Undercover
farming
ucf
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July/August 2019 Volume 16 No 4
I I R40.00
CROP PRODUCTION
greenhouses
FOOD SECURITY
produce
New Cucumber Varieties Page 4
Reducing Risks Page 6
Silicon the Solution? Page 10
Fertilization of Tomatoes Page 14
greenhouses I shade net I hydroponics I aquaponics
MAIN ARTICLE
PROPRIETOR I ADVERTISING SUZANNE OOSTHUIZEN 012-543 0880 I 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 ADDRESS PO Box 759, Montana Park 0159 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. COPYRIGHT Copyright is reserved and the content may only be reproduced with the consent of the Editor. Subscription Online subs: Email to suzanne@axxess.co.za If you subscribe on-line, e-mail your deposit and address details to: magazine@axxess.co.za. More information from Suzannne Oosthuizen: 012-543 0880. Subscription form available on inside back page. visit us at I besoek ons by
Scripture for Guidance
Isaiah 44:23 Sing Oh Heavens, for the Lord has done this wondrous thing. Shout, Oh Earth; break forth into song, Oh mountains and forests, yes, and every tree; for the Lord redeemed Jacob and is glorified in Israel!
Contents 4
Nuvance’s new cucumber varieties successfully time-slotted
6
Cultural practices to help reduce the risk of outbreaks in floriculture crops
8 Greenhouse Design & Layout: The economics of scale 10 Is silicon (Si) the wonder fungicide? 12 The yield and quality response of tomatoes to
FRONT PAGE: Nuvance’s new cucumber varieties successfully time-slotted. See pages 4 & 5.
INSIDE ...
N-source and its growth medium
14 Fertilization of tomatoes grown in greenhouses 16 Training and pruning greenhouse tomatoes for
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higher production
18 Why Aquaponics is (part of) the solution 19 New technologies: Transparent solar panels on the greenhouse roof
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19 Subscription form
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ike the rest of agricultural activities, undercover farming also experiences its hurdles. Our climate changes on Earth, the exchange rates and ever-changing consumer demand must be constantly adjusted to, and managed in order to stay in business. Whilst the larger entities with a back-up of investments or more readily access to capital, the smaller producers must constantly live close to the market to early detect changes and adjust accordingly. In a sense, groups of smaller producers can adjust, for instance, to alternative crops quicker than larger companies. Although we all stare wide-eyed at new technologies introduced almost daily to the greenhouse or shade-net producer market, the local financial scene unfortunately does not allow everybody to jump on the bandwagon to upgrade. The average producer must hold his own with what he has available and steer his business with a keen eye. The forthcoming Undercover Farming Western Cape Conference offers a good bevvy of speakers, and delegates to this event can look forward to another two days of excellent information and themes on undercover farming. The event will also host companies in the industry who will have representatives to answer questions on every production aspect. We believe every visitor and company representative will experience a most profitable time at this year’s Conference. In this edition we offer readers editorial content of interest at all levels. While we were compiling this edition, it once more came to mind that, although most producers come a long way with undercover farming, we still must constantly remind ourselves of the grassroots of hydroponics or in-soil production in greenhouses or under shade-nets. There are always certain basic elements that one should never over-look, and neither should your assistants who work in the greenhouses. We are glad for the Western Cape that their major dams are filled during winter and we are looking forward to early summer rains on the Highveld and general summer rainfall areas. Happy greenhouse farming.
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Nuvance’s new cucumber varieties successfully time-slotted The research and development team from Nuvance, along with the technical support from Seminis, identified two cucumber varieties, Hoplita* and SV5047CE*, which performed exceptionally well throughout variety selection trials.
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ith the clear potential shown by these two varieties, and to take it to the next level, they were then placed in semi-commercial trials with farmers in the main cucumber growing areas across the country including KwaZulu-Natal. The aim of these trials was to do “timeslotting”, in other words to determinate the right time of year to plant each variety. Both Hoplita* and SV5047CE* were planted in March and from these results it was clear that SV5047CE* was
more suitable for winter production in KwaZulu-Natal. Hoplita* was also well adapted for the winter production period but certainly better suited for the spring, summer, and autumn production cycle.
SV5047CE* SV5047CE* planted during March did not perform as well as the Hoplita* during the same period. Although the plant characteristics were very similar to that of Hoplita* and the powdery
mildew resistance was also excellent, the fruit did not reach the same size and the fruit necks were slightly longer. It became clear that the SV5047CE* was not planted in the correct slot. During winter, from June until September, SV5047CE* performed much better with only slightly shorter fruit and longer necks. The low winter temperatures will affect the growing capabilities of any cultivar and the SV5047CE* was also affected during July when temperatures were at their lowest. As soon as the day lengths increased and the temperatures 5
Left and below: The new Hoplita* cucumber variety in a greenhouse and freshly picked of the same in picking boxes.
