Organic residue and agricultural lime interactions on CO2 emissions from two contrasting soils: implications for carbon management in acid soils

Agricultural lime (aglime) has been recognised to promote the production of CO2 from acid soils. However, the role of organic residues in controlling the magnitude of these emissions is poorly understood. This study, therefore, investigated the interactive effects of aglime and organic residues on inorganic- and organic-derived CO2 emissions from two contrasting acid soils. The experiment was carried out as a completely randomised 2 × 2 × 4 factorial design where two contrasting acid soils (Nariva clay series, Mollic Fluvaquents and Piarco loam series, Typic Kanhaplaquults) were amended with varying rates of 13C-enriched aglime (0% w/w and 0.230% w/w Ca13CO3,13C 5.99% atom abundance) and organic residues (0% w/w and 1% w/w corn stover, poultry litter, or glucose) to give a total of 16 treatment combinations. These treatments were triplicated, resulting in 48 experimental units that were incubated for 103 days in 1-L media bottles. The mineralisation of carbon (C) in the Piarco soil increased by 27% with aglime addition relative to the no-organic residue control but decreased (by as much as 13.2%) when applied to the organic residue-amended soils. This interaction was, however, not evident in the Nariva soil, which may be attributed to the fact that aglime-induced priming effects were negligible in this soil. Results also show that the rate of aglime-CO2 emissions decreased with the application of poultry litter and corn stover, and increased with the application of glucose. This effect was particularly evident in the Piarco soil and is likely related to the organic residue-induced changes in the soil pH. Overall, our results highlight the importance of considering organic residue addition when assessing the global warming effect associated with aglime use. In addition to crop nutrition benefits, our results further emphasise the need to optimise liming and organic residue management practices to enhance C sequestration in acid soils.