1. Brandenburg E 1960 Landwirtsch. Forsch. 3, 107–133.
2. Burns G R 1967 Sulphur Inst. Techn. Bull. 13, Washington.
3. Davies L M 1974 Sulfur Inst. J. 10, 6–10.
4. Finck A 1982 Fertilizers and Fertilization. Verlag Chemie Weinheim, Dearfield Beach Flo.
5. Gissel-Nielsen G 1973 J. Sci. Food Agric. 24, 649–655.