Weed management and grain yield of rice sown at low seeding rates in mechanized dry-seeded systems

Because of the rapid depletion of water and shortage of labor, farmers in many Asian regions are moving from puddled transplanted rice to dry-seeded rice. However, weed infestations are a serious problem in dry-seeded rice systems because dry cultivation practices and aerobic soil conditions are conducive to the germination and growth of weeds. A field study was conducted in the wet season of 2011 and the dry season of 2012 to evaluate the effect of two rice cultivars and different herbicides on weed growth and rice yield under dry-seeded rice. The rice cultivars (one hybrid and one inbred) were dry-seeded at 20-22kgseedha-1 with a combine drill fitted with knife-point openers. Rice plant densities ranged from 44 to 56plantsm-2 in the first season and from 67 to 77plantsm-2 in the second season. Weed density, weed biomass, rice panicle number, and rice yield were not influenced by the cultivars; however, they were strongly influenced by the weed control treatments. In terms of percent, the hybrid cultivar had 11-12% higher yield than the inbred cultivar. Weed competition in the control plots (one hand-weeding) lowered yield by 39-41% compared with the weed-free plots. All herbicides significantly reduced weed biomass compared with the control treatment, providing 75-93% weed control. Herbicide-treated plots had similar grain yield and the yield in these plots was 76-86% of the yield of the weed-free plots (4.2-4.4tha-1), suggesting further scope to improve rice yield in dry-seeded systems. Compared with the control treatment (one hand-weeding), herbicide-treated plots had 27-41% greater yield. Future research in dry-seeded rice systems should focus on the integration of appropriate agronomic practices with herbicide application timing and combinations to improve the effectiveness of weed management practices