Effects of preharvest irrigation cutoff durations and postharvest water deprivation on almond tree performance
Plant water relations, tree growth, and yield components of mature almond trees [Prunus dulcis (Mill.) Webb cv. Nonpareil] were evaluated in response to ranges of irrigation cutoff durations immediately prior to harvest and to postharvest water deprivation. The preharvest cutoff regimes consisted of eight treatments that terminated irrigation from 8 to 57 days prior to tree shaking, resulting in 297 mm less preharvest-applied water for the longest cutoff regime. Postharvest irrigation totaled 206 mm. Predawn leaf water potential (LWP) declined rapidly after irrigation cutoff and reached −4.0 MPa prior to harvest in the most severe preharvest treatment. This resulted in reduced tree growth and near complete canopy defoliation. Individual kernel weight and full hull splitting were reduced by up to 17.2% and 71.1%, respectively, by the preharvest cutoff regimes, while bark damage due to mechanical shaking and fruit removal was unaffected. Hull rot at harvest was virtually eliminated with the longer preharvest cutoff durations. Depriving trees of postharvest irrigation had a greater impact on tree productivity than the preharvest irrigation cutoffs, even though the amount of postharvest-deprived water was less than that which occurred with the more severe preharvest cutoffs. In the season following postharvest water deprivation, bloom density and fruit set were reduced by up to 52.2% and 94.3%, respectively. This resulted in fruit load and kernel yield reductions of up to 76.7% and 73.6%, respectively. Even with the latest preharvest cutoff regime, fruit load and kernel yield were significantly lower without postharvest irrigation. We postulate that the sensitivity to postharvest water deficits is due to the late reproductive bud differentiation of almond, which may damage primordial flower parts and/or accelerate the emergence of the stamens during bloom, thus decreasing their pollen receptivity. Since postharvest water deficits are more damaging to sustained productivity than water deficits prior to harvest, growers with limited water supplies should bias irrigation towards the postharvest period.
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