Effect of nitrogen rates and weed control methods on weeds abundance and yield of direct-seeded rice

Field experiments were conducted at the Punjab Agricultural University, Ludhiana, India, during 2007-2008 to examine if nitrogen (N) rates and weed management practices using herbicides in combination with hand-weeding (HW) can improve crop competitiveness against weeds, and increase the yield, water productivity and profitability of direct-seeded rice (DSR). Increasing N application rate up to 150 kg ha(-1) caused significant improvement in grain yield when the weeds were well controlled either by Pendimethalin + Bispyribac Na or by Pendimethalin + Bispyribac Na + 1 HW, respectively; however, under poor weed control condition (Pendimethalin + 1 HW), it resulted in a drastic reduction in yield. The highest net returns ($1083) and water productivity (0.60 kg m (3)) were observed for N application of 150 kg ha (1) and weeds were controlled with Pendimethain + Bispyribac Na + 1 HW. We suggest that Pendimethalin + Bispyribac Na + 1 HW is the best integrated weed management strategy to control weeds, and to increase yield, water productivity, and profitability. We propose that the simulation modelling tool be utilized in future for evaluating options for improving sustainable N and weed management policies especially when crop, weeds, soil, weather and management data are available for calibration and validation of appropriate and existing simulation model of rice.