The biggest influence when determining optimum fertiliser rates in relation to price changes is the magnitude of the grain yield response from fertilisers, according to research presented at Grains Research Updates 2022 today.
Department of Primary Industries and Regional Development (DPRID) senior research scientist Craig Scanlan profiled the economic analysis of fertiliser rate trials at the Grains Research and Development Corporation’s (GRDC) virtual forum.
The analysis was prompted by the recent sharp increase in phosphorous, potassium and nitrogen fertiliser prices, which accounts for about one third of variable costs for Western Australian grain growers.
The project was undertaken with GRDC co-investment and support from the SoilsWest Alliance, which includes Murdoch University, The University of Western Australia and DPIRD, as well as CSBP, Summit Fertilizers and the University of Adelaide.
Dr Scanlan said the research highlighted the importance of soil testing to help tailor fertiliser applications for each paddock to maximise returns from fertiliser.
“Yield responses are dependent on soil nutrient supply so it is important to get good soil testing data to predict yield responses more accurately,” he said.
“We found that as the yield response to fertilser increased, the optimal rate increased but the sensitivity of the optimal rate to grain and fertiliser prices decreased.”
Dr Scanlan said the research also illustrated a low level of precision was sufficient to maximise net returns for nitrogen, phosphorous and potassium.
“The modelling showed fertiliser rates of plus or minus five kilograms per hectare for phosphorous, 20 for nitrogen and 15 for potassium of the calculated optimum are likely to fall within the range of rates where the maximum net return occurs,” he said.
“For growers reassessing rates due to higher prices, we suggest working with your fertiliser adviser to assess where you are likely to get the biggest response.
“Using your soil test data in combination with low, medium and high potential yields for your area in a recommendation model is a quick way to assess the expected yield response and returns from fertiliser.”
More details on the research can be obtained from the paper delivered to the forum, available via the GRDC website.
The virtual Grains Research Update continues on 1, 3, 8 and 10 March. To participate visit the GRDC Updates and events page.
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