Emergy-based analysis of grain production and trade in China during 2000-2015

The quantities of production, stocking and import of grain in China are growing rapidly, resulting in an evident disequilibrium in grain supply. Domestic production and international trade constitute a complete grain system to ensure the supply in China. Thus, it is very necessary to explore the strategy about how to improve the grain system in China by linking the production and trade processes of different grain types. However, the information on ecological consequences of the whole grain system in China from a time-series perspective has been lacking. Therefore, in this study, emergy evaluation is used to analyze the efficiency and sustainability of grain production and the balance of grain trade in China based on the official statistical data recorded during the 2000-2015 period. The results indicate that the unit emergy values (UEV) and nonrenewable resource efficiency (NRE) of wheat, maize, rice and soybean decreased by 37%-51%, and the emergy sustainability index (ESI) for the grain types improved by 8%-28% during the study period, showing the improved efficiency and sustainability of grain production in China. Meanwhile, the findings indicate that the average ESI value of soybean is 37%-53% higher than that of maize, wheat and rice, demonstrating that China's policy on increasing soybean area and reducing maize area is reasonable, because planting more soybean by replacing maize in some regions will contribute to the improvement of sustainability in the whole grain system in China. Furthermore, the emergy benefit ratios (EBRs) of wheat, maize, rice and soybean trade in China were 0.60, 1.11, 0.79 and 0.99, respectively, illustrating that only the trade of maize has been favorable to China in the past years, but the trades of other crops are causing the loss of emergy from China to trader partners. By comparing the emergy exchange ratios (EERs) of China's grain trade, this study advises China to reduce exported quantities of grain to industrial countries and to import maize and soybean from the USA, rice from Thailand and Vietnam, and wheat from Australia.