Machado, Pedro Luiz Oliveira de Almeida, and Marcos Antonio Pavan. “Evaluation of Chemical Methods for Extracting Available Zinc in Acid Soils for Coffee”. Pesquisa Agropecuaria Brasileira, vol. 22, no. 2, Apr. 2014, pp. 213-7, doi:10.1590/S1678-3921.pab1987.v22.14304.