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resistance to increased, the SV5047CE* variety disease and improved immensely going into August On the way to especially and September. the packhouse SV5047CE* powdery Hoplita* cucumbers by mildew. From March until May, Hoplita* Nuvance. Fruit yields performed very well. This variety showed were above excellent tolerance to powdery mildew average and yielded excellent quality fruit from but not top to bottom. The plants were also exceptional strong and healthy with good vigour. on both The fruit had outstanding longevity and varieties. overall this variety was certainly keeping Throughout up with various competitor varieties. the spring/ During a planting in late May however, summer this variety started to slow down. This months was a clear indication that Hoplita* Hoplita* (in KwaZulu-Natal), was essentially a started to summer variety. Since growers were outperform amazed by how well Hoplita* had SV5047CE* performed throughout late summer again. The the hot days and cold nights experienced into autumn, the trials were extended sowings were staggered from November during this period. The crops had to also throughout winter on both varieties. right through summer until March endure extended periods of overcast the following year. The observations During the spring plantings from weather and fluctuations in temperature. during regular trial September, both Such conditions had a negative effect on visits were that the varieties continued During the spring all the varieties. The Nuvance research Hoplita* continued to to perform well as plantings from September, team are however pleased to confirm that perform well but on the temperatures both varieties continued Hoplita* performed exceptionally well occasion produced and heat units were to perform well as the during the spring, summer and autumn fruits that were more constant. plantings, while SV5047CE* is best suited slightly longer. This temperatures and heat Both varieties still for the winter production period. could be as a result of units were more constant. displayed good
success is in the detail seeds | science | service SV5047CE* • • • • • • •
Plants have a very open structure Suitable for winter production Vigorous plants with short internodes Excellent fruit set Cylindrical and straight fruit High tolerance to Cca, Ccu Intermediate tolerance to CVYV, CYSDV, CMV, Px
Hoplita* • •
• • •
Vigorous plant Ideal for the summer months, but does also perform well during winter in the Lowveld Medium large fruit High tolerance of CVYV and Ccu Intermediate tolerance of CYSDV, Px, Cca
| www.nuvance.co.za |
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Cultural practices to help reduce the
risk of outbreaks in floriculture crops
The winter season is soon something of the past. By now, the greenhouse producer should already have made basic preparations for his new plants to enter the production area. Let us just run a checklist of sorts to make sure everything is ready or being made ready at this point and time.
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e often hear that good cultural practices are the foundation of every successful pest management program, but what does it entails? Here we consider several different ways to help us start with cleaner greenhouse crops and reduce the risk of new infestations throughout the season. Death, taxes… and weeds Few things are more dependable than weeds. We can predict with almost certainty that they’ll show up in our fields and our greenhouses sooner or later. It’s certainly not the most glamorous job and generally not one that most people look forward to doing, but consistent weed removal is an easy way to prevent them from becoming future sources of pests and diseases. Consider building in some time to walk down every path in the greenhouse once every two to three weeks. Carry trash bags and make sure all the weeds are thrown into the dumpster outside the greenhouse. Leaving a pile of weeds in an uncovered garbage can inside the greenhouse gives thrips and other pests an opportunity to escape back into the crop.
Without cleaning and sanitizing the greenhouse production area before new plantings, such an excellent-looking plant standing could go up in smoke!
Weed barriers Speaking of weeds, are any of your weed barriers getting old? Did you have a disease problem last year? Growers can easily recognize when a weed mat
Choosing from the plethora of commercially available greenhouse sanitizers can feel like a daunting task. Discuss your history of greenhouse diseases with your current supplier. is past its prime, but it’s much harder to tell if they’re harbouring infectious diseases. Many pathogens have life stages that help them persist in harsh environments, so replacing the weed barriers in areas that experienced heavy disease pressure or were infested with a particularly challenging pathogen (e.g., tobacco mosaic virus) is a relatively inexpensive way to reduce the risk of another disease outbreak.
Cleaning and sanitizing After removing weeds and replacing old or otherwise undesirable mats, it’s a good idea to deep clean and sanitize the greenhouse. Is there a difference?
