Assessing the efficiency and sustainability of wheat production systems in different climate zones in China using emergy analysis

China is the country with the largest wheat planting area in the world, and wheat is one of the two main staple food crops consumed in China. Wheat is widely cultivated in 15 provinces throughout the country and across 3 climate zones including the subtropical monsoon climate zone, temperate monsoon climate zone and temperate continental climate zone. The natural conditions of each climate zone are different, and the ways in which the wheat production system operates are different. To ultimately safeguard the production and explore the similarities and differences in input and output of the same system under different climate conditions, the emergy method was used to research the comprehensive performance of the wheat production system based on 2014 statistical data from China. The results indicate that there was a significant variance in the input of local renewable environmental resources, ranging from 0.48E+14 sej/ha in Xinjiang in the temperate continental climate zone to 4.46E+14 sej/ha in Shaanxi in the temperate monsoon climate zone. Among the three climatic zones, the temperate continental climate zone had the lowest emergy self-support ratio (0.13), followed by the temperate monsoon climate zone (0.15) and then the subtropical monsoon climate zone (0.20). Regions in which natural resources are insufficient, such as temperate continental climate zone, need additional purchased resources to maintain normal operation of the wheat production system. Compared with other intensive agricultural production systems, the wheat production system is extensive and low-cost and has room for improvement with more artificial input. The Middle-Lower Yangtze River Plain at the junction of temperate monsoon climate zone and subtropical monsoon climate zone is the most efficient region for planting wheat based on the ratio of the entire emergy input to the entire energy output. This ratio should be considered in the adjustment of the agricultural cropping structure to make use of resources more effectively.