Matthew Harrison, uTas, August 2024
With global temperature rise likely to exceed 1.5oC by 2050, interest in the development of skills, practices and technologies for removing carbon dioxide to avoid dangerous climate change abounds. One way to do this is via improved storage of soil organic carbon (SOC), as incremental gains in soil carbon at scale can have massive effect on residual CO2 circulating in the atmosphere.
Surprisingly however, even though Australian rangelands comprise over 70 per cent of the continent, little knowledge of existing storage and practices for improving soil carbon in rangelands exists. Recent research suggests that there is a distinct lack of measured SOC data in Australian rangelands.
The research found that:
- Stratified random sampling yields significantly more power and higher accuracy than random sampling per se. This means that costs of sampling soil carbon are likely to be lower for stratified sampling for the same levels of accuracy;
- On hilly terrain, sampling mid-slope yielded reliable estimates of soil carbon across the entire slope (from top to bottom of the hill);
- Higher fertility soils (addition of phosphorus) improved soil carbon at depths of up to 300 mm from the soil surface;
- Addition of phosphorus improved soil carbon homogeneity across paddocks (with nil fertility being most variable in soil carbon);
- A process-based model (accounting for N, P and C) reduced the number of physical samples required to detect change in SOC over time;
- For rangelands, sowing more productive grasses or legumes increased SOC, at a rate dependent on baseline soil condition and nitrogen (N) status;
- Prolonged high stocking intensity was associated with net loss of SOC relative to conservative stocking;
- Destocking or exclusion of grazing results in small increases in SOC, especially in degraded sites;
- Conversion of cropping land to permanent pasture results in SOC sequestration, influenced by management history and baseline condition;
- Rotational grazing strategies indicate negligible impact on SOC stocks relative to continuous grazing; and
- Waterponding increases SOC stocks initially, but persistence beyond five years is not known
Find the research here: