Ammonia exchange on grasslands in an intensive dairying region in central Japan

Abstract

In an intensive dairying region, N flow through ammonia (NH3) is comparatively important because of a high-N loading condition based on livestock manure. To elucidate part of the N flow in Orchardgrass (Dactylis glomerata L.) and Italian ryegrass (Lolium multiflorum Lam.) dominant cutting grasslands in an intensive dairy farming region in central Japan, the NH3 flux was measured using a gradient method over 3 years. The 3-year means of the annual balance of NH3 fluxes as the difference between emission and deposition were −14.4 kg N ha−1 in the manure plot and −18.6 kg N ha−1 in the chemical fertilizer plot, averaging −16.5 kg N ha−1. The balance shows the dominance of NH3 dry deposition in both plots, indicating that these grasslands acted as a net sink of NH3, receiving 16.5 kg N ha−1 year−1 of NH3 from the atmosphere. Applications of chemical fertilizer and composted manure caused temporary NH3 emissions equivalent to losses of 11.6 and 4.4%, respectively, of the applied NH4 +-N. A previous study has shown that wet deposition was 18 kg N ha−1 year−1 in this intensive dairy farming region, so atmospheric N input to the grassland was estimated to be 34.5 kg N ha−1 year−1as both dry and wet deposition. This amount equalled 17.3% of the 199 kg N ha−1 year−1 generated locally as manure in the region. Assuming that 25% was selected as a representative NH3 emission factor from livestock manure, atmospheric deposition of ammoniacal N corresponded to 69.5% of the emitted NH3 from livestock manure in the study area, indicating that emission and deposition of NH3 in the area is an important internal flow of the N cycle in this intensive dairying region in central Japan.