Crop yield response to water - Cra

used to collect the nuts, which are not allowed to drop to the ground. Drying is accomplishedat the processing plant rather than on the ground as for almonds. One primary reason for thisis that pistachio nuts need to be dried quickly, otherwise the shell can become stained, makingthem less attractive to buyers.PostharvestFrom harvest to the onset of defoliation, there is very little outward appearance of treeactivity. Following the removal of fruit, reproductive bud differentiation resumes andcontinues through October. Trees generally defoliate in mid to late November because of leafsenescence, which is accelerated by low temperatures.Responses to Water DeficitsPistachio has a well-deserved reputation as being drought tolerant. Measurable photosyntheticactivity in the leaf has been measured even when leaf water potential (LWP) was in excess of-5 MPa (Behboudian et al., 1986). This was attributed to the fact that pistachio trees had aturgor pressure of about 3 MPa even when the LWP was -6 MPa; a higher value that for evenother xerophytes. Pistachio can maintain high turgor even with high soil salinity levels (Walteret al., 1988), and high photosynthesis and stomatal conductance were found in differentpistachio species under severe stress (Steduto et al., 2002). Researchers ascribed this primarilyto an extensive rooting system rather than xerophytic morphologic characteristics. Unirrigatedtrees of P. atlantica had transpiration rates about three times higher than P. terebinthus(Germana, 1997).’ This suggests that pistachio trees can transpire at rates far higher than thosenormally found in mesophytes and that carbon assimilation with limited water supplies can bemuch higher than in other fruit crops, such as apple, peach, plum, cherry, citrus and almond.Pistachio exhibited a strong photosynthetic response to high N and water supply, althoughthe rates of unirrigated trees were also quite high (Steduto et al., 2002 and Aydın, 2004). Withrespect to water, pistachio is somewhat of a paradox; it transpires at an extremely rapid rate,in partly because the fact that its leaves are isolaterals meaning the upper and lower sides aresimilarly structured with almost identical stomatal density and conductance but, at the sametime, it is also extremely drought tolerant.Effects during Stage ISpann and others tested RDI regimes that imposed water deficits of about -1.6 MPa middayshaded LWP on mature trees of Kerman on PG1, Atlantica, and UCB rootstocks during Stage Iand both Stage I and Stage II. They found that especially for the ‘short’ shoots, those that arecharacterized as preformed growth, full elongation occurred by about the third week of April;well before the onset of Stage II. There were generally no reductions in this short shoot lengthbecause of these early season water deficits (Figure 3). However, stress during both Stages Iand II significantly reduced the growth of the ‘long’ shoots; the neoformed growth (Figure3). This did not decrease the number of fruiting positions since they are located mostly on theshort shoots. Indeed, they found no differences in fruit load, fruit size and yield between theseRDI regimes and the fully irrigated control. This was attributed to the fact that most fruit wasborne on the preformed growth and that reducing neoformed growth was actually beneficial incommercial production since it must be pruned. Water and pruning costs are about 30 percent420crop yield response to water