Ein Beitrag zur Stickstoffwirkung nach unterschiedlichen Verfahren stabilisierter Klärschlämme*

A distribution to the availability of the nitrogen in sewage sludges stabilized with different processes In two pot experiments the availability of the nitrogen in sewage sludges stabilized with different processes was investigated. Further it was examined whether the Quantofix-N-Volumeter (method for rapid determination of ammonia in slurries) is able to determine the plant available nitrogen in sewage sludge. The following results were obtained: In the experiment where same amounts of total N were applied as sewage sludge a highly significant correlation existed between the amount of NH₄-N applied and the N uptake of the plants. When equal amounts of NH₄-N were applied the N uptake was lowest with the sewage sludges with a high relative part of NH₄-N of the total N (thermophile-aerob; mesophile-anaerob). However the reason for this result was not only the lower application rate of total N with these sewage sludges but also the lower efficiency of the organically bound nitrogen. A very highly significant correlation existed between the application rate of organically bound nitrogen and the N uptake. The values of nitrogen in sewage sludges measured by the rapid method gave information about the plant available nitrogen in the year of application. A close quantitative agreement existed between the available nitrogen determined with the rapid method and the values calculated with the formula of Furrer and Bolliger (1978).