The ‘Deep-P calculator’ is a joint investment by the Grains Research and Development Corporation (GRDC) with the Queensland Department of Agriculture and Fisheries (DAF), and CSIRO and is available on the ARM Online website.

The online decision support tool, hosted by the University of Southern Queensland, was developed after research trials across the northern grain region found applying deep-P on soil deficient in phosphorus at depth paid dividends for growers with yield increases of five to 10 per cent or more at most sites.

The application of deep-P is quite different to other nutrient management decisions as it is a longer-term decision due to initial cost of application and phosphorus fertiliser having benefits that can last many seasons.

However there are risks due to unknown future season types. The grains industry wanted to be able to answer the question “how much phosphorus and how often?” The Deep-P Calculator provides a range of outputs that confidently answers this question for growers’ individual paddocks.

DAF senior development extension officer Jayne Gentry said the on-ground research led by Associate Professor Mike Bell from the University of Queensland was merged with sophisticated bioeconomical modelling and ground-truthed with growers and agronomists.

The result was an easy-to-use tool that calculates the economics of various application rates of phosphorus in different crop rotations.

“The deep-P calculator incorporates soil water-holding capacity, rainfall, machinery and fertiliser costs, crop value, nitrogen levels (nitrogen constraints will mask a phosphorous response) and crop rotation to calculate the economic benefits over a range of deep-P application rates and seasonal outcomes,” she said.