Adsorption of Ionizable Herbicides by Agricultural Soils without Amendment and Green Compost-Amended Soils

Abstract

The objective of this work was to study the adsorption of aminopyralid and iodosulfuron-methyl sodium, applied in post-emergence to wheat crops, and two degradation products, metsulfuron-methyl and 2-amino-4-methoxy- 6-methyl-1,3,5-triazine (AMMT), by green compost (GC) and by two agricultural soils (soil A and soil B) with different characteristics, without amendment and amended with GC at 2.5% w/w. The study of herbicide and metabolite adsorption by soils and GC was carried out using the batch equilibrium method. The equilibrium concentrations of the compounds were determined by HPLC-MS, except for ¹⁴C-iodosulfuron-methyl sodium, which was determined in a liquid scintillation counter. The adsorption isotherms were fitted to the Freundlich equation, presenting a linear form for the adsorption of the herbicides by the soil B + GC. The Kf values ​​of aminopyralid were higher than those of iodosulfuron-methyl sodium, indicating a greater adsorption of this herbicide by soils. The adsorption capacity of herbicides and their metabolites by amended soils depended on the soil organic carbon (OC) content and the pH. For all the compounds, the percentage adsorbed by GC was higher than by the soils.