| Nitrogen use efficiency of rice includes both uptake and transformation, and only two synergies can be achieved the real meaning of efficient utilization. In order to solve a series of problems caused by large amount of nitrogen fertilizer application, unreasonable ratio and timing of nitrogen application, this study was conducted with different nitrogen levels, nitrogen ratios of basal and tillering fertilizer and nitogen application timings at at three rice-growing locations (Panjin,Shenyang and Kaiyuan), focusing on environment and cultivation, through pot, PVC-tube planting, field experiment. Our research set 3 experiments (1) Effects of temperature and sunshine hour conditions on rice: the pot experiment was carried out in Kaiyuan, Shenyang and Panjin with Shennong 265(conventional japonica rice which has 15 leaves in main stem), respectively. The soils used in the experiment were similar. Low nitrogen (N-30%), normal nitrogen (N), high nitrogen (N+30%) and control treatment (N0,no nitrogen application) were used at each location. Three nitrogen ratios of base and tillering fertilizer and panicle fertilizer were set under each nitrogen application level (7:3,6:4 and 5.5:4.5). (2) Panicle fertilizer optimization on rice: field experiments with two rice cultivars(Shennong 265 and Liaoyou 4387) were conducted under nitrogen level of 225 kg ha-1 in Shenyang.We set control treatment and six different combinations of leaf stage nitrogen application under conventional nitrogen application management. (3) Accurate nitrogen application of different leaf stages on rice: PVC-tube planting experiment was conducted for Shennong 265 under the nitrogen level of 225 kg N ha-1 in Shenyang. Sample fertilizer application management with three timings nitrogen application (base fertilizer, tillering fertilizer and panicle fertilizer) was used in this study.According to timings of tillering and panicle fertilizer, we set 25 combinations of leaf stages under different tillering and panicle fertilizer ratios (8:2 and 6:4). The main findings are as follows:1. Rice yield and its componentsThe results of effects of temperature and sunshine hour conditions on rice found that the average yield of Kaiyuan, Shenyang and Panjin were 34.03 g pot-1, 39.17 g pot-1 and 40.69 g pot-1,respectively, and the temperature and light conditions in south of Liaoning were beneficial to obtain high yield. Grain yield showed a rising trend with the increasing ratio of panicle nitrogen fertilizer, and high yield was mainly caused by the higher number of effective panicles. The number of effective panicles in Panjin was 19.57% and 3.88% higher than Kaiyuan and Shenyang, respectively; while the difference of panicle size,percentage of filled grains and 103-grain yield was not significant.Our results of panicle fertilizer optimization on rice found the panicle N application, where spikelet-promoting fertilizer was applied at 4th top leaf stage and spikelet-protecting fertilizer was applied at 1st top leaf stage produced highest grain yield. This combination of leaf stages had largest number of effective panicles, and other yield components were not significant. The performances of conventional japonica rice and hybrid japonica rice were similar. The results of accurate nitrogen application of different leaf stages on rice showed that the leaf age of tillering fertilizer application timing which could obtain high yield were most at 8th, 9th and 10th leaf age, while the panicle fertilizer application timing were most at 11th and 12th leaf age (top 5th and 4th leaf). These combinations obtained higher grain yield, and the number of effective panicles, spikelets per panicle, percentage of filled grains and 103 grain weight maintained at high level. The results of above three experiments showed that increasing the number of panicles was an effective method for high rice yield in north area. On the operations of nitrogen fertilizer, appropriately increasing the ratio of panicle nitrogen fertilizer has been a trend. The functions of panicle fertilizer not only promote the spikelets and increase grains, but also increase the number of effective panicles. Because these stages (top 4th and 5th leaf stege) were both the beginning of panicle differentiation and the stage of tillering polarization differentiation. Nitrogen fertilizer application could push on the growing of small and mid tillers and promote tillers to panicles. Thus, panicle fertilizer could not only promote the spikelets and increase grains, but also protect the tillers to panicles. It could explain the reason of increasing the ratio of panicle fertilizer, and verified the exsistance and importance of "tillering-protecting fertilizer". It provided new ideas for nitrogen fertilizer regulation.2. Panicle development of riceEffects