1. Aiyer, S. P...Proc. Ind. Acad. Sci., 1946,23 B, 165.
2. —————.. Ibid., 1948,28 B, 202.
3. Hoagland, D. R. and Martin, J. C.Soil Sci., 1933,36, 1.
4. Ishizuka, Y. and Tanaka, A.J. Sci. Soil and Manure, Japan, 1951a,22, 7.
5. —————.. Ibid., 1951b,22, 103.