If you farm - you have heard of cover crops. They are a crop that is grown for the protection and enrichment of the soil.
Rather than being harvested for food, cover crops are tilled back into the soil at the end of their growing cycle where the nutrients are released as the plants decompose.
NRCS Resource Conservationist Ron Brooks says - cover crops are often used to replace nitrogen in the soil of organic farms.
"There are restrictions on what organic producers can apply to help provide nutrients to their crops. Cover crops can help do that. We can plan with an organic producer to plant species that will help add nitrogen to the system with the mix of plants that we would prescribe in a cover crop. Typically it is a mix of species that is planted in between crops. Kind of like a rotation crop. In a conventional type system you would view cover crops, let's say you harvest winter wheat in the fall, you would immediately plant a cover crop that would be in the ground over winter and that the next spring plant your next season's crop right after that cover crop. We encourage mixtures. It could be a grain crop mixed in with legumes and a nitrogen fixing type of crop like a vetch.