| China accounts for more than 35% of the overall consumption of chemical fertilizer in the world. The rate of nitrogen fertilizer in rice field of China is higher than the world's average by 75%. However, the high input of nitrogen fertilizer does not increase the grain yield of rice. Moreover, stagnation of grain yield with overuse of fertilizer, decrease of nutrient use efficiency, excessive accumulation of nutrient in the soil and various environmental problems have became serious issues in rice production in China. This research was conducted in the field at Dajin town, Wuxue city, in 2009 and 2010. Several high production and high efficiency agronomic practices were obtained by modification of the ratio of base fertilizer and topdressing at midtillering and panicle initiation stages, increasing the amount of potassium fertilizer, application of organic fertilizer, altering the amount of nitrogen fertilizer according to SSNM and increasing planting density. The five agronomic practices used in this study were Zero-Nitrogen Treatment (NO), Farmers' Conventional Cultivation Pattern (FFP), Modified Farmers'Conventional Cultivation Pattern (OPT1), Super High Yield Cultivation (SHY) and Modified Super High Yield Cultivation (OPT2). The objectives of this study is to study the effect of different agronomic practices on grain yield and nitrogen use efficiency of double season rice, and determine the physiological mechanisms of high grain yield and high nutrient use efficiency in rice production. The main results are as followings:(1) In 2009, for early rice, OPT1, SHY, and OPT2 had a higher grain yield than FFP by 4.7%,16.4% and 19.7%, respectively. For late rice, the increase in grain yield was 12.0%,13.4% and 10.5%, respectively. In 2010, grain yield of OPT1, SHY and OPT2 was 12.5%,36.5% and 33.4% higher than FFP in early rice, respectively. Late rice with OPT1, SHY and OPT2 outyielded FFP by 12.3%,10.4% and 11.6%, respectively. The higher grain yield of the three high production efficiency agronomic practices (OPT1, SHY and OPT2) was mainly due to its higher biomass production and greater sink size (spikelets m-2). (2) High production and efficiency agronomic practices accumulated more nitrogen, potassium and phosphorus at maturity than FFP. In early rice of both 2009 and 2010, agronomic nitrogen use efficiency of OPT1, SHY and OPT2 was 13.1-19.1 kg grain kg-1 N, which was significantly higher than 9.2-12.2 kg grain kg-1 N of FFP. Similarly, in late rice of both the two years, OPT1, SHY and OPT2 had significantly higher agronomic nitrogen use efficiency (10.2-11.8 kg grain kg-1 N) than FFP (6.8-7.0 kg grain kg-1 N). However, no significant differences were observed in grain and biomass production efficiency of potassium and phosphorus among the treatment.(3) Growth analysis showed that OPT1, SHY and OPT2 produced higher biomass, more tillers and greater leaf area index at key growth stages. There were no significant differences in plant height among different agronomic practices, except in comparison with NO treatment.(4) At key growth stages, FFP had lower leaf nitrogen content than OPT1, SHY and OPT2, and was more susceptible to early senescence. Comparable photosynthesis in the flag leaf was achieved at heading stage and middle grain filling stage by different agronomic practices.The results in this study demonstrated that farmers' convertional cultivation pattern can be optimized by modification of the application rate, timing and types of fertilizers and changing planting density, and etc. Modified agronomic practices can promote the production of biomass and the formation of large sink size, which lead to a higher grain yield. Moreover, modified agronomic practices can increase the accumulation of nitrogen, potassium and phosphorus, and improve nitrogen use efficiency. |
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