Response of soil microflora in herbicide residue of winter irrigated cotton

Field experiments were conducted during winter seasons of 2008–09 and 2009–10 at Eastern Block Farm, Tamil Nadu Agricultural University, Coimbatore to study the efficiency of new formulation pre-emergence herbicide pendimethalin 38.7% on growth and development of cotton to ensure the better weed management in a cost effective manner. Pendimethalin 38.7% was tried in four different doses viz., 1.5, 2.0, 2.5 and 4.0 kg/ha and it was compared with pendimethalin 30% @ 1.0 kg/ha, early post-emergence herbicide trifloxysulfuron, power weeders and hand weeding. The experimental results revealed that the herbicides exerted a significant detrimental effect on soil bacteria, fungi and actinomycetes. The counts of bacteria, fungus and actinomycetes recorded at 3 DAHS revealed that soil microbes were more sensitive to pendimethalin (38.7%) 1.5, 2.0, 2.5 and 4.0 kg/ha and pendimethalin (30%) 1.0 kg/ha as evident from significant reduction in their population on 15 and 30 DAHS, eventually microbial density started to recover slowly.