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 (CO 2 , CH 4 and N 2 O) 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 CO 2 emission under PT than NT (5.74 vs 4.55 Mg CO 2 -C ha−1). Annual CH 4 flux averaged − 0.1 and − 0.07 kg CH 4 -C ha−1 respectively under NT and PT, and was influenced by location and years under NT (greater rate of CH 4 uptake with longer duration of NT). Yet, the rate of CH 4 uptake in the agricultural soils was always < 15% of the rate in nearby forest soils (−1.16 kg CH 4 -C ha−1 y−1). Annual N 2 O emission was generally higher under PT than NT (6.70 vs 4.68 kg N 2 O-N ha−1), but an important deviation was observed at one site located on a poorly-drained silt loam soil where N 2 O 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 CO 2 equivalents ha−1 y−1 under PT and NT, respectively; N 2 O emission accounted for 5–60% of the GWP and that contribution increased with NT duration. These results underscore the significance of N 2 O 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 N 2 O 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. • NT fields were net CH 4 sinks, and CH 4 uptake rate increased with NT (no-till) duration. • During the corn crop, N 2 O emission increased with NT duration. • Except in poorly-drained soils, higher N 2 O emission was measured under PT (plow-till) than NT. • The global warming potential of agroecosystems was lower under NT than under PT. [ABSTRACT FROM AUTHOR]