Impacts of Rotational Grazing on Soil Carbon in Native Grass-Based Pastures in Southern Australia

PLoS ONE - Jonathan Sanderman et al.

Type: Research Paper
Knowledge level: Advanced

Farm Table says:

The authors conclude: "The evidence from this study suggests that in the short to medium term (< 15 years) measurable gains in SOC with adoption of rotational grazing in similar eco-climatic zones should not be expected to be observed. While we did not detect positive trends in SOC over time, NDVI data indicated that plant production was increasing slightly under rotational relative to continuous grazing."

What is the problem?

Interest in maintaining and enhancing soil organic carbon levels is high. The authors note, “Halting or reversing the decline in SOC in agricultural soils is seen as a win-win policy because of the dual benefits to soil sustainability/production and greenhouse gas abatement. Due to this fact, many nations are actively promoting management strategies that have the potential to sequester carbon.”

They state that the evidence to support improvement of SOC levels with the adoption of rotational grazing exists, but the field evidence for carbon sequestration is inconsistent. Therefore, this study sought to understand if rotational grazing (relative to continuous grazing) of remnant native grass-based pastures result in increases in SOC levels.

What did the research involve?

  • 20 landowners identified as having adopted rotational grazing practices in last 5-15 years in upper and mid-north of South Australia
  • Rainfall varies from 310 to 570mm / year
  • Pasture dominated by native perennial grasses (spear grass, wallaby grass) and annual grasses (wild oats, silver grass and brome grass)
  • 12 rotationally grazed paddocks were chosen based on: livestock had been managed consistently for at least 7-10 years, and nearby continuously grazed paddock on same soil type and landscape position was available.
  • Paddock information and management histories were collected
  • Climate data for 1980-2011 for each site extraced
  • Pasture productivity estimated using NDVI index
  • Refer to additional methodology steps in full paper.

What were the key findings?

  • Reality is that there are a myriad of implementations of each of these management practices (rotational and continuous grazing).
  • Cluster analysis demonstrated that there is a group of farmers who practice a more continuous form of rotational grazing (e.g., lower stocking rate and more grazing days than other rotational graziers) or a more rotational form of continuous stocking (e.g., multiple or longer rest periods).
  • Pasture productivity, as assessed by the mean annual summed NDVI over the number of years of rotational grazing implementation, was no different between the two management classes
  • However, a significant positive trend suggesting that under rotational grazing productivity can increase relative to continuous grazing.
  • Productivity has been found to increase through the implementation of rotational grazing, from both a pasture and livestock production perspective, although the experimental evidence is mixed.
  • Across all sampled paddocks, there were no significant differences for SOCeq or SOC0-10between management categories.
  • A finding suggests that amongst the rotationally grazed sites the sites with the strongest grazing pressure showed the greatest SOC response

Note: This project was supported by funding from the Australian Department of Agriculture, CSIRO Sustainable Agriculture Flagship and Rural Solutions South Australia. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

2015 - Australia - PLoS ONE - Jonathan Sanderman et al.
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