Crop yield response to water - Cra

yield of marketable product (split nuts) with Stage I stress (Goldhamer and Beede, 2004).More recent research has confirmed that shell splitting can be increased with Stage I stressbut at the expense of nut size (Goldhamer et al., 2005). Thus, the decision to use this strategywould depend on whether the grower had a severe problem with the production of closedshell nuts. Closed shell nuts can be as low as 5 percent of the harvested nut load and as highas 60 percent. Further, Stage I stress not only increased shell splitting but it increased the shellopening; the distance between shell halves at the distal end of the nut. This can result in theshell detaching from the kernel during commercial nut processing and the loose kernels candecrease the harvest value.Effects during Stage IIGoldhamer and Beede evaluated an array of RDI treatments that imposed either dryland,applied water at 25 percent ET c , or applied water at 50 percent ET c during Stage II on matureKerman on Atlantica rootstock under the high evaporative demand conditions of the westernSan Joaquin Valley in California (Goldhamer and Beede, 2004). These Stage II deficit irrigationtreatments were coupled with different postharverst water regimes. They found that noneof the Stage II stresses significantly reduced individual nut weight although there was a trendtoward lighter nuts when Stage II irrigation was totally eliminated. One of these Stage IIdryland treatments, when coupled with irrigation at 25 percent ET c postharvest, significantlyreduced the yield of split nuts. They concluded that Stage II was, indeed, a stress tolerantperiod, as has been found for other double sigmoid development fruit crops, such as peach,plum, and nectarine, and recommended an RDI regime that irrigated at 50 percent ET c duringStage II (Goldhamer and Beede, 2004).A June deficit irrigation schedule of 20 percent less than full irrigation doubled early splits,while a July deficit of 35 percent increased early splits by 30 percent (Sedaghati and Alipour,2006). Early splits are nuts that split well before the onset of normal shell splitting. Thesenuts are not commercially viable. Moreover, they are susceptible to fungal diseases that caneventually result in Aflatoxin contamination. Doster and Michailides (1995) recommendedthat water stress in mid-May be avoided to decrease the incidence of early splits.Effects during Stage IIIStress imposed during Stage III can have a dramatically negative impact on virtually all theyield components of pistachio. When a dryland treatment was imposed during Stage III, itwas found that this reduced individual kernel weight by 10.6 percent, increased the sum ofblanking and kernel abortion in the total tree nut load by 22.7 percent, and increased theproduction of closed shell nuts by 175 percent. Somewhat remarkably, the Stage III drylandtreatment had no affect on total tree nut load. However, the yield of split nuts was reducedby 62.6 percent (Goldhamer and Beede, 2004).Earlier work indicated that withholding irrigation during the first half of Stage III, whichreduced consumptive use by 320 mm, had no significant impact on shell splitting but increasedthe number of filled nuts left in the trees after mechanical shaking by 119 percent. On the otherhand, dryland conditions during the last half of Stage III (a 200 mm reduction in consumptive use)both increased the production of closed shell nuts at harvest by 31.6 percent and the number offilled nuts retained on the tree after mechanical shaking by 50 percent. It was concluded that422crop yield response to water