Can management induced changes in the carbonate system drive soil carbon sequestration? A review with particular focus on Australia

In many important agricultural regions, soil inorganic carbon (SIC) stocks can rival the amount of carbon found in organic form. Land management practices, including irrigation, fertilization and liming, have the potential to greatly alter the soil inorganic carbon cycle thus creating an important feedback to atmospheric CO2 concentrations. However, the current literature is less clear regarding the direction and magnitude of this feedback. Application of irrigation water, for example, can increase the rate of soil carbonate precipitation, but depending on the source of calcium and bicarbonate, the net reaction can be an atmospheric carbon sink, a carbon source or carbon neutral. Similarly, the accelerated dissolution of soil carbonates due to various acidifying processes can act as a net sink or source of atmospheric CO2 depending on the spatial and temporal frame of reference. While SIC stocks in agricultural soils have been found to increase or decrease by as much as 1.0 t C ha−1 yr−1, given the need to account for both the supply and fate of reactants and reaction products, ascribing these stock changes as a net sink or net source activity is difficult. This review paper provides an overview of the major inorganic carbon transformations in soils as affected by agricultural management, including the practice of liming to raise soil pH, and when these transformations should be considered a net atmospheric carbon source or sink.