1. Adriano, D. C., A. L. Page, A. A. Elseewi, A. C. Chang, and I. Straughan. 1980. J Environ Qual 9: 333–344.
2. Ahl, T., and E. Jönsson. 1972. Ambio 1: 66–70.
3. Alt, D., and W. Schwarz. 1973. Plant Soil39: 277–283.
4. Archer, F. C. 1980. Minist Agric Fish Food(Great Britain) 326: 184–190.
5. Arora, C. L., V. K. Nayyar, and N. S. Randhawa. 1975. Indian J Agric Sci45: 8085.