Foot, K.

Sinnett, Danielle

English

UWE Bristol Research Repository

DO YOU NEED TO CULTIVATEBEFORE WOODLANDESTABLISHMENT? BPG NOTE 3Best Practice Guidancefor Land RegenerationIntroductionSoil compaction is the key physical feature that can prevent sustainable woodlanddevelopment (Figure 1) from being achieved. Tree establishment and growth can beseverely affected where compaction restricts the exploration of soil by tree roots,placing limitations on the exploitation of air, water and nutrient resources by theroots. Trees that reach maturity can also suffer from an increased risk of physicalinstability and windthrow due to underdeveloped root systems. This Best PracticeGuidance Note brings up to date the guidance on the use of deep cultivation methodsto relieve compaction. The ROOTS software package contains further guidance oncultivation; information on this product can be found at www.roots-software.co.ukWhy compaction occursCompaction can occur at any depth in the soil profile.n In agricultural soils, compaction may occur at the base of the ploughed or tilledlayer at depths of between 20 and 35 cm; this is commonly referred to as a‘plough pan’.n Normal soils exposed to loading in wet or unsuitable conditions or to heavytrafficking may exhibit compaction between 30 and 70 cm in the profile, resultingfrom soil deformation due to wheel pressure.n In restored or reworked soils, soil compaction is common where these soils havebeen reinstated using construction machinery such as a dozer or scraper orsubjected to heavy trafficking in subsequent years by agricultural machinery.Soils which have been restored can exhibit compaction at any depth andsometimes so severely that the entire profile from 20 cm to over 120 cm depth is heavily compacted. Such soils are also highly sensitive to recompaction after loosening.Why loosening is neededRoots alone cannot break up or restructure heavily compacted soils. Mechanicalmethods of cultivation are essential to loosen topsoil and/or subsoil layers to allowdeep root penetration (Moffat and McNeill, 1994; Foot and Spoor, 2003). This will:n Provide root anchorage and reduce the risk of windthrow.n Create sufficient water storage and uptake to buffer against drought.n Aerate the soil to allow the movement of oxygen and gases within the root zone.n Enhance the ability of roots to exploit available nutrient reserves.n Maximise drainage and reduce the risk of waterlogging.n Improve establishment success and longer-term growth and productivity.Figure 1  Restored sites often requirecultivation prior to vegetation establishment.Kirsten Foot and Danielle SinnettBPG NOTE 3 PAGE 2Depth of loosening requiredTo ensure long-term sustainable growth, at least 1 m depth of uniformly loosened,well-drained and well-rooted soil is usually required. In some parts of the UK, theremay be a need for a greater thickness than this ‘rule of thumb’.The depth of cultivation or loosening required will vary according to the depth atwhich compaction has occurred. Thus in a soil with a shallow plough pan, it is onlynecessary to loosen the ground to 50 mm below the base of the plough pan, anoperation that is much cheaper and more effective for these soils than loosening tothe standard 40–45 cm depth prescribed by agricultural contractors. A standardagricultural loosening operation is not sufficient for soils with deeper compaction,below 0.5 m depth. Attempts to loosen ground that is not compact can also damagethe soil. Therefore, both the need for and depth of loosening should always bechecked by digging pits to inspect the soil condition in order to avoid unnecessarycost and to ensure that all compaction has been effectively treated.The required depth of loosening can best be determined by opening up a soil pit. Ifthere is a vegetation cover to the soil, observing root development can indicate wherecompaction is: areas of very sparse or no rooting in the profile are usually indicativeof compaction. Compaction can also be identified by the following soil features:n Hard or abnormally dry clods of soil in the compact zone.n After a rainfall event, very wet soil above the hard dry layer indicating ‘perchedwater’ and poor infiltration or impeded drainage.n Solid or ‘massive’ appearance to the soil, i.e. large or very large ‘lumps’ with verylimited structural fissures or cracks, or a plate-like appearance.n Poor penetrability, the soil does not deform readily and a lot of pressure isrequired to push a trowel or knife into the compact zone in the side of the pit.n High bulk density, greater than 1.4 to 1.6 g cm-3 depending upon soil texture.n Very low porosity, restricting the movement of air and water through the profile.It is important to record the