Impact Of Direct-seeding Densities On Comprehensive Productivity Of Different Genotypes Of Rice

With conventional mid-season japonica varieties Huaidao 9, Yanjing 9, conventional late-season japonica varieties Wuxiangjing 14, Wujing 15, Bing 03-123, Xiushui 128, Jia 33,and late-season hybrid varieties Changyou 1, E24, Suyou 22 as the test cultivars, the experiments were carried out at the Experimental Farm of Yangzhou University during the growing seasons of 2006 and 2007 to study the impact of different direct-seeding densities (conventional varieties: 20, 40, 60, 80, 100 thousand per 666.67m2 , hybrid varieties: 20, 30, 40, 50, 60 thousand per 666.67m2) on the growth period, yield, population quality, fertilizer utilization and rice quality of different genotypes of rice, and so as to provide a theoretical reference for the determination of suitable direct-seeding densities. The main results were as follows:1. The total growth period of different genotypes of rice prolonged accordingly along as plant density increased, but the variations ranged slightly at only 1-3 days. The differences among different genotypes were also observed.2. The relations between the yields of different genotypes of rice and planting densities could be described with a parabola equation, i.e. the yield first increased then decreased as planting density increased. As for yield components, the relations between the number of panicles per 666.67m2, seed setting rate and planting densities could also be expressed with parabola equations. The number of kernels per panicle and planting density was significantly negatively correlated. One-thousand-grain weight and planting density was also insignificantly negatively correlated.In this experiment, the number of panicles per 666.67m2 was suitable for obtaining the highest yield and the highest seed setting rate when the direct-seeding density of conventional varieties was 60 thousand and the direct-seeding density of hybrid varieties was 40 thousand. The differences of yield of different genotypes of rice were significant. The yield of conventional late-season japonica varieties was the highest, late-season hybrid varieties came the second, and conventional mid-season japonica varieties was the lowest.3. When direct-seeding density of conventional varieties was 60 thousand per 666.67m2 and direct-seeding density of hybrid varieties was 40 thousand per 666.67m2, the dynamic of tillers, LAI, dry matter accumulation, rice plant height at ripening stage, and stanza disposal were more advantageous over other treatments. And also, tiller survival rate and efficient leaves area rate were also improved.4,N,P,K accumulation in different genotypes of rice first increased then decreased during the whole growth period. Suitable planting densities benefited the N,P,K accumulation at all periods. In addition, N accumulation during the stage between jointing and heading occupied 50% of the total N accumulation. P accumulation both during the stage between jointing and heading, and during the stage between heading and maturity occupied 30% of the total P accumulation. K accumulation during the stage between jointing and heading occupied 40% of the total P accumulation. These indicated that jointing-heading stage is the most pivotal period for nutrition accumulation. So nutrition at jointing-heading stage and rice yield can be improved by regulating direct-seeding density. In the same planting density, N,P,K accumulation of all periods and stages of late-season varieties is higher than that of mid-season varieties. This is one of the reasons that the yield of late-season varieties was higher than mid-season varieties. 5,Suitable planting density improved manufacturing quality, appearance quality and nutrition quality of rice grains. Cooking quality could be maintained relatively good while the planting density increased. Along with the exaltation of density, manufacturing quality (brown rice rate, head rice rate, unbroken head rice rate),appearance quality (chalky grain rate, chalkiness size, chalkiness dimension) first become excellent then become inferior; amylase content descended; protein content first raised then descended; gel consistency enlarged; peak viscosity, hot viscosity, break down all descended; cool viscosity remarkably and set back increased; peak time shortened slightly; pasting temperature descended. Generally, late-season japonica varieties were best in rice quality, conventional mid-season japonica varieties came the second, and late-season hybrid varieties came the third.To sum up the growth period, yield and yield components, population quality, fertilizer utilization and rice grain quality of different genotypes in different planting densities, we could see that the comprehensive productivity were the highest when the planting density was 40 thousand per 666.67m2 for hybrid varieties, and 60 thousand per 666.67m2 for conventional varieties. Under these two planting densities, the yield, rice grain quality and production efficiency were easily harmonized. This paper also pointed out that conventional late-season japonica rice cultivars were ideal for direct-seeding rice production in the experimental and similar region.