Transport of Atrazine in Residue-Amended Soils

Abstract

In this study, our aim was to quantify the transport of atrazine in soil columns where sugarcane (Saccharum spp. hyb.) residue was incorporated. The residue is a result of sugarcane combine harvest technology where massive amount of residue is deposited on the soil surface after each harvest. Miscible displacement experiments were carried out to quantify the mobility of atrazine in soil columns where sugarcane residue was mixed a Commerce soil. The residue was either incorporated uniformly with the soil or applied as a thin mulch layer over surface soil. The incorporation of residue with the soil resulted in retarded atrazine mobility because of strong sorption and slow release of the breakthrough curves (BTCs) during leaching. Moreover, early arrival of atrazine in the column effluent was observed from BTC results where the residue was uniformly incorporated with the soil, which is possibly due to physical nonequilibrium conditions, that is, preferential flow or macropore flow. An equilibrium-type model was incapable of describing atrazine BTCs from all columns regardless of whether the residue was placed as a surface layer or incorporated in the soil. In contrast, good overall description of measured BTC results was realized when a fully kinetic model was used. Therefore, our hypothesis that kinetic rather than equilibrium-type reactions are the dominant mechanisms for the release of adsorbed atrazine from the residue is supported.