Effects of irrigation deprivation during the harvest period on yield determinants in mature almond trees

Effects of irrigation deprivation during the harvest period on yield determ inants in mature almond (Prunus dulcis (Mill.) D.A. Webb cv. Nonpareil) tre es were investigated during a 3-year field experiment. Return bloom and fru it set were measured on 2185 individually tagged spurs. Water stress result ing from irrigation deprivation during the harvest period, which purportedl y coincides with the time of flower initiation, had no effect on the percen tage of spurs that flowered or set fruit during subsequent years. Although water stress had no apparent effect on spur mortality, 66% of the tagged sp urs died within 3 years. In addition, many spurs were vegetative by the thi rd year, indicating the importance of spur renewal for sustained fruit prod uction. Reductions in nut yield were evident after two successive years of irrigation deprivation during the harvest period. Regression analysis indic ated a loss in yield of 7.7 kg tree(-1) in response to each 1 MPa decrease in stem water potential below -1.2 MPa during the previous seasons. The num ber of fruiting positions per tree (estimated indirectly for whole trees ba sed on weight of current-year shoots > 5 cm in length) was negatively assoc iated with water stress. Yield reduction in response to water stress during harvest appears to be a compound, multiyear effect, associated with reduce d annual growth and renewal of fruiting positions.