water use dynamics of young and mature apple trees planted in south african orchards: a case study of the golden delicious and cripps' pink cultivars

Apple orchards have previously been bearing 60–80 t ha⁻¹ at most. However in recent years yield has increased to more than 100 t ha⁻¹. There is need to understand the water requirements of the high yielding orchards, given that high crop loads are associated with high water use rates. The aim of this study was to quantify the water requirements of young and mature unstressed apple orchards. We also assess the impact of climate variables on transpiration rates. Data was collected in 4 orchards in the Western Cape Province. The orchards comprised young non-bearing (< 3 years) and mature trees planted to the Golden Delicious and Cripps' Pink cultivars, all under micro-sprinkler irrigation. Transpiration by the trees was measured using heat pulse velocity sap flow sensors hourly throughout the growing season (October–June). Weather was monitored using an automatic weather station. Tree transpiration was linearly related to the solar radiation, but the relationship with the vapour pressure deficit (VPD) was non-linear. There were no significant differences (p>0.05) in the sapflux density of the Golden Delicious and Cripp's Pink cultivars. This suggests that these two cultivars have similar water use characteristics. Mature orchards transpired between 6000 to 8000 m³ ha⁻¹ season⁻¹ while non-bearing orchards used between 2000 to 3000 m³ ha⁻¹ season⁻¹.