Developing and testing an analysis framework for long-term fertiliser decisions: Deep-P Calculator

Grain growers in Queensland and northern New South Wales are facing a new challenge in crop nutrition management: phosphorus (P) depletion of many soils below 10 cm. Research has indicated potential yield benefits from replenishing P in sub-surface layers (referred to as a ‘deep-P’ application). However, it was unknown if amelioration had economic merit. The fundamental question of deep-P placement is ‘how much P (what rate) should be applied and how often (at what frequency)?’ A program of close consultation was implemented, with leading scientists, fertiliser industry researchers, advisors and growers all contributing knowledge. Focus groups, a literature review and case studies were conducted. The iterative process implemented by this project effectively utilised various extension techniques to engage industry and leading researchers. This knowledge was used to develop a framework to produce a web-based tool that answers the fundamental question of deep-P fertiliser placement, ‘how much P and how often?’