In-Field Management Practices for Mitigating Soil CO2 and CH4 Fluxes under Corn (Zea mays) Production System in Middle Tennessee

The United States continues to be the largest corn producer in the world. How to maximize corn yield and at the same time reduce greenhouse gas emissions, is becoming a challenging effort for growers and researchers. As a result, our understanding of the responses of soil CO2 and CH4 fluxes to agricultural practices in cornfields is still limited. We conducted a 3-yr cornfield experiment to study the responses of soil CO2 and CH4 fluxes to various agricultural practices in middle Tennessee. The agricultural practices included no-tillage + regular applications of urea ammonium nitrate (NT-URAN); no-tillage + regular applications of URAN + denitrification inhibitor (NT-inhi- bitor); no-tillage + regular applications of URAN + biochar (NT-biochar); no-tillage + 20% applications of URAN + chicken litter (NT-litter); no-tillage + split applications of URAN (NT-split); and conventional tillage + regular applications of URAN as a control (CT-URAN). A randomized complete block design was used with six replications. The same amount of fertilizer equivalent to 217 kg・N・ha−1 was applied to all of the experimental plots. The results showed that improved fertilizer and soil management, except the NT-biochar treatment significantly increased soil CO2 flux as compared to the conventional tillage (CT-URAN, 487.05 mg CO2 m−2∙h−1). Soil CO2 flux increased exponentially with soil temperature (T 30˚C), and linearly with soil moisture (T ≥ 30˚C) in all treatments. Across all treatments, soil CO2 flux tended to be positively related to corn yield and/or soil moisture. Soil CH4 flux increased linearly with soil moisture in all treatments. Improved fertilizer and soil management did not alter soil CH4 flux, but significantly affected its moisture sensitivity. Our results indicated that agricultural practices enhancing corn yield may also result in a net increase in carbon emissions from soil, hence reducing the potential of carbon sequestration in croplands.