Elsevier

Livestock Science

Volume 147, Issues 1–3, August 2012, Pages 126-138
Livestock Science

The effect of future climate scenarios on the balance between productivity and greenhouse gas emissions from sheep grazing systems

https://doi.org/10.1016/j.livsci.2012.04.012Get rights and content

Abstract

Maintaining the supply of pasture based meat products such as lamb is likely to be challenged by warmer and drier future climatic conditions across southern Australia, whilst also minimising greenhouse gas (GHG) emissions. The aim of this study was to assess the effect of future climate scenarios on the balance between productivity and GHG emissions from sheep grazing systems. This study simulated sheep grazing systems at four sites that represented a range of climatic zones, soil and pasture types in southern Australia. This study used a biophysical and mechanistic whole farm system model (Sustainable Grazing Systems Pasture Model) to simulate the interactions between climate, soil properties, pasture species and a grazing animal on a daily time-step. Historical climate data were obtained from the years 1961 to 2000 (baseline climate) and for three future climate scenarios in the years 2030 and 2070 (with low and medium rates of warming), which were created using projected changes in the baseline climate; representing progressively warmer conditions. A dryland (i.e. rainfed) perennial pasture, characteristic of the region, was modelled at each site. Rules with regard to grazing management and supplementary feeding remained consistent in all simulations so comparison could be made. All sites lambed during the winter, with lambs removed from the system when weaned at 120 days of age. Simulated estimates of pasture intake, supplementary feed and lamb live weight at weaning were used to evaluate productivity. The annual net GHG emissions produced by the grazing system were estimated and expressed in carbon dioxide equivalent (CO2-eq.) emissions per hectare and per kg of lamb live weight at weaning. Stocking rates imposed at each site reflected the long-term carrying capacity of the grazing systems during the baseline years, which ranged from 11 to 15 sheep/ha across locations. This study showed that sites where the projections for declining rainfall were highest in future climate scenarios and simulated with C3 temperate pasture species, predicted lower pasture intakes and lamb live weights at weaning in future climates. At sites where future predicted rainfall declines were lower, pasture intakes and the live weight of lamb produced at weaning were maintained. The CO2-eq. emissions/ha (ranging from 4.1 to 5.6 t CO2-eq./ha) and per unit product (ranging from 11.0 to 21.7 kg CO2-eq./kg lamb live weight) across sites studied and across climate scenarios can potentially be minimised by maintaining a productive pasture base and lamb production. With warming, a site with a C4-based pasture system became significantly more productive and with a lower GHG emissions intensity, whereas some grazing systems may need to adapt their pasture-base to maintain productivity and minimise emissions intensity in the future. Within grazing systems, the N2O emissions by denitrification may become more significant as a result of warming. This study highlighted that the productivity and emissions changes of a grazing system in future climates are heavily dependent on the predicted climate, pasture species and the type of soil.

Introduction

Australia's grazing industries may need to adapt to maintain productivity under climatic change (Howden et al., 2008). Historically, the climate in southern Australia is highly variable and pasture systems have had to adapt to be resilient to the inter-annual variability (Chapman et al., 2009, Cullen et al., 2009). Typically, sheep grazing systems in the area are of low resource input and are heavily reliant on pasture as an affordable source of nutrients. Any nitrogen (N) inputs largely come from legume fixation, with supplementary feed being used to fill gaps in pasture supply. Howden et al. (2008) proposed that climate and atmospheric changes, as well as soil type and pasture species, are likely to further impact on the quality, quantity and reliability of forage production in the region. Given the uncertainties associated with future climate projections, estimates are for average daily temperatures to rise by up to 5 °C by 2070 in some regions of southern Australia and annual rainfall to change by −30 to +5% (CSIRO and BoM, 2007). The resilience of rainfed pastures is dependent on the current climate and future changes in temperature, rainfall and atmospheric carbon dioxide (CO2) (Cullen et al., 2009). The rise in temperature and increased atmospheric CO2 concentration should increase leaf photosynthetic potential, decrease plant N content and reduce stomatal conductance (Long et al., 2004). The increase in daily temperatures and elevated atmospheric CO2 concentration should make conditions more favourable for C4 grass species, which are more heat tolerant, cold sensitive and deeper rooting than C3 species; however, C4 grasses are generally less digestible than C3 grasses due to their relatively high fibre content (Howden et al., 2008). There is increasing interest in using tropical C4 grasses such as kikuyu (Pennisetum clandestinum) across southern Australia (Evergraze, 2008), which may have an impact on productivity and GHG emissions.

The main GHG emitted by livestock systems include methane (CH4), nitrous oxide (N2O) and CO2. Sources of CO2 emitted from livestock systems are mainly associated with fertiliser production, processing activities, electricity and fossil fuel use from the manufacturing and transport of agricultural inputs and products (Biswas et al., 2010, West and Marland, 2002). System CH4 emissions are produced by microorganisms called methanogens as a by-product of anaerobic fermentation via enteric or manure sources (McDonald et al., 1995). Nitrogen inputs, such as manure, can contribute to N2O being directly emitted by denitrification of nitrate or indirectly by denitrification of nitrogen lost in leaching, runoff or NH3 volatilisation (de Klein and Eckard, 2008). In Australia, agriculture contributes 16% (88 Mt CO2-eq.) of total emissions reported in the National Inventory (DCCEE, 2009). Agriculture is the dominant source of both CH4 and N2O emissions nationally, which account for 59% and 86% respectively of the net national emissions of these GHGs (DCCEE, 2009).

