Impacts of conservation agriculture and herbicides on weeds, nematodes, herbicide residue and productivity in direct-seeded rice

Abstract

The transplanted puddled rice (TPR) followed by (∼fb) conventional till wheat (CTW) system (TPR-CTW) in the Indo-Gangetic Plains (IGP) of India is the most remunerative cropping system, serving as the backbone of food security of India. Its sustainability, however, is threatened due to degradation/ scarcity of resources (soil, water, fuel/energy, labour), low inputs-use efficiencies, insurgence/resistance of new weeds/pests, and high pesticides use, and greenhouse gases (GHGs) emissions and global warming. Direct-seeded rice (DSR) can save resources, improve soil conditions, reduce GHGs emissions, and can reverse the declining trends. The performance of DSR, however, is largely influenced by weeds and nematodes. Therefore, this experiment was undertaken to evaluate the impacts of conservation agriculture (CA)-inclusive DSR, supplemented with herbicides/weed control measures on weeds, nematodes, and rice productivity and profitability. Results showed that the DSR fb ZTW had 82 % higher weed densities at 45 days after sowing (DAS) than TPR-CTW. The DSR fb ZTW, and DSR + brown manuring (BM) fb ZTW systems resulted in significantly higher parasitic nematodes, namely, Tylenchorhynchus brevilineatus Williams, Meloidogyne graminicola Golden & Birchfield, Pratylenchus thornei Sher & Allen than TPR-CTW. The CA-based triple cropping system with residue [∼DSR with mungbean residue (MR) fb ZTW with rice residue (RR) fb ZT mungbean (ZTMB) with wheat residue (WR)] led to considerable reduction of these nematodes. It gave similar rice yield with TPR-ZTW and TPR-CTW, and 40–43 % higher yield than DSR-ZTW. Pendimethalin 1.5 kg ha−1 at pre-emergence fb bispyribac-Na 25 g ha-1 at post-emergence and hand weeding (HW) at 35 DAS offered better weed control, higher rice yield (by 123–130 %), net returns (by 327–806 %) and net benefit:cost. The above CA-based triple cropping system with pendimethalin + bispyribac + HW would lead to an effective weed management in DSR without the risk of residual toxicities of pendimethalin and bispyribac-Na to crops grown in sequence. This can serve as an alternative to TPR in the Indian IGP, and in similar agro-ecologies. Controlling weeds using these herbicides may suppress nematodes and reduce the cost of nematodes control.