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Linking soil phosphorus to dissolved phosphorus losses in the Midwest
- Emily W. DUNCAN, Mark R. WILLIAMS, Greg LABARGE, Lindsay A. PEASE, Norman R. FAUSEY, Kevin W. King, Douglas R. Smith
- agricultural runoff, agricultural soils, fertilizer application, highlands, losses from soil, nutrient content, phosphorus, phosphorus fertilizers, pollution load, regression analysis, risk, screening, water quality, Ohio
- Harmful and nuisance algal blooms resulting from excess phosphorus (P) have placed agriculture in the spotlight of the water quality debate. Sixty-eight site years of P loading data (combined surface runoff and tile flow) from 36 fields in Ohio were used to see if a soil test P (STP) concentration could be identified that allowed P application while still meeting recommended loss thresholds. Regression analysis revealed that P application to soils with STP concentration in the “critical level” range would result in P losses above the recommended Annex 4 thresholds. In addition, fertilizer application increased the risk of dissolved reactive P (DRP) loss as compared to years in which fertilizer was not applied. We determined that STP was a good screening method to identify fields that are at risk for greater P loss, but STP alone was not a good predictor of DRP loss, suggesting that a more holistic approach that includes upland management, edge-of-field practices, and in-stream approaches will be required to decrease DRP loading.