Undercover Farming Magazine July/August 2020

Undercover

farming

ucf

I

JULY/AUGUST 2020 Volume 17 No 4

I  I R45.00 per issue

greenhouse

water quality

germination

hydroponics

The importance of pH management Page 6

Feeding water quality and your greenhouses irrigation system Page 11

Managing germination of peppers and tomatoes Page 16

Hydroponics for new entrants Page 18

Undercover growing solutions to help your business flourish

Turnkey Solutions

Greenhouse Structures

Irrigation

Cape Town

Climate Control

Crop Management Technology

Growing Products

Johannesburg

Telephone

021 987 6980

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011 974 5254

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Vegtech, 25 Kiaat Road, Kraaifontein

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Vegtech, 23 Brewery Street, Isando,

Industria, Cape Town, 7570.

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info@vegtech.co.za

Johannesburg, 1600.

Email

www.vegtech.co.za

info@vegtech.co.za

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 Fréda Prinsloo PRINTING Business Print Centre 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.

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Contents 4 6

PH management and production in the greenhouse Commercial greenhouse cooling systems: natural ventilation compared with forced evaporative pad and fan 8 Keeping the balance of leaf canopy to root mass crucial in achieving yield 9 Pruning & trellising of tomato plants to optimise greenhouse production 11 Feeding water quality and your greenhouse irrigation system 13 The choice of the correct grow media for your specific crop 16 Managing the seasonal germination of peppers and tomatoes 16 Keeping the balance in cucumber production 18 Hydroponics production for the new entrant to fresh produce farming 19 Subscription form

FRONT PAGE: Managing the pH in hydroponics systems is important for optimal quality and yield.

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A Scripture to strengthen your faith

John 14:1-2 (Jesus said)”Let not your heart be troubled, believe in God, also believe in Me. In my Father’s house are many mansions, if it were not so, I would have told you so. I am leaving to prepare a place for you.”

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he extremely cold conditions in a large part of the country will for sure take its toll on man and animal. For the undercover farming industry, it means additional costs of heating up greenhouses to maintain optimum plant production (and protection).

With coal prices at the level it runs, this increase production costs and leaves the producer with the question; “Will the already tight market through Covid-19 pay my price?”

Fortunately, the cold weather will soon change into spring and temperatures will normalize.

Still, our farmers are in a mode of ‘survival of the fittest’! With steadily relaxation of several stringent measures to curb spreading of Covid-19, and more and more news reaching us globally how this pandemic is actually an act by some force to control global business and people, we are all looking forward to get back to normal business and family life. We feel for the worst hit sector; the informal fresh produce vendors around the world who are bringing foodstuff within reach (and means) of the masses. This is where the Covid-19 pandemic really gave fresh food production a kick in the stomach. Nevertheless, as the British saying goes; “Keep a stiff upper lip and look to the future!” We envisage many more farming minded people to turn to greenhouse farming for the mere fact of utilizing a relatively small area for production, controlling and managing every aspect of this venture and playing a part in food security. The mega-farmers produce for export and the shrinking large supermarkets in malls offer opportunities for entrepreneurs to open suburban fresh produce outlets, nearer to homes. It is amazing how something like this global pandemic can make way for new avenues in almost all spheres of life! Come to think of it; why did I have to run barefoot in bitter Karoo winter cold to school, if only I had access to a laptop at that time (many years ago!). Chin up friends; let’s go undercover farming for a boom season!

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Improper 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.

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any 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 to 6.8 is considered ideal for mineral soils, and 5.8 to 6.2 are recommended for peat or bark media. Of course, this depends upon the crops grown. In grow media, cucumbers flourish at pH 5.8 - 6.0 while tomatoes requires a pH of 5.5 - 6.5 for healthy plants.

Except for nitrates, potassium, and total soluble salts, the availability of most fertilizer elements is affected to some extent by the pH of the media. Calcium and magnesium become more availa-ble 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 management and production

in the greenhouse irrigation source. Alkalinity levels indicate the relative ability of the media to resist or neutralize the effects of acids. The higher the alkalinity level, the greater the amounts of acidification that will be re-quired to produce a desired pH drop.

Lime Many horticultural soils require the addition of lime to correct its pH and to supply calcium and magnesium. Lime directly affects the alkalinity of the soil medium. The amount of lime needed What is pH? depends upon these factors: the type of PH measures the relative concentration lime, the fineness of the lime particles of hydrogen ions (H+) to hydroxide ions and the pH, acid content, and buffering (OH-). The greater the number of H+ capacity of the media. ions in relation to OH-, the more acidic Most potting soils today are amended with the solution becomes. The greater the dolomitic limestone to supply adequate ratio of OH- ions to H+, the more basic calcium and magnesium and to buffer the the solution becomes. PH is measured acid content of peat, a prime constituent on a scale of 1-14. A pH of 7 indicates of many potting soils. Other types of that the H+ and OH- ions are in balance. limestone include calcium carbonate, A reading below 7 means that there which supplies only calcium, and hydrated are more H+ ions lime, which reacts and a reading above Most potting soils today are very fast, but is not as 7 indicates more amended with dolomitic long lasting.

