Crop yield response to water - Cra

Table 2 Relative yield and gross revenue of table olives under deficit irrigation (Goldhamer et al., 1994).RegulateddeficitirrigationregimeConsumptiveuse(mm)Gross fruityield(t/ha)Grossrevenue(US$/ha)RelativeET c (%)Relativeyield (%)Relativegrossrevenue(%)Control 881 12.0 6725 100 100 100T2 759 12.3 6750 83.9 103.1 100.4T3 693 12.5 6700 75.4 103.7 99.6T5 546 10.8 5050 56.3 90.0 75.1Suggested RDI RegimesSeveral specific cases are developed below for different environments and water supplysituations. Table 3 illustrates an example of the water budget approach for irrigationscheduling of a young olive orchard in central Italy. Values are reported on a monthly basis,but during normal irrigation practice water budgets are calculated weekly. Two irrigationlevels are used, full irrigation and 50 percent deficit irrigation. It should be noted that theearly water deficit that occurred in April was unusual for this location, where the irrigationseason normally starts in June. In more arid climates it is normal that irrigation starts in springand may extend well into the fall season. Water is preferably applied to satisfy tree dailyneeds by microirrigation, but in poorly-drained soils it is desirable to reduce the frequencyof irrigation to 1-2 times a week. The use of longer intervals with microirrigation is ofteninefficient because there may be significant losses to deep percolation. When water agenciessupply water at longer intervals (2-4 weeks), it is desirable to build on-farm storage facilitiesto irrigate as frequently as needed.Three different RDI strategies have been successfully demonstrated for olive irrigation. Inthe first, the planned deficit is distributed evenly throughout the whole irrigation season(sustained deficit irrigation or SDI). In the second, the deficit is concentrated in the summerperiod, from pit hardening until the end of the summer (RDI 1 ). The third strategy (RDI 2 ) whichis intermediate between the previous two, alternates short cycles of stress and relief duringthe irrigation period, maintaining the SWP or predawn LWP at variable levels which aremoderately low during the fruit development period. The hypothetical seasonal course of treewater status under the three different DI strategies is represented schematically in Figure 5.There is no evidence to demonstrate the superiority of one RDI strategy over the others, asthey all seem to give good results (see below). In areas where rainfall patterns are typicallyMediterranean, and where soils have a reasonable water storage capacity (over 100 mm ofextractable water), the RDI strategies are easily implemented with irrigation systems that havelimited (below the ET needs) and fixed capacity (i.e. two emitters per tree). The irrigationsystem is run for the same period more or less throughout the entire season. In late spring,Olive 309