S7. Dark Surface

For use in LRRs K, L, M, N, P, Q, R, S, T, U, V, and Z.

A layer 10 cm (4 inches) thick, starting at a depth less than or equal to the upper 15 cm (6 inches) from the soil surface, with a matrix value 3 of or less and chroma of 1 or less. At least 70 percent of the visible soil particles must be masked with organic material, viewed through a 10x or 15x hand lens. Observed without a hand lens, the particles appear to be close to 100 percent masked. The matrix color of the layer directly below the dark layer must have the same colors as those described above or any color that has chroma of 2 or less.

User Notes: An undisturbed sample must be observed. Many wet soils have a ratio of about 50 percent soil particles that are masked with organic matter and about 50 percent unmasked soil particles, giving the soils a salt-and-pepper appearance. Where the coverage is less than 70 percent, the Dark Surface indicator does not occur.