Soil Texture-Greenhouse Gas-Leachate Linkages Reveal Liming Effects on C and N Cycling

Liming is an important agricultural practice for mitigating soil acidification and potentially reducing N₂O emissions. Although lime can act as either a CO₂ source or sink depending on proton donors driving dissolution i.e., strong acids vs. carbonic acid, IPCC assumes it as a 100% CO₂ source. Soil leachate and shallow groundwater chemistry can reveal the dominant proton donors governing these reactions; however, previous studies have primarily focused on gas emissions alone. To address this knowledge gap, we conducted a two-month mesocosm experiment with spring barley using ¹³C-labeled carbonate and ¹⁵N-labeled fertilizer in acidic sandy (pH = 5.42) and clayey soils (pH = 5.45), incorporating three simulated rainfall events. Lime and fertilizer were homogeneously mixed with the soil, and gas samples were collected immediately following setup (Day 0).

In lime-treated soils, both CO₂ and N₂O fluxes were elevated prior to crop emergence and peaked on Day 0, whereas in control treatment, CO₂ and N₂O slightly increased on Day 0 and peaked after the first rainfall event. This suggests that liming and tillage stimulate initial greenhouse gas emissions. Consistent with previous studies, about 13% of lime-derived C was emitted as CO₂, and N₂O emissions were low (N loss < 0.1% of applied fertilizer) over the experiment period. Cumulative N₂O fluxes slightly decreased in limed clayey soils but increased modestly in limed sandy soils relative to controls, suggesting soil texture and biological processes suppress N₂O production during barley growth.

Calcium, magnesium and bicarbonate concentrations in leachate following the first rainfall event indicate that lime dissolution was dominated by strong acids, most likely nitric acid derived from the fertilizer inputs, with lime as a resulting net CO₂ source. In contrast, during later rainfall events, lime acted as a CO₂ sink. Based on δ¹³C-dissolved inorganic carbon, additional bicarbonate was likely generated through lime dissolution driven by carbonic acid produced during aerobic organic matter degradation in sandy soils, but by Fe- and Mn-coupled degradation in clayey soils, consistent with increased soil pH at depth. After rainfall events, CO₂-lime levels remained stable in clayey soil but declined in sandy soils, while N₂O fluxes increased slightly in clayey soils but remained consistently low in sandy soils. This pattern corresponds to higher bicarbonate and nitrate concentrations in leachate from clayey soils compared with sandy soils, suggesting that soil texture regulates aerobic and anaerobic microbial processes, which in turn affect lime dissolution. By linking lime dissolution, alkalinity production, and soil physical controls on gas and solute transport, our results show that soil texture fundamentally regulates liming-driven carbon and nitrogen cycling across the soil-gas-shallow groundwater continuum, highlighting the need for an integrated perspective to better assess the impacts of liming in agricultural systems.