OH-ions. limestone to supply Hydrated lime is + OHseldom used alone adequate calcium and In horticulture we since it is very quick magnesium and to buffer traditionally used a acting and short lived. the acid content of peat. pH reading to make It is sometimes used amendments to our growing media and in emergencies to raise pH after the irrigation water. But while pH is a good plants have been potted, or as a partial indicator of the availability of dissolved component of the lime additives. fertilizers in the root zone, it is not at all For greenhouse and nursery soils, the good at predicting the effect that a given calcium carbonate or dolomite lime used irrigation source will have on the pH of should be rated as 65 mesh or better, the media. which means that 65% of the particles are For that, you must also know the buffering small enough to pass through a 100 mesh capacity or alkalinity of the media and the screen. This is often called pulverized

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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, propor-tionately 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 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 5

It is always best to catch pH problems early, before drastic steps are needed.

greenhouses I shade net I hydroponics I aquaponics PH Management and Production

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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 count. 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 wa-ter 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 bicar-bonate into the desired range. If insufficient bicarbonate is available naturally, then potassium bicarbonate can be added.

Both limestone and bicarbonate raise pH by the production of carbonate. Over time, high alka-linity water sources will tend to increase pH, while low alkalinity sources will decrease it, depend-ing 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.

the amount of modifying action needed are: soil temperature, root vol-ume, leaching fraction, the buffering capacity of both the soil medium, and the irrigation source.

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 over-shooting the tolerance range in the other direction.

Wild pH swings can be worse than the original problem.

Raising 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 li-tres 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 litres will add about 600 ppm bicarbonate to water plus 400 ppm potassium. However, it is best not 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 litres) with each watering are effective at raising pH over time.

Lowering pH Iron sulphate dissolved at 1-4 kg per 100 litres has been used where pH is too high.

The solution should be acidified enough to Changing Media pH dissolve all sulphate. Ammonium sulphate Understanding the relationship of alkalinity will lower pH slowly but very effectively to pH makes it easier to change the media due to the action of nitrifying bacteria. pH when required. Regular pH testing of The crops treated should be ammonium the root media is necessary to monitor tolerant, the pH should not be less than the condition of the root media and to 6.2, and the temperature should be above identify the need for amendment.

15oC. Several factors come into play when Fine ground elemental sulphur at 5 g per attempting pH alterations. Variables that 15 cm pot or 15 g per 2-3 gallon container can influence the rate of pH change and is recom-mended 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 pH. They work best if used as a regu-lar component of the feed solution to prevent the media from becoming too basic.

Plant roots are exposed to the substrate solution.

Reducing the feed solution to The root hairs, extensions of the root epidermal cells, are the interface between the plant and the substrate around pH 4, depending on the solution. Roots are very sensitive to pH. The acidity alkalinity, can be effective for or basicity of the substrate solution determines how producing a more rapid change, well the roots can take up nutrients and how well the but some nutrients may be tied plant can grow.

Hand held pH meters are available that gives an accurate reading of the media and solution in your greenhouse.

This is an essential tool every greenhouse manager should keep at hand. Keeping record of readings is essential for tracking problem areas in the production unit as a whole.

up. Most growers use a laboratory analysis or a trial and error method to calculate how much acid to add to a 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 sulphuric and phos-phoric 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.

Testing pH All commercial horticultural businesses, regardless of size, should have a reliable pH meter. Fol-low the instructions included to preserve the accuracy and life of your instrument. Solution sam-ples 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. Testing Alkalinity If you have regular solution analysis performed you can usually request an alkalinity or bicar-bonate 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 to take some of the guesswork out of managing pH in the media and solution.

By: J van Heerden

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Commercial greenhouse cooling systems: Natural ventilation compared with forced evaporative pad and fan High greenhouse temperatures are extremely detrimental to optimum plant health and growth, which obviously has a negative effect on commercial greenhouse farming yields and profitability.

It therefore goes without saying that an effective greenhouse cooling system is one of the most important considerations for greenhouse growers.

These solutions are either passive (natural) or forced (mechanical).

Forced Ventilation with Evaporative Pad and Fan Cooling Pad and fan he pad and fan cooling system work by using exhaust fans that suck warm air out of the greenhouse creating air flow over evaporative cooling pads.

This is a popular method for cooling greenhouses and can reduce tempe­ ratures significantly (between 5-10 °C

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depending on the relative humidity) but it has various disadvantages: 1. High energy costs.

