20Mar2017
1
PredictingSoilLossfrom
WaterErosion(notgully)
Lecture7
Reading:Chapter6-1thru6-4(esp.6-1
and6-3),7-2.1andsection19-2.7thru2.8
1
Whyisthereaneedtomeasure
soilerosion?
?Todetermineerosionpotentialwith
presentmanagement.
?Toevaluatealternativemethodsofcrop&
soilmanagement.
–Makewisedecisions
?Economic&Environmentalincentives
–Costshareprograms
2
USLE
?UniversalSoilLossEquation.
–1950s
–USDAARS(AgricultureResearchService)
andSCS(SoilConservationService,now
calledtheNRCS)
?A=RxKxLSxCxP.
?Designedforcroplandintheeastern
U.S.A.
?Laterappliedtomanykindsofcrops
throughouttheUSAandothercountries.
?Didnotaccuratelymeasuresoilloss.3
RUSLE
?RevisedUniversalSoilLossEquation.
?Usedforestimatingsoillossesfrom
pasture,range,forestlandandcropland.
?Computerizedprogramorbyhand.
?FirstreleasedbytheUSDA-ARSin1992.
?Plotrunoffstudies,rainfallsimulation
?“RUSLE2”releasedin2003
–Computer-based
–Thecurrentagencystandard4
RUSLE
?A=RxKx(LS)xCxP
“adjusted”Kf
?Factorsdon’treallyhaveunits
?Highertheindividualfactors,moresoilloss.
?Requiresuseoftablesorchartsorcomputer
software
?Usefulformanagementdecisions,i.e.weshould
askthequestion“Howcanthesenumbersbe
changed(reduced)?”
5
A
Predictedaverageannualsoilloss(sheet
andrillerosion)intonsperacreperyear.
6
20Mar2017
2
R
?Therainfallfactor.
?Measureofrainfallamount,energyand
intensityofstorms.
–Historicalweatherstationdata
?Staticnumber
?Missourirangesfrom175to270.
?Floridarangesfrom450to600.
?Dryerpartsofwest=10.
7
“R”
8
9
Example
?A=255x…
R
Keepinmindthatalargerresult(i.e.a
larger“A”product)meansmore
averageannualsoilloss…soifyou
startwithalargenumberyouneedto
domoretoreducepredictederosion.
10
K
?Soilerodibilityfactor.
?Measureofrelativeresistanceofasoilto
detachmentandtransportbywater.
?Reality:erodibilityvariesduringtheyear
duetoseasonalchangesintemperature
andrainfall.
?Valuesrangefrom0.02to0.60.
–Higherthenumber,moreerodible.
11
K(continued)
?Evaluatestexture(silt,veryfinesands,
sands),organicmatter,permeabilityof
soil,structure
–Determinedviaalaboratoryprocedure
?Numberschangewithdepth.
–Forsoillosscalculations,surfacelayeronly
?Staticnumberbutinrealitycanchangeby
makingsoillesserodible(increase
structuralstability),butneedlabto
measure.
12
20Mar2017
3
Fromsoilsurveytables:
13
Kf
?Indicatestheerodibilityofthefineearth
fractionoftexture.
?2mmandlessindiameter.
–Rocksdonoterodeundernormalrainfall
?Numbersrangefrom0.05to0.70.
?Rockysoil:KfwillbehigherthanK
?Soilwithlittlerockatsurface:Kf=K
14
AdjustedKf
?RUSLE
?Adjustmentsforseasonalchanges–
freezing/thawing,moisture,consolidation
?Variesaroundcountry.
?FindKf,thenusetheRUSLEtableto
adjust.
–TheadjustedKfisthe“K”usedinRUSLE
formula
1516
Example
?IfKfwas0.32inthesoilsurvey
?AdjustedKf=0.28
?Sofar:
A=255x0.28x…
RK
17
LS
?Slopeandslopelengthfactorcombined.
?Itisaratioofsoillossfromagivenfield
slopetothatfromaslopethathasalength
of72.6ft.and9%slope(theindexlength
andslope).
9%
18
20Mar2017
4
?Slope:%verticaldropoverahorizontal
distance
?Length:Horizontaldistancefromtheorigin
ofoverlandflowtothepointwheresoil
depositionoccursorrunoffisconcentrated
inadefinedchannel.
19
LS(con)
?Measureslopewithlevelorclinometer.
?Measurelengthwithtape,pacing,GPS
?UsetablestocomeupwithLSvalue.
?Steepertheslope,thehighertheLS
?Thelongertheslope,thehighertheLS
20
LS(con)
?CanchangetheLSofahillsideby
breakingthelength(L)with:
–Terraces
–Stripcropping
–Onlywithcertainterracescanyouchangethe
%slope(S).
