Amino acids and amino sugars extracted by EUF from a sandy soil incubated with green manure, bacterial biomass or cellulose

The extraction of soils by the electro-ultrafiltration (EUF) method yields organic N which has been used as an index for mineralisable N in soils. Thi s EUF extractable organic fraction contains a mixture of various N compound s not yet completely identified. It has been proposed that the amino N comp ounds are more indicative for the potentially mineralisable N in soils than the total organic N extracted (Mengel et al., 1999). An amendment of soils with easily mineralisable organic matter may, therefore, alter the amino N concentrations of the organic N extracted. Our determination of the amino N compounds aimed to prove this hypothesis. The principle of our experiment was to mix soil with green manure, bacteria l biomass and cellulose, respectively, and to incubate the treated soil aer obically for 80 days at 20 degrees C in the laboratory. Control treatments without organic amendment were also incubated. Soil samples were taken seve ral times during the incubation period and analysed for the inorganic N (NO 3--N and NH4+-N) and for the EUF extractable organic N. Amino acids and ami no sugars were determined in the hydrolysed EUF extracts. The concentrations of amino acids and amino sugars in the organic N extract ed varied with time and differed between the treatments. Glutamic acid has been found to be the most relevant amino acid in the EUF extracts and was p articularly indicative for the existence of mineralisable green manure in t he soil. Glucosamine was the most relevant amino sugar in the EUF extracts and this amino sugar appears to be indicative for the easily mineralisable relies of microbial cells in the soil.