Hadas, A., Inst. Soil, Water and Environ. Sci., A.R.O., Volcani Center, Bet-Dagan 50250, Israel
Kautsky, L., Inst. Soil, Water and Environ. Sci., A.R.O., Volcani Center, Bet-Dagan 50250, Israel
Goek, M., Department of Soil Science, Cukurova University, Adana, Turkey
Kara, E.E., Department of Environment, Faculty of Engineering, Nigde University, Nigde, Turkey

The dynamics of inorganic N in soil following the application of plant residues depends on their composition. We assumed that all plant materials are composed of similar components, each decomposing at a specific rate, but differ in the proportions of the various components. The NCSOIL model that simulates C and N turnover in soil was used to link the rates of residue decomposition to their composition, defined as soluble, cellulose-like and lignin-like C and N, and thereby integrate short and long-term effects of residues on available N dynamics in soil. Five plant residues in a wide range of C:N ratios were incubated in soil for 24 weeks at 30°C, during which C and N mineralization were measured. The materials with large C:N ratios (corn, rice hulls and wheat straw) were also incubated with NH4+-N to avoid N deficiency. The residues were analyzed for total and soluble C and N. The partitioning of insoluble C and N between cellulose- and lignin-like pools was optimized by best fit of simulated C and N mineralization to measured results. The decomposition rate constants of the soluble and lignin-like pools were assumed to be 1.0 and 10-5d-1, respectively, and that of the cellulose-like pool, obtained by model optimization against mineralization of cellulose with NH4+-N in soil, was 0.051d -1. The optimized, kinetically defined lignin-like pool of all residues was considerably larger than lignin contents normally found in plant residues by the Van Soest procedure. Gross N mineralization of tobacco and rape residues was similar, but N recovery from tobacco was larger, because a larger fraction of its C was in the lignin-like pool. N in rice hulls, corn and wheat residues was mostly recalcitrant, yet rice hulls did not cause N deficiency, because most of its C was recalcitrant too. The soluble components of the residues had strong short-term effects on available N in soil, but the cellulose-like pool was equally important for short and medium-term effects. Soluble and cellulose-like C were 29 and 42% of total C, respectively, in corn and 7 and 50% in wheat. Maximal net inorganic N losses, measured in both residue treatments after 2 weeks, were 42 mg g-1 C applied as corn and 31 mg g-1C applied as wheat, or 84 and 110 mg g-1 decomposed C of corn and wheat, respectively. Rice hulls immobilized N slowly, but by the end of 24 weeks all three residues immobilized 26-27mgNkg -1C applied. The different dynamics of N immobilization demonstrated the need to determine the decomposability of C and N rather than their total contents in plant residues. © 2003 Elsevier Ltd. All rights reserved.