Information

Level 4 Data summaries and links to related documents and reports (Brigalow  RS catchment study)

Key findings (brief)

  • Thornton et al. (2007) found total annual runoff increased to 11% and 9% of annual rainfall in the cropping catchment and pasture catchment respectively (average annual runoff in the virgin state is 5% of annual rainfall).
  • Radford et al. (2007) observed a decline in crop production per year by 20% between 2 successive 10-year periods.
  • Grain yield from 14 winter crops without added nutrients declined significantly in 20 years from 2.9 to 1.1 t/ha/year on the upper-slope clay soil (92 kg/ha/year) and from 2.4 to 0.6 t/ha/year on the Sodosol (88 kg/ha.year).
  • The grazed site had an initial pasture dry matter on offer of 8 t/ha which halved 3 years after clearing, and a decline in cattle liveweight gain of 4 kg/ha/year was observed over an 8-year period with constant stocking of 0.59 head/ha.
  • Thornton et al. (2012) found that subsequent reductions in soil chloride under cropping were only significant in the upper clay soil, while under pasture, no further significant change occurred.
  • Chloride mass balance analysis indicates deep drainage of 0.17 mm/year for clay soils and 0.26 mm/year for Sodosols under virgin brigalow scrub. These drainage rates increased during the land development phase to 59 mm/year for C2 and 32 mm/year for C3.

Table 1. Suspended sediment and nutrient export rates for Theodore (Titmarsh et al. 2009).

Catchment

Suspended sediment export rate kg/ha/mm

Average suspended sediment concentration, g/L

Total Nitrogen export rate, g/ha/mm

Average Total Nitrogen concentration, mg/L

Total Phosphorous export rate

g/ha/mm

Average Total Phosphorous concentration, mg/L

Theodore – Brigalow C1

14.2

1.4

134.1

7.8

6.2

0.4

Theodore – Brigalow C2

30.6

2.0

71.2

7.2

13.5

1.1

Theodore – Brigalow C3

19.9

0.8

28.6

2.3

3.8

0.4

Key table and figures extracted from data, literature, and miscellaneous publication

Various clippings

 

Level 1, level 2, level 3 and level 5