Grass Biomethane for Agriculture and Energy

Grass Biomethane for Agriculture and Energy Nicholas E. Korres, T. Thamsiriroj, B.M. Smyth, A.S. Nizami, A. Singh, and Jerry D. Murphy Abstract Many factors enforce the intensification of grassland utilization which is associated with significant environmental impacts subjected to various legislative constraints. Nevertheless, the need for diversification in agricultural production and the sustainability in energy within the European Union have advanced the role of grassland as a renewable source of energy in grass biomethane production with various environmental and socio-economic benefits. Here it is underlined that the essential question whether the gaseous biofuel meets the EU sustainability criteria of 60% greenhouse gas emission savings by 2020 can be met since savings up to 89.4% under various scenarios can be achieved. Grass biomethane production is very promising compared to other liquid biofuels either when these are produced by indigenous or imported feedstocks. Grass biomethane, given the mature and well known technology in agronomy and anaerobic digestion sectors and the need for rural development and sustainable energy production, is an attractive solution that fulfils many legislative, agronomic and environmental requirements. Keywords Grass • Grass silage • Pasture management • Anaerobic digestion • Biofuels • Biomethane • Legislation • Life cycle assessment N.E. Korres ()  T. Thamsiriroj  B.M. Smyth  A.S. Nizami  J.D. Murphy () Department of Civil and Environmental Engineering, University College Cork, Lee Road, Cork, Ireland Environmental Research Institute, University College Cork, Lee Road, Cork, Ireland e-mail: nkorres@yahoo.co.uk; jerry.murphy@ucc.ie A. Singh Quantitative Sustainability Assessment, Department of Management Engineering, Technical University of Denmark, Lyngby, Denmark e-mail: apsinghenv@gmail.com E. Lichtfouse (ed.), Genetics, Biofuels and Local Farming Systems, Sustainable Agriculture Reviews 7, DOI 10.1007/978-94-007-1521-9 2, © Springer Science+Business Media B.V. 2011 5 6 N.E. Korres et al. 1 Introduction Many factors enforce the intensification of grassland utilization (Kemp and Michalk 2007), which is associated with significant environmental impacts (Del Prado et al. 2006) and subjected to various legislative constraints (Anonymous 1997; UNECE 1999; EC 2000). Nevertheless, the need for diversification and sustainability in both agricultural and energy sectors has advanced the role of grassland with various environmental (Tilman et al. 2006) and socio-economic benefits (Baier and Grass 2001). The potential for biomethane as a transport fuel from grass and grass silage has been shown to be very promising (Smyth et al. 2009; Korres et al. 2010). This can enhance the regional and rural development with the creation of a domestic industry and employment opportunities (Del Rio and Burguillo 2009) in which sustainability of eco-friendly biomass production and conversion technologies is warranted (Singh et al. 2010a). Thus the role of grassland can be expanded beyond its traditional utilization as a source of animal feed. Among the methods of using grassland biomass for producing energy, biogas production currently is the most common practice in Europe. Surveys of agricultural biogas plants in Germany and Austria show, that grass silage, the second most frequent biomass feedstock after maize silage, is used as a feedstock in around 50% of the biogas plants (Weiland 2006). The aim of supplying crop feedstock for biomethane production is to achieve the highest possible methane yields per unit area, which are dependent on the biomass yield and the feedstock-specific methane yield (Prochnow et al. 2009). The biomethane yield from various plants across Europe using mainly grass and maize silage along with manures as feedstocks ranges from 10 to 1; 150 m3 h1 (Dena et al. 2009). The process of anaerobic digestion produces biogas, which typically consists of around 55% methane, 45% carbon dioxide and a number of minor constituents. Biomethane is biogas that has been upgraded to the same standard as natural gas and typically has a methane content of about 97% (Korres et al. 2010). In this chapter certain aspects of grass biomethane regarding its production along with certain agronomic and technological issues are covered. Why grass biomethane regarding current EU legislative issues merits consideration particularly under European agricultural and energy sectors? What is the energy balance and greenhouse emissions savings of grass biomethane in other words is grass biomethane an energy feasible and sustainable biofuel? What are the advantages of grass biomethane in comparison with other indigenous and imported feedstocks for the production of biofuels? What is the most appropriate technology for grass biomethane production? What are the agronomic/husbandry factors for pasture utilization for both purposes? Farmers, potential investors and policy makers through this chapter can shape a clear idea on the production of grass biomethane. 1.1 Setting the Boundaries – Grassland Classification Grassland holds an important role in global agriculture since occupies 69% of the global agricultural area or 26% of total land area (Reynolds 2005) and spans a Grass Biomethane for Agriculture and Energy 7 range of climatic conditions from arid to humid (Verchot et al. 2006). Grassland use is characterized by various modes and intensities. Grassland is predominantly used in animal husbandry, as a principal source of food for ruminants, as well as for its ecological functions, such as protection of soil from erosion, ground water formation, habitat function and formation of diverse cultural landscapes (Prochnow et al. 2009). Amongst its various characteristics i.e. long persistency of high dry matter yield; intercropping potential with legumes and subsequent reduction in fertilizer application rates; low lignin content compared with other second-generation lignocellulosic materials for the production of biofuels; the lower rates of pesticide application; the disappearance of the “cereal and oilseed rape premium” of the former Common Agricultural Policy (CAP) system; the protection of grassland area in the present CAP cross-compliance system; and the unstable status of fossil energy and input prices, can increase the attractiveness of perennial grasses and legumes for biomethane production compared with first generation biofuels (Peeters 2009). Grassland is an important carbon sink (Tilman et al. 2006) and source of energy production (Murphy and Power 2009; Prochnow et al. 2009). Grasslands vary greatly in their degree and intensity of management from extensively managed rangelands and savannahs to intensively managed continuous pasture and hay land (Verchot et al. 2006). More specifically, in Europe there are various types of grasslands, ranging from almost desertic types in south-east Spain through steppic and mesic types to humid grasslands/meadows, which dominate in the north and north-west (Silva et al. 2008). European grassland based on pasture management has been classified as rough mountain hill grazing, permanent and rotational or temporary grassland (Brockman and Wilkins 2003). The former is uncultivated grassland found in large enclosures on hills or unenclosed uplands, moorlands, heaths and downlands. It is characterised by high biodiversity, low stocking rates and low dry matter production. Permanent grassland is that observed in fields of relatively small enclosures with higher stocking rates compared to rough grazing. The last type of grassland is found within an arable rotation characterised by low species abundance and richness, and high stocking rates and production. Lockhart and Wiseman (1988) distinguished two types of grassland, namely uncultivated and cultivated. The former consists of rough mountain and lowland heath grassland, whereas the latter includes permanent grassland (over 5 years old) and leys or temporary grassland (less than 5 years old). This, based on perennial ryegrass percentage, can be further distinguished as first (>30%), second (20–29%), third (<20%) grade and poor grassland. This type of grassland, according to Fossitt (2000), can be classified as improved grassland that is highly modified, intensively managed with low biodiversity. It is used for heavy grazing and/or silage production and includes regularly reseeded monoculture grasslands dominated by perennial ryegrass that is planted as part of an arable rotation. In this chapter the case of intensively cultivated grassland is considered in which grass can be used for both animal and biomethane production. Rough grazing grassland is excluded as a potential source for biomethane production due to low dry matter production and the acidic or peaty soil, which is difficult to cultivate (Brockman and Wilkins 2003). 8 N.E. Korres et al. 1.2 Agricultural Transition Era and Sustainable Development In recent years agriculture has undergone many changes with a significant food production increase, structural upheavals in many agricultural systems and concurrent restructuring of many rural communities (Wilson 2007). Many authors have argued that conventional agriculture or “productivism agricultural era” and its exclusive purpose, the production of food and fibre is at its terminal stage and that a new agricultural regime or “post-productivism agricultural era” with a wider purpose, including the “production” of nature and environmental management (Braun and Castree 1998; Marsden 1999) is emerging. Holmes (2006) reported that the transition of agricultural structure from “productivism” to “post-productivism era” will be achieved through its multifunctional role. Multifunctionality is interpreted in various ways by different people (Wilson 2007). Marsden and Sonnino (2008), described three types of multifunctional agriculture: The first type is restricted to pluriactivity within an agro-industrial model. The second type rises from a ‘post-productivist’ paradigm as discussed above. Finally, the third type, as a part of a sustainable rural development paradigm in which agricultural production is seen to be intimately combined with the socioeconomic health of rural areas, is recognised as an economic sector that must be integrated into the wider economy. The authors of this chapter cannot find any reason why one type shouldn’t be interrelated with another under the broader frame of an agro-ecosystem as an inseparable part of rural areas. Hence, the multifunctional agricultural character is concerned with agricultural diversification, where agriculture is integrated into areas other than traditional farming. In other words, agricultural production can be integrated within an agro-industrial model under the wider concept of pluriactivity. This will result in generation of advantages towards increase non-farm income from the emerging opportunities such as grass biomethane production. Furthermore, sustainable development, in other words the fulfilment through the optimal use of any available source within a production system, in the agricultural sector, that facilitates continuing benefits from land, water and biological resources to satisfy the human populations’ current needs while preserving and bettering the base of all natural resources for