Status of Phosphorus and Potassium in the Indian Soils vis-a-vis World Soils

摘要

Phosphorus (P) and potassium (K) are essential for ensuring food security in India as well as worldwide. In acid soils of the world constituting 26% of world's arable soils, low P availability is one of the major causes for poor crop yields. Concurrently over-usage of P application in high runoff and erosion-prone ecosystems has become a significant source of degradation of water resources mainly through eutrophication. Phosphorus deficiency is widespread in the Indian as well as world soils and estimates forecast for no P-reserves by 2050; as such India does not have adequate reserves of rock phosphate posing threat to sustainable crop production. In case of K, total K as well as various forms of K are adequate in majority of the regions of India as well as worldwide. Light textured red and laterite soils dominated by kaolinitic clay are low in exchangeable as well as non-exchangeable K. Because of dynamic equilibrium operating among various forms of K, non-exchangeable pool has been critical in facilitating the luxurious K uptake by crops. Non-existent or scanty application of K-fertiliser in many parts of the country, especially in intensively cropped/rainfed areas, depletion of available K has been reported. In eastern region of the country because of "low" K content, K has started limiting the responses to applied N and P. Therefore the way forward is to address the P deficiency and low P use efficiency and in case of K, to arrest its over-mining. In India, for adoption at farmers' level, the districts/areas/regions with low and medium P or K status are to be addressed with soil test crop response based integrated plant nutrition system (STCR-IPNS) prescriptions along with secondary and micronutrients to various crops and cropping sequences in a holistic way. The GPS/GIS-based soil fertility mapping can enhance the utility of database and its utility among the stake holders. This would avoid either over-usage or under-usage of fertilisers and definitely enhance the use efficiency of applied fertiliser inputs, and ultimately improve the soil fertility and in-turn the crop production.