The objectives of this study were to clarify the effect of chemical fertilizer and manure application on methane (CH 4 ) and nitrous oxide (N 2 O) emissions from intensively managed grassland on Andosols in Japan and to determine the controlling factors of the CH 4 and N 2 O emissions. The emission factors (EF) for both fertilizerand manure-induced N 2 O emissions were calculated. Three experimental plots were set up in five grasslands across four climatic regions in Japan: one plot for treatment with chemical fertilizer (fertilizer plot); another plot for treatment with cattle manure and chemical fertilizer (manure plot), and the final plot was not treated with chemical fertilizer or manure (control plot). The type of chemical fertilizer was ammonium-based fertilizer or a combination fertilizer of ammonium and urea. CH 4 and N 2 O emissions were measured at the study sites for six years. For the manure plot, a supplement of chemical fertilizer was added to equalize the supply rate of mineral nitrogen (N) relative to that of the fertilizer plots. There were no significant differences in CH 4 emissions among the treatment plots, and the effect of fertilizer or manure application was not evident. CH 4 emissions tended to be larger at sites with higher soil moisture content. The application of chemical fertilizer or manure increased N 2 O emissions at all the sites, and there were significant differences among the sites and across different years. Background N 2 O emissions (N 2 O emissions at the control plot) had strong positive correlations with air temperature and precipitation, along with weak positive correlations with soil carbon and N content. Therefore, an empirical model (Background N 2 O emission ¼ 0.298 Â air temperature þ 0.512 Â soil N content À3.77) was established. Fertilizer-induced N 2 O emission factor (EF) had a positive correlation (R 2 ¼ 0.50, p < 0.01) with precipitation (Fertilizer-induced EF ¼ 0.0022 Â precipitation À1.3), and increasing precipitation enhanced N 2 O production through the denitrification process due to applied fertilizer N. There were no significant differences in manure-induced EFs among the sites, and the average was 0.36% except for an outlier.

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In a number of plant species, nitrogen fertilization leads to a higher oxalate content of the plant. Various tropical grasses sometimes contain oxalate in sufficient concentrations to induce calcium deficiency in grazing animals. The present study was undertaken to investigate the effect of increasing level of N (0, 10, 30, 60 and 90 g N m−2 using urea) on oxalate and some mineral contents in napiergrass (cv. dwarf‐late). We found that the total dry matter yield increased significantly (P < 0.001) with increasing N up to 30 g N m−2 applied, but no significant difference was observed among the N levels of 30, 60 and 90 g m−2. The oxalate content was not increased with increased levels of N fertilization in all cut forages, except for insoluble oxalate content at third‐cut forage which increased significantly (P < 0.05) with increased level of N fertilizer. The content of soluble oxalate in plants was positively correlated (r2 = 0.76, P < 0.001) with potassium concentration, while the content of insoluble oxalate was positively correlated with calcium (r2 = 0.69, P < 0.001) and magnesium (r2 = 0.65, P < 0.001) concentrations. The study suggests that while applying N fertilizer as urea during cultivation of napiergrass, oxalate accumulation may not be a matter of concern.