Effects of Sowing Density on Quality of Medium-seedling Nursed with Two-layer Plastic Film and Grain Yield in Mechanical Transplanting Rice

Wuyunjing 7, a semi-erect panicle, high-yield and lodging-resistant japonica cultivar, was used to investigate the effects of five sowing densities (170.7, 229.4, 285.4, 342.7 and 400.1 germinated grains per dm 2) on quality of medium-seedling nursed with two-layer plastic film and grain yield in mechanical transplanting. The results showed that the main indices of seedling quality, root-developing ability in field, the ratio of dry weight to seedling height, above ground dry weight and the base stem thickness, became worse with the increase of the sowing density when the seedlings were transplanted at 3-leaf age. The indices for the least density (170.7 grains/dm 2) treatment were significantly or obviously superior to other treatments, but its grain yield was significantly lower than others due to higher empty hill percentage and less seedlings per hill in the field. Although there existed a decreasing trend in seedling quality with the increase of the sowing densities from 229.4 grains/dm 2 to 400.1 grains/dm 2, the differences among the treatments were not significant for grain yields. It suggested that the most suitable sowing density for nursing the strongest seedlings was not the density for mechanical transplanting. The reasonable sowing density for mechanical transplanting was around 229 grains/dm 2 due to extended suitable seedling age. The peak seedling dry weight appeared at 20th day after sowing when the leaf age of the seedling was 3.8-4.1 for all the density treatments except for 170.7 grains/dm 2 treatment. The seedling quality 20 days after sowing declined with increasing of sowing density, which indicated that the critical suitable transplanting time was at 20th day after sowing and a critical leaf age of seedlings was 3.8-4.1.