C:N ratio Posted on September 13, 2016November 10, 2022 by PlumeriaDB ALL0-9ABCDEFGHIJKLMNOPQRSTUVWXYZ Share This Tweet Share The ratio of carbon to nitrogen in organic materials. Materials with a high C:N ratio (high in carbon) are good bulking agents in compost piles, while those with a low C:N ratio (high in nitrogen) are good energy sources. Related Images: