The weather dynamic: the challenge of winter grazing and the parameters of sustainability
Authors: Barnes, A.P.*1, Rees, R.M.1, Morgan, C.,3 VosoughAhmadi, B.1, Stott, A.W5, Marley, C.L.4, McGechan, M.2, Topp, C.F.E.2, Hyslop, J.J3.
1: Department of Land Economy, Environment and Society, SRUC, West Mains Road, Edinburgh, EH9 3JG
2: Department of Crop and Soil Science, SRUC, West Mains Road, Edinburgh, EH9 3JG
3: Farm Rural Business Services, SRUC, 2 Technopole Centre, Bush Estate, Penicuik, EH26 0PJ
4: Animal Systems Research Group , Institute of Biological, Environmental & Rural Sciences (IBERS), Aberystwyth University, Penglais, Aberystwyth, Ceredigion, SY23 3DA
5: Future Farming Systems Group, SRUC, West Mains Road, Edinburgh, EH9 3JG
* Corresponding Author: Dr Andrew Barnes, Department of Land Economy, Environment and Society, SRUC, Edinburgh, EH9 3JG.
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Abstract:
Livestock production has significant impacts on the environment as a consequence of greenhouse gas production, nutrient and pathogen release to stream water and impacts on soil and plant communities. The way in which livestock are managed within a farming system can have important implications for the magnitude of these impacts. A management strategy that has grown in popularity recently in temperate regions of Europe, is wintering cattle on grassland. This infers managing cattle for part or whole of the winter season on designated grassland areas.
Outwintering is mostly driven by the desire to maintain financial sustainability under increasing economic and policy pressures, as it obviates the need for high capital investment in housing. Assessment of the outwintering system must therefore be on economic, social and environmental parameters. We present a classification schema for different types of outwintering system and assess the impact on sustainability of adoption of these systems.
The literature reveals large gaps in our understanding towards outwintering on grasslands and work partially related to outwintering has to be used to infer impact of this system. Whilst we find that outwintering tends to improve both the gross and net margins within a farm, and, if managed correctly, has benefits for animal welfare when compared to indoor systems. The main pressures are on environmental criteria, concentrated on damage to grassland both during and post-grazing period in periods of increased precipitation. However, correct management of these factors, dictated by site choice, management of cattle in extreme events and post-treatment of the field will, we argue, serve to temper the negative environmental effects.
Outwintering on grasslands entwines farm system research with future government ambitions related to sustainability of the farming sector and targets on greenhouse gas emissions. It is clear that these impacts have been understudied for a management system which is proving increasingly popular in the UK and elsewhere. We conclude that the dimensions for sustainability assessment need to be widened to encompass outwintering cattle, as there is a strong temporal element which will negate some of the environmental damage, and also a spatial element, with respect to site choice and proximity of outwintered cattle to fragile ecosystems. In addition, we show how modelling frameworks are needed to combine these impacts to fully understand the synergies and trade-offs within the outwintering system and so satisfy the needs of policy.
1.0Introduction
Grasslands occupy 60% of the UK’s agricultural land area (DEFRA, June Agricultural and Horticultural Census 2008), and provide a wide variety of ecosystem services. These include the provision of human and animal food materials, the buffering of pollutant transfers to water, the provision of a habitat for plant, animal and soil microbial biodiversity, carbon storage, and landscape and recreational value.
Livestock production has significant impacts on the environment as a consequence of greenhouse gas production, nutrient and pathogen release to stream water and impacts on soil and plant communities (Steinfeld et al., 2006). The way in which livestock are managed can have important implications for the magnitude of these impacts. A range of technologies have been suggested for these farming systems which mitigate greenhouse gases and also maintain or extend production output goals(Macleod et al., 2010; Moran et al., 2011; Shortall and Barnes, 2013).
