Spatial Variability of Nitrous Oxide Emissions and Their Soil‐Related Determining Factors in an Agricultural Field

To evaluate spatial variability of nitrous oxide (N 2 O) emissions and to elucidate their determining factors on a field‐scale basis, N 2 O fluxes and various soil properties were evaluated in a 100‐ × 100‐m onion ( Allium cepa L.) field. Nitrous oxide fluxes were determined by a closed chamber method from the one‐hundred 10‐ × 10‐m plots. Physical (e.g., bulk density and water content), chemical (e.g., total N and pH), and biological (e.g., microbial biomass C and N) properties were determined from surface soil samples (0–0.1 m) of each plot. Geostatistical analysis was performed to examine spatial variability of both N 2 O fluxes and soil properties. Multivariate analysis was also conducted to elucidate relationships between soil properties and observed fluxes. Nitrous oxide fluxes were highly variable (average 331 μg N m −2 h −1 , CV 217%) and were log–normally distributed. Log‐transformed N 2 O fluxes had moderate spatial dependence with a range of >75 m. High N 2 O fluxes were observed at sites with relatively low elevation. Multivariate analysis indicated that an organic matter factor and a pH factor of the principal component analysis were the main soil‐related determining factors of log‐transformed N 2 O fluxes. By combining multivariate analysis with geostatistics, a map of predicted N 2 O fluxes closely matched the spatial pattern of measured fluxes. The regression equation based on the soil properties explained 56% of the spatially structured variation of the log‐transformed N 2 O fluxes. Site‐specific management to regulate organic matter content and water status of a soil could be a promising means of reducing N 2 O emissions from agricultural fields.