Abstract: 【Objective】 In order to explore the effect of straw retention on SOC（soil organic carbon）content, the contributions of wheat and corn residues (root and straw) to SOC under fluvo-aquic soil area were studied, which have a great significance to take technical measures to promote SOC content of winter wheat-summer corn rotation system.【Method】The optimized DPM/RPM values (the ratio of decomposable plant material to resistant plant material) of different residues in Roth C-26.3 model was adjusted on the basis of the remaining rates of different organic materials after their decomposition. The modified model was validated with the data obtained from the short-time decomposition experiment (2012.11-2013.11) and the long-term trial conducted in Zhengzhou (1990-2008). Based on the optimized DPM/RPM parameters of Roth C-26.3 model, the contributions of wheat and corn residues to SOC in winter wheat-summer corn rotation system in northern China under three different fertilizer treatments (no fertilizer CK, chemical fertilizer NPK, chemical fertilizer combined with straw NPKS) were simulated. 【Result】DPM/RPM values of wheat root (WR), wheat straw(WS), corn root (CR), corn straw (CS) were 0.89, 3.04, 4.35 and 3.25, respectively, when the model was in optimal condition. It showed that in CK treatment, the carbon input derived from wheat root and corn root were 50%, respectively, while the contributions of wheat root and corn root to newly-formed soil organic (0-20 cm) were 60% and 40%, the retention coefficients of wheat root and corn root were 15.5% and 10.8%, respectively; in NPK treatment the carbon input derived from wheat root and corn root were 60% and 40%, respectively, while the contributions of wheat root and corn root to newly-formed soil organic (0-20 cm) were 71% and 29%, the retention coefficients of wheat root and corn root were 17.5% and 11.4%, respectively; in NPKS treatment the carbon input derived from wheat root and corn root were 47%, 21% and 32%, respectively, while the contributions of wheat root and corn root to newly-formed soil organic (0-20 cm) were 50%, 22% and 28%, the retention coefficients of wheat root and corn root were 16.9%, 11.2% and 11.4%, respectively. In a word, the contribution of wheat residue (50% -71%) to newly-formed SOC was greater than corn residue (22%-40%) in winter wheat-summer corn rotation system in north China whether no fertilization, balanced fertilization or straw returned. The ratio of SOC derived from wheat to newly-formed SOC was greater than the proportion of the carbon input from wheat to total carbon input, instead of the carbon input of corn and its contribution to newly-formed SOC. The carbon efficiency of wheat root (15.5% -17.5%) was more than the carbon efficiency of corn root and corn straw (10.8% -11.4%).【Conclusion】The modified RothC model can be used to explore the contributions of wheat and corn residues to newly-formed SOC in fluvo-aquic soil area. The contribution of wheat root to SOC was greater than corn root in winter wheat-summer corn rotation system in the North China and the retention coefficient of corn root was greater than the corn straw in NPKS treatment, so the application of root residues (especially wheat roots) could promote the soil organic carbon stock.

Key words: RothC model, wheat residue, corn residue, soil organic carbon, fluvo-aquic