In addition, a raised food security agenda emphasises the role of increasing productivity on scarce land (Royal Society, 2011). From a farming perspective the management of livestock incur financial burdens which may not, without the aid of subsidy, prove to be economically worthwhile (SAC, 2008, Acs et al., 2010). In managing cattle the high capital investment costs for housing and slurry storage facilities, as well as increasing pressures on market prices has led farmers, in temperate areas, to considerthe merits of keeping cattle outside for a greater proportion of the year,or out-wintering non-lactating cattle for the whole winter period. Whilst these grazing systems offer benefits by reducing production costs, there will be implications for the environment as wetter weather coupled with stocking activity on grassland, will lead to a degradationofsoil and water quality. In addition, some issues may arise for the health and welfare of the cattle, particularly with regard to the hardiness and suitability of certain dairy breeds. These systems may also require additional labour input to ensure grazing areas are managed according to the requirements of policy (e.g. cross-compliance) and to ensure that animal health and welfare, and thus performance, are not compromised. Sustainability indicators, however, tend to focus on 1-point estimates, given constraints in data collection, which usually do not accommodate the dynamics of a livestock grazing system over a whole year period. The influence of extreme weather events will increase pressure on a system to remain sustainable, both environmentally and economically throughout the year. This is further complicated by the requirement to design management strategies that promote pollution swapping (i.e. the substitution of one form of pollution by another), as would be the case if reduced nitrate leaching was replaced by increased emissions of nitrous oxide.
The only record of outwinteringactivity seems to be the farm practices survey (Defra, 2008) which surveys livestock farms in England and Wales. High numbers of farmers were conducting some form of cattle outwintering, the most prevalent being grazing farms in Less Favoured Areas (88%), and in lowland areas (70%). This survey also found that the smaller farms are the most likely to outwinter, possibly because it obviates the need for high capital investment.
A number of outwinteringstrategies are available to farmers, these either rely on providing brassicas to support nutrition through part of the winter period, offering temporary grazing, or at the most extreme, sacrificing a field over the winter period and providing feed when grazing quality degrades. The majority of UK farmers were found to use temporary grazing or sacrifice fields (Defra, 2008). A sacrifice field can be defined asa field or part of a field that is allowed to deteriorate as a result of winter grazing. Consequently, it seems to present an extreme form of management which may have severe environmental consequences. Specific grassland issues revolve around soil damage from cattle movement, subsequent water and air pollution effects, as well as impacts on the underlying biodiversity in and around the grazing area.
Despite the popularity of outwintering, little is known about the implications of grazing over an extended winter period, especially under a strategy of sacrificing a field. Though damage is expected due to the degradation of the field, there may also be benefits compared to other strategies which house cattle, e.g. through reduced energy costs and the impact on greenhouse gas emissions.
The purpose of this paper is to review the current literature available related to the practice of outwintering cattle, in order to present a framework and typology of these impacts and, thus, provide a basis for future study within this research area. The next section presents a schema for outlining the types of cattle that may be managed under a sacrifice field system.
2.0.A typology of cattle outwintering management on sacrifice fields
Table 1 presents a typology of outwintering strategies for the cattle sector. For the dairy sector it is unlikely that dairy cows that are lactating will be outwintered, as cold weather tends to adversely affect lactation. However, in each herd there are a number of non-lactating animals which could potentially be managed in this way. These animals fall into three categories:
Dairy Cows
Dry pregnant cows [Table 1, category 1] : these are cows in the late stages of pregnancy that have been dried off in preparation for the birth of the calf and the new lactation. Young heifers pre-mating [Table 1, category 2] : these are the animals selected to form replacements and are between 3 and 15 months of age for herds that are calving at two years of age. Yearling heifers post-mating [Table 1, category 3] : these are the replacement stock that have been served and are between 15 months and 2 years of age.
Dairy beef animals
These two categories [Table 1, category 4] and [Table 1, category 5] refer to steers and heifers that are produced by the dairy cow and are being reared for beef production. Depending on the season of calving and finishing system there will be varying proportions of these two classes of stock.