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Discuss your history of greenhouse You bet! Cleaning is when you remove diseases with your current supplier. the “big” stuff—dirt, algae, dust, plant residues, etc. When you follow up Soil treatment with a sanitizer, you’re going after the Many thrips species pupate in the soil. “small” stuff: pathogenic microbes. The When plants are small, thrips pupae are primary benefit from all this is that we most likely to be found in the growing significantly reduce the risk of seasonmedia. As plants start to grow wider to-season transference of insect pests than their containers, more pupae will and diseases. find their way to the ground. It’s easy When we remove all the big stuff, what to imagine that pupae from hanging we’re really doing is removing food, baskets, weeds and refuge and breeding containers at the Cutting suppliers and sites for insects and edge of the mat rooting stations spend a pathogens. It’s all could eventually about reducing the lot of time and money on find their way risk of re-infestation. their insect and disease around the weed All that big stuff management programs. barrier and into the can carry left-over Despite their best efforts, dirt. At this point diseases, algae and the earth inside it’s almost impossible decaying organic the greenhouse to catch every single matter attract fungus becomes a source gnats and white fly, microscopic invader. of thrips. and both of those For greenhouses or multi-spans with pests can transport certain diseases consistently high thrips pressure, a soil throughout the greenhouse. treatment may be an option to consider. A couple of extra thoughts on Treatment recommendations for cleansers and sanitizers: these situations in previous years have included the use of products containing Consider using a combination of tools chlorpyrifos or imidacloprid at grub to deep clean your growing spaces. rates. Probably Shop vacuums and brooms can help you the most clean up the sidewalks and brush off acceptable walls, pipes, heaters and other structural and biological objects. Power washing with cleansers way now is or soaps comes highly recommended, to have your but don’t forget to rinse off the surfaces production soil when you’re done. Many of those steam cleaned. products are caustic and can eat away at internal structures. Quarantine Choosing from the plethora of area commercially available greenhouse Cutting sanitizers can feel like a daunting task. suppliers and
rooting stations spend a lot of time and money on their insect and disease management programs. Despite their best efforts, it’s almost impossible to catch every single microscopic invader. When plugs and liners roll off the delivery truck and into our receiving bay, where do we put them? If we’re not careful, those carts could end up sitting near production areas where any hitch-hiking pest has access to our clean crops. Some growers have found it helpful to set aside an area where new plant material can be isolated and observed for a short period of time. The simple act of placing some yellow sticky traps in the rack and checking them in the morning can help you reduce the risk of introducing pests into the production area. Prevention and sanitation are the key philosophical concepts that help reduce the risk of insect and disease outbreaks in the greenhouse. By starting with the final crop in mind and staying as clean as possible, we may be saving ourselves quite a few headaches at shipping time.
By: Jeremy Jubenville
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Greenhouse Design & Layout:
The economics of scale
There is a recent boost in the number of people who are keen to enter the greenhouse business. Undercover growing of vegetables is hot, and lots of options are available about the set-up and the design of the operation. Thus, a lot of choices must be made. The Economics of scale and the functional design very important choice to make is the scale of the operation and the functional design. Take into consideration that the offered single span tunnels of approximately 300 m2 are not a real option for various reasons, because of: • The post height of those green houses is too low to facilitate required climate conditions for high growing vegetable crops such as tomato, sweet pepper and English cucumber. The temperature in the arch of those greenhouses will simply be too high, and we observed many crops burned by that. • Economics of scale requires at least a starting business of 5.000-10.000 m2 of greenhouse area. Logistic-wise and from a management point of view it is a nightmare to have 15 to 30 different single spans next to each other at the start of your business. Monitoring of diseases as well as supervising the labourers is not possible in this setup. • So the advised greenhouse is a multi-span greenhouse with a post height of at least 5 metres, a span width of 8 or 9,60 meters is fine; the choice for either Natural top and Side ventilation or just Side ventilation only is dependent of the area (climate zone) you start your operation, as well as the choice of crops you intend to grow. • Even Forced Ventilation with so-called Pad & Fan systems is still an
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Before jumping into greenhouse farming, it is essential to prepare a business plan, find the right company to establish you and who are prepared to see you through the learning stages of this business.
option, however due to the height of as attractable shading screens and the greenhouse, a Natural ventilated humidification (fogging) systems. house will generate a nice “chimney This equipment has a huge cooling effect” which provides very good down effect to your greenhouse; up air circulation to 40°C decrease of Once you grasp the and cooling temperature and an down; as long increase of your RH economical scale, you as the outside with approximately should approach at least temperatures are 20%. 2 or 3 greenhouse suppliers not higher than • Because of to ask for quotations between 35 and the mentioned for a structure, technical 400°C. economics of scale, a • Nowadays we equipment and set-up. “square” greenhouse have modern of 120 x 100 metre technology to is a good and cost-effective choice. control the greenhouse climate, such Just by “blocking” four of those Compartments in a square set-up you generate a nice square 4,8 ha. operation. Compartments (and plantings) of smaller than 10.000 m2 are considered as not efficient and thus not viable.
