ABSTRACT
The application of sewage sludge in soils can cause N enrichment of surface soil and groundwater. To prevent this kind of pollution the sewage sludge has to be spread on the soil at the correct time and in reasonable quantities. The form of nitrogen present in sludges must be studied in order to estimate the quantity of plant available nitrogen. The mineral nitrogen for example: NH4 -N; NO2 -N; NO3 -N is easily absorbed by the crops. The organic form of nitrogen must be mineralized through microorganisms before they are available to the plants. For the estimation of nitrogen value of sludge the amount of mineralizable nitrogen must be determined. In this paper a few models assessing the potentially mineralizable nitrogen will be discussed.
