Stalebed with tillage, pendimethalin & bispyribac provided highest rice grain yield.
Stalebed with tillage, pendimethalin & bispyribac provided highest economic returns.
All seedbed treatments had higher weed seedbank at crop harvest than at sowing.
Stalebed reduced grass weeds viable seedbank at rice sowing than without stalebed.
Stalebed enhanced weed seedlings emergence by 1.9–2.2- fold at rice sowing.
Dry-seeded rice (DSR) grown with alternate wetting and drying water management (AWD) has recently been introduced in northwest India as an alternative to conventional puddled hand-transplanted rice which is labour, water and energy intensive. The aerobic seedbed of DSR can be extremely susceptible to invasion by diverse weed flora, and if weeds are not controlled effectively, yield losses can be very high. This study was undertaken to investigate the impacts of stale seedbed techniques on the soil weed seedbank and weed infestation in DSR, and to determine the influence of integration of the stale seedbed methods with post sowing herbicides on weed control and rice grain yield. The study, conducted in 2014 and 2015, comprised three seedbed treatments in main plots: without stale seedbed-conventional method, stale seedbed with glyphosate 1 kg ha −1 andstale seedbed with shallow (5 cm) tillage, and four post sowing herbicide treatments in sub plots: unsprayed check, pendimethalin 0.75 kg ha −1 (pre-emergence), bispyribac-sodium 0.025 kg ha −1 (post-emergence) and pendimethalin followed by bispyribac-sodium. The two stale seedbed treatments included one additional irrigation prior to sowing which increased weed seedling emergence prior to sowing by 1.9–2.2-fold; weeds in the stale seedbed treatments were then killed with the application of glyphosate or shallow tillage. At sowing, both stale seedbed treatments significantly decreased the viable seedbank of Echinochloa colona and Dactyloctenium aegyptium to 25–30% of that without a stale seedbed. After rice harvest, both stale seedbed treatments had a significantly lower seedbank than without a stale seedbed, by 13–33%; the stale seedbed with tillage had significantly lower seedbank at harvest than the stale seedbed with glyphosate in the second year. The sequential application of pendimethalin and bispyribac resulted in a significantly lower seedbank of both these grass weed species at harvest. At 20 DAS, both stale seedbed methods had 22–51% lower density of Cyperus rotundus and 42–67% less grass weeds than rice sown without a stale seedbed. There was more than a 2-fold increase in C. rotundus density from 2014 to 2015 without a stale seedbed and with the stale seedbed with glyphosate, and a 1.6-fold increase in the stale seedbed with tillage. In the absence of post sowing herbicides, the stale seedbed with tillage increased grain yield from 0.7–1.0 t ha −1 to 2.1–2.5 t ha −1 , while the stale seedbed with glyphosate only increased grain yield in 2015. The combination of the stale seedbed with tillage, pendimethalin and bispyribac had the highest rice grain yield (7.3 t ha −1 ) and the highest economic returns ($ 1310 ha −1 ); the returns in this treatment were $ 260 ha −1 higher than using the same herbicides used without a stale seedbed. The results indicate that integrated use of a stale seedbed with shallow tillage followed by the sequential application of post sowing herbicides has potential to control the complex weed flora in dry-seeded rice. The reasons for greater consistency in weed control with the stale seedbed with tillage than glyphosate are unclear and need further investigation in dry seeded rice, as do the long term effects of use of stale seedbeds.
Direct seeding can curtail water and labor inputs involved in rice production; nevertheless, its large-scale adoption is impeded by heavy weed infestation. A field study was undertaken in 2011 and 2012 to evaluate the effects of crop row spacing (20 and 10 cm) and postemergence herbicides on weed growth and yield of dry-seeded rice. As a herbicide, pyrazosulfuron ethyl at 30 g ha –1 , bispyribac-sodium at 30 g ha –1 , or penoxsulam at 15 g ha –1 was applied (15 days after sowing, DAS) alone or in combination with fenoxaprop-p-ethyl at 86.25 g ha –1 subsequently (30 DAS). In addition, a partial weedy plot (manually weeded once at 28 DAS), and a weed-free plot were established for each row spacing In the partial weedy plot with 10-cm row spacing, the weed density was only 21 and 25% lower than that in the plot with 20-cm row spacing in 2011 and 2012, respectively. The sole application of an early postemergence herbicide restricted weed growth, while subsequent application of fenoxaprop as late postemergence application suppressed weed growth further, the magnitude of suppression being more pronounced in the plot with narrow row spacing. The density and biomass of weeds were lowest in the plot with 10-cm row spacing applied bispyribac-sodium followed by fenoxaprop . Under weed-free conditions, yields were 29% higher in the plot with 10-cm row spacing (4.18 t ha –1 ) than in that with 20-cm row spacing (3.23 t ha –1 ). Grain yield in the herbicide-treated plots was 87 – 188% higher than that in the partial weedy plots. These results suggested that narrow row spacing and sequential herbicide application can help tackle recalcitrant weed flora in dry-seeded rice fields.