Impact of animal manure addition on the weathering of agricultural lime in acidic soils: The agent of carbonate weathering

Fertilization and aglime (agricultural lime) application, as important agricultural activities in acid soil, exert an influence on the fluxes of carbon both between and within ecosystems. Animal manure added to soil can elevate the soil CO2 and release organic acid due to microbial decomposition of the high organic matter content of animal manure. Additionally, the elevated CO2 can accelerate carbonate weathering in alkaline soil, such as lime soil. However, in acidic soil, it is unclear whether the chemical weathering of additive aglime can be quickened by the elevated CO2 due to animal manure addition. Thus, to ascertain the impact of animal manure addition on aglime weathering in acidic soil and to understand the weathering agent of aglime or underlying carbonate in the acidic soil profile, we established two contrasting profiles (control profile and manurial profile) in a cabbage-corn or capsicum-corn rotation in a field experiment site located in the HuaXi district of Guiyang, China, and buried carbonate rock tablets at different depths of soil profiles to calculate the dissolution rate of carbonate rock by monitoring the weights of the tablets. The results indicated that soil CO2 increased due to animal manure addition, but the rate of dissolution of the carbonate rock tablets was reduced, which was attributed to the increase in the pH in acidic soil after animal manure addition because the relationship between the dissolution rate of carbonate rock and soil pH indicated that the weathering rate of carbonate rock was controlled by pH and not by CO2 in acidic soil. Thus, the contribution of H+ ions (mainly exchangeable acid) in acid soil as a weathering agent to the weathering of underlying carbonate (and/or aglime) may lead to the overestimation of the CO2 consumption through chemical weathering at the regional/global scale using hydro-chemical methods.