the future generations (Siardos 1994; Boyazoglu 1998) can be promoted through grass biomethane production. The need for integration of potential sources implies that any evaluation of agroecosystem sustainability must consider the dynamics of multiple components (Belcher et al. 2004). The challenge of agricultural development is to counteract the dependence on nonrenewable resources and environmental services whose seemingly unrestrained availability is made apparent by inadequate market forces and economic policies that hinder sustainability (Pezzey 1992). Grass Biomethane for Agriculture and Energy 9 2 Biofuels Use in Europe Increasing fossil fuel prices, energy security concerns and environmental consciousness, especially related to climate change stabilization, have motivated countries to explore alternative energy sources, such as biofuels, fuels derived from biomass, (Zarrilli and Burnett 2008). The use of biofuels as a means of “greening” the transport sector, which is a sectors with high pollution impact (Reay and Grace 2007), by using renewable energy resources is strongly supported by European policy (EEA 2004). EU Directive 2009/28/EC on renewable energy sets a mandatory target for each European Union (EU) Member State for 10% of transport energy to be met with renewable sources in 2020 (EC 2009). The main biofuels are biodiesel and bioethanol (USDA 2006). The EU is by far the world’s biggest producer of biodiesel, with Germany, France and Italy producing over half of the EU’s biodiesel (Demirbas 2009) (Table 1). The main feedstock of biodiesel production from the biggest EU producing countries is rapeseed whereas in USA, Brazil and Argentina, the biggest biodiesel producers outside EU, is soybean (Table 1). The use of biogas as a transport fuel, via anaerobic digestion of various feedstocks, after upgrading to biomethane, has recently started to gain attention in many European countries, such as in Sweden, Austria, France and Switzerland (Mathiasson 2008). Additionally, biogas production from biomass has been strongly promoted in many developing regions including Asia, Latin America and some regions of West Africa (Eisentraut 2010). Agricultural and environmental related legislative issues along with sustainability criteria concerning renewables, as discussed in the following sections, prove that grass biomethane is an alternative that satisfies European conditions and merits considerable attention. Table 1 Biofuel production worldwide (Smyth et al. 2010) Country Ethanol Principal (billion l) % Total feedstock Country USA Brazil China 34 27 1:9 50:7 40 2:8 Germany USA France 2:2 2 1:6 18:3 16:7 13:3 Rapeseed Soybean Rapeseed France 1:2 1:8 Brazil 1:2 10 Soybean Canada 0:9 1:3 Argentina 1:2 10 Soybean 65 2:8 97 4:2 Total top 5 Total EU Total world 67 100 Corn Sugarcane Corn, wheat Sugar beet, cereals Corn, wheat Biodiesel (billion l) Total top 5 8:2 Sugar beet, Total EU 8 wheat – Total world 12 Principal % Total feedstock 68:3 66:7 100 Rapeseed, sunflower – 10 N.E. Korres et al. 2.1 Why Grass Biomethane – Policy Drivers The renewable energy sector is amongst the fastest growing in the EU, with an annual turnover of A C15 billion, more than 200,000 employees and more than 4.5 million green-power consumers (EC 2006). Within the renewable energy sector, substantial economic and environmental results are achieved through a combination of targets, fiscal incentives and market mechanisms (EC 2006). The European Commission introduced the Renewable Directive (EC 2009) on the promotion of the use of energy from renewable sources, which includes, among many other provisions, sustainability criteria for biofuels and other bioliquids. Amongst the sustainability criteria are requirements for lower limits of greenhouse gas emissions from biofuels compared to the fossil fuel replaced, restrictions on land use change and environmental requirements for agriculture (Zarrilli and Burnett 2008). Additionally, in the agricultural sector, policy enforces environmentally friendly production systems which will affect agricultural status quo and production chains. 2.1.1 Agricultural Legislation Agriculture releases significant amounts of greenhouse gases such as CO2 ; CH4 , and N2 O, along with ammonia (NH3 ) emissions to the atmosphere (Paustian et al. 2004). The main mechanisms of gaseous emissions from agriculture comprise microbial decay or burning of plant litter and soil organic matter (Janzen 2004), decomposition of organic materials in oxygen-deprived conditions, notably from fermentative digestion by ruminant livestock and stored manures (Mosier et al. 1998), and the microbial transformation of nitrogen in soils and manures which is often enhanced where available nitrogen exceeds plant requirements, especially under wet conditions (Oenema et al. 2005). EU crop production patterns have traditionally been heavily influenced by the Common Agricultural Policy with its high support prices, planting restrictions, intervention buying, stock management and rigid border controls (Schnepf 2006). The adverse effects of agricultural intensification on the environment under previous EU agricultural support mechanisms have directed attention towards environmental issues, and have influenced the development of CAP and the promotion of sustainable agriculture (Clergue et al. 2005). As such, the 2003 Mid Review of the CAP directed that agricultural support payments be conditional upon compliance with environmental standards and “Good Farming Practice”. Community initiatives, amongst others, aim to limit agricultural pollution and to promote the development of the production and use of biofuels (Osterburg et al. 2005). With the same objectives, CAP reforms also established a special aid for energy crops grown on non-set-aside land. Energy crops, these grown for the production of biofuels, including biogas, or for use as biomass in the production of electric and thermal energy, are eligible for a premium of A C45 per hectare. Attaching conditions to the receipt of agricultural subsidies is a policy tool known as cross compliance and aims to improve standards in modern farming practices Grass Biomethane for Agriculture and Energy 11 (Farmer and Swales 2004). The 2003 reform of the EU’s Common Agricultural Policy made cross compliance mandatory for all Member States (EC 2003 and EC 2004). The cross compliance standards consist of two strands, the Good Agricultural and Environmental Condition, which sets out minimum requirements for soil conditions and land maintenance, and the Statutory Management Requirements, which relate to animal welfare, and environmental, public, and plant health (Mussner et al. 2006). Land suitability is often a key for evaluating the potential of biofuels (Ragaglini et al. 2010). Cross compliance (EC 2003) requires Member States to ensure that land declared as under permanent pasture in 2003 is maintained under permanent pasture. Additionally, Article 3 of Regulation 796/2004 states that Member States should ensure that the ratio of land under permanent pasture in relation to the total agricultural area of the Member State does not decrease by 10% or more of the 2003 reference level (EC 2004). EU Member states are therefore under obligation not to allow any significant reduction in the total area of permanent pasture. Other measures to encourage environmentally friendly agricultural practices, such as the Rural Environment Schemes (REPS), were introduced under Council regulation EEC/2078/1992 (EC 1992). These, according to the report prepared by Directorate General for Agriculture and Rural Development, have to be applied beyond usual Good Farming Practice, which is defined as the level of environmental care that a reasonable farmer is expected to practice (EC 2005a). Under the Sixth Environment Action Programme (EC 2001), various Directives, such as the Water Framework Directive (EC 2000) and the Nitrates Directive (EEC 1991), introduced a series of measures that aim to reduce greenhouse gas emissions at farm level via lower stocking rates and could free up grassland for other purposes. Proposals for protecting waters through reducing nutrient losses include reducing stocking rates, harvesting grasslands for silage/hay instead of cattle grazing, and reducing the length of the grazing season. The adoption of batch storage for slurry has also been suggested (Chardon and Schoumans 2008), which could make it amenable to anaerobic digestion and biofuel production. Biofuels are also influenced by the Biodiversity Action Plan (Caslin 2009) which aims to improve or maintain biodiversity and prevent further biodiversity loss due to agricultural activities. Priorities include restricting intensive farming and establishing sustainable resource management. Finally, Regulation EC/1698/2005 (EC 2005b) interlinks sustainable development and the diversification of the rural economy through, among other measures, the introduction of new technologies and innovation in non-food sectors such as renewable energy. This is of great importance, considering the efforts and policies that have been put in action to dismantle protectionist agricultural subsidies in order to combat rural poverty in Southern Europe, especially the livelihoods of marginal farmers, and policies to protect the environmental integrity of the countryside in the developed Northern European countries (Potter and Tilzey 2007). Environmental legislative issues, changes in market dynamics imposed by the decoupling of the majority of direct aid (EC 2003), discussions about trade liberalization, e.g. Doha Round trade negotiations in the World Trade Organization, will most probably influence the dynamics of agri-food supply chains (McCorriston 12 N.E. Korres et al. and Sheldon 2007). In addition, the need for a multifunctional agriculture for optimal use of any available resources and the achievement of maximum potential (Boyazoglu 1998) necessitate the rapprochement of grassland utilization. In the face of climate change and growing demands for agricultural productivity, future pressures on grassland ecosystems will intensify (Watkinson and Ormerod 2001). Moreover, most grassland in the EU is devoted to meat (cattle and sheep) production where profitability is low and farmers often rely on EU single farm payments to survive, thus grassland farming can face considerable challenges in implementing new environmental measures without financial supports (Boyle 2008). As suggested in this chapter, diversification of grassland, except for livestock production, could include its utilization as a source of biomethane production for transport purposes. Major reform of CAP is expected in 2013 and this may have implications for energy crops and biofuels. 2.1.2 Energy Legislation – Biofuels as a Means for Bypassing Fossilization Various policy goals, which focus on boosting the decarbonisation of transport fuels, diversifying fuel supply sources and developing long-term replacements for fossil oil, have motivated the European Union to promote the production and use of biofuels (Schnepf 2006). With increasing use of biomass for energy, questions arise about the energy efficiency of the renewable energy source and its validity as a means of reducing greenhouse gas emissions and dependence on fossil fuels (Haas et al. 2001; Gerin et al. 2008; Cherubini et al. 2009). The policies effectively impose constraints on many conventional energy crop biofuels and reinforce the merits of using biomethane as a transport fuel. Renewable Directive 2009/28/EC (EC 2009) states that biofuels must meet the following criteria in order to be considered sustainable and to be counted for the purposes of meeting EU biofuels targets: • Greenhouse gas emission savings from the use of biofuels and bioliquids shall be at least 35%, and by 2017 savings of at least 50% compared with fossil fuel replaced must be achieved. From 1 January 2018, greenhouse gas emissions savings should be at least 60% for biofuels and bioliquids produced in installations in which production started on or after 1 January 2017. • Biofuels from peatlands and land with high biodiversity value or high carbon stock may not be used (e.g. permanent grassland). • Impact of biofuel policy on social sustainability, food prices and other development issues is to be assessed, in particular for people living in developing countries. 2.2 Life Cycle Assessment (LCA) To understand and manage the energy efficiency of renewable energy sources and related greenhouse gas emissions, the whole system should be considered Grass Biomethane for Agriculture and Energy Stage Energy Crop production Production of fertilizer, herbicide, seed and lime Diesel 13 Process Seeding, cultivation, harvesting Grass Transport Storage Biogas production Product Silage Electricity Macerating Heat and electricity Anaerobic digestion Biogas Digestate Cleaning and upgrading Biomethane Biomethane production Electricity Compression Compressed biomethane Distribution and pumping Digestate use Diesel Transport Fertilizer Fig. 1 Flow chart of grass biomethane production system (Smyth et al. 2009) (Phetteplace et al. 2001). The production of energy crops for anaerobic digestion should result in a net production of renewable energy and a net reduction of greenhouse gas emissions (Gerin et al. 2008). The energy balance and related greenhouse gas emissions of the grass silage biomethane system therefore need to be quantified (Fig. 1). In the figure above (Fig. 1) the whole cycle of grass biomethane production is represented in a clear and distinguishable way. Each production stage and 14 N.E. Korres et al. energy related issues for the processes within each stage and the final product are highlighted. Based on this flow chart estimations of energy input and outputs and related greenhouse gas emissions can be made. There is a broad agreement in the scientific community that LCA is one of the best methodologies for the evaluation of the environmental burdens associated with biofuel production (Consoli et al. 1993) and the resources utilised during the life of the product. Therefore, LCA offers a holistic and systematic view of a product through its whole life cycle (Payraudeau et al. 2007). According to the International Organization for Standardization (ISO) 14000 series (ISO 14041-43) the technical framework for the LCA methodology consists of four phases, namely goal definition, scope definition and functional unit determination; inventory analysis; impact assessment; and interpretation (ISO 2006). The systematic nature of LCA requires the definition of goal, scope and functional unit as the first step of the study. The goal of an LCA study shall unambiguously state the intended application to the intended audience of the study. The scope should be sufficiently well defined to ensure its compatibility with the goal. The functional unit sets the scale for comparison of two or more products, provides a reference to which the input and output data are normalised and harmonises the establishment of the inventory (Jensen et al. 1997). In the inventory phase information is gathered about input and emissions for all processes in the studied system. The impact assessment phase follows the inventory phase and performs an assessment of all relevant environmental impacts on human health, environment and resources depletion, which are associated with the input and emissions mapped in the inventory phase (SAIC 2006). In the case of biofuels, there is requirement to express greenhouse gas emission savings in terms of Global Warming Potential (GWP) of carbon dioxide, nitrous oxide and methane emissions in relation to the fossil fuels under replacement. Guidelines for the estimation of energy and related greenhouse gas emissions throughout the production cycle of biofuels are provided in the Renewable Directive (EC 2009). 2.2.1 Grass Biomethane – Energy Efficiency and Criteria for Sustainability For the determination of the energy efficiency of a renewable energy source, all energy inputs and outputs through the whole production cycle of the product need to be taken into consideration (Salter and Banks 2009). Oilseed rape, for example, covers about 80% of the set-aside land devoted to non-food energy crops for biodiesel production in the EU (Table 1), (Bauen 2005). Smyth et al. (2009) reported that the gross and net energy of rapeseed biodiesel and wheat bioethanol are much less than those for grass biomethane, palm oil biodiesel and sugar cane bioethanol (palm oil and sugar cane are non-indigenous European crops) (Fig. 2). Importing feedstock from tropical countries, such as Malaysia or Indonesia in the case of biodiesel, may not be an option. The increasing demand for palm oil production from these countries, which account for about 80% (FAOSTAT, undated) of global production, is contributing to deforestation at an annual rate of Grass Biomethane for Agriculture and Energy 15 Crop energy (GJ/ha/yr) 150 135 Gross energy 120 120 122 Net energy 100 74 66 69 46 50 25 4 0 Rapeseed biodiesel Wheat ethanol Palm oil biodiesel Sugarcane ethanol Grass biomethane Fig. 2 Comparison of gross and net energy per hectare of selected energy crop biofuel systems (Smyth et al. 2009). Note: Net energy is defined by gross energy yield (biomass dry matter yield  specific methane yield) minus inputs (direct and indirect energy) for cultivation of feedstock and biomethane production 1.5% (Fargione et al. 2008). With land use change, there are no net GHG savings (Reinhard and Zah 2009). Consequently, palm oil biodiesel, for example, is not considered a biofuel according to Directive 2009/28/EC, which requires greenhouse gas savings of 60% by 2020. Additionally, increases in palm oil production cause habitat loss and drainage of peatlands (Wakker 2004; Greenpeace 2007), whereas land tenure conflict, particularly in Indonesia (Colchester et al. 2006), raise further concerns regarding the sustainable supply of biodiesel. Although, in theory, palm oil for biodiesel could be taken from existing supplies and new capacity achieved by development on previously cultivated land and/or via yield improvements, in practice, any incentivisation of palm oil-derived biodiesel for the EU market is likely to provide an indirect stimulus for land clearance (Thornley et al. 2009). Similar concerns regarding, amongst others, deforestation, decarbonisation and degradation of soils have arisen for sugar cane ethanol (Goldemberg et al. 2008). In comparison, grass biomethane, an indigenous European crop that performs much better than rapeseed biodiesel and wheat ethanol, and that has a similar energy balance to tropical based biofuels, seems an attractive alternative for the EU (Fig. 2). Tilman et al. (2006) stated that biofuels derived from low-input native grassland perennials can provide more usable energy, greater greenhouse gas reductions and less agrochemical pollution per hectare than arable crops, such as corn grain ethanol or soybean biodiesel. Finally, to promote non-food feedstock the Renewable Directive (EC 2009) considers the contribution made by biofuels produced from wastes, residues and lignocellulosic material to be twice that made by other biofuels for the purposes of demonstrating compliance with the 10% target. Many authors considered grass as a lignocellulosic feedstock for biomethane production (Peeters 2009; Eisentraut 2010; Singh et al. 2010b). 16 N.E. Korres et al. Table 2 Summary of greenhouse gas emissions from the production of grass biomethane (Korres et al. 2010) Total Total Indirectb Directa .g CO2 e MJ1 .g CO2 e MJ1 (g CO2 e MJ1 (kg CO2 e ha1 energy replaced) energy replaced) energy replaced) year1 / Parameters Agriculture Crop production 2:67 6:34 9:01 893 Herbicide 0:05 – 0:05 5.44 volatilization Lime dissolution 5:55 – 5:55 550 N2 O emissions 5:18 0:11 5:29 525 Total agricultural 13:45 6:45 19:90 1,973 emissions Transportationc – 0:89 0:89 88 Biomethane production process Anaerobic digestion plant Upgrading Total processing emissions Biogas losses Total 18:25 7:24 25:49 2,524 18:25 12:64 19:88 12:64 38:13 1,251 3,775 10:82 45:75 27:11 10:82 69:74 1,071 6,904 The analysis was based on a grass biomethane system using 7; 500 t year1 of grass silage (137.5 ha), with a net biomethane yield of 99 GJha1 year1 a Direct greenhouse gas emissions are defined as the emissions from agronomic operations, e.g. ploughing, harrowing, rolling, application of agrochemicals, harvesting etc., and from energy consumed in anaerobic digestion plant e.g. heating of digesters b Indirect greenhouse gas emissions are defined as the emissions from the production of pasture inputs, e.g. fertilizers, herbicides etc., and from the maceration, mixing and water pumping activities in anaerobic digestion plant c Transportation includes emissions from lime and silage transportation to the field 2.2.2 Grass Biomethane – Greenhouse Gas Emissions A greenhouse gas analysis conducted by Korres et al. (2010) determined the greenhouse gas emissions from grass biomethane, produced by anaerobic digestion and used as a transport fuel in place of diesel, as 69:74 gCO2e MJ1 energy replaced or 6; 904 kgCO2e ha1 year1 (Table 2). The largest contributors were emissions from crop production and from the anaerobic digestion process. Indirect emissions from the production of nitrogen and potassium fertilizers were the major contributors to agricultural emissions and, in the biomethane production process, the largest source of emissions was from digester heating. When compared with emissions from fossil diesel grass biomethane production under the base case scenario, which includes the production of grass silage and transportation of feedstock to anaerobic digestion plant and digestate back to field, greenhouse gas emissions savings were estimated to 21.5% (Fig. 3). Grass Biomethane for Agriculture and Energy 17 Greenhouse gas savings of energy crops Wheat ethanol 32 45 Rapeseed biodiesel 58 Sunflower biodiesel Biogas from Municipal Solid Wastes 80 Grass biomethane-Base case scenario 21.5 Grass biomethane-Wind energy for electricity 42 Grass biomethane-Vehicle effiiciency 54.2 68.9 Grass biomethane-Wood chips for heat demand Grass biomethane-0.6 t/ha/yr C sequestration 89.4 0 10 20 30 40 50 60 70 80 90 100 % CO2 savings Fig. 3 Cumulative greenhouse gas emissions savings of grass biomethane over fossil diesel (Korres et al. 2010) (Note: Default values for wheat ethanol, rapeseed biodiesel, sunflower biodiesel and biogas from municipal wastes were adopted from 2009/28/EC Renewable directive (EC 2009)) Nevertheless, cumulative greenhouse gas emissions savings under various scenarios, i.e. incorporating