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.