Carbon footprint of grain crop production in China - based on farm survey data

Quantifying the carbon footprint of crop production can help identify key options to mitigate greenhouse gas emissions from agriculture. Using farm survey data from eastern China, the carbon footprints of three major grain crops (rice, wheat and maize) were assessed by quantifying the greenhouse gas emissions from individual inputs and farming operations with a full life cycle assessment methodology. The farm carbon footprint in terms of farm area was estimated to be 6.0 ± 0.1, 3.0 ± 0.2, and 2.3 ± 0.1 t CO2-eq ha−1, and the product carbon footprint in terms of grain produced was 0.80 ± 0.02, 0.66 ± 0.03, and 0.33 ± 0.02 t CO2-eq t−1 grain for rice, wheat and maize, respectively. Use of synthetic nitrogen fertilizers contributed 44-79% and mechanical operations 8-15%, of the total carbon footprints. Irrigation and direct methane emission made a significant contribution by 19% and by 25%, on average respectively for rice production. However, irrigation was only responsible for 2-3% of the total carbon footprints in wheat and maize. The carbon footprints of wheat and maize production varied among climate regions, and this was explained largely by the differences in inputs of nitrogen fertilizers and mechanical operations to support crop management. Moreover, a significant decrease (22-28%) in the product carbon footprint both of wheat and maize was found in large sized farms, compared to smaller ones. This study demonstrated that carbon footprint of crop production could be affected by farm size and climate condition as well as crop management practices. Improving crop management practices by reducing nitrogen fertilizer use and developing large scaled farms with intensive farming could be strategic options to mitigate climate change in Chinese agriculture.