Sorption of atrazine and ametryn by carbonatic and non-carbonatic soils of varied origin

Sorption of two s-triazines, atrazine and ametryn, by carbonatic soils. Histosols, Spodosols and Oxisols was examined. Linear isotherms were observed and sorption coefficients (K-d) of both compounds were significantly lower (alpha = 0.05) onto carbonatic soils compared to non-carbonatic soils. Furthermore, among carbonatic soil types, the marl-carbonatic soils had the lowest sorption affinities. K-d and organic carbon content were highly correlated, suggesting predominant influence of organic carbon in the sorption of the s-triazine, except in Oxisols and Spodosols where variations suggest other factors. Upon removal of organic matter (OM) using sodium hypochlorite and hydrogen peroxide, the K-d values were reduced by similar to 90%, indicating minimal contribution of mineral surfaces. Thus OM compositional differences likely explain the large variation in s-triazine sorption within and between soil orders. This study highlights the need to consider OM composition in addition to quantity when determining pesticide applications rates, particularly for carbonatic soils. (c) 2012 Elsevier Ltd. All rights reserved.