Soil degradation risk indicator : soil compaction component.

62 Pages·1997·2.6 MB·English

by  McBride, R. A. (Raymond Allan)

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AGRI-ENVIRONMENTAL INDICATOR PROJECT
Agriculture and Agri-Food Canada
REPORT
NO. 23
SOIL DEGRADATION RISK INDICATOR:
SOIL COMPACTION COMPONENT
Technical Report: Feasibility Study on the Development and
Testing of Agri-Environmental Indicators of Soil
Compaction Risk (Eastern Canada)
Prepared by:
R. A. McBride, University of Guelph, Department of Land Resource Science
G.C. Watson, University of Guelph, Department of Land Resource Science
G. Wall, Research Branch, Agriculture and Agri-Food Canada
333.76 OCTOBER 1997
A278
R 23
1997
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CANADA K1A 0C5
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PREFACE
The Agri-Environmental Indicator (AEI) Project ofAgriculture and Agri-Food Canada (AAFC)
was initiated in 1993 in response to recommendations made by several agencies, organizations
and special studies. The overall objective ofthe project is to develop and provide information to
help integrate environmental considerations into decision-making processes ofthe agri-food
sector.
The project aims to develop a core set ofregionally-sensitive national indicators that build on and
enhance the information base currently available on environmental conditions and trends related to
primary agriculture in Canada. The feasibility study on the soil compaction risk component ofthe
Soil Degradation Risk indicator is an important part ofthe agri-environmental indicator set.
Indicators are also being developed for other aspects ofsoil degradation risk and in relation to
issues ofwater quality, agroecosystem biodiversity, farm resource management, agricultural
greenhouse gases and agricultural production efficiency.
Research results in the form ofdiscussion papers, scientific articles and progress reports are
released as they become available. A comprehensive report is planned for fiscal-year 1998-1999
which will include data from the 1996 Statistics Canada Census ofAgriculture.
Comments and questions on this paper as well as about the tabular data created and used in the
feasibility study on the soil compaction component should be addressed to:
Dr. Greg Wall
Ontario Land Resource Unit
Greenhouse and Processing Crops Research Centre
Research Branch, Agriculture and Agri-Food Canada
Guelph, Ontario
N1H 3N6
Telephone: [phone]
Facsimile: [phone]
E-mail: [email protected]
Digitized by the Internet Archive
in 2012 with funding from
Agriculture and Agri-Food Canada - Agriculture et Agroalimentaire Canada
http://archive.org/details/soildegradationr23mcbr
4
TABLE OF CONTENTS
PREFACE
i
TABLE OF CONTENTS
1
LIST OF MAPS 2
LIST OF TABLES 3
INTRODUCTION
1. 4
1.1 SonProcessesandPedotransferFunctions 4
1.2 PTF Calculations 6
1.3 SoilLandscapes of Canada(SLC) 7
1.4 Objectives 8
METHODS
2. 9
2.1 DataAcquisition 9
2.2 SoilPropertyEstimations 9
2.3 InclusionCriteria 12
2.4 PTF CalculationandDataAnalysis 12
3. RESULTS AND DISCUSSION 15
3.1 Preconsolidation StressEstimates (<yc) 15
3.1.1 AllFiveProvinces 22
3.1.2 Ontario 22
3.1.3 Newfoundland 23
3.1.4 NovaScotia 24
3.1.5 PrinceEdwardIsland 24
3.1.6 NewBrunswick 25
3.2 Areas ofPotential Soil StructuralImprovement 26
3.3 Areas ofPotential Soil StructuralDegradation 31
3 Comparisonof SLC AnalysisandDetailed Soil Survey Analysis 31
.
