Monday, 6 October 2008
George R. Brown Convention Center, Exhibit Hall E
While phosphorus (P) sorption in mineral soils has been extensively studied, P sorption in organic-rich soils is less known. This study was conducted to examine relationships between Langmuir P sorption maxima (Smax) and selected physicochemical properties in soils varying in OM content. The Smax of 72 North Carolina Coastal Plain soils was determined and same soils were analyzed for pH, clay, OM, oxalate extractable P (Pox), Al (Alox), and Fe (Feox), and Mehlich-3 (M3) extractable P (PM3), Al (AlM3), and Fe (FeM3). Along with simple correlation analysis, path analysis was used to examine direct and indirect effects of soil properties on Smax based on oxalate and M3 extractions. In the oxalate path analysis, direct effects of clay, Alox, and Feox on Smax were significant in the order of Alox > clay > Feox while OM showed a unique indirect effect on Smax through metal-OM complexes. A positive relationship between Smax and OM up to 50 g OM kg-1 shifted to a ten-fold lower linear regression slope for soils with OM ≥ 50 g kg-1. This finding suggested that non-crystalline or organically bound Al and Fe in soils with OM ≥ 50 g kg-1 are less accessible for P sorption than in soils with OM < 50 g kg-1. In the M3 path analysis, direct effects of clay, OM, and AlM3 on Smax were significant in the order of AlM3 > OM > clay (p < 0.05) while direct effect of FeM3 on Smax was not significant due to a poor Fe extraction efficacy of M3. Oxalate extractable Al and Fe better accounted for the role of OM-metal complexes in estimating P sorption capacity.