Sinnett, Danielle

English

UWE Bristol Research Repository

COMPLETE CULTIVATION BPG NOTE 13Best Practice Guidancefor Land RegenerationIntroductionCompaction remains the key physical feature preventing the sustainableestablishment of greenspace on restored sites. Compacted soil inhibits rootdevelopment and affects the soil moisture and oxygen status, often resulting indrought conditions during dry spells and waterlogging in wetter periods. Thesefactors have a detrimental effect on vegetation establishment, reducing the ability ofthe vegetation to exploit water and nutrient resources in the soil and, in the case oftrees, increasing the risk of windthrow. More information on compaction and therequirement for cultivation can be found in BPG Note 3: Do you need to cultivatebefore woodland establishment?Current guidelines for tree planting recommend an average soil depth of at least 1.0 mfor restored sites, although this may vary depending on initial soil conditions andclimatic location within the UK. Soil placement on restored sites should follow theloose tipping method, which is detailed in BPG Note 4: Loose tipping. However, there isa legacy of brownfield land within the UK, where traditional soil placement techniquesusing dozers followed by industrial ripping are still commonly practised. Incorrectapplication of these techniques can often result in severe levels of deep compaction.Where compaction has occurred following soil reinstatement, it is necessary tocultivate the soil prior to any greenspace establishment. In such situations the bestpractice method for soil loosening is complete (or total) cultivation.Advantages of complete cultivationComplete cultivation uses an excavator to progressively remove and replace the soilwithout trafficking over the cultivated soil surface (Figure 1). Although this method isrelatively expensive compared with alternative methods of cultivation, it hassignificant advantages that are particularly relevant to greenspace establishment: Achieving target loosening depth. The depth of soil loosening achieved withcomplete cultivation can be adapted to the planned vegetation. The recommendationfor a soil depth of at least 1.0 m can be easily achieved and it is also possible tocultivate to greater depths where the site conditions dictate this to be appropriate.Alternative methods, such as deep ripping, are often unable to achieve soilloosening to depths greater than 0.6 m (Moffat and Boswell, 1997; Sinnett et al.,2006), which is insufficient for deep-rooting vegetation such as trees. Loosening uniformity. Complete cultivation involves removing soil material fromthe area being worked and replacing the broken-down material (Figure 2). Thismethod therefore produces uniform soil loosening that allows root developmentthroughout the entire profile. In contrast, cultivation using ripping machineryoften results in compacted clods between tine channels that can restrict rootdevelopment, particularly if vegetation is planted directly above these areas. Incorporation of soil amendments. Complete cultivation can also be used wherethe incorporation of soil amendments is also required to improve the soilresource available on a site, as the cultivation and incorporation can be carriedout simultaneously. Further details can be found in BPG Note 6: Application ofsewage sludges and composts.Danielle SinnettFigure 1 An excavator removing soil.BPG NOTE 13 PAGE 2The 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 2008 Sustained loosening. The level of soil loosening that is achieved usingcomplete cultivation is often sustained over subsequent years. In contrast,although ripping technologies are capable of providing a loosened soil profile,this is often subject to recompaction within one year of cultivation (Moffat andBoswell, 1997). This is particularly important in the case of trees, which rootrelatively slowly compared with other vegetation, and therefore can notdevelop a sufficient root structure before recompaction takes place.All of these factors mean that the vegetation performance is often significantlyimproved using complete cultivation rather than ripping technologies. Moffat andBending (2000) reported significant increases in survival of common alder andJapanese larch of between 10 % and 20 % when complete cultivation wascompared with industrial ripping. After only three growing seasons they alsofound increases of 50 % and 100 % in the height of Italian alder and Japaneselarch grown on restored soil treated with complete cultivation, compared withindustrial rip. This is important from both a forestry and community greenspacedevelopment perspective. Increased survival and growth has obvious economicbenefits, but will also accelerate the aesthetic improvements that result fromgreenspace establishment on restored sites.Methods of complete cultivationA number of methods of complete cultivation are available, but the ‘Profile StripMethod’ has been found to be the most cost-effective and versatile whencompared with others tested by Forest Research’s Technical Development Branch(Reynolds, 1999). This method is shown in detail in Figure 2. The costs of thismethod will vary depending on the excavator used, the width of working and thesoil material present on the site. Reynolds (1999) found that when this methodwas employed on a restored colliery, using a Caterpillar 320B (20 tonnes) and aworking width of 8 m, the cost was approximately £500 per ha. This does notinclude the costs of machine transport and overheads associated with siteassessment, supervision, etc.ReferencesMoffat, A.J. and Bending, N.A.D. (2000).Replacement of soil and soil-formingmaterials by loose tipping in reclamation towoodland. Soil Use and Management 16,75–81.Moffat, A.J. and Boswell, R.C. (1997). Theeffectiveness of cultivation using the wingedtine on restored sand and gravel workings.Soil and Tillage Research 40, 111–124.Reynolds, C. (1999). Total cultivation ofcompacted soils on reclamation sites. ForestResearch Technical Note 30/98, ForestResearch Technical Development Branch, AeVillage, Dumfries.Sinnett, D., Poole, J. and Hutchings, T.R.(2006). The efficacy of three techniques toalleviate soil compaction at a restored sandand gravel quarry. Soil Use and Management22, 362–371.Figure 2 Profile strip method (from Reynolds, 1999).1.  Strip top layer. This may be accomplished in two or more passes 15 to 25 cm in thickness depending on friability. Cultivate in an arc to a final working width of between 7 to 8 metres.2 - 4 m2.  Place the spoil in front of the void.  Drop material from height to further assist the break up. Large lumps may require further breaking up at this stage. Repeat (1) until final working width of between 2 to 4 metres is accomplished.3.  On completion of working width the next stage can be started. Cultivate second layer to required depth. If friable this may be broken up by simply lifting and raking the spoil. Long teeth on the bucket can assist in the breaking up process.4.  If material is not friable, scrape in 15 to 25 cm layers; lift and drop to assist break up. Spoil is replaced directly into the bottom of the void.  Cultivate entire working length lifting spoil and dropping to increase the cultivating effect.6.  The finished profile. 5.  Move machine forward and pull top layer into void. Level off and move back 3 to 4 metres. Repeat (1) through (5) until strip complete.

Best Practice Guidance Note for Land Regeneration 13: Complete Cultivation

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Best Practice Guidance Note for Land Regeneration 13: Complete Cultivation

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