electricity from wind, improved vehicle efficiency, energy from wood chips for anaerobic digestion heat demands and carbon sequestration of 0:6 t C ha1 year1 (a minimum value for most European permanent crops and grasslands according to Freibauer et al. (2004) and Jones and Donnelly (2004)), resulted in greenhouse gas emissions savings of up to 89.4%. This easily meets the 60% greenhouse gas savings required in 2018 by EU Directive 2009/28/EC. In contrast, liquid biofuels produced by indigenous European feedstock, such as wheat ethanol, rapeseed biodiesel and sunflower biodiesel, do not meet the requirement for 60% greenhouse gas savings (Fig. 3). Oilseed rape is a crop with high nitrogen and pesticide demand, which heavily influences the greenhouse gas balance for biodiesel production (Thornley et al. 2009). Additionally, the overall carbon balance for rapeseed biodiesel production using existing technology is poor and any preference for better performing feedstocks in terms of carbon reduction potential will constrain the contribution of rape seed to bioenergy targets (Thornley et al. 2009). Production of wheat bioethanol is accompanied by low greenhouse gas savings, mainly due to nitrous oxide emissions during cultivation, the fuel used in the ethanol production plant, the fate of by-products and the low biofuel yields of only 3,220 L/ha (Smith et al. 2005; Borjesson 2009). Studies on sunflower biodiesel have shown that areas, such as in the case of Tuscany in Italy, classified as suitable for biodiesel production could only provide efficient conversion rates to meet the current requirement for 35% greenhouse gas savings on 30% of arable land (Ragaglini et al. 2010). Other studies on sunflower biodiesel, although reporting promising environmental benefits, haven’t highlighted in a clear way its potential as a sustainable renewable energy source (Sanz-Requena et al. 2010; Tsoutsos et al. 2010). Manure, on the other hand, is an easily available resource on farms and biogas from manure results in high greenhouse gas savings. However, the limited production rate, low biogas yields due to the high water content and high investment costs make the economical feasibility of manure biogas difficult (Gerin et al. 2008). Nevertheless, co-digestion of various substrates, including manure, often results in 18 N.E. Korres et al. a higher methane yield (Jagadabhi et al. 2008), due to synergistic effects of the co-substrates, which provide the missing nutrients for methanogenic bacteria and balance the substrate composition (Mata-Alvarez et al. 2000; Umetsu et al. 2006; Lehtomaki et al. 2007). 2.2.3 Digestate – A Hidden Anaerobic Digestion Residue with Added Value Grass biomethane production results in the generation of “residues” known as digestate. It can replace conventional fertilizer providing further environmental benefits to the biofuel process chain (Cherubini et al. 2009), because the nutrient cycle is almost closed (Seppala et al. 2009). Nitrogen use efficiency within intensive farming systems has been shown to be very low. For example, on intensive dairy farms in the Netherlands only 16% of the N inputs (feed, fertilizer etc.) are captured as outputs (meat, milk etc.) (Aarts et al. 2000). Improved N-use efficiency within farm systems is achieved by maximising utilisation of the N circulating within the system, e.g. utilising the N in organic manures, the N supplied by soil, the N supplied by biological fixation through clover and the use of digestate as fertilizer. This results in increased production efficiency and profitability due to lower costs of production while at the same time reduces losses to the environment. Gerin et al. (2008) examined the production of maize and grass silage as a feedstock for biogas and the use of digestate as substitute for mineral fertilizer for both crops. Furthermore, Matsunaka et al. (2006) reported positive effects on dry matter increases of Phleum pratense (timothy grass) with the application of digestate from various organic materials. They also reported that digestate positively affects N uptake by grass, particularly when applied in spring. Additionally, Salter and Banks (2009) stated that digestate can be separated into liquid and fibre components. A proportion of liquid can be recirculated back to the anaerobic digestion process to increase its efficiency, and the remaining quantity can be processed into liquid biofertilizer and/or can be used as a multi-purpose press juice (Berglund and Borjesson 2006). The solid digestate can be processed into fibres, which can either be applied to land as a soil conditioner or processed into high value insulation boards (Grass 2004; Salter and Banks 2009). Under this scenario, a new concept of green biorefinery (Fig. 4) can be developed (Kamm et al. 1998; Narodoslawsky 1999; Kamm and Kamm 2004), which will further enhance the role of grassland as a major agricultural, industrial and economic resource. According to Grass (2004), a green biorefinery will also increase greenhouse gas emissions savings. 3 Anaerobic Digestion – Grass and Grass Silage as a Feedstock Anaerobic digestion is the conversion of organic matter to a biogas under anaerobic conditions. Four successive biological processes are involved in the anaerobic degradation of organic matter: hydrolysis, acidogenesis, acetogenesis and Grass Biomethane for Agriculture and Energy 19 Recirculation back to crop production process Biofertilizer Liquid digestate Press Juice Digestate Solid digestate Carbohydrates Proteins Enzymes Chemicals Dyes Value added products Animal fodder Solid fuel Syngas Soil conditioner Fibre i.e. insulation boards, textile Chemicals Hydrocarbons Fig. 4 Value-added products of digestate (Based on Kamm and Kamm 2004; Salter and Banks 2009) methanogenesis. Complex polymers are converted into monomers by extra-cellular enzymes during hydrolysis while these monomers are transformed into volatile fatty acids (acetic, propionic and butyric acids) and hydrogen (H2 ) during acidogenesis. Acetate, carbon dioxide .CO2 / and H2 are produced from volatile fatty acids during acetogenesis and finally converted into methane .CH4 / during methanogenesis (Bernet and Beline 2009). The biogas produced during anaerobic digestion, mainly composed of CH4 (55–80%) and CO2 (20–45%) can be used as an energy source, generally as heat and/or electricity, or as a biofuel (Murphy and Power 2009). This process has been widely applied for years to the treatment of organic waste, including manure (Chynoweth et al. 1999; Burton and Turner 2003) and other farm waste, wastewater, industrial organic waste, municipal solid waste, agricultural residues, crops and crop residues (Vandevivere 1999). Nevertheless, as stated by Tabajdi (2008), both the production of biogas and the number of biogas installations are unevenly distributed in Europe, demonstrating untapped potential. Grass and grass silage have recently received considerable attention in the EU (Braun and Steffen 1997; Mahnert et al. 2005), as the crop can be utilised as a beneficial feedstock for the production of biomethane due to high yield, its perennial nature (a low energy input crop), the high volatile content and the associated relatively high biomethane yield (Hall 1997; Murphy and Power 2009; Seppala et al. 2009). Many factors are involved in biomethane production chain namely agricultural and operational procedures along with pre- and post-treatments of the raw feedstock and digestate respectively (Fig. 5). Relevant factors to the scope of this chapter are the agronomic/husbandry factors which determine the quality of grass and grass silage for higher biomethane production. The reader can be advised in more detail about operational measures, pre- and post treatments in Nizami et al. (2009). 20 N.E. Korres et al. ticle Par ze si Retention time Re circ ula pH ng ixi ion lat su rd In boa Agricultural procedures ten rve Ha ime t r ze tili Fe r Grass e than Biome Po st Cotion diges Ino c nu ulum ad trien / dit t ion Output Post-treatment Physical Chemical Biological Thermal Ensiling e Anaerobic Digester tur Input Pre-treatment est Harv cy en u q e fr ra e mp tia typ l gra ss e Operational measures Te M tion P t r o e rich in juice Fig. 5 Circular diagram of the main factors affecting biomethane yield of an anaerobic digester (Nizami et al. 2009) 3.1 Anaerobic Digester Designs Anaerobic digester design and configuration are important components of anaerobic digestion technology, as they promote the efficient conversion of organics to gaseous products (Demirbas and Ozturk 2005). A range of digester types and configurations exists based on various process parameters. The parameters that classify anaerobic digesters are the moisture content of the feedstock (wet digestion vs. dry); the number of phases/stages of digestion activity (single or two/multi-stage); operating temperature (thermophillic or mesophilic); method of feeding the substrate (batch or continuous) and retention time (Vandevivere et al. 2003; Karagiannidis and Perkoulidis 2009; Nizami and Murphy 2010), (Fig. 6). Various researchers have reviewed and compared different digesters suitable for anaerobic digestion of solid wastes (De Baere and Mattheeuws 2008; Vandevivere Grass Biomethane for Agriculture and Energy Biogas Biogas b Biogas Recycle Mixer Effluent Effluent Substrate Substrate One stage;wet/continuous/ Two stage;wet/Continuous/ batch/dry/CSTR batch/CSTR Effluent Mixer DRANCO Kompogas Biogas Biogas Effluent Substrate Substrate c Biogas Biogas Recycle a 21 Effluent Substrate Substrate Biogas recirculation Percolation liquid storage tank Pump Valorga Single phase wet digesters d Biogas Biogas Biogas Single phase dry Continuous digesters Biogas Biogas e Single phase dry batch digesters Biogas Leach beds Substrate UASB New Mature UASB Old Two-stage /Sequential-batch Hybrid batch-UASB Two-phase dry batch digesters Leachate tank Two phase sequencing fed leach bed digesters coupled with UASB Fig. 6 Various types of anaerobic digesters (a) single phase wet digesters (b) single phase dry continuous digesters (c) single phase dry batch digester (d) two-phase dry batch digesters (e) two phase sequencing fed leach bed digesters coupled with UASB (Vandevivere et al. 2003; Nizami and Murphy 2010). Note: In single phase digesters, all phases of anaerobic digestion (hydrolysis, acidogenesis, acetogenesis and methanogenesis) occur within the same compartment in the digester. In two phase digesters, hydrolysis, acidogenesis and acetogenesis are separated from methanogenesis. In batch digesters, the feedstock is inserted once into the digester for a certain period of time to complete the digestion activity. In continuous digesters, the feedstock is constantly or regularly fed, either mechanically or by force of the new feed. In dry digesters, high solid feedstock with dry matter ranging from 20 to 50% is used as substrate. Wet digesters operate for substrates with total solids content less than 13%. CSTR Continuously Stirred Tank Reactor, UASB Upflow Anaerobic Sludge Blanket et al. 2003). As Murphy and Power (2009) reported, digester design is based on the nature of the feedstock regarding its volatile solid content and is an important factor for anaerobic digestion efficiency. Digesters, for example, optimized for the organic fraction of municipal solid wastes (OFMSW) may not be ideal for grass silage because the volatile solids content of grass silage is significantly higher than that of OFMSW, i.e. up to 92% compared to values as low as 60%. Thus the digestate from grass may be quite liquid in nature (solids content of less than 5%) as opposed to digestate from OFMSW which may have a solids content of over 20%. This will lead to significant effects on materials handling. For example, vertical garage door batch digesters may be suitable for OFMSW, but not for grass. Two-phase digester configuration supports high growth rates of hydrolytic and methanogenic bacteria (Gunaseelan and Nallathambi 1997; Verrier et al. 1987; Mata-Alvarez 1987); hence this design/configuration is most appropriate for high solid feedstocks, such as grass silage. Furthermore, work conducted by Lehtomaki (2006) and Yu (2002) suggests that incorporation of a high rate reactor, such as a Upflow Anaerobic Sludge Blanket, with a Continuously Stirred Tank 22 N.E. Korres et al. Reactor is an efficient digester configuration for grass and grass silage. According to Nizami and Murphy (2010), wet continuous, dry batch and dry continuous systems, such as sequencing batch leach-beds coupled with a Upflow Anaerobic Sludge Blanket offer greater potential for grass biomethane production. 