Prevention of environmental pollution from agricultural activity: guidance

Section 3: soil protection and sustainability

Note: of the amber points below, the "Do" numbered 2 relates to Soil Organic Matter, and the "Dos" numbered 3 to 8 relate to Soil Erosion. The "Don't" numbered 3 relates to Soil Structure.

Dos **1. Comply with the Sludge (Use in Agriculture) Regulations 1989 (as amended) if sewage sludge is to be applied to prevent contamination with Potentially Toxic Elements (PTEs). *2. On arable land: (i) use suitable break crops in an arable rotation  (ii) optimise the use of organic materials by basing rates of application on soil and crop needs. Where break crops are not used, a record should be kept for five years of organic materials and the quantities applied to arable land [GAEC measure 7] *3. Follow the latest edition of the Muirburn Code. [GAEC measure 6] *4. All cropped land over the following winter must, where soil conditions after harvest allow, have either: crop cover, grass cover, stubble cover, ploughed surface or a roughly cultivated surface. Fine seedbeds must only be created very close to sowing. [GAEC measure 1] *5. (i) Maintain functional field drainage systems, including clearing ditches, unless environmental gain is to be achieved by not maintaining field drainage systems. (ii) Where environmental gain is to be achieved, this must be declared on the IACS return. [GAEC measure 5] *6. In areas prone to wind erosion you must take steps to reduce the risk of soil loss in spring by maintaining crop cover, using coarse seedbeds, shelter belts or nurse crops, or use other appropriate measures with an equivalent effect. [GAEC measure 2] *7. On sites where capping is a problem you must form a coarse seedbed or break any cap that forms to avoid erosion. [GAEC measure 3] *8. (i) Prevent erosion of land, particularly, banks of watercourses, watering points and feeding areas from overgrazing, heavy trampling or heavy poaching by livestock. (ii) Where this occurs, reduce stock until the land has recovered. All problems should be rectified at any time during the next growing season after the period that the problem has occurred. (iii) This measure does not apply to areas within 10m of a gateway and 3m of farm tracks necessarily used during wet periods. [GAEC measure 4] 9. Inspect soils routinely for loss of structure, signs of damage, capping and erosion. 10. Identify and protect vulnerable soils prone to erosion and leaching. 11. Ensure effective use of chemical and organic fertilisers by basing rates of application on soil analysis and identified crop needs. 12. Maintain soil structure and avoid over-working and compaction. 13. Correct deep soil compaction by carrying out subsoiling on suitable soils with satisfactory drainage. 14. When irrigating, ensure water application is uniform and rates are not too high or droplets too large. This will avoid sealing the soil surface and minimise run-off and soil erosion. 15. Alleviate compaction and rutting as soon as practical after late harvested crops such as maize or potatoes to reduce run-off. 16. Leave vegetated buffer strips adjacent to watercourses, wetlands and waterbodies to trap sediment. 17. Incorporate chopped straw evenly. 18. Carefully plan the movement and feeding of livestock on your farm. The inappropriate location of tracks or ring feeders can lead to significant soil erosion. 19. Understand the capabilities and limitations of the soil you are managing. 20. Sample and analyse soil, approximately every five years, and apply lime to achieve target pH for crop or grass growth. 21. Divert track run-off to buffer strips or vegetated areas to remove sediment. Don'ts **1. Don't strip or remove topsoil for sale, as this is an offence unless you have planning permission. **2. Don't apply non-agricultural wastes to agricultural land without obtaining the necessary permit or exemption from SEPA. *3. Do not carry out any cultivations if water is standing on the surface or the soil is saturated. [GAEC measure 9] 4. Don't apply inorganic fertilisers or organic manures without taking account of soil nutrient status and crop requirements. 5. Don't leave the bed or banks of ditches bare, as this may lead to erosion and inhibit filtration. 6. Don't clear out entire lengths of ditch at one time. Clear only one side of the ditch or leave vegetation breaks within the ditch to maintain wildlife corridors. 7. Don't allow soils to become contaminated with PTEs. 8. Don't position access points and gateways at the lowest point of a field (to reduce the potential for channelling surface water run-off and to cut off the route for any eroded soil particles). 9. Don't carry out significant excavation works in watercourses without consulting with SEPA. 10. Don't erect physical barriers in watercourses, as these can cause serious erosion.

