Airborne nitrogen input at four locations in the German state of Saxony-Anhalt -: Measurements using the 15N-based ITNI-system

The amount of atmospheric N deposition in Germany is actual rather uncertain. Estimates using standard methods indicate an N deposition of 30-35 kg N/ha x year. However, the results of long-term field experiments and newly by the ITNI (Integrated Total Nitrogen Input) system could prove a much higher N input of about 50-60 kg N/ha x year. The reason for this difference is that standard methods use wet-only or bulk collectors, which neglect gaseous and organic N deposition as well as direct N uptake by aerial plant parts. By contrast, the ITNI-system is able to measure the total atmospheric N input using the N-15 isotope dilution method. The input of airborne N into a soil/ plant system leads to a dilution of the abundance of a previously applied N-15 tracer over a defined time period. The atmospheric N deposition can be calculated from this dilution. To estimate the actual N input in Central Germany, ITNI measurements were carried out from autumn 1998 to autumn 2000 at four locations in the German state of Saxony-Anhalt. Atmospheric N depositions between 45 and 75 kg N/ha x year were determined depending on the location. These results closely match to N balances of long-term field experiments. Furthermore, a relationship was found between N deposition and the plant species used as well as plant development.