Crop yield response to water - Cra

figure 6 The water balance of an orchard showing the disposition of irrigation water. E: Evaporation fromsoil; Tr: Transpiration; RO: Runoff; DP: Deep percolation, and, ±SW: Changes in water content ofthe root zone. Note that irrigation system losses in RO and DP may be recovered if the returnflows are used elsewhere.microirrigation, that have high potential application efficiency. Also, technical irrigationscheduling procedures that match water applications close to the water-use rates, are usedmore often when irrigation water is scarce. However, there are practical limits to reducingwater losses associated with irrigation. Once these losses are nearly eliminated, furtherreductions in water supply will unavoidably result in crop-water deficits. When this occurs, itis important to understand the species-specific physiological responses to water deficits.Water deficits that reduce plant transpiration also decrease the production of biomass inall crops. If the crop is being grown for its biomass, such as alfalfa or corn silage, there willbe a reduction in farmers’ income. For the main annual crops such as wheat, maize, andrice, a reduction in transpiration also decreases grain yield and gross income. However, formany tree crops and vines (and for some annual crops, such as cotton) where the fruit is theeconomic product, a reduction in biomass production does not always result in a parallelreduction in fruit production. Nevertheless, some quality parameters, such as fruit size orappearance, may be negatively affected.The other distinctive feature of the response of perennial crops to water deficits is thecarryover effects of water deficits that affect production in subsequent years. It is notknown if the longevity of plantations may be affected by long-term water deficits; insome species, such as peach or some citrus, shorter longevity may not be too important, asnew cultivars with better market opportunities are replacing older ones well ahead of fullorchard maturity. In other species, however, it may have important economic consequencesthat must be considered.Further, there may be cases of water deficits having beneficial effects on the production oftrees and vines. It has long been known that fruit from trees grown under water deficitsYield Response to Water of Fruit Trees and Vines 253