Effect of pendimethalin herbicide on Azotobacter and PSB population in soil during crop growth under conventional and zero tillage ​

The development of more productive and sustainable agricultural systems essentially requires the assessment of the population and diversity of microorganisms in soils under different management practices. The conservation agriculture (CA) systems are considered very important for soil health, biodiversity and environmental quality. But the use of herbicides is substantially increased under CA systems which may cause adverse impacts on human and ecosystem health. Moreover, the literature pertaining to the consequence of herbicides on soil microorganisms is quite controversial, and largely based either on laboratory or short-term field experiments. Therefore, the impact of pendimethalin herbicide on the population of Azotobacter and phosphorus solubilising bacteria (PSB) under CA system was taken up during _summer, 2019_ at Soil Research Farm, CCS Haryana Agricultural University, Hisar in alluvial sandy loam soil (Typic Haplustept). The experiment included two cropping systems (mungbean - wheat and sorghum - wheat), with three tillage practices, viz., zero tillage with surface retention of crop residues 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). Resultes revealed an increase in the population of both Azotobacter and PSB under ZT-ZT as compared to CT-CT practice at different depths. In surface 0-5 cm soil, the ZT-ZT practice increased the population of Azotobacter and PSB by 65.6 and 30.0%, respectively, over CT-CT practice in 13 years of experimentation. Application of pendimethalin provided stimulation to the population of both the microbes till 15th day of it application under all the tillage practices. This stimulation in population was of almost similar order (21-23%) for under ZT-ZT practice but greater stimulation (29.8%) in the population of Azotobacter as compared to PSB (13.5%) under CT-CT practice accentuated Azotobacter to be more efficient in utilizing easily available pendimethalin for their augmentation of the proliferation.. The influence of cropping systems on microbes upon application of pendimethalin was largely non-significant