SOIL SURVEY

-183-Organic horizons are found in Organic soils and commonly at the surfac eof mineral soils or at any depth beneath the surface in buried soils . Theycontain more than 17 percent organic carbon . Two groups of these horizon sare recognized :O -An organic horizon developed mainly from mosses, rushe sand woody materials .Of - Fibric horizon, an organic horizon which is the least de -composed of all the organic soil materials . It has larg eamounts of well-preserved fiber that is readily identifiableas to botanical origin .Om -Oh -Mesic horizon, an organic horizon which is intermediat ein decomposition between the less decomposed fibric an dmore decomposed humic materials . This material ha sintermediate values for fiber content, bulk density an dwater contents . The material is partly altered bot hphysically and biochemically .Humic horizon, an organic horizon which is the mos tdecomposed of all the organic soil materials . It has th eleast amount of plant fiber, the highest bulk densit yvalues and the lowest saturated water holding capacity .This material is relatively stable having undergon econsiderable change from the fibric state primarily becauseof oxidation and humification .L,F,H - These are organic horizons developed mainly from leaves ,twigs and woody materials with or without a minor componentof mosses . Usually they are not saturated withwater for long periods .L -The original structures of the organic material are easil yrecognized .F The accumulated organic matter is partly decomposed .H -The original structures of the organic material are unrecognizable.Master mineral horizons and layers contain less than 17% organic carbon .A -A mineral horizon or horizons formed at or near th esurface in the zone of removal of materials in solutionand suspension and maximum in situ accumulation of