Cultivation can alleviate soil compaction, improve soil structure and reduce weed competition which enables successful vegetation establishment. Cultivation breaks up the soil profile and improves its structure, and this increases the pore size, allowing the infiltration of water and air and provides the necessary space for root development.
On newly restored sites, soils should be placed using the loose tipping technique, which ensures that soils are loosely deposited in the final landform without the need for more movement of vehicles over the soil surface. Using this technique results in a soil profile suitable for vegetation establishment without the need for further cultivation.
A number of different cultivation techniques can be employed to alleviate compaction; including the use of an agricultural ripper, an excavator, or air injection. The choice of technique will depend on a number of factors, including the depth of compaction, the soil type, and the type of vegetation planned for the site. Although the cost of cultivation may play a significant role in the choice of method, it should be borne in mind that if compaction is not dealt with prior to greenspace establishment it may result in a substantial reduction in the growth and health of the vegetation.
This is particularly important where tree planting is planned, as any adverse affects of compaction may not become apparent until a few years after planting, when the roots reach the compacted profile. Where trees are planted, the only real opportunity for cultivation is before planting, and if a loosened profile is not achieved it can result in the trees having to be removed and the cultivation repeated. Trees that are not allowed to develop their root systems fully are also at a higher risk of windthrow, which may have significant financial and health-and-safety implications when trees are mature.
Further considerations and cultivation techniques
The main cultivation techniques for alleviating compaction are described in the table below. The choice of technique may depend on the degree of compaction and its depth, the proposed vegetation type and its rooting depth, as well as the ground formation, presence of large boulders, buried debris, slope and soil texture.
The time of year of operations is also important, as some methods should be carried out only during dry periods to prevent recompaction of the soil. Consideration should also be given to any archaeology that may be present on the site, as this may be damaged by any cultivation method. Cultivation techniques can be targeted to the type of vegetation planted on the site, or the soil conditions on the site. For example, complete cultivation could be used on areas intended for tree cover, and ripping on those with shorter vegetation where less root development is expected, or where compaction is less severe.
|No cultivation||Only where no compaction is present. Mechanical/hand-weeding and herbicide/fertiliser application may be necessary to reduce weed competition and provide nutrients.||May be necessary on steep slopes and other areas where machine access is restricted. May be the safest option where the environmental impact of cultivation is of concern.||Success depends on the quality of plants used and the amount of weed competition expected. Generally the poorest option for good survival and early growth.|
|Scarification||Includes disc trenching, furrowing and screefing. Shallow cultivation to 20 cm depth. Not suitable where compaction is present. Aims to prepare planting positions by scraping off surface vegetation.||Soil, humus and litter are mixed. May increase soil temperature and reduce weed competition.||Steep slopes and access restrictions may mean hand screefing is necessary.|
|Subsurface treatments||Includes ploughing, moling, subsoiling and ripping. Suitable for shallow compaction as cultivation is achieved to 45–60 cm depth. Aims to provide a loosened soil profile to allow deep rooting and improve site drainage.||Can provide a loosened soil profile at relatively low cost. Particularly effective for shallower-rooting vegetation such as grass or shorter species where risk of windthrow maybe lower. Subsoiling or deep ripping should be used where deep compaction occurs.||Not suitable where boulders and other obstructions may be present in the soil. Must be carried out during dry periods; in wet conditions the soil will collapse back into position. Not suitable for severe or deep compaction as loosening is not deep enough for tree root development and soils often recompact before tree roots can penetrate the loosened profile. Subsoiling and ploughing can result in a rapid nutrient release, which may result in nutrient losses.|
|Mounding||Provides regularly spaced heaps of soil around a planting position.||Forms a raised, well drained planting position on the mound which has higher soil temperature and less weed competition.||Mineral mounds may freeze more readily. Should be used with caution on sites subject to summer drought.|
|Complete cultivation||Involves use of an excavator to progressively remove soil and loosely redeposit without the need to retraffic over the soil surface. Particularly suited to deep compaction often associated with brownfield land. It is also possible to dig pits to accommodate individual trees, although care must be taken to ensure pits are large enough to support mature tree root systems.||Capable of reaching the depths recommended to support tree root development (1 m). More uniform cultivation of the soil profile and reduced risk of recompaction after cultivation compared with ripping techniques.||More expensive and labour intensive than other methodologies. Steep slopes and access restrictions may limit use of the excavator. Must be carried out during dry periods; in wet conditions the soil will collapse back into position.|
(Source: Paterson and Mason, 1999.)
