Characteristics of resource allocation and utilization of rice-wheat double cropping system in the Jianghuai Area

Rice-wheat double cropping system is the main cropping pattern in the Jianghuai Area. The characteristics of natural resource allocation and utilization and their relationship with yield are still unclear. It is necessary to establish a quantitative evaluation index system for the systematic guidance of the double cropping system. In this study, resources distribution between two seasons, resources utilization efficiencies, and yield of rice-wheat double cropping system in three regions of the Jianghuai Area:along Huaihe River region (AHR), Jianghuai region (JH), and along Yangtze River region (AYR), were quantitatively analyzed using the large database created from high yield field experiments during 2008-2017. The results were as follows:radiation during wheat season and per year decreased in the region, while in the rice season radiation increased in AHR and JH but decreased in AYR. The accumulated temperature increased in wheat season and decreased in rice season, and the annual accumulated temperature increased in AHR and decreased in JH and AYR. Precipitation during wheat season, rice season, and per year increased. The annual radiation in the Jianghuai area increased from the north to the south with no significant difference between japonica rice-wheat system and indica rice-wheat system. The radiation distribution rate of wheat season and rice season were 53.1% and 51.9%, respectively, for the japonica rice-wheat double cropping system, and 55.0% and 49.8%, respectively, for the indica rice-wheat double cropping system. The cumulative accumulated temperature and precipitation gradually increased from the north to the south of Jianghuai area, with no significant difference between two systems, but there were significant differences between different regions. The distribution rate of accumulated temperature in wheat and rice season were 38.5% and 67.3%, respectively, for the japonica rice-wheat, and were 40.7%, 65.1%, respectively for the indica rice-wheat double cropping system. The accumulated precipitation distribution rate of wheat season and rice season were 32.8% and 70.5%, respectively, for the AHR region; 40.8% and 64.7% respectively, for the JH region; and 46.2%, 57.2%, respectively, for the AYR region. Under the current production pattern, rice production had the highest yield proportion of the wheat-rice double cropping system, with an average of 57.0%. The temperature production efficiency in wheat season was higher in AHR than in JH and AYR; during rice season this did not change greatly between the two systems and among the three regions. The annual temperature production efficiency order for the three regions was:AHR > JH > AYR. Radiation use efficiency of crops was not different for different seasons. The rain production efficiency in wheat and rice seasons and per year was significantly lower in AYR than both in AHR and JH. Rice production in the JH region was mainly affected by radiation, and wheat production was mainly affected by rainfall, which limited further increase in crop yield potential. Climate change effects tended to be unfavorable to the evolution of climate resources in the future. When compared with wheat, rice had higher efficient utilization of radiation resources, which was important for improving yield and the resource use efficiency of rice-wheat double cropping system in the JH region. Based on the analysis, we put forward the principle of annual high efficiency utilization, because radiation was the main factor between the two wheat-rice double cropping system, when considering rainfall and growth degree-days. Cultivation measures such as sowing date adjustment and annual cultivars combination can allocate more resources to rice season, thus improving the yield and resource utilization efficiency.