Crop yield response to water - Cra

Lead AuthorDavid A. Goldhamer(formerly University of California,Davis, USA; currentlyCooperative Extension Emeritus)Contributing AuthorRiza Kanber(Cukurova University,Adana, Turkey)PistachioIntroduction and BackgroundPistachio (Pistacia vera L.), is native to the Near East, primarily Syriaand Iran, with large areas planted just recently in the United States.In 2009, there were 586 000 ha globally with an average yield of 1.1tonne/ha (FAO, 2011). Figure 1 presents the production trends of the mainproducing countries since 1985. The bulk of Near East production is drylandas the pistachio tree is very drought tolerant. Most of the production in theUnited States is in California, which is irrigated. There is a huge difference inproductivity between dryland and irrigated trees. For example, the averagedryland yield in Turkey is only 1.4 kg per tree compared with 16-18 kg pertree under irrigation in California (Tekin et al., 1990). While the value ofirrigation for pistachio production is currently unchallenged, there are stillsome growers in rainfed areas who have the misconception that irrigation isharmful (Kanber et al., 1993). Much of the Near East production is on marginalsoils because the tree is perceived to be drought tolerant and good soils arescarce. This is not the case in California where irrigated orchards have beenplanted on productive valley soils.The pistachio tree is dioecious; the male flowers are borne on one tree andfemale flowers on another. The male trees do not produce nuts. However, acertain percentage of the orchard, generally around 4 percent in commercialorchards, must be planted with male trees to ensure adequate pollination.Among fruit and nut trees, pistachio has one of the highest degrees ofalternate bearing. Crop yields can show up to a 90 percent year-to-yearreduction. The physiological mechanisms of alternate bearing in pistachioare not well understood. It is likely to involve carbohydrate levels and/orcompetition with hormonal activity also being a possible factor. Alternatebearing is first manifested during nut filling in early July when the fruit buds(for next year) die and abscise. The heavier the crop, the greater is the budabscission. The alternate bearing cycle is expressed not only for individualtrees but for entire growing regions. It is thought that low productionresulting from poor weather in a given year puts the entire region on thesame alternate bearing cycle. Excessive alternate bearing in a region can causea marketing problem for the industry. The current state of the art controlof alternate bearing is pruning; heavily prior to an ‘on’ year and minimallygoing into an ‘off’ alternate bearing year. The fact that pistachio fruit areborne on year-old wood dictate the location and severity of pruning practicesdesigned to mitigate alternate bearing. Moreover, pistachio shoot growth canbe characterized as either preformed or neoformed, which is based on when416crop yield response to water