21
TerracesaffectLS
broadbased
grassedback
22
(annualcropswithtillage)
Notethatyoucaninterpolatetoseethattheindexslopeof76’at9%is1.00
2324
20Mar2017
5
25
Example
?5%slope;200’slopelength(rowcrops
withtillage)
?LS=0.85
?Sofar:
A=255x0.28x0.85x…
RKLS
26
C
?Coverandmanagementfactor.
?Ratioofsoillossfromlandcroppedunder
specifiedconditionstothelossfromclean-
tilled,continuousfallow.
?Rangefrom0.01to0.48.
27
C(con)
?Throughcalculationofanaverage,Cestimates
thecombinedeffectofallinterrelatedcoverand
managementvariables.
–Differentcroprotations
–Differenttillagesystems(i.e.residuelevels,timing)
?Cropyieldsimpacttheactualresult(becauseyieldisrelated
tothebiomassofresidueleftbehind)buttablesusesone
yield.
–Covercrops
–Useofcrop(grainvssilage)
?Considersgroundandcanopycover.
–Considersdistributionof“R”throughyear
28
?Averageofallcrops/tillageand
managementforthelengthoftherotation
–Forexample:corn-soybean-wheatrotation
–Anumberforeachcrop,addup,divideby3
?Continuouspermanentgrass.
?Cfactoristheeasiestandmost
manageablefactortochangetoreduce
soilloss.
29
Example
?Corn-Soybeanrotation(2yearrotation)
–Cornforgrain
–Soybeans(widerow)
–Tillage
?Soybeanresiduetilledinspring,cornplanted(20%)
?Cornresidueprimarytillageinfall,secondarytillage
inspring,soybeansplanted(30%)
30
20Mar2017
6
JFMAMJJASONDJFMAMJJASOND
Corn-Soybeanrotation(2yearrotation)
Tillage
tools
Plant
corn
(20%)
Growcorn
Harvestcorn
Chisel
plow
corn
residue
Sec.
tillage
tools
CORNYEARSOYBEANYEAR
Plant
soybeans
(30%)
Growbeans
Harvestbeans
31
Example
CornSoytotallengthaverage
0.23+0.12=0.35/2years=0.175
C=0.175
Sofar:
A=255x0.28x0.85x0.175x…
RKLSC
32
P
?SupportPracticefactorisaproductof
multiplyingthreefactorstogether.
?Ratioofsoillosswithaspecificsupport
practicetothecorrespondingsoillosswith
uphillanddownhilltillageoperations.
?Includesthreedifferentsupportpractices
–contouring
–strip-cropping
–terracing
33
P(con)
?Contouring(Pc)
?Stripcropping(Ps)
?Terraces(Pt)
?PcxPsxPt=P
?Ifpracticenotinplacesuchas:no
contouring(up/downhill),nostrip
cropping,noterraces;P=1(multiply
anythingby1andnothingchanges)
34
?Pc(Contouring)verycomplicated.
–Considersmanagementofcover,ridge
heights,rowgrade,10yearstormerosion
index,soilhydrologicgroup(A-D)
–MostMOcontouringaround0.8(Depends!)
?Crossslopefarmingconsideredbeneficial
?Pt(Terraces)
–Considerswhether“open”outlets
(waterways),“closed”outlets(underground
outlets),interval,gradeofterracechannel.
–Rangesfrom0.5to1.0
3536
20Mar2017
7
?Ps(Stripcropping)complicated
–Considersslope,numberofstrips,amountof
grassstripsversuscropstrips,widthofstrips.
–Rangesfrom0.64to1.0
37
Example
?P=0.89(Pcwithnoterracesorstrips)
?Sofar:
A=255x0.28x0.85x0.175x0.89
RKLSCP
38
ExamplesofRUSLE
A=RxKxLSxCxP
255x0.28x0.85x0.175x0.89=9.5t/A/yr
Isthisgoodorbad?
Highorlow?
39
Double-checkfor“feedback”
?Buildingterracesorstripcropping(P
factors)willchangeLSandPc
?Usingcontinuousno-tillwillchangeLS
table,andCvalueswillchange
40
Tolerable(T)rates
?“themaximumlevelofsoilerosion(sheet
andrill)thatwillpermitahighlevelofcrop
productivitytobesustainedeconomically
andindefinitely”
?Trangesfrom1to5t/A/y
–Gasconadesoilseries=1.0t/a/y.
–Captinasoilseries=3.0t/A/y.
–Newtoniasoilseries=5.0t/A/y.
41
“T”considerstheentiresoilprofile.
–Depthofsoil.
–Parentmaterial.
