Freitas, L. C.; Gloria, N. A. da. Colorimietric Determination of Silicon in Soils: II - Aplication of the Yellow Silicomolybdic and Molybdenum Blue Methods in the Determination of Total and Soluble Silica in Soils . An. Esc. Super. Agr. Luiz de Queiroz 1976, 33, 15-33. https://doi.org/10.1590/S0071-12761976000100002.