[en] Isotopic variations of nitrogen in soils may have their roots in three different forms: fluctuations of the isotopic composition in nitrogen compounds of the precipitations (inputs), the result of isotope effects in ion exchange processes and lastly of isotope effects in metabolic processes. Arable fields may be changed by anthropogenic processes, especially by applying nitrogenous fertilizers. The different isotopic compositions of the nitrogen compounds in soils may be used as natural tracers, i.e. tracing substances in soils and ground waters. (author)