Suckler beef animals
In Britain outwintering management is most commonly applied to pregnant, non-lactating spring calving cows [Table 1, category 6]. The nutrient requirements of these cows are relatively low and can be easily met by appropriate supplementation of the natural grass cover. It is less common to outwinter lactating autumn calving suckler cows [Table 1, category 7] as their nutrient requirements are higher and they have a young calf which is susceptible to adverse effects of the weather. Recently there has been renewed interest in outwintering young 6 month old spring born [Table 1, category 8] and yearling autumn born [Table 1, category 9] steers and heifers being raised for beef production.
Criteria for measuring impacts
Given the range of systems which can be outwintered, the next section provides a review of the possible impacts from these systems. This must be assessed against specific criteria for assessing sustainability, which follows the standard criteria set out by the Brundtland Commission (WCED, 1987) and we take the prime indicators of livestock management as proxies for environmental, economic and social sustainability.
Within the UK, the policy focus is now on sustainable production and consumption, with more targeted goals centred on a sustainable food and farming system (Defra, 2012) . This translates into a suite of regulatory and voluntary interventions, including research funding, that promotes best practice within the food supply chain, provides information for consumers and enhances the range of ecosystems services emerging from agricultural activity and food production and consumption. Accordingly, what follows is an attempt to translate these goals and concepts to the practice ofoutwintering, which represent an activity driven by the need for financial sustainability, but which adds significant pressure on a fragile set of ecosystems. These are categorised as grassland management, reflective of environmental dimensions, farm level finance, reflective of economic dimensions, and animal welfare impacts, reflective of social impacts.
3.0.Results
3.1.Grassland Management
Grassland plays an important role in the management of air and water pollution. The role of grasslands in terms of interaction with the environment is becoming increasingly apparent (Hooda et al. 2000;ADAS, 2007). This interaction includes both beneficial and detrimental effects. Grasslands act as a medium that exchange both energy and nutrients, but are also managed through human activity in a way that can result in major changes in nutrient and energy exchange.
3.1.1.Gaseous Exchange
Grasslands play an important role in the exchange of radiatively active gases (greenhouse gases) between the land surface and our atmosphere (Hynst et al., 2007;Soussana et al. 2007). Our understanding of this role has developed rapidly in recent years with the development of advanced micrometeorological techniques allowing continuous measurement of C exchange and measurements of other greenhouse gases (Sutton et al., 2007). Many grassland systems offer the opportunity to remove large amounts of CO2 from the atmosphere on an annual basis by photosynthesis (Rees et al., 2005). Grasslands exchange CO2 in two directions with the atmosphere, but the difference between net ecosystem loss (by respiration) and net C uptake (by photosynthesis) is defined as net ecosystem exchange (NEE), and provides a measure C sequestration potential by a particular system. Uptake of CO2 ranges from 0.07-to 4.5 t C ha-1 yr-1 in a range of studies recently reviewed (Rees et al. 130-54). There is however significant annual variability between uptake rates with studies indicating a fourfold variation as a result of climatic variability (Emmerich, 2004).
Grassland systems also play an important role in the exchange of other greenhouse gases. Thus in the UK grassland ecosystems are the single most important source of nitrous oxide, and where grazing animals are present, they also contribute to significant amounts of methane emissions. Nitrous oxide emissions can be particularly large where there are large inputs of fertiliser nitrogen, although emissions tend not to be evenly distributed across the country. Grasslands in wetter parts of the country in southwest England and West of Scotland tend to be particularly prone to large emissions (Jarvis et al., 2001; Jones et al.,2007). There is considerable uncertainty regarding the magnitude of N2O release from grasslands, however, we know that emissions tend to be geographically variable and unevenly distributed throughout the year. Particularly high emissions are associated with periods when there are high levels of available nitrogen in the soil to coincide with periods of soil wetness.