Quotation Phase and Preparing a Business plan Before starting, one needs to prepare a business plan, to see in what way you
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can make your plans financially viable. • Once you grasp the economical scale, you should approach at least 2 or 3 greenhouse suppliers to ask for quotations for a structure, technical equipment and set-up. • Make your yield estimations together with a crop Consultant of Delphy to generate the annual forecasted yield for the commodities you are opting for. of steps to be • The market Maintenance such as taken. We will not demand will elaborate on that guide you in replacement of plastic cover here. the direction of needs to be taken into which crop is in • The Tender consideration as well. demand both for procedure is starting the short term after approval of the as well as for the long-term. financial agreement. Comparing of the different offers, what is the best • The agreement with an off-take value for money? Delphy can also party is crucial to proof that the support in this step. turnover figures used in the business plan are realistic. This party will be Construction Support and leading the final choice for the type Capacity Building and even the variety chosen. • As soon as the real construction • The business plan needs to be as phase starts, a very close supervision accurate as possible. Next to the is required to observe that total investment, the estimate everything is executed according to running costs such as labour costs, the specifications. fertilizer and water, energy and • Simultaneously the recruiting plant costs must be calculated in a and Capacity sustainable way. Building • Take into consideration your learning of Skills curve of 3 to 5 years, in which Development your costs will be higher, and your of the yield estimates lower, call it ‘paying dedicated school fees’. management and workers • Maintenance such as replacement of must start. plastic cover needs to be taken into consideration as well. • It is efficient to plan those • Delphy is experienced in reviews of two events business plans. together, Funding and Tender procedure since the • Now we are ready to present our Delphy business plan to a financier. This Consultant is a challenging process, with lots
can do both during the same visits. Actual Growing process • Now you are finally ready to start the real growing process. • To avoid too high school fees / beginner mistakes, or generate a steep learning curve, it is wise to contract the Delphy crop consultant for coaching and mentoring during the crop phase. • We are experienced in vegetable crops of tomato, sweet pepper and cucumber, as well as lettuces and herbs. For optional commodities we will introduce you to foreign experts. We wish you a fruitful future in Horticulture!
Herbert Stolker, Director; Delphy
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Is silicon (Si) the wonder fungicide? Si (Silicon) is readily available in the soil, being the second most abundant element, after oxygen, present in the earth’s crust as silicon dioxide (sand) and various silicates or sheet silicates. Silicon is extracted from sheet silicates as silicic acid. Silicate minerals weather to clay, which forms the soils in which plants grow.
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oil water generally contains 50 to 400 ppm silicic acid, which is readily absorbed by plants. Hydroponic nutrient solutions should contain potassium silicate or treated with10 parts per million of silicic acid (H²SiO³), although hydroponically grown cucumbers are often grown in nutrient solutions without added Si. Studies of plant tissue have found a range of silicon content from a fraction of 1% dry matter to as high as 10%. In plants, the silicon seems to play a role in growth, mineral nutrition, mechanical strength, resistance to fungal diseases, and reaction to adverse chemical conditions. Further studies regarding silicate applied as a fungicide at the Pacific Agri-food Without cleaning and sanitizing the greenhouse production area before new plantings, such Research Centre (PARC) in British an excellent-looking plant standing could go up in smoke! Columbia first explored powdery mildew (PM) control and increased yield by adding silicate to growing media, with good control of powdery mildew on cells. Cucumber plants treated with and deposited either as hydrated silicon grapes, melons, zucchini, and cucumber. Si accumulate phenolic materials much dioxide, silica gel or poly-silicic acid. Continuing studies reveal that the form more quickly than infected cells of nonOnce the silicon is incorporated into of silicon in solution and the solution pH amended plants. tissue, it doesn’t move, so a regular greatly affect the efficacy. supply is necessary. Cucumbers are These phenolics were also conclusively shown to take up Fungal disease shown to be fungitoxic as fungal hyphae Silicon is transported from Si passively. resistance in penetrating the phenolic-laden cells of the roots to shoot through greenhouse Si amended plants were found to be Soluble Si taken the transpiration stream and cucumbers was seriously damaged by the accumulated up by plants tends deposited either as hydrated shown to increase phenolics. It therefore appears likely to accumulate substantially that Si fertilization reduces disease in the apoplast, silicon dioxide, silica gel or in response to susceptibility primarily by stimulating particularly in poly-silicic acid. Si fertilization. hostplant defences, although it is possible epidermal cell Different rates of Si fertilization that already silicified epidermal cells may walls, thus investigators hypothesized (potassium silicate) on powdery play a role in disease inhibition. that Si inhibits fungal disease by mildew was tested on cucumber leaves physically inhibiting The question (inoculated PM conidia), results showed fungal germ tube comes to mind, Besides being an effective that leaf area covered by powdery penetration of the why has Si not fungicide, Si may well mildew reduced by as much as 98%, epidermis. been added to reduce the need for synthetic with concentrations of 100 ppm or more hydroponic nutrient Subsequently fungicides as well as being of SiO² giving best results. solutions as is often investigators have beneficial to our health. It was found that nutrient concentrations done in Europe? found that only of 100 to 200 ppm SiO² significantly Do farmers buy Si the trichome bases reduced root mortality, root decay and based sprays and treat crops themselves on the cucumber epidermis tend to yield losses on plants inoculated with or are fertilizer companies going to take become silicified. Pythium ultimum as well as treated the plunge? Si is observed to accumulate around plants being more productive than those Besides being an effective fungicide, fungal hyphae and infection pegs not treated with Si. Si may well reduce the need for synthetic in infected host plant cells and Mode of action fungicides as well as being beneficial to investigators have shown that phenolic our health. materials and chitinases also rapidly Silicon is transported from the roots to accumulate in these infected host shoot through the transpiration stream By: M. Haupt
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The yield and quality response of tomatoes to N-source and its growth medium
Generally, pine sawdust-shavings (Pinus spp.) has always been a very popular soilless substrate employed in South African greenhouses. Some growers still use fresh pine sawdust-shavings (which is biologically highly unstable) as a substrate.
