Spatial and temporal changes in carbon footprint for oilseed rape production in the middle and lower reaches of Yangtze River during 2004-2015

The Yangtze River is one of the major oilseed rape producing areas in China. It is therefore of great significance to analyze the carbon footprint of oilseed rape, for developing low-carbon agriculture and for climate change mitigation in this region. Based on the statistical data of sown area, crop yield, and farmland investment of oilseed rape production along the Yangtze River, the spatiotemporal dynamic change in carbon footprint and its composition of oilseed rape during 2004-2015 in the middle and lower reaches of Yangtze River was estimated using the theory of carbon footprint and life cycle assessment method in the agricultural sector. The results showed the carbon footprint of oilseed rape at first decreased and then increased, the lowest point being 2 177.6 kg·hm^-2 in 2013. The main components of the carbon footprint for oilseed rape production were fertilizer (50.9%-53.1%) and labor (5.8%-8.4%). Obvious differences were found among main agricultural provinces in the study area. The carbon footprint per unit area (CF_a) and per unit yield (CF_y) of Jiangsu and Zhejiang Provinces were higher, while that of Hunan and Jiangxi Provinces were lower. What was more, the CF_a and CF_y in high yield regions were significantly higher than that in low yield regions. Among them, the carbon footprint of nitrogenous fertilizer, phosphate fertilizer, and compound fertilizer was significantly higher than that for low-yielding provinces, which increased by 81.7%, 81.2%, and 112.8%, respectively, (P < 0.05). The results suggest that improving crop management practices that limit fertilizer consumption and strengthen mechanical integration technology to reduce labor costs could help mitigate greenhouse gas emissions from oilseed rape production along the middle and lower reaches of Yangtze River.