Subsoil phosphorus (P) deficiency costs growers in Queensland and Northern NSW around $80–100 million each year in reduced yield. Deep P fertiliser applications into the subsoil can improve yield but are a long-term decision. They are moderately expensive and returns are not immediate. The Deep-P calculator helps Northern region growers decide if deep P will provide an economic benefit.
How it works
- paddock properties such as crop rotation and P levels, and
- economic data such as grain and fertiliser price.
The Deep-P calculator estimates:
- optimal deep P application rate
- expected $/ha net benefit
- internal rate of return
- payback probability.
Users can compare the financial benefits of the P-rate through average, poor, and excellent seasons. Growers can run different scenarios that might affect the return on investment.
Optimum P rate
How season might affect the optimum P rate net benefit.
The tool is based on a number of assumptions relevant to Queensland and Northern NSW:
- Starter P is applied
- 50% P is used from the topsoil, and 50% from subsoil
- P in stubble is not returned to the subsoil P pool.
There are other factors used in the model that will improve as research continues. These include the critical soil P values that affect yield, the degree of yield reduction caused by deep P deficiency, and how P cycles between soil pools.
The deep P calculator should be used as a decision support tool, rather than a strict cost-benefit analysis. Used properly, the tool can help growers quantify the potential economic benefits and payback period for deep P applications.
The online Deep-P calculator tool is available here. A video on how to use it is included with the calculator.