IMMOBILIZATION AND REMINERALIZATION OF AMMONIUM AND NITRATE AFTER ADDITION OF DIFFERENT ENERGY-SOURCES TO SOIL

The technique of crosswise labelling two otherwise identical laboratory incubation series was used in three different experiments to study immobilization and remineralization of mineral N in a sandy moraine loam soil. In experiments I and II the two series were cross-wise labelled with15NH4NO3 and NH415NO3 at the start of the experiment. In experiment I glucose was used as an energy source for the heterotrophic microorganisms, in experiment II barley straw was used. In experiment III the soil was amended with unlabelled NH4NO3 and15NH4NO3, one series receiving the labelled compound at the start of the experiment, the other on day 10. Barley straw was used as an energy source. In experiments I and II, no significant difference was found in the remineralization rates of immobilized NH4-N and NO3-N. In experiment III, NH4-N immobilized during the first 10 days of straw decomposition was found to gain more stability against mineralization than NH4-N immobilized between days 10 and 21. The data obtained are discussed in connection with problems of interpreting tracer data in studies on N mineralization and immobilization in soil. © 1987 Martinus Nijhoff Publishers.