‘Hidden’ soil carbon at risk of erosion in the rangelands

Dr Susan Orgill1,2,3, Dr Cathleen Waters1, Dr  Craig Strong2

1NSW Department Of Primary Industries, Wagga Wagga, Australia, 2Fenner School, Australian National University , Acton, Australia, 3Graham Centre for Agricultural Innovation, Wagga Wagga, Australia

Wind erosion preferentially removes fine organic carbon (OC) and nutrient rich soil. Enriched dust can be transported long distances resulting in a net loss from the terrestrial ecosystem and reduced soil fertility, moisture holding capacity and soil aggregate stability which may feedback to promote more erosion. Changes in the structure and spatial distribution of vegetation associated with land management can accelerate soil erosion and carbon loss. This study was located in the semi-arid rangelands of western New South Wales (NSW) where over 2.7M ha of land has been contracted to sequester carbon (C) in woody vegetation under the Emission Reduction Fund. We investigated the location and form of OC within the soil matrix and assessed the capacity of soil to protect OC from erosion under different vegetation communities. Surface soil samples were collected from plots comprised of five replicates of three densities (high, medium and low) for Pine (Calitris glaucaphylla), Box (Eucalyptus populnea) and Mulga (Acacia aneura) communities. Soil samples (0-1 and 1-5cm) were dry and wet sieved, then each aggregate class was analysed for total OC (dry combustion) and OC fractions (MIR). Vegetation community significantly influenced aggregate stability, size distribution, SOC concentration and fractions, with Box communities having a higher degree of aggregation and SOC compared with Pine and Mulga. Box communities are located along drainage lines and these areas typically have higher soil moisture and nutrient content and typically accumulate water-transported sediment high in OC. The high concentration of SOC (specifically humic-OC) within the high proportion of <0.83mm (dry sieved) aggregates, and poor aggregate stability in the surface 1cm of all soils highlights the vulnerability of SOC to loss via erosion. Thus our results suggest it is important to account for potential loss of SOC (via wind erosion) when considering the quantum abatement in western NSW.


Biography: Dr Susan Orgill has worked in the field of soil management for NSW Department of Primary Industries (DPI) since 2005. Susan is based at the Wagga Wagga Agricultural Institute and leads the Soils South team. She is passionate about delivering industry and farm-ready research, and her research relates to strategies to increase organic carbon accumulation and storage, and nutrient cycling in agricultural soil.

SOIL ORGANIC MATTER

7th International Symposium
Soil Organic Matter

6 – 11 October 2019

Hilton Adelaide

Adelaide, South Australia

Australia

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