Abstract
Abstract. 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.
Highlights
South Africa is currently the 7th biggest exporter of apples (Malus domestica Borkh.) in the world
An important information gap currently exists regarding the water requirements of high yielding (≥ 100 t ha−2) apple orchards which have become the norm in this region in recent years
Several studies have quantified water use by apple orchards (Braun et al, 2000; Volschenk et al, 2003; Dragoni et al, 2005; Gush and Taylor, 2014) these studies were not done in exceptionally high yielding orchards
Summary
South Africa is currently the 7th biggest exporter of apples (Malus domestica Borkh.) in the world. The Western Cape experiences Mediterranean climatic conditions and most of the rain falls outside the fruit growing season in winter This region is projected to experience severe water shortages in future due to the rapidly increasing population, increasing agricultural and industrial activities and climate change (Midgley and Lötze, 2011). Accurate information on water use by apple orchards is critical for the sustainability of the multi-billion Rand deciduous fruit industry This information will be useful for, among other things: (1) developing irrigation scheduling guidelines for the apple industry, (2) water allocation and planning, and; (3) developing strategies for coping with drought whose frequency and severity is expected to increase in the near future in the South Western parts of the country.
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