秸秆腐解对土壤镉赋存形态和生物有效性的影响机理

Cadmium beyond standard of agricultural product and cadmium pollution of farmland has become more and more serious. The remediation and safe utilization has being a research focus. Application of straw for the remediation of cadmium in soils not only adapts to national conditions of China but consists with the demand of sustainable agriculture. However, researches on the effect of straw decomposition on cadmium availability are rarely reported. It is necessary to study the effect of straw decomposition on the speciation and availability of cadmium in soils and the related mechanisms in order for appropriate application of straw in the remediation of cadmium in contaminated soils. Based on the application of advanced analytical equipments such as infrared spectroscopy, nuclear magnetic resonance (NMR), this project will be accomplished around three aspects: Firstly, the changes of cadmium fractions in soils after the application of straw will be monitored to ascertain the effect of straw decomposition. Secondly, the content, optical properties and functional groups of degradation products will be monitored to ascertain the regulation of straw decomposition in soils, analysis its relationship with cadmium fractions and reveal the mechanism of the effect of straw decomposition on cadmium in soils. Thirdly, cadmium concentrations in plants will be tested to validate the effect of straw decomposition on cadmium availability. The research results of this project can provide theoretical basis for obtaining the new method of improving the quality and safety level of agricultural products and new approach for the remediation of cadmium polluted soils by the application of straw.

随着农产品镉含量超标严重，镉污染农田面积不断扩大，镉污染土壤的修复和安全利用已成为国内外的研究热点。利用秸秆治理镉污染土壤适合我国国情，也符合可持续发展农业的要求。目前关于秸秆腐解对土壤镉有效性的影响鲜有报道，明确秸秆腐解对土壤镉赋存形态及有效性的影响效果和机理对合理利用秸秆治理土壤镉污染有重要意义。本项目基于红外光谱仪、核磁共振谱等先进仪器，拟通过监测施用秸秆后不同时期土壤镉形态变化规律，明确秸秆腐解对土壤镉赋存形态的影响效果；通过监测施用秸秆不同时期降解产物含量、光学性质和官能团的变化及与镉的配合情况，明确秸秆腐解产物变化规律，探析其与土壤镉赋存形态之间的关系，揭示秸秆腐解对镉形态的影响机理。通过多茬植物吸收镉的情况，验证秸秆腐解对土壤镉有效性的影响效果。本项目研究结果可为利用秸秆获得提高农产品质量安全的新方法和修复镉污染农田土壤的新途径提供理论依据。

本项目针对目前我国农田镉污染日益严重，农产品镉含量超标严重，而施用秸秆作为一项符合可持续发展农业要求的措施，其腐解对镉有效性的影响鲜有报道的问题而开展了秸秆腐解中土壤镉形态转化、酸碱度、有机质组分的数量及结构特征变化的研究，来明确秸秆腐解对土壤镉形态转化及生物有效性的影响效果和机理，取得以下主要研究成果：.1.明确了玉米秸秆腐解对土壤镉赋存形态的影响规律。结果表明秸秆可显著影响土壤镉形态分布，且该影响随秸秆腐解过程的进行呈现出不同的效果。秸秆施入潮土后的前225天，可促进镉由活性较低的碳酸盐结合态等形态向高活性的交换态转化。随着腐解的进行，从270天开始，交换态镉含量则开始降低，碳酸盐结合态等形态镉含量有所增加。在红壤中秸秆腐解对土壤镉形态转化也表现出相同的变化规律。但在红壤中秸秆对交换态镉含量降低的效果从第315天才表现出来。.2. 探索了玉米秸秆腐解对土壤pH的影响及其与土壤镉活性的关系。秸秆腐解可显著影响土壤pH，但相关分析的结果证实添加秸秆后pH不是引起土壤镉形态转化的主要因素。.3. 监测了玉米秸秆腐解过程中土壤中有机组分的含量、结构特征，明确了秸秆腐解产物与镉形态之间的关系。结果表明：1）添加秸秆后土壤水溶性有机质含量随秸秆腐解而变化，但其不是影响土壤镉形态转化的主要因素。2）秸秆腐解可使土壤胡敏酸与富里酸比值（H/F）先降低后增加。H/F的变化是秸秆腐解影响土壤镉形态转化的原因之一。3）应用红外光谱和核磁共振波谱对土壤有机质结构特征分析的结果表明，秸秆腐解前期有机质结构简单利于土壤镉的活化，秸秆腐解后期有机质结构趋于复杂可抑制土壤镉的活化。添加秸秆后土壤有机质组分结构特征变化为土壤镉形态转化的主要因素之一。.4. 验证了玉米秸秆腐解对土壤镉生物有效性的影响效果。生物盆栽试验进一步证实秸秆施入土壤后期（潮土：第6茬，红壤：第7茬）显著抑制了小油菜对土壤镉的吸收，可实现污染土壤的安全利用。