Nutrient performance indicators for the Australian grains industry
This project aims to develop and test a process to measure and report the nutrient use benchmarks partial nutrient balance (PNB) and partial factor productivity (PFP) for N, P, K and S for grain production systems against which growers can assess their nutrient management practices. These metrics will be derived at national, agroecological zone, regional and farm levels using published and surveyed information.
IPNI-2015-AUS-023
22 May 2017
2016 Annual Interpretive Summary
With financial support from the Grains Research and Development Corporation, data were collected from five years of cropping from over 500 cropping fields in south-eastern Australia. Crop yield, residue management and fertilizer use were used to estimate removal and use of [nitrogen (N), phosphorus (P), potassium (K), and sulfur (S)] in aggregate from the field over the study period. Legume N input was estimated from pasture or pulse production using common indicators of N derived from the atmosphere. These data were then used to estimate partial nutrient balance (PNB), partial factor productivity (PFP) and nutrient balance intensity for the fields studied.
The frequency distributions of PNB and PFP were skewed to the right, with the mean larger than the median, so comparing mean regional values is not statistically valid. Because of this, data were best presented as distributions.
The data from the 500 fields reported showed N-PNB was generally greater than 1.0, while P-PNB generally less than 1.0. The N-PNB is higher than 1.0 for over half the fields assessed in all regions except the Mallee where 39% were above 1.0. In aggregate, around 15% of the fields surveyed showed N removals twice N supply, with the balance coming (most probably) from the mineralization of organic matter in the soils. The P-PNB value reported in this study is lower than data from other countries and this is likely a consequence of the P-sorbing soils fixing some of the applied P.
The P-PFP values collected from the farms surveyed are generally around 200 kg grain/kg P. The N-PFP values show wide variations due to rotation and soil N status and around half the values from the farmers’ fields are less than 50 kg grain/kg N, suggesting that those low values may be limited by some biotic or abiotic constraints other than nutrients. It is debatable if the high values indicate that N supply is limiting production, but rather that extra N is being drawn from soil reserves either from new or old organic N sources.
These data will be used in discussion with growers and researchers on benchmarks for nutrient performance over time for the grains industry.