U.S. agricultural phosphorus partial nutrient balances and temporal nutrient use trends within Minnesota.

Abstract

The intensity of phosphorus use in United States food production systems has raised concerns about the use-efficiency of this non-renewable resource. Past research modeling the material flows of phosphorus has found that approximately one quarter of all phosphorus losses occur within the crop cultivation phase of phosphorus’s life cycle. Imbalanced phosphorus inputs and output can result in accumulations of phosphorus within the soil environment and possible phosphorus flows out of cropland. Improvements in phosphorus management are important because excess phosphorus input into the environment can drive hypoxia and cause eutrophication in freshwater, marine, and estuary aquatic ecosystems. The research being conducted in this study builds upon previous material flow analysis (MFA) research and quantifies the partial nutrient balance of phosphorus. Research conducted in this study uses nutrient use efficiency metrics to quantify the ratio of nutrient applied and crop biomass removal. Calculations of phosphorus partial nutrient balances measure system nutrient use sustainability, specifically by calculating the ratio of biomass removal to nutrient input application. Partial nutrient balances were calculated for 1997 within 48 states and within 84 Minnesota counties in 1987, 1992, and 1997. Research conducted in this study has found that phosphorus inputs at the state and county level exceed annual crop harvest, except for a few instances when nutrient removal exceeds inputs. The temporal analysis of partial nutrient balance change has determined that the balance of phosphorus removal and input has improved from 1987 to 1997. These results show that soil fertility, crop uptake, and nutrient application vary and agricultural land management may be improved to better balance crop removal with nutrient inputs.