Water productivity of high performing apple orchards in the winter rainfall area of South Africa

摘要

Increasing pressure on South Africa's water resources from rising and competing user demand and climate change threatens the sustainability of the deciduous fruit industry. Commercial apple production in South Africa is entirely reliant on irrigation.Furthermore, high yielding (>1001 ha-1) apple orchards have become common, raising the need for detailed information on water use and water productivity (WP) of these orchards. This study, conducted from 2014 to 2017, investigated the dynamics of wateruse in four 'Golden Delicious' and four 'Cripps Pink' orchards in the winter rainfall Western Cape region. Yields ranged between 11 and 1401 ha-1 in younger to full-bearing orchards. The orchards were in two key apple producing regions with contrasting climates. The full study included detailed quantification of orchard water use using sap flow sensors, eddy covariance evapotranspiration (ET) measurements, and ET modelling. In this paper we present the analysis of WP, together with fruit quality and gross income. We define WP as kg of fruit produced m 3 of water consumed, based on both whole tree transpiration (T) and ET. We also calculate "economic water productivity" (EWP) as gross income nr3 of water consumed. The key driver of WP (T-based) was thecanopy leaf area. However, lower transpiration from smaller canopies of 'Cripps Pink1 was compensated by higher evaporation from the orchard floor, resulting in comparable WP (ET-based) between the cultivars. WP based on ET increased with increasing yield. Differences in ET due to the length of the growing season were insignificant since the canopies continued to be active for ca. eight weeks between harvest (mid-April) and late autumn (early June) in both cultivars. Exceptionally high yields resulted in smaller fruit size in 'Golden Delicious' orchards which reduced the pack out of export quality fruit and lowered the EWP. The premium prices obtained for 'Cripps Pink* compared to 'Golden Delicious' drove up the EWP.