Carry-over Effects of Water Stress in the Vegetative Development, Flowering, Fruit Set, and Yield of Almond Trees

Mature, drip irrigated Nonpareil almond trees on a low water holding capacity soil were subjected to a single year at three severities of drought (rainfall only, 94, 185, or 795 [control] mm of irrigation), followed by one year of normal irrigation. As a possible strategy for improving drought survival, rainfall trees were divided into three canopy treatments applied in the spring of the drought year (50% reduction, 50% reduction + kaolin spray, and none), and 94 and 185 mm trees were divided into two treatments (kaolin spray and none). All trees survived the drought treatment, but there was a strong linear reduction in kernel weight associated with the level of current-year water stress, and a similarly strong carry-over effect on tree yield and number of nuts. Reductions in flowering and % set could account for the observed carry-over effects on tree yield. Canopy treatments had non-significant effects.