1. Adriano, D. C. (2001). Trace elements in terrestrial environments (2nd ed.). New York: Springer.
2. Edwards, R., Lepp, N. W., & Jones, K. C. (1995). Other less abundant elements of potential environmental significance. In B. J. Alloway (Ed.), Heavy metals in soils (2nd ed., pp. 306–352). Glasgow: Blackie. Chapter 14.
3. Emsley, J. (1989). The elements. Oxford: Oxford University Press.
4. Fageria, N. K., Baligar, V. C., & Clark, R. B. (2002). Micronutrients in crop production. Advances in Agronomy, 77, 185–268.
5. Fageria, N. K. (2009). The use of nutrients in crop plants. Boca Raton: CRC Press.