Effect of rock phosphate, superphosphate and their mixtures with FYM on soybean and soil-P pools in a typic hapludalf of Meghalaya

Abstract

A field experiment was conducted for five consecutive years on a phosphorus-deficient Typic Hapludalf to study the efficiency of SSP (single superphosphate), RP (rock phosphate) and their mixtures along with FYM on soybean. The yield, P uptake, protein and oil content of soybean increased significantly with P alone or with FYM irrespective of sources over control and maximum values were recorded with SSP @ 60 kg P2O5 ha−1 + FYM, followed by SSP + RP (1:1) @ 60 kg P2O5 ha−1 + FYM. The organic carbon, available P and N in soil increased by 11.5 to 35.4, 23.1 to 199 and 7.5 to 15.5%, respectively over the initial status in various treatments after 5 years of cropping. The fate of applied P in soil indicated that total and organic P increased significantly with different sources of applied P and organic P contributed 48.9 to 53.7% of total P. Among inorganic fractions, significant increase in saloid-P, Al-P, Fe-P and Ca-P but depletion in reductantsoluble and occluded-P was observed. The P use efficiency was higher at lower doses of applied P with the maximum value (21.3%) recorded with SSP @ 30 kg P2O5 ha−1 + FYM treatment. Application of 60 kg P2O5 ha−1 through SSP alone or with FYM was most efficient dose for production of high quality soybean and forms of P build up followed by 60 kg P2O5 ha−1 as SSP + RP (1:1) with or without FYM in acid Alfisol of Meghalaya.