Phosphorus Fractions under Different Cropping Systems

Phosphorus is the tenth most abundant element in the earth's crust and its average content is nearly 0.12 per cent. In lithosphere, it always occurs in the pentavalent oxidation state. Phosphorus is an essential element for plant growth. Therefore, maintenance of an adequate amount of soil phosphorus through application of inorganic and/ or organic phosphorus is critical for the sustainability of cropping systems.Phosphorus use efficiency in agricultural systems is very low, with only 10-20% of fertilizer P used by crops. Knowledge of amount of each fraction and their relationship with soil characteristics is very useful in assessing phosphorus nutrition of plants. Since various P fractions and their contribution to available phosphorus provide useful information in assessing the available P status of soils and various forms of soil phosphorus have different solubility under varying soil condition. Available P content increases with the application of P. The increase in available P is a function of certain physical and chemical soil properties, such as clay, organic carbon, Fe, Al and calcium carbonate contents.