Effects Of Edaphoclimatic Conditions On The Sorption Of Alachlor In Brazilian Oxisols Under No-Till System.

No-till system is extensively adopted in Brazil due to its role in improvements in soil quality and reduction in yield costs. The different edaphoclimatic conditions and the adoption of different inter-harvest crops can lead to differences in the amount and quality of soil organic carbon (SOC) and its persistence. Considering the important role that SOC chemistry can play in determining the sorption of herbicides, this research evaluated sorption of alachlor in representative soils of different edaphoclimatic regions (subtropical and tropical) under no-till system. Six samples of subtropical and five of tropical Oxisols were collected to perform sorption of ¹⁴C-alachlor by batch equilibration method. Sorption coefficients (K_d) correlated well to SOC contents (r = 0.74, ρ < 0.01) ratifying their influence on alachlor sorption. Although on the same order of magnitude, the average K_oc for the subtropical soils (50.29 ± 7.02L kg^-1) was significantly lower than for the tropical soils (70.85 ± 6.75 L kg^-1). The soils LV1 (subtropical) and LV9 (tropical) had similar physical-chemical attributes (CEC ≈ 190 mmol_c kg^-1, OC ≈ 3.75%; Clay ≈ 65%), but differed on their sorption potentials (K_d = 1.65 ± 0.043 and 2.59 ± 0.006 and K_oc = 44.16 ± 1.15 and 69.68 ± 0.15 L kg^-1 for LV1 and LV9, respectively) indicating that SOC chemistry (besides quantity) and sites availability may affect alachlor sorption. Tropical conditions favor SOC decomposition that precludes protective mechanisms during organo-mineral complexes formation and, therefore, exposes more sites for sorption. These results enable to improve herbicide management strategies depending on the climatic regions in order of to improve compound efficacy and/or avoid environmental pollution.