| The researches and applications of direct seeding in rice have developed rapidly in recently years, especially in the areas of Jiangsu and Zhejiang provinces where account for most area of the rice production. Researches about seeding rates, cultivars, sowing date and the application of fertilizer under direct seeding in order to improve rice yield capacities have been carried out for many years. However, there are still many problems limiting the rice yield improvement and technology application under direct seeding such as seed selection, direct seeding method, seeding rates, full stand, nitrogen fertilizer management and weed control and resistance. Based on the special ecological conditions of Sichuan Basin (rainy, wet and low light), we carried out this research. The objectives of this study were to investigate the relationships between the methods of direct seeding (including broadcast sowing, drill seeding, wide-narrow drill seeding and precision dibbling), seeding rates, nitrogen fertilizer management, lodging-resistance capability, nitrogen utilization and yields of hybrid rice.3 seeding rates (15.0 kg/hm2, S1; 22.5 kg/hm2, S2; and 30 kg/hm2, S3),3 nitrogen fertilizer utilization (total 150 kg/hm2, base:tillering:earing fertilizer,5:2:3, Nl; 3:3:4 N2; 4:1:5, N3),4 direct seeding (broadcast sowing, D1; row sowing, D2; wide-narrow sowing, D3; precise sowing, D4), and 3 nitrogen initiation date (P1, P2 and P3), respectively, were used to study the effects of direct seeding on lodging-resistance, dry matter production, nitrogen use efficiency, and yields which carried out in 2013 and 2014. The main results are as follows:1. Effects of seeding rates, direct seeding and nitrogen management on lodging resistance of hybrid riceThe physical and chemical properties and lodging-resistance of rice culm were significantly affected by seeding rates and nitrogen management. The risks of lodging-resistance were lower with the increase in seeding rates. Unlike seeding rates, the impacts of fertilizer management on lodging-resistance were different. When seeding rates were less than 22.5 kg/hm2, through antedisplacement of nitrogen could cut down the base internode length, decrease the flat ration and cavity area, increase breaking resistance and cellulose and lignin contents, thus enhance the lodging-resistance. However, the application of nitrogen needed to be postponed in order to enhance lodging-resistance when the seeding rates were increased to 30 kg/hm2.Compared to different direct seeding methods, the wide-narrow row sowing increased the lodging-resistance via shorting internodes and plant height, decreasing cavity area and increasing the concentrations of cellulose, lignin and carbohydrate. Besides, broadcast and drill sowing under P1 or P2, and precise dibbling under P3 also significantly increased the lodging-resistance. The increases in lodging-resistance were mainly reflected on the shorted internodes and plant height, better stem substantial degree and higher concentrations of cellulose, lignin, and soluble carbohydrates.2. Effects of seeding rates, direct seeding and nitrogen application on dry matter production of hybrid riceWith the increasing seeding rates, the total dry matte accumulation increased, whereas, the dry matter of stem-sheath during heading and maturity stages, the dry matter, and the export and translocation percentage of stem-sheath after heading stage increased first and then declined. The dry matter production was significantly affected by nitrogen fertilizer management where postponed the nitrogen application would beneficial for the accumulation of dry matter when seeding rates were less than 22.5 kg/hm2. Furthermore, postponed nitrogen application increased dry matter accumulation initially but decreased finally when seeding rates were above 30 kg/hm2.Compared to drilling sowing and precise dibbling, the wide-narrow row sowing obtained higher dry matter production especially at full heading stage. Instead, the export and translocation percentages of the stem-sheath were lower than other seeding methods. The export and translocation percentages and dry matter accumulation of stem-sheath at full heading stage were higher under broadcast sowing, however, the yields were lower than wide-narrow sowing due to decreased relatively dry matter after heading stage. Though the patterns of export and translocation percentages of stem-sheath were higher under both drill sowing and precise dibbling, the yields were still declined because of lower storage of substance before full heading stage. For panicle fertilizer management, the accumulation of dry matter and the export and translocation percentages increased when the panicle fertilizers were applied on the 2nd leaf from the top under broadcast sowing (P3), and applied equivalently on the 4th and 2nd from the top under drilling sowing, wide-narrow sowing and precise dibbling, respectively.3. Effects of seeding rates, direct seeding and nitrogen application on the nitrogen use efficiency of hybrid riceThe effects of increased seed rates on rice differed where nitrogen accumulation and the nitrogen use efficiency for biomass and grain production were increased, while the nitrogen translocation of stem-sheath and utilization efficiency were increased first and then dropped. There was little effect of seedling rate on nitrogen harvest index. Postponed nitrogen application enhanced the nitrogen accumulation, agronomic efficiency and use efficiency, however, it would lead to the decrease in the nitrogen use efficiency for grain production and nitrogen harvest index when seeding rates were below 22.5 kg/hm2. With the increase in seeding rates, postponed nitrogen application improved the nitrogen use efficiency for biomass production, whereas no effect observed for the grain yields.Compared to other three direct seeding methods, the concentrations of nitrogen were higher while the nitrogen translocation efficiency and conversion rate were lower under wide-narrow sowing. Besides, the sowing method decreased the nitrogen use efficiency for biomass production and nitrogen harvest index while increased the partial factor productivity of nitrogen and nitrogen use efficiency. The patterns of nitrogen translocation concentration, efficiency and conversion rate were higher at either P1 under broadcast, drilling sowing and precise dibbling, or at P2 under wide-narrow sowing. Totally, the nitrogen production efficiency, the partial factor productivity of applied nitrogen and the nitrogen agronomic efficiency were increased at P1, and the nitrogen uptake of grain were higher at P3.4. Effects of seeding rates, direct seeding and nitrogen application on grain yields and its components of hybrid riceThe highest yields were obtained under the 22.5 kg/hm2 seeding rates where reflected from the increased number of effective panicles, the filled grains per panicle and the thousand grain weight. The grain yields and its components were evidently affected by the interactions of seeding rates and nitrogen fertilizer management. Under the 22.5 kg/hm2 seeding rates, the treatment of N3 was beneficial for the number of effective panicle, filled grains per panicle, setting rate and the thousand grain weight, thus increased grain yields. Similarly, the grain yields were promoted under N2 when seeding rates were above 30 kg/hm2.In view of these direct seeding methods, the broadcast sowing could promote the formation of the number of effective panicles, setting rates and grain yields, the drilling sowing could enhance the setting rate, and the precise dibbling could increase the filled grains per panicle and the thousand grain weight. For nitrogen management, all the seeding methods obtained the highest grain yields under the treatment of P2 except broadcast sowing which showed no effect on both yields and thousand grain weight. |
PDF Full Text Request