Closing nutrient cycles is a process which aims to compensate the exit of mineral elements that are necessary for animals and plants, such as nitrogen, phosphorus, potassium, and sulphur. Closing those cycles can improve self-sufficiency of farms and territories.
In agriculture, nutrient cycles can be open in two different ways. First, when animals and/or plants leave the farm because of harvesting, or slaughtering of animals. The second way is by leaks towards the environment, leading to a pollution of water and air. These leaks can come from leaching (when a nutrient goes down deep into the ground to the water table), volatilization, denitrification, runoff, or erosion.
Several levers operating at different scales can help to close nutrient cycles:
- At the plot level, closing nutrient cycles can be achieved by developing ecological processing. For example, integrating leguminous plants into the crop rotation– they fix the nitrogen in the ground which allows farmers to reduce chemical fertilizer use. Also, permanent soil cover can prevent leaching, and agroforestry makes nutrient recycling easier.
- At the farm level, integrated crop-livestock systems can limit the input of external nutrients by fertilizing the plants with the animals’ dejections and by using the crop products as animal feed.
- Finally, at the territory level, the diversification of the productions helps to get nutrients from nearby farms, and to limit any outputs towards other territories. Cooperation between livestock farms and arable farms is indeed interesting because the animals can help fertilize the plants, and the plants can feed the animals.
Billen G., Lassaletta L., Garnier J. 2014. A biogeochemical view of the global agro-food system : nitrogen flows associated with protein production, consumption and trade. Global Food Security, 3, pp. 209 – 219.
Elser J., Bennet E. 2011. Phosphorus cycle : a broken biogeochemical cycle. Nature, 478, pp. 29-31.
Green Alliance. 2007. The nutrient cycle : closing the loop. 47p. ISBN 978-1-905869-03-9.