Adsorption of Atrazine and Terbacil by Soils

Abstract

The differential in the adsorption capacity of 2-chloro-4-(ethylamino)-6- (isopropylamino)-s-triazine (Atrazine) and 3-tert.-butyl-5-chloro-6-methyl- uracil (Terbacil) by 34 Puerto Rican soils was studied in the laboratory using C¹⁴-labeled herbicides. The various soils differed greatly in their capacity to adsorb Atrazine and Terbacil. The Caño Tiburones soil was found to be the most adsorptive for both herbicides; the Toa sandy loam and Talante sandy loam the least for Atrazine and Terbacil, respectively. Atrazine was consistently adsorbed to a greater degree than Terbacil. Adsorption of Atrazine was correlated positively with organic matter content, cation exchange capacity and magnesium and silt content but negatively with sand content. Adsorption of Terbacil was positively correlated with organic matter, cation exchange capacity, soil pH, content of phosphorus, calcium, magnesium and clay but negatively with sand content of the soil. Representative adsorption isotherms of Atrazine and Terbacil on several important island soils devoted to sugarcane cultivation are also presented in this report.