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

C .Soil Interpretations for Water ErosionI.J. Shelton, Agriculture Canada, L.W. Schut,Ontario Ministry of Agriculture and Food, andG.J. Wall, Agriculture Canada(1) IntroductionSoil erosion by water is a naturally occurringprocess that can be greatly accelerated by man'sactivity. Any practice that accelerates surfacerunoff, or reduces the natural protection affordedby vegetative cover, will generally lead toincreasing erosion levels . Uncontrolled soilerosion can reduce production potential, depletenutrients, and degrade soil quality . Sediment,fertilizers, and pesticides can adversely affectdownstream water quality after they have beenremoved from the land by water erosion .A widely accepted water erosion relationship,A = R x K x ILS x C x P, used to predict averageannual soil loss through sheet and rill erosion, iscalled the Universal Soil Loss Equation or US.L .E .(28), where:A is the average annual soil loss;R is the rainfall erosivity factor;K is the soil erodibility factor;L is the slope length factor;S is the slope gradient factor,C is the crop cover factor; andP is the conservation or management practicefactor .This section of the report provides basicinformation on the factors of the U.S.L.E. relevantto Elgin County. It also includes a briefdescription of the methodology needed to applythe U.S.L .E. to the soils in the County. For moredetailed information on the factors, andbackground informationon the methodology, referto Shelton and Wall (29) .In order to apply the U.S.L .E., values must bedetermined for the factors which compose it . ForElgin County the "R" value is 90 (30) . Soilerodibility or 'IC" values, and associated potentialsoil erosion classes for each soil type, are reportedin Table 9 . Slope length and gradient values, or"LS" values, for combinations of slope length andgradient and for representative map symbol slopeclasses, are given in Tables 10 and 11, respectively.A quick reference table for determining potentialsoil losses for given K values and slope conditionsin the County is provided in Table 12 . The soillosses provided in Table 12 are metric unit values.Crop cover values, or "C" values, for a variety ofcrops and rotations found in the County are givenin Tables 13, 14, 15, and 16. Management practicefactor 'P" values are provided in Table 17. Theguidelines used to assess potential soil erosionclasses are included in Table 18 . Information fromthese tables can be used to make site specific ormap symbol assessments of soil erosion potentialby water.(2) Potential Soil Erosion ClassesThe average annual soil loss, or "A", which isdetermined using the US .L .E. is an estimate of thepotential soil loss that can be expected for thatsoil . When the crop cover factor (C) andmanagement practice factor (P) are not included inthe equation, the calculated soil loss (A = R x K xLS) is an estimate of the potential soil loss that canbe expected under bare field conditions. Based onthis calculation, the soil can then be placed in toone of five potential soil erosion classes .Descriptions of the classes are as follows:Class 1 - Negligible - Soils in this class havevery slight to no erosion potential . Minimalerosion problems should occur if good soilmanagement practices are used . The soils in thisclass should be able to maintain sustainableproductivity under average managementpractices . The tolerable soil loss limit may beexceeded for soils that are shallow, low in organicmatter, of poor structure or previously eroded .Potential soil erosion loss is less than 6tonnes/hectare/year (3 tons/acre/year) . Thisamount represents the tolerable soil loss for mostOntario soils.Class 2 - Low - Without the use of croprotations and cross slope farming, low to moderatesoil losses will occur. Potential soil erosion lossesrange from 6-11 tonnes/hectare/year (3-5tons/acre/year) . This amount exceeds thetolerable soil loss limit for all but the deepestOntario soils.Class 3 - Moderate - Unless conservationmeasures such as conservation tillage, contourcropping and grass waterways are used, moderateto high soil erosion losses will occur. Potentialsoil erosion losses range from 11-22tonnes/hectare/year (5-10 tons/acre/year).Class 4 - High - Unless measures such asconservation tillage, forage-based rotations,terraces, cross-slope or contour strip cropping areemployed, high erosion losses will occur.Potential soil erosion losses range from 22-33tonnes/hectare/year (10-15 tons/acre/year) .Class 5 - Severe - Unless a soil cover ofpermanent vegetation is maintained, severe103