Introduction

3.1 Soil quality and husbandry is fundamental to the sustainability of agriculture, landscapes and biodiversity. Soils not only form the basis of agricultural production, but also filter and buffer pollutants. Good soil management practices will help ensure that the requirements of Good Agricultural and Environmental Condition (GAEC) are met with regard to soil erosion, soil organic matter, soil structure and minimum levels of soil maintenance. Good soil management also plays a significant role in minimising diffuse pollution.

3.2 Soil is a finite resource which should be well managed to meet the needs of the present without compromising the ability of future generations to meet their own needs. The stripping or removal of soil for sale is an offence unless you have planning permission. Full details of the main pressures and impacts on soils in Scotland associated with all land uses are available in the Soil Quality Report published by SEPA in 2001. The Environmental Impact Assessment (Uncultivated Land and Semi-Natural Areas) (Scotland) Regulations 2002 were introduced to ensure that proposals which could lead to significant effects on the environment are given proper consideration.

Soil Quality and Nutrient Status

3.3 Soil fertility and structure are key factors affecting healthy plant growth, which are particularly important in agricultural soils and are dependent on good soil husbandry as well as the appropriate application of lime and nutrients.

3.4 The quality of soil and its inherent fertility depends upon:

• the nutrient content and its balanced supply to plants

• organic matter content

• soil pH

• biological activity

• the physical condition of the soil

3.5 Plants require adequate supplies of N, P, K, magnesium, calcium, sulphur and trace elements to grow satisfactorily. These are generally supplied from soil reserves, supplemented particularly for N, P and K by organic manures and inorganic fertilisers. Soils should be sampled and analysed approximately every five years, and apply the appropriate type of lime to achieve the correct balance between nutrients and target pH for crop or grass growth.

3.6 As long as the soil pH and organic matter are maintained at appropriate levels, N, P, K and sulphur inputs and/or soil reserves can meet most plant nutrient requirements. Excessive soil nutrient levels (particularly N and P) should be avoided as leaching or erosion of nutrient rich soils to watercourses can cause pollution and promote algal growth (i.e. eutrophication).

3.7 Applications of inorganic fertilisers, livestock manures and other organic wastes should match crop requirements calculated by nutrient planning, for example by following the farm nutrient component within "The 4 Point Plan". The individual components of the Plan (copies of which are available from SEERAD Area Offices) are as follows:

• minimising dirty water around the steading

• better nutrient use

• a risk assessment for manure and slurry

• managing water margins

3.8 Non-agricultural wastes should not be applied to agricultural land unless they are beneficial to the soil or growing crop and should be applied only when ground and weather conditions are suitable. All proposed applications of non-agricultural wastes to agricultural land must be registered with SEPA. 

Acidification

3.9 The majority of Scottish soils are naturally acidic and are subject to natural acidification processes from fertiliser and manure use, plant growth and rainfall, to local deposition of ammonia from farming and to other pollutants from industry. Soil susceptibility depends on soil type and cropping. The result is a reduction in the soil pH level over time unless the soil is naturally calcareous or regular applications of an appropriate type of lime are made. For most arable crops, the pH of mineral soils should be maintained at pH 6.3, while for lowland grassland the soil pH should be maintained at 5.8. The reduction in lime application is resulting in more acid soils. This will reduce crop yield as well as support a more limited range of crops. Acidic soils will produce acidic drainage and may therefore result in a deterioration in water quality. It is equally important not to over-lime soils as this will reduce the chemical availability and uptake of some trace elements resulting in reduced plant growth.

Organic Matter

3.10 Organic matter in the topsoil influences its physical, chemical and biological behavior, particularly its structural stability, ease of cultivation, water retention capacity and nutrient availability to plants. Most soils have a reasonable supply but if the organic matter in a soil falls, it can impair its ability to support plant growth. Where organic matter levels are lower than is desirable, they can usually be increased by sowing a grass ley or by incorporating crop residues or organic manures over several years. Incorporate any organic manures and chopped straw evenly. The incorporation of crop residues can maintain organic matter levels in arable soils. This is a requirement of Good Agricultural and Environmental Condition (GAEC).

