bd2304 soil compaction appendix1 iph2

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Appendix to SID5 Soil compaction in England and Wales January 2008 1 BD2304 Scoping study to assess soil compaction affecting upland and lowland grassland in England and Wales APPENDICES TO SID5 The appendices give more detail about each part of the project and include all relevant references at the end of each section. APPENDIX 1 Mapping the extent of soil compaction (Work Package 1) APPENDIX 2 The causes of soil compaction (Work Package 2a) APPENDIX 3 The impacts of soil compaction (Work Package 2b) APPENDIX 4 Conflicts and synergies within existing and potential ES options, between objectives relating to soil compaction and its remediation and other scheme objectives (Work Package 3) APPENDIX 5 Responses received at the Stakeholder workshop (Work Package 5) APPENDIX 6 Glossary of terms

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Page 1: BD2304 soil compaction appendix1 IPH2

Appendix to SID5Soil compaction in England and WalesJanuary 2008

1

BD2304

Scoping study to assess soilcompaction affecting upland andlowland grassland in England and

Wales

APPENDICES TO SID5

The appendices give more detail about each part of the project and include allrelevant references at the end of each section.

APPENDIX 1 Mapping the extent of soil compaction (Work Package 1)

APPENDIX 2 The causes of soil compaction (Work Package 2a)

APPENDIX 3 The impacts of soil compaction (Work Package 2b)

APPENDIX 4 Conflicts and synergies within existing and potential ES options,between objectives relating to soil compaction and its remediation and otherscheme objectives (Work Package 3)

APPENDIX 5 Responses received at the Stakeholder workshop (WorkPackage 5)

APPENDIX 6 Glossary of terms

Administrator
Highlight
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APPENDIX 1: Mapping the extent of soil compaction

IntroductionA staged approach has been used to map the extent of compaction risk in grasslandlandscapes. The term 'grassland landscapes' is taken to mean landscapes that are dominatedby enclosed managed grassland used for livestock or dairy production. Semi-naturalvegetation on hill land, although it may be grazed, is excluded. The term compaction is usedto include all forms of soil structural degradation and deformation.

1.1 Grassland landscapesThere are two readily available sources of digital spatial information on the extent ofgrassland. The June Agricultural Census data and the CEH Land Cover data set. The valuesof these for this project have been compared. The CEH Land Cover Classification identifies anumber of grass-dominated classes which fail to easily distinguish between enclosedgrassland and open hill land covered by semi-natural vegetation with significant proportions ofgrasses and sedges. Agricultural statistics, based on the statutory returns made by farmersand organised by parish, do make this distinction and are therefore seen as a moreappropriate basis on which to map the extent of grassland landscapes. The individual returnsfrom farmers aggregated to parish level have been transposed to a 1 km grid (ADAS priv.comm.) for England but only to a 2 km grid for Wales (source EDINA data library). The mostrecent data that are available are from June 2004. The questionnaires, by which the returnsare organised, although different, request the same details for grassland in Wales andEngland. Farmers are asked to report on the extent of Grass sown in 2000 or later and Allother grassland (not rough grazing). When filling in their return, they are asked to include landactively farmed for grazing, conserved forage for livestock fee or herbage.

While it is recognised that fodder maize is a feature of grassland landscapes in certain areasthis had not been included in this work package. The management of forage maize is verydifferent from grassland and, while compaction is a common feature in harvested maizefields, the subsequent cultivation of the fields normally removes it. It is concluded that thegrassland landscape should be defined in terms of the aggregated extent of the two grasslandclasses identified on the June Census returns. Grassland landscapes exist where theseexceed 40 per cent by area of any individual 1 km or 2 km square (Figure 1).

This definition excludes forms of rough grazing which is defined, for Wales at least, asmountain, heath, moor, down and other rough land used for gazing with sole grazing rights.These forms of land present a whole set of different conditions from the enclosed managedlowland and upland grasslands that are seen as the focus of this project.

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Appendix to SID5Soil compaction in England and WalesJanuary 2008

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Figure 1. Grassland landscapes (from June Census Returns)

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1.1.1 Vulnerability to compactionJones et al. (2003) discuss the physics of soil resistance to compaction and forms ofstructural deformation in a paper that is focused on subsoil compaction by tillage. For thisproject, a model of soil vulnerability to compaction is needed that:

is focused on soils under grassland, caters for the climatic ranges experienced by grassland in England and Wales, and uses properties of the soil and of climate that are available in digital form and as

spatial data sets covering England and Wales.

