Crop yield response to water - Cra

figure 14Response of an almond orchard to three DI regimes: pre- and postharvest DI, and SDI over fouryears. Note that the yield decline is highest for the postharvest DI and that in this case, the SDIis the most advantageous DI strategy (after Goldhamer et al., 2006).A preharvest deficitsB postharvest deficitsC sustained DI2 200Kernel yield (kg ha -1 )2 0001 800CACABCBA(control)1 600B1 400500 600 700 800 900 1 000Applied water (mm)be avoided by adjusting the fertilizer application scheme to ensure that the recommendedamounts are added. There is little evidence that RDI results in lower levels of nutrients inthe plant, at least based on leaf tissue analysis. This may be because RDI reduces leaf growthand thus, tissue concentrations are the same even though there is less nutrient uptake fromthe soil. There are positive and negative interactions between DI and the incidence of pestand diseases. In the specific crop sections, stress-related pest management and plant diseaseconsiderations are presented where appropriate.Salinity management under deficit irrigationAll irrigation water contains salts but only pure water evaporates from plants and from thesoil and the salts are left behind. Therefore, the process of irrigation concentrates salts in thesoil profile to the point that they can reach harmful levels unless they are leached out of theroot zone. The rate at which salts are concentrated as a result of irrigation depends on thequality of the irrigation water, the amount of annual rainfall, the irrigation amounts and theET c . If the seasonal water balance is such that there is a certain amount of drainage, salts willbe displaced from the root zone and will move with the drainage waters below the root zone.In many cases, artificial drainage networks are needed to evacuate the excess water and thesalts outside irrigated areas to ensure the sustainability of irrigated agriculture. The FAO I&DNo. 25 publication provides water quality guidelines and procedures to assess the leachingrequirements, and on how to quantify the impact of salinity on crop yields.When DI is practised, the amount of applied irrigation water is less than the ET c and the waterbalance of the root zone is such that little or no leaching would occur during the irrigationYield Response to Water of Fruit Trees and Vines 293