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.