Mineralogy in Relation to Phosphorus Sorption and Dissolved Phosphorus Losses in Runoff

the relationship between some measure of soil P and runoff dissolved P (Gburek et al., 2000; Coale et al., The relationship between soil test P (STP) and dissolved reactive 2002; Vadas et al., 2002). However, recent research has P (DRP) in runoff has been shown to vary with soil type due to differences in soil properties. This study was conducted to determine shown that this relationship will vary based on soil type the effect of mineralogy on P sorption behavior and DRP losses in (Sharpley, 1995; Sharpley et al., 1996; Pote et al., 1999; runoff using simulated rainfall. Nine different soil types were sampled Torbert et al., 2002). Therefore, an understanding of from four different fields to provide a range in STP. Unamended soils how different soil properties affect P concentrations in were packed into runoff boxes for use in a rainfall simulation study solution, leachate, and runoff is necessary to determine (7.5 cm h 1 for 30 min). A mineralogical analysis and adsorptionthe effect of soil type on the relationship between STP desorption isotherm was conducted on one representative sample and runoff P losses. from each soil type. Results indicated that P retention for adsorption One of the most influential soil properties in regard and desorption in separated clay fractions and whole soils was well to P sorption is soil clay content, which has often been correlated to Al bearing minerals such as hydroxy-interlayered-vercorrelated to P sorption parameters (Fox and Kamprath, miculite (HIV), gibbsite, and amorphous Al. However, P retention was negatively related to kaolinite content, which was also confirmed 1970; Loganathan et al., 1987; Solis and Torrent, 1989; by isotherms conducted on pure clay minerals. Based on the isotherm Bennoah and Acquaye, 1989). However, it is the high results, all soils were split into two groups based on the ratio of HIV/ surface area and presence of various P sorbing minerals kaolinite. Soils with a HIV/kaolinite ratio 0.5 had a significantly that results in the common observation that high clay lower concentration of DRP in runoff for a given soil water soluble soils often adsorb more P compared with coarse-texP level compared with soils with a ratio 0.5. tured soils (Loganathan et al., 1987). Phosphate sorption is attributed primarily to ligand exchange reactions between hydroxyls exposed on surfaces of minerals and P losses from agricultural soils to surface the phosphate molecule in soil solution. The mineralogy waters have been of recent public concern due to of a soil will take into account both surface area (due to the negative effects of increased P concentrations on the fact that most phyllosilicates and oxides/hydroxides surface water quality (Sharpley et al., 2000). Agriculeach have a specific range in surface area) and the Fe/Al tural soils considered high in P can cause significant content of a soil. Therefore, analysis of mineral types movement of P into waterways in the form of dissolved P and content should provide an estimate of potential and particulate P (Sims, 1998). Although erosion control P-sorption sites (Jones, 1981; Sposito, 1984; Parfitt, has been shown to decrease total P and particulate P 1989) and the potential for a soil to release P into runoff. losses (Quinton et al., 2001), significant concentrations Variation in surface area and differences in the ability of dissolved P can occur in runoff from soils where of different minerals to retain P should be responsible erosion is kept at a minimum, particularly from soils that for the observed differences in the relationship between are high in STP or having received recent P applications soil P levels and runoff dissolved P concentrations (Sharpley et al., 1978; Daniel et al., 1994; Daverede et among soil types. al., 2003). Dissolved P concentrations in surface runoff Although there has been significant work conducted from unamended soils are typically much less relative on P adsorption in regard to soil mineralogy, few minerto P losses from soils that have recently received P alogical studies have been performed in conjunction amendments (Moore et al., 2000), However, significant with P desorption isotherms or runoff studies. The obdissolved P losses can occur from high P, nonamended jectives of this study were to (i) investigate the role of soils (Pote et al., 1996; Schroeder et al., 2004). soil mineralogy on P adsorption/desorption behavior in With the established link between STP concentrations Virginia soils, and (ii) relate soil mineralogy and adsorpand dissolved P losses in runoff (Sims et al., 2002), many tion–desorption behavior to potential dissolved P losses model and risk indicators of P loss have incorporated in surface runoff from Virginia soils. MATERIALS AND METHODS C.J. Penn, USDA-ARS, PSWMRU, 3702 Curtain Rd., University Park, PA 16802; G.L. Mullins and L.W. Zelazny, Dep. of Crop, Soil, Nine soil types were chosen to represent the major agriculand Environmental Sciences, Virginia Tech, 330 Smyth Hall, Blackstural soils of the Piedmont, Coastal Plain, and Ridge and burg, VA 24061. Received 2 July 2004. *Corresponding author Valley physiographic provinces of Virginia. Among each soil ([email protected]). type, four different soils (i.e., locations) were collected to provide a range in Mehlich-1 extractable P (M1-P) from below Published in Soil Sci. Soc. Am. J. 69:1532–1540 (2005). Pedology, Soil Mineralogy, Soil Chemistry, Soil & Water Management & Conservation Abbreviations: DRP, dissolved reactive P; HIV, hydroxy-interlayered vermiculite; M1-P, Mehlich-1 phosphorus; subscript [ox], ammonium doi:10.2136/sssaj2004.0224 © Soil Science Society of America oxalate extractable; STP, soil test phosphorus; WSP, water-soluble phosphorus. 677 S. Segoe Rd., Madison, WI 53711 USA 1532 Published online August 4, 2005