Effect of Seeding Rate on Plant Growth, Grain Yield, Yield Components, Milling Quality and Weed Density of Organic Rice.

Seeding rate plays an important role in optimizing yield and yield components of rice, yet its effect on organic rice production is still limited. This project was conducted in two continuous years to evaluate the effect of seeding rate (108, 161, 215, 269, 323, 376, and 431 seeds m^-2) and rice variety (Presidio and XL753) on plant growth, grain yield, yield components, milling quality and weed density in an organic field. Seeding rate had significant effects on plant density (p < 0.0001) and dry biomass (p < 0.05) with positive linear correlations (R² > 0.84); while, its effect on plant height was insignificant. With increasing of seeding rate, yields grew linearly (p < 0.0001; Presidio R² = 0.88, XL753 R² = 0.92), which were 3,462 and 7,508 kg ha^-1 for Presidio and XL753, respectively, at the highest seeding rate. Panicle number and filled grains per panicle are two important components contributing to yield. The number of panicles was positively correlated with seeding rate (p < 0.0001; Presidio R² = 0.86, XL753 R² = 0.69), while the effect of which on other yield components and milling quality varied between years and varieties. Nevertheless, it was consistent that XL753 had a significantly (p < 0.0001) higher plant density, height, biomass, number of spikelet and full grain per panicle, and percentage of total grain; but a significantly (p < 0.0001) lower percentage of full grain, whole / broken grain ratio, and weed density, compared to Presidio. Caution should be exercised when apply conventional optimal seeding rate to organic rice production. In organic rice system, a high seeding rate improved plant growth and panicle number while hardly influenced the number of filled grains per panicle or 1,000-grain weight, therefore, it could be an effective potential approach to maintain high yield or economic sound yield.