The Inorganic Soil Phosphorus Fractions and Available P as Influenced by Greenmanuring, Cropping and P Fertilization

Laboratory and greenhouse experiments were conducted on ten soils (eight alkaline and two acid soils) to study the effect of added P, greenmanuring and cropping on Olsen's P and inorganic soil P fractions. The amount of Olsen's extractable P decreased during first forty days but increased thereafter. Extractable P was higher in green manured soil samples, the effect being higher in Nathupur sand. P fertilization resulted inincrease in all the estimated P fractions. Soils testing low in Olsen's P had a greater percentage increase in saloid P. In alkaline soils, added P transformed more into saloid P and Ca-P while in acid soils, higher amount of Al-P and saloid P was formed. Due to green manure addition, saloid P increased at the expense of other P fractions. Cropping with maize increased saloid P and Ca-P but decreased Fe-P and Al-P. Regression analysis indicated that maize crop utilized more of saloid P and Al-P.