Couto, Eduardo Guimarães, and Egon Klamt. “Spatial Variability of Microelements in Soil under Center Pivot Irrigation System in Southern Mato Grosso State, Brazil”. Pesquisa Agropecuaria Brasileira, vol. 34, no. 12, Dec. 1999, pp. 2321-9, doi:10.1590/S1678-3921.pab1999.v34.5567.