4 Pasture Management for Both Animal and Biomethane Production To resolve many varying dilemmas in the agricultural sector, and to attain what appears to be an increasingly difficult balance between sustainable grassland production and rural socio-economic status, there is a need both to raise the profile of grassland issues and to improve our understanding of applied grassland utilization under the wider frame of agro-industrial development. The authors of this chapter do not ignore the fact that energy security is a significant geopolitical concern for the EU but, equally, and perhaps of greater importance, is the issue of food security. It is therefore necessary to consider the possible impacts of biofuels, and more specifically grass biomethane, on food production and food prices before the examination on the suitability of main pasture practices for both systems. 4.1 Food versus Biofuels In many developing countries, increased demand for food products has resulted in price pressures in markets. This pressure can be either direct, through growing demand and changes in consumption patterns as incomes rise, or indirect, as alternative uses of food crops, such as for biofuels, have led to higher domestic prices (OECD 2008a,b). There is no consensus on how large the impact of biofuels production is on food price increases. According to a study published by the World Bank, between 70 and 75% of the increase in the price of food commodities from January 2002 to June 2008 is attributed to biofuels and the related consequences of low grain stocks, large land use shifts, speculative activity and export bans (Mitchell 2008). A US Council of Economic Advisors study found that the contribution of biofuels to the price increase of agricultural commodities was 3% (CEA 2008) whereas a report from the Organisation for Economic Co-operation and Development (OECD) concludes that biofuels are responsible for 15% of the food price increases (OECD 2008a,b). Nevertheless, other factors can influence food price increases, including poor harvests due to extreme weather events; increased demand for meat and milk products, pushing up the demand for animal fodder; high energy prices raising the price of producing, processing and transporting food (Glauber 2008); and international and national agricultural policies. It is worth noting that since biofuels have dampened the increase in oil prices, they have limited Grass Biomethane for Agriculture and Energy 23 one of the factors leading to an increase in food prices. Additionally, hyper-food inflation is unlikely because, amongst other reasons which are beyond the scope of this chapter, the globalization of the food economy and the greater diversification of crop and food production will act as a barrier to food price inflation (Alexander and Hurt 2007). Ruminant livestock farming, the dominant grass-based farming system, is paramount to the development of depressed areas where grassland occupies a significant proportion of the agricultural area (Veysset et al. 2010). Recent reform of the CAP has removed the link between financial support and the obligation to retain specific animal numbers, and will probably enhance the declining trend in livestock populations (Smyth et al. 2010). Additionally, animal breeding and structural adaptations in agriculture (Rosch et al. 2009), increased cost of land, feed and energy, alongside restricted government support, will most probably result in reductions in livestock population (Flach 2009). According to Food and Agricultural Organization (FAO 2006), the numbers of cattle and sheep in the EU-25 declined by 10.3% and 11.4% respectively between 1990 and 2003. Also, the area of grasslands in the EU declined by 12.8% from 1990 to 2003 and only few Member States managed to prevent this trend (FAO 2006). Rosch et al. (2009) reported that in some regions of Germany almost one-quarter of the grassland is not used in animal husbandry. Additionally, more traditional farmland areas, where socio-economic conditions for extensive agriculture are generally unfavourable, tend to be abandoned, particularly in central and Eastern Europe, where political and economic changes have negatively affected farming conditions (Silva et al. 2008). For example, a survey of Estonia in 2000 found that some 56% of the permanent grassland was abandoned (Silva et al. 2008). Against this background, and along with the increased demand of biomass feedstock for energy purposes and the political and financial support for renewable energy, “surplus” grassland biomass could be used as an additional energy resource (Rosch et al. 2009). This will prevent abandonment of grassland and will enhance EU policy for sustainable energy and agricultural development. 4.2 Evaluation of Grass for Both Animal and Biomethane Production Grassland use is characterized by various modes and intensities but its role as a principal source of food for ruminants dominates. Grassland husbandry has evolved as modern scientific approaches to farming have been developed. Agronomists and progressive farmers require the cultivation of highly productive grass species for highly productive pastures (Connolly 2001), which under appropriate pasture management allows full utilisation of the grassland (Walker 1995). Full utilisation of grass and grass silage can be achieved by using the crop both for animal feed and as a feedstock for biomethane production. 24 N.E. Korres et al. Forage quality is a function of nutrient value, amount of forage intake (consumption of forage by the animal), digestibility (the fraction of the dry matter that remains in the body on passage through the gut tract and is positively related with the dry matter intake by the animals) and partitioning of metabolised products within animals that is usually determined by animal performance when forages are fed to livestock (Wheeler and Corbett 1989; Buxton 1996; Brown 1999). Particularly in ruminants, where rumen fermentation modifies the actual diet received by the animal, forage and fibre chemical, physical and nutritional nature hold an important role (Van Soest et al. 1991). Many indices have been used for quality evaluation of grass and grass silage, including the factors affecting digestibility and voluntary intake such as crude or true protein (Keady et al. 2000; Krizsan and Randby 2007), water soluble carbohydrates concentration (O’Kiely et al. 2002) (carbohydrates classified based on cold water solubility of non-structural carbohydrates, namely monosaccharides, oligosaccharides and some polysaccharides so as to distinguish them from the starches) and fibre content, including neutral and acid detergent fibres (NDF and ADF respectively) (De Boever et al. 1993; Bach-Knudsen 1997; Keady et al. 2000; Nordheim-Viken and Volden 2009). Most of these indices reflect a particular agronomic factor such as growth stage at harvest (Peyraud et al. 1997; Van Dorland et al. 2006), nitrogen application (Peyraud et al. 1997; Keady et al. 2000), ensiling process (Nsereko et al. 1998; Dawson et al. 1999; Charmley 2001; Van Dorland et al. 2006) or pasture composition (Stypinski 1993; Soegaard 1993; Lee et al. 2009). The main polymers found in the plant cell walls of lignocellulosic materials like grasses are cellulose, hemicellulose and lignin. The strong inter-linkages between these polymers, and non-covalent and covalent cross linkages between them, provide the plant a stable shape and structure (Perez et al. 2002). They are relatively resistant to hydrolysis and their degradation largely depends on microbial activity (Orr and Kirk 2003). The crude (structural carbohydrates including lignin and pectin) and neutral detergent fibre (the insoluble fibre mainly cellulose and hemicellulose) are the most used indices for determining the feed value for the ruminant (Van Soest et al. 1991; Bach-Knudsen 1997). Additionally, many authors have used acid detergent fibre for cellulose and lignin estimations (De Boever et al. 1993; Keady et al. 2000). According to Bach-Knudsen (1997), calculated and analysed values regarding the fibre components of fibre rich materials can deviate significantly. Plant cell walls, composed mostly of structural carbohydrates and lignin, account for 40–80% of the organic matter in forage crops and, depending on their concentration, can limit feed intake and digestibility of forages (Buxton 1996). Neutral detergent fibre is resistant to mammalian enzyme degradation (Van Soest et al. 1991). The crystalline structure of cellulose acts a barrier for microbial and enzymatic degradation in anaerobic digestion (Lehtomaki 2006). On the contrary, hemicellulose is easily hydrolysed by hemicellulase enzymes (Clavero and Razz 2002). Lignin is the most recalcitrant part of the structural carbohydrates because of its non-water soluble nature and resistance to microbial action and oxidative forces Grass Biomethane for Agriculture and Energy 25 (Lewis and Davin 1998; Hendriks and Zeeman 2009). Therefore, the biodegradability of grass and grass silage in an anaerobic digester is limited by the higher concentration of cellulose and lignin (acid detergent fibre values) (Lehtomaki and Bjornsson 2006). Inefficient biodegradation results in reduced solubilisation of grass silage, which limits the conversion of volatile solids to chemical oxygen demand and consequently biomethane production (Nizami and Murphy 2010). The components of grass in the cell cytoplasm are proteins and nitrogenous compounds, lipids and non-structural carbohydrates (McDonald et al. 1991). The protein, lipid and extracted fractions of carbohydrates, often known as water soluble carbohydrates, are the soluble parts of grass silage that are sources of energy in both the rumen and for anaerobic digestion microorganisms (Hendriks and Zeeman 2009). High specific methane yields can be achieved when crop substances are characterised by low lignin concentrations and high concentrations of easily degradable components in other words non-structural carbohydrates and soluble cell components (Amon et al. 2007a; Schittenhelm 2008). The direct relationship between pasture management practices and those attributes that influence the production of high value grass and grass silage suitable for animal and biomethane production necessitates the examination of these agronomic practices. This is an important step for sustainable development in both agricultural and energy sectors. 