Soil test phosphorus and phosphorus balance trends: A county‐level analysis in Ohio

Off‐site transport of phosphorus (P) is a concern with Lake Erie and other Ohio surface waters. Baseline knowledge of and long‐term trends in soil test P (STP) and P balance are important as farmers are under increased scrutiny due to ongoing water quality concerns. The objectives of this work were to examine Ohio county‐level trends in STP, P inputs, P outputs, and P balance. Soil test P data from all 88 Ohio counties were obtained from 1993 to 2015 from the three major soil test laboratories that service Ohio farmers. County‐level P inputs (fertilizer and manure), outputs (crop removal), and balance (inputs minus outputs) were obtained from the International Plant Nutrition Institute's Nutrient Use Geographic Information System database. Regression analysis techniques were used to identify long‐term trends. Across multiple percentile levels, 44–63% of Ohio counties had decreasing long‐term STP trends, while 11–21% had increasing trends. Eighty‐four percent of Ohio counties had a negative P balance in 2014, meaning P outputs exceeded P inputs. Decreasing long‐term trends in STP and P balance, suggest that farmers are taking steps to manage P inputs and STP, which should result in reduced P runoff concentrations.