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herefore, the greenhouse industry looked at alternative organic substrates such as coco peat, which already went through a decomposition process and is more stable. A biological inactive substrate such as sand was included to compare micro-organism activity with organic substrates. The main objective of a study at the University of Stellenbosch, was to compare the growth, yield and quality of hydroponically grown tomatoes in response to different growth mediums in combination with nitrogen source, irrigation frequency, period of substrate uses and liming. In general, the drainage water pH declined with an increase in NH4+-N in the nutrient solution. Low pH values in the drainage water, especially when coco peat was used, had a detrimental effect on marketable yield. The drainage water pH of pine sawdustshavings increased during the growing season when 100 % NO3--N was used. Due to the higher cation exchange capacity of coco peat, the drainage water electrical conductivity tends to increase more rapidly than with pine sawdust-shavings, during conditions with high temperatures and when insufficient irrigation volumes per irrigation cycle is applied. As expected, the drainage water NO3--N content decreased as the NH4+-N content increased in the nutrient solution. Pine sawdust-shavings recorded a much lower NO3--N and NH4+-N content than sand and coco peat and thus supports the The main objective of a hypothesis that study at the University of microbiological Stellenbosch, was to compare activity is higher the growth, yield and quality in pine sawdustof hydroponically grown shavings, especially in the second tomatoes in response to season of substrate different growth mediums in use. combination with nitrogen Also, coco peat source, irrigation frequency, produced the period of substrate uses and highest number of liming. marketable fruit
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Tomatoes grown in a saw dust medium.
and yield per plant, followed by pine sawdust-shavings and sand in the first season of substrate use. The number of marketable fruit and yield decreased with an increase in NH4+-N content in the nutrient solution during production in warmer, summer conditions.
Contrary to these findings, production in cooler, winter conditions recorded high yields when only NO3--N or 80% NO3--N: 20% NH4+-N was applied. The unmarketable yield increased with an increase in NH4+-N in the nutrient solution. Visual evaluations showed that blossom-end rot (BER) was the main contributor to unmarketable yield. Increasing levels of NO3--N as nitrogen source in the nutrient solution, reduced weight loss and increased the loss of fruit firmness of tomatoes during
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storage. Increasing levels of NO3--N NH4+-N was used. In the second also increased fruit pH and reduced season of substrate use, stem diameter total titratable acidity. decreased significantly when 20 - 40% NH4+-N was used in sand and coco Coco peat produced fruit with a higher peat, but plants grown in pine sawdustpH than pine sawdust-shavings. An shavings only indicated a decrease in increase in irrigation frequency affected stem diameter when 40% NH4+-N fruit firmness negatively when coco was used. A similar trend was observed peat was used as substrate. Different between the first and second season of irrigation and fertigation practices are substrate use. needed for different growth mediums and management needs to be adapted Fruit quality according to the growing season Increasing levels of NO3--N as nitrogen (winter vs. summer). source in the nutrient solution, reduced Electrical conductivity weight loss and increased the loss The drainage water electrical of fruit firmness of tomatoes during conductivity (EC) increased during storage. Increasing levels of NO3--N production in warmer, summer also increased fruit pH and reduced growing conditions due to the buildtotal titratable acidity as a result of the up of fertilizer salts as a result of high negative correlation that exists between temperatures and insufficient water these parameters. However, 100% volumes applied per irrigation cycle. NO3--N was responsible for the highest However, the increase in EC was increase in fruit pH during storage. significantly higher in coco peat than Coco peat produced fruit with a higher pine sawdust-shavings or sand. During pH than pine sawdust-shavings. Fruit cooler, winter conditions the EC was firmness was the lowest in sand before generally lower and more acceptable storage, and after storage when 3 for production in irrigations were all the substrates, The complexity of the applied per day but but coco peat and effect of cultural practices increased with 6 sand still recorded a and 12 irrigations and climatic conditions higher EC than pine per day. on the productivity of a sawdust-shavings. Furthermore, coco crop complicates the daily Growth and fruit peat produced the management of a growth yield highest number of medium. marketable fruit and Stem diameter yield per plant, but it is of the utmost of tomato plants decreased in pine importance to treat the substrate with sawdust-shavings and coco peat when lime prior to planting to prevent the the NH4+-N content of the nutrient development of BER and a low drainage solution was increased from 0% to water pH during the growing season. 40% in the first season of substrate Coco peat needs to be irrigated at use. However, no difference was least 12 x per day to ensure high yields. recorded when only NO3--N and 20%
Irrigation scheduling is very important when coco peat is used. Since growth media is mixed with perlite it increased the moist retention of the substrate (coco peat, bark, etc.) and is now used widely by greenhouse operators in their media. The results emphasized that the level of management of the growing regime is influenced by a combination of factors, including the type of substrate that is used, irrigation and fertigation practices and the growing season (winter vs. summer). The complexity of the effect of cultural practices and climatic conditions on the productivity of a crop complicates the daily management of a growth medium. New media on the market which has been thoroughly researched and trialed on various plants are in use throughout the world and offer excellent results.