depth at which soil compaction is first encountered andthe lowest depth in the profile at which compaction is observed. It is also importantto excavate further pits across the site to identify the extent of the compaction. Thesoil condition should ideally be examined by a soil surveyor in the spring, to give timefor remedial cultivations to be conducted in the late summer or autumn prior towoodland planting in the winter.The depth of the loosening operation should be targeted specifically at the zone ofcompaction in the soil that needs to be treated. If a plough pan or a defined layer ofcompaction is present within the profile, loosening just below the compaction or panwill cause the pan to break up and will enable rooting to penetrate into theunderlying looser soil. The working depth of the loosening operation should be set at5 cm below the pan or compacted layer, whatever the loosening method used.Where deeper compaction is present then the greater the depth of the initialcultivation, the greater the benefit to soil condition and rooting achieved. Looseningto relieve deep compaction in restored soils should therefore aim to reach themaximum possible loosening depth in the first loosening operation, given the equipmentavailable, and ideally this should be greater than 1 m depth, since root developmentis unlikely to extend below the cultivated layer.In restored soils of very poor condition (especially in sand and gravel or non-swellingheavy clay substrates), it would be advisable to sow grass and to delay tree plantingfor 1 to 2 years to allow a 1 m deep loosening followed by shallower (up to 0.5 mdepth) agricultural-type loosening operations to be conducted in subsequent years inorder to relieve any residual or recompaction in the upper soil layers. The need, forBPG NOTE 3 PAGE 3and working depth of, the subsequent shallower operations is again best determinedby opening up a soil pit to check soil and rooting conditions. For maximum benefit inthe shallower operations, the subsoiling tines should work in the poorly rooted orcompacted zones at a depth of 100 to 150 mm below the depth where good rootingfinishes.Figure 2 illustrates how to select the required working depth for looseningoperations (Foot and Spoor, 2003). In examples A and B there is deep compaction,but the rooting in the upper layers is substantially better in B than in A. Both requirean initial one-off deep loosening operation to 0.8–1 m depth. Further shallowloosening operations are required in A to break up the soil and improve rooting in theupper layers, and the tine working depth should be 100 to 150 mm into the compactlayer. B would not benefit from shallow loosening since good rooting already extendsbelow 0.5 m depth. In example C, there is good rooting throughout most of theprofile, but recompaction in the upper subsoil has resulted in the formation of a pan.In this instance, the lower depth of loosening (e.g. for ripping, this would be the tineworking depth) should be set just below the compact zone.Types of loosening methodsTopsoils are easily accessible and can be cultivated using normal agriculturalequipment (for example, using discs, ploughs, or chisel tines as appropriate for thesoil type). Subsoils are more difficult to treat as it becomes harder and more costly topull implements into the ground to loosen the underlying soil layers.Compaction up to 0.5 m deep can be treated using agricultural-type subsoilers fittedwith wings. Deep compaction extending below 0.5 m depth in the profile is moredifficult to treat and requires deep cultivation. The methods available for deeploosening below 0.5 m are: total cultivation, deep ripping, and double digging using aspading machine.When to conduct looseningMoisture conditions are critical in all loosening operations, particularly in the layersabove and just below the compacted zone. It is essential that the soil is dry andfriable during the operation, to avoid damaging the upper layers and to achieve goodloosening performance. This is a requirement for all types of loosening operation,whether by total cultivation, ripping or agricultural subsoiling.The most suitable time for loosening is therefore in late July to late August but theactual timing will depend upon local climatic conditions, the antecedent rainfall andthe type of compaction which is to be treated. Spring loosening should never beattempted. In heavily compacted, restored soils which have never been loosenedeffectively, ripping can be very difficult in extremely dry summer conditions and somay be postponed up to the end of November after the first autumn rains. However,the loosening operation itself must be conducted when the upper soil layers havedried out.Good rootingPoor