An environmental soil test to estimate the intrinsic risk of sediment and phosphorus mobilization from European soils

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AbstractMethodologies are required to help identify soils that are vulnerable to both suspended sediment (SS) and phosphorus (P) transfer in land run‐off to combat the adverse impacts of agriculture on water quality. A laboratory test that quantifies dispersed particles and associated P in the same suspension was developed to estimate the potential mobilization of SS and P due to rainfall impact from 26 European soils with varied soil physical and chemical properties and P inputs. The test recovers an aliquot of the clay and fine silt (<20 μm) fraction of soils after gently shaking in distilled water for 1 min at a 1:50 soil‐to‐solution ratio and measures the dry residue, total P and dissolved (<0.45 μm) P content. The results of the test correlated well (r2 = 0.7–0.8) with the amounts of SS, total P and dissolved P in overland flow generated by indoor simulated rainfall (intensity 60 mm h−1 for 30 min and a 5° slope). Variation in SS and particulate P mobilization was linked to soil pH, organic matter (or clay) and sesquioxide content, although a multiple regression analysis showed these factors accounted for no more than 55% of this variation. Ranking showed that the soils generating the most sediment did not necessarily generate the most P loss due to variable degrees of P enrichment of the particulate fraction and variable contributions of dissolved P. Particulate P enrichment was related weakly (r2 = 0.5) to soil total P, while dissolved P fractions were predicted well (r2 = 0.8–0.9) by conventional soil P tests (water and Olsen). The environmental soil test has a potential role in identifying the comparative risk of sediment and P mobilization from critical source areas connected via both surface and subsurface pathways, and in providing data for incorporation into models predicting sediment and P transfer at the field and catchment scale.