Water use, yield and fruit quality of lysimeter-grown apple trees: Responses to deficit irrigation and to crop load

Effective irrigation scheduling for maximum crop yield and quality in a sustainable environment requires a good understanding of crop water use in relation to crop load and soil water availability. This study determined tree water use (TWU), fruit growth, yield, and quality of 'Braeburn' apple grown in lysimeters in response to two irrigation regimes and two crop loads in the growing season of 1997/1998. The irrigation regimes tested were control level of irrigation (CI) and deficit irrigation (DI) and the crop loads were commercial crop load (CCL) and light crop load (LCL) which was equivalent to 60% of the CCL. Tree water use was measured using two methods: soil-water balance through lysimetry and by a heat-pulse technique. There was no significant interaction between irrigation and crop load treatments and therefore only results for the main effects, irrigation and crop load, are presented. DI and LCL reduced TWU. Higher stomatal conductance (gs) was responsible for the higher TWU in CI but not in CCL. Increased mean fruit weight but decreased gross yield was observed in LCL. DI reduced mean fruit weight but had no significant effect on gross yield. Fruit quality, in terms of flesh firmness, total soluble solids, and dry matter concentration, was improved in DI both at harvest and after 12 weeks of cold storage but was, generally, not affected by crop load.