Crop yield response to water - Cra

Tomato requires soils with proper water-holding capacity and aeration. Well drained, deep,sandy loam soils are preferred, but heavier soils can also be highly productive under propermanagement. Tomato is intolerant to soil compaction and waterlogging, thus the upper 15-20 cm soil layer needs to be permeable. In clay soils, deep ploughing is sometimes necessaryto allows for water drainage and better root penetration. At some locations tomato needs a3-year rotation, with crops other than solanaceous (e.g. potato, pepper, eggplant, tobacco),to minimize nematodes, virus and bacterial diseases. Generally tomato is grown in rotation,often with only a 2-year cycle.Growth and developmentMore commonly, tomatoes are transplanted to achieve more uniform plant emergence,density and development. Because of its small seeds it is difficult to attain uniformity andhigh percentage of emergence when sown in the field. Direct sowing is usually limited tostandard cultivars, with hybrids this method is uneconomic because of the high seed cost.Seed beds must be carefully prepared to eliminate soil clogs for direct sowing. The use ofprecision sowing machines, compared to traditional planters or manual sowing, allows for theuse of pelleted seed and avoids the thinning at the fourth leaf or later stage. Tomatoes arebest sown when the 7-day average soil temperature of the top 100 mm layer is ≥ 10 °C. Sowingperiod ranges from end of February to May in the Northern Hemisphere, or from August tomid-December in the Southern Hemisphere. Of course, the season is much less defined in thetropics and subtropics.The optimal sowing depth is 2-4 cm. The density of sown processing tomatoes is generallyhigher than those that are transplanted because, up to a point, higher plant densities lead tohigher yields and this is counter-balanced by the increasing cost of seedlings for transplantingat higher densities. About 100 000 seeds per hectare (1-1.5 kg/ha) are necessary whentraditionally sowing processing tomato. In contrast, 0.3-0.5 kg/ha of seeds are used in caseof precision sowing with pelleted seeds. Seedlings for transplanting are sown in a nursery inplug trays (25-35 mm diameter per seedling) at a density of between 750 and 1 000 seedlings/m 2 , and transplanted at 25 000-33 000 plant/ha. Seedlings are commonly transplanted atthe 4-5 true-leaf stage, 4 to 7 weeks after sowing. Seedlings should be short, 150-200 mm,including the root clod, and less if transplanting is by machine, and should have a thick stembase (diameter ≥ 4 mm). These requirements are met only if the radiation level is high in thenursery. The transplanting period ranges from the end of March to the end of June-early July inthe Northern Hemisphere, or from September to mid-December in the Southern Hemisphere.Plant spacing varies widely depending on conditions, seed or seedling cost, plant type andcultivars and local practices. Density ranges from 2 to 6 plants/m 2 and row spacing ranges from0.75 m to 1.6 m, with processing tomato often planted more densely than market tomato. inthe latter case, wider space is left for picker’s access, so that the ripe fruit can be harvestedfrequently. On wide beds, processing tomato may be planted in double rows to obtain aslightly higher yield. Generally, tomato starts to flower early, 25-40 days after transplantingor 35-50 days after emergence, depending largely on temperature. The life cycle varies from95-115 days for processing tomato or up to more than 145 days for undetermined fresh markettomato.194crop yield response to water