rooting or compactionA: Shallow rooting depthProfiledepth1metre Good rootingPoor rooting or compactionB: Moderate rooting depthGood rootingPoor rooting or compactionC: Subsoil pansTineworkingdepthrequired No rootsNo rootsNo roots Maximumrooting depthTineworkingdepthrequiredGood or moderate rootingFigure 2 How to determine the loosening depth required (from Foot and Spoor, 2003).BPG NOTE 3 PAGE 4There is only one real opportunity to loosen the ground to best effect for woodlandsand this is prior to planting the trees. Ripping between tree lines after planting is notsuitable and can cause damage to planted tree stock.How soon can you plant after loosening?Tree planting needs to be conducted while the trees are dormant, usually betweenmid November and late March, irrespective of the timing of cultivations. After anyform of cultivation, the ground will be prone to resettlement and slumping if exposedto wet weather conditions or trafficking. Also, where deep loosening has beenconducted, there may be some resettlement leading to an uneven soil surface,depending upon the loosening method selected.The ground condition after cultivation will stabilise more rapidly and retain a goodstructure for much longer if ground cover is established as soon as possible after theloosening operation. It can be highly beneficial to sow a low-competition grass swardin the September immediately after cultivation to keep soil fissures and cracks openand maintain good drainage through the soil. Grass roots grow very rapidly, producedense fibrous and deep-rooting networks and are better than tree roots at breakingup and stabilising soil structure. They also create root channels which tree roots canlater exploit. Tree planting can then take place into the grass sward and variousmethods (including mechanised weed control systems) are currently used by theForestry Commission for managing the sward between the planted tree rows.Research suggests that in a restored soil that has been completely re-loosened it cantake up to 3 years for grass or tree roots to penetrate to the full soil profile depth(Spoor and Foot, 2000).Careful and sensitive site management will be required to ensure that the benefits ofloosening are retained. Vehicular access to the site must be restricted and site workssuch as fence lines and access roads need to be installed prior to the looseningoperation.Summary of recommendationsThe following checks are essential to identify if soil loosening is required:n Investigate the soil condition early, preferably in the spring before tree planting.n Examine the soil by digging a pit and observing any signs of compaction. Recordthe depths at which compaction or poor rooting starts and finishes.n Identify which parts of the site will require loosening. Excavate further pits toidentify if compaction extends across entire fields or is located only in a portion ofthe site.n Seek professional advice from a soil surveyor where appropriate.n Use Figure 1 to identify an appropriate loosening depth technique which willaddress the compaction at the observed depths.n Ensure that cultivations can be performed within the planned timetable. Ifcompaction is severe, it is imperative that planting is delayed until loosening hasbeen conducted.ReferencesFoot, K.J. and Spoor, G. (2003). Breakingrestored ground – ripping really works!Mineral Planning 94, 6–9.www.defra.gov.uk/environ/landuse/restore/groundbreak.pdfMoffat, A.J. and McNeill, J.D. (1994).Reclaiming disturbed land for forestry. ForestryCommission Bulletin 110. HMSO, LondonSpoor, G. and Foot, K.J. (2000). Trials toevaluate the effectiveness of subsoilingtreatments on soil structure on mineral sitesduring the five year aftercare period. FinalScientific Report to MAFF. Contract CSA 2695 / CTE 9406D. Cranfield University, February 2000: 20pp.www.defra.gov.uk/environ/landuse/soilguid/subsoilreport.pdfUseful linksDEFRA Good practice guide to handling soils.www.defra.gov.uk/environ/landuse/soilguid/index.htmNational Soil Resources Institute Guide tobetter soil structure.www.silsoe.cranfield.ac.uk/nsri/services/publications.htm www.roots-software.co.ukThe Land Regeneration and Urban Greening Research GroupForest Research, Alice Holt Lodge, Farnham, Surrey  GU10 4LHPhone: +44 (0) 1420 22255      Fax: +44 (0) 1420 520180      E-mail: landrec@forestry.gsi.gov.ukWebsite: www.forestresearch.gov.uk © Crown copyright 2006

Best Practice Guidance for Land Regeneration Note 3: Do you need to cultivate before woodland establishment

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Best Practice Guidance for Land Regeneration Note 3: Do you need to cultivate before woodland establishment

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