Potential of existing strategies to reduce net anthropogenic inputs of phosphorus to land in the United States

Abstract

Improving phosphorus (P) management is important for both ecosystem protection and avoiding mineable P scarcity. In order to inform the development of impactful solutions to both of these issues, we assessed the potential of several specific management strategies to reduce demand for new mined P in fertilizers and supplements for livestock, thereby reducing net P inputs to land. The strategies assessed were variable rate fertilizer (VRF) application, improvements to P digestibility for livestock, efficient utilization of manure and wastewater treatment (WWT) P, and elimination of avoidable domestic food waste. The potential of these strategies to reduce net anthropogenic P inputs was assessed at the county level for the coterminous US using the commodity-specific net anthropogenic P and nitrogen inputs (CSNAPNI) model. The largest contributions toward eliminating NAPI in the US can come from efficient manure utilization either at national (30%–50% NAPI reduction) or county-level (21%–30% NAPI reduction). However, widespread adoption of VRF (10%–41% NAPI reduction), and all other strategies considered (5% or greater NAPI reductions each) could make significant contributions. In combinations of strategies that included VRF or P digestibility improvements, negative feedbacks occurred. VRF reduced demand for fertilizer, thereby reducing the potential for efficient manure and WWT P utilization at the county-level. P digestibility improvements in poultry and swine diets reduced the expected production of recoverable manure P by 36%, decreasing the total manure P that could be used to replace mined P fertilizer. However, P digestibility improvements also reduced county-level excess manure P by 25%. Prior studies have focused on quantifying P inputs or the potential of in-situ best management practices to reduce losses to water, but strategies to reduce P inputs are understudied.