SUMMARY AND CONCLUSIONS
4. 37
REFERENCES
5. 39
LIST OF MAPS
Map Preconsolidation stressestimatesfortheagricultural subsurface
1
.
layersofthedominant soilcomponents inthe southernhalfof
Ontario 18
Map2. Preconsolidationstressestimatesfortheagricultural subsurface
layersofthedominantsoilcomponentsinNova Scotia 19
Map 3 Preconsolidationstressestimatesfortheagricultural subsurface
.
layers ofthedominant soilcomponentsinprinceedwardisland 20
Map4. Preconsolidation stressestimatesfortheagricultural subsurface
layers ofthedominant soilcomponents pnNewBrunswick 21
Map 5. Areas pnthe southernhalf of Ontario wherethe soils are significantly
overconsolidatedbutthe currentagricultural cropppngpatternmay
improve soil structural characteristics overtime 27
Map 6. Areas inNova Scotia wherethe soilsare significantly
overconsolidatedbutthecurrentagriculturalcroppingpatternmay
improve soil structuralcharacteristics overtime 28
Map 7. Areas pnPrinceEdwardIsland wherethe soilsare significantly
overconsolidatedbutthecurrentagriculturalcropppngpatternmay
improve soil structuralcharacteristicsovertime 29
Map 8. Areas inNewBrunswickwherethe soils are significantly
overconsolidatedbutthecurrentagriculturalcroppingpatternmay
improve soil structuralcharacteristicsovertime 30
Map 9. Areas inthe southernhalf of Ontariowherethecombinationof
significantsoil susceptibilitytocompactionandagriculturalcropping
patternsarelikelytodegrade soil structuralcharacteristics over
TIME 32
Map 10. Areas pnNova Scotia wherethecombpnationof significantsoil
susceptibility tocompactionandagriculturalcroppingpatterns are
likelytodegrade soil structuralcharacteristics overtime 33
Map 1 1. Areas inPrpnceEdward Island wherethecombpnationof significant
soil susceptibilitytocompactionandagriculturalcroppingpatternsare
likelytodegrade soil structuralcharacteristics overtime 34
Map 12. Areas inNewBrunswickwherethecombpnationof significant soil
susceptibilitytocompactionandagriculturalcropppngpatterns are
likelytodegrade soil structuralcharacteristics overtime 35
LIST OF TABLES
Table 1. Atterberglimitregressionresults 10
Table2. Claycontentestimatebytexturalclass 11
Table3. Analysisresultsof dc estimatesforsurfacesoilcomponents 16
Table4. Analysisofresultsof dc estimatesforsubsurfacesoilcomponents 16
Table5. MeanvaluesofinputsintoPTF 17
Table6. ResultsofaGeneralLinearModelanalysisondc estimatesof 127
SUBSOILHORIZONSFROMAFIVE-COUNTYREGIONINSOUTHWESTERNONTARIO(AFTER
McBrideandJoosse, 1996) 36
Table7. Comparativeresultsof dc estimatedforthesamefive-countyregion
USINGTHE SLC DATABASE 36
1. Introduction
Surveys commissionedby Agriculture and Agri-Food Canada (AAFC) have shown
that agricultural soil compaction isthe soil and water conservation problem identified most
frequently by corn producers in southern Ontario as a concern ontheirfarms (Deloitte and
Touche, 1991). It has furtherbeen estimated that 50 to 70 percent ofthe fine-textured soils of
southwestern Ontario havebeen adversely affected by soil compaction, with 3A ofthis affected
land arearated as moderately compacted and V* as severely compacted (Can-AgEnterprises,
1988). Many parts oftheMaritime provinces also have naturally compacted subsoils (Carter et
al., 1996). Soil compaction caused by the use ofheavy machinery (Hakansson et al., 1987)
M
may be costing the Ontario agricultural economy $21 annually and the Quebec economy
$100M (Science Council ofCanada, 1986).
Recent advancements inthe field ofpedotechnology make it possible to estimate the
maximum compactive stresses which have acted upon a soil with minimal soil inventory data
(McBride and Joosse, 1996). Using generalized soil inventory data at a national scale, such as
the Soil Landscapes ofCanada (SLC) database, it is possible to assess the present state of
overconsolidation ofsoils in many regions ofeastern Canada.
1.1 SoilProcesses and PedotransferFunctions
Soil structural degradation caused by wheel traffic from heavy agricultural vehicles can
take on many forms. Apart from soil compaction, other processes include plastic deformation
and shearfailure. Some ofthese other soil processes are often mistakenly referred to as soil
compaction. This term, in fact, only refers to the process ofincreasing the dry bulk density of
an unsaturated soil by packing the primary soil particles and aggregates more closely together
with a reduction in the volume ofair in soil pores Many soil compaction models are currently
available, and the better examples include all ofthe elements necessary to simulate soil
mechanical behaviourunder a range ofinitial conditions (Jakobsen and Dexter, 1989; Plouffe et
al., 1994). Many ofthese models, however, have very extensive input data requirements which
makes them difficult to apply to regional, provincial or national studies ofsoil compaction risk
(Boberetal., 1996).
