SOIL SURVEY

-185-h - An horizon enriched with organic matter .Ah - An A horizon of organic matter accumulation . Itcontains less than 17% organic carbon . It is one Munsel lunit of color value darker than the layer immediatel ybelow, or it has at least 0 .5% more organic carbon tha nthe IC, or both .Ahe - This horizon has been degraded, as indicate dby streaks and splotches of light and dark gray materia land often by platy structure .Bh - This horizon contains more than 1% organic carbo nand less than 0 .3% pyrophosphate-extractable Fe; theratio of organic carbon to pyrophosphate-extractabl eFe is 20 or more .k -m -tPresence of carbonate as indicated by visible effervescenc ewith dilute HCI .A horizon slightly altered by hydrolysis, oxidation o rsolution, or all of them to give a change in color o rstructure or both .A horizon enriched with silicate clay, as indicated by ahigher clay content (by specified amounts) than the overlyingeluvial horizon, a thickness of at least 5 cm, orientedclay in some pores, or on ped surfaces, or both, and usuall ya higher ratio of fine (less than 0 .2 ,v) to total clay tha nin the IC horizon .Soil structure - The combination or arrangement of primary soil particles into secondaryparticles, units or peds . The secondary units are characterized and classifie don the basis of size, shape and degree of distinctness into classes, types an dgrades, respectively . The following structure descriptions are used in thi sreport (CSSC 1976) :Platy - Thin, horizontal plates ; the horizontal axis is longer than the vertical .Prismatic - Aggregates with vertical axis longer than the horizontal and wit hwell defined surfaces and edges .Blocky - Block-like aggregates; the vertical and horizontal axes are aboutthe same length, usually with sharp edges .Subangular blocky - Block-like aggregates; the vertical and horizonta laxes are about the same length with subrounded edges .