Path and Multiple Regression Analyses of Phosphorus Sorption Capacity

Abstract

Soil P saturation indices and P Langmuir adsorption maximum (Smax) are two environmental soil tests that provide valuable information for the proper management P in soils to avoid the overapplication of P. The objectives of this study were to determine Smax and develop P saturation indices for 28 Oklahoma benchmark soils and to use path analysis and multiple regression to examine the relationships between Smax and soil properties. Soil samples were analyzed for pH, clay content, oxalate extractable P (Pox), Al (Alox), Fe (Feox), and Mehlich-3 (M3) extractable P (PM3), Al (AlM3), Fe (FeM3), Ca (CaM3), and Mg (MgM3). The Smax value and saturation indices based on oxalate and M3 extractions were determined. The Smax value ranged from 34 to 500 mg kg−1 and was highly correlated with clay content (r = 0.79), organic C (r = 0.80), Alox (r = 0.88), and Feox (r = 0.83). Soil pH was not correlated (p> 0.05) with Smax Path analysis showed significant direct effects (p< 0.01) between Alox and Smax and between Feox and Smax but these relationships were highly influenced by indirect effects of Alox and Feox Multiple regression agreed well with path analysis and found that the combination of Alox and Feox were the two most important soil properties related to Smax of the soils studied. Significant relationships existed between AlM3 (r = 0.54) and Smax and between FeM3 (r = 0.54) and Smax Three P saturation indices studied were highly correlated (p< 0.05) with each other. Our results show that Smax of Oklahoma soils may be predicted with oxalate extractable Al and Fe or M3 extractable Al, Fe, and Ca.