What's the water worth?

While wheat growers have known that moisture at one metre or deeper can be important for crop yield, the actual value of such water has never been quantified.

Dr John Kirkegaard and his CSIRO team based in Canberra used irrigation to establish wheat crops with moisture to two different depths, 130 and 170 centimetres. Automatic rainout shelters excluded rainfall from flowering to the time of harvest.

After first season harvests, the plot with moisture to 170 centimetres produced an extra 67 kilograms of grain per hectare, per millimetre of moisture used in the 130 to 170cm zone. This equates to an extra tonne of grain per hectare if 15 millimetres of water was used from the deeper zones.

Previous research has established that wheat plants yield an average of 20 kilograms of grain per hectare, per millimetre of total moisture throughout the season, but the effect of subsoil moisture has never been separated from that figure. It now appears that water deep in the soil can be used very efficiently in some seasons.

Over the next two years the project will look at the seasonal factors that influence crop water use, the types of management or variety improvements that could make better use of subsoil water, and the distribution, morphology and function of deep wheat roots, which have never been studied in such detail previously.

This research is supported by the Grains Research and Development Corporation (GRDC).

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