Co-Authors:
Hadas, A., Inst. of Soils and Water, ARO, P.O. Box 6, Bet Dagan, Israel
Sofer, M., Inst. of Soils and Water, ARO, P.O. Box 6, Bet Dagan, Israel
Feigenbaum, S., Inst. of Soils and Water, ARO, P.O. Box 6, Bet Dagan, Israel
Molina, J.A.E., Inst. of Soils and Water, ARO, P.O. Box 6, Bet Dagan, Israel
Clapp, C.E., Soil Science Dept., Univ. of Minnesota, St. Paul, 55108, United States
Abstract:
Microbial biomass is determined from the excess of extractable organic N released from fumigated soil samples. In the presence of relatively high contents of labeled mineral N, small differences in organic N and 15N may not be detectable. Two approaches were tested to determine organic N content and its 15N enrichment in the presence of considerably greater concentrations of labeled mineral N(i) Removal of mineral N from mixed solutions of alanine and NH4 or NO3 by reduction and boiling under alkaline conditions, prior to Kjeldahl digestion. (ii) Including mineral N in Kjeldahl N analysis, by reduction under acidic conditions prior to digestion and calculating organic N and 15N content by subtracting mineral N and 15N. The removal of mineral N was either incomplete- particularly regarding labeled mineral N, or partly destroyed organic N as well. When mineral N was included in the digest, the recovery of N and 15N was sufficiently accurate to obtain good results of organic N and 15N by subtracting the known quantities of mineral N, even when organic N was only 20% of the total Kjeldahl N. This procedure was used to determine the flush of Kjeldahl N in fumigated soils that were incubated with labeled mineral N and cellulose. Copyright © 1989 by Marcel Dekker, Inc.
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