Responses of Pink Lady apple to deficit irrigation and partial rootzone drying: physiology, growth, yield, and fruit quality

Abstract. Partial rootzone drying (PRD) is a new irrigation strategy whereby water is withheld from part of the rootzone while another part is well watered. A successful PRD strategy should reduce tree water use through stomatal control of transpiration and reduce vegetative growth while maintaining fruit size and yield. A field experiment examined crop water relations and production performance of PRD in a commercial apple orchard on loam soil in the Goulburn Valley, Australia. The orchard consisted of high-density (1420 trees/ha) 8-year-old ’Pink Lady ’ apple trees trained as central leader and irrigated by microjets. The effects of PRD on leaf/stem water potential, vegetative growth, yield components and fruit quality were investigated during two seasons (2001–02, Year 1 and 2002–03, Year 2). The 2-year average growing season reference crop evapotranspiration and rainfall was 954 and 168mm, respectively. Three irrigation treatments were established: (1) deficit irrigation (DI, supplied 50 % of water to a fixed side of tree); (2) PRD supplied 50 % of water to alternating sides of tree; (3) and conventional irrigation (CI, supplied 100 % water to both sides of tree). Irrigation input