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Nitrogen Oxide and Methane Emissions under Varying Tillage and Fertilizer Management

^a USDA-ARS, Soil and Water Management Unit, 1991 Upper Buford Circle, St. Paul, MN 55108
^b Department of Plant Sciences, One Shields Avenue, University of California, Davis, CA 95616
^c Department of Soil, Water, and Climate, 1991 Upper Buford Circle, University of Minnesota, St. Paul, MN 55108
^d Current address: USDA-ARS, North Central Soil Conservation Research Laboratory, 803 Iowa Avenue, Morris, MN 56267

View larger version (33K): [in a new window]   Fig. 1. Location of field site in southeastern Minnesota, and plot layout. Main treatments were conventional tillage (CT), conservation tillage (CsT), and no till (NT). Plots measured 27.4 m wide by 61 m long. Plots used in 2004 were split into three fertilizer subplots, indicated by dashed lines. Plots with no designation received treatments not examined in current study.

View larger version (46K): [in a new window]   Fig. 2. Environmental variables and gas fluxes during 2003 (mean ± standard error, n = 3). (a) Precipitation (cumulative during previous 10 d) and soil water content (0–10 cm), (b) air and soil (5-cm depth) temperatures, (c) N2O fluxes, and (d) CH4 fluxes under conventional (CT), conservation (CsT), and no tillage (NT). Values in parentheses in (c) are mean soil NO3– concentrations (mg N kg–1) over 0 to 10 cm across tillage treatments. Solid urea fertilizer was broadcast on 23 June.

View larger version (57K): [in a new window]   Fig. 3. Environmental variables and N2O fluxes during 2004 (mean ± standard error, n = 3). (a) Precipitation (cumulative during previous 10 d) and soil water content (0–10 cm), (b) air and soil (5-cm depth) temperatures, and N2O fluxes in (c) anhydrous ammonia (AA), (d) urea ammonium nitrate (UAN), and (e) broadcast urea (BU) treated plots under conventional (CT), conservation (CsT), and no tillage (NT). Values in parentheses in (c–e) are mean soil NO3– concentrations (mg N kg–1) over 0 to 20 cm across tillage treatments.

View larger version (17K): [in a new window]   Fig. 4. Methane fluxes from plots under conventional (CT), conservation (CsT), and no tillage (NT) during 2004 (means across all fertilizer treatments, ±standard error, n = 9).

View larger version (52K): [in a new window]   Fig. 5. Total integrated emissions of (a) N2O, and (b) CH4, expressed as mass flux (left-hand axes) and CO2 equivalents (right-hand axes), and (c) total non-CO2 greenhouse gas (GHG) emissions (i.e., N2O + CH4) expressed as CO2 equivalents from anhydrous ammonia (AA), urea ammonium nitrate (UAN), and broadcast urea (BU) treated plots under conventional (CT), conservation (CsT), and no tillage (NT) (mean ± standard error, n = 3). For each parameter and within each year, bars with the same letter designation are not significantly different (p > 0.05).

View larger version (39K): [in a new window]   Fig. 6. Nitric oxide fluxes from (a) anhydrous ammonia (AA), (b) urea ammonium nitrate (UAN), and (c) broadcast urea (BU) treated plots under conventional (CT) and no tillage (NT) during 2004 (mean ± standard error, n = 3).

View larger version (43K): [in a new window]   Fig. 7. Total integrated emissions of NO, N2O, and NO + N2O from anhydrous ammonia (AA), urea ammonium nitrate (UAN), and broadcast urea (BU) treated plots under conventional tillage (CT) and no tillage (NT) during 2004. Values indicate mean (±standard error, n = 3) NO and NO + N2O emissions. For each component (NO, or NO + N2O), bars with the same letter designation are not significantly different (p > 0.05).