Most farmers worldwide use manure as a nitrogen fertilizer because it is inexpensive and readily available. The amount of manure used is almost equal to the use of conventional ammonia-based fertilizer, with 108 million tons of manure and 107 million tons of synthetic fertilizer used annually. Manure use alone leads to emissions of 1.5 GT of CO2 equivalent, and when including storage emissions, the total amount doubles.

Synthetic fertilizer is preferred in industrial agriculture for its consistent nitrogen content and ease of use. In 2022, the production of 107 million tons of synthetic fertilizer led to 1.3 GT emissions, with over half of the emissions occurring during the manufacturing process. Each ton of urea fertilizer produces 12.5 tons of CO2 equivalent emissions, making it the largest supply chain emission source for practically all non-animal foods products.