4.2.1 Grass Species and Biomethane Production The advantages of perennial grasses over arable crops as a feedstock for biofuel production due to better energy balance and environmental benefits have resulted in a diversion of interest from arable crops to perennial grasses. Research on Panicum vigratum (switchgrass) (McLaughlin and Kszos 2005), Miscanthus  Giganteous (miscanthus) (Clifton-Brown et al. 2004), Phalaris arundinacea (reed canary grass) and Phleum pratence (timothy) (Lewandowski et al. 2003), Andropogon gerardii (big bluestem) (Weimer and Springer 2007), Lolium perenne (perennial ryegrass) (Smyth et al. 2009; Korres et al. 2010) as energy crops has been accelerated. Nevertheless, the selection of grass species and seed mixtures is determined by the purpose for which the sward is to be used, in this case for both animal and biomethane production, along with the prevailing environmental conditions (Feehan 2003). Furthermore, the physiology of grasses, considering for example their photosynthetic (PS) pathway, i.e. C-3 (cool season or temperate species) vs. C-4 (warm season or tropical species), imposes environmental specificity and hence differences in the adaptability, productivity (Niu et al. 2006) and qualitative aspects, such as water soluble carbohydrates and possible biomethane yield (Table 3), of the grasses. There are distinctive differences between C-3 and C-4 species that affect their productivity, for example the former fix CO2 in lower temperatures and they respond to N fertilizer early in the spring, whereas in high temperatures their growth rates are reduced. In contrast, C-4 species require less N to achieve the same light-saturated assimilation rate, leading to higher photosynthetic N use efficiency, are more efficient at fixing carbon dioxide in warm environments and are more tolerant of 26 N.E. Korres et al. Table 3 Potential perennial grasses as energy crops in Europe and methane yields per hectare and per ton of dry mattera (DM), Photosynthesis (PS) Common name Ryegrass Miscanthus Switchgrass Reed canary grass Timothy Meadow foxtail Big bluestem Cocksfoot Tall fescue Napier grass Sudan grass Cypergrass Latin name Lolium perenne Miscanthus  Giganteous Panicum vigratum Phalaris arundinacea Phleum pratence Alopecurus pratensis Andropogon gerardii Dactylis glomerata Festuca arundinacea Pennisetum purpureum Sorghum  drummondii Cyperus longus Methane PS pathway (m3 ha1 ) C-3 2,500–6,150 C-4 1,432–5,450 Yield (t DM ha1 ) 9–15b 5–44 Methane (m3 t1 DM) 278–410 124–286 C-4 900–7820c 5–23 180–340 C-3 1,700–4,730 7–13 243–364 C-3 C-3 1,362–5,800 1,463 9–18 6–13 151–322 112–243 C-4 – 8–15 – C-3 1,480–3,800 8–10 185–380 C-3 1,462–2,000 8–14 183–143 C-4 0:19–0:34d 27 – C-4 2,130–6,060 10–20 213–303 C-4 – 4–19 – Data were adopted from Lewandowski et al. (2003); Prochnow et al. (2009); Braun et al. (undated); Seppala et al. (2009) a Methane yields per ton of dry matter were estimated based on the methane yield ha1 and potential dry matter yields ha1 b Yields of early, intermediate and late perennial ryegrass were reported equal to 16.7, 15.3 and 15 t DM ha1 year1 respectively (Lockhart and Wiseman 1988) c Based on 0:18–0:34 m3 CH4 kg1 dry matter (Chynoweth et al. 2001; Sampson 2006) d L CH4 g1 of Volatile Solids (Wilkie 2008) water stress conditions (Winslow et al. 2003; Lunt et al. 2007; Nippert et al. 2007). Additionally, as mentioned by White (1973), the enzymes which convert CO2 into organic compounds in C-3 and C-4 (ribulose-1,5-diphosphate carboxylase and phosphoenolpyruvate carboxylase for C-3 and C-4 species respectively) are affected by temperature. Hence, temperate grasses require lower optimum growth temperatures in comparison to tropical species, a fact that can influence the distribution of grasses based on annual temperature fluctuations, their nutritive value and yield, along with biomethane potential. Despite the positive greenhouse gas balance of miscanthus (Styles and Jones 2007; Lewandowski et al. 1995), impacts on biodiversity have raised a few concerns (Semere and Slater 2007a and b) about its sustainability as a potential energy crop in European temperate climates. The energy ratios for switchgrass production are generally very positive (Thornley et al. 2009) and there are particular biodiversity benefits for pheasants, Grass Biomethane for Agriculture and Energy 27 Table 4 Dry Matter Intake (DMI), Dry Matter Digestibility (DMD) and Acid Detergent Fibres (ADF) concentration of C-3 and C-4 grasses, Dry matter (DM) Grass type C-4 (sheep) C-3 (sheep) C-4 (sheep) C-3 (sheep) C-4 (cattle) C-3 (cattle) DMI .g day1 kg0:75 /a 56 71 65.7 66.2 89.8 89.5 DMD (%) 62 71 54.5 65.5 60 67 ADF (% of DM) – – 42.5 35.8 42.7 38.3 Adopted from Brown (1999) a DM intake is linked to energy requirements that are proportional to 0.75 power of body weight (Allison 1985) quail and rabbits. Agro-chemical inputs are low and nitrogen leaching rates and soil erosion rates are both low compared to arable crops (Thornley et al. 2009). The unfamiliarity of EU farmers with these crops and the lack of research data on the crops under European conditions are the main issues causing concern on their suitability. Reed canary grass is widely distributed in temperate regions of Europe (Thornley et al. 2009) but the high nitrogen requirements (Geber 2002), concerns about invasiveness, the relatively low yields (Riche 2005) that results in a poor energy balance and the susceptibility to pests and diseases affect its sustainability as a potential energy crop (Thornley et al. 2009). However, productivity of animals consuming mostly forage is directly related to the quality of the forage and the amount consumed (Penning et al. 1995; Buxton 1996; Fontaneli et al. 2001). C-4 grass species are lower in dry matter digestibility and usually in dry matter intake than C-3 species, mainly because of their higher fibre concentrations (Minson 1981; Reid et al. 1988) (Table 4). Additionally, the neutral detergent fibres of forages grown under high temperatures is usually less digestible than that of forages grown under lower temperatures because of increased lignification (Buxton and Fales 1994). The lower digestibility of warm grasses due to their higher fibre content is indicative of possible lower biomethane yields, since digestibility of dry matter may be equated to the potential digestibility of the silage in the cattle paunch (Robson et al. 1989). In temperate grassland regions, perennial ryegrass (Lolium perenne) is preferred for digestion because of its high digestibility (Robson et al. 1989), water soluble and non-structural carbohydrates content (Smith et al. 2002; Buxton and O’Kiely 2005) (Fig. 7) and reduced concentration of crude fibre (Nizami et al. 2009). As Mahnert et al. (2005) reported perennial ryegrass produced the highest biogas yield (0:83–0:86 m3 kg1 VS added) in comparison to other grasses (both fresh and ensiled); for example, cocksfoot resulted a biogas yield of 0:65–0:72 m3 kg1 VS added. Tetraploid ryegrass varieties are recommended due to high sugars levels (Dieterich 2008). Tetraploid varieties remain an important component of grass seed mixtures because of their higher water soluble carbohydrate content, their increased 28 N.E. Korres et al. NS-carbohydrate content (g kg −1 DM) a Grass carbohydrates 400 350 336 NS carbohydrates content (leaf+stem) 250 228 183 182 150 108 115 108 100 74 123 98 67 50 111 87 96 86 40 58 57 54 0 200 Phleum pratense Festuca pratensis Dactylis glomerata Digitaria eriantha (C-3) (C-3) (C-3) (C-4) Cenchrus ciliaris Setaria sphacelata (C-4) (C-4) 181 170 180 WSC content (g kg−1 DM) Stem 209 182 200 Lolium perenne (C-3) b Leaf 300 160 140 120 110 96 100 79 80 60 40 20 0 Lolium multiflorum Lolium perenne Phleum pratense Festuca pratensis Dactylis glomerata Fig. 7 Non-structural (NS) content of temperate (C-3) and tropical (C-4) grasses (a) and water soluble carbohydrate (WSC) content of temperate grasses (b) (Based on Buxton and O’Kiely 2005) palatability (leading to higher intake by livestock) and their tolerance to drought. However, they tend to have lower tiller densities, resulting in more open swards and lower dry matter, compared with diploids (Anonymous 2008). Seppala et al. (2009) reported that cocksfoot, tall fescue and timothy are better than reed canary grass for biogas production in boreal conditions because they offer higher specific methane yields, higher dry matter yields per hectare and better regrowth ability. As reported by Mahnert et al. (2005), the supply of a high quality feedstock in combination with high yielding ryegrass cultivars for silage production is an essential prerequisite to obtain optimal gas yields. Selection of the appropriate grass species should consider not only biomethane potential but also suitability for animal production systems. In Western Europe, perennial ryegrass is the most widely used grass species for grazing cattle, because of its high productivity, palatability and nutritive value (Taweel et al. 2005). Additionally, O’Kiely et al. (2005) stated that the main benefits of perennial ryegrass swards are that they produce high yields in response to fertilizer application, have high digestibility when harvested at the appropriate growth stage, are relatively easy to preserve as silage due to their superior content of sugar and persist as permanent swards where favourable management practices prevail. Grass Biomethane for Agriculture and Energy 29 4.2.2 Grass and Clover Mixed Pastures As stated by Kelm et al. (2004), an integrated approach to crop production should consider both productivity and environmental trade-offs as for example energy efficiency, fertilization and strategies for reducing N2 O emissions through different cropping strategies (pure grass swards vs. clover/grass swards, fertilization strategies). In Europe, during the last decade, interest for feeding temperate forage legumes, both in fresh and conserved form, has grown particularly in extensive grass-based farming systems (Parente and Frame 1993). This renewed attention was due to changes in agricultural policy, which supports extensive and sustainable farming systems (EC 2003). Forage legumes are considered environmental friendly alternatives with regard to artificial nitrogen fertilizer (Evers et al. 1993) and also have benefits in their nutritional composition, both as protein (N) and energy sources for ruminants in low-concentrate input systems (Van Dorland et al. 2006). Woodmansee (1978) reported the fixation of 25 kg Nha1 by the incorporation of Trifolium spp. (clover) in annual grassland whereas Brockman and Wilkins (2003) and Moller et al. (2002) reported a range between 3 and 150 kg N ha1 depending on the percentage of clover into the sward. This is very important considering, as mentioned in the previous sections, the contribution of nitrogen fertilization in nitrous oxide emissions. Additionally, Stypinski (1993), in a 5 year field experiment using three grass species (cocksfoot, timothy and ryegrass) in a mixture with and without clover, found that white clover (Trifolium repens) improved the pasture value with regard to protein content, energy content, the concentration of macro and micro-nutrients, as well as digestibility. However, the fibre content of the feed with clover was lower than that without clover (Fig. 8). Mixed pastures can influence the level of intake and hence digestibility. Comparisons of grasses with legumes, such as white clover, are often associated with higher level of intake (Ribeiro et al. 2003). Baumont (1996), Rutter et al. (2004), and Assoumaya et al. (2007) have explained that forage legumes are reduced more quickly into small particles than grasses and that less time is needed to take and masticate a similar bite for clover than for grass. As suggested by Rutter et al. (2004), further research is required regarding this. Nevertheless, digestibility of pure grass compared to grass mixed with white clover varies because it depends on the environmental conditions, the grass species involved, the defoliation management and other factors (Soegaard 1993). As reported by Cavallero et al. (1993), grass species as in the case of cocksfoot vs. perennial ryegrass along with other factors can affect the establishment of a white clover population in the sward. These authors reported that, after 3 years of experimentation, a steady equilibrium was achieved for cocksfoot-clover but not for perennial ryegrass-clover mixture, under both continuous and rotational grazing. Grass varieties with high tillering capacity, which results in dense pastures, should be avoided in grass/clover pastures (Sheehy and Culleton 2002). Breeding clover cultivars to withstand grass competition enables the establishment of grass/clover under a wide range of grass varietal selection. Tetraploids are 30 N.E. Korres et al. Dry matter (%) 30 28.2 26.6 25.7 25 20 21.4 19.6 19.9 16.1 15 13.6 10.6 10 5 0 White clover Crude Protein Grasses Pure Protein Mixture Crude Fibre Fig. 8 Effects of white clover on qualitative characteristics of animal feed (Based on Stypinski 1993) particularly suitable because of their open sward, hence permitting the development of the clover. As an example, a 50:50 mixture of a medium diploid and a tetraploid variety of ryegrass would be suitable for most situations (Sheehy and Culleton 2002). Frankow-Lindberg et al. (1996) reported that the marginal cost of grass/clover is half that of a grass/fertilised N production system, one of the main reasons for which is the reduced N fertilisation rate in the former. Grass species may vary in terms of their chemical composition hence methane yields from grassland could possibly depend on the mixture of species within the vegetation (Prochnow et al. 2009). Mixtures of grasses result in increased methane yields compared to a single grass type such as in Cynodon spp. (Bermuda grass) (Gunaseelan and Nallathambi 1997). Additionally, Plochl and Heiermann (2006) reported methane production from forage and paddock mixtures of 297–370 and 246 m3 t1 organic dry matter (ODM), respectively. The efficiency of anaerobic digestion can be considerably improved when using mixed feedstock, such as grass with legumes, because the neutral detergent fibre concentration of grasses is usually greater than that of legumes. This is caused mostly by differences in neutral detergent fibre concentration between grass and legumes leaves (Buxton 1996). Hence, increasing the proportion of legumes, particularly clover, and consequently the leaf to stem ratio of forage, results in lower cell wall concentration, or in other words reduced indigestible material and increased feedstock digestibility. This improves the efficiency of lignocellulosic decomposers and possibly increases biomethane production (Table 5). Silage from mixed grass pastures with clover tends to produce higher methane yields than silage from mixed pastures without clover; however, the anaerobic digestion conditions are also significant factors for biomethane production. Grass Biomethane for Agriculture and Energy 31 Table 5 Effects of pasture type on methane production (Prochnow et al. 2005) Substrate Intensive grassland (monoculture fresh, silage) Extensive grassland (fresh and silage) Extensive grassland (fresh and hay) Biogas yield (L/kg VS) 700–720 Methane yield (L/kg VS) – 540–580 – 500–600 – Extensive grassland (silage) Mixed pasture grassland (fresh and silage) Mixed pasture grassland (silage) 500–550 – 650–860 310–360 560–610 300–320 Grasses and clover (silage) Intensive grassland (monoculture, silage) 532, 474, 427a 370, 326, 297a – 390 Extensive grassland (silage) – 220 Conditions Batch=35ı C=25 d Semi-continuous, 35ı C, 18–36 d, co-digestion Continuous, 35ı C, 20 d, co-digestion Batch, 35ı C, 28 d, mono-digestion Semi-continuous, 35ı C, 28 d, mono-digestion Batch, 37–39ı C, 58 d, mono-digestion Semi-continuous, 37ı C, 25–60 d, co-digestion Semi-continuous, 37ı C, 25–60 d, co-digestion a Harvesting mid-May (before anthesis); end of May (anthesis); mid-June (after anthesis) respectively. Note: VS D Volatile Solids 4.2.3 Fertilization Management Fertilization of grassland, particularly nitrogen fertilization, for higher yields is probably one of the most important husbandry factors, because nitrogen facilitates many functions in plants, including photosynthesis, enzyme synthesis, and nucleic acid, protein and cell walls formation (Addiscot 2005). Inorganic nitrogen fertiliser is applied to grassland to ensure that economically viable yields are available for harvesting at a time when the feed value of the grass is adequate (O’Kiely et al. 2002). N fertiliser has been increasingly seen as management tool (Vellinga et al. 2004) for herbage yield and quality increases (Eckersten et al. 2007) and for efficient grazing and cutting planning. The increased growth rate following N application reduces the growth time required between grazing and silage cuts and results in more cuts per year (Van Burg et al. 1981). The amount of N losses through ammonia volatilisation, nitrate leaching, nitrous oxide emission and denitrification can be reduced by appropriate timing of fertilization and cutting (Jarvis 1996; Whitehead 2000). The effects of N fertilizer on the chemical composition of grass have been studied extensively. Nordheim-Viken and Volden (2009), investigating the effects 32 N.E. Korres et al. Celullose (g/kg) 288 286 284 282 280 278 276 274 272 Hemicellulose (g/kg) Cellulose Hemicellulose 265 287 262 260 281 278 251 278 258 255 278 252 250 249 245 240 N1 (72) N2 (96) N3 (120) N4 (144) N5 (168) N fertilizer (kg N/ha) Fig. 9 Effects of N fertilization on cellulose and hemicellulose content in perennial ryegrass (Based on Keady et al. 2000) of nitrogen fertilization rate during 3 years experimentation on timothy, observed that increases in fertilization rate tend to increase neutral detergent fibres content. Furthermore, Keady et al. (2000) reported increases of cellulose and hemicellulose content in perennial ryegrass (Fig. 9), and therefore increases in its digestibility, when N fertilizer application rate was increased. In general, the results of nitrogen fertilization on fibre digestibility are moderate. As such, Peyraud et al. (1997) found that unfertilised perennial ryegrass had decreased fibre digestibility when provided as a feed for dairy cattle, but had moderate increases in neutral detergent fibres, acid detergent fibres and acid detergent lignins with nitrogen application. Several authors have reported lower water soluble carbohydrates in grasses with increased N fertilization (Van Soest et al. 1978; Buxton and Fales 1994; Tremblay et al. 2005-cited by Nordheim-Viken and Volden 2009). O’Kiely et al. (2002) stated that lower water soluble carbohydrates content and increased buffering capacity of perennial ryegrass, due to increased N fertilization rate, negatively affects the ensilability of grass. Dry matter yield and crude protein content is positively affected by increased N application rate in timothy (Belanger and McQueen 1999; Nordheim-Viken and Volden 2009), perennial ryegrass (Keady et al. 2000; O’Kiely et al. 2002), and cocksfoot (Mills et al. 2009). There has been limited research into the effects of nitrogen management, specifically with regard to application rate .kg Nha1 / and fertilizer form (organic, inorganic), on biomethane production from grass and grass silage. For the purpose of this chapter the potential grass biomethane production was estimated, based on the work conducted by Seppala et al. (2009) and Kaiser and Gronauer (2007), as between 0.325 and 0:339 m3 CH4 kg1 volatile solids. This is the average biomethane production for a wide range of fertilizer forms (mineral, organic and combination) and grass species (cocksfoot, reed canary grass, timothy and tall fescue). Grass Biomethane for Agriculture and Energy 33 Early harvested forage Late harvested forage A Cell wall Cytoplasm Nucleic acid Amino acid Proteins Other N compounds Monosaccharides Oligosaccharides Refractory compounds Thin cell wall Low Neutral Detergent Fibres=High intake Low Acid Detergent Fibres=High energy Hemicellulose Neutral Detergent Fibres Cellulose Acid Detergent Fibres Lignins Bound N Cell wall A Cytoplasm Thick cell wall High Neutral Detergent Fibres=Low intake High Acid Detergent Fibres=Low energy Fig. 10 Grass cell anatomical and biochemical characteristics that affect ruminant nutrition, according to harvesting date (Note: The relative changes in structural and chemical composition between early and late harvested forage depict generalised differences which (a) developed as plant matures, (b) exist between leaf and stem tissues and (c) exist between C-3 (cool season) and C-4 (warm season) plants. Refractory compounds: a diverse group of primarily secondary plant compounds, in addition to lignin, which affects the digestibility and/or nutritive value of plant tissue. Included are tannins, flavones, essential oils, steroids, saponins, waxes and alkaloids. These types of compounds have been variously isolated from the neutral detergent solubles and neutral detergent fibres fractions (Huston and Pinchak 2007)) 4.2.4 Harvesting Date The structural characteristics of forage are described in various ways. Botanists and agronomists approach plant cellular structure from the standpoint of biosynthesis whereas animal nutritionists emphasize the attributes of cells and tissues that enhance bio-degradation (Van Soest 1982) and liberation of nutrients. Most probably the same approach would be taken by an engineer, who investigates methods for higher biomethane production from biomass and more specifically from grass and grass silage. Harvesting date is of prime importance for grass species digestibility, intake, and for grass biomethane production. As the grass matures, the proportion of the cell wall components (cellulose, hemicellulose and lignin) increases (De Boever et al. 1993), while the proportion of cell contents decreases (Bruinenberg et al. 2002) (Fig. 10). The leaves of grass are more digestible than the stems (Gilliland 1997; Bruinenberg et al. 2002) due to their higher protein content (Nissinen 2004-cited in Seppala et al. 2009). In the generative growth stage, the total