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Fertilization of tomatoes grown in greenhouses Whether producing a field crop or tomatoes, there are perhaps as many recipes for ideal tomato production in hydroponics systems. There are many different media being utilized as growing medium and each medium requires its own programme for optimal crop production.
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here is no ideal generalized programme that could be used as a ubiquitous nutrient solution for production of tomatoes in many different areas and under many different conditions. There are many factors that can affect the composition of the nutrient solution for optimal production of tomatoes in hydroponics. Firstly, the environment, primarily temperatures and humidity, water quality, nutrient composition of the water, growing medium, season and type of tomato being produced. The designing of any nutrient solution should begin with the quality of water to be used. A complete water analysis should be conducted on a regular basis to ascertain what nutrients can be found in the water. If managed correctly, a large proportion of these nutrients can be incorporated into the nutrient solution, thereby reducing the required amount of fertilizers to achieve the specified nutrient solution. Temperature, humidity and season, all affect the movement of water through the plants and consequently the uptake of nutrients by the plant. Although not all nutrients are taken up through the transpirational stream, some essential nutrients are. Growing media react differently to the nutrient solution, whether shavings or coir, rockwool or sand. There are many different types of media available to the farmer. Even the bags or troughs used will affect the final nutrient composition for your crop. Then there is the tomato crop itself. Not just whether producing a saladette, salad, cherry or pink tomatoes, but also the phase of growth of the tomato crop. Understanding the requirements and growth phases of the crop are just as essential in a hydroponics crop as to a field crop. Often however, there are limitations within a system preventing the use of two different nutrient solutions on different phases at the same time. Available standard “complete” mix products are designed to be an easy to use mix of nutrients. A standard recipe is usually provided requiring a specific mix of up to 3 products to achieve a certain nutrient regime in the solution.
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Understanding the requirements and growth phases of the crop are just as essential in a hydroponics crop as to a field crop.
be the nutrient norms of one of the These mixes are used often more for complete mixes mentioned above, convenience than for achieving an ideal mixed as individual products to create solution for a crop. your solution, considering the nutrient The cost of these solutions is often composition of your water. Taking leaf generally higher than the “straight mixes” analyses regularly during your crop which are composed of up to 7 different will help to determine the nutrient products in varying amounts to achieve a composition of your crop at that specific nutrient regime. point in time. Associated with all the “ideal” nutrient The nutrient solution can be adjusted solutions and norms that are available to based on the leaf analysis results, and the tunnel tomato farmer, one can find perhaps even on the just as many if not visual perception of The designing of any more nutrient ratios the crop. It is not to design an ideal nutrient solution should recommended to nutrient solution. N:K begin with the quality of take leaf analyses ratios varying from water to be used. more frequently than 1.8 to 2.2 depending every month as it on growth phase, can take as much time for the plant to Ca:Mg ratios of 3.5 – 4, Ca:K of between correct itself from the previous change. 1 – 2. These variations represent This is a slow process, but over time, differences of up to 50% of the nutrient it is possible to have an “ideal” solution content in the solution. for your location that is unique to your Despite this, these ratios can be very environment and conditions. helpful in providing the necessary There is much discussion in the industry suspected requirements of the crop as to the EC (Electrical Conductivity) within the area of production. Not all that is optimum for tomato production. the ratios are right, and not all of these The EC is a measurement of all the salts are wrong either. Each norm is perhaps and nutrients that may be found in the developed under certain conditions and nutrient solution. It is unable to tell the performed best under those conditions. user what is in the solution, just how Then how does one achieve the ultimate much of everything is present. nutrient solution? It is achievable but There has been a lot of work done does take a lot of time and effort to around the world looking at different establish. A good starting point would
