Using soil survey data for series-level environmental phosphorus risk assessment

Choosing soil series scale for assessing phosphorus (P) retention and release characteristics may help relate routinely collected series-specific soil survey data with P retention and aid in designing series-specific P management strategies. Phosphorus retention and release characteristics of pedons collected from two benchmark upland soil series (Berks and Monongahela) and two floodplain (Huntington and Lindside) soil series of West Virginia (USA) were assessed by evaluating P sorption capacity (PSC, Langmuir method) and its major determinants, and effect of different levels of degree of P saturation (DPS) and soil test P (STP, Mehlich-1 P) on the desorbable P (0.01 M CaCl₂-extractable) concentrations. The PSC of the two floodplain soils, Huntington and Lindside, was similar but lower than PSC of upland Berks and Monongahela soils. However, thicker A horizons of Huntington and Lindside soils may compensate for their lower PSC. The B horizons exhibited higher PSC than A horizons. However, slow permeability and thinness of such horizons may discount the higher PSC effect. Relationship of PSC with ammonium oxalate extractable Al (AOX-Al) and Fe (AOX-Fe), dithionite–citrate–bicarbonate extractable Al (DCB-Al) and Fe (DCB-Fe), total C, clay content, and pH [soil:water ratio 1:1 (pH-water) and soil:0.01 M CaCl₂ solution ratio 1:2 (pH-CaCl₂)] showed that in general all except Fe and total C influenced PSC significantly. Aluminum associated with crystalline clay minerals particularly affected PSC, especially of upland soils. Most of the soils did not release considerable P even beyond the conventional critical limit of 25 % DPS for well-drained soils. DPS-desorbable P relationships, though, reflected poor reliability of DPS as an environmental index. At a given DPS and STP, surface horizons released more P than their subsurface counterparts and thus reflected the net sink character of subsurface horizons. Most of the soils did not show considerable release of P even beyond agronomically high STP levels (>23 mg kg^?1). The study provides an economical alternative to time and money-intensive lysimetric studies for assessing subsurface P loss. It reveals the workability of integrating environmental P studies with soil survey data and superiority of integrated assessment of environmental indices of P over the use of any single index.