Dr Susan Orgill1,3, Dr Jason Condon1,3, Dr Mark Conyers1,3, Dr Belinda Hackney1,3, Ms Joanna Powells2
1NSW Department Of Primary Industries, Wagga Wagga, Australia, 2South East Local Land Services , Cooma, Australia, 3Graham Centre for Agricultural Innovation, Wagga Wagga, Australia
Well-managed perennial pastures are thought to represent the maximum opportunity for agricultural soils to accumulate organic carbon (OC), but in southern Australia does climate variability override this potential? Despite the considerable efforts over the past decade to collect field information on the influence of land management on OC stocks, few studies have monitored temporal changes in OC stocks under permanent pastures. A field survey of 31 permanent pastures (mean age 31 years) in the Monaro region of south-eastern Australia compared the influence of recent climate on SOC stock and soil properties to 0.70m. Baseline samples were collected in 2009, during the Millennium Drought that southern Australia experienced from late 1996 to mid-2010. Sites were resampled in 2012 and 2015 following the record high annual rainfall as a consequence of La Niña, then again in 2018 when the region was experiencing drought. There was a significant (P<0.05) increase in the stock of OC in the 0 to 0.30 m soil layer (based on an equivalent mass of soil) when the 2012 and 2015 survey data were compared with the 2009 baseline, and mean carbon (C) sequestration rates of over 2 Mg C/ha/yr. However, these increases were not sustained in when sites were revisited in 2018. While the increase in OC stocks from 2009 to 2015 corresponded with an increase in annual rainfall, the concentration of OC was also positively and significantly (P<0.05) correlated with total nitrogen (N) and available sulfur (S). Similar to other studies, there was a positive trend between the concentration of OC and available phosphorus (P), however this was not significant. These results suggest increases in SOC concentration are more responsive to seasonal conditions than management factors for temperate pastures in southern Australia, and importantly highlight the vulnerability of such rapid SOC accumulation under a variable climate.
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.