Spatial irrigation scheduling for variable rate irrigation.

Recent unprecedented demands on freshwater for irrigation have led to over-allocations and restrictions. Variable rate irrigation (VRI) aims to optimise scheduling according to soil differences using irrigation prescription maps coupled with software-driven variable rate irrigators and individual sprinkler control for site specific management. Irrigation scheduling is varied using soil available water holding capacity (AWC) maps, generated from soil apparent electrical conductivity maps, with real time soil moisture monitoring using wireless sensor networks (WSN). Simulated results for a Canterbury site show that water savings between 2004 and 2009 are between 4 and 7% for any one season, the years with larger savings relating to rainfall events during the irrigation period. Drainage during the irrigation period was reduced by between 16 and 33%. VRI allows irrigation to be placed where it has greatest benefit; this is particularly important when freshwater is limited during peak growth periods. It aims for improved water productivity with environmental benefits of reduced run-off and drainage.