NSW Central Regional Summary

The region

The NSW Central agroecological zone extends from Cobar in the north, Deniliquin in the south and Dareton to the west. Rainfall in the zone ranges from > 500 mm annum^-1 in the east to < 400 mm annum^-1 in the west and rainfall seasonality ranges from winter-dominant in the south to seasonally neutral in the north. 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 field peas for the region were produced. A wheat crop with a 2.2 t ha^-1 yield and 30 kg of fertiliser N applied ha ^-1, a barley crop with a yield of 2.3 t ha^-1 with 7 kg fertiliser N ha ^-1 applied and a field peas crop with a yield of 1.6 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.
• Split fertiliser applications were used for wheat crops
• Three fallow sprays were used in wheat and field pea crops and two fallow sprays were used in barley. Two in-crop sprays were applied to wheat and one each to barley and field peas. One pesticide application was applied to field peas.
• Stubble was retained
• Lime was applied at the equivalent rate of 2 t ha^-1 every decade and incorporated through scarification

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 field peas in the region. Lime use in the region resulted in a reduction in free hydrogen ions in the soil for all crops and soil erosion was estimated at between 4.3 and 4.5 t soil loss t product^-1. Analysis indicated that Global warming impacts associated with the production of these crops ranged from between 102 and 283 kg CO₂-e, Eutrophication impacts ranged between 0.9 and 2.0 kg PO₄-e and Particulate Matter impacts ranged between 0.12 and 0.26 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 field peas in the NSW Central agroecological zone.

Greenhouse gas emissions sources

On-farm emissions sources of all three crops are shown below in Figure 2. For wheat, the greatest contributions to the total Global Warming impacts were the production and use of fertiliser. Residue emissions also made a considerable contribution to Global Warming impacts. The relatively low rates of fertiliser use for barley and lupins production meant that residue emissions were the dominant source of Global Warming impacts for these crops and that impacts associated with the production of fertiliser, tractor operations and chemical production were relatively high.

Greenhouse gas mitigation strategies

Mitigation strategies tested for the region were;

• Sustainable intensification
• Additional applications of lime
• Variable rate fertiliser applications
• 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;

• 42% through the implementation of sustainable intensification
• 17% by additional lime applications
• 14% 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 149%.

Figure 3 Reductions in greenhouse gas emissions for wheat production when grown with sustainable intensification, variable fertiliser, additional lime applications and legume - wheat mitigation strategies in the NSW Central agroecological zone

More information

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