A system was devised by Thomasson (Bradley et al. 2000) during work on the revised SoilSurvey Field Handbook derives four structural stability classes according to topsoil texturalgroupings, topsoil organic carbon and soil wetness class. This system seems relativelyinsensitive to climate and has been devised for application to arable soils. It assumes apositive relationship between SOC and stability and does not consider the wettest soils(Wetness Classes V and VI are identified as 'not applicable'). Bradley et al (2000) applied thissystem alongside a model for the assessment of structural regeneration and it was lateradopted in a modified form by Palmer et al. (2004) for the Environment Agency Toolkit ofNSRI Soil Property Data for Hydrogeological Studies. In this toolkit, soils are categorisedaccording to their (1) structural susceptibility to topsoil slaking, (2) structural susceptibility tocompaction and (3) natural regeneration to compaction. For structural susceptibility tocompaction there are four classes identified ranging from very susceptible to very slightlysusceptible. In the original spreadsheets of soil properties that were created for this project,there was a fifth class 'not cultivated' used to cover upland soils that are not conventionallycultivated. This fifth class is now cited as 'not susceptible' on a map provided to the projectteam by the Environment Agency. Again, this system is focused on structural degradationassociated with tillage and arable systems.

Only one approach is tailored to structural degradation under grassland. Harrod (1979)devised a Grassland Suitability model that comprised Yield and Trafficability components.Trafficability was intended to account for the impacts of both machines and stock on soilstructure and appears to be a candidate for prediction of relative vulnerability to compactionfrom traffic and livestock. Harrod based his assessment of trafficability on a number of soilproperties.

topsoil retained water capacity (Hall et al. 1977), depth to impermeable horizon (Avery 1980), and a combined soil and climate factor (soil wetness class) (Robson and Thomasson

1977),

A further climate factor is used to differentiate moist and dry climate zones separated on the100 mm Moisture Deficit isopleth. The model attempts to classify land according to therelative duration of wet soil conditions when topsoil is in an easily deformable state. Soilstrength and soil shear resistance vary with the nature of the soil and decrease with watercontent.

Given that this project is focused on compaction in grassland landscapes, it seems logicalthat Harrod's (op cit) trafficability model is used to characterise soil vulnerability to soilcompaction, remembering that compaction is used in this project to include all forms ofstructural degradation. Figure 2 is a 1 km raster map of five classes of relative landvulnerability to soil compaction based on this model.

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Figure 2 Land Vulnerability to soil compaction (based on Harrod, 1979)

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1.1.2 Stress factorsThe likelihood of soils becoming compacted is a factor of the land vulnerability of the soil tocompaction, as described above, and the aggregate stress resulting from livestock andmachinery acting on the topsoil.

Appendix 2 describes the farm management and land use practices that have been identifiedas causing compaction of the soil. To generate a map of soil compaction risk, these stressfactors need to be linked to mappable agricultural land use and management statistics. Table1 identifies attributes that are common to the 2004 national agricultural parish statistics forboth Wales and England and attempts to link them to the identified causes of compactionstress.

Table 1. Candidate grassland farming data sets captured in the June CensusAgricultural Parish Statistics

Wales England Linked stress2 Grassland (c2)3 Permanent grassland(c3)

29 Permanent grass (c29) Non-specific - grazed andtrafficked

5 New grassland (c5) 30 Temporary grass (c30) Potentially more vulnerable topoaching and vehicle wheelingas the surface vegetation mathas been destroyed.

17 Total sheep (c17) 107 Total sheep (c107)18 Breeding ewes (c18) 101 Total breeding flock

(c101)100 Other breeding sheep(c100)

21 Other sheep (c21) 103 Other sheep (c103)

Poaching and trafficassociated with feeding anddamage to soils aroundfeeding troughs, particularlyduring the winter period; mostsheep are out-wintered

22 Total cattle (c22) 84 Total cattle (c84) Composite of factors identifiedfor dairy and beef stock.

23 Dairy (c23) 59 Dairy herd (c59) Poaching from early and lategrazing, strip or small paddockgrazing practices; localdamage from daily stockmovements associated withmilking; vehicle-relateddamage from silage-makingand from slurry spreading ontosoils at field capacity.

24 Beef (c24) 60 Beef herd (c60) Poaching from early or lategrazing and out-wintering ofstock; traffic associated withfeeding of out-wintered stock;damage around feeders;spreading of slurry onto soilsat field capacity.

