Difference of Phosphorus Fractions and Availability of Different Calcareous Soils

The differences of total P and P fractions of 26 farmland calcareous soils sampled from the basin and hilly regions in middle and midwest parts of Shanxi province and the relations of different P fractions with available P were studied with path analysis to understand the effect of utilization on total quantity,fraction distribution,and availability of P in experimental soils.The results showed that the contents of inorganic and organic P were significantly different between the 26 soils.Ca-P was the chief part in inorganic P and MLOP was the chief part in organic P.The contents of Ca8-P were higher than that of Ca10-P in the greenhouse calcic cinnamon soils,and the contents of Ca2-P,Ca8-P,and Al-P were all much higher than that in the other experimental soils.The contents of MLOP in the greenhouse calcic cinnamon soils were significantly higher than that in the other experimental soils and the contents of LOP and MROP were all relatively higher too.All of the inorganic P factions were significantly positively related to available P,and all organic P fractions but HROP were significantly positively related to available P too.Path analysis further indicated that the direct effect of Ca2-P on available P was significant and the indirect effects of the five other inorganic P fractions on available P through Ca2-P were significant.The direct effects of LOP and MLOP on available P were both significant and both LOP and MROP had significant indirect effects on available P through MLOP,but HROP had neither direct nor indirect effect on available P.Utilization intensity especially fertilization is the major factor that leads to the differences of total quantity and fraction distribution of P in experimental soils.Path analysis is a simple and explicit method for analyzing the effect of different P fractions on soil available P.