Synergistic Effects of Lime–Organic Amendment Interactions in Acidic Soils

Calcitic lime (CaCO3) is commonly used to ameliorate soil acidity, but its effectiveness is limited by slow solubility. This study aims to evaluate interactive effects of lime (90% calcite, 6% quartz) and organic amendments on lime dissolution and soil acidity neutralisation. The experiment utilised various organic amendments with the following differing decomposability: (i) readily decomposable faba bean straw, and (ii) more resistant blended poultry litter, biochar, and compost, with average organic carbon mineralisation indices (OCMI) of 29%, 6%, 4%, and 6%, respectively. The lime–faba bean straw combination produced the highest partial pressure of CO2 (pCO2) (1398 μatm) compared to lime alone (375 μatm). The net average increase in dissolved inorganic carbon (DIC) due to the synergistic interaction between lime and organic amendments ranged from +0.3 mg L−1 for the lime–blended poultry litter treatment to +1.9 mg L−1 for the lime–compost combination, representing a 2‐ to 5‐fold increase. The dissolved organic carbon (DOC) content in lime–organic amendment mixes also increased by 29%–36% compared to organic amendments alone. The pCO2/DIC ratio decreased when lime was combined with organic materials compared to when it was applied alone, indicating more efficient conversion of respired CO2 to H2CO3* (* indicates this comprises both dissolved CO2 and carbonic acid, H2CO3). A lower DIC/carbonate alkalinity (DIC/CarbAlk) ratio and a positive calcite saturation index (SIC) in the combined treatments further confirmed the increased generation of HCO3− and CO32−, reducing acidity. The co‐application of lime and organic amendments also mobilised Ca2+ while reducing potential Al3+ bioavailability and phytotoxicity. These beneficial synergies highlight the potential for improved acid soil remediation strategies using combined lime–organic matter amendments.