Lower Seedling Density Induces Plant Growth with a Higher Panicle-weight Type in Direct-seeded Rice on Well-drained Paddy Field

[摘要] To elucidate the effect of seedling density on the growth and yield components of direct-seeded rice on well-drained paddy fields, we conducted a three-year field experiment using high-yielding rice cultivars “Minachikara” and “Hokuriku 193”. Plots sparsely seeded (17 seedlings m -2 ) and moderately seeded (33 seedlings m -2 ) were set by thinning seedlings artificially, to compare plant growth with densely seeded plots (43–169 seedlings m -2 ) which was the original seedling establishment by the conventional method. The sparsely seeded plot had fewer tillers per unit area, and heading date was later than in the densely seeded plot. At the vegetative stage, the average single tiller weight did not differ with the seedling density, but after heading, it was significantly heavier in the sparsely seeded plot than in the densely seeded plot. The number of panicles per unit area decreased with decreasing density, while the number of spikelets per panicle increased with decreasing density. The grain yield per unit area in the sparsely seeded plot slightly decreased or was the same as that in the densely seeded plot. However, we obtained over 900 gm -2 grain yield in the sparsely seeded plot with “Hokuriku 193” in 2018. The yield was the same in the densely seeded plot even though the number of seedlings was only one-tenth of that in the densely seeded plot. In conclusion, lower density of seedlings induced plant growth to give a higher panicle-weight type. Therefore, the seedling density was considered an important factor in the growth control of direct-seeded rice.

[关键词] Density of seedling establishment;Direct-seeding on well-drained paddy field;High-yielding cultivar;Panicle-weight type;Plant type;Sparsely seeded.