1. LU YUKUN, Acta Pedologica Sinica, 10 (1962) 12.
2. LIU XINGDE Hubei Agric. Sci. 4 (1963) 28.
3. N. P. ARKHIPOV, Soil Fertilizer, 3 (1984) 39.
4. I. A. PIVOVAROVA, Progress Soil Sci., 3 (1984) 26.
5. K. MENGEL, Plant Nutriology, Beijing Agricultural Publisher, Beijing China, 1987, p. 400.