To map soil compaction risk classes, certain of these factors need to be combined to createthree classes of relative compaction stress. In the absence of reliable information on theextent of actual compaction under different farming systems, it was concluded that acombined livestock factor expressing the aggregate intensity of all forms of livestock farmingwithin each 1 km square was the most realistic way of expressing stress. Table 2 outlines analgorithm for a simplified Grazing Livestock Unit calculation.

The risk of soil compaction is seasonally variable as soils are more vulnerable to compactionand structural deformation when wet. The impact of winter field traffic and grazing is thereforegreater than the same practice during summer months. The seasonality of grassland

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management and grazing practices is not easily captured spatially as it is not recorded byfarmers in any returns that they make.

For a number of reasons, it is difficult to use parish-based agricultural statistics for anythingother than a generalised assessment of the pressures on soils. The means of their collectionand aggregation mean that the spatial link between specific soils and land uses and practicesis lost at source. Precise management practices such as grazing regimes and timing, thetiming of machinery-based activities such as silage-harvesting is very variable and, in part,determined by the widespread use of contractors or collectively-owned machinery. It istherefore unrealistic in a review of this nature to go beyond this generalised assessment.While recognising this weakness in the methodology, it has been decided to assume that therelative compaction stress on grassland across England and Wales can reasonably beestimated from the overall stocking density. A plot of grazing livestock units per per centgrassland for each 1 km square was made. This shifted the pattern of high stress toward thelowlands and beef/milk based grasslands and away from the more extensive grasslands ofthe uplands. Consideration was given to using this as the basis for the stress factor but it wasfelt that total grazing livestock units was as good a representation of the management stressas any other given the usable data available on management practices.

Table 2 Derivation of the Pressure for Soil Compaction

Original GLU formula Simplified formula to be used forthis project

Type of stock GLUfactor1

Type of stock GLUfactor1

Dairy cows 1.0Dairy bulls 0.7Dairy replacements <12mths

0.4

Dairy replacements 12-24mths

0.6

Dairy replacements >24mths

0.8

Beef cows 0.6Beef bulls 0.7Beef replacements <12mths

0.4

Beef replacements 12-24mths

0.6

Beef replacements >24mths

0.8

Total cattle 0.8Lambs <12 mths 0.06Ewes and rams 0.1

Total sheep 0.11 The number of livestock is multiplied by this factor to derive Grazing Livestock Units

Figure 3 shows the distribution of Grazing Livestock Units for each 1 km square with inexcess of 40 per cent grassland. Numbers range up to 284 GLU.

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Figure 3 Distribution of Grazing Livestock Units (based on June Census Returns)

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1.2 Risk of soil compactionLand vulnerability to soil compaction is a factor of soil/climate-based vulnerability andcompaction stress. Three classes of relative risk are derived by applying the decision matrixin Figure 4 to all 1 km squares with more than 40 per cent grassland. Figure 5 is a map of thedistribution of these three classes.

Figure 4 Derivation of risk of compaction classes

Stress classes

Lowest third

(0 - 89GLUs)

Middle third

(90 - 121 GLUs)

Highest third

(122 - 284 GLUs)

HighMEDIUM HIGH HIGH

Medium-High MEDIUM MEDIUM HIGH

MediumLOW MEDIUM HIGH

Medium-Low LOW MEDIUM MEDIUM

Vulnerability tocompactionclasses

LowLOW LOW MEDIUM

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Figure 5 Risk of Soil compaction

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1.3 Actual extent of compactionThe consistent characterisation of the degree and nature of compaction in soils is challengingas the various forms of structural condition are difficult to measure quantitatively and todescribe qualitatively. Work by Palmer (2004) using a technique developed during work onflood-affected catchments in 2000 provides the most significant body of evidence of the extentof compaction. Sites were characterised as having severe, high, moderate or low soilstructural degradation (see Table 1 in main report for definitions) on the basis of surfacerutting and poaching and the inspection of a small number of soil profiles from representativesites within each field. Sites were chosen to represent the dominant soils and landmanagement systems within each catchment. Palmer has only surveyed soil structuralconditions in twelve catchments mostly in the south and west of the country (one is fromWales) and the sites cannot be claimed to be representative of the country as a whole as theyare biased towards one region and are catchments that have a history of water qualityproblems associated with soil conditions. The work was responsive rather than strategic.