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There has been a recent trend in various EC’s and the effects on yield, quality and growth of tomato plants. There are many parts of the country where high EC’s are used in the initial phases of growth, different theories available to the farmer lowering to “normal” levels as above, as to starting EC, changing through to for example, starting at an EC of 3 mS/ harvest and the end of the crop. cm and ending at 2.2 mS/cm. The idea The EC’s chosen should be related to behind this is to stress the young plant the variety being grown. Some varieties into flowering sooner. Inherent problems are more vigorous and prefer lower with this include the lasting impact of EC’s, whilst other varieties can tolerate that stress on the young plant. higher EC’s. Knowing the requirements If not carefully of the variety will Temperature, humidity managed, such high help also with the and season, all affect initial EC’s can cause ratios. serious damage to the the movement of water Starting at a low EC young plant. Also, the through the plants and and gradually building up over the growth consequently the uptake of effect of the high EC may not cause earlier of the crop, according nutrients by the plant. flowering since often, to growth phase, for the flowers are formed in the nursery example starting at EC of 1.5 mS/cm before the plants reach the farm. If such and ending at an EC of 2 to 2.2 mS/cm a practice is found to bring about earlier has many benefits to tomato production. flowering, does the increased cost of Applying lower concentrations of production by a minimum of 50% result nutrients at an earlier stage will supply in increased savings of at least 50%. A the plant with more of what it requires simple question – if it does not provide at the young stage without imposing the returns, why increase your costs? stress on the plant. This is a more controlled approach where only limited A study was conducted by the University amounts of fertilizer reach the plant of Stellenbosch to establish whether preventing it from becoming to vigorous, it was feasible to use higher EC’s in an undesirable attribute in tunnel tomato production, particularly in production. achieving higher flavoured tomatoes.
A 30% reduction in yield was found by increasing the EC from 2.2 to 3.9 mS/ cm. This loss in yield was not attributed to reduced numbers of fruit, but more to reduced fruit size. An interesting point to note was that taste was not improved at higher EC’s, however they did find the total soluble salts was increased (TSS, % Brix). Cultivar choice could be a more effective choice at improved flavour than increased EC. Where chain stores are demanding improved flavour tomatoes, these studies did show that it can be achieved by higher EC’s or by cultivar choice. The problems facing the farmer would then include reduced yields combined with increased costs in production and the same returns in production. Just as with field production, hydroponics tomato production with regards to fertilization is becoming more important with increased care and attention being required to achieve the results being demanded. Critical management of costs of production are also just as important for a grower to remain competitive in such a tough market.
From studies made by Prof Nic Combrink.
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Training and pruning greenhouse tomatoes
for higher production
Some growers still ask, “Why train and prune greenhouse tomatoes?”
T
he main reason for this procedure, i.e. removing excess shoots, leaves, flowers, and fruits maximizes ease of harvest and fruit quality. Obviously this system is only for indeterminate, non-“bush” type tomato varieties.
Training Stretch a strong wire cable over each row of tomatoes at a height of about 2.5 meters. Hang enough string (polypropylene or hemp, 6 ply) above each plant to reach the base of the stem and tie or lip the string to the main stem (Fig. 1). Figure 4. Mature green stage As the tomato plant grows, wrap or clip the string around the plant. Lean and drop each tomato plant in one direction when it reaches the cable by releasing some string from the wire (Fig. 2). Pruning Side shoots: Prune tomato plants to a single stem by off any side shoots (Fig. 3). Do not use a knife. Do this at least once per week; remove side shoots when they are very small. Do not remove side shoots above the newest flower cluster. Leaves: Remove the two to three leaves under fruit clusters that begin to yellow, and wilt and the fruit matures. Make sure the fruit is at the mature green stage (Fig. 4) before removing leaves. Flowers and Fruits (optional): Prune flower clusters and fruits to help achieve larger tomatoes. Prune remaining flowers in clusters once there are three to four well-formed fruit on that cluster. Remove any abnormal flowers and deformed fruits to reduce competition between growing fruit. Growing points (optional): For fall crops, remove the growing point of the main stem about 45 days before harvesting the last fruits. Leave two to three leaves above the top cluster
Figure 1. Securing string to tomato stem
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Training up tomatoes and managing each plant for top performance is a continuous process.
to shade and feed the top fruits. For summer crops, do not remove the growing point of the main stem. Instead stop pollination or remove flower clusters about 45 days before harvesting the last fruits. By: Gary Pearson
Figure 2. Tomato plant at left will be lowered to position on right by releasing some string from support wire
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Fig 3. Pinching-off side shoots
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Why Aquaponics is (part of) the solution In his latest newsletter, Leslie Ter Morshuizen of Aquaponics Africa explains the background of aquaponics and how the system evolved as we utilise it today. This is an interesting piece of research and most certainly emphasise the urgent subject of our use of water to provide healthy food for millions of people.