2. Higher maintenance costs.

3. Significant temperature variance 4. Mainly effective in dryer climates.

5. Water consumption is higher in pad and fan cooling compared with high pressure fogging.

Natural, Passive Ventilation with High Pressure Fogging Natural ventilation Natural ventilation is the result of

The pad and fan cooling system work by using exhaust fans that suck warm air out of the greenhouse creating air flow over evaporative cooling pads. pressure differences created by the wind and temperature in the inside and outside of a greenhouse.

It requires less energy n comparison with pad and fan cooling.

High Pressure Fogging (HPF) If the above-mentioned natural ventilation options are not sufficient 7

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for cooling the greenhouse, they can be used in conjunction with high pressure fogging.

Documented in a recent Natural ventilation is research paper, the result of pressure experiments differences created were done by the wind and on naturally temperature in the ventilated greenhouses in inside and outside Pietermaritzburg, of a greenhouse.

KZN. It was found that by using HPF, the internal temperature can be reduced up to 10 °C (E. du Plessis, 2016).

In conclusion In a comparison using a 1ha greenhouse, the following assumptions can be made: • The fans run on average for 4 hours per day throughout the entire year (this can be double in some areas depending on the climate). Water is recycled through the system and only evaporation water is counted; • The HPF runs on average 4 hours per day throughout the entire year (the system switches on and off intermittently as required throughout the day and will change during seasons); • Average electricity rate of R1, 2/kWh, and • Standard designs are assumed.

The electricity expense per year for the 1ha pad and fan

greenhouse accumulates to at least R210 000 per annum, in comparison to R 40 000 per annum for the HPF in a naturally ventilated greenhouse.

The water consumption for the 1ha pad and fan greenhouse is 45 000m3/year versus the HPF system that consumes 7 500 m3/ year.

Your unique greenhouse ventilation requirements may require expert advice to guide your decision-making process. Readers may contact Bosman Van Zaal South Africa to obtain further assistance in this regard.

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greenhouses I shade net I hydroponics I aquaponics A poor canopy as result of poor nutrition, disease or climatic conditions will have a reduced capacity to produce energy required for fruit development.

Keeping the balance of leaf canopy to root mass crucial in achieving yield Taking cucumber plants as an example to explain the advantages of keeping the balance of leaf canopy and root mass, the information in this editorial becomes apparent.

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ucumber roots have a high oxygen requirement and sudden temporary wilt, ‘epinasty’, of greenhouse cucumber plants is often noted. A high solution temperature also reduces the amount of dissolved oxygen in the solution. Oxygen diffuses through air 10 000 times the rate at which it diffuses through water, thus waterlogged soils and media are undesirable. Oxygen content of a fully aerated solution at 10˚C is 13 ppm and at 30˚C it is 7ppm.

This may not seem significant but at higher temperatures the oxygen requirement increases as respiration increases. Alcohol, hydrogen sulphide and ethylene are produced in the roots in waterlogged soils and media and hormone production is also disturbed. Media such as sawdust often compact over time, which leads to water logging and results in low oxygen levels in the root zone and impaired potassium, phosphate, manganese and iron uptake. The ability of water to move into the roots is reduced almost threefold in the absence of oxygen in the root zone, mainly under waterlogged conditions.

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The combined effects of these changes are seen as stunted or wilted tops and root death; roots will often be at the surface of the media where oxygen is available. In such circumstances, the balance of leaf canopy to roots is compromised. In addition, Pythium is an opportunistic fungus and often takes hold of plants stressed by a combination of high temperatures and low oxygen levels in the root zone.

Bearing the above in mind, basics such as media amelioration should be considered mandatory to further improve media properties and boost oxygen levels.

Oxygen is part of the respiration process whereby carbohydrates are broken down to provide energy for the plant, this being the opposite process of photosynthesis.

Products of respiration are carbon dioxide as well as a wide range of carbon compounds exuded from the roots.

Carbohydrate + O² ↔ CO² + H²O + energy Growers often avoid removing the lower fruit on cucumber plants in a bid to get quick yields, this load on the plant at such early developmental stages

draws energy from the plant that would normally be used for root development, thus reducing the root mass. Similarly, loss of leaves in the lower extremities of the plant are often evident, due to low light or infection, yet growers allow fruit to develop on these nodes where leaf abscission is noted.

These fruit have no “neighbouring” leaves to supply the energy for the development of these fruit, and thus draw energy from the plant that would usually be used by the root system, thus causing a decline in the efficacy of the root system.

Conversely, a poor canopy as result of poor nutrition, disease or climatic conditions will have a reduced capacity to produce energy required for fruit development and in turn having reduced energy for root development and root exudates, further exacerbating the problem and diminishing the yield potential. In such cases growers should be able to “read” the plant and remove fruit to allow the plant to carry a suitable fruit load without compromising the root system or plant health.

By Mike Haupt

greenhouses I shade net I hydroponics I aquaponics

Pruning & trellising of tomato plants

to optimise greenhouse production

Shaping 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 1. 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 2. Reduces the incidence of fruit rot and soil-borne diseases 3. Maximizes the efficiency of photosynthesis 4. 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 1. Requires expertise (good management and skilled workers) 2. Trellising and pruning need to be done regularly – labour intensive 3. Plants can be damaged during training and harvesting.

