Soil water extraction by sugar cane beyond the readily available limit

Readily available water (RAW) has been defined in terms of an irrigation requirement to maintain stalk elongation at or above 50% of potential. Plant extractable soil water (PESW) has been defined as the total amount of water plants can extract prior to death. While stalk growth will slow and eventually cease at some point after RAW has been exhausted, other growth processes proceed albeit at a reduced rate. It is necessary to account for the water used during this reduced rate of growth in order to explain the behaviour and yield of crops that are sUbjected to moderate and severe levels of water stress. This will assist with decisions about the use of limited irrigation water and decisions about drying-off in fully irrigated crops. Although RAW has been determined for a number of soils in the sugar industry, experimental crops in Australia have seldom been forced to extract all PESW, so there is little published data available. Cane yield may not increase much after RAW has been extracted, but sugar yield can increase substantially while the remaining soil water is being extracted. Consequently, knowledge about total soil water supply wiIllead to better use of limited irrigation water and better drying-off decisions and will allow the identification of management strategies to maximise profitability rather than productivity.