Nitrogen management key driver of WUE

The rate of nitrogen (N) fertiliser applied is the stand-out variable influencing water use efficiency (WUE) in wheat crops. This was the main finding in a four-year research trial in western Victoria. Ten variables accounted for a third of the WUE variation between sites.

Trial set up

Data collection points were set up in 136 wheat paddocks between 2013 and 2016. There were three datum points per paddock, sited 50 metres apart. The sites covered obvious variations in the paddock. There were 53 variables analysed. Any with less than 350 observations were ignored.

The Wimmera region was the focus of the trial. But the 2014 and 2015 trials included sites in the Mallee and High Rainfall Zone (HRZ) near Hamilton. All the sites experienced a range of seasonal conditions over the trial period.

Key findings

The ten most influential variables on WUE from these trials were:

  1. Rate of N fertiliser applied
  2. Crop rotation (previous year’s crop)
  3. Variety of wheat
  4. Sowing date
  5. Soil Mn levels
  6. Crop maturity type
  7. Soil mineral N levels
  8. Rate of P fertiliser applied
  9. Crown Rot risk
  10. Soil P levels.

The rate of N fertiliser applied is over three times more influential than any other variable. Applying the optimum rate of N increased WUE from 8kg grain per millimetre of water to 15kg/mm of water.

Lessons learnt

Some of the trial conclusions requiring further research include:

  • WUE in wheat in these areas is well below physiological potential.
  • Significant variation in WUE remains unexplained but may be influenced by factors not considered such as frost and heat shock.
  • Grower management is important and accounts for the top two variables, but a range of factors have a cumulative contribution to WUE.

Acknowledgements

Roger Perris, Mel Munn, Pete Hekmeijer, Katherine Dunsford, Kerry Bell, Franz Waldner and Zvi Hochman

More

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IPNI: Crop Nutrient Decisions in High Rainfall Zones

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