Simulation of Nitrogen-15 Immobilization by the Model NCSOIL

Hadas, Aviva; Molina, J. A. E.; Feigenbaum, Sala; Clapp, C. E.

Simulation of Nitrogen-15 Immobilization by the Model NCSOIL

1987

Hadas, Aviva | Molina, J. A. E. | Feigenbaum, Sala | Clapp, C. E.

The computer model NCSOIL computes the dynamics of C and N transformations in soil. In its original version, the microbial biomass assimilated organic N from the decay of organic pools, and inorganic N was immobilized only when decomposed organics were deficient in N with respect to biomass needs for growth (NCSOIL—direct version). A new version was presented in which it was assumed that microbial biomass immobilized N only from the inorganic pool, while the decay of organic N always resulted in N mineralization (NCSOIL-MIT version). NCSOIL-MIT was calibrated and tested for the incorporation of inorganic ¹⁵N in the organic soil N against experimental data and compared with the direct version. Net N mineralization was highly sensitive to the microbial efficiency of soil decomposable organic C incorporation. An efficiency of 0.2 gave a good account of net N mineralization for soils unamended with organic substances. NCSOIL-MIT simulated the incorporation of ¹⁵N, added as NH₄, into the organic soil pools. The kinetics of ¹⁵N immobilization was sensitive to microbial efficiency as well as to other parameters that control soil N turnover. NCSOIL—direct version required the decomposition of polysaccharide-like material in order to obtain ¹⁵N incorporation in the soil organic pools, and the kinetics of ¹⁵N immobilization depended on the rate of polysaccharide decomposition.

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