WA Eastern Regional Summary

The region

The WA Eastern agroecological zone is centered around Merredin and extends to Mount Gibson in the north and Narembeen in the south. Rainfall in the zone averages around 400 mm annum^-1 and rainfall seasonality is winter-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 and lupins for the region were produced. A wheat crop with a 1.0 t ha^-1 yield and 13 kg of fertiliser N applied ha ^-1 and a lupins crop with a yield of 0.4 t ha^-1 and 2 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 canola crops
• It was assumed that wheat and lupins crops had two fallow sprays. Wheat and lupins had one in-crop herbicide and lupins also had one pesticide application.
• Stubble was retained
• Lime was applied at the equivalent rate of 4 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 or lupins 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 5.6 and 12.2 t soil loss t product^-1. Analysis indicated that Global warming impacts associated with the production of these crops ranged from between 351 and 418 kg CO₂-e, Eutrophication impacts ranged between 1.7 and 2.1 kg PO₄-e and Particulate Matter impacts ranged between 0.45 and 0.46 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 and lupins in the WA Eastern agroecological zone.