Abstract

Phosphorus is one of the most important nutrients essen- tial for growth of leguminous green manure crops. Since most of the Indian soils are deficient in phosphorus, much attention is paid to phosphate manuring of legumes in recent years. The application of phosphatic fertilizers has been reported to increase the yield of green manure crops by Taylor and Ghose (1923), Ramachandra Rao (1923), Parr and Bose (1944, 1945, 1947), Parr and Sen (1948), Desai and Parr (1949), Russel (1962), Sen and Bains (1951) and Sanyasi Raju (1953). However, the results of experiments conducted in the Agricultural Research Stations at Tirurkuppam and Coimbatore of Tamil Nadu (Anon 1952 to 1953) and the work done under the 1.C.A.R. Scheme on the uptake of phosphate by legumes at the same stations during the years 1958 to 1963 (Anon 1962-63) have shown no significant increase in green manure yields. Similar conclusions have been reported by Krishna Rao et al (1962) in Andhra State and by Soundararajan (1965) with certain paddy soils from Maharashtra, Madhya Pradesh, West Bengal and Assam. From the foregoing, it is seen that the results regarding the response of green manures to phosphate application are much varied. There is therefore the need to understand better, the utilisation of soil and fertiliser phosphate by green manures and their relation- ship to soil properties with reference to the soils of our State. The tracer technique using radioactive phosphorus (P) is of immense value in this respect and the results of the studies conducted on four important paddy soils of Tamil Nadu with sunnhemp (Crotalaria juncea) as the green manure crop, are reported in this paper.

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