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 (Kd) of both compounds were significantly lower (α = 0.05) onto carbonatic soils compared to non-carbonatic soils. Furthermore, among carbonatic soil types, the marl-carbonatic soils had the lowest sorption affinities. Kd 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 Kd values were reduced by ∼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.

► The s-triazine sorption affinities (Kd) were lower (α = 0.05) in carbonatic soils.
► The marl-carbonatic soil types had the lowest sorption affinities.
► Highly correlated Kd/OC suggests predominant influence of OC in s-triazine sorption.
► Organic matter removal resulted in ∼90% reduction of the Kd values.
► OM compositional differences likely explain the large variation in s-triazine sorption in Oxisols and Spodosols.