N2O and CH4 fluxes from a volcanic grassland soil in Nasu, Japan:: Comparison between manure plus fertilizer plot and fertilizer-only plot

We examined the effects of manure + fertilizer application and fertilizer-only application on nitrous oxide (N(2)O) and methane (CH(4)) fluxes from a volcanic grassland soil in Nasu, Japan. In the manure + fertilizer applied plot (manure plot), the sum of N mineralized from the manure and N applied as ammonium sulfate was adjusted to 210 kg N ha(-1) year(-1). In the fertilizer-only applied plot (fertilizer plot), 210 kg N ha(-1) year(-1) was applied as ammonium sulfate. The manure was applied to the manure plot in November and the fertilizer was applied to both plots in March, May, July and September. From November 2004 to November 2006, we regularly measured N(2)O and CH(4) fluxes using closed chambers. Annual N(2)O emissions from the manure and fertilizer plots ranged from 7.0 to 11.0 and from 4.7 to 9.1 kg N ha(-1), respectively. Annual N(2)O emissions were greater from the manure plot than from the fertilizer plot (P < 0.05). This difference could be attributed to NO emissions following manure application. N(2)O fluxes were correlated with soil temperature (R = 0.70, P < 0.001), NH(4)(+) concentration in the soil (R = 0.67, P < 0.001), soil pH (R = -0.46, P < 0.001) and NO(3)(-) concentration in the soil (R = 0.40, P < 0.001). When included in the multiple regression model (R = 0.72, P < 0.001), however, the following variables were significant: NH(4)(+) concentration in the soil (beta = 0.52, P < 0.001), soil temperature (beta = 0.36, P < 0.001) and soil moisture content (beta = 0.26, P < 0.001). Annual CH(4) emissions from the manure and fertilizer plots ranged from -0.74 to -0.16 and from -0.84 to -0.52 kg C ha(-1), respectively. No significant difference was observed in annual CH(4) emissions between the plots. During the third grass-growing period from July to September, however, cumulative CH(4) emissions were greater from the manure plot than from the fertilizer plot (P < 0.05). CH(4) fluxes were correlated with NH(4)(+) concentration in the soil (R = 0.21, P < 0.05) and soil moisture content (R = 0.20, P < 0.05). When included in the multiple regression model (R = 0.29, P 0.05), both NH(4)(+) concentration in the soil (beta= 0.20, P < 0.05) and soil moisture content (P = 0.20, P < 0.05) were significant.