Direct and Indirect Effects of Soil Properties on Phosphorus Retention Capacity

Abstract

Phosphorus retention ability of soil has been predicted from different combinations of soil properties as a result of significant correlations between these variables. However, a significant correlation between P retention capacity and a soil property does not necessarily imply a significant direct effect of the soil property on P retention. The objective of this study was, therefore, to evaluate the direct and indirect influence of soil properties on P retention capacity of neutral to calcareous soils of Manitoba (Canada). One hundred fifteen archived surface soil samples representing major soils of Manitoba were used for the study. The P retention index (PRI) of these soils was determined by the single‐point adsorption method. The relationships between P retention and soil properties were evaluated by correlation analyses while the direct and indirect influences of these soil properties on P retention were evaluated using the path analysis procedures. Significant correlations (p = 0.05) were observed between PRI and pH; CO32−; organic C; sand content; silt content; clay content; exchangeable Ca (CaEx); exchangeable Mg (MgEx); cation exchange capaciaty (CEC); Mehlich‐3 extractable Ca (CaM3); Mehlich‐3 extractable Mg (MgM3); and oxalate extractable Al (AlOx). However, path analysis showed that only CaM3 D = 0.62), MgM3 (D = 0.26), and AlOx (D = 0.21) had significant direct effects (p = 0.05) on PRI. The significant effect of sand (soil texture) was due to the indirect influence of CaM3 Our results show that the PRI for the neutral to calcareous soils of Manitoba is best predicted from CaM3, MgM3, and AlOx Similar analysis conducted to relate the classical Langmuir adsorption maximum with the properties of a subset of soils also showed CaM3, MgM3, and AlM3 as the soil variables that had significant direct effects on soil's P retention.