Soil carbon and related soil properties along a soil type and land‐use intensity gradient, New South Wales, Australia

Abstract

The aim of this study was to systematically quantify differences in soil carbon and key related soil properties along a replicated land‐use intensity gradient on three soil landscapes in northwest New South Wales, Australia. Our results demonstrate consistent land‐use effects across all soil types where C, N and C:N ratio were in the order woodland > unimproved pasture = improved pasture > cultivation while bulk density broadly showed the reverse pattern. These land‐use effects were largely restricted to the near surface soil layers. Improved pasture was associated with a significant soil acidification, indicating that strategies to increase soil carbon through pasture improvement in these environments might also have associated soil degradation issues. Total soil carbon stocks were significantly larger in woodland soils, across all soil types, compared with the other land‐uses studied. Non‐wooded systems, however, had statistically similar carbon stocks and this pattern persisted whether or not carbon quantity was corrected for equivalent mass. Our results suggest that conversion from cultivation to pasture in this environment would yield between 0.06 and 0.15 t C/ha/yr which is at the lower end of predicted ranges in Australia and well below values measured in other cooler, wetter environments. We estimate that a 10% conversion rate (cultivation to pasture) across NSW would yield around 0.36 Mt CO2‐e/yr which would contribute little to emission reductions in NSW. We conclude that carbon accumulation in agricultural soils in this environment might be more modest than current predictions suggest and that systematically collected, regionally specific data are required for the vegetation communities and full range of land‐uses before accurate and reliable predictions of soil carbon change can be made across these extensive landscapes.

Variations in Soil Carbon Stocks with Texture and Previous Landuse in North-western NSW, Australia

“…The results most directly comparable with ours are those for Wilson et al (2011) who assessed the effect of land use on carbon levels of soils in the Northern Tablelands and Northwest Slopes of NSW. They present their results by 5 cm depth intervals allowing calculation of carbon density for 0-10 cm for comparison with our results.…”

“…Similar to the findings of Young et al (2005) and Wilson et al (2011), there was no interaction between soil texture and land use history, that is, the effects of land use were similar on soils of varying clay content.…”

Factors Controlling Soil Organic Carbon Stocks with Depth in Eastern Australia

“…Land use, as represented by LDI is shown to have a relatively low influence on SOC levels at this sub-continental scale, but it may be at least partly masked by the vegetation cover factor. Its influence appears to decline further with depth, similarly reported by others (Luo et al, 2010;Wilson et al, 2010Wilson et al, , 2011Allen et al, 2013;Badgery et al, 2013), Nevertheless the factor is still considered important in subsoils (Guo and Gifford, 2002;Wright et al, 2007;Meersmans et al, 2009;Follett et al, 2009;Vasques et al, 2010;Rumpel and Kögel-Knabner 2011). It has been suggested that SOC in deeper soil layers might reflect historic rather than current land use (Schulp and Veldkamp, 2008;Wilson and Lonergan, 2013).…”

“…It becomes the clearly dominant influence in the mid and lower layers. The importance of parent material in controlling SOC has also been reported by several recent workers (Mishra et al, 2012;Chaplot et al, 2010;Vasques et al, 2010;Powers et al, 2011;Wilson et al, 2011;Cotching, 2012;Badgery et al, 2013;Viscarra Rossel et al, 2014). Its influence is primarily due to its control of soil texture and clay content which serves to protect SOC from mineralization (Oades, 1988;Paustian et al, 1997;Baldock and Skjemstad, 1999;Baldock et al, 2009b;Heckman et al, 2009) and its control of soil fertility and nutrient supply to promote production of organic material (Badgery et al, 2013).…”

Change in Soil Organic Carbon Stocks under 12 Climate Change Projections over New South Wales, Australia

“…The maps deserve consideration during any climate change mitigation programs that are based on increased soil C sequestration (Lal et al, 2007;Wilson et al, 2011;Baldock et al, 2012;Smith, 2012). Those regions of NSW, where the soil C storage has been shown to have a declining trend, such as in the east and south, will require even greater C-enhancing actions to produce the desired soil C increases.…”