Natural England Technical Information Note TIN045 The use of lime on semi-natural grassland in agri-environment schemes

Soil pH is an important factor influencing the species composition of semi-natural grassland. Soil pH is controlled by geology, rainfall, soil texture and management practices. The maintenance and restoration of the biodiversity value of species-rich neutral grassland and some types of fen meadows on soils prone to acidity through leaching is dependent on the periodic application of lime.

Liming is a traditional grassland management practice which aims to raise pH to around 6.0, which is the optimum pH for grass production. Although grassland productivity per se is not a management objective for semi-natural grasslands, many species-rich neutral grasslands owe their biodiversity value to past management practices such as liming and manuring for agricultural production purposes albeit at a lower intensity compared to the management of recent improved productive grasslands. In addition, for hay meadows in particular, continued management for biodiversity objectives requires maintenance of enough productivity to ensure continuation of cutting for livestock forage.

This note provides guidance on the use of lime on semi-natural grasslands under Environmental Stewardship agreement. pH and soil acidity the main constituents of liming materials which pH is a measure of acidity - the concentration of have been used for centuries to act both as hydrogen ions in solution. Soil pH is the most acidity neutralisers and essential plant nutrients. important factor in soil productivity mainly due to Calcium is held in the soil mainly on clay and its effect on the availability of plant nutrients and organic matter particles where it is exchanged the activity of soil organisms. It normally falls with other nutrients. At neutral and slightly acid within the range 3.5 on acid soils to 8.0 on pH there is sufficient exchangeable calcium in alkaline soils. The optimum pH for grassland the soil to meet requirements for optimum production is 6.0. growth. As pH falls, particularly below 5.0, plant growth is can be limited by the restricted Acidity is counteracted by the presence in the soil of chemical bases such as calcium, sometimes with magnesium. These bases are

First edition 15 September 2008 www.naturalengland.org.uk Natural England Technical Information Note TIN045 The use of lime on semi-natural grassland in agri- environment schemes

availability and uptake of calcium and other plant • Acid grassland - (pH 3.5 to 5.5) largely nutrients and the presence of toxic ions, such as comprising calcifuges. High frequency of aluminium. species with an Ellenberg R value of 3 or below, such as heath bedstraw, green-ribbed Factors controlling soil acidity are: sedge and heath milkwort. • Neutral grassland - (pH 4.9 to 6.5) comprising • Geology - soils derived from weathering of species with wide tolerances, those that prefer acidic rocks such as sandstones have lower neither strongly acid nor calcareous conditions. pH values than those derived from limestones. Ellenberg R values are typically 5-7. The Where there is cover of glacial drift and where Danthonia decumbens (heath grass) sub- there are deeper soils, such as in valley community of the MG5 Cynosurus cristatus - bottoms, underlying rocks have less influence. Centaurea nigra neutral grassland type • Rainfall - rainwater is slightly acid due to (MG5c) occurs on soils which are moderately dissolved carbon dioxide, sulphur dioxide and acidic (pH 4.9 to 5.4) and, whilst also ammonia. It dissolves lime in the soil and comprised of species with wide tolerances, it leaches it into drainage systems. High rainfall has a significant presence of species such as areas therefore tend towards more acid soils. tormentil, heath grass, devil’s bit scabious, • Soil texture - in coarse-textured free-draining bitter-vetch and betony with Ellenberg R soils lime is leached out more quickly. values between 3 and 5. It occurs on soils on • Management practices - harvesting of hay the upland fringes or on acid rocks that have crop removes nutrients such as calcium. been limed in the recent past to increase pH Nitrogen fertiliser has an acidifying effect, and on strongly leached or acid soils overlying although normal dressings of FYM or slurry limestone. have little influence on soil pH. • Calcareous grassland - (pH 6.5 to 8.0) comprising species with wide pH tolerances, Soil acidity and grassland types but with more specialist lime-loving species Most plants grow in a range of pH conditions, making up a significant part of the community. but the ability of individual species to survive in a Ellenberg R values normally 7 and above for vegetation community depends on how well they most species in the community. compete with other species in a given situation and this is related to a number of environmental Variations in soil pH and grassland types may and management effects. Ellenberg values are a occur within relatively small areas such as a relative measure based on the recorded field, eg where limestone outcrops emerge occurrences of plants in a range of vegetation amongst neutral glacial drift or due to the effects communities and indicate the influence of factors of flushing from base-rich springs. such as light, moisture, fertility and pH on plant species. More information can be found at It should be stressed that the Ellenberg values www.ceh.ac.uk/products/publications/untitle are an approximation derived from both expert d.html. The Ellenberg R value relates to soil pH, opinion and objective studies. They are a such that plants with an index of 1 are always particularly useful tool for interpreting found on soils of high acidity (calcifuges) and environmental monitoring data. Thus, while they species with an index of 9 are always on soils can be useful for giving a broad indication of the with high pH (calcicoles). Most plants occur prevailing environmental conditions, they should somewhere in between and in some situations not be used too rigidly or uncritically for other factors may be dominant over pH. informing land management decisions. Agriculturally improved grasslands, for example, occur over a range of pH values due to the effect Recommendations on liming of high nutrient levels. Nevertheless, soil acidity The use of lime in ES options aimed at has an influence on grassland type and plant maintenance and restoration of species-rich species composition. grassland should normally be confined to sites where the objective is to maintain, restore or Page 2 Natural England Technical Information Note TIN045 The use of lime on semi-natural grassland in agri- environment schemes

