Above-and belowground responses to shifts in soil moisture in bearing apple trees

Abstract

Limiting irrigation to increase fruit quality as well as conserve limited water resources is of increasing importance. We examined the links of aboveground growth and physiology to root growth and distribution under cultural practices associated with restricted irrigation and mulching in an apple (‘Gala/M.9’; Malus × domestica Borkh.) orchard in a semiarid climate. Trees were either mulched to maintain a 10-cm depth or left unmulched. After orchard establishment, half the trees (partially irrigated) received daily drip irrigation only sufficient to meet 50% of daily evapotranspiration for 45 days before fruit harvest using one emitter per tree. The other trees continued to receive 100% irrigation using two emitters. Over three growing seasons, fruit yield was strongly affected in 2 of 3 years by partial irrigation if trees were unmulched but not if mulched. Fruit size and other quality parameters were minimally affected by partial irrigation. Total fine root length in fully irrigated trees was nearly double that of partially irrigated trees. Our results suggest that increases in soil moisture associated with mulching enabled mulched apple trees to tolerate deficit irrigation with minimal consequences for production and quality of apples, but with an overall less extensive and smaller root system.