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Nutrient Management & Soil & Plant Analysis

Estimating Dissolved Phosphorus Concentrations in Runoff from Three Physiographic Regions of Virginia

^a Dep. of Plant and Soil Sciences, Oklahoma State Univ., 367 Agricultural Hall, Stillwater, OK 74078
^b Dep. of Plant and Environmental Sciences, New Mexico State Univ., Las Cruces, NM 88003
^c Dep. of Crop, Soil, and Environmental Sciences, Virginia Tech, 330 Smyth Hall, Blacksburg, VA 24061
^d USDA ARS, PSRMRU, 3702 Curtin Rd., State College, PA 16802

^* Corresponding author (chad.penn{at}okstate.edu)

The relationship between STP (soil test P) and DRP (dissolved reactive P) in runoff has been shown to vary with soil type due to differences in soil properties. The purpose of this study was to determine if soil tests could indirectly take into account differences in soil properties and thus provide one relationship with STP and runoff DRP among a variety of soil types. Nine different soil types were sampled from four different fields to provide a range in STP. Unamended soils were packed into runoff boxes for use in a rainfall simulation study. All soils were analyzed for P, Al, and Fe using various extractions, and correlated to runoff DRP concentrations from all soils when grouped based on soil type and physiographic region. Slopes and intercepts were unique to soil type for the STP vs. runoff DRP relationship among all soil P tests except for WSP (water-soluble P) slopes, resulting in an overall universal slope of 0.0125 mg DRP L^–1, which agrees with past studies. The y intercepts from the soil WSP vs. runoff DRP relationship were well related to soil clay content (negative relationship) in addition to the fact that Coastal Plain soils had a significantly greater y intercept than Piedmont and Ridge and Valley soils when grouped by physiographic region. This suggests that Coastal Plain soils possess a greater potential for releasing DRP into runoff compared with Ridge and Valley and Piedmont soil at equivalent WSP values. This study provides a means with which to estimate potential runoff DRP concentrations by use of soil WSP and clay content.

Abbreviations: DPS, degree of phosphorus saturation • DRP, dissolved reactive phosphorus • Fe-strip P, iron strip extractable phosphorus • HIV, hydroxy-interlayered vermiculite • M1-P, Mehlich-1 phosphorus • M3-P, M3-Al, and M3-Fe, Mehlich-3 extractable phosphorus, aluminum, and iron, respectively • P_ox, Al_ox, and Fe_ox, ammonium oxalate extractable phosphorus, aluminum, and iron, respectively • Psat_M3 and Psat_ox, phosphorus saturation ratio as determined by Mehlich 3 and ammonium oxalate, respectively • STP, soil test phosphorus • WSP, water-soluble phosphorus