Scottish Government

GROUP 7 Soil Organic Material Use on Land

Working group members:

Soil Organic Material Use on Land

Outline of the issue

8.1 A wide range of materials, including farm manures and slurries, sewage sludges, composts and other non-agricultural wastes are used in farmland, forestry, land restoration, landfill reclamation, landscaping and domestic gardens. Organic materials have been used to improve soil for many hundreds of years and nowadays there are a number of controls in place to protect human health and the environment.

8.2 Farm manures and slurries are the main type of organic material used on land and account for over 92% of the total applied. Non-agricultural materials including sewage sludges and composts supply the remaining eight percent of the total.

8.3 Well managed use of materials on land for agricultural benefit or environmental improvement can be the Best Practical Environmental Option ( BPEO) in many circumstances. Potential benefits include the supply of nutrients and organic matter to the soil. However the use of organic materials must be managed properly to meet the specific requirements of the site, soil and its land use to avoid harming human health or the environment, including the soil itself.

8.4 In most circumstances use of organic materials is well managed, but where poor management occurs it can cause water pollution through leaching or run-off and may also increase gaseous losses of ammonia, nitrous oxide and methane. Certain organic materials can have high levels of potentially toxic elements ( PTEs) or other substances which can be potentially harmful to soil and the greater environment. These contaminants must be considered when deciding on the suitability or application rates for organic materials.

8.5 Pressures are being driven by a number of instruments to increase the recycling of materials to soil e.g. the Waste Framework Directive and the targets associated with the Landfill Directive. There is a need to ensure that an appropriate balance is struck between these needs and the requirement to ensure that soil and its functions are protected. While there has been a long history of using farm manures on soil and much research demonstrating its benefits, there is less knowledge on the use of some other organic materials.

Impact on soils

8.6 Use of organic materials on land can provide many benefits to soil depending on the soil type, source of organic material and its management. The main benefits normally stem from the supply of nutrients and organic matter to the soil. Nitrogen, phosphorus and potassium are major nutrients which are normally supplied in most organic materials and will assist plant growth. Minor nutrients such as sulphur and magnesium and trace elements such as copper and zinc may also be supplied by organic materials.

8.7 Organic matter addition will maintain or increase the soil's organic matter content and therefore can improve its structure, nutrient holding capacity and biological fertility. Organic matter addition in some situations can reduce the risk of soil erosion, and may also increase the soil's capacity to hold water thereby helping to reduce flood risk. Further information on the value of soil organic matter is given in the " Soil o rganic matter loss" section of this report.

8.8 The main potential benefits to soil functions from organic materials application are therefore an improvement in the food and biomass production and also carbon storage functions of soils. Organic materials also have an indirect effect on the regulation of water supply through the filtering function of soil if the application modifies nutrient status, topsoil structure and water holding capacity. Organic materials can be used for land restoration of derelict sites which have little or no topsoils and this can improve the biodiversity of the site.

8.9 The use of organic materials must be managed properly to meet the specific requirements of the site, soil and its land use and to avoid harming human health or the environment, including soil. As with the use of inorganic fertilisers, nutrients in organic materials have the potential to cause water pollution. There may also be contaminants that need to be considered when deciding the suitability and / or application rates for organic materials.

8.10 Inorganic fertilisers are manufactured to a set of Fertiliser Regulations which place controls on their composition. Organic materials are not subject to such strict controls on nutrient and contaminant content. This variability means it can be difficult to match the application rates to the requirement of the growing crops.

8.11 The potential negative impacts on soil functions which can be caused by organic materials are a potential reduction in the biomass production and a decrease in the size and diversity of the soil microbial population. Poorly managed application can also have a detrimental effect on the soil's functions in relation to regulating water supply and maintaining the balance of gases in the air. Organic materials therefore provide both positive and negative impacts on soil function, depending on their management.

Impact in Scotland

Current and future use of organic materials

8.12 Approximately 25 million tonnes of organic materials are applied to an estimated area of 260,000 hectares of land every year in Scotland. The amount of agricultural manures and slurries spread is 23 million tonnes per year and this quantity is expected to remain about the same in future years. This is a far larger amount compared to non-agricultural wastes (1.5 million tonnes in 2005) and also sewage sludge (65 thousand tonnes of dry solids in 2005/06). Scottish Water's present draft sludge strategy envisages recovering about a half of Scotland's sludge to agricultural land compared to a current percentage of 28%. In addition, approximately 50,000 tonnes of compost is applied annually to land including the regeneration of brownfield sites across Scotland. The National Waste Plan for Scotland (2003) estimates that by 2020 about 290,000 tonnes per year of segregated household waste and up to 150,000 tonnes per year of garden and other green waste will be collected for composting. Over the next few years there is likely to be a significant increase in the production of composts from green waste and other organic materials that are diverted away from landfill in order to meet the UK's recycling targets.

