Aspects of carbon and nitrogen cycling in soils of the Bornhöved Lake district. I. Microbial characteristics and emissions of carbon dioxide and nitrous oxide of arable and grassland soils

Soil microbial biomass content, organic carbonmineralization as well as arginine ammonificationrates were estimated in samples from arable andgrassland soils and carbon dioxide and nitrous oxideemission rates were measured in situ at four sitesalong a catena. Soil microbial biomass contentincreased in the order, maize monoculture < croprotation < dry grassland < wet grassland. The twoarable soils had similar rates of carbonmineralization in the laboratory at 22 °C (basalrespiration) as well as in situ (carbon dioxideemission) at field temperature. Under crop rotation,maize monoculture and dry grassland, the arginineammonification rate significantly correlated to themicrobial biomass content. In contrast, thebiomass-specific ammonification rate was low in wetgrassland soil, as were in situ N2O emission rates.Data from all sites together revealed no generalrelationship between microbial biomass content and Cand N mineralization rates. In addition, there was nogeneral relationship between the quantity of soilmicrobial biomass and the emission rates of thegreenhouse gases CO2 and N2O. The maize monocultureinduced a soil microbial community that was lessefficient in using organic carbon compounds, as shownby the high metabolic quotient (respiration rate perunit of biomass). However, microbial biomass contentwas proportional to basal respiration rate in soilsunder crop rotation, dry and wet grassland. Arginineammonification rate was related to microbial biomasscontent only in fertilized soils. Applications of highquantities of inorganic nitrogen and farmyard manureapparently increase in situ N2O emission rates,particularly under crop rotation. The microbialbiomass in the unfertilized wet grassland soil seemsto be a sink for nitrogen.