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
02 Jun 2018
2017 Annual Interpretive Summary
This project aimed to develop nutrient performance indicators for Australian grain farms. Data on nutrient removal, nutrient use, crop management and estimates of nitrogen (N) fixation from 500 paddocks was collected and collated. A series of articles on this work was developed in collaboration with the ExtensioAus network to share these results with growers and advisors across the nation.
The survey found that one third of the paddocks had 50% more N removed than supplied. This led to declining soil organic matter as the extra N to balance crop demand comes from mineralization of that important organic matter. In terms of N effectiveness, on average there were 77 kg of grain produced for every kilogram of N supplied - which came from fixed and fertilizer sources.
Unlike the deficit of N, about 80% of the paddocks surveyed had more phosphorus (P) applied than was removed. In terms of production efficiency, these paddocks produced 227 kg of grain per kilogram of P applied. Results for potassium and sulfur varied across the region.
The key messages to growers and advisors was to make those long term (five year or greater) estimates of performance indicators, but take care not to focus on a single number for a paddock when looking at partial nutrient balance (PNB) or partial factor productivity (PFP), but consider a whole farm context. High or low values for PNB or PFP do not mean the systems being evaluated are inherently efficient or inefficient. A PNB greater than one may be a viable strategy to exploit excess soil nutrients, or if there is a need to build soil test levels, a PNB less than one may be appropriate. Similarly, the magnitude of the deficit or surplus of nutrient should be viewed in relation to the productivity of the system - for example, a 5 kg N/ha deficit in a low rainfall area with low soil organic matter may be more significant than the same deficit in a high rainfall area with higher soil organic matter. Alignment with changes in soil tests can provide growers with strategies for more effective nutrient use.