–Relativeproductionpotential.
–Amountofpreviouserosion.
Farmingto<“T”shouldbethegoal.
42
“Conservation…doesthatsimplymeanwedestroy
somethingoveralongerperiodoftime?”
20Mar2017
8
Backtothesoilsurveytables
43
A=
255x0.28x0.85x0.175x0.89=9.5t/A/y
IfT=4t/A/y…Bad!
44
Whatcanbechangedtogetto“T”?
R=no
K=nofortheequation,yesinrealityifmanage
forimprovementoverextendedtime
S=no,unlesscertainterraces
L=yes,withterraces,bufferstrips/strip
cropping
C=absolutely!Uselesstillage(timing),add
lesserosivecropstorotation
P=yes,betterjobofcontouring,addstripsor
terraces.
45
Someexamplechanges
?UseaCorn-Corn-Soybeanrotation
–Notill(drill)soybeansinsteadofwiderow(
–Nofalltillageforcorn(springmulchtillage,
30%coveratplanting)
?Addterraces
–Closedoutlets(undergroundoutlets)@125
footspacing
46
Corn-Corn-Soybean
?CornafterSoybean:0.14(notilldrill,20%cover)
?CornafterCorn:0.13(springmulchtill,30%)
?SoybeanafterCorn:0.04(50%cover)
CaftSCaftCSaftCtotalyrsaverage
0.14+0.13+0.04=0.31/3=0.103
WhyisSoybeanafterCornsolow?
47
HowmuchdidchangingChelp?
A=255x0.28x0.85x0.103x0.89=5.6t/A/y
Soillossestimatereducedby4t/A/y(40%)
Goodstart!
48
20Mar2017
9
Addingterraces
Willprobablychangethreenumbers:
1.Terracefactor(Pt)
2.ReduceLS;lengthgoesfrom200’to125’.
3.Terracesareclosedwithunderground
outlets.Contourfarmingoperationsfollow
terraces,givingabetterPcvalue
4950
x
InterpolatetogetanLSestimateof~0.7151
RKLSCP
255x0.28x0.71x0.103x0.48=2.5t/ac/yr
0.8(Pc)x0.6(Pt)x1(Ps)
T=4t/ac/yr
Soilloss=2.5t/ac/yr
GOOD!
52
ConservationCompliance
?AgriculturalResourcesand
EnvironmentalIndicators.USDA,
EconomicResearchService,NaturalResources
andEnvironmentDivision.Agricultural
HandbookNo.705.
?ConservationandEnvironmentalPrograms
?Conservationcomplianceandsodbuster
?http://www.ers.usda.gov/media/871561/arei6-3.pdf
(1994)
?http://www.ers.usda.gov/media/872940/eib16.pdf
pp.184-191(2006)
53
About10yrsaftertheenactmentofthe1985
FoodSecurityAct(“FarmBill”thatrequired
conservationcomplianceinordertobe
eligibleforfederalprogramsandcost-
shares),USDAconductedareviewofHighly
ErodibleLands:
“Forthe98millionacrescurrently[1994]in
fullcompliance,[NRCS]estimatesthat
averageannualerosionhasbeenreduced
from19.8tonsperacreto5.9tons.”(AREI)
54
20Mar2017
10
ConservationCompliance
?Isreducingerosionbyafactorof3
enough?
?Whatdoesittaketobein“compliance”in
termsofT?
55
ExampleandImpactof
improperpasture
management
(SeethePastureC-factortable
forMOonBlackboard)
56
Poorsite
57
SHEET&RILLEROSON:RUSLE
50%groundcover,10%canopycover,lowvigor/production/fertility
7%slope,150’slopelength
averageOzarksoil(e.g.Wilderness)(T=3)inGreeneCounty
RKLSCP
A=___X_____X___X____X1.0=____t/ac/yr
58
Bettersite
59
SHEET&RILLEROSON:RUSLE
80%groundcover,10%canopycover,mediumvigor/production/fertility
7%slope,150’slopelength
averageOzarksoil(e.g.Wilderness)(T=3)inGreeneCounty
RKLSCP
A=____X____X____X_____X1.0=____t/ac/yr
60
20Mar2017
11
InfiltrationandRunoffUnderGrazing
Condition
LighttoModGrazing
HeavyGrazing
0.33”1.00”0.66”
0.29”
0.11”0.00”
0.09”
0.60”
0.33”
SansarcShallowClayRangeSite
5%Slope(Spaethetal.,1991)
61
Moreinformation
?RUSLE
–K.G.Renard,etal.1994.RUSLErevisited:
status,questions,answers,andthefuture.
JournalofSoilandWaterConservation.
49(3):213-220.
62
|
|
