Previously well irrigated mature `Nonpareil' almond trees (Prunus dulcis) were subjected to varying periods of water deprivation prior to harvest and then to either full or no postharvest irrigation. Eight preharvest water deprivation (PWD) lengths ranging from 14 to 63 days were evaluated on a sandy loam soil with a rooting depth of about 1.5 m.
Development of tree water deficits occurred rapidly following PWD. Predawn leaf water potential decreased to about -1.8 and -3.1 MPa after 10 and 20 days, respectively. Defoliation began about 30 days after PWD and trees subjected to more than 50 days completely defoliated. The rate of hull split was directly related to the PWD duration. With early cutoffs, the size of the hull split-arrested nuts at harvest was large compared with the same nut type in later cutoffs suggesting that as nuts develop, large nuts are preferential sinks for assimilates. Kernel size was only mildly reduced by PWD during the first study year. There was a trend toward lower total kernel yield with longer PWD as a result of smaller kernel girth but yield differences were not significant. The number of nuts remaining in the tree after shaking was not related to PWD. Bark strength increased after PWD with 10 to 14 days required to prevent shaker damage. Postharvest irrigation resulted in late season defoliation but no rebloom. Bloom density reductions in 1990 were related more to the lack of 1989 postharvest irrigation than to early PWD.