Ammonia exchange on grasslands in an intensive dairying region in central Japan(Environment)

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In an intensive dairying region, N flow through ammonia (NH_3) 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 NH_3 flux was measured using a gradient method over 3 years. The 3-year means of the annual balance of NH_3 fluxes as the difference between emission and deposition were -14.4kg N ha^<-1> in the manure plot and -18.6kg N ha^<-1> in the chemical fertilizer plot, averaging -16.5kg N ha^<-1>. The balance shows the dominance of NH_3 dry deposition in both plots, indicating that these grasslands acted as a net sink of NH_3, receiving 16.5kg N ha^<-1> year^<-1> of NH_3 from the atmosphere. Applications of chemical fertilizer and composted manure caused temporary NH_3 emissions equivalent to losses of 11.6 and 4.4%, respectively, of the applied NH_4^+-N. A previous study has shown that wet deposition was 18kg N ha^<-1> year^<-1> in this intensive dairy farming region, so atmospheric N input to the grassland was estimated to be 34.5kg N ha^<-1> year^<-1> as both dry and wet deposition. This amount equalled 17.3% of the 199kg N ha^<-1> year^<-1> generated locally as manure in the region. Assuming that 25% was selected as a representative NH_3 emission factor from livestock manure, atmospheric deposition of ammoniacal N corresponded to 69.5% of the emitted NH_3 from livestock manure in the study area, indicating that emission and deposition of NH_3 in the area is an important internal flow of the N cycle in this intensive dairying region in central Japan.

Ammonia exchange on grasslands in an intensive dairying region in central Japan(Environment)

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