SOIL SURVEY

-184-organic carbon, or both .BC -RA mineral horizon characterized by one or more of th efollowing : (1) an enrichment in silicate clay, iron ,aluminum or humus, alone or in combination (Bt, Bf ,Bfh, and Bh); (2) an alteration by hydrolysis, reductio nor oxidation to give a change in color or structure fro mhorizons above or below, or both .A mineral horizon comparatively unaffected by th epedogenic processes operative in A and B, except gleying ,and the accumulation of calcium and magnesium carbonate sand more soluble salts (Cca, Csa, Cg and C) .Underlying consolidated bedrock that is too hard to brea kwith the hands or dig when moist .Lower case suffixes .b - Buried soil horizon .ca -e -A horizon with secondary carbonate enrichment where th econcentration of lime exceeds that present in the unenriche dparent material .A horizon characterized by removal of clay, aluminum o rorganic matter alone or in combination . It is higher i ncolor value by one or more units when dry than an underlyingB horizon . It is used with A(Ae) .f A horizon enriched with amorphous material, principall yFe and Al combined with organic matter . It usually ha sa chroma of 3 or more . The criteria for an f horizo nexcept for Bgf are : it contains 0 .6% or more pyrophosphateextractableFe plus Al in textures finer than sand and 0 .4%or more in sands ; the ratio of pyrophosphate-extractable Feplus Al to clay (less than 2 /m ) is greater than 0 .5; andorganic carbon exceeds 0 .5% . These horizons are differentiatedon the basis of organic carbon content into : Bf,0 .5% organic carbon Bhf, more than 5% organic carbon .g -A horizon characterized by gray colors and/or prominentmottles indicative of permanent or periodic intense reduction .