| To investigate the adaptability of double-cropping rice to nitrogen-decreasing and density-increasing cultivation,taking two early rice varieties and two late rice varieties as materials with four nitrogen fertilizer density treatments.No nitrogen with conventional density(N 0kg/ha,286000 hole/ha),no nitrogen with high density(N0 kg/ha,286000 hole/ha),low nitrogen rate with high density(N 120kg/ha,364000 hole/ha)and conventional nitrogen with conventional density(N 150kg/ha,286000 hole/ha)were set up using split panel design.The change of growth status,yield and yield components,nitrogen accumulation and nitrogen use efficiency of mechanically inserted double cropping rice were studied under the condition of three consecutive years of nitrogen-decreasing and density-increasing.The results show that:(1)Compare to conventional cultivation,under the condition of consecutive three years of nitrogen-decreasing and density-increasing cultivation,the relative chlorophyll content(SPAD value)of double-cropping rice was decreased in different degree,but the population growth indexes such as tillers number,dry matter weight of population,dry matter accumulation of population stage,leaf area index and so on were not significantly changed,which indicated that appropriately reducing nitrogen fertilizer rate combine with increasing plant density was not influenced the population growth of rice.(2)Compare to conventional cultivation,under the condition of consecutive three years of nitrogen-decreasing and density-increasing cultivation,there was no significant change in yields of machine-transplanted double-cropping rice,which the effective panicles was increased while the number of spikelets per panicle was reduced,and 1000-grain weight and seed-setting rate was not significantly changed.The three-year average yield of Zhuliangyou 819,Zhongjiazao 17,Taiyou 390 and Xiangwanxian 13 were 7320 kg/ha,6737kg/ha,8570kg/ha and 6957kg/ha for conventional cultivation,6643kg/ha、6367kg/ha、8283kg/ha and 6933 kg/ha for nitrogen-decreasing and density-increasing cultivation,respectively.Except for the yield Zhuliangyou 819 in 2017 was significantly decreased,compare to conventional nitrogen with conventional density treatment,the other rices yield in different years were no significant difference between the treatments of nitrogen-decreasing and density-increasing and conventional nitrogen with conventional density.Which showed that under the condition of 20% reduction of nitrogen application,the rice yield was not significantly decreased by increased the planting density with 27.3%.(3)The analysis of yield sustainability and coefficient of variation shows that the difference between different nitrogen and density treatments was no significantly,while the difference between varieties was obviously.Compared with conventional cultivation,The nitrogen reduction and densification of two hybrid varieties was slightly higher than that of conventional cultivation treatment,the yield variation coefficient was slightly higher than that of conventional cultivation treatment,and the late hybrid rice was the opposite,but there was no difference between different nitrogen density treatment of hybrid early rice.In all treatments,the highest yield sustainability was Taiyou 390 under the treatment of nitrogen-decreasing and density-increasing,and the smallest yield coefficient of variation was also Taiyou390 under this treatment,which showed that the cultivation of nitrogen-decreasing and density-increasing could maintain the same yield sustainability and stability,compared to conventional cultivation.Moreover,the yield sustainability and stability of hybrid rice was higher than those of conventional rice.(4)Compare with conventional cultivation,The nitrogen accumulation of double cropping rice was increased by nitrogen-decreasing and density-increasing,and further improved the nitrogen use efficiency of the double-season rice.Based on the three-year average values of nitrogen partial productivity,nitrogen agronomic utilization,nitrogen uptake utilization and nitrogen harvest index,The conventional cultivation of Zhu Liangyou 819 was 49.00 kg/kg 、 19.03kg/kg and 29.37%,and the nitrogen-reducing and density-increasing cultivation was 59.87 kg/kg、21.9kg/kg and 32.03%,respectively.The conventional cultivation in Zhongjiazao 17 was 49.43 kg/kg、17.33kg/kg and 30.93%,the nitrogen-reducing and densifying cultivation was 58.57 kg/kg、20.13kg/kg and 33.00%,respectively,the nitrogen-reducing and densifying cultivation increased 18.48%,16.15% and 6.67%,the conventional cultivation in Taiyou 390 was 57.10 kg/kg、14.57kg/kg and 41.03%,the nitrogen-reducing and densifying cultivation was 70.30 kg/kg、14.20kg/kg and 42.80%,the nitrogen-reducing and densifying cultivation increased 23.12% and 4.31%,and the agronomic utilization ratio decreased 2.52%,respectively.The conventional cultivation of Xiangwanxian 13 was 46.37 kg/kg、10.13kg/kg and 40.43%,and the nitrogen reduction and densification cultivation was 61.37 kg/kg 、 13.17kg/kg and 45.37%,respectively.The nitrogen reduction and densification cultivation increased by 32.35%,29.93% and 12.2%... |
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