Impact of farming practices on soil greenhouse gas emissions

Abstract

Agricultural soils are notable contributors of greenhouse gases (GHG), particularly carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Employing sustainable soil management practices, such as the incorporation of cover crops (CC), mulching, and organic amendments (compost tea), has been identified as effective in enhancing soil and mitigating GHG emissions. This study investigates the impact of diverse farming practices on soil conditions and GHG emissions, focusing on two farms: EarthSeed Farm in Sebastopol, California, and Good Courage Farm in Hutchinson, Minnesota. Measurements include soil CO2, N2O, and CH4 gas fluxes using a closed chamber with a GasMet GT5000 Terra FTIR gas analyzer. Soil-atmosphere gas fluxes were calculated by determining the rate of change of gas concentrations over time in the chamber. Soil characteristics were analyzed through measurements of soil infiltration, temperature, moisture, bulk density, and mineral loss on ignition (LOI). Both farms were found to be sources of CO2 (averages ± one standard deviation include: EarthSeed 0.16 ± 0.15 mg m- ²s-1 ; Good Courage 0.25 ± 0.16 mg m- ²s-1 ) and N2O (EarthSeed 0.03 ± 0.05 µg m-2 s-1 ; Good Courage 0.04 ± 0.04 µg m-2 s-1 ). Good Courage was a weak CH4 sink (-0.05 ± 0.03 µg m-2 s-1 ). Although minimal, EarthSeed exhibited seasonal fluctuations between acting as weak sources and sinks of CH4 (0.15 ± 0.8 µg m-2 s-1 on average). Strong seasonality of gas fluxes was observed, particularly the CO2 flux, which was predominantly driven by soil water content (SWC) and soil temperature, with the highest CO2 fluxes at EarthSeed Farm occurring when SWC was 20 - 25%. Compost tea amendments did not statistically significantly alter soil conditions or soil gas fluxesrelative to the control. Notably, at Good Courage Farm, the presence of poultry led to elevated CO2 and N2O fluxes as well as a greater amount of organic LOI compared to the control blocks. Environmental conditions were the greatest drivers of gas fluxes. However, research focused on individual management practices over an extended temporal span or targeting projects established for at least three years is recommended to yield greater comprehension of the long-term impacts of farming practices on soil health and greenhouse gas emissions.

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