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Decomposition of Nitrogen‐15‐Labeled Wheat and Cellulose in Soil: Modeling Tracer Dynamics
Author(s) -
Hadas Aviva,
Feigenbaum Sala,
Sofer M.,
Molina J. A. E.,
Clapp C. E.
Publication year - 1993
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1993.03615995005700040019x
Subject(s) - mineralization (soil science) , cellulose , decomposition , chemistry , nitrogen , soil water , kjeldahl method , dilution , reaction rate constant , tracer , kinetics , biochemistry , organic chemistry , ecology , biology , thermodynamics , physics , quantum mechanics , nuclear physics
The decomposition of heterogeneous plant material could be described more generally if it were based on decomposition rates of defined materials. In this study, mineralization of 15 N‐labeled wheat ( Triticum aestivum L.) and 15 N turnover linked with the decomposition of cellulose in soil were measured and compared with simulated kinetics computed by the model NCSOIL. Dried wheat shoots (2 g C kg −1 ) with a C/N ratio of 14.4, or cellulose with ( 15 NH 4 ) 2 SO 4 at the same C rate and C/N ratio, were added to two soils and incubated for 32 wk at 30 °C and 60% water‐holding capacity. Inorganic and Kjeldahl N and 15 N were measured and compared with simulated data. Cellulose induced net immobilization of 70 mg N kg −1 within 2 wk; thereafter, net N mineralization was greater than for untreated soils. The decomposition rate constant of cellulose, computed by optimization of the model, was 0.024 d −1 . The model underestimated N immobilization, the subsequent rate of net N mineralization, and the isotopic dilution of inorganic N. These discrepancies probably resulted from slower turnover of microbial biomass than simulated. Wheat decomposition was divided into three stages, corresponding to soluble, cellulose‐like, and resistant fractions that decomposed with rate constants of 3.0, 0.024, and 4 × 10 −8 d −1 and accounted for 19, 45, and 36%, respectively, of organic wheat N. The computed gross mineralization of wheat N after 32 wk totaled 64% of added organic N, whereas 15 N recovery as inorganic N was 40 to 50%, depending on the soil. The difference was attributed to concurrent assimilation of labeled N by soil microbial biomass that depended partly on native soil N concentrations and should be considered in interpreting tracer experiments.