GRDC research targets water-use efficiency gains

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Advances in management practices mean growers have been making steady improvements in water-use efficiency over the past 30 years.

However, future climate variability in southern Australia is likely to deliver warmer and drier springs. So storing as much water in the soil as possible prior to sowing will become vital if maximum productivity is to be achieved.

The Grains Research & Development Corporation is funding 19 research projects across the southern and western regions of Australia, to the value of US$17.6 million over four years.

The aim is to deliver a 10 percent improvement in water-use efficiency in each region. The 19 projects are targeting four key areas of interest including:

  • Increasing the capture, storage and use of out-of-season rainfall through improved summer weed control and stubble management.
  • The use of break crops to improve water-use efficiency of the following year’s crop. This includes investigating how break crops fit into systems and how they can be managed for less risk.
  • Better matching crop inputs to water-limited yield potential in order to improve water-use efficiency but reduce risk.
  • Changing the division and distribution of water-use during the growing season, focusing on reducing evaporation, and making as much water as possible available to the crop during the critical flowering and grain-filling stages of crop development. This includes investigating the impacts of sowing time, seeding rates and nitrogen management on water use.

CSIRO scientist James Hunt, one of the team working on the research, says the GRDC project is aimed at striking a balance between reaching the upper limits of achievable water-use efficiency for grain yield, but also recognising what is reasonable in terms of profitability and risk.

He says while this research is continuing, there are already many things growers can do to reduce exposure to hot dry springs.

Grain growers are encouraged to capture more out-of-season rainfall so it is available during the growing season and can support crops during critical growth stages. While forecasts for climate change predict reduced spring rainfall and hotter temperatures, summer rainfall may marginally increase.

Controlling summer weeds and retaining stubble will enable retention of more moisture. Complementary management strategies include sowing earlier to minimise growth during hot and dry spring periods and if this is not possible, using shorter season varieties.

Dr Hunt says the best way for grain growers to know whether the extra measures taken to store out-of-season rainfall are working is to measure soil water on their farm. He says many farming decisions can be based on how much soil water is available at sowing, since growing season rainfall is always going to be variable and seasonal forecasts are not reliable early in the season.

He says knowing the amount of stored soil water at the beginning of the growing season can tell grain growers a lot about their production risk for the season, which enables decisions to be made to match seasonal and crop needs.

For example, there are potential yield gains from sowing early when stored soil water is available. Under these circumstances, the risk of having a crop failure when sowing dry or early on a smaller rainfall event is also reduced. Dr Hunt says measuring stored soil water enables grain growers to make these sorts of decisions with confidence.

He says there are many gains to be made in improving water-use efficiency through tools such as Yield Prophet. From 2004 to 2007, Yield Prophet users achieved an average water use efficiency of 15kg/ha.mm, while other published on-farm water use efficiency figures average around 8-10 kg/ha.mm. He does point out that this could be because better farmers choose to use Yield Prophet®, rather than Yield Prophet making farmers better!

The most water-efficient crop is not necessarily the most profitable crop. If excessive inputs are required to achieve maximum water use efficiency, production is risky, and the resulting yields may not be profitable given the inputs invested.

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