Effect of weed control on weed competition, soil microbial activity and rice productivity in conservation agriculture-based direct-seeded rice (Oryza sativa)-wheat (Triticum aestivum) cropping system

A field experiment was carried out during 2012–13 and 2013–14 at New Delhi, to evaluate the effects of weedcontrol options on weed interference, microbial activity and direct-seeded rice (DSR) productivity in a conservation agriculture (CA)-based rice (Oryza sativa L.)-wheat (Triticum aestivum L. emend. Fiori et Paol) cropping system. The CA practices such as brown manuring, mungbean [Vigna radiata (L.) R. Wilczek] residue (MR) and rice-residue (RR) retention, zero tillage (ZT) significantly influenced weed density, microbial activity and crop yield. Grassy weeds were more dominant among the weeds. The DSR practices encountered more weed infestations than transplanted rice (TPR). The sequential applications of pendimethalin @ 1.5 kg/ha as pre-emergence, and bispyribac-Na @ 25 g/ha at 25 days after sowing/transplanting (DAS/DAT) as post-emergence resulted in better control of weeds and higher weed-control efficiency (WCE), but this combination plus 1 hand-weeding (HW) at 45 DAS was the best weed-control option in DSR. Higher WCE of 50% and 52% obtained from this treatment respectively, in 2012 and 2013. These herbicides applications slightly reduced microbial activity at 40 DAS. Soil microbial activity positively responded to CA practices. Soil-dehydrogenase activity (DHA) and microbial biomass carbon (MBC) were significantly higher in DSR than TPR. The rice yields were comparable between the TPR-ZTW and DSR + MR-ZTW + RR-SMB + wheat residue (WR) systems, but higher than in other CA-based DSR-wheat systems. Treatment DSR + MR-ZTW + RR-SMB + WR provided higher grain yield 4.41 t/ha and 4.53 t/ha in 2012 and 2013, respectively.