create species-rich neutral grassland and certain dissectum-Molinia caerulea fen meadow, types of fen meadow/rush pasture (M23 Juncus typical sub-community. effusus/acutiflorus-Galium palustre rush-pasture • Mosaics of neutral grassland NVC sub-types and M24 Cirsium dissectum-Molinia caerulea fen (MG5c, MG5a (Lathyrus pratensis sub- meadow - M24b typical sub-community). Priority community, MG5b (Galium verum sub- should be given to sites supporting species-rich community). neutral grassland/fen meadow, where there is a risk of undesirable botanical change due to For the above grassland types, the pH may be in acidification and where there is a known history the range 4.9 to 5.4 and there may be significant of liming. Maintenance of pH between 5.5 and cover of species with Ellenberg R values in the 6.0 through liming would be appropriate in these range 3-5. cases provided that other management factors, particularly grazing and/or hay cutting are in The general advice is that application of lime as place to meet objectives. specified above (Recommendations on liming) is required in these situations. This approach If the site is known to support plant species of can be justified as the acid-neutral species with national or local importance eg uncommon lower Ellenberg R values in the range 3-5 have a plants, waxcap fungi and species included in broad tolerance to increases in pH resulting from local Biodiversity Action Plans, or where there the addition of lime provided that sustainable are important invertebrate species that rely on grassland management practices are also particular plants, then the recommendation maintained (see advice in Crofts & Jefferson should ensure that liming will be beneficial to 1999). For example, tormentil has an Ellenberg these species. Liming should never be carried value of 3 but it can also occur in both neutral out where there are uncommon strict calcifuge and calcareous grassland types. It is probable species present. that the observed distribution pattern of acid- neutral species in semi-natural neutral grassland If liming is appropriate, the following should be is controlled by factors in addition to pH such as included in the HLS agreement: soil moisture levels and competition.

Prescription However, should advisers remain concerned • On neutral grassland apply lime, subject to soil over applications of lime in these circumstances test, to raise pH to 6.0. and, there is no evidence of historic liming practice, then further specialist advice should be Indicator of success sought. • The soil pH should be between 5.5 and 6.0. Liming to enhance faunal interest or to In classic schemes, guidance should be given to ameliorate the environmental impacts of the agreement holder and a derogation may be acidification needed to allow the addition of lime. Where there are requests to carry out liming for other reasons to change the vegetation Advice on MG5c neutral grassland /fen community from acid to neutral, for example to meadows including mosaics enhance soil conditions for feeding birds, to This section provides advice on liming in the reduce uptake of heavy metals or to prevent following situations: acidification of water bodies, then the decision should be based on whether this will help • Neutral grassland conforming to the more achieve scheme targets without any detriment to acidic Danthonia decumbens sub-community existing interest. of MG5 Cynosurus cristatus-Centaurea nigra meadow and pasture (MG5c). Specialist advice may be required in these cases • M23 Juncus effusus/acutiflorus-Galium and others where there is any doubt about the palustre rush-pasture and M24b Cirsium need for liming. Page 3 Natural England Technical Information Note TIN045 The use of lime on semi-natural grassland in agri- environment schemes

