For use in LRR M and N; for testing in LRRs A, B, E, K, L, and S (except for MLRA 148).

A layer of muck 2 cm (0.75 inch) or more thick with value of 3 or less and chroma of 1 or less, starting at a depth of 15 cm (6 inches) or less from the soil surface.

User Notes: This indicator requires a minimum muck thickness of 2 cm. Normally, this expression of anaerobiosis is at the soil surface; however, it may occur at any depth of 15 cm (6 inches) or less. Muck is sapric soil material with a minimum content of 12 percent organic carbon. Organic soil material is called muck if virtually all of the material has undergone sufficient decomposition to limit the recognition of plant parts. Mucky peat (hemic material) and/or peat (fibric material) do not qualify. Generally, muck is black and has a “greasy” feel; sand grains should not be evident.