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DIVISION S-6—SOIL & WATER MANAGEMENT & CONSERVATION

Modifying FHANTM 2.0 to Estimate Phosphorus Concentrations in Runoff from Mid-Atlantic Coastal Plain Soils

^a USDA-ARS-ANRI-AMBL, B-163F Rm. 5, BARC-East, 10300 Baltimore Ave., Beltsville, MD 20705
^b Dep. of Plant and Soil Sciences, 152 Townsend Hall, Univ. of Delaware, Newark, DE 19717
^c USDA-ARS Northwest Irrigation and Soils Lab, 3793 North, 3600 East, Kimberly, ID 83341
^d Dep. of Crop Soil Environmental Sciences, Smyth Hall, Blacksburg, VA 24061

* Corresponding author (pvadas{at}anri.barc.usda.gov)

Phosphorus lost from agricultural soils has been identified as a nonpoint source pollutant of surface waters in Delaware and throughout the Mid-Atlantic Coastal Plain. The Field Hydrologic and Nutrient Transport Model (FHANTM) 2.0 can help identify areas with a high potential for P loss, but the method used to estimate P concentrations in runoff waters needs reevaluation. The equation P_d = KP_otW^ß has been proposed to predict P desorption from soil to runoff. To test this equation for use in Delaware and the Mid-Atlantic Coastal Plain, we conducted rainfall simulations for 14 Delaware and Maryland soils packed into 5 by 20 by 100 cm boxes at a rainfall intensity of 7.5 cm h^-1 and a slope of 5% for 30 min. We collected all runoff and measured an average soluble P concentration in runoff for the entire simulation. We predicted P concentrations using the above equation and compared them with measured values. Predicted values were well correlated to measured values (r² = 0.78), but P concentrations were overpredicted by an average of 20 times. After we added a calibration factor to the equation based on the amount of sediment lost in runoff during the rainfall simulation, measured and predicted soluble P concentrations exhibited a nearly 1:1 relationship. Results suggest that eroded sediment in runoff may resorb P from the runoff solution, causing the desorption equation to overpredict soluble P concentrations in runoff.

Abbreviations: Al_ox, acid ammonium oxalate-extractable Al • B, extraction coefficient used in FHANTM 2.0 • (C_av)_p, quantity of P in the topsoil available for runoff used in FHANTM 2.0 • (C_w)_p, concentration of P in runoff used in FHANTM 2.0 • EDI, effective depth of interaction • Fe_ox, acid ammonium oxalate-extractable Fe • FHANTM 2.0, field hydrologic and nutrient transport model, Version 2.0 • ICP-AES, inductively coupled plasma atomic emission spectroscopy • K, empirical constant in P desorption equation • K_d, partitioning coefficient used in the FHANTM 2.0 model • OC, organic C • P_o, initial concentration of desorbable P in P desorption equation • PL, poultry litter • STP, soil test P • t, Time (min) of P desorption in P desorption equation • TMDL, total maximum daily load • UDSTP, University of Delaware Soil Testing Program • W, water/soil ratio (cm³ g^-1) during P desorption in P desorption equation • , empirical constant in P desorption equation • ß, empirical constant in P desorption equation

This article has been cited by other articles:

				C. J. Penn, G. L. Mullins, and L. W. Zelazny Mineralogy in Relation to Phosphorus Sorption and Dissolved Phosphorus Losses in Runoff Soil Sci. Soc. Am. J., August 4, 2005; 69(5): 1532 - 1540. [Abstract] [Full Text] [PDF]

				J. L. Havlin Technical basis for quantifying phosphorus transport to surface and groundwaters J Anim Sci, January 1, 2004; 82(13_suppl): E277 - 291. [Abstract] [Full Text] [PDF]