of temperature and sunshine hour conditions on rice found that the number of primary branches showed a down trend from north to south, while the number of secondary branches increased significantly. However, the effect of temperature and sunshine hour conditions on the number of total spikelets was not significant. The results of panicle fertilizer optimization on rice showed that it is beneficial to decrease spikelet degeneration of secondary branches and reconcile grain fillings in later growth stage which prolongs spikelet-protecting fertilizer application by one leaf age (top 1st leaf) with the same timing of spikelet-promoting fertilizer application. The results of accurate nitrogen application of different leaf stages on rice showed that the panicle fertilizer which applied at 12th and 13th leaf stage (top 4th and 3th leaf) could increase the number of differentiated spikelets and optical spikelets. Therefore, the effects of promoting-fertilizer and protecting-fertilizer were significantly differnet, and promoting-fertilizer was more important than protecting-fertilizer. The ratio of tillering and panicle fertilizer at 6:4 could increase the number of differentiated spikelets and optical spikelets compared with 8:2. We believed that the increasing of panicle fertilizer could promote the differentiation and formation of spikelets.3. The physiological characteristics during the key period of riceThe net photosynthetic rate and soluble protein content of flag leaf were measured under different temperature and light conditions with different levels and timings of nitrogen application. Our results found that nitrogen application could improve the net photosynthetic rate and soluble protein content of flag leaf at heading stage for Shennong 265 compared with control treatment (NO). The net photosynthetic rate at heading stage in Panjin was 15.05% and 5.36% higher than Kaiyuan and Shenyang, respectively. Nitrogen ratio had no significant effect on the net photosynthetic rate. The soluble protein content of flag leaf in Panjin was 41.83% and 24.25% higher than Kaiyuan and Shenyang, respectively, and the difference was significant. The net photosynthetic rate, soluble protein content, nitrate reductase and glutamine synthetase activity were measured at heading and grain filling stage. The results showed that there was no significant difference in the net photosynthetic rate under different combinations of spikelet-promoting and spikelet-protecting fertilizer except control treatment.The content of soluble protein, nitrate reductase and glutamine synthetase in heading stage were higher than that at grain filling stage. The panicle fertilizer combination of 4th top and 1st leaf age obtained higher soluble protein content, nitrate reductase and glutamine synthetase. In addition, the two cultivars were consistent.4. Nitrogen absorption and transport efficiency of riceThe results found that nitrogen recovery efficiency and nitrogen physiological efficiency showed an increasing trend from north to south. The nitrogen recovery efficiency of Panjin was 17.60% and 14.23% higher than Kaiyuan and Shenyang, respectively; while the nitrogen physiological efficiency was 29.11% and 23.58%, respectively. Nitrogen recovery efficiency and nitrogen physiological efficiency with nitrogen ratio of 5.5:4.5 were higher than that of 7:3 and 6:4. With the increasing of panicle nitrogen ratio, nitrogen use efficiency showed a rising trend, and the performance of three experimental locations was consistent. The leaf age of tillering fertilizer application timing which could obtain high NRE and NPE were most at 8th , 9th and 10th leaf age, while the panicle fertilizer application timing were most at 11th, 12th and 13th leaf age under the sample nitrogen management.This result was similar with that of grain yield.In conclusion, rice yield and nitrogen use efficiency were significantly affected by temperature and sunshine hour conditions, timings of panicle nitrogen application and nitrogen application raitos.Panjin which had higher accumulated and mean temperature produced highest grain yield and nitrogen use efficiency, the second is Shenyang and the lowest is Kaiyuan. It is suggested that the climatic conditions in south of Liaoning Province beneficial to improve both nitrogen uptake and transformation. Under the conventional nitrogen management,delaying the applied timing of spikelet-protection fertilizer properly is better for getting high yield, and this method was suitable for conventional japonica rice and hybrid japonica rice. Under the sample nitrogen management, we should pay more attention to the application of tillering-protection and spikelet-promoting fertilizer in order to improve nitrogen use efficiency in south area of Northeast China. |
PDF Full Text Request