A field method for the determination of nitrogen mineralization in forest soils

摘要

The mineralization of nitrogen in forest soils, one of the processes that provides forest ecosystems with nitrogen, has practically not been studied in Russia. A variant of the method used for the measurement of the nitrogen mineralization in forest soils is proposed, and a description of its field and laboratory stages is given. At the field stage, as the ammonium concentrations are determined in the soil horizons, eight soil samples free of plants and plant roots are recommended to be exposed in a uniform forest area in order to provide a 10% error of the average. The results obtained in a laboratory by the traditional method of measuring the ammonium content in litter extracts may be overstated by 5 times (on the average, by 1.7 times) as compared to the results obtained by the diffusion-isothermic method proposed. The source of errors in the former method is the specific features of Nessler's reagent, which forms colored complexes with metals and organic compounds. In addition, extracts from loamy soils often grow turbid and opalescent at the addition of Nessler's reagent, which makes the measurement of the optical density impossible. A highly sensitive and well-reproducible method is recommended for the reduction of nitrates to nitrites in a column with coppered cadmium. The methods proposed are simple and reliable and do not require the expensive autoanalyzers that are used abroad.