Grasslands can also act as a small source of methane (Yamulki and Jarvis, 2002), however, the major source is derived from ruminant livestock. Annual emissions from this source in Europe are variable, with a recent study reporting emissions from cut and grazed grasslands of between 11-140 kg CH4 y-1. Diet is known to be one of the factors influencing methane emissions (Vlaming et al., 2008). The amount of digestible nutrients contained in the diet appears to be directly linked to methane emissions (Jentsch et al., 2007), thus animals fed on lower quality feed that may be present in low input systems may have a higher CH4 emission per unit of intake, although emissions per unit area may be less than those in more intensively managed systems (Pinares-Patino et al., 2007).
The combined emissions of methane and nitrous oxide effectively offset the uptake of carbon through carbon sequestration. This is most clearly illustrated when the greenhouse gas budget of a grassland system is expressed on the basis of global warming potential (GWP) which expresses the warming potential of CO2, N2O and CH4 in units of CO2. A study of seven grassland systems across Europe showed that net ecosystem exchange varied between -13 – 419 g C m-1 y-1 (Soussana et al.,2007). However, when the emissions of N2O and CH4 were taken into account the carbon sink strength reduced by an average of 19%. The UK is known to have relatively high emissions of nitrous oxide on an European basis (Flechard et al., 2007), and mitigation options that can reduce these emissions are likely to make an important contribution to mitigation of UK greenhouse gas emissions.
Ammonia is an important pollutant in the UK, contributing to acidification and nutrient enrichment (Erisman et al., 2008). In 2007 there was a deposition of 289 tons of ammonia 91% of which originated from Agriculture (NAEI, 2007). Livestock farming is a particularly important source, with dairy farming becoming more important (Jarvis and Ledgard, 2002). Manure is the source of much of the ammonia emissions associated with livestock farming and therefore mitigation opportunities centre around improved manure management (Misselbrook et al., 2000).
3.1.2.Nutrient exchange
Many intensively managed grasslands receive large inputs of synthetic fertilisers, containing the elements nitrogen and phosphorus. Additional nutrients are added in the form of slurries and manures leading to higher total nutrient loadings. Although these nutrient inputs are controlled by the statutory regulations associated with NVZ regulations, and advisory recommendations, there remains a potential for significant nutrient loss to drainage water. These losses are most likely to occur in circumstances where the supply of nutrient inputs exceeds the demand by plants for nutrient uptake (Jarvis, 2000). This is most likely to occur during winter periods and plant growth is reduced, and excess rainfall will contributed to the leaching of nutrient elements from the soil. A study of slurry applications to grasslands in the autumn and winter has shown that N leaching losses over 4 years could vary between 0-50% of the N applied (Smith et al., 2002) In circumstances where heavy rainfall falls on already saturated ground, overland flow can contribute to nutrient inputs to river water systems are from sources that have bypass the normal drain flow (Petry et al., 2002). In such a circumstances the loss of surface applied slurries and manures poses a particular hazard to streams and rivers (McGechan, Lewis, and Provolo, 1998), and codes of good practice have been designed in order to try to minimise this risk.
The transfer of N to adjacent water bodies can be reduced by the use of grass buffer strips to which no applications of slurries or fertilisers are made, however these need to be at least 10 m in width and take account of local slope and drainage characteristics.
Grazed grasslands can represent a significant non-point source of P to river systems (Hawkins and Scholefield, 1996). Because soils can store large amounts of P, inputs from grazing livestock can sometimes be buffered, but, applications of livestock manures have been shown over the long term to increase losses (Sentran and Ndayegamiye, 1995).
Livestock systems pose a particular risk to the contamination of water by pathogens (Hooda et al., 2000) Overland flow associated with heavy rainfall events has been shown to be particularly important in contributing to the transfer of pathogens to surface water bodies (Vinten et al.,2004). The risk is more acute where grazing animals are depositing dung directly on fields than in circumstances where fields are treated with applications of slurry (Vinten et al. 2004). This appears to be a consequence of the decline in pathogen numbers with time in slurry stores, and their adsorption onto soil particles once applied to the field. Previous studies do however highlight the risk that is posed by grazing animals in an overwintering situation in circumstances where winter rainfall events could contribute to significant episodes of pollution.