Direct and residual effect of herbicides on weed dynamics and productivity of soybean (Glycine max) -wheat (Triticum aestivum) cropping system

A field experiment aimed to evaluate the bio-efficacy of new low dose herbicides applied in soybean and their residual effect on succeeding wheat was conducted during 2007-08 and 2008-09 at New Delhi. Results revealed that in soybean, post-emergence application of imazethapyr (100 g/ha) was more effective against Trianthema portulacastrum, Commelina benghalensis, Digitaria sanguinalis and Dactyloctenium aegyptium but pendimethalin (1500 g/ha) against Dactyloctenium aegyptium, Digitaria sanguinalis and Trianthema portulacastrum. Chlorimuron-ethyl provided effective control of broad-leaved weeds but failed to control grasses and sedges. Application of imazethapyr (100 g/ha) increased the seed yield of soybean by 66.49% over weedy check. Herbicidal application significantly suppressed the microbial population at 30 DAS which recovered at the harvest of soybean. The residual effect of chlorimuron-ethyl (6-12 g/ha) and imazethapyr (50-100 g/ha) applied in soybean resulted in significant reduction in population of all major weeds except Avena ludoviciana in wheat grown in rotation. No injury to wheat plant was observed due to residues of chlorimuron-ethyl (6-12 g/ha) and imazethapyr (50-100 g/ha) and other herbicides applied in soybean