P
ost WW2, 1st world nations established lifestyles based on abundant food, cheap power, freely available fresh water, plenty of work opportunities, the convenience of private motor cars and the contraceptive pill; never had a generation had it this good! Unfortunately, as the world population soars towards 8 billion people, our planet earth is facing challenges that threaten to destabilise life as we know it – and not only for the 1st world.
are going to address any of the other challenges sustainably, as every one of the other problems has its roots firmly planted in the unsustainably high human population,” Leslie writes.
Many of the challenges that face Earth are noticeable in geo-climatic symptoms such as climate change, an increase in natural hazards such a fires and flooding, rising sea levels, low rainfall and increased atmospheric heat. These factors appear to be as a direct consequence of human activities associated primarily with forest clearing, “In researching this article, I came burning fossil fuels, across many articles Finally, Aquaponics accelerated methane listing challenges to turns biological wastes production and monoour global society crop farming. and planet, but to into human food, me the primary crisis reducing environmental In line with our is the current world booming population impacts associated population (7.7bn we also generate with pollution and people) and the many different forms simultaneously alarming rate at which of pollution and have producing crops. What recently become it continues to grow. There are simply too aware of the wideis there not to love many people for the ranging dangers that about Aquaponics? world to support! micro plastic pollution represents to fish, and to entire eco “Strangely, the sites I visited seldom systems. mentioned this directly as if it is a taboo to speak of slowing the birth rate: one site listed 42 global challenges in the 21st century – without mentioning the human population once! We must urgently reduce the rate of births if we
As the world population grew through the 1900s, we had an increasing impact on natural resources, such as fresh water, plant species, fish stocks and wild animals, causing more people to
turn to agriculture to feed themselves. However, the lower rainfall associated with climate change means that these agricultural activities are often no longer suitable to feed the farmers, increasing food insecurity, malnutrition and poverty. Many rural people move into cities to seek work in the hope of improving their situation, increasing the complexities of urban planning and the drain on state coffers. “The situation seems bleak and our future seems unattractive. However, there are things we can and must do immediately to arrest the situation and start winding back the clock of environmental harm. Firstly, the taboo must be set aside, and world influencers must instantly and urgently find ways of educating and incentivising people to have smaller families. Secondly, we need to profoundly reduce all forms of pollution. Thirdly, we need to adopt planet friendly methods of farming that satisfy a range of desirable objectives simultaneously,” Leslie advises. According to him Aquaponics has a massive potential role to play in these suggested solutions by producing a range of healthy, tasty crops including both fish and vegetables, using technology that can be run completely on renewable energy sources. Furthermore, Aquaponics requires little new water, reducing the water debt relative to traditional crop farming methods. Aquaponics can also be performed in rural areas, combating urban migration and the associated challenges. Finally, Aquaponics turns biological wastes into human food, reducing environmental impacts associated with pollution and simultaneously producing crops. What is there not to love about Aquaponics?
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New technologies: Transparent solar panels on the greenhouse roof
Light is important for greenhouse horticulture. The more light, the higher the production. For that reason alone, it is not profitable for entrepreneurs to place regular solar panels on the roof of their greenhouse in order to generate electricity.
B
ut what if those solar panels are partially transparent? Would the loss of light outweigh the production of electricity? To answer that question, the Greenhouse Horticulture Business Unit of Wageningen University & Research is examining existing semi-transparent solar panels. The range of semi-transparent solar panels is limited but growing. There are various systems. The Bright Solar company has solar panels whose cells allow a large part of the light to pass through, and therefore only use a limited part of the light to produce electricity. The panels from Soliculture consist partly of non-transparent solar cells and partly of “open” space where a spectral selective part of incoming solar radiation is directed to normal solar cells via fluorescence. Finally, UbiQD works on solar panels that are luminescent: the classic luminescent solar collector in which the non-transparent cells are only processed at the edges of the glass and only a part of the spectrum is very selectively intercepted via the fluorescent dye. Suitable for greenhouse roofs? The question is whether the panels are suitable for a greenhouse roof. The panels of Bright Solar are being placed on a test
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New Cucumber Varieties Page 4
Reducing Risks Page 12
silicon the solution? Page 14
Fertilization of tomatoes Page 8
greenhouse in Greece and the trials of SoliCulture in the US are in full swing. However, the reference and conditions are not comparable with those in Europe. In addition, all crops are different: fruit vegetable crops can use all light, pot plants also thrive well with less radiation and many ornamental crops need protection against excessive radiation. Experiment In May, WUR started a project in which measurements in the lab are used to determine how much light the various
panels intercept, and to calculate what this means for cultivation. The balance between the profit from electricity production and the (expected) negative effect on cultivation is drawn up for three different crops: tomatoes, potted plants and cut flowers. For this part of the test, (semi) transparent solar panels may still be registered. Depending on the test results, a practical test follows, in which the panels are mounted on a greenhouse roof.
Source: Wageningen University
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