fertilizers and electronics system to finetune mixing.
E
fficient fertilizers and fertilization methods have become the main answer to the ever-growing demand for agricultural products. Modern agriculture must supply crops with optimal rates of nutrients throughout the growth cycle in the most efficient manner possible, and without degrading soil and water resources. Nutrigation™ (Fertigation) and foliar nutrition enable highly efficient use of nutrients. All of Haifa’s water soluble fertilizers are fully water soluble and comprised of 100% plant macronutrients. It is virtually free of chloride, sodium and other detrimental elements for plants. Efficient absorption by plants Water soluble fertilizers are fertilizers that can be dissolved in water and added or
leached out of the soil easily. With water soluble fertilizers it is easy to control the precise amount of nutrients available to your plants (the control is more exact with soilless mixes). Soluble fertilizers usually have N-P-K numbers listed on their label. The N is for nitrogen, the P is for phosphorus and the K is for potassium or potash. Of the 16 (12 of which are contained in water soluble fertilizers) known elements necessary for plant life, N-P-K, are the three that are of the most importance and always listed on water soluble fertilizers, in that order. Following N-P-K, calcium (Ca) and magnesium (Mg) is the two second most important nutrients listed on the label. The rest, iron (Fe), sulphur (S), manganese (Mn), boron (B), molybdenum (Mo), zinc (Zn) and copper (Cu) are trace elements or micronutrients. Nitrogen is the most important of the nutrients. It controls the processes used to make proteins vital to new protoplasm in the cells. Nitrogen is essential to the production of chlorophyll and is responsible for leaf growth, as well as overall size and vigour. Phosphorus is necessary for photosynthesis and provides a mechanism for energy transfer within the plant. Phosphorus is associated with overall vigor and is used at its highest levels during germination, seedling and the fruiting or flowering stages of growth.
Tanks filled with different soluble fertilizers and electronics system to finetune mixing. Potassium, or potash, provides the manufacturing and movement of sugars and starches, as well as, growth by cell division. It also increases chlorophyll levels in the foliage and helps regulate the stomata openings so plants make better use of light and air. Potassium is important in all stages of plant growth. Magnesium is the central atom in every chlorophyll molecule and is essential to the absorption of light. It aids in the utilisation of nutrients and also neutralises soil acids and toxic compounds produced by the plant. Adding dolomite lime before planting helps stabilize pH and adds magnesium and calcium to the soil. The other secondary nutrient, calcium, is for the manufacturing of cells and overall growth. Trace elements are vital to chlorophyll formation and must be present in minute amounts. Little is known about the exact amounts needed. They function mainly as a catalyst to the plant’s processes and the utilization of other elements. The ultimate goal of fertilizing is to supply your plant with the right amount of nutrients, yet, at the same time not toxifying the soil via over-fertilization. Tanks filled with different soluble fertilizers and electronics system to finetune mixing. With water soluble fertilizers it is easy to control the precise amount of nutrients available to your plants (the control is more exact with soilless mixes).
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GREENHOUSES I SHADE NET I HYDROPONICS I AQUAPONICS
THE ADVANTAGES OF PERLITE
in Greenhouse Production
T
he Department of Agriculture, Land Reform and Rural Development has unveiled a master plan to industrialise and commercialise the R28 billion cannabis industry. The master plan focuses on the cultivation of hemp and marijuana. South Africa legalised marijuana for personal use in 2018, setting the wheels in motion for the government’s master plan to regulate and formalise the industry. This has resulted in cannabis becoming a key focus for sustainable farming practices. Thus, Perlite-based horticultural growing media stands to play a major role in the burgeoning cannabis farming sector. Using the product is a highly cost-efficient means to boost yields for sustainable small-scale and large-scale farming practices producers says.
content level in the root zone.
Perlite is available nationwide in various grade sizes to cater for specific blends. The fact that it is free of weeds and pathogenic microbes makes it an ideal horticultural growing medium. In addition, it promotes water drainage while still retaining an ideal moisture
Perlite is processed at temperatures in excess of 950°C, resulting in a completely sterile and safe product. The strong surface structure of perlite means it does not deteriorate during transportation or when it is mixed. This unique feature
The Perlite raw material is processed in proprietary furnaces to produce products that enhance agricultural practices and increase crop yields. Tiny micropores on the surface of the expanded Perlite particles capture nutrients and water molecules.
means hydroponic farmers, for example, can reuse the product for more than one season, increasing its cost-effectiveness.
The capillary action in the voids between the particles ensures uniform distribution of water and nutrients, resulting in consistent crops. Perlite also maintains optimal soil aeration. This is a critical factor in normal plant growth, as the supply of oxygen to roots in adequate quantities is essential for healthy plants.
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GREENHOUSES I SHADE NET I HYDROPONICS I AQUAPONICS
Getting the right mix of fertilizer to plants is required for optimal productivity.