Generalized soil inventory information exists for most ofthe settled part ofOntario, but
the development ofuseful soil survey interpretation schemes (or"pedotransferfunctions"
A
[PTFs]) hasgenerally lagged farbehind. recent study carried out in southern Ontario,
however, investigated theusefulness ofthe "preconsolidation stress" (cr^ ) in characterizing the
pre- and post-traffic structural state ofagricultural soils aswell as theirvulnerabilityto further
loss oftotal porositywithwheel traffic (VeenhofandMcBride, 1996; McBride and Joosse,
1996). In soil mechanics, this empirically-measured variable is defined as the maximum vertical
stressthat has acted on an overconsolidated (saturated) soil in the past. In unsaturated soils,
however, this variable is regarded more commonly asthe stress above which soil deformation
greatly increases, since many otherfactors contributingto structural strength come into play
such as large effective stresses caused byfreezing or drying, the presence oforganic and
inorganic stabilizing materials, and age-hardening or hard setting behaviour (Kay, 1990). This
variable was found to be very useful in establishing the degree ofagricultural soil
overconsolidation as well as maximum allowable wheel loads to avoid further compression of
soils in agricultural fields.
Recent research has corroborated the hypothesisthat the compressive behaviour
(static, uniaxial) ofstructured subsoils in Ontario can be predicted reasonablywell fromthe
consolidation behaviour ofthose same soils when in a remoulded (slurried) condition, and
hence from their Atterberg consistency limits (McBride and Baumgartner, 1992). As a result, a
PTF has been developed that can assist in characterizing the degree ofoverconsolidation of
soils without the need for an extensive and costly soil compression testing program. This
simple set offunctions estimatesthe preconsolidation stress from dry bulk densities (void
ratios) measured in situ and from other soil properties needed to estimate the normal
consolidation line.
Preliminary testing ofthePTF has been carried out by assembling the necessary data on
soil physical properties for all soil series characterized by O.C.S.R.E. (Ontario Centre for Soil
ResourceEvaluation) during the course ofthe last five county-level soil inventory upgrades in
southwestern Ontario that meet the minimum data requirements (i.e., 282 horizons from 91 soil
profiles [McBride and Joosse, 1996]). Unfortunately, these soil sampling locations were
selected more for pedological and taxonomic reasonsthan fortheir representativeness ofthe
soil and crop management practices most commonly applied to these soil series/associations.
Consequently, thePTF needsto betested further onmore appropriate data sets (e.g., Tillage
2000).
1.2 PTFCalculations
McBride and Joosse (1996) introduced a series ofcalculationswhich determinethe
"minimum possible oT fromthe estimated normal compression line (NCL) ofa soil. This
sequence ofequations is presented inEq. [1] through [7] and comprisethePTF. To express
theNCL in e(logo/) co-ordinates, Eq. [1] to [3] areused to convert the in situ dry bulk density
ofa soil, aswell as its liquid and plastic limits, into void ratios. Field drybulk densities are
transformed with
= £
e - 1 [1]
where e is the in situ void ratio, pp is the in situ dry bulk density (Mg m"3), and Db is the soil
particle density (Mg m"3). Given that Atterberg limits can be measured by slurry consolidation
(McBride and Baumgartner, 1992), thesetest indices can be taken to represent saturated water
contents as follows:
—Wlr-P*p
=
«-t [2]
where eWL andwL represent the liquid limit expressed as avoid ratio and gravimetric soil water
content (kg kg"1), respectively, and pw is the density ofwater (Mg m"3) and
—
w
P 7-p1
[3]
where e„p andwp represent the plastic limit expressed as avoid ratio and agravimetric soil
water content (kg kg'1 respectively.
),
The effective stresses at the liquid limit (o'wl) and plastic limit (oV) were estimated
withEq. [4] and a constant 420 kPa, respectively (McBride and Baumgartner, 1992):