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 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 10

Growing-point

Sucker/ side-shoot

Side-shoots

The removal of sucker/side-shoots with the thumb and forefinger – sanitizing hands is a must in any greenhouse to ensure disease control.

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greenhouses I shade net I hydroponics I aquaponics Pruning & trellising of tomato plants

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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 Removal of the older leaves results in trusses facing towards the walkway, which makes harvesting easier. suckers above the first truss will result in lower yield. the other hand. It is important not to Removing the growing points of a When the plant matures, especially remove the green leaves since they plant will stop growth and enhance when the first two trusses have been function as a source of fruit ripening. With approaching low harvested, lower leaves food supply to the fruits.

Water should be temperatures (frost), it is important turn yellow. Generally, The figure below shows to prune the growing points of all chemically analysed in remove yellow leaves how a plant should the plants. This is because tomato is below the ripening fruit order to determine the look after removing the sensitive to low temperatures, so by clusters. These yellow levels of the different old leaves. Old leaves removing the growing points will stop leaves should be snapped nutrients in solution. should be removed far fruit bearing and ripening of fruits will off with fingers and In low rainfall areas, from the production be enhanced. removed as they are not actively photosynthesizing. high levels of salts are area and destroyed to Trellising prevent the spreading In addition, this will usually present.

Trellising is done by tying twine from or build up of diseases. enhance air circulation the bag to the stay wire above the plant. around the base of the plant, and will Indeterminate cultivars grow very The stem is then twisted around the help to reduce fungal and bacterial tall, and with time the yield and fruit twine to give support. Trellising should disease build-up. This can be done size become progressively smaller. be done two weeks after transplanting. by holding the main stem with one If transplants are not trellised hand and snapping off the leaf where at early stage, they become it is attached to the main stem using 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.

Source: ARC Vegetable and Ornamental Plant campus.

Trellising shows the stem twisted around the twine, which is attached to the stay wire.

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The term ‘feeding water’ is used to describe an untreated water source that is available to prepare nutrient solutions for soilless crop production.

Different factors can be used to define feeding water quality, but the chemical composition and the presence of potentially dangerous microorganisms need special attention.

Feeding water quality and your greenhouse irrigation system

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ooking at the chemical composition, firstly the concentration of ions, measured as EC, can be used as indication of the potential quality of feeding water.

Water with a low EC can be used to grow any crop. High EC feeding water, usually high in sodium (Na+), magnesium (Mg2+), sulphate (SO42-) and chloride (Cl-) can only be used to grow salinetolerant crops.

These include amaranths, Swiss chard, melon and cherry tomatoes. Examples of crops that are extremely sensitive to saline conditions are blueberries, disas, anthurium, cymbidium and roses. Most of the remaining greenhouse crops vary between moderately sensitive to moderately tolerant, as can be deducted from the EC levels, associated with the nutrient solutions as recommended for different crops.

It should be kept in mind that the absorption of water is restricted at increased root zone EC levels. The water in the lake of Galilee is widely used in Israel, even though it has an EC of ±1.0 mS cm-1. The EC of water in the Vaal Dam varies between 0.3 and 0.9 mS cm-1 but the EC in the lower Vaal River may be higher in relatively dry seasons.

Compared to this, the quality of Stellenbosch’s water is excellent, with an EC of about 0.1 mS cm-1, as is also found in other water streams from unpolluted, high rainfall mountain areas.

However, there is no guarantee that water with a low EC can safely be used for soil-less crop production,

sulphate (SO42-) may also be present in since micronutrients may be present at high-EC water. The other essential ions phytotoxic levels without affecting the are usually found at lower EC. Two examples are Water should be concentrations, depending high zinc (Zn) levels in rainwater gathered from chemically analysed in on the area and the galvanised roof surfaces order to determine the water source. The higher the ratio of useful ions and high copper (Cu) levels of the different compared to Na+ and Cl-, levels where copper nutrients in solution. the better the potential of water pipes are used.

In low rainfall areas, the water.

Macronutrients in high levels of salts are These essential nutrients feeding water usually present. should be topped up Water should be to optimum levels. chemically analysed in 2+ may be present at high Since Mg order to determine the levels of the concentrations in high-EC water, it may different nutrients in solution. In low reach toxic levels when Mg fertilizers rainfall areas, high levels of salts are are simply added to the water at normal usually present. Apart from Na+ and Cl-, recipe levels.

A high Mg2+ concentration high levels of essential nutrients such as in a nutrient solution may restrict the calcium (Ca2+) magnesium (Mg2+) and

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Strawberries need relatively low boron (B) levels due to physiological problems with B at >0.32 mg L-1.