solids (TS) yield increases to over 200 kg TS/ha per day; however, digestibility (Ito et al. 1997) and the amount of raw protein decrease by 0.5–1.0 percentage units per day (Nissinen 2004-cited in Seppala et al. 2009). Forage quality is reduced with maturity due to a decrease in leaf-to-stem ratio and an increase in fibre components (Ugherughe 1986). The development stage is an 34 N.E. Korres et al. important factor in determining the chemical composition and quality of forage legumes; for example, in red clover forage (Vasiljevic et al. 2005), young red clover plants have large leaf mass, high content of moisture, protein and minerals and a low fibre content, whereas as the plant matures, the protein and mineral content, and consequently also the intake and digestibility, decline. Nordheim-Viken and Volden (2009) recorded decreases in crude protein content in timothy with increased maturity under various environments. Additionally, De Boever et al. (1993) reported that most of the chemical, physical and biological characteristics of the grass were more favourable in early cut silage than in intermediate or late cut silage. As the sward matures, there are a higher proportion of stems due to decreases in leaf-to-stem ratio. According to Benvenutti et al. (2006), stems can have a barrier effect on bite size and instantaneous intake rate. The higher the stems density, the smaller the bite area and the slower the biting rate. This leads to a decrease of the instantaneous intake rate. Boval et al. (2007) confirms that stem length and stem proportion in the sward have a negative impact on biting rate. Harvesting date is an important factor for feedstock specific methane yield (Prochnow et al. 2009). It has been reported by several authors that the specific methane of the feedstock decreases with advancing stage of maturity since increases in non-degradable fibre content limit biomethane production potential (Shiralipour and Smith 1984; Weiland 2001). Additionally, the decrease crude protein and crude lipid content with maturity (Holmes 1980) negatively affects methane percentages in biogas, as these components contribute to methane production (Weiland 2001). Seppala et al. (2009), in an investigation of the methane potential of four grass species at various locations, fertilizer regimes and harvesting intervals, reported that the methane yield from the 1st harvest of all grasses was higher than for following harvests. Nizami et al. (2009) reported that grass for silage is usually harvested at a less mature stage of growth (leafy and non-lignified) since the aim is to obtain a crop with a relatively high content of fermentable substrate and a low content of fibre. As Woolford (1984) stated, the crop at early growth stages usually exhibits a high leaf-to-stem ratio. This is supported in the case of Pennisetum purpureum (Napier grass) as reported by Gunaseelan and Nallathambi (1997). Amon et al. (2007a, b) on a multifaceted crop rotation aiming to increase the yield of methane per hectare reported that the first cut at vegetative stage was selected as the optimum option for harvesting. Kaparaju et al. (2002) found that Trifolium spp. (clover) produced 50% more methane per tonne of volatile solids at vegetative stage than at flowering stage. Nevertheless results recorded by Pouech et al. (1998) show that methane yield per tonne of volatile solids was 32% lower at vegetative stage than at flowering stage when similar experiments were conducted. The content of total and volatile solids in grass depends on several factors, such as location and origin, seasonal variations, cultivation practices, type of soil, pre-treatment of the biomass, and the nutrient composition of the grass (Bauer et al. 2007). These factors could affect the yield of grass biomethane in anaerobic digestion (Nizami and Murphy 2010). The diurnal and seasonal variation of carbohydrates in grasses influences the harvesting date of the sward since studies on various grass species have shown Grass Biomethane for Agriculture and Energy 35 that the concentration of total non-structural carbohydrates was lowest at 6 am and increased linearly to a high at 6 pm (White 1973). Additionally, as the same author stated, the seasonal variation of carbohydrates differs among grass species; in some species the level is lowest when the second or third leaf emerges, but in other species, the reserve level is lowest after seed ripening. Taking into consideration the importance of non-structural carbohydrates in animal and biofuel production systems, harvesting should be commenced at a time when the level of carbohydrates is highest. 4.2.5 Grass Silage High forage systems, as opposed to concentrate feeding systems, have been shown to have beneficial effects in terms of meat quality, stability and sensory characteristics (Lee et al. 2009). Grass, and in particular grass silage, form the basal diet for the vast majority of ruminants in many parts of the world during the winter feeding period (Charmley 2001). The transformation of harvested herbage to silage is therefore considered as part of grassland management and, as mentioned in previous sections, pasture management that affects quantitative and qualitative characteristics of grass production would affect the same characteristics of grass silage. Furthermore, the use of various crop silages, such as fodder and sugar beets, grain crops and grass silages has been studied for a number of biogas processes (Amon et al. 2007a; Lehtomäki et al. 2008). In order to ensure constant quality and supply of substrate to an anaerobic digestion facility, the ensiling of grass as silage is preferable to the utilization of fresh grass (Nizami et al. 2009). Ensiled grass has lower organic matter losses and more independent of weather conditions than hay (dried grass) (Egg et al. 1993). The basic principles for silage production are based on the reduction of fresh grass moisture content (dehydration) and the prevention of bacteria and fungi growth (which can deteriorate the final product), usually with the use of inhibitors or an acid medium (O’Kiely et al. 2002). Normally during ensiling, the fodder undergoes acid fermentation in which bacteria produce lactic, acetic and butyric acids from sugars present in the raw material. The net result is a reduction in pH which prevents the growth of spoilage microorganisms, the majority of which are intolerant of acid conditions (Woolford 1984). Plant aerobic respiration and enzymatic fermentation are the major processes determining silage quality and ensiling efficiency (Murdoch 1980), and possibly also anaerobic digestion. According to the same author the action of enzymes on the carbohydrate content of the herbage result in the production of heat, water and carbon dioxide, accompanied with a restriction of lactic acid formation. Additionally, increased heat results in increased silage temperature and a reduction in protein digestibility. Coinciding with and following plant respiration, bacterial fermentation occurs, and a major aim in silage making is to control this bacterial action. Silage which has undergone an undesirable fermentation is characterised by a relatively high butyric acid content and an extensive degree of proteolysis, resulting in reduced 36 N.E. Korres et al. digestibility and low intake characteristics (Murdoch 1980). Silage fermentation also depletes soluble carbohydrate concentration (Chamberlain et al. 1985; Khalili and Huhtanen 1991; Charmley 2001). Moreover, there is a need to restrict clostridia growth, which consumes lactic acid (Murdoch 1980), and causes deterioration in silage quality (Woolford 1984). Ammonia may act as a simple index of silage fermentation quality (Charmley 2001), since is predominantly a product of clostridia fermentation of amino acids and its excess indicates a low quality product. Fermentation of non-structural carbohydrate in silage has a direct effect on the pattern of volatile fatty acids production in the rumen since the concentration of soluble sugars in silages that have undergone extensive homolactic fermentation is almost negligible (Charmley 2001). This affects both animal (Cushnahan and Mayne 1995; Keady and Murphy 1996) and biomethane production (Madhukara et al. 1993). Keady et al. (2002) reported that improvements in silage fermentation could be indicated by decreases in pH and ammonia-N due to various factors, such as the use of additives. Silage additives may influence methane yields indirectly via silage quality or directly by providing additional feed for lactic acid bacteria with sugars, by improving degradability of organic matter with enzymes or by inhibiting or promoting micro-organisms with acids (Kung et al. 2003). Nevertheless, effects of additives on grass silage methane potential are moderate. Prochnow et al. (2009) reported various silage additive treatments for different feedstocks, and their use resulted in increased biomethane production in some cases and had no effect in others. Additionally, other studies have shown contrasting results (Madhukara et al. 1997; Rani and Nand 2004; Neureiter et al. 2005). 5 Conclusion Most grassland in the EU is devoted to meat (cattle and sheep) production where profitability is low and farmers often rely on EU single farm payments to survive; thus grassland farming can face considerable challenges in implementing new environmental measures without financial supports (Boyle 2008). Additionally, the response to climate change must not restrict the opportunities for the agricultural sector to create employment, develop export markets and expand into emerging markets (Walshe 2009). Effective solutions to climate change may require integrated multi-sectoral approaches based on new sources of energy and industrial feedstock, new technologies for emissions capture and reduction as well as new mechanisms for balancing an immediate need for food and energy with the long-term goal of sustainability (Teagasc 2008). Current economic and environmental concerns require the control of inputs in intensive grassland systems in order to maximize efficiency and to reduce potential pollution sources. The authors of this chapter do not ignore the fact that energy security is a significant issue and geopolitical concern for the EU; the issue of food security is equally important. We propose the integration of grass and grass silage production with a biomethane production Grass Biomethane for Agriculture and Energy 37 system because such a system: (1) will diversify agricultural production (2) will improve agricultural competitiveness (3) is an environmental friendly technology well established across Europe (4) enhances security and sustainability of energy supply and (5) offers great opportunities for rural development by creating a domestic industry with associated employment opportunities. Acknowledgements The authors are deeply indebted to the Irish Environmental Protection Agency for funding this study. They also acknowledge the suggestions and recommendations of the three anonymous reviewers and these of the chief editor which have improved the quality of this chapter greatly. References Aarts HFM, Habekotte B, Van Keulen H (2000) Efficiency of nitrogen (N) management in the “De Marke” dairy farming system. 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