8.13 The availability of a suitable landbank, at both a national and local level, will be a key factor in deciding to what extent it is feasible and practical to recycle extra quantities of non-agricultural materials across Scotland.

8.14 This will need to take into account the following factors when assessing the suitability of soils and land for the recycling of organic materials. These include suitability for spreading (e.g. soil type, nutrient and PTE analysis, slope, proximity to watercourses etc.) and the risks of physical damage to the soil (e.g. trafficability and compaction risk). The assessment will also take account of the location of a site with respect to administrative or legal boundaries (e.g. land in an NVZ, under a agri-environmental agreement, organically farmed land, SSSIs etc.), along with catchment, topographic and climatic conditions that could impact upon nutrient (e.g. nitrate and phosphorus) losses to sensitive water bodies. This would provide a strategic overview to guide policy development by identifying areas in Scotland where there is a potential shortage or surplus of available land for recycling organic materials.

Nutrient contribution

8.15 The total quantity of nutrients annually applied to land from manures and slurries is 178 thousand tonnes of nitrogen and 31 thousand tonnes of phosphorus. At current fertiliser prices the potential annual value of these nutrients is approximately £90 million. The actual value is far less because of losses of nutrients during the materials collection, storage and application. Although 100% efficiency of these nutrients is not possible even a relatively small increase in overall efficiency of nutrient use from organic materials would benefit agriculture at scales ranging from farm through to national level.

8.16 Statistics on fertiliser usage indicate that some farmers make insufficient allowance for the contribution of manures to crop fertiliser requirements. Perceived lack of control over the amount spread and the spread pattern achieved as well as insufficient full awareness of the nutrient value is seen as an important element in the farmers' lack of confidence in the use of organic materials.

Climate Change

8.17 The scale and direction of climate shifts in Scotland is not certain, but possible changes identified in UKCIP02 scenarios include: increasing summer temperatures, increasing winter temperatures, more extreme high temperatures, less extreme low temperatures, higher winter rainfall, less summer rainfall, more intense rainfall and more winter storms.

8.18 The soil nutrient cycle and its ability to degrade organic materials will react to such changes in temperature and water content, but with an as yet unknown degree of resilience and resistance. Thus climate change may impact on the contribution that organic materials make to soil organic matter and nutrient contribution. Possible climate change effects could include increased risk of organic materials and their components affecting water quality (dissolved organic carbon and nitrate etc), and changes in greenhouse gas release from soil.

8.19 Climate change may also have indirect impacts because as soils become saturated for longer periods of time with heavier rainfall and changes in vegetation cover, there may be increased occurrence and intensity of runoff, erosion and flooding events. This could reduce the time period when soils will be suitable for application of organic materials.

8.20 Application of organic materials to land has the potential to increase the carbon stock of Scottish soils at a time when there is evidence that soils may be losing carbon at rates hitherto unforeseen. As a general objective, the principles of this approach are sound but there are more detailed considerations to be made. Soils have a natural upper capacity of organic matter content before their desired functions become impaired, for example naturally poorly drained soils have workability and trafficability limitations that would increase with the additional organic matter. Climate change may affect soil carbon turnover in a number of different ways and in different soils; the added organic matter from organic materials may not behave in the way that it currently does.

8.21 Climate change can directly effect the land suitability for application and there are also indirect impacts via land use change and policy change. There is a continuing increase in the area of biofuel crops and there is considerable increase in utilising sewage sludge on these crops.

8.22 Applying organic materials to the land should reduce the need for inorganic fertilisers which are either mined from natural resources or manufactured in energy intensive processes. By replacing these with organic material we may reduce the impact of these processes, which in turn reduces carbon dioxide emissions. Another possible energy benefit that can result from organic materials use is improved workability of heavy soils which will result in lower fuel use in land preparation.

Water pollution

8.23 The Scottish Agricultural Pollution Group reported ⁷ that there were 104 water pollution incidents caused by agricultural manure run-off, 14 from exempt wastes and four incidents from sewage sludge in between 1999 and 2002. These measurements do not include the contribution of organic materials to diffuse pollution. Further information on this topic is given in the " Diffuse pollution" section of this report.

