Degradation Behaviour of Pre-emergence Herbicides in a Rice-Mustard Cropping System: Impact of Tillage and Residue Management

Abstract

Understanding the environmental fate of herbicides is essential for ensuring safe and sustainable crop production systems. This study evaluates the degradation behavior of herbicides in the soil and mustard crop in a rice-mustard cropping system by assessing the combined effects of tillage practises and residue retention. A field experiment was conducted using a split-plot design under conventional tillage without residue (CT-R) and zero tillage with residue retention (ZT + R), involving pre-emergence applications of pendimethalin at 339 and 500 g/ha and pyroxasulfone at 76.5 and 102 g/ha. The herbicides were extracted using ultrasound-assisted extraction and method showed good linearity, minimal matrix effect, high sensitivity and good recoveries confirming its suitability for quantifying herbicides in soil and mustard samples. The half-lives (DT₅₀) of pyroxasulfone ranged from 11.38 to 13.19 and 6.78 to 10.07 days under CT-R and ZT + R, respectively across both years. Pendimethalin exhibited biphasic degradation with initial-phase DT₅₀ ranging from 3.61 to 5.15 and 3.66 to 3.92 days, while final-phase DT₅₀ ranging from 20.21 to 28.51 and 14.34 to 23.73 days in CT-R and ZT + R, respectively. The residues of herbicides in soil (< 0.01 µg/g) and mustard (< 0.05 µg/g) at harvest were below the limit of detection, indicating their safe degradation by crop maturity. The study demonstrates that conservation tillage practices can enhance herbicide degradation dynamics, contributing to safer environmental outcomes and supporting the sustainable intensification of mustard-based cropping systems.

Keywords: Conservation tillage; Herbicide dissipation; Pendimethalin; Pyroxasulfone; Sustainability.