Forest Research has evaluated methods of maximising the soil depth available for tree rooting by loosening ground to depths of 1 m. A long-term trial was established at a restored sand and gravel quarry to assess the effectiveness of deep cultivation methods on the survival, growth and root development of Italian alder, Corsican pine, Japanese larch and silver birch.
Tested cultivation methods were:
- Complete cultivation to 1.1 m
- Standard industrial ripping to 0.9 m
- Deep ripping to 0.75 and 0.9 m using a prototype ripper, the mega-lift (developed by Tim Howard Engineering Ltd)
- An unloosened control.
The effectiveness of the cultivations was assessed in terms of:
- Depth and nature of loosening achieved following cultivation
- Improvements in soil penetration resistance (a measure of compaction) and longevity
- Improvements in tree rooting
- Tree survival in the first years following planting
- Tree growth rates and health.
- Corsican pine appeared to be capable of rooting into more compact soils.
- Differences in soil penetration resistance and tree performance between treatments suggest that complete cultivation remains the most effective method of alleviating soil compaction.
Models have been developed to predict the critical penetration resistance value at which a significant reduction in rooting should be expected, and the relationship between two methods for measuring penetration resistance (the penetrometer and the ‘lifting driving tool’).
It was found that:
- the 'lifting tool' can be used as an alternative measure of soil penetration resistance
- This equipment is more cost effective, easier to use and capable of measurements at greater depth.
Forest Research has over 40 years’ experience in establishing vegetation on brownfield sites, often where soil compaction is the key limitation to sustainable plant survival and growth. This research has informed our guidance on tree establishment on these types of site.
Forest Research frequently provides consultancy and research services to the Forestry Commission and external clients:
- Soil surveys, including for the presence and extent of soil compaction
- Advice and recommendations on the cultivation of compacted soils at a range of sites, including landfills, mine spoils and restored mineral workings
- Research on tree establishment on compacted soils, including effects of soil compaction on tree survival and growth; suitability of cultivation methods for a range of soil and site types; and testing new developments in cultivation methods.
Forest Research Best Practice Guidance
Foot, K. and Sinnett, D. (2006a). Do You Need to Cultivate before Woodland Establishment? (PDF-291K) Best Practice Guidance for Land Regeneration, BPG Note 3. Forest Research, Farnham.
Foot, K. and Sinnett, D. (2006b). Imported Soil or Soil-Forming Materials Placement (PDF-191K). Best Practice Guidance for Land Regeneration, BPG Note 5. Forest Research, Farnham.
Moffat, A. (2006). Loose Tipping (PDF-608K). Best Practice Guidance for Land Regeneration, BPG Note 4. Forest Research, Farnham.
Sinnett, D. (2006). Complete Cultivation (PDF-581K). Best Practice Guidance for Land Regeneration, BPG Note 13. Forest Research, Farnham.
Bending, N.A.D., McRae, S.G. and Moffat, A.J. (1999). Soil-forming Materials: Their Use in Land Reclamation. Stationery Office, London.
Moffat, A.J. and McNeill, J. (1994). Reclaiming Disturbed Land for Forestry. Forestry Commission Bulletin 110. HMSO, London.
Paterson, D.B. and Mason, W.L. (1999). Cultivation of Soils for Forestry. Forestry Commission Bulletin 119. Forestry Commission, Scotland.
Sinnett, D., Morgan, D., Williams, M. and Hutchings, T.R. (2008). Soil penetration resistance and tree root development. Soil Use and Management 24, 273-280.