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Rates of decomposition of plant residues and available nitrogen in soil, related to residue composition through simulation of carbon and nitrogen turnover |
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| Authors: | Aviva Hadas Larissa Kautsky Emine Erman Kara |
| Institution: | a Institute of Soil, Water and Environmental Sciences, A.R.O., The Volcani Center, Bet-Dagan 50250, Israel b Department of Soil Science, Cukurova University, Adana, Turkey c Department of Environment, Faculty of Engineering, Nigde University, Nigde, Turkey |
| Abstract: | 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 10−5 d−1, respectively, and that of the cellulose-like pool, obtained by model optimization against mineralization of cellulose with NH4+-N in soil, was 0.051 d−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−1 C 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 26-27 mg N kg−1 C 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. |
| Keywords: | Plant residues C and N partitioning in residues Decomposition C and N mineralization Cellulose Model N immobilization |
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