The Soils of Brant County - Agriculture and Agri-Food Canada

HOW THE SOILS WERE MAPPEDAND CLASSIFIEDSoil MappingInitially, existing resource publications were studied toobtain relevant, current information on the characteristics anddistribution of the soil/land resources . These included the oldsoil map, geological, and physiographic maps and reports .This provided a general description of soil materials for apreliminary soil legend, and their geographic distribution inthe area .Strong reliance was placed on the use of up-to-date aerialphotographs of 1 :15,840 scale for the identification and classificationof soil and landscape features and for accurate delineation of soil boundaries . Prior to commencement of fieldwork, stereoscopic study of aerial photographs was carried outto establish tentative slope, landform andparentmaterial separations. Existing soil, geological and topographic informationalso were utilized during the pre-typing phase of the work .Extensive field work was conducted to gather further information. This included driving all roads to examine soils exposedin road cuts, or digging soil pits before commencing mapping .Traverses on foot were then arranged to cross as many boundariesas possible, examining soils in different landscape positionsto determine soil characteristics, variability anddistribution . The frequency of examination was such that thesmallest areas delineated on the map (approximately 4 hectares)usually had at least one examination site, and the largerareas, naturally, manymore . While in the field, the boundarieswere finalized and the delineated areas classified . Any opensoil boundaries were extended and finalized with furtherstereoscopic study of the photographs soon after completionof field traverse ofan area .Soil correlation to ensure consistency and quality controlin the soil mapping was achieved by the soil survey party leader,who established benchmark sites at regular intervals which themappers could easily refer to, discussed with the surveyors anyproblems encountered in mapping or classification, andchecked the final map . Numerous soil samples were collectedfor laboratory analysis in order to relate soil morphologicalproperties, which are the basis of field mapping, to accuratelydetermined chemical or physical tests.Complete characterization of the soils in the County wasachieved through detailed descriptions and sampling of representativesites, followed by laboratory analyses . For the majorsoils, data was obtained at 3 or 4 sites to satisfactorily representthe range in properties which may be expected within that soil .Survey Intensity and Map ReliabilitySurvey intensity level is an indication ofthe precision withwhich the soils of a region have been described and mapped .Five levels of survey intensity have been defined (10) . Level l isthe highest intensity, with the most detailed procedures resultingin the most precise map . Level 5 is the lowest intensity, theleast detailed and giving a generalized map . The survey intensitylevel of the Brant County soil survey is at an intermediatelevel, between 2 and 3 .In this survey there was at least one soil inspection in mostmap delineations . Most boundaries were checked in the fieldduring traverses on foot at intervals of approximately 0.5 kmfor small and medium-sized delineations, and at intervals ofseveral kilometres forlarge delineations .Soil inspections were made by examination of vertical soilsections with a hand auger, probe or shovel to a depth ofabout1 m . In roadcut exposures, or along stream banks, the depth ofsoil examination usually increased to 1 to 2m .Considering the survey intensity level and scale of soilmapping in Brant County, the most appropriate uses of theinformation are for planning purposes of land areas such astownships, watersheds, large urban subdivisions, or largefarms . Use of the information for decisions on smaller areassuch as small farms, small subdivisions, building sites, etc . isless appropriate because of soil or landscape variability whichcan occur over short distances . Inthese instances, the soil mapscan be used to predict whatconditions are most likely to occur,but the final decision should be made only after on-siteexamination .Soil ClassificationThe interaction of soil-forming factors such as parentmaterial, climate and vegetation acting over thousands ofyears have produced soils in Brant County with characteristicsthat are a reflection of their environments . These characteristicstake the form of a sequence of layers (horizons) that differin colour, texture, thickness and structure . Collectively thesehorizons constitute the soil profile.The soil profile comprises a vertical section of the soilthrough all its horizons extending downward into the unweatheredparent material . The number, colour, sequence and composition of the various horizons are the basis upon which soilsare recognized, classified and mapped .The various horizons of mineral soils are differentiated asA, B and C horizons and are subdivided further, as required,using lower case letters . Figure 12 is an illustration ofa soil profile in a well-drained landscape position, the horizons beingreadily recognizable by colour differences . The Ah horizonowes its dark colour to the incorporation of organic matter ; thesubscript "h" infers humus accumulation . Theunderlying Bmhorizon is lighter in colour due to its lowhumus content and theeluviation and weatheringof constituents such as iron and clay.The Bt horizon is generally a reddish-brown colour due to theenrichment of iron and other sesquioxides that have beenleached from the upper horizons and deposited in this lowerlayer. The lower-case letter "t" is an indication of clay enrichmentresulting fromthedownward movement ofthese fine particlesin leaching water and subsequent flocculation anddepositionin the B horizon .