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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.

There have been few practical ways of measuring physiological determinants of rice yield. Rapid evaluation of yield determination traits may expedite breeding of high-yielding rice. Here, we report a new remote-sensing technique for the evaluation of canopy ecophysiological status under field conditions developed based on simultaneous measurements of sunlit and suddenly shaded canopy temperatures. This technique has the advantage of instantaneous estimation of aerodynamic resistance ( r a ) and canopy diffusive resistance ( r c ) without measuring wind velocity. Canopy diffusive conductance (1 / r c ) estimated by the remote sensing method was closely related to leaf stomatal conductance (g s ) measured with a portable gas exchange system. This result supported the validity of this new method for quantitative estimation of canopy physiological characteristics. Significant genotypic differences were obtained in canopy-air temperature difference ( T c − − − − T a ), r c and 1 / r c during the 2-week period preceding full heading for two years, and 1 / r c was highly correlated with crop growth rate (CGR), which was closely related to the final yield. These results suggest that 1 / r c can be an effective criterion for the selection of high-yielding rice genotypes, and the remote sensing technique proposed here can be a powerful tool for the rapid evaluation of 1 / r c under field conditions.

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 N 2 O emissions following manure application. N 2 O fluxes were correlated with soil temperature (R = 0.70, P < 0.001), concentration in the soil (R = 0.67, P < 0.001), soil pH (R = -0.46, P < 0.001) and 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: concentration in the soil (β = 0.52, P < 0.001), soil temperature (β = 0.36, P < 0.001) and soil moisture content (β = 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 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 concentration in the soil (β = 0.20, P < 0.05) and soil moisture content (β = 0.20, P < 0.05) were significant.

A ground-based network of spectral observations is useful for ecosystem monitoring and validation of satellite data. However, these observations contain inherent uncertainties due to the change of sunlight conditions. This study investigated the impact of changing solar zenith angles and diffuse/direct light conditions on the consistency of vegetation indices (normalized difference vegetation index (NDVI) and green-red vegetation index (GRVI)) derived from ground-based spectral measurements in three different types of cropland (paddy field, upland field, cultivated grassland) in Japan. In general, the vegetation indices decreased with decreasing solar zenith angle. This response was affected significantly by the growth stage and diffuse/direct light conditions. The decreasing response of the NDVI to the decreasing solar zenith angle was high during the middle growth stage (0.4 < NDVI < 0.8). On the other hand, a similar response of the GRVI was evident except in the early growth stage (GRVI < 0). The response of OPEN ACCESSRemote Sens. 2015, 7 14080 vegetation indices to the solar zenith angle was evident under clear sky conditions but almost negligible under cloudy sky conditions. At large solar zenith angles, neither the NDVI nor the GRVI were affected by diffuse/direct light conditions in any growth stage. These experimental results were supported well by the results of simulations based on a physically-based canopy reflectance model (PROSAIL). Systematic selection of the data from continuous diurnal spectral measurements in consideration of the solar light conditions would be effective for accurate and consistent assessment of the canopy structure and functioning.