Abstract. Increasing salinity (high levels of water-soluble salts) and sodicity (high levels of exchangeable sodium) are serious land degradation issues worldwide. In Australia, salinity and sodicity affect a large proportion of the landscape and often coincide with agricultural land. Despite the areal extent of salt-affected soils, both worldwide and in Australia, few data exist on soil organic carbon (SOC) stocks in these areas. For this study, the level of SOC was determined in scalded (bare areas without vegetation), scalded-eroded, vegetated, and revegetated (i.e. sown pasture) soil profiles from 2 sites in the Southern Tablelands region of New South Wales, Australia. SOC concentration was significantly higher in the profiles that were vegetated with native pasture (1.96-2.71% in the 0-0.05 m layer) or revegetated with sown pasture (2.35% in the 0-0.05 m layer), and lower in those profiles that were scalded (1.52% in the 0-0.05 m layer) or scalded-eroded (0.16-0.30% in the 0-0.05 m layer). These lower SOC levels are reflected throughout the profiles of the scalded and scalded-eroded soils. The soil carbon stocks to 0.30 m are also much lower in the scalded and scalded-eroded soils that have been affected by salinity and sodicity. The profiles that were vegetated with native pasture had carbon stocks to 0.30m of 35.2-53.5 t/ha, while the sown pasture had 42.1 t/ha. This compares with the scalded profiles with 19.8 t/ha and the scalded-eroded profiles with 7.7-11.4 t/ha to 0.30 m. The presence of vegetation ameliorates several soil properties and results in the differences in SOC and other soil properties between scalded and vegetated profiles at the surface and at depth.
Additional keywords: salinity, sodicity, revegetation, eroded, SOC.
Worldwide, approximately 932 million ha of land is estimated to be salt-affected, with salinity affecting 23% of arable land, and saline-sodic soils affecting a further 10% (Szabolcs 1989). Salinisation and sodification of soils are serious land degradation issues in Australia, where it is estimated that salinity affects 17 million ha and sodicity approximately 340 million ha of land (Szabolcs 1989). While the deleterious effects of soil salinity and sodicity, termed collectively 'salt-affected soils', have been extensively studied in the past, particularly with regard to soil structure and vegetation health (e.g. Shainberg and Letey 1984; Levy et al. 1998; Rengasamy and Sumner 1998; Peck and Hatton 2003; Rengasamy 2006), the effects on carbon (C) dynamics with respect to emissions and stocks is not as well documented. This is particularly pertinent given the large area affected by salinity and sodicity, which is usually coincident with agricultural areas. In these areas, C stocks are likely to be directly related to decreased plant inputs due to low biomass production and, hence, low soil organic matter (SOM) accumulation. The maintenance of soil organic C (SOC) stocks in Australian soils is particularly important, as it is estimated that 75% of Australian soils display gravimetric SOC contents [less than or equal to] 1% in their Al horizons, which range from 0.05 to 0.15m in depth (Spain era/. 1983).
The accumulation of SOC is a...