Biosphere - Atmosphere exchange of NH3, NO and N2O in an agroecosystem.

In spring 1996 we started a four year research project to quantify the hi-directional exchange of nitrogen-containing trace gases between an agricultural ecosystem and the atmosphere. In the first year we intended to identify the most important processes that govern the exchange of nitrogen-containing trace gases between a field planted with winter wheat and the atmosphere during a vegetation period. NH3 profiles within the canopy were monitored with a continuous four channel analyser. We employed semipermeable membrane tubes to monitor vertical NO concentration profiles in the open pore space of the soil. N2O profiles were taken periodically. Preliminary results show that the NH3 exchange is dominated by the upper part of the canopy. During daylight hours the highest concentration of NH3, was found on the flag leaf/ear level. NO concentration in the soil was strongly enhanced in spring after the first rainfall following fertiliser application and was highest in the upper soil layer. N2O concentration generally increased with soil depth. High concentrations were measured in spring, decreasing during plant growth. During fructification of wheat the N2O concentration in deeper layers was elevated again.