Supporting or contextual information of calcium carbonate, with varying amounts of • Objective of management/target grassland magnesium. type: It is important to be clear at the outset as Those most commonly used are: to what is the target grassland to be maintained or restored. Consideration needs to • Ground limestone; be given as to the broad grassland type that would occur at a site taking into account • Screened limestone or limestone dust; geology, soils, management history, rainfall, • Coarse screened limestone or coarse landscape and topography. screened limestone dust; • Soils and geology: Basic information on soil • Ground chalk, and; types and geology is available on the National • Screened chalk. Soil Map stored on stand-alone GEN-i. On-line soil maps can be found at: A number of industrial by-products are also www.landis.org.uk/soilscapes/. Soil maps used as liming materials. These include sugar also exist as MapInfo GIS tables available on beet factory lime, paper pulp, blast furnace the Natural England M: drive (Mapdata) and on slag and basic slag etc. Marine calcareous GeniOnline in some NE offices. There may sands and calcified seaweed are also also be more detailed information in local marketed as liming agents. offices to help further on individual sites. Due Applications of these other products (typically to considerable differences within individual industrial by-products, calcareous sand and areas and fields that can occur, local calcified seaweed) can contain a range of knowledge should also be sought wherever nutrients and contaminants and their use in possible. agri-environment schemes is not generally • Soil test: All decisions should be supported by recommended. Exceptions would require the a soil test carried out in line with Technical recommendation of relevant specialists. Information Note TIN035 - Soil sampling and analysis for habitat re-creation and restoration • Timing and amount: Lime can be added at in agri-environment schemes - and TIN036 any time of year provided that soil conditions Soils and agri-environment schemes: are suitable for machinery. Time will be interpretation of soil analysis. Note that there needed for the liming material to penetrate the will be variation across the field and more than soil and this will depend on the type of material one set of samples may be needed in certain used and the soil type. Work should never take fields if there are obvious differences. pH also place where this may affect ground nesting changes with depth in the soil profile. Leaching birds or other conservation interest. may acidify the upper 1-2 centimetres of the profile compared to lower down. Soil samples The amount of liming material required to raise on grassland are normally taken to a depth of pH depends on soil texture and soil organic 7.5cm so care will need to be taken in matter. Light sandy soils rapidly lose calcium interpreting results. and need small frequent additions to raise pH. • Material: Liming materials are regulated such Heavier clay soils hold calcium for long that there must be a declaration of their periods, but need heavier dressings. Neutralising Value (NV - a measure of Recommendations are often given in terms of effectiveness in raising pH compared to pure equivalent ground limestone or chalk (NV 50- calcium oxide) and the fineness of grinding 55). More detailed information can be found in (relates to the speed of action). The term ‘lime’ Defra’s Fertiliser Recommendations for also refers to calcium oxide (quick lime) and Agricultural and Horticultural Crops booklet - calcium hydroxide (slaked lime) produced by RB209; burning limestone. Liming materials used www.defra.gov.uk/farm/environment/land- today are usually mechanically ground forms manage/nutrient/fert/rb209/index.htm (pages 5-7) or;

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www.aglime.org.uk/technical05.htm. No RODWELL, J S ed. (1992). British Plant more than 7 tonnes/ha of ground limestone Communities 3: Grassland and Montane equivalent should be applied at one dressing communities. Cambridge University Press, to the surface of grassland. However, for Cambridge. applications towards the maximum rate recommendation, it may be advisable to split TALLOWIN, J.R.B. (1998). Use and effects of the dressing into two applications over 2 years. lime application on semi-natural grasslands in This would allow the soil microbial community Britain. Countryside Council for Wales Contract more scope for adjustment and prevent Science report No. 261. excessive smothering of the sward. However, it needs to be weighed against the additional Further information impact on biodiversity caused by the additional Natural England publications are available to disturbance and compaction resulting from two download from the Natural England website: applications compared to one. www.naturalengland.org.uk. In particular:

Subsequent applications should be informed • TIN035 - Soil sampling and analysis for habitat by repeat soil sampling and monitoring of the re-creation and restoration in agri-environment botanical composition of the sward. schemes. • TIN036 Soils and agri-environment schemes: • Historic practice: Many inputs may have interpretation of soil analysis. been added to even species-rich grassland, including waste products. The farmer or landowner may be aware of practices and For further information contact your local Natural there may be evidence from old marl pits, England office. Details of local offices can be limekilns or agricultural records. Although obtained from the Natural England Enquiry farmyard manure has an alkaline pH (typically Service on 0845 600 3078 or e-mail: 7.7 to 9.5) it will have little, if any, practical [email protected]. liming effect, especially at the rates allowed in agri-environment schemes. Authors Selected References This note was written by Graham Walsh, Steve Peel and Richard Jefferson. The note benefited CROFTS, A. & JEFFERSON, R.G. (1999). The from comments from Brian Chambers (ADAS), Lowland Grassland Management Handbook. Adam Kwolek and Audra Hurst (both Natural 2nd edition. English Nature/The Wildlife Trusts, England). Peterborough.

RODWELL, J S ed. (1991). British Plant Communities Volume 2: Mires and heaths. Cambridge: Cambridge University Press.

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