Driving efficiency – the key to reducing the carbon footprint of beef?
Climate change has been attributed to greenhouse gas emissions namely carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and chlorofluorocarbons (CFC). Figure 1 illustrates that methane is the predominant gas from beef production systems and contributes 70% of total emissions. Nitrous oxide from the spreading and storage of inorganic and organic fertiliser and the deposition of dung and urine during grazing contributes 30% of total emissions. Carbon dioxide is produced during the production and transport of feeds and fertilisers, but CO2 is also absorbed by grassland and forests (carbon sequestration). The cumulative effect of these gases on climate change is called the carbon footprint. Relative to other food products such as poultry/eggs/pigs and milk products, beef and sheep meat has a much higher carbon footprint. In view of the requirements of the UK Climate Change Committee where an 8.5% reduction in GHG emissions from Agriculture has been stipulated, the challenge facing beef producers is to reduce GHG emissions and carbon footprint. The aim of this report is to summarise data from modelling exercises undertaken at AFBI Hillsborough to evaluate the impact of adopting mitigation strategies on carbon footprint of beef production.
Figure 1. Sources of greenhouse gases emissions from beef production systems
Results based on a 500 kg steer, inorganic fertiliser application rate of
100 kg N per ha. All figures based on carbon dioxide equivalents (Dawson et al 2009).
Reducing the carbon footprint of beef
Two main mitigation strategies can be adopted to reduce the carbon footprint of beef production:
Maintaining high levels of animal performance
Management of soils and fertiliser
Systems which reduce age at slaughter and promote high lifetime growth rates will reduce carbon footprint. This is illustrated by the data from two modelling studies undertaken at AFBI Hillsborough. In the first study the performance and carbon footprint of bulls housed throughout their life and offered concentrates ad libitum or turned out to grass in their first summer followed by grass silage/ concentrate diet (50:50 on a dry matter basis) from housing until slaughter was compared with the carbon footprint of steers offered grazed grass during the summer and grass silage/concentrates during the winter. Bulls were slaughtered at 16 months of age and steers at 25 months of age. As shown in Figure 2, bulls had a superior performance relative to steers, produced a greater margin over feed costs (6-8 p per day) and had 43% lower of carbon footprint. The lower carbon footprint for bulls is mainly attributed to their higher growth rates, improved efficiency and resulting shorter production lifecycle. Of particular interest is that fact that the intensively finished bulls had a similar carbon footprint to the grass/grass silage fed bulls and a similar margin over feed costs. These results demonstrate that by ensuring that diets offered to beef cattle are of high quality irrespective of diet type - concentrate or forage-based diets, there is potential to achieve high levels of performance and lower carbon footprint from grass-based systems
Figure 2. Comparison of the performance of bulls (intensive and forage/concentrate) and steers (forage/concentrate)
In the second study the impact of improving dietary energy intake/quality on carbon footprint was determined. Figure 3 demonstrates that as quality of diet improved, growth rate increased and carbon footprint was reduced by 22%. This decrease is due to the shorter production cycle coupled with the better quality diet.
Figure 3. Effect of growth rate/energy intake on carbon footprint
2.Management of Soils and Fertiliser
Adoption of best management practices for soil and fertiliser management will reduce carbon footprint. A summary of the effect of a number of management practices on carbon footprint of beef production is presented in Figure 4. As the rate of nitrogen application increases, losses of nitrous oxide also increases, therefore one scenario by which nitrous oxide and thus carbon footprint can be reduced is by reducing inputs of inorganic fertiliser. Data from AFBI Hillsborough have shown that reducing inputs of inorganic fertiliser N by 50% reduces carbon footprint by 7%. However, it is important to note that reducing inorganic fertiliser N inputs will also decrease grass growth, which in turn reduces animal output per hectare and increases area required to maintain animal performance.
In addition to reducing fertiliser inputs it is also important to consider conditions when fertiliser is being sown. AFBI research has demonstrated that when conditions were wet in May, N2O-N emissions were up to three times greater from CAN [DEFINE] compared to the other N fertiliser forms. As a result losses of nitrous oxide under wet conditions can be up to three times greater than under average conditions which results in an increase in carbon footprint of 16%.
The beneficial effects on grass yield, N efficiency and inorganic fertiliser N savings through the application of slurry using trailing shoe technology relative to splash plate have been demonstrated by research at AFBI. The trailing shoe increases grass yield through improving N use and reduces the amount of inorganic fertiliser that needs to be applied by up to 44 kg per ha relative to slurry applied by the splash plate. On this basis, the potential benefit in terms of carbon footprint can be two fold. Firstly, through reducing inputs of inorganic fertiliser N and secondly through reducing greenhouse gas emissions. The saving in inorganic fertiliser N will result in a reduction in carbon footprint of 7%.
Inclusion of white clover in grass swards reduces carbon footprint by 19% through a reduction in greenhouse gas emissions associated with the manufacture of fertiliser N and direct emissions which occur during the spreading of inorganic fertiliser N.
Figure 4 Impact of soil and fertiliser management on carbon footprint of beef production systems
Research undertaken at AFBI has shown that application of cattle slurry by the splash plate method increased N2O-N losses when applied with liquid nitrate fertiliser compared with liquid nitrate fertiliser on its own. The study also demonstrated that applying cattle slurry 3 or 4 days before liquid nitrate fertiliser had no effect on N2O-N emissions and as the interval between cattle slurry and nitrate application decreased (2 days to zero) N2O losses increased. This research demonstrates that there is potential to reduce N2O losses by allowing an interval of at least three days between applying slurry by the splash plate method and liquid nitrate-containing inorganic fertiliser particularly under wet ground conditions. Further research is required to determine if the effects observed are the same when granular CAN is used or when alternative methods of spreading slurry are adopted.
A carbon sink removes CO2 from the atmosphere and stores carbon thus beneficially reducing carbon footprint. Examples of carbon sinks include grassland and forestry and as Northern Ireland beef production is based on grass-based systems there is considerable potential to make use of the ability of grassland to remove carbon from the atmosphere to reduce the carbon footprint of beef. The ability of grassland to remove CO2 from the atmosphere however depends on how it is managed. Reducing fertiliser N input, converting grass to grass/legume mixtures and moving from short duration leys to permanent grassland all increase carbon storage thus reducing carbon footprint. On the other hand intensification of nutrient poor grassland can led to carbon being released to the atmosphere. Changing land use can also affect the amount of carbon stored and moving from arable to grassland or grassland to forest increases the amount of carbon stored thus reducing carbon footprint, while moving from grassland to arable reduces carbon stored.
Systems which reduce age at slaughter and promote high lifetime growth rates will reduce carbon footprint. This will achieved by ensuring that diets offered to beef cattle are of high quality irrespective of diet type - concentrate or forage-based diets
As methane production is determined by dry matter intake, systems which reduce total dry matter intake will reduce carbon footprint. A reduction in dry matter intake coupled with increased or maintained performance will increase efficiency of production and reduce carbon footprint.
Management of soils and fertiliser
Nitrous oxide emissions and carbon footprint can be reduced by:
Reducing inorganic fertiliser N inputs
Avoiding spreading nitrate-containing inorganic fertiliser in wet conditions
Spreading slurry at least 3 days before applying inorganic fertiliser
Use of trailing shoe for slurry applications
Inclusion of clover in grass swards
by Lynne Dawson, Head of Beef Research, AFBI Hillsborough