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We have four 8 by 15m greenhouses in which we planted tomatoes. We had water challenges and our production was quite low, managing to get only Sh80,000 from the greenhouses at the end of three months.
We visited two other farmers with greenhouses and with plenty of water but their returns were also not so great. We had an agricultural officer from Kalro to assist us during the process.
Our question is, in a 8x15m greenhouse, what is the realistic profit to expect from tomatoes at the end of production when all factors are right?
I would say what you got from the four greenhouses, Sh20,000 from each is not bad for a start because tomato yield normally fluctuates. Mostly, it depends on the prevailing condition of the greenhouse linked to biotic (pest and diseases) and abiotic (climatic and nutritional) factors.
From your experience, you will realise that water unavailability alone is not the only challenge for better greenhouse tomato yield because it is intertwined with nutrition and condition of the soil as media for production.
For instance, contaminated water is common in areas where farmers plant crops like potatoes and tomatoes and water flowing downstream is collected for greenhouse farming.
This introduces bacterial wilt in greenhouse tomato. Lack of quality water sources in many parts of the country can contribute low yield of greenhouse tomato.
Similarly, available water could be saline, chlorinated or contaminated with diseases like bacterial wilt reducing tomato yield and quality
Technology in greenhouse tomato production
For nearly 100 years, tomatoes have been grown in greenhouses and there are many techniques applicable for farming them in the structures.
The media for greenhouse tomato production can be purely soil, soilless culture or mixes, substrate or hydroponics. Each of these methods has merits and demerits.
There is no single best way to grow greenhouse tomatoes. An individual grower must develop experience in tomato production to determine the best and most economic techniques in her greenhouse.
It is highly recommended that for the method used, be it soil or soilless media, the required conditions are strictly followed, especially on the micro-climatic condition of the tomato developed in greenhouse and this will consequently impact the yield.
Let us focus a few factors that are major in greenhouse tomato production.
Light, temperature and relative humidity control
Tomatoes are a warm season vegetable crop. They grow best under conditions of high light and warm temperatures. Low light through shading reduces tomato ability to photosynthesise hence poor yield.
This is similar to temperature and relative humidity, where many farmers fail to get good profits from greenhouse crops because they cannot manage the two important factors that determine plant growth and productivity.
Greenhouse temperatures below 13 degrees Celsius and above 30 degrees Celsius in the case of dry air or higher than 30 to 35 degrees Celsius in cases of high air humidity affect growth and productivity of tomato.
The optimal temperatures for production of greenhouse tomatoes, pepper and eggplant should be 15 to 30 degrees Celsius and not beyond 35 degrees Celsius.
The temperatures should be maintained at around 16 to 30 degrees Celsius during the day and 13 to 18 degrees Celsius during the night.
Some tomato farmers close the greenhouses the whole day without ventilation resulting in excessively high temperatures beyond 40 degrees Celsius that lead to reduced performance of the crops.
As reported earlier by Dr Nyalala and Mutua of Crops, Horticulture and Soils Department, Egerton University, small-scale greenhouses are prone to overheating when the sun is too hot.
Farmers should, therefore, open the doors and sides of the greenhouse from 8am to 5pm for ventilation and close them at night to reduce heat loss.
Greenhouses with only insect nets on the walls are unsuitable for areas with low temperatures like the highlands of Kericho, Mau Narok, Molo and Mt Kenya regions but may have positive effects in hot and warm areas such as Mombasa, Kitui, Kisumu, Machakos and Garissa.
Ideally, farmers should have a thermometre for measuring temperature inside the greenhouse for effective management.
This is good for enhanced production of greenhouse tomato.
Water, fertiliser and growing media
Tomato production requires that plant nutrition is monitored carefully and regularly. Tomatoes require a well-drained growing medium, regular watering and regular applications of fertiliser.
The application of water is typically done with a trickle irrigation system composed of distribution lines with drip tubes or spray stakes.
Drip tubes or spray stakes are placed at the base of each plant. Tomatoes use a great deal of water, especially in warm weather, so to control the irrigation system is highly recommended and relatively inexpensive for good yield of tomato.
On feeding regimes of greenhouse tomato, many types of fertiliser have been used.
Generally, the fertiliser is moderate in nitrogen and high in phosphorus, potassium, calcium and magnesium. A grower must be sure that calcium and magnesium are included in the fertiliser programme for better yield of tomato.
Normal plant and fruit growth requires these nutrients to be present in the correct amounts. The fertiliser typically comes in two parts, calcium nitrate and a complete fertiliser (without calcium).
This is because calcium nitrate is not compatible with other fertilisers in the concentrated form.
Many growing media can be used successfully for greenhouse tomatoes.
Good field soil in the greenhouse floor or packaged commercial growing media composed primarily of composted bark, peat or coir, perlite alone, peat-lite mixes, rock wool slabs and straw bales.
However, these are not locally available, therefore, greenhouse soil media should be amended with organic fertiliser regularly to retain soil health.
Farm yard manure should be used to keep soil organic matter status high.
Pruning and suckering
Tomato plants in a greenhouse are pruned to a single stem. All lateral branches or suckers must be removed when they are one to three inches long.
This allows for maximum air circulation and simplifies pest control problems. Suckering must be done regularly as plants should be checked at least once per week.
If this is not done, excess leaves in tomato will become sink (burden) to the growing plant since photosynthates are diverted from fruit formation, hence lower yield.
This cultural practice creates a balance between plant roots and shoot functions in tomato development.
Pest and disease control
Insects and diseases can be a big problem because so few pesticides are labelled for greenhouse vegetables, and their use should be the last solution to pest and disease management in tomato.
The best method in disease management is forecasting the disease incidence, especially late blight and early blight.
Their incidence is normally attached to the weather condition in the greenhouse, and destructive humid warm conditions.
This should be avoided by placing good ventilation system to control greenhouse microclimate.
Peter Caleb Otieno,
Crops, Horticulture and Soils, Egerton University.