Potentially toxic elements

8.24 A major study ⁸ was started in 1993 to study the effect of sewage sludge on soil fertility at nine UK experimental sites, including two in Scotland. This project provides evidence that zinc accumulation can be detrimental to soil biological fertility where sewage sludge and other wastes are applied to land and that certain soils in Scotland may be particularly sensitive. The research showed that loss of rhizobia occurred at zinc concentrations below the current maximum limits and with sludge additions that are permissible under the Sewage Sludge Regulations. Although the rhizobia used in this trial are relevant primarily to grassland, the effects seen could be indicative of further effects on soil microbes and on biological fertility in general. ⁹

8.25 Another sewage sludge research project ¹⁰, across six contrasting sites and soils, showed that the maximum allowable concentration of cadmium in the soil may need to be reduced. This work showed that the current UK soil total Cd limit of 3 mg/kg was not sufficiently protective against producing grain above the EU grain Cd Maximum Permissible Concentration ( MPC), unless the soil pH was greater than 6.8. The research showed that grain would be below the MPC at a total Cd concentrations in soils receiving sludge of 0.5 mg/kg for soils of pH 5-6, 1 mg /kg for soils of pH 6-7, and 1.5 mg kg for soils of pH 7. Because Scottish soils tend be more acidic and cadmium availability to plants increases with soil acidity there is greater significance of these results to Scotland and a need to re-assess current soil metal limits.

Relevant Policies

8.26 There is a relative abundance of advice and guidelines for users of organic materials on soil, and a relative dearth of direct regulation. Guidance is chiefly aimed at land managers, notably farmers and foresters, and ranges from the specific, such as on the use of sewage sludge in forestry, to the general, such as the Prevention of Environmental Pollution from Agricultural Activity ( PEPFAA) ¹¹ code of good practice.

8.27 The need to maintain healthy soil is at the heart of this guidance, but is not necessarily explicit, since it may often concern more directly pollution threats which may arise, for example to water, through incorrect use of materials on land. The same is true of the economic instruments which help re-inforce good practice.

8.28 As a result of Common Agricultural Policy ( CAP) reform farmers must meet a set of requirements including Good Agricultural And Environmental Condition ( GAEC) and compliance with the Sludge (Use in Agriculture) Regulations and other Statutory Management Requirements to be eligible for direct support payments. GAEC requires that soil organic matter levels are maintained through appropriate practices including the use of organic materials by basing rates of application on soil and crop needs.

8.29 Economic instruments may be described as either positive, in which a perceived good is paid for; or negative, in which case support will be denied if standards are not met. The requirements for GAEC and cross compliance, which must be taken into account by nearly all farmers, are of the latter nature. Cross Compliance and Statutory Management Requirements & Good Agricultural and Environmental Condition apply which includes requirements on sludge use, as well as the NVZ regulations is given on the following link http://www.scotland.gov.uk/Topics/Agriculture/grants/Schemes/ccompliance.

8.30 Cross-compliance, however, illustrates the partial nature of regulation for soil. Amongst the instruments which it makes compulsory is the Sludge Directive (86/278/ EC), which deals only with a specific organic material in specific circumstances. Explicit regulation on organic materials to land tends to relate only to materials, like sludge, which are wastes. Wastes, such as sludges, discarded ashes and minerals, and off-specification composts, make up a small proportion of organic materials put to land. Recovered materials, such as composts meeting specifications, and materials which have never been discarded in the first place, in this context chiefly manures and slurries, are not waste and are not subject to waste regulation.

8.31 The Waste Framework Directive classifies as a waste recovery operation "R10 Land treatment resulting in benefit to agriculture or ecological improvement". The Directive's basic requirement is for those carrying out waste recovery operations to hold a permit authorising them to do so. But the Directive gives discretion to provide permit exemptions and almost all land treatment by waste in the Scotland is carried out under the terms of exemptions provided by the Scottish Government. These permit exemptions are valid only if the objectives of Article 4 of the Directive are met - and those objectives are to ensure that "…waste is recovered or disposed of without endangering human health and without using processes or methods which could harm the environment, and in particular: (a) without risk to water, air or soil, or to plants or animals…."

