Qld Central Regional Summary

The region

The QLD Central agroecological zone extends from Copabella in the north to Tooma in the south. Rainfall in the zone ranges from > 1000 mm annum^-1 in the north-east to < 600 mm annum^-1 in the south-west of the zone and rainfall seasonality is generally summer dominant. Boundaries for the zone are shown in Figure 1.

Modelling regional practices

Producing models that reflect all farming practices throughout a region is difficult so “common practice” models for wheat, sorghum and chickpeas for the region were produced. A wheat crop with a 1.8 t ha^-1 yield and 40 kg of fertiliser N applied ha ^-1, a sorghum crop with a yield of 2.3 t ha^-1 with 49 kg fertiliser N ha ^-1 applied and a chickpeas crop with a yield of 1.1 t ha^-1 and 7 kg of fertiliser N ha ^-1 applied were modelled. The key assumptions of these models were that;

• Only one pass was made at sowing
• Split fertiliser applications were used for wheat and sorghum crops
• It was assumed that wheat had two fallow herbicide applications while sorghum and chickpeas had three fallow sprays. All crops had on in-crop herbicide application and one in-crop fungicide application.
• Stubble was retained

Impact indicators

Hydrogen ion impacts estimate the release of hydrogen ions to the soil associated with crop production. A negative value indicates a reduction in soil acidity whereas a positive value indicates an increase in soil acidity. Soil erosion is an estimate of soil loss that occurs during the production of the crop. The depth of soil lost will depend on many things but an approximate conversion is that 1.5 t of soil loss equals 1 mm of soil. Global warming impacts are the release of greenhouse gases to the atmosphere expressed as carbon dioxide equivalents (CO₂-e), Eutrophication impacts are the release of phosphorous to the environment and are expressed as phosphate equivalents and Particulate Matter impacts are the release of fine particles less than 2.3 micrometres in diameter.

Benchmark results

Results below in Table 1 show the environmental impacts of producing a t of wheat, sorghum or chickpeas in the region. An absence of lime use in the region resulted in an increase in free hydrogen ions in the soil for all crops and soil erosion was estimated at between 3.5 and 7.3 t soil loss t product^-1. Analysis indicated that Global warming impacts associated with the production of these crops ranged from between 171 and 386 kg CO₂-e, Eutrophication impacts ranged between 1.1 and 1.5 kg PO₄-e and Particulate Matter impacts ranged between 0.21 and 0.37 kg of < 2.3 µm particulate matter t product^-1.

Table 1: Hydrogen ion changes, soil erosion and Global Warming, Eutrophication and Particulate matter impacts associated with the production of wheat, sorghum and chickpeas in the Qld Central agroecological zone.

Greenhouse gas emissions

On-farm emissions sources of all three crops are shown below in Figure 2. For wheat and sorghum, the greatest contributions to the total Global Warming impacts were the production and use of fertiliser. The relatively low rates of fertiliser use for chickpea production meant that emissions from fertiliser production and use, residue emissions, tractor operation and chemical production made the greatest contributions to GLobal Warming impacts.

Greenhouse gas mitigation strategies

Mitigation strategies tested for the region were;

• Sustainable intensification
• Implementation of variable rate fertiliser technology
• Changing a wheat-wheat rotation to a legume-wheat rotation

More information on the assumptions used to test these strategies and how they might reflect individual enterprises are available on the Mitigation strategies page.

Results (figure 3 below) indicate that emissions of a t of wheat can be reduced by;

• 93% through the implementation of sustainable intensification
• 13% by implementation of variable rate fertiliser technology

Results also indicate the replacing a wheat crop with a legume crop in a two-crop rotation can increase greenhouse gas emissions intensity by 129%.

More information

Dr Aaron Simmons
Orange Agricultural Institute
1447 Forest Road
Orange NSW 2800
P: 02 63913894
E: aaron.simmons@dpi.nsw.gov.au