Biological Activity

3.11 The natural soil biological processes, which are vital for healthy soils, are dependent on soil organisms ranging from bacteria and fungi to earthworms. Soil management and the presence of contaminants affect the activities of these organisms. Heavy metals, excessive fertiliser and organic chemical loadings (including pesticides) can suppress such biological activity. Good soil husbandry, nutrient planning and careful use of pesticides combined with a well-managed crop rotation will maintain good biological activity. 

Physical Condition

3.12 Soil structure has a major influence on the rooting potential, drainage, water-holding capacity, strength and consistency of soils. Any degradation of structure will result in limited land use and agricultural potential.

3.13 Over-compaction, due to damage caused by machinery and high stocking densities, is an increasing problem. Compaction restricts root growth and limits soil drainage which in turn results in increased run-off, more frequent flooding, increased erosion and the transfer of potential pollutants to surface waters. In compacted, wet soils, aeration is reduced resulting in poor root growth and reduced availability of plant nutrients. To avoid the degradation of soil structure ensure land drainage systems are maintained, avoid the use of heavy machinery and livestock poaching when soils are soft or saturated and select appropriate cultivation techniques for different soil types.

3.14 Preventing compaction is easier than correcting it and regular soil profile inspections should be made, particularly on headlands and tramlines, to assess soil conditions. 3.11, 3.12 and 3.13 are all requirements of GAEC.

Restoration of Disturbed Soils

3.15 Agricultural activity can be disrupted due to soil disturbance by extraction of minerals, pipeline installation, landfilling and other civil engineering works. This can result in severe soil degradation problems if soils are not stripped, stored and reinstated by appropriate methods. Farmers should seek to ensure that before site works start the developer or operator has provided a detailed inventory of the quality of the land and the condition of both topsoil and subsoil and a detailed specification and method statement.

Contamination of Soils

3.16 To protect the long-term productivity of the soil it is necessary to be aware of the many potential sources of contamination, to assess their significance and then take the necessary steps to prevent, limit or remedy their effects.

3.17 Soil contamination may affect:

• soil processes - (physical, chemical and biological) leading to degradation of soil quality

• plant growth

• human or animal health, by uptake of pesticides or Potentially Toxic Elements (PTEs) into plants resulting in entry of toxins into the food chain

• watercourses by run off, leaching or erosion from contaminated land

3.18 Although a wide range of PTEs may contaminate soils, in practice problems usually arise from a relatively small number of elements. The following PTEs may cause problems due to the presence of excessive amounts in soils: zinc, copper, lead, cadmium, arsenic, fluorine, nickel, chromium, mercury, selenium and molybdenum. While the presence of essential trace elements such as zinc and copper is necessary for plant and animal nutrition, excessive concentrations under certain pH conditions can affect the health of plants, animals and humans. The most likely source of such PTEs is from the application of sewage sludge and non-agricultural waste. Copper and zinc may also be added to soils from pig slurry or poultry manures. Industrial organic chemicals, oils and solvents and persistent pesticides can also contaminate soil.

3.19 The assessment of the suitability of a waste and the receiving soil for disposal to agricultural land should take account of:

• waste degradation rates and the release of nutrients and other substances during its breakdown

• the chemical form of the element and its likely interaction with the soil, given the pH values and the existing "background" concentration of the element in the receiving soil

• the effect of the element upon soil organisms and processes

• the timing of application

• the effects upon plant growth

• the possibility of uptake of potentially harmful substance to edible parts of plants

• the effects upon livestock, by consumption of stored and conserved crops, grazing herbage or direct ingestion of contaminated soil

• the possible effects on the human food chain

3.20 Where there is any uncertainty about the current level of soil contamination or where a new potentially contaminating waste is to be introduced to farmland, then the farmer should seek professional guidance to determine if land application is legally permissible and, if so, at what rate. It is necessary to comply with the Sludge (Use in Agriculture) Regulations 1989 (as amended) if sewage sludge is to be applied to agricultural land.

Oil Spillage

3.21 If a loss of oil to land occurs, specialist advice and assistance may be necessary. SEPA should be notified of any loss that might cause pollution.

