Effects of seeding rate and nitrogen fertilizer management on lodging resistance potential and grain yield of direct-seeding hybrid rice

Direct-seeding rice is becoming more and more popular because of its simplification, which can effectively reduce the demands of labors for rice production. However, it usually needs larger planting density to achieve high grain yields which easily leads to an oversize rice population, and hence the lodging problem can not be ignored. Many researches have reported the significant influence of nitrogen application and planting density on lodging resistance and grain yield of transplanting rice. But the work on lodging resistance of direct-seeding rice is still less reported.The objective of this study was to investigate the effects of seeding rate and nitrogen fertilizer management on lodging resistance and grain yield of direct-seeding hybrid rice with 446A/518 as the experimental material, and the correlations between lodging index and some physical and chemical characteristics of stems or grain yield of rice plants were also analyzed.The results indicated that there were significant influences of seeding rate and nitrogen fertilizer management on the physical and chemical characteristics of different internodes, lodging resistance and grain yield of directseeding rice. With the increase of seeding rate, the lodging resistance had a certain degree of reduction. When the seeding rate was less than 22.5 kg per hectare, the lodging resistance would reduce with the increase of panicle fertilizer. However, more panicle fertilizer was beneficial to improve the lodging resistance of rice plants when the seeding rate increased from 22.5 to 30.0 kg per hectare. The shorter basal internodes, the smaller cavity area and flat ratio, the larger breaking resistance, and the higher contents of cellulose and lignin of the internodes may play important roles to the higher lodging index. Correlation analysis indicated that not only the physical and chemical characteristics of stems but also grain yield and its components both had close relationships with lodging resistance of direct-seeding rice. In this experiment, grain yield would grow till it reached the highest when the seeding rate increased to 22.5 kg per hectare, and decreased significantly afterwards when the seeding rate was 30 kg per hectare. Besides the simple effect of seeding rate and nitrogen fertilizer management, their interaction effect was also significant, and the influences of nitrogen fertilizer management on grain yield and its components were various under the different seeding rates. Under the seeding rate of 15 kg per hectare, the highest grain yield was gained when the ratios of basal∶ tillering∶panicle nitrogen fertilizers was 4∶1∶5, but the fifth internode was easy to lodging. When the seeding rate was 22.5 kg per hectare, the ratios of basal∶tillering∶panicle nitrogen fertilizers were 5∶2∶3 (N1) and 4∶1∶5 (N3) had the higher grain yield, but the N1 management was more resistant to lodging. However, when the seeding rate was 30.0 kg per hectare and the ratio of basal∶tillering∶ panicle nitrogen fertilizers was 3∶3∶4 (N2), all the yield components were gained except for the seeding-setting rate, which might decrease the grain yield significantly.In sum, the relatively high grain yield and a better lodging resistance was gained simultaneously when the seeding rate was 22.5 kg per hectare and the ratio of basal∶tillering∶panicle nitrogen fertilizers was 5∶2∶3, so it is the optimal cultivation measure in this experiment.