Toward low-carbon livestock: The central role of manure and crop management in feed emissions

Feed production is one of the largest contributors to livestock carbon intensity scores. Therefore, reducing the carbon intensity of feed is an effective approach to reduce the carbon intensity of livestock. This study assesses the carbon intensity of corn, soybeans, corn dried distiller grains with solubles, and soybean meal produced from all ninety-nine Iowa counties and evaluates trends to imply practical methods of CO 2 e reduction in crop and feed production. This study quantifies swine feed carbon intensity reduction caused by effective manure management, alternative crop management, (no-tillage and cover cropping) and diet selection. Greater yields and greater percentages of corn land area using manure nitrogen were associated with reduced carbon intensity scores for crops and feed. Compared to an average farm, a farm practicing no-tillage, cover cropping, and manure application can produce feed with a 33% lower carbon intensity, potentially translating to $0.93 pig -1 on the voluntary carbon credit market. Diets composed of corn and soybean meal achieve carbon intensity scores 19% lower than diets composed of corn and corn dried distiller grains with solubles. The greatest sources of CO 2 e from corn production were field N 2 O emissions (57% of overall CO 2 e emissions), synthetic fertilizer production (17%), and liming (15%), all of which are related to the amount of applied nitrogen, emphasizing the importance of correctly assessing the nitrogen necessary for each farm. Manure application reduces synthetic fertilizer usage and promotes soil organic carbon, characterizing itself as a heavily influential factor in determining the carbon intensity score of crops and feed. Careful attention to effective manure application could drive down feed, meat, and milk carbon intensity scores around the world.