Tomato Crop Guide

Tomato (Lycopersicon esculentum) is the second most important vegetable crop next to potato. Present world production is about 100 million tons fresh fruit from 3.7 million ha.(FAOSTAT, 2001).

Tomato is a rapidly growing crop with a growing period of 90 to 150 days. It is a daylength neutral plant. Optimum mean daily temperature for growth is 18 to 25ºC with night temperatures between 10 and 20ºC. Larger differences between day and night temperatures, however, adversely affect yield. The crop is very sensitive to frost. Temperatures above 25ºC, when accompanied by high humidity and strong wind, result in reduced yield. Night temperatures above 2OºC accompanied by high humidity and low sunshine lead to excessive vegetative growth and poor fruit production. High humidity leads to a greater incidence of pests and diseases and fruit rotting. Dry climates are therefore preferred for tomato production.

Tomato can be grown on a wide range of soils but a well-drained, light loam soil with pH of 5 to 7 is preferred. Waterlogging increases the incidence of diseases such as bacterial wilt. The fertilizer requirements amount, for high producing varieties, to 100 to 150 kg/ha N, 65 to 110 kg/ha P and 160 to 240 kg/ha K.

The seed is generally sown in nursery plots and emergence is within 10 days. Seedlings are transplanted in the field after 25 to 35 days. In the nursery the row distance is about 10 cm. In the field spacing ranges from 0.3/0.6 x 0.6/1 m with a population of about 40,000 plants per ha. The crop should be grown in a rotation with crops such as maize, cabbage, cowpea, to reduce pests and disease infestations.

The crop is moderately sensitive to soil salinity. Yield decrease at various ECe values is: 0% at ECe 2.5 mmhos/cm, 10% at 3.5, 25% at 5.0, 50% at 7.6 and 100’/. at ECe 12.5 mmhos/cm. The most sensitive period to salinity is during germination and early plant development, and necessary leaching of salts is therefore frequently practised during pre-irrigation or by over-watering during the initial irrigation application.

The graph below depicts the crop stages of tomato, and the table summarises the main crop coefficients used for water management.

Total water requirements (ETm) after transplanting, of a tomato crop grown in the field for 90 to 120 days, are 400 to 600 mm, depending on the climate. Water requirements related to reference evapotranspiration (ETo) in mm/period are given by the crop factor (Kc) for different crop development stages, or: during the initial stage 0. 4-0. 5 (10 to 15 days), the development stage 0. 7-0.8 (20 to 30 days), the mid- season stage 1.05-1.25 (30 to 40 days), the late-season stage 0.8-0.9 (30 to 40 days) and at harvest 0.6-0.65.

The crop performance is sensitive to the irrigation practices. In general a prolonged severe water deficit limits growth and reduces yields which cannot be corrected by heavy watering later on. Highest demand for water is during flowering. however, withholding irrigation during this period is sometimes recommended to force less mature plants into flowering in order to obtain uniform flowering and ripening. Care should be exercised in this to avoid damage to the mature plants.

Excessive watering during the flowering period (2) has been shown to increase flower drop and reduce fruit set. Also this may cause excessive vegetative growth and a delay in ripening. Water supply during and after fruit set must be limited to a rate which will prevent stimulation of new growth at the expense of fruit development. Heavy, irregular irrigations or dry periods alternating with wet periods should be avoided. For production of salad tomato with more than one harvest, the crop flourishes best under light, frequent irrigation, well-distributed over the growing period with the soil depletion level during the different growth periods remaining below 40 percent (p < 0.4). This promotes optimum growth during the total growing period and results in high yield of good quality. With one harvest uniform ripening is required and the depletion level during this period may increase to 60 to 70 percent.

When water supply is limited, application for a salad crop can be concentrated during periods of transplanting, flowering (2) and yield formation (3). For a crop grown for paste production, a more extensive irrigation may be applied with last heavy irrigation applied prior to flowering.

Surface irrigation by furrow is commonly practised. Under sprinkler irrigation the occurrence of fungal diseases and possibly bacterial canker may become a major problem. Further, under sprinkler, fruit set may be reduced with an increase in fruit rotting. In the case of poor quality water, leaf burn will occur with sprinkler irriga-tion; this may be reduced by sprinkling at night and shifting of sprinkler lines with the direction of the prevailing wind. Due to the crops specific demands for a high soil water content achieved without leaf wetting, trickle or drip irrigation has been successfully applied.