| Field experiments were carried out in 2012-2013 and 2013-2014 growing season. Two different spike type cultivars, Tainong 18(a large spike type cultivar; T18) and Shannong 15(a small spike type cultivar; S15) were used as the experimental materials. The winter wheat were sown on three dates(early sowing on 1 Octobor, conventional sowing on 8 Octobor and late sowing on 15 Octobor,, respectively) and the plant densities were 1.35, 2.70, 4.05 and 5.40 million plants ha-1 for T18, and 0.90, 1.725, 3.45 and 5.175 million plants ha-1 for S15, respectively. This experiment was aimed to investigate the effects of plant density and sowing date on the grain yield and morphological features, the culm lodging resistance index related to lodging resistance. The main results were shown as follows,The effects of plant density were significant on grain yield, the culm height of center gravity, culm mechanical strength, the culm lodging resistance index. The effect of sowing dates on grain yield was not significant. The interaction of plant density and sowing date on the grain yield was not significant. The effects of plant density, sowing date and the interaction were significant on the culm height of center gravity, culm mechanical strength, the culm lodging resistance index. 1. Effects of plant density on the grain yield and yield components of winter wheatUnder the condition of this study, spikes per unit area increased gradually, the number of per spike and the 1000-grain weight decreased, and the grain yield have a trend of after first increases slightly reduced with the increase of plant density. Increasing plant density from 1.35 to 4.05 million plants ha-1for the cultivar T18 and from 0.9 to 1.725 million plants ha-1 for the cultivar S15 significantly increased spikes per unit area but also decreased kernels per spike and kernel weight. But the increases of spikes per unit area for each cultivar were much higher than decreases of kernels per spike and kernel weight. Therefore, the grain yield was improved. Then with the continue increase of plant density(T18 at 5.40 million plants ha-1 and S15 at 345 or 5.175 million plants ha-1), the spikes per unit area keep the same, but kernels per spike and kernel weight significantly decreased, then the grain yield decreased. 2. Effects of sowing date on the grain yield and yield components of winter wheatIn present study, the spikes per unit area decreased, the kernels per spike increased and kernel weight keep the same with delay of the sowing. Compared with the early and conventional sowing, the spikes per unit area of late sowing significantly decreased but the kernels per spike significantly increased, the 1000- kernel weight always remain constant, As a result, the grain yield remain constant with delayed sowing date. The mutually complementary between the spikes per unit area and the kernels per spike embodied the coordinated relationship between group and individual. 3. Effects of plant density and sowing date on lodging resistance of winter wheatWith the increasing of plant density, the length of second internode and plant height significantly increased, and therefore CHCG significantly increased; meanwhile, the diameter, wall thickness and filling degree of the second internode decreased, therefore CMS significantly decreased. Therefore the lodging resistance of winter wheat decreased with the increase of plant density, and then increased the risk of lodging.The plant height and the length of the second internode decreased with the delay of sowing, and then the CHCG significantly decreased; meanwhile, the diameter, wall thickness, dry weight and filling degree of the late sowing treatment significantly increased, CMS significantly increased. Therefore the lodging resistance of winter wheat increased with delay of sowing.Correlation analysis results show that, the CLRI was positively related to the diameter, wall thickness, dry weight, filling degree and the CMS, and was negatively related to the plant height the length of the second internode, and the CHCG. The CHCG was positively related to the plant height the length of the second internode, and the CMS was positively related to the diameter, wall thickness, dry weight and the filling degree.Effect of interaction between plant density and sowing date existed in the highest lodging resistance under a combination of late sowing with a lowest plant density and the lowest lodging resistance under a combination of early sowing with a highest plant density first. The effect of interaction also exists in the optimizing to the combination of late sowing and high plant density. In present study, the values of plant height, the length of the second internode and the CHCG of the highest yielding of 4.05 million plants ha-1 for the cultivar T18 and 1.725 million plants ha-1 for the cultivar S15 with late sowing could be optimized to the equivalent or even lower levels which were observed with relatively lower plant density at early or conventional sowing. The values of the diameter, wall thickness, dry weight, the filling degree and the CMS of the second internode could be optimized to the equivalent or even higher levels which were observed with relatively lower plant density at early or conventional sowing. Suggesting that, the reduction in the CLRI through increasing plant density could be compensated through sowing late, the CLRI of the highest yield plant densities with late sowing can attain or even exceed the CLRI which were observed with relatively lower plant density at early or conventional sowing, reduced the lodging risk greatly.In the present study, along with the advancement of the growing period after flower, the CHCG of high plant density with late sowing treatment remained a lower level, and the CMS remained a higher level. To delay lodging time in a certain extent, further improve the lodging resistance, decrease lodging risk.Based on the comprehensive analysis of the effects of plant density and sowing date on the grain yield and the lodging resistance of winter wheat indicated that sowing late with high plant density could achieve high grain yield and high lodging resistance in winter wheat production. 4.05 million plants ha-1 for the cultivar T18, and 1.725 million plants ha-1 for the cultivar S15 with the late sowing on 15 Octobor, not only increase the lodging resistance and maintaining a higher grain yield, but also extend the growth period of maize, laying the foundation for late harvest-increasing production, is a community building model for achieving high grain yield, high lodging resistance in winter wheat production. |
