A Comparative Study On The Varieties Of Double Cropping Rice Transplanting At Different Maturity In Southern Hunan

Through the experiment,the early and late rice varieties with different maturity which are suitable for the machine transplanting in southern Hunan were selected,which can provide reference for the annual double cropping rice yield improvement in southern Hunan.In this paper,nine combinations of early and late rice varieties with different maturity were tested in Yongzhou area,southern Hunan Province.The results are as follows:（1）in recent ten years（2010-2019）,the early sowing limit period（hybrid indica rice≥12℃）of niujiaoba Town,Lengshuitan District,Yongzhou City was around March 25.From September 21 to September 25,when the daily average temperature is stable through 21℃,the continuous days when the daily average temperature is stable at 12℃～21℃are 180～189 days,and the accumulated temperature is 4401～4500℃.From September 16 to September 20,when the daily average temperature is stable through 23℃,170-179 days when the daily average temperature is stable at 12℃～23℃,and the accumulated temperature is 4501-4600℃.（2）The results showed that the yield of lingliangyou 268+Taiyou 871 was the highest,reaching16.29t/hm²,and the lowest was Zhuliangyou 819+Fengyou 9,only 13.76t/hm².（3）In the experiment,the early and late rice varieties with the shortest growth period were selected,the growth period was 232 days,the longest growth period was 244 days.All of the 9patterns can successfully complete the mature harvest process in southern Hunan.（4）In the experiment,the dry matter accumulation of early rice was lower than that of late rice.The dry matter accumulation of early rice was 14491.7kg/hm²,and that of late rice was18843.06kg/hm².The accumulation of early rice is higher than that of the whole growth period,and the accumulation of late rice at full heading stage is higher than that of the whole growth period.（5）the leaf area index of early rice is lower than that of late rice.There was little difference between the change of Lai in early rice and that in late rice.The leaf area index of late rice increased faster than that of early rice,and decreased faster after heading than that of early rice.（6）The results showed that the average difference of effective accumulated temperature and light resources between 9 patterns was not significant.The pattern of late Early Rice+late late late rice had the longest growth period and the highest utilization rate of temperature and light resources in the whole year.The effective accumulated temperature was 3251.5℃,the effective accumulated temperature distribution rate was 49.51%,the annual effective accumulated temperature utilization rate was 87.24%,and the heat utilization rate was 5.01kg·hm^-2·℃^-1·d^-1。The utilization efficiency of accumulated temperature increased with the extension of growth period.（7）In the process of mechanized cultivation of double cropping rice,the utilization rate of temperature and light resources of late rice was significantly higher than that of early rice,resulting in a higher final yield of late rice than that of early rice.When planting double season rice in southern Hunan,it is recommended that early rice should use varieties with growth period of more than 100 days and less than 110 days,so as to provide sufficient temperature and light resources for late rice to ensure high yield of double season rice throughout the year.