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phytotoxic effect of high Municipal Cu-levels is well-known. uptake of Ca2+ and K+. quality Most crops need Cu at water -1 Micronutrients in feeding water 0.05 mg L . According to Apart from high sodium, chloride Steiner (1984), Cu may Corrosive or macronutrient levels in high-EC be phytotoxic when its mountain water water, it may also contain high or toxic concentration is doubled to micronutrient levels. Micronutrients are 0.1 mg L-1. Copper pipes usually present at such low concentrations should thus be avoided in Limestone that even at relatively high micronutrient hydroponic units. pebbles in concentrations they do not affect EC Manganese toxicity problems a 30 000 L readings. Should feeding water contain tank may develop on lettuce micronutrients at high levels exceeding (open or loose tulip shaped the concentrations prescribed for heads) where seedlings are Figure1. Treating acidic- or zero-alkalinity feeding water different crops, the water should be grown on sphagnum peat, with limestone pebbles. avoided or handled with care. As with due to high levels of Mn in macronutrients, the micronutrient levels this European substrate. High in feeding water should be considered Thus, the total alkalinity of the water iron (Fe) and manganese when planning nutrient solutions and should not be too small to prevent the (Mn) levels in some feeding water sources should be topped up to optimum levels. pH from dropping when these fertilizers may block irrigation drippers. These are dissolved. In mountainous, high rainfall water sources should be treated to lower Micronutrient phyto-toxicity areas, low-EC water may be acidic with a Fe and Mn levels.

Tomatoes can tolerate total alkalinity of zero. In order to remove B at levels of up to 1.1 In order to remove the Total alkalinity (pH) the corrosiveness of such a feeding mg L-1, almost four corrosiveness of such a The pH of water and water, a huge reservoir can be filled with times higher than the nutrient solutions can be limestone pebbles (Aquastab) to let the feeding water, a huge recommended level. It manipulated by adjusting water pass though it (Figure 1). reservoir can be filled is recommend that Zn the total alkalinity.

Municipalities use this technique to treat with limestone pebbles be used at 0.33 mg L-1 Total alkalinity is the corrosive water in order to protect (Aquastab) to let the for substrate-grown aggregate concentration their water pipes. Since the solubility of tomatoes, but toxicity water pass though it. of carbonate, bicarbonate limestone is very low, almost insoluble, can be expected at only and hydroxide. The total Municipalities use it only adds a very small alkalinity to the twice this concentration. of these ions (CO32- & this technique to treat water while it will also neutralize acids High Zn-levels are that may be present in the water. The corrosive water in order HCO3 & OH ) in water usually found in water is determined with a water coming from a lime-pebble tank to protect their water gathered from galvanised titration, by adding acid will be suitable to be used for normal pipes. roof surfaces. to the sample until the greenhouse crops. Should a corrosive, pH reaches a level of 4.5.

Copper-sulphate is a low-EC water be treated with limestone Some water-soluble fertilizers may be well-known chemical, used to kill algae pebbles, it is possible that its pH may rise slightly acidic. in swimming pools. Thus, the potential to a level higher than 7. However, due to the low total alkalinity of these low-EC water sources, its pH should drop when fertilizers, containing some acid residues, are added.

Apart from the limestone pebble treatment, the alkalinity of feeding water can also be increased by using soluble hydroxides such as potassium hydroxide (KOH) or calcium hydroxide (Ca(OH)2).

However, the dosage of these products should be accurately calculated and applied to lift the total alkalinity and pH to higher levels. Water with a high total alkalinity needs to be treated with acid to lower its alkalinity before fertilizers can be added. feeding water quality

Seedlings being moisturised with water that was tested before to ensure no damaging pathogens reach the tiny plants.

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Harmful micro-organisms in water The levels of plant pathogens are usually very low in water from boreholes. When using water from rivers, the incidence of plant pathogenic organisms is much higher. Due to informal settlements and urbanization, water sources that were relatively free from plant 14

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The choice of the correct grow media for your specific crop

T

oday we have many different options to choose from. We mention amongst others Wood Shavings (Sawdust), Perlite, Bark, Peat moss and last but not least Cocopeat (Coir). Most of the used materials are of natural origin, bearing a risk in it for contamination with soil-born diseases, weeds etc. This goes especially for Bark and for Peat moss and for Cocopeat as well. So it is important to purchase from a reliable, certified Supplier. I have seen too many cases of grow media (Bark) badly contaminated with soil borne diseases.

But for all grow media rules that we need to adjust the Water Management according to the specifications (structure and texture) of the media as well as according to the crop stage.

Requirements The main property of a grow media is the existence of small pores in it mainly for Water holding capacity and very important the presence of bigger pores for air (Oxygen) holding capacity. As mentioned the majority of our media is from natural origin and we have to anticipate the process of decomposing.

As the time goes, the media will change its texture due to the mentioned decomposing with change of water and air holding capacity.

