Weed Management in Dry-Seeded Fine Rice under Varying Row Spacing in the Rice-Wheat System of Punjab, Pakistan

Abstract

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.