Persistence of acetochlor, atrazine, and S‐metolachlor in surface and subsurface horizons of 2 typic argiudolls under no‐tillage

Abstract

Variations of soil properties with depth strongly influence degradation and persistence of herbicides, underlining the importance of studying these processes in soil horizons with distinctively different properties. The persistence of herbicides acetochlor, atrazine and S-metolachlor was measured in samples of the A, B and C horizons of two Typic Argiudolls from Argentina under no-till management. The soils studied differed in soil organic carbon (OC) content, pH, particle size distribution, and structure. Quantification of herbicides in soil was done through High Performance Liquid Chromatography with Diode Array Detector (HPLC-DAD). There were interactions herbicide x horizon (p < 0.01) that resulted in degradation rates (k) of all herbicides decreasing, and their corresponding half-life (DT₅₀) values increasing, with soil depth. Herbicide persistence across all soils and horizons ranged from 15 to 73 days for acetochlor, 13 to 29 days for atrazine, and 82 to 141 days for S-metolachlor, which had significantly (p < 0.01) greater persistence than atrazine and acetochlor. Values of DT₅₀ of herbicides were negatively correlated with the contents of OC, with correlation coefficients ranging from -0.496 to -0.773, phosphorus (-0.427 to -0.564), and nitrogen-nitrate (-0.507 to -0.662), and with microbial activity (-0.454 to -0.687), and the adsorption coefficient K_d (-0.530 to -0.595), and positively correlated with pH (0.366 to 0.648). Adsorption was likely the most influential process in determining persistence of these herbicides in surface and subsurface horizons. This study can potentially improve the prediction of the fate of acetochlor, atrazine and S-metolachlor in soils because it includes much needed information on degradation of the herbicides in subsurface horizons. This article is protected by copyright. All rights reserved