Study On Relieving Cold Stress For Direct-Seeded Rice Of Double Season At Seedling And Heading Stage By Water And Fertilizer Regulation And Chemical Control

A light and simple cultivation technique of saving labor and cost as well as increasing efficiency,direct seeding rice has been widely used in the middle and lower reaches of the Yangtze River in southern China.In most areas,the seedling stage of direct seeding early rice and the seedling stage of direct seeding late rice are vulnerable to low temperature chilling injury.In this paper,early rice varieties with low temperature tolerance suitable for direct seeding of southern double cropping rice were selected based on large-scale popularizing varieties in the middle and lower reaches of the Yangtze River.The effects of fertilizer and water and chemical control measures on the growth and yield of double-cropping direct seeding rice under Cold Dew wind condition at seedling stage and late rice heading and flowering stage were studied.The main findings are as follows:(1)The plant height,root length,root number,root volume,dry matter mass and leaf area of each early rice variety were significantly different from those under normal temperature(5℃,8℃,11℃)at seedling stage.The coefficient of variation among the indexes of 5℃ low temperature treatment was the largest,which indicated that 5℃ low temperature was more suitable for the selection of varieties with low temperature tolerance.The results of principal component analysis showed that dry weight and plant height could be used as indicators of cold tolerance in seedling stage,and the tested varieties could be classified into three groups by using membership function and cluster analysis.The first category was composed of 15 varieties with strong cold tolerance(Zhuliangyou1hao,Wufengyou 623,Xiangzaoxian6 hao,etc.).The second category is for 17 varieties of cold tolerance(Lingliangyou 661,Lingliangyou 7717,Lingliangyou 0516,etc.).The third category is sensitive to low temperature(Liangyou 287,Zhongjiazao 17,Zhuliangyou 819,etc).(2)Under the condition of low temperature at seedling stage of early rice,the yield of early rice decreased obviously compared with the control,and the decrease range of different varieties was obviously different,and the decrease range of low temperature tolerant variety was obviously lower than that of cold sensitive variety.The descending order was Zhuliangyou 819> Zhongjiazao 17>Xiangzaoxian 6 hao>Wufengyou 623;under low temperature,potassium fertilizer,silicon fertilizer or deep-water irrigation could significantly increase seedling survival rate,seedling height,root length,root number,root volume,dry matter mass,leaf area,stem tiller number and stem tiller number.The seed setting rate was increased,the weight of 1000 grains and the number of grains per panicle were increased.On the whole,different measures of controlling fertilizer and water could effectively increase the yield of early rice under low temperature,and the effect of increasing silicon fertilizer was the best.(3)Spraying chemical regulator on leaf surface before heading stage of late rice effectively alleviated the decrease of net photosynthetic rate and increased SPAD value,spraying different chemical regulators increased 1000-grain weight and seed setting rate,and the yield was significantly higher than that of the control.Moreover,the processing quality and appearance quality of rice were obviously improved,especially the mixed application of potassium dihydrogen phosphate + gibberellin + 0.01% brassin had the best effect.