Emissions of carbon dioxide, methane, and nitrous oxide from short- and long-term organic farming Andosols in central Japan

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Here we have investigated the emission of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from long- and short-term organic farming Andosols in Matsumoto city of Nagano, in central Japan. We focus on three upland plots in Matsumoto, distinguished by how long they had each experienced continuous organic farming (OF)—in these three cases, since 1971, 2009, and 2010 (plots hereafter termed M39-OF, M1-OF, and M1F-OF, respectively). Since 2001, in M39-OF, mainly rye (Secale cereale L., as green manure) and soybeans [Glycine max (L.) Merril, as crop] were cultivated, in winter and summer respectively, without tillage, other fertilizers and agro-chemicals. In contrast, from 2001 to 2008 in M1-OF, and from 2001 to 2009 in M1F-OF, these plots underwent conventional farming of some vegetables with tillage, fertilizer and agro-chemicals. Soils sampled from M39-OF and M1-OF in August 2009 were incubated for 4 weeks in darkness at 25°C. During these 4 weeks, M39-OF emitted 8.0 times more CO2 and 274 times more N2O than M1-OF. Less than 2 µg carbon (C) kg–1 dry soil of CH4 was emitted from both soils. From February 2010 until January 2011, CO2, CH4, and N2O emission rates of M39-OF and M1F-OF were measured almost monthly, using a closed-chamber method. Annual CO2, CH4, and N2O emissions were 317, –1.7, and 27 g CO2-C equivalent m–2 in M39-OF, and 138, –0.2, and 21 g CO2-C equivalent m–2 in M1F-OF, respectively. The rye yield in M39-OF was 334 g C m–2. Soybeans in M39-OF and M1F-OF yielded 290 and 286 g C m–2, and withdrew 230 and 224 g C m–2, respectively. Greenhouse gas (GHG) balance was calculated at –52 and 97 g CO2-C equivalent m–2 in M39-OF and M1F-OF, respectively. Negative GHG balance indicated that M39-OF was acting as a GHG sink, with higher CH4 absorption than M1F-OF. Further, this beneficial function for global warming was thought to be based on its cultivation system, which had included green manure application since 2001. The difference in gas exchange between incubation and field experiments was considered a reason for the difference in N2O emission between incubation and field experiments.