Organic Gardener's Composting by Steve Solomon

The protein content of vegetation is very similar to its ratio of carbon (C) compared to nitrogen (N). Quick laboratory analysis of protein content is not done by measuring actual protein itself but by measuring the amount of combined nitrogen the protein gives off while decomposing. Acacia, alder, and leaves of other proteinaceous legumes such as locust, mesquite, scotch broom, vetch, alfalfa, beans, and peas have low C/N ratios because legume roots uniquely can shelter clusters of nitrogen-fixing rhizobia. These microorganisms can supply all the nitrate nitrogen fast-growing legumes can use if the soil is also well endowed with other mineral nutrients rhizobia need, especially calcium and phosphorus. Most other plant families are entirely dependent on nitrate supplies presented to them by the soil. Consequently, those regions or locations with soils deficient in mineral nutrients tend to grow coniferous forests while richer soils support forests with more protein in their leaves. There may also be climatic conditions that favor conifers over deciduous trees, regardless of soil fertility.

It is generally true that organic matter with a high ratio of carbon to nitrogen also will have a high ratio of carbon to other minerals. And low C/N materials will contain much larger amounts of other vital mineral nutrients. When we make compost from a wide variety of materials there are probably enough quantity and variety of nutrients in the plant residues to form large populations of humus-forming soil animals and microorganisms. However, when making compost primarily with high C/N stuff we need to blend in other substances containing sufficient fixed nitrogen and other vital nutrient minerals. Otherwise, the decomposition process will take a very long time because large numbers of decomposing organisms will not be able to develop.