Wood shavings option Wood shavings are usually easy available, and if you choose for a courser option and put it in closed horizontal so-called ‘pillow’ bags with plant holes on top, this results in a reliable and relatively sustainable medium since the shavings in those closed bags have a better water holding capacity than the ones in the

open top bags which are often in the start judged as too dry in the top layer and later in the season all of a sudden very wet in the down part of the bag especially when the finer sawdust is used. The mentioned pillow bags are successfully implemented in cucumbers where even two crop cycles are planted in the same bags before replacing.

The choice of a right grow media is one of the most important choices to make your crop cycle to a success.

lower water holding capacity but with better air holding capacity.

Another benefit with courser medium is the easier dry back during overnight and in case of overcast or rainy weather.

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Cocopeat option By far the best option however is Cocopeat since that is the most sustainable choice for most circumstances.

It is important to choose for the right mix between course and finer material. In general for Bell peppers we go for the courser mix (60% course/40% fine), tomato 50/50 and English cucumber the finest mix (60% fine). But also we have to take into consideration the Irrigation system.

When the water supply is stable and secure, we tend to go for slightly courser material with

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But also with cocopeat we opt for horizontal closed bags, and not for the open top bags. The latter results also in less efficient use of the top layer. Since this is too dry, so observe hardly any roots in the top. For tomato cropping we advise to replace the bags after one year of usage. Bell Peppers often use the bags one or even two years before replacement. For English cucumbers the practice is to plant two or three crop cycles in the same bag before replacing.

The practice of using the slabs for additional planting cycles before replacing makes it viable to invest in this medium with savings on replacement and labour costs.

Other options Other above-mentioned options I like to point briefly. Perlite is sometimes successfully used or mixed with Peat moss or even in soil as soil improvement. This medium has lots of big bores (air holding capacity) but less water holding capacity.

Bark in vegetable crops is trialled but in practice often judged as too wet and not disease free delivered. Bark is worldwide successfully used in pot plant (Orchid) cultures.

Last mentioned option Peat Moss is feeding water quality

12

pathogens a few years ago, might have deteriorated, needing sterilization before it can be safely used for soil-less crop production.

Several laboratories do bacterial counts.

As indication of the total number of bacteria in the water (good and bad), they determine the number of ‘coliforms per 100 ml’. Irrigation water should contain less than 1000 coliforms per 100 ml water, but a more reliable norm for the quality of the water is to measure the number of harmful bacteria such as Escherichia coli and Salmonella.

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widely used as Seedling Mix. And for this option also the choice for a reliable certified supplier is crucial.

Water Management After choosing the right medium it is important to pay attention to the water management. We have to make the right choices for daily start and stop times of irrigation, shot and interval length as well as drain (run-off) percentage and monitoring. Dryback overnight results in Oxygen penetration to the root zone.

Monitoring of the Water Content by weight scales or moisture probes gives you the requested information about your irrigation practices.

Crop Balance and optimal yield The best performance of a crop and the highest yield can be reached by the right choices in Climate Control, Crop Maintenance and Irrigation / Fertigation practices. This requires an experienced Grower who is often making use of

Coaching by a Crop Consultant.

Delphy is a Worldwide renowned and independent Research and Consultancy Company. Contact us in case of inquiries and we will try to find the best solutions for making the next step in your Company future.

These bacteria should not be present in the water used for overhead irrigation systems (<1 per 100 ml). With a drip irrigation system, the norm is <10 per 100 ml. Where water is needed to rinse vegetable products, it should be municipality standard and fit for human consumption. According to SANS (2017), this means that the E. coli and Salmonella counts should be <1 per 100 ml water.

Apart from chlorination, as used by municipalities and some growers, or hydrogen peroxide, as used by some lettuce and blueberry growers, other sterilization options are also available.

Due to the importance to have nutrient solutions sterilized before it is reused in closed production systems, several alternative sterilization options will be discussed in the next edition of Undercover Farming.

By Dr NJJ (Nic) Combrink of the Horticultural Faculty, University of Stellenbosch. Readers who wish to obtain his very valuable updated manual on Nutrient Solution Management, may contact him at njjc@sun.co.za.

Dr NJJ Combrink

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Managing the seasonal

germination of peppers and tomatoes Seedling nurseries are often asked during the cooler months, to produce tomato and pepper seedlings for producers in warmer climate areas, or those wanting to get into the market early. Unlike summer seedling production, the management of winter seedling production requires much more management intensity to ensure maximal protection of the seed and seedlings from cold and the damages it may cause.

S

eed is a living organism and is sensitive to the environment that it is subjected to. During the germination and subsequent development of the seedling, it is just as important to control the surrounding environment.

Many seedling nurseries do just that using heated germination rooms where seedling trays are stacked for a predetermined amount of time to allow germination to occur. At emergence, the trays are usually transferred out into the nursery where the seedlings are allowed to develop.

The management of the germinating seed is essential to ensure maximum germination and subsequent development of the plant. Tomatoes require the following temperature conditions for germination: Table 1: Seed Germination Temperature for Tomatoes Characteristic Seed Temperature (˚C) Germination Minimum 10 Optimum Range 16 - 29.5 Optimum 29.5 Maximum 35

Not only does the temperature impact the actual germination process, but also the rate of seedling emergence:

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Evenly sized tomato seedlings in a seedling tray.

Table 2: Days to Seedling Emergence for Tomatoes Soil Temperatures for Germination (˚C)

Seedling Emergence (Days)

10 43 15 14 20 8 25 6 30 6 35 9 This information highlights the importance of temperature on the most important phases of the germination and emergence of tomato seed. Peppers have a similar sensitivity to temperature and should also be managed accordingly.

During the cooler periods of the year, temperature fluctuations during germination and emergence of the seedlings will result in poor germination, uneven emergence, slow development of seedlings and sometimes a poor pull rate.

This common occurrence is often mistaken for poor quality seed, but the same seed lot will provide almost perfect germination, emergence and development when temperatures rise.

Most seed companies provide with their tomato and pepper seed what is termed ‘a range test’. The range test describes the effect of various temperatures on the germination of the particular lot.

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Each seed lot responds differently to temperature regimes and therefore, each seed lot is tested accordingly.

The importance of these range tests is that it illustrates how that particular lot needs to be treated to achieve the best germination and emergence of the peppers and tomatoes.

During warmer periods of the year, the relatively higher temperature of the air outside the germination room prevents excessive heat loss from the room resulting in better control of the temperature within the germination room. However, during cooler periods, the lower ambient temperature makes it more difficult to maintain a constant temperature within the germination room.

There are many methods, varying in expense, used for heating these germination rooms. Some nurseries do not heat; others use simple bar heaters or oil fin heaters or air conditioners.

These methods are completely satisfactory if managed correctly. The size of the room should determine the number of heaters or size of conditioner required to maintain the temperatures required for proper germination and emergence.

Strict control of the room temperature is not possible with a heater, unlike the air conditioners. If the temperature is maintained within the correct

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range it should not pose a problem.

Nurseries that do not provide any heating should not produce these more sensitive seedlings out of season. It is recommended that germination rooms be installed to assist in the production of high quality seedlings to their clients.

There are other temperature relating factors that can influence the germination of tomato and pepper seed.

• The temperature of the growing medium in the trays • The temperature of the water being used to irrigate the trays prior to moving them into the growing room • The number of trays in a stack and within a germination room • The size of a stack of trays • The shape of a stack of trays • The size of the germination room • The efficiency of the insulation material in the germination room • The movement of air within the germination room.

When cold medium and cold water are used to fill and water the trays, it will take longer to warm up the medium

to reach the optimal range for germination and emergence. If a large number of trays are stacked together before being put into the germination room, it will take longer for the trays in the centre of the stack to heat up.

If a large number of trays or several stacks are placed into the germination room at the same time, more heat will be required to raise the temperatures of all the trays.

The size and shape of the stack of trays will affect the ability of the warm air to heat up the cells in the centre of the stack. During the cooler season, smaller stacks should be used to allow for better heating of the trays. Trays should be arranged into longer thinner stacks to allow for better heat penetration.

Most seed companies provide with their tomato and pepper seed what is termed ‘a range test’.

The range test describes the effect of various temperatures on the germination of the particular lot.

Healthy seedlings become strong plants and ensure good yield potential.

Proper seedling management results in a grower’s quality harvest.

A larger germination room will obviously require more heat to raise the temperature to optimum levels, and when a large number of trays are installed into the room, even more heat is required. Rooms that are not adequately insulated will also require more heat to maintain adequate temperatures, and should a sudden temperature drop be experienced, a large amount of heat may be lost from the room resulting in a reduction in germination and emergence.

The movement of air in a germination room is also extremely important.

Smaller germination rooms may only use a small heater resulting in a large difference in temperature from one side of the room to the other. Allowing adequate air movement within the room will assist in reducing the temperature gradients that may be present. Adequate ventilation around each stack of trays will also reduce the amount of time taken to raise the temperature of the medium in the cells to optimum levels.

Correct management of the temperature within a germination room is advantageous to any nurseryman.

The result is better germination and emergence of seedlings, higher pull rates and better quality seedlings, all of which will result in better returns and financial stability. Proper seedling grower management pays!

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Soilless cultivation of lettuce, tomatoes, peppers and cucumbers has over the past two decades gained popularity in South Africa because of improved yield and quality. The majority of vegetables in South Africa were always grown in open field systems, but undercover farming yields much higher whilst using less water. Hydroponics and even aquaponics (where fish are used to enrich the water under the plants) are being practiced under protection, e.g. shade net houses and greenhouses.

Hydroponics production for the new

entrant to fresh produce farming

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he ARC-Roodeplaat mainly utilizes two hydroponic systems, i.e. gravel film technique (closed system) and open bag systems for research trials.

