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Organic Agriculture and Nitrous Oxide Emissions at Sub-Zero Soil Temperatures

USDA-ARS, Northern Great Plains Research Lab., Box 459, Mandan, ND 58554

View larger version (82K): [in this window] [in a new window]   Fig. 1. Overall map of the field site area (47°01' N; 96°36' W), located in Clay County, MN where soil and gas flux sample were collected in the Red River Valley (RRV) agricultural region. Weather station location is also shown, from which continuous soil temperature data were collected. Above the regional map is an aerial photograph (2004) indicating proximity of organic field (T2O), conventional field (T2C), and reference site to each other.

View larger version (13K): [in this window] [in a new window]   Fig. 2. Nitrous oxide flux partitioning for comparison between organically and conventionally managed soils collected in July and at 23% WFPS. Soils were incubated under ambient air, then under 10 Pa C2H2, then under 10 K Pa C2H2 at field moisture and temperature to determine sources of rates of N2O emissions and N produced during denitrification. Mean (n = 10) ± SEM are shown for each treatment and incubation.

View larger version (12K): [in this window] [in a new window]   Fig. 3. Nitrous oxide flux and denitrification for intact core incubations at field moisture (40% WFPS) and temperature (–2.5°C) 17 d following T2O manure amendment. Soil cores were incubated under ambient air, then under 10 K Pa C2H2 to determine rates of N2O emissions and N produced during denitrification. Mean (n = 5) ± SEM are shown for each treatment and incubation.

View larger version (17K): [in this window] [in a new window]   Fig. 4. Nitrous oxide fluxes (mean ± SEM) measured at the soil-atmosphere interface between 4 Aug. 2004 and 8 Apr. 2005 with respect to number of days following manure amendment application for organic (T2O), conventional (T2C), and reference sites. Soybeans were in both fields between days –112 and –55. Fields were fallowed between days –8 and 135.

View larger version (22K): [in this window] [in a new window]   Fig. 5. Mean (± SD) for air and soil temperature collected manually at the field site for each field during flux sampling and soil temperature collected continuously at the weather station located north of the field site (see Fig. 1).