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: email@example.com
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.