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