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

the average annual soil loss using all of theUS .L.E . factors:1) Take any map symbol designation from anElgin County soil map.e.g.BEcBased on the 'TCey to the Map Symbols" and"Legend" descriptions provided on each soilmap, this map symbol represents a Berrien(BE) soil which occurs on a complex c slope of2 to 5% . For the purpose of this example, thecrop/vegetation cover for the soil is fallploughed silage corn, with the previous year'scrop being winter wheat. No conservationpractices have been employed .2) Select the appropriate R, K, LS, Cand P factorvalues for the soil and slope components ofthe symbol from the tables provided .R value for Elgin County = 90Kvalue for Berrien (BE) soil = 0.18 (Table 9)LS value for c slope = 0.39 (Table 11)C value for fall ploughed silage corn(previous year winter wheat) = 0.48(Table 13)P value for no conservation practices =1 .00(Table 17)3) Using the Universal Soil Loss Equationand themetric conversion factor of 2.24, calculatethe potential average annual soil loss (A) bywater:A=RxKxLSxCxP=90 x0.18 x039 x0.48 x1.00= 3.0 t/ac/y x 2.24= 6.7 t/ha/y4) The potential average annual soil loss for themap symbol is 6.7 t/ha/y.(5) How to Determine Potential SoilLoss at Field SitesSite or field specific interpretations are usefulfor on-farm management purposes because theyprovide farm managers or extension personnelwith a general indication of the erosion-reducingeffectiveness of various crop and managementsystems . The example which follows outlines theprocedure which should be used to estimate theaverage annual soil loss for a particular field site.The potential soil erosion class for the soil at thatsite can then be determined using Table 18.'Example ,- A particular farm field is thought tohave an ongoing water erosion problem, and thefarm manager would like to know if this is so .The field is in a corn-corn-soybeans (3yr.) rotation,and is fall moldboard ploughed . As aconservation measure, contour farming is carriedout as a standard management practice .Procedure :1) First determine the soil conditions for the field.For the purpose of this example, soilinvestigations indicate that the field iscomposed of Tavistock soils (TA) which havea slope gradient of 5%, and slope lengths of200 metres.2) Now determine all of theUS.L.E . factor valuesfor the field . For this example they are.R value for Elgin County = 90K value for Tavistock soil (TA) = 0.27(Table 9)LS value = 1.37 (for combination of slopelength = 200 metres, and slope gradient= 5%; Table 10)C value = 0.39 * see belowP value = 050 (contour farming; Table 17)* C values for a variety of crops and rotations aregiven in Tables 13,14,15, and 16 . The C value forthis particular rotation, however, is not given inthose tables and is determined as follows:The C value for corn following soybeans, withfall moldboard ploughing (FMP), is 0.47 (Table13)The C value for corn following corn, with fallmoldboard ploughing (FMP), is 0.35 (Table 13)The C value for soybeans following corn, withfall moldboard ploughing (FMP), is 0.36 (Table13)Therefore, the rotational C value isC= 0.47+0.35+0.36 =0.393 (years)3) Using the metric conversion factor of 2.24,calculate the average annual soil loss (A) bywater :A=RxKXLSxCxP=90 x0.27 x1.37 x0.39 x0.50= 6.5 t/ac/y x 2.24= 14 .6 t/ha/y= Moderate (Soil Erosion Potential Class 3;Table 18)4) Since the tolerable"A" value for deepagricultural soils is 6.0 t/ha/yr (3.0 t/ac/y) orless, the results indicate that the potentialerosion for the farm field is above the tolerablelevel. Therefore, a change in cropping orconservation practices are needed to reducethe average annual soil loss to a moreacceptable rate.106