Soil-Atmosphere Exchange of NH3 and NOx in Differently Managed Vegetation Types of Southern Germany

Ammonia (NH3) and Nitrogen Oxides (NOx = NO + NO2) emissions from soils and vegetation, and their subsequent deposition are key factors in global Nitrogen (N) cycling and have important functions in atmospheric and ecosystem degradation processes. To better understand their contribution, NH3 and NOx gases were simultaneously measured from differently managed vegetation types using a dynamic-chamber method. Biomass and N yields were higher from unfertilized clover-grass than fertilized oilseed radish. Summer cuts of clover-grass resulted in 137% higher biomass and 2.7-3.7% N concentrations than autumn cuts. Mulching reduced the re-growth and biomass production in clover-grass by 16% compared to cutting. The relative loss of NH3 through mulching was higher from the clover-grass (2.18%) than in the oilseed radish (0.08%). The total NH3 release over the four cuts of the clover-grass was 0.58% of the N removed. The influence of biomass-N, either mulched or cut, on the total NOx emission was temporary, resulted in net deposition (0.02-0.15% of the added/removed biomass-N). The ecosystems acted as sources for NH3, with the rate being weakly related to the added biomass-N, air temperature and humidity (R2 = 0.58, p<0.07), and sinks for NOx, with the rate influenced significantly by sunshine hours, precipitation and amount of biomass-N added (R2 = 0.87, p<0.001). We conclude that cutting clover-grass multiple times could be a good option to reduce the emissions of reactive N species and increase fodder yields with moderate N. Additionally, clover-grass could be superior for soil conservation measures over oilseed radish. Results imply further studies on the annual exchanges of gaseous N between the ecosystems and the atmosphere through long-term measurements.