Quantification of airborne N-input in long-term field experiments and its validation through measurements using N-15 isotope dilution

The N-deposition in Germany is commonly calculated as values of about 20-30 kg/ha.yr. This range is based on the measurements of the nitrate and ammon ium nitrogen bulk deposition, which does not include the gaseous N-depositi on and the direct N-uptake by plants. The calculation of airbone N-deposition from N-balances of the Static Ferti lization Experiment Bad Lauchstadt came to 50-58 kg/ha yr. This is consiste nt with results from other European long-term experiments. Using the newly developed N-15-based ITNI-system, the total airborne N-depo sition can be determined. For Bad Lauchstadt analogous to results of former measuring periods an annual N-deposition of 65 kg/ha.yr was measured in 19 98, a figure greater than the balanced values. The balanced and measured values show, that airborne N-deposition is often underestimated and amounts to at least 50-58 kg/ha yr, which is a significa nt burden on natural ecosystems. By taking this extra N-input into account in calculations for fertilizer recommendations in agriculture a decrease of N-losses can be achieved which, in turn can also induce a decrease in airb orne N-deposition.