Phosphorus constraints to potential land area cropped under organic and regenerative systems in Australia

Abstract

Context The removal of phosphorus (P) in harvested grain and poor recycling of P creates unique concerns for farming systems that aim to reduce reliance on non-renewable fertiliser inputs, such as ‘regenerative’ farming systems, or for organic grain growers for whom synthetic P inputs are prohibited. Aims and methods We examine gross P budgets across the Australian cropping landscape and explore implications for the land area that could be potentially cropped if all P removed in harvested produce was replaced using domestic recycled P sources. Key results Major cereal, pulse and oilseed crops occupied 21.7 million ha year−1 on average from 2000 to 2018, removing around 136 274 t P year−1. The 27 200 t P in captured animal manure could only sustain around 20% of this area. A further 23%, around 4.9 million ha, could be sustained from sewage and greenwaste resources, but potential pathogens/contaminants limit their current use on organic farmland, and on other farmland when contaminant levels exceed thresholds. Conclusions Development of technologies acceptable to organic certifying agencies to extract P from sewage and greenwaste would expand available resources for organic and regenerative farming and would enable systems to move further towards closed loop nutrient cycling. Ultimately, export of grain overseas results in a large deficit between the 136 000 t P removed annually from fields and domestic recyclable P (around 74 000 t P year−1). Implications Apart from importing rock phosphate-based P or recycled P products, this deficit could only be overcome in the long term by reducing grain exports, or by reducing the concentration of P in exported grain.