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

2) To determine the average annual soil loss, orA, values for the R, K, and LS factors areneeded. When adjusted for snowmeltconditions, the R factor value for Elgin Countyis always 90 .3) K factor values for all of the soil types mappedin the County are given in Table 9 . Usingthat table, find the symbols 'BV" and 'TA" inthe first column tided "Map Symbol" . Nowmove horizontally across each line to thecolumn tided 'Mean K value", where the Kvalues for each soil type are given. The Kvalue for the BV soil type is 0.29, and the Kvalue for the TA soil type is 0.27.4) IS factor values for slope classes mapped inthe County are given in Table 11 . Using thattable, refer to the column titled "Complexslope" . Move down the column and find slopeclasses "b" and "c", then move horizontallyacross each line to determine the IS value foreach slope class . The LS value for the b slopeclass is 0.20, and the LS value for the c slopeclass is 0.39 .5) Calculate the average annual soil loss, A, foreach soil type by multiplying the values forthe R, K and LS factors. To convert theaverage annual soil loss, A, fromtons/acre/year to tonnes/hectare/year,multiply by 2.24 .The average annual soil loss for Beverly (BV)soils on b slopes, assuming bare soilconditions, is :A=RxKXLS=90 x0.29 x0.20 x2.24= 5.2 t/ha/yThe average annual soil loss for Tavistock (TA)soils on c slopes, assuming bare soilconditions, is :A=RxKxLS=90 x0.27 x0.39 x2.24= 9.5 t/ha/y6) The results indicate that the Beverly soils,which are the dominant soils in the area, havea lower potential erosion than the Tavistocksoils .Method 2The potential average annual soil loss for soiltypes identified in the map symbols can bedetermined from Table 12 . . The average annualsoil loss values given in Table 12 are in metricunits, and are based on an R value of 90 andestimated slope lengths for each slope class. Anexample is as follows:1) Take any map symbol designation from anElgin County soil map.e.g .BV.L>TO.Ld>bBased on the "Key to the Map Symbols" and"Legend" descriptions provided on each soilmap, 40 to 80% of the area represented by thesymbol consists of Beverly loamy phase (BV.L)soils which occur on complex d slopes of 5 to9%, and 20% to less than 40% of the areaconsists of Toledo loamy phase (TO.L) soilswhich occur on complex b slopes of 0.5 to 2%.A potential average annual soil loss for each ofthese soils must therefore be determined.2) Using Table 9, find the symbols 'BV.L" and'TO1" in the first column titled 'MapSymbol".3) Nowmove horizontally across each line to thecolumn titled 'Mean K value", where the Kvalues for each soil type are given. The Kvalue for the BV .L soil type is 0.32, and the Kvalue for the TO.L soil type is 0.23.4) Proceed to Table 12 and find the 0.32 K valuein the left hand column. Now movehorizontally across the line to the "d" slopeclass column. The annual soil loss for theBV .L soil is 53 .5 t/ha/y and is shown wherethe line and column intersect.5) Still using Table 12, find the 0.23 K value inthe left hand column, and then movehorizontally across the line to the "b" slopeclass column. The annual soil loss for theTO .L soil is 9.3 t/ha/y and is shown wherethe line and column intersect .6) The results indicate that the Beverly loamyphase (BVI) soil, which is the dominant soil,has a higher potential erosion than the Toledoloamy phase (TO.L) soil, mainly because of thesteeper slopes associated with that soil.(b)Determining average annual soilloss under known crop coversand management practicesThe preceding methods for determining theaverage annual soil loss do not take into accountvegetative cover or conservation managementpractices which maybe employed. To determinethe average annual soil loss under theseconditions, the R, K, and LS values for the soilmust be multiplied by the appropriate C and Pvalues from Tables 13, 14, 15, 16, and 17. Theexample which follows demonstrates theprocedure which should be followed to determine105