Crop yield response to water - Cra

Figure 12Patterns of seasonal applied water to an orchard under full, regulated (RDI), andsustained (SDI) deficit irrigation.Appliedwater(mm)700600500RDISDIControl400300200100Harvest0120 140 160 180 200 220 240 260Day of yearversus the alternate drying cycles. Indeed, the comparisons between PRD and other forms ofDI, which apply the same irrigation levels under field conditions, have not shown any specificadvantage of PRD over RDI in terms of production per unit irrigation water in a significantnumber of experiments (Figure 13) (Sadras, 2009).Responses to deficit irrigationAll DI strategies aim to control crop water deficits by manipulating water supply as best aspossible to maintain growers’ revenues in water–limiting situations. Contrary to the responsesof most annual crops, where yield declines linearly with ET under many watering regimes, themodulation of water deficits have a different impact on tree crops and vines. As an example,Figure 14 shows that three different DI strategies for almond trees had very different impactson the yield response to applied water.Most current RDI management approaches are based on irrigating a certain percentage ofET during stress-tolerant periods of the season. This concept works relative well in the midand later parts of the season, after the soil moisture reservoir has been depleted of winterrainfall. However, early in the season stored water in the soil profile often buffers the impactof deficit irrigation on plant stress. Thus, even though one reduces irrigation, there will likelybe a lag in terms of producing the desired plant stress. The duration of the lag depends on thedepth of the root zone, soil water holding capacity, effective winter rainfall, and atmosphericevaporative demand. Therefore, there is greater need for precise plant-based water stressindicators, such as pressure chamber measurements, early in the season when using RDI. Forexample, one winegrape RDI strategy recommends delaying irrigation until a target leaf waterpotential is reached and then irrigating at a certain percentage of ET until after fruit colourchange (veraison stage).Yield Response to Water of Fruit Trees and Vines 291