The Renewable Heat Incentive scheme in the United Kingdom has led some industries to turn much of their organic waste into feedstocks for energy production. Previously, this material — such as biosolids from water processing — was used to replenish soil carbon. This switch might inadvertently undermine the global initiative to increase soil carbon to mitigate climate change, which was ratified in 2015.
This potential conflict needs to be part of the policy discourse and research agenda for energy and the environment. Reductions in organic carbon hamper soil functions, such as water-holding capacity, and reduce crop productivity. But knowledge gaps remain about the necessary level, composition and quality of carbon required to maintain and improve soil health and fertility.
The products of anaerobic digestion of organic wastes for heat production are widely used as soil conditioners. But they have a lower ratio of carbon to nitrogen than do conventional composted vegetation and food waste. It is not known just how low the ratio of such wastes can go before it becomes worthless to return them to the soil.