Distribution of inorganic P fractions and critical limits of available P in rice soils of Mizoram

The available P in some of the rice soils of Mizoram was evaluated by various methods. The results of the study revealed that the sequential occurrence of various inorganic P fractions followed the order: RS-P > Fe-P > Al-P > Ca-P > S-P. Among the P availability indices, highest extractable P was recorded with Bray P₂ method (25.93 kg ha⁻¹) followed by North Carolina method (21.58 kg ha⁻¹), while it was lowest with Bray P₁ reagent (8.36 kg ha⁻¹). Aluminium bound P was found to be the major contributing P fraction to the available P pool as extracted by Bray's and Olsen's methods, whereas Fe-P was the main contributor to the available P as estimated by North Carolina method and Ca-P in respect of Saunder's-P. The Al-P had significant influence on the dry matter yield as well as P nutrition of rice. Of all the P availability indices, Bray P₁ method found to be much superior to the other methods as it had highly significant relationship with all the biological indices with a critical limit of 8.2 kg P ha⁻¹ and hence it can be used for fertilizer adjustments for rice.