MEASURING OF THE INTEGRAL AIRBORNE NITROGEN-INPUT INTO A SOIL-PLANT SYSTEM BY THE N-15-ISOTOPE DILUTION METHOD

Airborne nitrogen-inputs so far have only been measured in single fractions (deposition on plant surfaces or on soil and direct absorption of nitrogen containing gases by plants) by intensive exposition experiments in gas chambers, measurement of wet and dry N-deposition in the field and very expensive micrometereological field measurements. It is very difficult to estimate any overall N-input with practical relevance from these single N-component measurements. In this introduced field experiment an isolated measuring system is labelled with a N-15-tracer since it is not possible to label the nitrogen compounds of the atmosphere (e. g. NH3, NO4) which are to be absorbed. Through the dilution of this N-15-tracer by nitrogen derived from the atmosphere the total input of airborne nitrogen is determined. As soil resembling substrate sand was used and summer wheat was planted. With the regular and automated irrigation of nitrogen-free nutrient solution and the collection of precipitation surpluses this system measured the total input of airborne nitrogen for one vegetation period. The first application of the described system gave an airborne nitrogen input into the soil-plant system during a vegetation period of 10 weeks (April-June) of about 32 kg ha(-1).