Release Behaviour of Phosphorus and Its Fractions in Different Phosphorus Status Soils

Phosphorus is essential to all forms of life and its contribution towards aiding the native soil fertility and sustaining it, is well known. With passage of time, P added to soil undergoes transformation into various unavailable forms. Native P compounds, some being highly insoluble are mostly unavailable for plant uptake. The availability of phosphorus to the plants depends on soil properties, soil pH, soluble iron, aluminum and manganese, calcium minerals, organic matter, activities of microorganisms thus availability of P may vary according to soil types. Knowing the changes in P fractions especially in low and in high P status soils is much more important for P availability to plant. Therefore, the release behaviour of phosphorus and its fraction in different P status soils was assessed over 5 weeks under laboratory incubation periods using a sequential fractionation procedure. The results of the experiment revealed that the content of available P and different P fractions were higher in high P status soil as compared to low P status soil. Among the various P fractions, Ca-P was the dominant fraction in both soils. The release of available P was first increased up to 21 and 28 days in low and high P status soil, respectively and the release of different forms of P fractions in both soils increased up to 28 days after incubation and then decreased with further increase in incubation period.