Crop sequences in Western Australia: what are they and are they sustainable? Findings of a four-year survey

A survey was conducted of commercial broadacre paddocks in the south-west cropping zone of Western Australia from 2010 to 2013. In total, 687 paddock years of data were sampled from 184 paddocks. The land use of each paddock was recorded together with measurements of weed density, the incidence of soilborne pathogen DNA, and soil inorganic nitrogen (nitrate and ammonium). The dynamics of these biophysical variables were related to the crop and pasture sequences employed. Wheat was the most frequent land use (60% of paddock years), followed by canola and pasture (12% each), and lupins and barley (6% each). Four crop species, wheat, canola, barley and lupins, accounted for 84% of land use. By region, wheat, canola, barley and lupin accounted for 90% of land use in the Northern Agricultural Region (NAR), 83% in the Central Agricultural Region (CAR) and 78% in the Southern Agricultural Region (SAR). Conversely, pasture usage in the SAR was 21%, compared with 12% in the CAR and 7% in the NAR. Over the surveyed paddocks, weed density, soilborne pathogens and soil N were maintained at levels suitable for wheat production. The inclusion of land uses other than wheat at the frequency reported maintained the condition of these biophysical variables.