Greenhouse gas fluxes in a no-tillage chronosequence in Central Ohio

A no-till chronosequence study was conducted to assess the impact of continuous no-till (NT) on greenhouse gases (CO₂, CH₄ and N₂O) emission and the global warming potential (GWP) of agroecosystems. Five paired sites in Central Ohio (USA) under plow till (PT) and NT for 9, 13, 36, 48 and 49 years were selected, and GHG fluxes were measured over a 2-year period. Nearby deciduous forests were included for comparative purposes. Results showed higher CO₂ emission under PT than NT (5.74 vs 4.55 Mg CO₂-C ha⁻¹). Annual CH₄ flux averaged − 0.1 and − 0.07 kg CH₄-C ha⁻¹ respectively under NT and PT, and was influenced by location and years under NT (greater rate of CH₄ uptake with longer duration of NT). Yet, the rate of CH₄ uptake in the agricultural soils was always < 15% of the rate in nearby forest soils (−1.16 kg CH₄-C ha⁻¹ y⁻¹). Annual N₂O emission was generally higher under PT than NT (6.70 vs 4.68 kg N₂O-N ha⁻¹), but an important deviation was observed at one site located on a poorly-drained silt loam soil where N₂O emission was 1.8-fold greater under NT than PT, likely due to wet soil conditions and labile organic carbon availability near the soil surface. The GWP of agroecosystems at the study sites averaged 23.1 and 19.9 Mg CO₂ equivalents ha⁻¹ y⁻¹ under PT and NT, respectively; N₂O emission accounted for 5–60% of the GWP and that contribution increased with NT duration. These results underscore the significance of N₂O in defining the climate mitigation potential of agriculture, and also highlight the need for improved N fertilizer management practices (eg. split application, injection) to minimize N₂O emission from fields under long-term NT. Even without consideration of agricultural inputs (i.e. fuel, fertilizers, pesticides) and change in soil C storage, the GHG flux data showed that sustained application of NT can help decrease the GWP of agroecosystems, further demonstrating the potential climate mitigation benefits of NT farming.