Path and Multiple Regression Analyses of Phosphorus Sorption Capacity

Abstract

Soil P saturation indices and P Langmuir adsorption maximum (S max ) 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 S max and develop P saturation indices for 28 Oklahoma benchmark soils and to use path analysis and multiple regression to examine the relationships between S max and soil properties. Soil samples were analyzed for pH, clay content, oxalate extractable P (P ox ), Al (Al ox ), Fe (Fe ox ), and Mehlich‐3 (M3) extractable P (P M3 ), Al (Al M3 ), Fe (Fe M3 ), Ca (Ca M3 ), and Mg (Mg M3 ). The S max value and saturation indices based on oxalate and M3 extractions were determined. The S max value ranged from 34 to 500 mg kg −1 and was highly correlated with clay content ( r = 0.79), organic C ( r = 0.80), Al ox ( r = 0.88), and Fe ox ( r = 0.83). Soil pH was not correlated ( p > 0.05) with S max Path analysis showed significant direct effects ( p < 0.01) between Al ox and S max and between Fe ox and S max but these relationships were highly influenced by indirect effects of Al ox and Fe ox Multiple regression agreed well with path analysis and found that the combination of Al ox and Fe ox were the two most important soil properties related to S max of the soils studied. Significant relationships existed between Al M3 ( r = 0.54) and S max and between Fe M3 ( r = 0.54) and S max Three P saturation indices studied were highly correlated ( p < 0.05) with each other. Our results show that S max of Oklahoma soils may be predicted with oxalate extractable Al and Fe or M3 extractable Al, Fe, and Ca.