Table 3 is a compilation of the records from these catchments of the sites under grassland.Key aspects have been summarised in Figures 6 to 8. Given that the sites are, in no way,representative of the grasslands of England and Wales broad conclusions about soilconditions under grassland are ill-advised. However for the catchments studied, less than 1per cent of sites had Severe degradation but 21 per cent were placed in the High degradationcategory with a further 60 per cent in Moderate. Figure 6 demonstrates that the relativeproportions of sites in the different categories are variable. Figure 7 shows the spread ofdegradation classes across the poaching vulnerability classes used to characterise landvulnerability to compaction (mapped in Figure 2). The data indicate a correlation betweenvulnerability and actual degradation in so far as low vulnerability soils were found to havepredominantly low levels of actual degradation and, conversely, high vulnerability soils werelinked to the highest proportion of high degradation sites. Figure 8 suggests that soils underley grassland are more susceptible to compaction that those under permanent grassland. It isdifficult to draw any further or firmer conclusions from the data. The lack of information on thenature and intensity of management systems and grazing in the catchments and at the actualsites visited is a source of uncertainty that limits the scope for analysis of the survey results inthis context.

Figure 6. Soil structural degradation under grass by catchmentBased on figures from Palmer 2002; 2003a,b; 2004a, b, c; 2005a, b

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SevereModerate

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20

30

40

50

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70

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Severe

High

Moderate

Low

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Figure 7. Grassland soil structural degradation in all catchments by poachingvulnerability classBased on figures from Palmer 2002; 2003a, b; 2004a, b, c; 2005a,b

12

34

5

Severe

High

Moderate

Low

0

10

20

30

40

50

60

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80

%

Poaching vuln. class

Degradation

SevereHighModerateLow

Figure 8. Soil structural degradation under different grassland typesBased on figures from Palmer 2002; 2003a, b; 2004a, b, c; 2005a, b

All grassLey grass

Permanent grass

Severe

High

Moderate

Low

0

10

20

30

40

50

60

70

%

Grassland type

Soil structural degradation

SevereHighModerateLow

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Table 3 Soil structural degradation in a number of catchments (Palmer, 2004)

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References

Avery, B.W. (1980) Soil classification for England and Wales (Higher Categories). Soil Surv.Tech. Monogr. No 14.Bradley, R.I. (2000) A national soil vulnerability based framework for the provision of farm specificguidance on the management of soil structure. Defra Research Report SP0305.#Hall, D.G.M., Reeve, M.J., Thomasson, A.J. and Wright, V.F. (1977) Water retention, porosity anddensity of field soils. Soil Surv. Tech Monogr No 9.Harrod, T.R. (1979) Soil suitability for grassland. In: Jarvis, M.G. and Mackney, D. Soil SurveyApplications. Soil Surv. Tech Monogr No 13.Holman, I.P., Hollis, J.M., and Thompson, T.R.E. (2002) Impact of agricultural soil conditions onfloods - Autumn 2000. R&D Technical Report W5C(00)04, Environment Agency.Jones, R.J.A., Spoor, G. and Thomasson, A.J. (2003) Vulnerability of subsoils in Europe tocompaction: a preliminary analysis. Soil and Tillage Research 73, 131-43.Robson. J.D. and Thomasson, A.J. (1977) Soil water regimes. Soil Surv. Tech Monogr No 11.Palmer, R.C. (2005a). Soil structural conditions in the Frome catchment during March 2004.NSRI research report No. YSR 9145V for Environment Agency.Palmer, R.C. (2005b) Soil structure survey in Pontbren and associated catchments in March2005. Unpublished internal NSRI report.Palmer, R.C. (2004a). Soil structural conditions in the Axe and Char catchments during March2004. NSRI research report No. YSR 9127V for FWAG (Devon) and Environment Agency, 20p.Palmer, R.C. (2004b). Soil structural conditions in the catchments leading to the Golden Mile andMarazion Marsh during late winter 2004. NSRI Research Report No. YSR 9124V forEnvironment Agency, 30p.Palmer, R.C. (2004c) Preliminary estimation of soil structural conditions within 10 soil landscapesin South West England during 2002 and 2004. Final Report to Environment Agency for Englandand Wales, Bristol.Palmer, R.C. (2003a). Soil structural conditions in the Upper Avon, Nadder and Wylyecatchments during late winter 2003. Unpubl. Rep. for Environment Agency. SR 9095V.Palmer, R.C. (2003b). Soil structural conditions in the Tone and Parrett catchments duringFebruary and March 2003. Unpubl. Rep. for Environment Agency. SR 9094V.Palmer, R.C., Holman, I.P., Burton, R.G.O. and Bellamy, P.H. (2004) Toolkit of NSRI soil propertydata for hydrogeological studies. Draft Report to Environment Agency for England and Wales,Bristol.