Ploughing (or digging) is necessary to prepare the land for a new crop. It improves the structure and water holding capacity. In areas where water is a limiting factor, ploughing enhances water conservation as well. Fallow ploughing the land after harvesting the previous crop improves the soil structure and water-holding capacity. It also helps to reduce soil-borne pests and diseases by exposing the soil to the hot sun. Deep ploughing is necessary to break an impermeable hard sub-soil layer (ploughing pan), remove the weeds and bring the land to fine tilth. It also encourages root growth. It is often necessary to harrow two times, breaking the clods and removing crop residues to level the land.
Cultivating tomato on raised beds, ridges or furrows facilitates drain-age of water and irrigation. Despite this, more than 60% of the crop is still cultivated using flood irrigation.
Tomatoes are normally transplanted because much better results are gained when seedlings are raised in a nursery. Two methods of raising seedling in nurseries can be used:
- Sowing in seedbed
- Sowing in seedling tray
Smaller quantities of seed are needed, the seedlings can be selected for growth and health before planting in the field, the plantlets can be well protected and the planting distance is more regular than after sowing directly in the field.
The seedbed should be 60-120 cm wide and 20-25 cm high. The length depends on the number of seedlings wanted. Remove clods of earth and stubble. Add well decomposed farmyard manure and fine sand. Bring the seedbed to fine tilth. To raise a sufficient amount of plants for one hectare, 150-200 g seeds should be sown on 250 m2 of seedbed.
Draw lines, 10-15 cm apart, over the length of the seedbed. Sow the seeds thinly spaced on the lines and press gently. Cover the seeds with fine sand and straw. Water the seedbeds twice a day to ensure sufficient moisture for germination. After germination the straw must be removed.
Transplant the seedling to the field 3 to 6 weeks after sowing. A week before transplanting, seedlings should be hardened by reducing the application of water, but 12-14 hours before they are taken out of the seedbed they should be thoroughly watered again to avoid excessive damage to the roots. Seedlings of 15-25 cm tall with 3-5 true leaves are most suitable for transplanting. Transplanting should be done in the afternoon or on a cloudy day to reduce the transplanting shock.
Water the plants immediately once they have been transplanted. When removing the seedlings, keep a large clump of soil attached to the roots to prevent them from being damaged. Spacing between plants and rows depends on the cultivar growth habit, soil type, cropping system and also whether the plants are to be supported by stakes or left on the ground. The common spacing is 50 cm between plants and 75 – 100 cm between rows. If the tomatoes are to be supported by sticks, then the distances between rows can be decreased to 20-40 cm. Make the holes for the plants deep enough so that the lowest leaves are at ground level. Press the soil firmly around the root, and water around the base of the plant to settle the soil.
After transplanting, mulch can be placed on the ground around the plants to protect them from heat during the first five days. Mulch is composed of plant remains (e.g. rice-straw or sorghum-straw) used to cover the soil to control weed growth, prevent erosion and conserve water. Care should be taken not to wet the lowest leaves, as this can stimulate the growth of mould. A more advanced method is to put plastic mulch on the beds and punch holes in the plastic before planting. The transplanted plants should be protected from heat during the first five days, e.g. by covering them with large leaves.
- If there are still seedlings left on your seedbed don’t destroy them all, leave them so that you can replace those seedlings which have dried up in the main field. This process is known as Napping. It ensures that you maintain the correct plant population on your field.
Type of plant
Distance between rows and plants
|Bush type (determinate)||1.0 x 0.5 m|
|Semi-bush type (semi-determinate)||0.75 x 0.5 m|
|Tall type (indeterminate)||0.75 x 0.5 m|
Manures and fertilisers
To get high yields, tomatoes need to be fertilised. There are two groups of crop nutrients: organic manures and chemical fertilisers.
Farmyard manure, poultry manure and compost are three types of organic manures. They are described in this section.
The most common kinds of farmyard manures are horse, cow and pig manure. Of these three kinds, horse manure has the best balance of nutrients. Cow manure has relatively little phosphate. Pig manure is usually rich in mineral salts but has relatively little potassium. Manure from goat and sheep is also good organic manure.
It is better to use farmyard manure on sandy soils than on clay soil, because it is quite sticky. Sandy soils will not fall apart as easily if manure is added, and will therefore be able to hold more water.
If only farmyard manure is used, 12.5-25 tons/hectare/year (5-10 tons/acre/year) is a reasonable amount to apply. Smaller applications of manure can also be enough if growing conditions are not so good or if chemical fertiliser is also applied. Use it with 200kg DAP per hectare.
Poultry manure is usually three to four times as strong as farmyard manure. It is a very valuable kind of manure as plants can easily absorb the nutrients from it. A good way to apply poultry manure is by first mixing it with an equal amount of crumbly soil or sand. Sprinkle this mixture between rows, and then rake or hoe it lightly. Poultry manure, unlike farmyard manure can be used on clayey soils because it is not too sticky. It is also suitable for acid soils because it contains a lot of calcium (alkaline).
It is advisable to plough dry manure into the ground as fresh manure is too strong and can damage the sprouting plants.
Compost is easy to make from all kinds of organic materials. Examples of materials that can be used are crop residues, kitchen wastes, garden cuttings and manure. Compost is a rich source of macro- and micronutrients. It supplies nutrients at the right time in required quantities. It is especially useful for improving the soil structure and fertility.
It is important to have manure that is well decomposed, and which is not too sticky or too wet. It must not be too dry, as it is difficult to moisten manure again.
