Nitrogen Oxide and Methane Emissions under Varying Tillage and Fertilizer Management

Comprehensive assessment of the total greenhouse gas (GHG) budget of reduced tillage agricultural systems must consider emissions of nitrous oxide (N 2 O) and methane (CH 4 ), each of which have higher global warming potentials than carbon dioxide (CO 2 ). Tillage intensity may also impact nitric oxide (NO) emissions, which can have various environmental and agronomic impacts. In 2003 and 2004, we used chambers to measure N 2 O, CH 4 , and NO fluxes from plots that had been managed under differing tillage intensity since 1991. The effect of tillage on non‐CO 2 GHG emissions varied, in both magnitude and direction, depending on fertilizer practices. Emissions of N 2 O following broadcast urea (BU) application were higher under no till (NT) and conservation tillage (CsT) compared to conventional tillage (CT). In contrast, following anhydrous ammonia (AA) injection, N 2 O emissions were higher under CT and CsT compared to NT. Emissions following surface urea ammonium nitrate (UAN) application did not vary with tillage. Total growing season non‐CO 2 GHG emissions were equivalent to CO 2 emissions of 0.15 to 1.9 Mg CO 2 ha −1 yr −1 or 0.04 to 0.53 Mg soil‐C ha −1 yr −1 Emissions of N 2 O from AA‐amended plots were two to four times greater than UAN‐ and BU‐amended plots. Total NO + N 2 O losses in the UAN treatment were approximately 50% lower than AA and BU. This study demonstrates that N 2 O emissions can represent a substantial component of the total GHG budget of reduced tillage systems, and that interactions between fertilizer and tillage practices can be important in controlling non‐CO 2 GHG emissions.