Indian Institute of Soil Science Indian Institute of Soil Science

भाकृअनुप-भारतीय मृदा विज्ञान संस्थान


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Fertilizer Phosphorus: Scope for Saving

Phosphorus (P) is one of the essential plant nutrients playing an important role in food and nutritional security of a country. Most of the Indian soils are low in available P and its application helps in increasing the crop productivity to a very large extent. However, because of its high reactiveness, it is fixed in the soil. In alkaline soils it is fixed as calcium phosphate (DCP, TCP, apatite, etc.) while in acid soils it is converted into non-labile aluminum and iron P. Long- term fertilizer experiments (LTFE) of AICRP under ICAR-IISS have revealed that, continuous application of P fertilizers enhanced available P from 9 kg to 73 kg ha-1 in inceptisol of Ludhiana; 8.4 to 35 kg ha-1 in vertisol of Jabalpur; and from 12 to 153 kg ha-1 in Alfisol of Ranchi. The soil fertility maps developed by the ICAR-IISS, Bhopal have indicated that some districts which were earlier categorized as low in available P have now become medium or high in P; the districts which were earlier medium in the available P content have reached to very high P category. Majority of P fertilizers or their raw materials are imported and the cost has been on rise with time thereby increasing the cost of cultivation. Thus, to decrease the burden on foreign exchequer due to their import and to reduce the cost of cultivation, it is very pertinent to find out strategies to mobilize and reutilize the immobilized P in soil. Results from AICRP on LTFE have clearly revealed very high P accumulation in soils of Punjab; and, based on field trails, prescribed either no or half of the recommended dose of P fertilizer application. In India, nearly 50 million hectares area is under acid soils, out of which 25 million ha is under different field crops, where, P is a major yield limiting factor. Application of organic materials (FYM or green manures) helps in the mobilization of soil P. Apart from this, crop residue is another organic source not only for P, but also for K and N during crop growth. Studies at ICRISAT have also demonstrated that addition of crop residues, FYM and green manure in acid soil increases the availability of P in soil. Further, the long-term studies have revealed that application of organic manure not only moderates the soil conditions but also mobilizes recalcitrant soil P which meets P requirement of the crops. Reduction in P fertilizers dose not only increase cost: benefit ratio of the farm, but also reduce the P import. Primary data generated from AICRP on LTFE across the country for the last 40 years showed that reduction in P application up to 50 per cent in continuous P applied field (20-25 years) did not affect crop productivity at all the places. Thus curtailing P dose in high P soils would enhance P efficiency. As per the FAI (2014) report approximately 3 million tonnes of P fertilizers are used in Haryana, Punjab and western Uttar Pradesh. Reduction in P application to half of the recommended dose would save 1 million tonnes of P which is equivalent to about Rs. 5,000 crore. Use of fertilizer prescription equations emanated from AICRP (STCR) will further help in saving of P-fertilizers in some specific situations. Thus adopting these technologies would enhance P use efficiency and reduce burden on government exchequer towards P fertilizer import.

Dr. Ashok K. Patra
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