潮土区小麦、玉米残体对土壤有机碳的贡献——基于改进的RothC模型

【目的】为进一步了解秸秆还田对土壤有机碳(SOC)的提升效果,探究作物残体(根系与秸秆)对潮土区SOC的贡献,为华北冬小麦-夏玉米区SOC提升提供理论依据。【方法】基于腐解试验的有机物料碳残留率数据,获得4种有机物料在RothC-26.3模型最优时对应的DPM/RPM参数值(易分解植物残体和难分解植物残体的比值)。利用修订的DPM/RPM参数,获得了改进的RothC-26.3模型,并用郑州潮土区短期腐解试验(2012年11月至2013年11月)和长期定位试验数据(1990—2008年)进行验证,模拟出郑州潮土区冬小麦-夏玉米轮作系统中小麦、玉米残体在3种不同施肥处理下(不施肥CK,平衡施肥NPK和秸秆还田NPKS)对新形成SOC的贡献。【结果】在模型达到最优时,小麦根系(wheat root,WR)、小麦秸秆(wheat straw,WS)、玉米根系(corn root,CR)和玉米秸秆(corn straw,CS)的DPM/RPM值分别为0.89、3.04、4.35和3.25。模型结果显示,CK处理小麦根系、玉米根系的碳投入占碳投入的比例均为50%,而来源于小麦根系、玉米根系的SOC(0—20 cm)占新形成的SOC比例分别为60%、40%;小麦根和玉米根固碳效率分别为15.5%、10.8%;NPK处理小麦根系、玉米根系的碳投入占碳投入的比例分别为60%、40%,而来源于小麦根系、玉米根系的SOC(0—20 cm)占新形成SOC的比例分别为71%、29%;小麦根和玉米根固碳效率分别为17.5%、11.4%;NPKS处理小麦根系、玉米根系、玉米秸秆的碳投入的比例分别为47%、21%、32%,而小麦根系、玉米根系、玉米秸秆对新形成的SOC(0—20 cm)贡献分别为50%、22%、28%;小麦根系、玉米根系、玉米秸秆的固碳效率分别为16.9%、11.2%、11.4%。总之,冬小麦-夏玉米轮作系统中无论是不施肥、平衡施肥还是秸秆还田处理,小麦根系对新形成SOC的贡献率(50%—71%)大于玉米根系和玉米秸秆对新形成SOC贡献率(22%—40%)。源自小麦的SOC占新形成SOC的比例均分别大于源自小麦的碳投入占总碳投入的比例,而源自玉米的投入及其对新形成SOC的贡献则反之。小麦根系的固碳效率(15.5%—17.5%)大于玉米根系和玉米秸秆的固碳效率(10.8%—11.4%)。【结论】改进后的RothC模型可用来探究潮土区冬小麦-夏玉米轮作系统中小麦、玉米残体对新形成SOC的贡献。郑州潮土区冬小麦-夏玉米轮作系统中小麦根系对新形成SOC的贡献率均大于玉米根系和玉米秸秆的贡献率。根茬还田(尤其是小麦根茬还田)更有利于提升土壤有机碳含量。

Contributions of Wheat and Corn Residues to Soil Organic Carbon Under Fluvo-Aquic Soil Area—Based on the Modified RothC Model

【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.