| Chemical fertilizer application plays an important role for the yield increase in rice production. However, overuse of chemical fertilizer, especially the nitrogen (N) fertilizer, can not only reduce the N use efficiency but also cause the environmental problem. In the present study, we analyzed yield formation characteristics of super rice grown under different ecological conditions and N application rates as well as N use efficiency and N accumulation characteristics under different yield levels. Our objective was to determine whether it is possible to achieve both high yield and high N use efficiency in super rice production in China. Field experiments were conducted in five major rice-producing provinces in China in2011and2012. The experimental sites were located in Binyang, Huaiji, Haikou, Changsha, and Xingyi of Guangxi, Guangdong, Hainan, Hunan, and Guizhou provinces, respectively. Four super rice varieties (Liangyoupeijiu, Y liangyou1, Yuxiangyouzhan, and Huanghuazhan) were grown in single-rice growing season in Haikou, Changsha and Xingyi and in double-rice growing seasons in Binyang and Huaiji under three N rates (N1:225kg/hm2, N2:112.5kg/hm2, N3:0kg/hm2). The treatments were arranged in a split-plot design with N rates as main plots and varieties as subplots. The experiment was replicated three times. The results were shown as following:1Yield performance of super riceA significant difference in grain yield was observed among the experimental sites. Xingyi produced the highest grain yield, which was22.7%,36.8%,83.2%and160.6%higher than that produced in Changsha, Haikou, Binyang, and Huaiji, respectively. A significant difference in grain yield was observed among the varieties. Average grain yield of super hybrid varieties (Liangyoupeijiu and Y liangyou1) was10.5%higher than that of super inbred varieties (Yuxiangyouzhan and Huanghuazhan) in Haikou, Changsha, and Xingyi, however, there was an insignificant difference in grain yield between super hybrid varieties and super inbred varieties in Binyang and Huaiji. A significant difference in grain yield was observed among the three N rates. In2011, grain yield was higher under N2than under N1in Bingyang, whereas in Changsha and Huaiji, it was higher under N1than under N2. In2012, except Huaiji and Haikou, grain yield under N2was higher than that under N1. 2Yield components of super riceThere was a significant difference in yield components among the experimental sites. Panicles per m2, spikelets per panicle, spikelets per m2and grain filling were relatively higher in Xingyi, whereas those were relatively lower in Huaiji. A significant difference in grain weight was observed between super hybrid cultivars and super inbred cultivars but not between the same groups. Yield components of super rice were significantly affected by genotype. The spikelets per panicle was the lowest in Huanghuazhan and highest in Yuxiangyouzhan. On the contrary, the panicles per m2was the lowest in Yuxiangyouzhan and highest in Huanghuazhan. At maturity, the grain yield of super rice was positively correlated to the panicles per m2, spikelets per m2, spikelets per panicle, and grain filling.3Biomass production and harvest index of super riceA significant difference in biomass of super rice was observed among the experimental sites. Dry matter production at heading and maturity were relatively higher in Xingyi but were relatively lower in Huaiji. Dry matter production of super rice was significantly affected by genotype. When grain yield>9t ha-1, dry matter production of super hybrid cultivars was higher than that of super inbred cultivars at heading and maturity. However, when grain yield<9t ha-1,there was an insignificant difference in dry matter production between super hybrid cultivars and super inbred cultivars. Grain yield of super rice was positively correlated to the dry matter accumulation at heading and maturity as well as from heading to maturity under different ecological conditions and N application rates. The harvest index of super rice was significantly affected by N application rate. N3had the highest harvest index. A significant difference in harvest index of super rice was observed among the experimental sites. Xingyi had the highest harvest index, which was0.553-0.578. At maturity, the grain yield of super rice was positively correlated to the harvest index.4N, P and K uptake amounts of super riceSignificant differences in N, P and K uptake amounts were observed among the N application rates and the experimental sites. The highest N uptake amount was observed in Xingyi, which was23.5%,98.2%,67.8%, and175.6%higher than Changsha, Haikou, Binyang, and Huaiji, respectively. The higher P and K uptake amounts was observed in Changsha, which were4.3～4.7g m-2and20.5～21.7g m-2, respectively. Except early rice in Binyang and late rice in Huaiji, the N, P and K uptake amount was ordered as:N1>N2>N3.5N, P and K harvest indexes of super riceThere were significant differences in N, P and K harvest indexes among the N application rates and the experimental sites. The highest N and P harvest indexes was observed in Xingyi, which was0.690and0.777across the four varieties. The highest K harvest index was achieved in Haikou, which was0.135across the four varieties. With the increase of grain yield, the N and P harvest indexes were increased. The N, P and K harvest indexes under N3were higher than those under N1. Grain yield was positively correlated to the N and P harvest indexes but not correlated to K harvest index. Differences in N, P and K harvest index were small and inconsistent across the four varieties.6N, P and K uptake amount aboveground plants to produce1000kg grain of super riceA significant difference in N, P and K uptake amount aboveground plants to produce1000kg grain was observed among the experimental sites. N requirement for producing1000kg grain was the lowest in Huaiji, which was13.5～16.9kg, and was highest in Changsha, which was22.0～23.6kg. P requirement for producing1000kg grain was the lowest in Xingyi, and was highest in Binyang. K requirement for producing1000kg grain was the lowest in Xingyi and Huaiji. The grain yield was negatively correlated to the N, P and K uptake amount aboveground plants to produce1000kg grain.7N use efficiency of super riceThere was a significant difference in N use efficiency among the experimental sites and the three N rates. The higher N agronomy efficiency was observed in Huaiji, while the higher partial factor production and N recovery efficiency was observed in Xingyi. N agronomy efficiency, partial factor production and N recovery efficiency under N2was higher than those under N1. Furthermore, the N use efficiency was increased with increasing grain yield.The above findings indicated that a significant difference in nitrogen use efficiency and grain yield of super rice was observed among the five experimental sites and the three N rates and genotypes, and the highest grain yield of super rice was achieved in Xingyi, and the higher fertilizer use efficiency as well. It can make a conclusion that there was a closely coordinated relationship existed between higher yield and higher N use efficiency in super rice. In super rice production in a given planting area, a target yield should be decided according local ecological condition, and then using correspondingly quantified cultivation techniques and population regulating techniques to achieve the target yield and high N use efficiency. In addition, the high N use efficiency should be taken as the selection target in rice breeding. |
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