Grains Research and Development

Date: 04.07.2016

Grain growers well set for positive greenhouse role

Author: Nikki Dumbrell, Elizabeth Meier, Marit Kragt, Peter Thorburn and Jody Biggs

Agriculture remains a target in the world’s push to reduce greenhouse gas emissions, but local studies show the industry here has ready-to-hand options that should not compromise production or profitability

Image of Nikki Dumbbell and Marit Kragt

Greenhouse gas reduction researchers Marit Kragt (left) and Nikki Dumbrell at the University of Western Australia.

PHOTO: Evan Collis

In research looking at ways to reduce cropping’s contribution to greenhouse gas emissions, common management practices such as no-till and stubble retention have emerged as ready-made tools. However, the extent to which these practices and other management changes help to reduce carbon dioxide and nitrous oxide emissions will vary across climate zones and soils.

Early results from a GRDC-supported joint CSIRO and University of Western Australia research project show that emissions reductions from practice changes are achievable, but growers will need to know which options are relevant in their region and the possible effects on profitability (Table 1).

Case study farm
Scenarios that reduce greenhouse gas emissions and ...
Decrease profitability
Maintain/increase profitability
Dalwallinu and
Kellerberrin
(Western Australia)
  • Retained stubble and 25% less N fertiliser
  • Retained stubble with opportunistic summer cropping with green manure legume
  • Retained stubble with opportunistic summer cropping and improved legume pastures in winter fallows
  • Retained stubble
  • Retained stubble and 25% more N fertiliser
  • Retained stubble with improved legume pastures in winter fallows
  • Retained stubble and feedlot manure applied at 5t/ha every five years
Wimmera
(Victoria)
  • Retained stubble with opportunistic summer cropping with green manure legume
  • Retained stubble with opportunistic summer cropping and improved legume pastures in winter fallows
  • Retained stubble with improved legume pastures in winter fallows
Southern Mallee
(Victoria)
  • Retained stubble with opportunistic summer cropping with green manure legume
  • Retained stubble with opportunistic summer cropping and improved legume pastures in winter fallows
  • Retained stubble
  • Retained stubble with improved legume pastures in winter fallows
  • Retained stubble and feedlot manure applied at 5t/ha every five years
Brigalow
(Queensland)
  • Retained stubble with short-term legumes as green manure crops in fallows
  • Retained stubble, N fertiliser applied at sowing (instead of four weeks prior to sowing)
  • Retained stubble with short-term legumes as green manure crops in fallows

The modelling study was part of the Carbon Farming Futures Filling the Research Gap project. It was conducted to predict the trade-offs between yield, farm profitability and greenhouse gas reductions under different management and conditions for representative case-study farms.

The research findings show a range of management practices can potentially reduce greenhouse gas emissions in the GRDC’s western, southern and northern regions.

Western region

In the western region, representative case-study farms were defined for the Dalwallinu and Kellerberrin areas. The modelling suggests that greenhouse gas reductions could come mainly from practices that help to increase carbon in the soil, namely:
  • retaining stubble;
  • using improved legume pastures instead of volunteer weedy pastures in winter fallows;
  • opportunistic summer cropping with a short-term green manure legume; and
  • regular applications of feedlot manure (if available).

The maximum predicted emissions reduction in these areas, compared to not retaining any stubble, is about 0.8 tonnes of carbon dioxide equivalents (CO2-e) per hectare per year over a 100-year period. For a 1000ha farm, this emissions reduction would offset the emissions produced from burning about 270,000 litres of diesel every year.

The costs of implementing practices to achieve emissions reductions vary. For example, improved pastures in crop rotations could increase farm operating profits by an average of $30/ha/year when averaged across all soil types and typical rotations. By comparison, summer cropping could reduce profits by $30 to $40/ha/year compared to baseline (current) practices (chemical fallows over summer). This is driven by higher costs associated with planting and managing the summer crop and lower yields for the subsequent winter crops.

The impact of manure on profitability also varies. Averaged over time, the results indicate the use of manure could help to at least maintain and potentially increase profitability in these case-study areas. However, there would be considerable year-to-year variability.

Southern region

In the southern region, representative case-study farms were established for the Wimmera and southern Mallee areas. In these regions, practices that help to both increase carbon input into the soil and reduce nitrous oxide emissions include:

  • retaining stubble;
  • using improved legume pastures instead of winter fallows;
  • opportunistic summer cropping with a short-term green manure legume; and
  • regular applications of feedlot manure (if available) on lighter soil types.

The maximum emissions reduction predicted in these areas, compared to not retaining any stubble, is about 1.0t CO2-e/ha/year over 100 years. For a 1000ha farm, this emissions reduction would offset the emissions produced from burning about 333,000L of diesel every year. Averaging across all soil types and typical crop rotations, improved pastures in place of fallows could increase profits by an average of $40 to $70/ha/year. On the other hand, a practice such as summer cropping could reduce profitability by $70 to $75/ha/year.

Adding manure or extra nitrogen fertiliser to crops can reduce greenhouse gas emissions by increasing the biomass of the plants, thereby increasing the soil organic matter. However, any potential yield (and revenue) benefits have to be traded off against the costs of purchasing and applying the manure and extra nitrogen.

Northern region

In the northern region, representative case-study farms were modelled for the Brigalow and Chinchilla areas. Results suggest that greenhouse gas reductions could come from efforts to reduce nitrous oxide emissions by the following changes in management:
  • applying up to 25 per cent less nitrogen fertiliser;
  • using short-term, green manure legume crops in place of fallows;
  • regular applications of beef or chicken feedlot manure (if available); and
  • nitrogen fertiliser applied at sowing instead of at four to six weeks prior to sowing.

Maximum emissions reductions predicted in these areas, compared to not retaining any stubble, are about 0.4t CO2-e/ha/year over a 100-year period. For a 1000ha farm this emissions reduction would offset the emissions produced from burning about 135,000L of diesel every year.

On non-irrigated lands, reduced nitrogen fertiliser rates are predicted to maintain profits relative to baseline management because yield losses would be offset by lower input costs.

On irrigated paddocks a reduction of nitrogen fertiliser rates leads to a reduction in profitability of about $120/ha/year because crop yields are reduced. Similar reductions in profitability ($110/ha/year) are predicted when short-term green manure crops are introduced in place of chemical fallows on non-irrigated lands.

Conclusion

Overall, the results show it is possible to reduce greenhouse gas emissions on Australian grain farms by adopting practices that increase soil carbon and/or reduce soil nitrous oxide emissions.

Additionally, the results show that feasible changes to farm practices (for example, retaining stubble or reducing over-fertilisation with nitrogen) can reduce net greenhouse gas emissions, and may not necessarily reduce profitability.

However, to achieve the maximum reductions stated in this article, more substantial changes to the system were required (for example, summer cropping) and tended to decrease farm operating profits to an extent that would not be covered by the average price paid for greenhouse gas reductions in the 2015 Emissions Reduction Fund auctions ($13.95 and $12.25 per tonne of CO2-e).

The greenhouse gas emissions reductions that can be achieved by changing practices will be site-specific and will vary with climate, soil type and crop rotations. Emissions reductions are also a trade-off between reductions in nitrous oxide and increases in soil carbon stocks. Because of these factors, it remains important to be engaged with local research and to be aware of any opportunities for grain growers to participate in future emissions reduction programs.

More information:

Elizabeth Meier,

elizabeth.meier@csiro.au

Nikki Dumbrell,
nikki.dumbrell@uwa.edu.au

The study is a Carbon Farming Futures Filling the Research Gap project funded by the Australian Department of Agriculture and Water Resources and the GRDC.

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