The loss of nutrients that contribute to GHG emissions from a system can be evaluated by assessing the CO2-eq. emissions associated with production. The amount of CO2-eq. emissions are often expressed per unit product and/or per unit area (i.e. emissions intensity, Guinée et al., 2002). There are few published studies that have investigated the influence of geographic location on the relationship between animal productivity and associated greenhouse gas emission intensity in a changing climate.

The objectives of the present study were to quantify the net effects on sheep grazing systems in southern Australia of future climate scenarios on (1) total annual pasture intake, supplementary feed intake and lamb live weight at weaning per hectare, and (2) the net CO2-eq. emissions/ha and per kg lamb live weight at weaning for sites with different climatic zones, soil types and pastures using a whole farm system model.

Section snippets

Sites simulated

The productivity and CO2-eq. emissions from sheep grazing systems were modelled at four sites in southern Australia (Table 1). The four sites studied were chosen to represent a range of climatic zones and soil types in the region. Regionally specific dryland (i.e. rainfed) perennial pasture systems were modelled at each site characteristic of the region, which was based on sites used in the Sustainable Grazing Systems (SGS) Program. The SGS Program, which investigated various aspects of

Feed intake and productivity

Sheep at Albany on the kikuyu/subclover pasture had on average a higher annual total feed intake compared to the other sites studied across climate scenarios (averaging 0.45–0.47 t DM yr−1 compared to 0.41–0.44 t DM yr−1 respectively; Table 3). Due to the management of supplementary feed in the simulations, all the grazing systems maintained the daily live weight of a ewe between 55 and 64 kg over a year, depending on level of feed intake. Fig. 1 shows that the average annual pasture intake of a ewe

Discussion

The simulation results presented indicate that pasture systems that can continue to be productive in warmer and drier climates have the potential to maintain lamb production and this should be linked to lower GHG emissions intensity per ha and per unit of lamb production (Fig. 3, Fig. 4, Fig. 5). This is illustrated by a comparison of the Albany and Dookie sites. At Albany the kikuyu based pasture increased pasture intake in future climate scenarios, which maintained productivity of lamb live

Implications

If the future brings warmer conditions, then this study showed that some pasture systems in southern Australia may have to adapt both pasture species and the grazing system to remain productive. The C3-species grazing systems may benefit from the inclusion of a pasture species that is more tolerant of warmer and drier conditions in the future to help maintain pasture supply, which may not necessarily mean higher emissions intensities per ha or per unit product. As expected, higher rainfall

Conflict of interest statement

There is no conflict of interest associated with this work.

Acknowledgements

This work was supported by funding from the Dairy Australia, the Meat and Livestock Australia and the Australian Government Department of Agriculture, Fisheries and Forestry under its Australia's Farming Future Climate Change Research Program.

References (54)

  • T.O. West et al.

    A synthesis of carbon sequestration, carbon emissions, and net carbon flux in agriculture: comparing tillage practices in the United States

    Agric. Ecosyst. Environ.

    (2002)
  • M.H. Andrew et al.

    The Sustainable Grazing Systems National Experiment: 1. Introduction and methods

    Aust. J. Exp. Agric.

    (2003)
  • Ash, A.J., Prinsen, J.H., Myles, D.J., Hendricksen, R.E., 1982. Short-term effects of burning native pasture in spring...
  • M.J. Bell et al.

    Modelling methane output from lactating and dry dairy cows

  • K.L. Blaxter et al.

    Prediction of the amount of methane produced by ruminants

    Br. J. Nutr.

    (1965)
  • P. Boeckx et al.

    Estimates of N2O and CH4 fluxes from agricultural lands in various regions in Europe

    Nutr. Cycling Agroecosyst.

    (2001)
  • D.F. Chapman et al.

    Effect of grazing method and fertiliser inputs on the productivity and sustainability of phalaris-based pastures in Western Victoria

    Aust. J. Exp. Agric.

    (2003)
  • D.F. Chapman et al.

    Interannual variation in pasture growth rate in Australian and New Zealand dairy regions and its consequences for system management

    Anim. Prod. Sci.

    (2009)
  • CSIRO and BoM, 2007. Climate change in Australia. Technical Report, 2007. (Eds. Pearce, K.B., Holper, P.N., Hopkins,...
  • B.R. Cullen et al.

    Simulating pasture growth rates in Australian and New Zealand grazing systems

    Aust. J. Agric. Res.

    (2008)
  • B.R. Cullen et al.

    Climate change effects on pasture systems in south-eastern Australia

    Crop Pasture Sci.

    (2009)
  • R. Dalal et al.

    Nitrous oxide emission from Australian agricultural lands and mitigation options: a review

    Aust. J. Soil Res.

    (2003)
  • DCCEE (Department of Climate Change and Energy Efficiency), 2009. National Inventory Report 2007—volume 1. The...
  • C.A.M. de Klein et al.

    Targeted technologies for nitrous oxide abatement from animal agriculture

    Aust. J. Exp. Agric.

    (2008)
  • Evergraze, 2008. Growing kikuyu for summer feed and soil cover. Accessed March 15, 2012....
  • J.F. Graham et al.

    SGS Animal Production Theme: effect of grazing system on animal productivity and sustainability across southern Australia

    Aust. J. Exp. Agric.

    (2003)
  • T. Granli et al.

    Nitrous oxide from agriculture

    Norw. J. Agric. Sci.

    (1994)
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