Hadas, A., Inst of Soils and Water, ARO, The Volcani Center, Bet Dagan 50250, Israel
Molina, J.A.E., Inst of Soils and Water, ARO, The Volcani Center, Bet Dagan 50250, Israel
Feigenbaum, S., Inst of Soils and Water, ARO, The Volcani Center, Bet Dagan 50250, Israel
Clapp, C.E., Inst of Soils and Water, ARO, The Volcani Center, Bet Dagan 50250, Israel

Different N flow schemes for N immobilization were tested by comparing the kinetics of CO2 evolution, NH+ 4-N, NO- 3-N, inorganic 15N, and organic 15N excess, measured in soils incubated with 200 mg kg-1 of 15N-labeled NH+ 4-N, with data simulated by the computer model NCSOIL structured to represent several pathways of C and N turnover. Cumulative N immobilization was up to 10% of the N added and was greater when NH+ 4 was added to dry soils than when added to preincubated soils. The immobilization was primarily due to the microbial biomass drawing N from the inorganic pool, rather than utilizing N directly from the decomposing soil organic matter. Nitrate formed by nitrification seemed to have also been immobilized. -from Authors