Chemistry and Dynamics of P in Indian Soils in Relation to Crop Nutrition

摘要

The phosphorus (P) availability in soil to plant is largely governed by the dynamics of P in soil, which, in turn, is intimately related to its chemistry in soil and hence to the properties of the soil concerned. Such dynamics of P transformations in soils and its fixation and release characteristics are governed primarily by adsorption-desorption as well as precipitation-dissolution reactions in soil. Indeed, the short-term aspect of the relative efficiency/inefficiency of fertiliser-P is governed by adsorption of P onto surface of soil particles, leading to decrease in soil solution P and a decrease in its effective diffusion coefficient in soil solution, which restricts the plant availability of P. The long-term effect is caused by diffusive penetration of P into the adsorbing materials, the reversibility of which is slow, thereby decreasing the efficiency of P fertilisers. The existence of different pools of P in soil and their accessibility to crops and cropping systems in India is recognized by researchers as discussed in this article. A number of issues affecting the plant availability of the native and applied P in soils have been related to the chemistry of the underlying processes in terms of the P buffering capacity of soil, hysteresis effect, as well as the thermodynamic and kinetic parameters, characterizing the P fixation in soil and hence its plant availability. The article also discusses the major phosphatic fertilisers and their reactions in soils as well as the corresponding reaction products, P fertiliser management options in different soil and crop situations, economics of P fertilisation with emphasis on the increasing cost of fertiliser P and hence the need to improve the P-use efficiency in a way that optimizes both crop and economic responses, as well as the need for judicious site-specific P management strategy for ensuring optimum crop yield with lesser environmental footprint.