Comparative Efficiency of Sulphur Fortified Mono-Ammonium Phosphate.
N.S. Pasricha, Potash Research Institute of India, 219 - C, Bhai Randhir Singh Nagar, Block C, Ludhiana, India and Ramendra Singh, Mosaic India Pvt. Ltd.,, DLF City, Gurgaon, 122002, India, Gurgaon, India.
Sulphur is increasingly becoming a limiting factor in crop production in highly intensive irrigation agriculture systems in the Indo-Gangetic alluvial soils. Decrease in S additions to the soil with decreased use of S containing P and N fertilizers is the major reason for its deficiency. Its use in balanced fertilization for yield and quality can be more effectively assured if S is a constituent part of fertilizers containing major plant nutrients like N and P. Sulphur containing Mono-Ammonium Phosphate (MAPS) is a promising complex fertilizer of this kind with N-P2O5-K-S composition of 13-33-0-15, with 50% S present in elemental form and rest as SO4. Therefore, several field experiments were conducted across Indo-Gangetic plain on research farms and farmer's fields during 2001-03 to evaluate its efficiency vis-à-vis diammonium phosphate (DAP, with and without S additions). MAPS at similar doses of P (N-compensated), gave higher grain yields of soybean, maize and wheat than DAP. Additional yields could be attributed to S contained in MAPS, because when S in DAP was compensated, both sources proved equally effective. Relatively higher effectiveness in terms of P and S recovery from MAPS has important environmental implications as it leaves lesser amounts of unused nutrient in soil. Acidification of micro-zones in rhizosphere due to oxidation of elemental S to SO4 could be the reason for improved recovery of P and S from MAPS. Acidifying effect of elemental S present in intimately impregnated form in the paletted MAPS helped in prolonging the plant availability of P in these, otherwise P– fixing alkaline soils. In DAP+S, S (50% elemental form + 50% as SO4 from gypsum) on physically mixing may not be in intimate contact with P in soil where its uptake could be influenced when S oxidation causes a decrease in pH in the micro-zones of soil rhizosphere.