REMOVE UNWANTED IONS FROM WATER to ensure quality water is fed to Greenhouse plants
I
t is found that high levels of soluble (ferrous) iron are present in wells or boreholes from the mountainous areas of the Cape, along the Drakensberg and a few other areas. This iron is in a reduced state (Fe2+). When the Fe-rich water is used for sprinkler irrigation, ferrous iron is oxidized to form an insoluble ferric iron Fe3+ and it may be visible as a brownred substance on leaves and garden walls. Manganese (Mn) is also soluble in its reduced state and precipitates as insoluble MnO2 when oxidized. When using water with high Fe or Mn concentrations for drip irrigation, the ions are oxidized, and these insoluble salts block the drippers. Apart from oxidation due to aeration, ferric and manganese bacteria are chemotropic and contribute to oxidize Fe and Mn. These ferric and manganese bacteria cause the oxidized residues to
accumulate among the bacterial waste, creating a slimy residue, also blocking drippers. Fe and Mn concentrations in water are important feeding water quality parameters in areas with high levels of these ions in the water. Good quality is regarded as safe to use, where Fe and Mn levels are <0.1 and <0.02 mg L-1, respectively. Medium quality water may contain Fe at 0.1 to 0.5 and Mn at 0.02 to 0.3 mg L-1. Poor quality water contains Fe at >0.5 or Mn at >0.3 mg L-1, needing pre-treatment to lower their concentrations where drippers are used. By aerating feeding water, Fe and Mn can be oxidized. Small oxidized particles can then be removed with filters. The oxidizing process is extremely slow in acidic water. By increasing the pH of the water before aeration, the oxidation time can be reduced substantially.
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The oxidation of ferrous iron may also be accelerated with UV tubes, the addition of chlorine gas (Cl2), ozone (O3) or peroxide (H2O2). Growers who make use of drip irrigation should remove as much Fe as possible from the feeding water. According to Deckers (2002), the natural Fe content of feeding water cannot be absorbed by plant roots and should be considered as not available. Other nutrients in feeding water can be topped up, but the total Fe-need should be applied, using Fe-chelate. With production systems, where drippers are not used, removal of Fe is not critically important. Sodium, chloride and other unwanted ions Should Na+ and Cl- levels exceed the maximum limits, it should not be used as feeding water. However, it may be
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GREENHOUSES I SHADE NET I HYDROPONICS I AQUAPONICS
diluted with rainwater or the ions can be removed with reverse osmosis, an expensive water purification system. This system removes all ions (macro- and micronutrients) from the water, although some boron (B) may slip through the membranes (Deckers, 2012). This method of water purification creates a large percentage of saline wastewater which should be well-managed to prevent pollution of soil and rivers. Ions associated with alkalinity The alkalinity level in saline feeding water is usually high, due to high levels of one or more of the following: CO3 2-, HCO3- and OH-. In the presence of Ca2+ and Mg2+ and under high pH conditions, a whitish-grey deposit of Caand Mg-carbonate (lime) may form when this water is used in kettles and geysers. Gadgets to desalinise or to soften water may be suggested by some institutions, but their claims should be tested by chemical analyses, before and after a water treatment. An inline cylinder, known as ‘Protection against total hardness’ (PTH, 2019), exposes water to a combination of special metals that may lower Ca-, Mg and bicarbonate levels due to the precipitation of these ions as insoluble Ca and Mg-carbonate crystals that remain in suspension. This may allow the water to be used with less damage to elements of electric kettles and geysers. Apart from the danger that Ca- and Mg carbonate particles may block drippers, these crystals will react with applied acids during the acidifying process when nutrient solutions are mixed. Ca and Mg will then be released as ions. Thus,
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Too little iron in the irrigation mix shows up on the leaves of a plant – proof of Fe deficiency. PTH-treated water is not recommended for hydroponics production systems but may soften water used for gardening or households. The alkalinity anions (CO3 2-, HCO3and OH-) can be replaced by nitrate, phosphate or sulphate, by adding nitric- or phosphoric-, or sulphuric acid respectively. With a very high total alkalinity, special procedures should be followed and provision should be made for the release of CO2-gas. This will be explained in the following edition of Undercover Farming. By Dr NJJC Combrink from his book; Nutrient Solution Management. Available at njjc@sun.co.za Too much iron content in the irrigation water is visible in the red spots on the leaves. (Pic: Rutgers)
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MELONS IN A GREENHOUSE
AGRICULTURAL e-TRADE
COTTON IN GREENHOUSES?
GREENHOUSE MIXING TANKS
Melons in a greenhouse _ the basic facts Page 4
Agricultural e-Trade offers a key enabler for Africa Page 9
Cotton Production in Greenhouses investigated Page 13
Dissolving macro- and micronutrients Page 17
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