Crop yield response to water - Cra

Tomato flowers develop from buds situated in the axis of the angle between the leaf and stem.Consequently, flowers form in sequence as the number of leaves increases on the stem, andflower and fruit initiation overlap vegetative growth for the whole period. This period lastslonger in the indeterminate than the determinate type because of the difference in how longnew leaves keep on developing. The first nodes on the stem that can potentially form flowersoccur between the fifth and the seventh node, according to cultivar and temperatures in theinitial weeks of crop (Dieleman and Heuvelink, 1992); however, there is not much differentbetween the three determinacy types.Tomato has a strong tendency to drop early flower buds, flowers and young fruit under certainconditions, including low solar radiation level and temperature and high humidity. Nitrogenand water status of the plant are equally influential. High nitrogen and/or high water statusstimulates vegetative growth, this apparently competes with the developing flowers and fruitfor assimilates, causing abscission of flowers and abortion of young fruit. In addition, restrictedwater supply can suppress new leaf development, resulting in a shortened yield formationperiod. Hence, field observation of phenological stages of tomato can be quite variable at times,even for the same cultivar and plant type, making it difficult to generalize. On the other hand,the remarkable adaptability of the tomato plant means cultivation worldwide is possible alongwith the application of diverse cropping techniques in greenhouses and in the field.Tomato plants grown from seed develop a strong taproot that reaches a depth > 1.5 m insoils without impeding layers restricting root growth (Battilani et al., 2002). In good anddeep soils in California, rooting down to nearly 3 m has been documented. However, mostwater and nutrient uptake occurs in the 0.2-0.75 m soil layer, where 50-80 percent of theroots concentrate. Lateral roots are normally initiated within 5 cm of the tip of the taproot,increasing in length upward along the taproot to a position about 20 cm from the taproot tip.The taproot of transplant is broken or curved, thus, several large laterals develop in the first3-4 weeks as main roots and penetrated downward. When soil receives water intermittentlyas rain or irrigation, the higher root length density is in the top 40 cm soil layer, where themajority of the active roots are concentrated. Drip irrigation alters root development pattern;however, roots grow preferentially in wet soil, irrespective of the areas wetted by surface orsubsurface drip (Oliveira et al., 1996).Water Use and ProductivityProcessing tomato consumes 400-800 mm of water from emergence/transplanting to harvest,depending on climate, plant type, soil, irrigation and crop management. Tomato plants cantolerate drought to some degree, therefore soil moisture levels can reach 50 percent of totalavailable water (TAW) without significant yield losses after the development of the canopyis completed. It is important to maintain adequate soil moisture levels early in the life cycle,at transplanting, and from the first flower until complete fruit setting (e.g. of the fifth trusson the main axes). Irrigation can stop a few weeks prior to harvest, depending on soil waterstorage and rainfall expectancy. Over the peak growing period, maximum water use averages4-7 mm/day in a sub humid climate, but can reach 8-9 mm/day in more arid areas. Tomato waterproductivity for biomass (WP B/et ) ranges from 1.3 to 3.5 kg/m 3 , with 3 kg/m 3 being consideredas common for favourable conditions and practices (Battilani, 2006). The low end of the rangeis likely observed in climates of high evaporative demand, as well as where canopy cover is lowTOMATO 195