Flooding

3.22 Agricultural land that is used for flood management has an increased risk of the deposition of contaminated sediments, spoils or wastes in certain locations. Carrying out significant excavation works or erecting physical barriers to watercourses can cause flooding or serious erosion problems to adjacent agricultural land. Before undertaking such work SEPA, SNH and local authorities should be consulted. It should also be borne in mind that a new set of risk-based controls on river engineering operations is due to be introduced as from the end of 2005. SEPA should be contacted to discuss how any proposed engineering operations short-term measures following the event, such as controlling grazing to reduce the exposure of stock to contaminating materials. In the medium term, site investigation should be carried out to establish the extent and significance of any contamination.

3.23 Appropriate action to deal with a surface accumulation might include cultivating the soil, mixing the contaminant in order to dilute and disperse it or where the contaminating material is considered to have potentially harmful effects, its removal, if feasible, may be justified.

3.24 The deposition of inert material can cause structural deterioration of the soil, such as sealing and blockage of pipe drainage systems, which may lead to surface ponding and secondary effects upon soil processes due to reduced aeration. The impairment of soil strength can lead to greater risks of damage by livestock and machinery, which may be overcome by remedial soil cultivation or sediment removal.

3.25 Land management techniques, such as the direction in which fields are ploughed, can help to reduce any flood risk on adjacent land.

Soil Erosion

3.26 Soil erosion is a natural process, caused by the action of both wind and water, though it can be exacerbated by inappropriate management. Certain soils are more susceptible to erosion than others and inappropriate soil and water management can increase the degree of risk. Loss of agricultural soils through erosion can affect productivity and profitability and result in off-site problems in water pollution, flooding and road blockage. GAEC sets the minimum standard for protecting agricultural soils from erosion and provides a number of measures that must be taken as a requirement of cross-compliance.

Wind Erosion

3.27 In Scotland significant wind erosion is normally confined to exposed expanses of sandy and peaty soils. This results in the loss of valuable topsoil as well as potential damage to crops and archaeological sites, and can be a public nuisance. The extent of wind erosion can be controlled by measures aimed at reducing wind velocity at ground level, stabilizing the soil surface and/or trapping the soil particles already moving. Such measures can include:

• rows of trees and hedges planted to provide shelter for crops grown in their lee. Effective protection normally extends for a distance of 20 times the height of the shelter

• leaving crop stubble uncultivated or leaving coarse seed beds over winter

• mulches such as organic manures and sewage sludge applied to sands

• minimal cultivation techniques for sandy soils by ploughing and rolling in one operation with the crop sown at right angles to the direction of rolling

• the sowing of permanent or semi-permanent grassland as a cover crop

• sand dunes stabilized by planting species such as marram grass to prevent windblown sand being deposited on agricultural land

Water Erosion

3.28 Soil loss by water erosion occurs from sloping arable and rotational grassland, particularly on sandy and loamy soils. Water erosion may occur whenever rainfall intensity exceeds the infiltration rate of the soil surface and the surface run-off is heavy and fast enough to move soil particles. When losses from parts of fields are in excess of about 3 tonnes/ha, irreversible loss of fertility is likely to occur. Bare soils, fine seedbeds, potato drills and ridged beds are particularly at risk from water erosion.

3.29 Careful management can substantially reduce the risk of this occurring. The following measures might apply:

• maintain field drainage systems, outlets and ditches in good operating condition to minimize ponding and run-off. Surface water should be channelled away from areas prone to erosion, e.g. long slopes, by using interceptor ditches

• reduce run-off by increasing surface drainage using subsoilers or mole ploughs

• encourage topsoil stability by using organic manures; avoid over-cultivation and over-deep working of the land

• avoid soil compaction by minimizing the weight on each wheel and by spreading the load over as large an area as possible by using dual and/or flotation tyres

• establish crops as early as possible

• sow autumn crops early enough to establish cover over winter

• use minimal cultivation techniques for susceptible soils e.g. by ploughing and rolling in one operation with the crop sown at right angles to the direction of rolling

• use permanent grass buffer strips both within fields and between fields to control the impact on watercourses

• avoid overgrazing and poaching on banks of watercourses, particularly watering points and feeding areas

• encourage regeneration of trees, shrubs and vegetation which help to stabilize the borders adjacent to flowing water

• sow permanent grass if repetitive water erosion which cannot be controlled by changes in husbandry or cropping

• when irrigating, ensure water application is uniform and rates are not too high or droplets too large. This will avoid sealing the soil surface and minimize run-off and soil erosion