Optimal Configuration And Efficient Utilization Of Annual Climate Resources In Rice–Wheat Double Cropping In Yangtze-Huaihe Rivers

Rice-wheat double cropping is one of the most important cropping systems in Yangtze-Huaihe Rivers.Due to the impacts of climate change,as well as the emergence of large-scale and intensive land use and different planting modes,the in-depth utilization of temperature and light resources and the full development of variety production potential are realized with the focus on optimizing the planting area and variety layout.This not only makes a significant contribution to the past grain production increase,but also is an important measure to implement a new round of action to increase grain production capacity of 100 billion kilograms in the future.Therefore,this study aims at the prominent issues of irrational allocation of climate resources in the rice wheat double cropping system caused by climate warming,as well as the mismatch between variety types,sowing dates,and growth period processes with light,temperature,and water resources,which can affect the growth and development of crops,limit annual yield,and improve resource utilization efficiency,By combining the statistical analysis of historical data on rice wheat double cropping production data and meteorological data with multiple years of staged sowing experiments on different types of varieties in the field,the characteristics of climate resource optimization and efficient allocation between seasons of rice wheat double cropping system were studied,and an annual high yield and efficient technical system was established.The main research results are as follows:1.Analyze the historical evolution of the phenological period and annual distribution and utilization of light and temperature resources in the rice wheat double cropping system in Yangtze-Huaihe Rivers,identify the key climatic factors that affect the annual yield of rice and wheat,and determine that the rice wheat double cropping system should focus on the dominant crop rice to optimize the allocation of light,temperature,and water climatic resources.Climate change has significantly advanced the sowing date,heading date,and maturity date of rice,with the largest advance in sowing date and an increase in overall growth and development;Wheat has the same trend of change,but the trend is not obvious,and the impact of rice phenology is significantly greater than that of wheat.Climate change has an increasing trend in the cumulative temperature distribution during the rice and wheat annual double cropping rice season,with a decreasing trend in the cumulative temperature distribution of wheat,and an increasing trend in the radiation distribution of wheat.However,the rice season has a decreasing trend in precipitation,while the wheat season has an increasing trend.The key climatic factors affecting the annual yield of rice and wheat are excessive accumulated temperature and precipitation during the rice season,while wheat has no significant correlation with accumulated temperature,radiation,and precipitation.2.In order to maximize the high yield potential of rice,the quantitative relationship between rice yield formation and climatic factors such as light and temperature was studied.The key time and climate factors affecting rice yield are the daily average temperature 40 days after full heading.In addition,there was a positive correlation between indica rice and accumulated temperature before full heading,while japonica rice was negatively correlated with accumulated precipitation,wind speed,and accumulated temperature before full heading.Define the daily average temperature threshold when rice reaches the maximum yield.The yield of indica rice was the highest when the daily average temperature was24.4 ℃ at the filling stage 40 days after full heading,with a decreasing effect of-85.93kg/hm2 above 24.4 ℃.The yield of japonica rice was the highest when the daily average temperature was 22.6 ℃ at the filling stage 40 days after full heading,with a decreasing effect of-56.65 kg/hm2 above 22.6 ℃.In the past 30 years,the daily average temperature during the rice growing season has shown a significant increase trend,increasing by0.29℃to 0.34℃every 10 years,the average maximum temperature increasing by 0.36℃ to0.43℃,and the average minimum temperature increasing by 0.25℃to 0.4℃,respectively.3.On the basis of analyzing the occurrence law of high temperature and heat damage of rice,the best sowing date and harvest date of annual high yield of rice-wheat double cropping system were finely determined at county level,and the optimization and efficient allocation of annual climate resources of rice-wheat in Yangtze-Huaihe Rivers,which is dominated by heat,were made clear.The best sowing date of wheat along the Huaihe River and northern Jianghuai is from October 20 th to October 25 th,and the best sowing date along the Huaihe River and southern Jianghuai is from October 25 th to October 30 th.The sowing period of wheat in the south of Yangtze River is from October 30 th to November6 th.The maturity period between Huaihe River and Jianghuai River is from May 23 rd to May 28 th,and the maturity period along the Yangtze River and Jiangnan River is from May 18 th to May 22 nd.The maximum probability of high-temperature heat damage in most areas along the Huaihe River and between Jianghuai and Huaihe River occurs on July23-25,while most areas along the Yangtze River and south of the Yangtze River occur around July 30.The sowing date of indica-wheat double cropping direct seeding rice along Huaihe River and northern Jianghuai should be arranged from the end of May to the beginning of June,and the sowing date of transplanted rice should be in early May.The whole growth period of wheat varieties should be less than 220 days,that of direct seeding indica rice varieties should be about 120 days,and that of transplanted indica rice varieties should be about 140 days.The sowing date of direct seeding rice should be at the end of May,and the sowing date of transplanted rice should be in the middle of May.The whole growth period of direct seeding indica rice varieties should be about 130 days.The whole growth period of transplanted indica rice varieties should be about 140 days.The sowing date of direct seeding rice along the Huaihe River and the northern part of the Yangtze River and Huaihe River should be in early June,the sowing date of transplanted rice should be in early May,and the whole growth period of direct seeding japonica rice varieties should be about 130 days.The sowing date of direct seeding rice should be at the end of May,and the sowing date of transplanted rice should be in the middle and late May.The whole growth period of direct seeding japonica rice varieties should be about 140-150 days.The whole growth period of transplanted japonica rice varieties should be about 150 days.The distribution rates of accumulated temperature in indica-wheat model are 38%(wheat)and 65%(rice),while those in japonica-wheat model are 36%(wheat)and 67%(rice),and the ratio of specific accumulated temperature in two seasons(wheat/rice)is 0.58 and 0.54,respectively.4.Studying the effects of sowing date,nitrogen application rate,and planting methods on the annual yield and resource utilization efficiency of rice and wheat,it was found that the yield of late maturing medium indica,early maturing late japonica,and mid maturing late japonica rice decreased significantly with the delay of sowing date,while no significant changes were found in mid maturing medium japonica and late maturing medium japonica.The yield of wheat decreased with the delay of sowing date,but the difference between sowing dates was not significant.The influence of sowing date on growth period is shown as late maturing medium indica rice<medium maturing late japonica rice<late maturing medium japonica rice<early maturing late japonica rice<medium maturing medium japonica rice.In the south of Jianghuai region,it is advisable to choose the late maturing medium indica wheat sowing date combination model on May 10 th and November 4th,with the highest annual light and temperature utilization efficiency.The photosynthetic potential,net assimilation rate,average specific leaf weight,and average dry matter weight of different types of rice from heading to maturity were significantly positively correlated with grain weight.Hybrid varieties should be planted by hand or machine,while conventional rice can be planted by direct seeding.Reasonable amount of nitrogen fertilizer and planting methods are important ways to achieve high yield and high efficiency of rice.To sum up,climate warming has changed the phenology of rice and wheat,affecting the configuration of climate resources in the rice wheat double cropping system;Define the daily average temperature during the grain filling period of the dominant crop rice to achieve high yield,while avoiding high temperature and heat damage during the rice heading period,and determine the optimal sowing and harvest dates for the annual high yield of the rice wheat double cropping system in a refined manner,exploring the effects of sowing date,nitrogen application,and planting methods on the annual yield and resource utilization efficiency of rice and wheat,in order to achieve optimal configuration of climate resources and efficient utilization within the seasons of rice and wheat double cropping system in Yangtze-Huaihe Rivers and provide theoretical support for the annual yield and efficiency increase of the rice wheat double cropping system.