Impact of long-term conservation agriculture induced changes in soil properties on persistence of pendimethalin under different cropping systems

Increasing use of herbicides in modern agriculture poses potential risks of crop phytotoxicity, contamination of land and water resources, and adverse impacts on human and ecosystem health. Apart from climatic conditions and soil properties, agronomic practices can significantly influence the persistence of herbicides in soil. Therefore, we assessed the impact of 13-year conservation agriculture (CA) on soil properties as well as on the fate (persistence and leaching) of pendimethalin herbicide in an alluvial sandy loam soil (Typic Haplustept) in comparison with an intensively tillage-based conventional system. The experiment involved two cropping systems (mungbean (Vigna radiata L.)-wheat (Triticum aestivum L.) and sorghum (Sorghum bicolor L.)-wheat as summer and winter crops respectively) and three tillage practices: zero tillage with crop residue retention in both summer and winter seasons (ZT-ZT), conventional tillage in summer and zero tillage with residue retention in winter (CT-ZT) and conventional tillage in both seasons (CT-CT). The adoption of ZT-ZT system resulted in a 24% increase in infiltration rate, 13% greater moisture retention and 69% higher organic carbon content in surface (0-0.05 m) soil over CT-CT. In contrast, under the CT-ZT treatment, only a small change in the above soil properties was observed, which indicated that the benefits associated with CA were negated as soon as the soil was tilled in the subsequent season. In terms of herbicide leaching, under ZT-ZT, a greater fraction (4.1% vs 2.6%) of pendimethalin residues percolated down into the subsurface soil (0.15-0.30 m) than under the CT-CT system, most likely due to greater pore connectivity with the zero-till situation. However, there was a non-significant difference in the overall dissipation of the herbicide from the surface soil (0-0.05 m) under different systems. The field study illustrated that long-term adoption of CA under mungbean-wheat and sorghum-wheat cropping systems can lead to a significant change in soil properties and these in turn can influence the fate of herbicides in soils.