Freitas, L.C. and Gloria, N.A. da 1976. 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 . Anais da Escola Superior de Agricultura Luiz de Queiroz. 33, (Jan. 1976), 15–33. DOI:https://doi.org/10.1590/S0071-12761976000100002.