8.32 Waste regulation explicitly protects from harm to the environment and risk to human health. While this is a good aim for the use of organic materials on soil it would be highly undesirable - and practically exceedingly difficult - to extend waste regulation to non-waste materials such as manures and slurries. However, soil is a conductor by which pollution causing environmental harm or risks to human health is transmitted to media such as air and water. In this context there is a great deal of regulation, notably (under the Water Environment and Water Services (Scotland) Act 2003 ¹² and related legislation) in respect of water pollution. This legislation allows remedial work to be specified where necessary, which may include work on soils. 8.33 The regulatory environment at a European level is changing, with discussions on a revision of the Waste Framework Directive ongoing, and proposals for Directives on Sludge and Biowaste. These, again, relate to wastes rather than the wider range of organic materials to soil, and are unlikely to change the existing legal mechanisms other than in detail. Soils will continue to rely for their protection against inappropriate use of organic materials on guidance and regulation designed chiefly to protect other media. However, this work is very relevant to the health of soils and, allied to the land manager's own interest in maintaining the quality of soils, is likely to prove sufficient - provided it takes account of developing scientific knowledge, particularly relating to longer term threats. 8.34 Sewage sludge use on farmland is well regulated and enforced. The EU Sludge Directive seeks to encourage the use of sewage sludge in agriculture and to regulate its use in such a way as to prevent harmful effects on soil, vegetation, animals and man. The Sludge Directive is due to be revised in 2008. The current Sludge Directive was transposed into UK law by way of the Sludge (Use in Agriculture) Regulations 1989 ¹³. There is a Sludge Code of Practice produced by Defra to complement the Regulations. The current Regulations are used alongside the Safe Sludge Matrix which is a voluntary code fully followed by Scottish Water. In addition, Scottish Water uses Hazard Analysis and Critical Control Points ( HACCP) at all Sludge Treatment Centres which produce sludge for application to agricultural land to ensure that the treatment meets the requirements of the Safe Sludge Matrix.

8.35 The Forestry Commission has published an Information Note ¹⁴ to help foresters and companies trading in sludge, compost and other organic waste products to make informed decisions about the use of sludge on forest land.

8.36 Sewage sludge use on non-agricultural land is exempt from licensing if the activity meets the requirements detailed in Regulation 17 and 18 of the Waste Management Licensing Regulations ( WMLR) 1994, as amended ¹⁵. Although an activity may be exempt from licensing, it is still subject to statutory controls to prevent environmental pollution and harm to human health. The controls under Regulation 18 relate to registration of exempt activities. The controls under Regulation 17 relate to certain conditions being met in order for the activity to be exempt, which includes the requirement that the activity must not endanger human health or harm the environment by: presenting a risk to water, air, soil, plants or animals; causing nuisance through noise or odours; or adversely affecting the countryside or places of special interest.

8.37 Further information is given in http://www.sepa.org.uk/regulation/waste/exemptions.htm This site provides SEPA's Registration Forms, Registration Guidance Notes and Technical Issues Notes for Paragraph 7 (treatment of land for agricultural benefit or ecological improvement) and Paragraph 9 (treatment of land for reclamation or improvement).

8.38 If compost meets the BSI Publicly Available Specification ( PAS 100) for Composted Materials the compost ceases to be waste and the WMLR controls do not apply.

8.39 If the land is in a Nitrate Vulnerable Zone ( NVZ) and also used for agriculture, then the provisions of the NVZ Action Programme will also apply. This includes rules and controls on all nitrogen containing organic materials. The following links to the Scottish Executive website which contains nitrate vulnerable zones maps, the legislation and further guidance. http://www.scotland.gov.uk/Resource/Doc/1057/0023330.PDF.

8.40 There is currently no a Code of Practice (CoP) or published guidance on the use of sludge composts and biowastes for land restoration despite the fact that this activity is increasing nationally. Such a CoP would assist waste producers comply and reassure land owners that good practice was being followed. Political interest is high and there is an urgent need to pull together recent scientific findings into a format suitable for all stakeholders. The PEPFAA Code, exists for organic materials including sewage sludge use in agriculture and there is published guidance for forestry use. Poorly managed waste practices can result in risks to human health, water, air, soil quality and biodiversity.

Reference

Report for the Scottish Executive on the current state and threats to Scotland's soil resource 2006
http://www.scotland.gov.uk/Publications/2006/09/21115639/0

SEPA State of the Environment: Soil Quality Report 2001
http://www.sepa.org.uk/pdf/publications/state_of/soil/soil_report.pdf

SEPA State of the Environment: Soil Quality Report 2001-
http://www.sepa.org.uk/pdf/publications/state_of/soil/soil_report.pdf

Impact of Industrial Waste and Sheep Dip Chemicals applied to agricultural land on Soil Quality
http://www.sepa.org.uk/pdf/publications/reports4sepa/industrial_waste_sheep_dip_chemicals.pdf

Gibbs, P. A., Chambers, B. J., Chaudri, A. M., McGrath, S. P., Carlton-Smith, C. H., Bacon, J. R., Campbell, C. D. ,and Aitken M. N. (2006) Initial results from a long-term, multi-site field study of the effects on soil fertility and microbial activity of sludge cakes containing heavy metals. Soil Use and Management 22 (1):11-21.