The three-year National Grains Project benchmarked the greenhouse gas (GHG) emissions intensity of key grain crops across Australia
Consumer demand to understand grain production’s environmental impacts, the introduction of non-tariff trade barriers and the political drive to meet Australia’s Paris Agreement commitment to emissions reduction will inevitably affect future grain production.
The New South Wales Department of Primary Industries, in collaboration with CSIRO and consultancy Lifecycles, has completed a GRDC-funded project to benchmark the environmental impact of key grain crops for 14 GRDC agroecological zones.
The impact of wheat production was benchmarked for all zones, with further benchmarks developed for other cereals, oilseeds and legumes where applicable.
This work is important because it puts the Australian grains industry on the front foot. Australia’s grain production systems are comparatively efficient so rather than having cropping products allocated a global default value for impact, Australia now has data to support its claims of environmental stewardship.
The project engaged with growers, farm groups, agribusiness and agronomists for the collection of typical agronomic data (inputs and yield data) for cereals, oilseed and legumes. This data was then built into a framework known as life-cycle assessment (LCA), which can be used to benchmark the environmental impact of crops, but is best suited to estimate the environmental impacts of proposed changes to production systems. For this project LCA was first used to estimate the ‘cradle-to-farmgate’ greenhouse gas (GHG) emissions intensity of:
- producing a tonne of crop; and
- the production, transport and use of all inputs and on-farm processes to produce a tonne of grain.
Emissions intensity benchmarks
Many GHG are emitted to the atmosphere, but total emissions are expressed in carbon dioxide equivalents (CO2-e).
Emissions associated with wheat production ranged from 500 kilograms CO2-e per tonne of wheat in the north-east NSW/south-east Queensland zone to 197kg CO2-e per tonne of wheat in the north-west NSW/south-west Queensland zone (Figure 1).
- Ranges of emissions intensity for other crops were between:
- 333 to 361kg CO2-e per tonne of sorghum;
- 167 to 260kg CO2-e per tonne of barley; and
- 74 to 351kg CO2-e per tonne of legume.
In comparison, wheat production in New Zealand has been estimated to emit 1000kg CO2-e per tonne.
Figure 1 Kilograms of carbon dioxide equivalents (CO2-e) emitted per tonne of wheat for 14 agroecological zones.
SOURCE: NSW DPI
Breaking down GHG emissions sources allowed the activities that make the largest contribution to overall emissions intensity to be identified.
Data from the production of wheat, barley and field peas in the NSW Central zone (Figure 2) show that where nitrogen fertilisers are used (such as for wheat) the production, transport and use of these fertilisers make the greatest contribution to the overall emissions intensity.
Where nitrogen fertiliser use is minimal (such as for field peas) emissions associated with fertiliser production, transport and use make a relatively minor contribution to emissions intensity.
Emissions in these crops are primarily associated with crop residues, tractor operations and lime use and production. For lupins, this is in part due to lower yields condensing these emissions and also because legume crop residues have a lower C:N ratio that results in more nitrous oxide (N2O) emissions from residue breakdown.
However, the study also showed that lupins could increase the intensity of GHG emissions, from a global perspective, if the wheat production they replaced in Australia was picked up by less efficient wheat producers elsewhere in the world.
The project also used LCA to assess the climate-mitigation potential of four management strategies for wheat production.
The method used to assess potential climate-mitigation strategies considered global outcomes of management changes. For exampe, if a government decided to implement a policy that reduced a particular crop output, it was assumed this would be picked up elsewhere in the world if consumer demand remained for that production.
Mitigation strategies in the study were selected because they were either implementable with current capital assets or were newer technologies already being adopted by growers. The four strategies were:
- sustainable intensification: examining the climate-mitigation impact of closing the yield gap for each zone;
- additional lime applications (in zones with acid soils): assuming that doubling the frequency of lime applications would result in an average yield increase of 20 per cent;
- implementation of variable-rate (VR) fertiliser technology: assuming yields are maintained with 20 per cent less nitrogen fertiliser inputs; and
- changing to a wheat/legume/wheat rotation: changing a wheat/wheat rotation to a wheat/legume rotation assumed the most common legume grown in the region replaced a wheat crop in the first year of the two-year rotation and that the second wheat crop received a 20 per cent yield increase due to the nitrogen biologically fixed by the legume crop.
Trends in mitigation potential were consistent across all zones with these strategies.
Data for the Western Australian Central zone showed that, relative to wheat production, sustainable intensification, VR fertiliser implementation and additional lime applications reduced the emissions associated with a tonne of wheat by 80, 34 and 26 per cent, respectively.
Replacing a wheat crop with a lupin crop, however, increased the emissions intensity of producing a tonne of wheat by 123 per cent if local wheat production was taken up by low-efficiency producers elsewhere.
Data for the Queensland Central zone showed that sustainable intensification and implementation of VR technology reduced the emissions associated with wheat production by 93 and 30 per cent, respectively, and that replacing a wheat crop with a chickpea crop increased the emissions intensity of wheat production by 129 per cent.
Vertesols that are alkaline are primarily used for cropping in this region so additional lime applications were not included as a mitigation strategy.
Sustainable intensification and additional lime applications were considered mitigation strategies because increasing wheat yields diluted the emissions associated with lime use, crop residues, tractor operations and also avoided wheat production shifting elsewhere in the world. Avoiding this is important because Australian wheat production systems are comparatiely more efficient.
This is why, in the study, replacing a wheat crop with a legume crop increased the emissions intensity of wheat primarily because growing a legume crop meant displacing local wheat production to a comparatively inefficient production system elsewhere in the world.
However, this does not mean legume crops should be taken out of rotations because they have other wider benefits. Legumes, for example, provide disease breaks that are vital to healthy wheat production systems.
The implementation of variable fertiliser was a mitigation strategy because it reduced the GHG emissions associated with the production, transport and use of nitrogen fertilisers.
The financial viability of these mitigation strategies was not assessed because it would differ for each enterprise based on variables such as debt, climate and soil type.
GRDC Research Code DAN00186
Dr Aaron Simmons
0418 259 550