Vendrame, Pedro Rodolfo Siqueira, et al. “Availability of Copper, Iron, Manganese and Zinc in Soils under Pastures in the Brazilian Cerrado”. Pesquisa Agropecuaria Brasileira, vol. 42, no. 6, June 2007, pp. 859-64, doi:10.1590/S1678-3921.pab2007.v42.7639.