Effect of combined application of manure and fertilizer on N2O fluxes from a grassland soil in Nasu, Japan

The manure application rate to grassland is often limited by the manureʹs potassium content. As a result, supplemental nitrogen (N) or phosphorus fertilizer may be required. In Japan, bark or sawdust are often added to manure to reduce its moisture content as a part of the composting process, and composted manure is spread on fields in late autumn to free storage space to hold the manure produced during the winter. We evaluated the effects of a combined application of bark- or sawdust-containing dairy cattle compost in late autumn and supplemental fertilizer supply on the N2O emissions from grassland for 5 years. N2O emissions from the manure plus fertilizer plot, fertilizer-only plot, and no N (control) plot were measured using closed chambers. The cumulative precipitation during the 18-day period before and the 12-day period after N application were important control factors for N2O emissions. In addition, N2O emissions increased drastically when the average air temperature during the 12-day period after the N application exceeded 15 °C. Therefore, the timing of N application with respect to precipitation and temperature was the most important factor controlling N2O emissions. By combining manure application in late autumn with reduced application of N fertilizer during the summer growing season, it may be possible to mitigate N2O emissions from Japanese grasslands.