NSW NW Qld SW Regional Summary

The region

The NSW NW Qld SW agroecological zone extends from north of Roma, Qld to Narromine, NSW in the south. Rainfall in the zone ranges from > 600 mm annum^-1 in the east to < 500 mm annum^-1 in the west and rainfall seasonality ranges from summer dominant in the north to seasonally neutral in the south. 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, barley and chickpeas for the region were produced. A wheat crop with a 1.8 t ha^-1 yield and 6 kg of fertiliser N applied ha ^-1, a barley crop with a yield of 1.5 t ha^-1 with 6 kg fertiliser N ha ^-1 applied and a chickpeas crop with a yield of 1.1 t ha^-1 and 4 kg of fertiliser N ha ^-1 applied were modelled. The key assumptions of these models were that;

• Only one pass was made at sowing
• All fertiliser was applied at sowing
• Four fallow sprays were used in all crops. One in-crop spray was applied to wheat and barley and two were applied to chickpeas. Wheat had one fungicide application and chickpeas had two, and chickpeas also had one pesticide 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, barley 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 6.0 t soil loss t product^-1. Analysis indicated that Global warming impacts associated with the production of these crops ranged from between 161 and 202 kg CO₂-e, Eutrophication impacts ranged between 0.7 and 1.1 kg PO₄-e and Particulate Matter impacts ranged between 0.14 and 0.21 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, barley and chickpeas in the NSW NW Qld SW agroecological zone

Greenhouse gas emissions

On-farm emissions sources of all three crops are shown below in Figure 2. For wheat and barley, the greatest contributions to the total Global Warming impacts were the production of fertilisers, residues, tractor operations and chemical production and use. In cnotrast with other regions, fertiliser use made a relatively minor contribution to Global Warming impacts. For chickpea production, emissions from crop residues and chemical production were the dominant source of Global Warming impacts and impacts associated with the production and use of fertiliser, and tractor operations were relatively low.

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;

• 83% through the implementation of sustainable intensification
• 44% by implementing 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 261%.

More information

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