These two systems are commercially used in South Africa. The Gravel Film Technique (GFT) is the most popular re-circulating hydroponic system in South Africa especially for new entrants to greenhouse production. They produce leafy vegetables in a gravel film system, with a well-balanced nutrient solution that is pumped to the top of hydroponics system lines and flows down a 3% slope by gravity.

The nutrient solution is collected in a reservoir at the bottom and is pumped back through the hydrolines (re-circulated). The gravelâ&#x20AC;&#x2122;s major role is to give support to the plant, cover the root system and prevent the nutrient solution from being exposed to sunlight.

Different types of lettuce, celery, leafy herbs (e.g. parsely, basil), spinach and Swiss chard, leeks, spring onion, chives, different types of cabbage and mustards can be produced in this system.

In an open bag system, plants are grown in a plastic bag filled with a grow medium (e.g. sawdust, coir or cocopeat) where nutrient solutions are dripped onto the growth medium and there is a drainage allowance of 10-15%. The system is utilized in shade net houses or plastic tunnels with or without temperature control â&#x20AC;&#x201C; this can be manually controlled by opening doors or the sides of the greenhouse.

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Tomatoes, sweet The population increased tremendously pruning, and peppers and comparative in South Africa and improvement of cucumbers are the standard of living has resulted in performance the major fresh of vegetables an increased demand for fresh produce such as products grown of high value and quality. in an open bag tomatoes, hydroponics cucumbers, system in a plastic covered tunnel. The lettuce and peppers in different open bag system is well adapted for production systems. The current the production of tomatoes, peppers, research can be summarized as follows: cucumbers, strawberries, and beans.

Production systems for tomatoes ARC-Roodeplaatsâ&#x20AC;&#x2122; research is focused Tomatoes are widely grown in South on fertigation of lettuce and tomatoes, Africa and rank second cultivar evaluation, stem and fruit 19

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Trelissed plants are producing much more in a greenhouse than on open land and uses less water.

hydroponics production

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after potato as a vegetable commodity.

Growers in South Africa are faced with the challenge of producing high yield combined with good quality in order to satisfy the local demand. Before the increase in undercover farming, the demand for these produce were not met, mainly due to inadequate plant nutrition, adverse climatic conditions, or pests and disease infestation because of open land production.

The population increased tremendously in South Africa and improvement of the standard of living has resulted in an increased demand for fresh produce of high value and quality. An increasing number of vegetable growers in and around South Africa have become interested in greenhouse cultivation of fresh produce of many kinds.

Plant growth manipulation of indeterminate vegetable crops in hydroponics production systems Tomatoes, cucumbers and sweet peppers are important crops in South Africa and their commercial importance is continuously increasing in South Africaâ&#x20AC;&#x2DC;s retail markets. For new entrants to this important market, it is imperative to obtain training on hydroponics systems, plant feed and irrigation. Also, training on how spacing, fruit and stem pruning influence fruit size and yield should be obtained.

Yield and quality variation might occur due to variation in cultural practices, e.g. plant spacing, stem and fruit pruning. Optimal plant spacing may help in proper utilization of space and for obtaining good quality fruits. Optimum marketable yields per unit area may result from canopy structures created by particular combinations of plant

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greenhouses I shade net I hydroponics I aquaponics

densities and trellising systems. Stem pruning might also influence the yield production.

excellent results and sustainability. The low input production systems refer to those technologies that are aimed at optimizing the on-farm input resources, Fertigation of lettuce e.g. crop residues and reduction of farm Crisp head lettuce is becoming an resources such as chemical fertilizers increasingly important item in salads in to reduce input costs. These low input South Africa. Its popularity has led to an production systems are investigated, increase in production and consumption documented and evaluated in order to in urban areas. develop improved methods.

New cultivars are introduced each year At ARC-Roodeplaat (ARC-Vegetable & by seed companies which might not Ornamental Plants Campus), a training be suitable for year-round open land unit exists where new entrants to fresh production. This necessitates cultivar produce farming may obtain training and evaluation trials of other information in theory and growing systems such as practice of greenhouse At ARC-Roodeplaat the gravel-film technique production. This could (ARC-Vegetable & or aquaponics. put them in a position Ornamental Plants to market their produce Low Input Production Campus), a training to informal traders or Systems unit exists where by themselves off their Vegetables are important farms. new entrants to fresh for food security and ARC-VOP produce farming poverty alleviation. may obtain training Nevertheless, in South Africa food insecurity and information in still exist, particularly theory and practice of with resource greenhouse production. poor farmers and communities. This can be ascribed to higher costs involved in vegetable production as well as high food retail prices. The introduction of modern technology to address the needs of rural farmers are often not accepted because of several reasons, including management skills, high input costs, etc.

However, several low input production systems are implemented by resource poor farmers with Electronic subscription for 6 bi-monthly issues is R 350.00 (ZAR) annually

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