[Carbon footprint of major grain crops in the middle and lower reaches of the Yangtze River during 2011-2020]

The middle and lower reaches of the Yangtze River is one of main grain production areas in China, which is of great significance to food security. Understanding the carbon footprint of major grain crop production is helpful to develop high-yield and low-carbon agriculture. Based on the data of yield, sown area and farmland production input of main grain crops (rice, wheat and maize) in six provinces (Jiangsu, Anhui, Jiangxi, Hubei, Hunan, and Zhejiang) in the middle and lower reaches of the Yangtze River from 2011 to 2020, we estimated carbon footprint in the production of the three grain crops. The results showed that from 2011 to 2020, yield per unit area, planting area, and total yield of rice, wheat and maize were the highest in Jiangsu Province. In terms of area-scaled carbon footprint, rice in the middle and lower reaches of the Yangtze River had the highest area-scaled carbon footprint, with an average of 2.0 t CE·hm^-2, followed by wheat and maize. The area-scaled carbon footprint of the three staple crops was increasing. In terms of yield-scaled carbon footprint, rice was the highest, with an average of 0.8 kg CE·kg^-1, followed by wheat and maize. In terms of carbon input structure, irrigation electricity, chemical fertilizers and pesticides accounted for a relatively high proportion. Irrigation electricity accounted for 35.0%, 36.3%, and 33.2% of the total carbon input of rice, wheat and maize, respectively. Chemical fertilizers accounted for 28.8%, 32.5%, and 32.5%, respectively, while pesticides accounted for 24.2%, 13.3% and 11.5%, respectively. In terms of carbon efficiency, maize had the highest (3.9 kg·kg^-1 CE), followed by rice and wheat. With the green development of agriculture, carbon emission in the production of major grain crops in the middle and lower reaches of the Yangtze River could be reduced by improving irrigation efficiency, fertilizer utilization efficiency, pesticide utilization efficiency and mechanized operation efficiency, as well as diversification of straw returning, cultivation of new varieties and policy leverage.