Interactive effects of liming and nitrogen management on carbon mineralization in grassland soils

Grassland management has the potential to modify soil carbon (C) mineralization, but the relative importance of combined soil improvers or fertilizers and land use intensity on C mineralization remains unclear. We used laboratory incubations to examine the interactive effects of lime addition, mineral N inputs and grassland management intensity on soil C mineralization potential over 84 days. Monitoring of CO2 production and O2 consumption was coupled with measurements of soil pH and microbial biomass for soils obtained from grasslands with contrasting levels of land management intensity (extensive versus intensive N management) at each of three upland sites. Lime addition increased soil pH, cumulative CO2 production and O2 consumption across all N treatments and soils. These positive effects of liming either partly or fully compensated the observed negative effects of N on CO2 and O2 fluxes. Responses to combined liming and N addition varied depending on management intensity; N addition had no effect on liming response ratios for O2 consumption at intensively-managed sites, but increased the magnitude of positive liming response ratios for O2 consumption at extensively-managed sites. Overall, our results suggest that the magnitude of liming-induced increases in C mineralization is mediated by effects of both past and present N management on the soil microbial community. This highlights the importance of considering agricultural practices when assessing the net contribution of agricultural liming to soil-atmosphere feedbacks on climate change.