Linking Soil Phosphorus to Dissolved Phosphorus Losses in the Midwest

Abstract

Core Ideas Soil test phosphorus remains an important factor in studying dissolved reactive P loss. Identifying higher risk fields with STP could inform future management practices to reduce DRP loss. STP was linearly related to DRP concentration loads in tile‐drained fields. Monitoring STP in addition to implementing other BMPs should be considered to decrease DRP loss. 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.

Development of phosphorus sorption capacity‐based environmental indices for tile‐drained systems

“…Therefore, this study further highlights the urgent need identified by Duncan et al. (2017) to reanalyze the agronomic recommendations where the buildup or maintenance approach to fertilizer applications may turn soils into P sources, exacerbating DRP losses to surface waters.…”

“…Duncan et al. (2017) found that Ohio soils with STP values above the regionally recommended agronomic critical STP (Vitosh et al., 1995) were more likely to lose DRP at annual concentrations above the 0.05‐mg P L −1 USEPA‐mandated threshold (USEPA, 2017). Therefore, this study further highlights the urgent need identified by Duncan et al.…”

A Global Perspective on Integrated Strategies to Manage Soil Phosphorus Status for Eutrophication Control without Limiting Land Productivity

“…Legislation to help reduce STP levels to the agronomic optimum has been generally slow to implement despite widespread eutrophication problems, and there is a lack of general guidelines on ways to manage a reduction in STP and the amount by which to reduce it. Even if soil P concentrations were reduced to the agronomic optimum, it is not clear whether this is sufficient to reduce P concentrations in runoff sufficiently to help alleviate eutrophication problems (Cassidy et al, 2017; Duncan et al, 2017). The concentrations of SRP or total P required to limit algal growth in flowing and standing waters are extremely low (20–100 μg L −1 ) in relation to the variably high concentrations of P (often >1–2 mg L −1 ) in runoff from agricultural soils (Chambers et al, 2012; Withers and Bowes, 2018).…”

Watershed‐scale phosphorus balances to establish reasonable water quality expectations

“…When phosphorus inputs into the watershed are greater than deliberate phosphorus outputs, either ∆P or the soil test phosphorus (STP) concentrations within the watershed increase or phosphorus is running off the landscape and into the watershed's waterways. Research has demonstrated decreased dissolved phosphorus runoff losses as STP concentrations decline (Duncan et al, 2017). When this is not the case, it could mean that the fertilizer or manure applied was lost to surface runoff before crop utilization.…”