Some effects of water stress in late spring on apple trees

SummaryNine-year-old Cox’s Orange Pippin apple trees in a hedgerow-type orchard were deprived of water, by using a soil cover to intercept rainfall, from late March until mid-June, 1973. Trees in adjacent rows received normal rainfall and other trees were given supplementary irrigation. Total plant water potential was monitored by means of a pressure bomb, soil water status was assessed by gypsum resistance blocks, and various micrometeorological parameters were measured.Fruit-set was considerably reduced by plant water stress, and in addition the trees with minimal water stress retained more fruits per cluster than the droughted ones.Interactions between soil water status and evaporative demand, and the effects of these factors on plant water status, were demonstrated, and these have been interpreted within a theoretical framework. Plant impedance values, calculated on the basis of the theory presented, indicate that resistance to water flow through the plant may not be a constant.