A new rainfall adjusted nitrogen nutrition index is promising to assess the risk of achieving desired key performance indicators for wheat production in Western Australia

Andreas Neuhaus1, Marianne Hoogmoed2, Victor Sadras2

1 CSBP Limited, Kwinana Beach Rd, PO Box 345, Kwinana, Western Australia 6966.

2 South Australian Research & Development Institute, Waite Campus, Urrbrae, SA, 5064.

Corresponding author: andreas.neuhaus@csbp.com.au


In-season nitrogen (N) applications are an important farm management tool to influence crop profitability in Western Australia (WA). Agronomic benchmarking tools have been developed to guide such N decisions, but these often lack evaluation. This study compared and tested a new nitrogen nutrition index (NNI) with a CSBP plant N status (NUlogic®). It introduced a new NNI for wheat, developed for water limited regions like WA, on the basis of minimum N concentration (Nc) needed in shoots to achieve maximum shoot growth. It then adjusted that critical N curve using the rainfall and nitrate variable to best correlate with relative yield. The NUlogic method was directly calibrated on grain yield, using an N dilution curve derived from shoot Nc versus grain yield. Data from thirty-two WA field trials on N were used in this study. Both approaches were equally suited to predict N deficiencies, identify yield gaps and inform about N- (NUE) and water-use efficiency (WUE) in-season. However, the NNI method had to be adjusted for lower rainfall, indicating that targeting maximum shoot growth without rainfall adjustment would over-estimate N deficiency. An adjusted NNI ≥ 1 was likely to close yield and protein gaps. The maximum WUE increased up to a NNI of 1.5. Thereafter NUE declined sharply unlike the WUE. A “sufficient” or higher NUlogic N status behaved similar to a NNI ≥ 1. While this is work in progress, both tools look promising to assess the risk of these key performance indicators to guide profitable N applications in-season.


The Australian Society of Agronomy is the professional body for agronomists in Australia. It has approximately 500 active members drawn from government, universities, research organisations and the private sector.

Photo Credits

David Marland Photography david_marland@hotmail.com Southern Farming Systems Agriculture Victoria

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