Implications of plant geometry and weed control options in designing a low-seeding seed-drill for dry-seeded rice systems

Farmers in many Asian countries are moving from puddled-transplanted rice to dry seeded rice systems as they respond to increased costs or decreased availability of labor or water. Hybrid rice has the potential to grow in dry-seeded conditions and can perform well even if seeds can be planted at low seedling rates. A field study was conducted in the wet season of 2011 and dry season of 2012 to evaluate the effect of plant-to plant spacing (10 or 20 cm), the number of rice seeds planted per spacing (2 or 3), and weed control methods (42 days weedy, weed-free, and oxadiazon followed by penoxsulam + cyhalofop) on the growth and yield of rice under a dry-seeded rice system. The crop was planted at 20-cm row spacing. Herbicide-treated plots had fewer rice plants than the 42 days weedy and weed-free plots when rain occurred before crop emergence. However, the herbicide treatment provided 81-93% better weed control than the 42 days weedy treatment, which resulted in 54-125% yield advantages over no weeding for 42 days. Grain yield in the herbicide-treated plots was only 75-88% of the grain yield in the weed free plots, suggesting further scope to improve rice yield in dry-seeded systems. Grain yield was similar across plant-to-plant spacing and the number of seeds planted per spacing. Our study suggests that hybrids can be grown at low seeding rates at 20-cm plant-to-plant spacing, provided there is no herbicide phytotoxicity on crop emergence and rice plant density is uniform. These results may help manufacturers in designing sowing drills with precise seed-metering systems for dry-seeded rice systems in Asia.