Crop yield response to water - Cra

Figure 6Production function developed using RDI strategies that imposed stress during Stages I, II, andpostharvest only for at least a four-year duration. Eight studies from USA and Europe met thiscriterion and are presented. The dashed line shows linear regression from full yield, throughzero yield with a 7% ET c ; the level assumed necessary for tree survival.110+100Relative yield of split nuts9080706050++Kettleman City, CA, AtlanticaMadera, CA, PG1Parlier, CA, AtlanticaParlier, CA, PG1Lost Hills, CA, AtlanticaMadera, CA, AtlanticaTurkey, UzunSpain, Terebinthus+4040506070 80 90 100110Relative consumptive use (ETc)Since the contribution of soil moisture to ET c is difficult to determine, especially early inthe season, the RDI management strategy of only irrigating at certain percentages of ET c isproblematic. An alternative is to use a plant-based indicator of tree water stress, such as leaf/spur water potential with the pressure chamber. In the studies cited above, midday shaded LWPduring Stage I, Stage II, and postharvest did not exceed -1.8 to -2.0 MPa. Recommended valuesfor fully irrigated, mature pistachio trees grown under high evaporative demand conditionsshould have midday shaded LWP values for Stage I, Stage II, Stage III, and postharvest of -0.7to -0.8 MPa, -0.8 to -1.0 MPa, -1.0 to -1.1 MPa, and -1.0 to -1.2 MPa, respectively.One pistachio grower in California has observed that there is little need to irrigate male treesat full ET c since their only role is to supply pollen very early in the season. He suggests thatmale tree irrigation can be eliminated or substantially reduced after Stage I with no negativeimpact on the subsequent season’s pollen formation. This can be accomplished relatively easilywith microirrigation systems. However, given that male trees usually make up only about4 percent of all trees, the reduction in irrigation would be small.Typical microsprinkler application:Tree spacing 289 ft 2Application rate1.47 ft 3 /hrDepth application rate per plant 0.01 ft/hr (0.06 in/hr)Amount per irrigation 1.47 in/24 hr (37.2 mm/24 hr)The grower would keep track of cumulative amounts to be applied with RDI scenarios. Whenthe total is 37 mm, he irrigates. Thus, there would be one irrigation in April 16-30 with full watersupply but with 300 mm available case, first irrigation would not be until third week of June.PISTACHIO 427