Tomato is not resistant to drought. Yields decrease considerably after short periods of water deficiency. It is important to water the plants regularly, especially during flowering and fruit formation. The amount of water that is needed depends on the type of soil and on the weather (amount of rain, humidity and temperature). It is especially important to water regularly (e.g. 3 times a week) on sandy soils. Under good circumstances once a week should be enough.
Weeds compete with the tomato plants for light, water and nutrients. Sometimes they provide shelter for organisms that cause tomato dis-eases, such as Tomato Yellow Leaf Curl Virus (TYLCV), and reduce the yield. Effective non-chemical weed management begins with deep ploughing, diverse crop rotations and competitive cover crops.
- Weeds are controlled through either pre-or post emergence herbicides. Be careful not use counterfeit products. Buy only from registered agrostore dealers.
- Hand weeding, Polythene mulch and Grass mulch.
- You should take care not to damage tomato roots and stems.
- Too much shaking should be avoided. This will cause immature fruit fall.
Tomatoes need to be stalked to get growth support. Stalking your tomatoes helps in producing clean fruits, controlling disease outbreaks, makes it easier to spray your plants, harvesting is simplified, it produces clean fruits, leaves productivity is increased and the leaves are exposed well to the sun for photosynthesis. This done by using 2m high sticks;
- The sticks are stuck firmly on the ground next to the tomato plants.
- A sisal string is then tied on the tomato and top of the stick.
After the tomatoes have grown, they should be pruned (removing shoots and suckers) from the main stem. You then leave the main tomato stem (two or three main shoots per plant)This is the process of removing unnecessary shoots and suckers from the main tomato stem, leaving only one to three main shoots per plant. This will give the best yield per plant and increase farm efficiency. Some reasons for pruning are;
- Too much vegetative growth hinders fruit development.
- It makes it hard to spray if the plant is bushy and also wastes chemicals.
- If the fruits and leaves that grow too near to the ground it will increase the chance of getting blight.
- The terminal bud is removed in tall varieties to limit their growth to 1.5- 1.8m high. Doing this controls upward growth and encourages development of large fruits.
Where tomato is planted in monoculture, crop rotation is important. Crop rotation means planting different crops on the field each season and only returning the same crop after at least three growing seasons. This interrupts the life cycle of pathogens and reduces the chance of damage by diseases or pests.
Do not rotate tomato with potato, tobacco or eggplant (aubergine) because these plants belong to the same family (Solanaceae) and have the same types of pests and diseases.
Some examples of crop rotation with tomato are:
- Tomato followed by maize and beans.
- Tomato followed by upland or irrigated rice. It is best to plant tomato two weeks before the second upland rice harvest.
Tomato can be grown in monoculture or in an intercropping system. Intercropping has advantages because this reduces the incidence of diseases and pests. Smallholders will gain the most from the advan-tages of mixed cropping.
Some examples of intercropping systems:
- Tomato intercropped with sugarcane . The dwarf cultivars of tomato are planted on a raised bed about 1.2 m wide, with sugarcane grown in the furrows between the beds.
- Tall type tomatoes are grown along stalks covering 0.6 m of the bed. Next to the bed, about 0.6 m higher, pepper and cauliflower are grown. The furrows are 0.3 m wide and serve as a path.
- Intercropping of tomato with cabbage. Combining these crops will reduce the damage done by the diamond-back moth.
- Alternate climbers, such as runner beans and peas, with tomato. Two weeks before tomato is harvested, the beans and peas can be planted in between the tomatoes. The sticks supporting the tomato can be used for the new crop.
Tomato fits well with different cropping systems of cereals, grains and oil seeds. Cropping systems like rice-tomato, rice-maize. Cauliflower-okra-sunflower-cabbage-tomato, maize-tomato-water melon and rice-peas-tomato have been proved economical systems. Leafy green vegetables or radish can be grown successfully as tomato intercrops. In India farmers follow a unique mixed cropping system. Fifteen days before transplanting a tomato crop, marigold (Tagetes erecta and other closely related varieties) is sown along the field border and also along the water channels in the field. This mixed cropping system helps to control the fruit borer in tomato. Crop rotation with cereals and other leguminous crops improves the soil health and reduce the pest infestation. Crop rotation with cereals or millets is effective in controlling the nematode population.
Before starting a greenhouse project one must carefully check whether all requirements for its success have been met.
As far as the climate is concerned, besides protection against fluctuating temperatures, protection is also needed against the sun’s powerful rays (solar radiation), heavy rain, hail and strong wind. Crops often need to be protected against a combination of weather conditions. The climatic data from the FAO (Food and Agriculture Organisation) database can serve as the basis.
High standards will need to be placed on the type of soil, the soil pro-file and the location. Thus, if at all possible, choose soil with a good structure in a flat area for your greenhouse project.
In view of the more expensive production equipment and the higher quality of the product, it is important to consider the location of your farm carefully. Greenhouse cultivation needs more attention than out-door cultivation. Therefore, you need to be within easy reach of your business at all times. Good infrastructure for transporting materials and products is also of importance, as is the availability of electricity. Finally, you need to know how you can sell the products you want to grow.
Whenever growers decide to invest in improvements to their production systems they need to make sure that their income will also grow adequately. Care needs to be taken that the investment also means improvement of the market value of the product. The golden rule is that the greenhouse grower starts on a small scale, gains experience and only then considers expanding the business and investing more.