Land Use on Volcanic Ash Soils and its Influence on Greenhouse Gases Emissions Under Laboratory Conditions

Carbon dioxide (CO 2 ) and nitrous oxide (N 2 O) are important greenhouse effect gases (GHG). Soil gas emissions have a lack of research on volcanic ash soils under contrasting land uses in Chile. We propose that different intensities of land use affect soil gas fluxes. We incubated volcanic soils (5 cm depth) from crops, grasslands, silvopastures, and forestry plantations, under three levels of moisture (WFPS, water-filled pore space: 30%, 60%, and 90%), with different contents of nitrate already pre-existing in the soil. Air samples were measured by gas chromatography after 2 h of soil gas effluxes from closed passive airtight chambers. There was no significant effect of soil use intensity on CO 2 fluxes, but a significant effect of WFPS was found. The N 2 O fluxes also responded to WFPS; soil use effects were found at 90% WFPS, where only agriculture crops surpassed permanent grasslands. The soil nitrate content had a negative and significant relation with CO 2 fluxes. The legacy of the original soil may have contributed to the general absence of land use effect on gas emissions, irrespective of its management history, because soil use changes from agriculture to forest plantations are recent (only 10–12 years ago) following intensive use during centuries that may have exhausted the soil carbon and nitrogen pools. However, the fluxes were more responsive to soil water content and nitrate, suggesting that if land uses were more coupled to these driving environmental factors, differences among land use GHG emissions should occur.