长期秸秆还田下土壤纳米和微纳米颗粒供钾特征

Direct straw returning is an important means of supplementing soil potassium. The study on the change of soil potassium supply characteristics under straw returning plays an important role in potassium management. The mainly clay minerals of soil nano- and micro-nano-particles are single type, small crystal size and weak crystallization, which are susceptible to the environment impact. However, the potassium supply characteristics of soil nano-particles and micro-nanoparticles under long-term straw returning are still unclear. In this project, using long-term (14 years) positioning experiment of rice-wheat rotation, inorganic and organic-inorganic complex particles of nanometer (25-100 nm), micro-nanometer (100-450 nm) and micrometer (450-2000 and < 2000 nm) were separated and extracted. Studying the composition and structure characteristics of clay minerals in different clay particles, combining with the morphology, content and potassium release characteristics of clay particles, revealing the effects of long-term straw returning on clay mineral composition and structure and relationship with potassium supply characteristics in soil nanoparticles, micro-nanoparticles and micro-particles. The characteristics of adsorption and desorption of potassium by pure minerals were studied through simulation experiments, and the similarities and differences of fixation and release mechanism of potassium by different size minerals were explored. The results will enrich and develop the basic theory of potassium nutrient transformation under straw returning and the characteristics of soil potassium supply, provide theoretical basis for the recycling of rice straw and wheat straw and the management of soil potassium fertilizer in China.

秸秆直接还田是补充土壤钾素的重要手段，研究秸秆还田下土壤供钾特征的变化对钾肥管理具有重要作用。土壤纳米和微纳米颗粒主要以类型单一、晶体尺寸小、结晶弱的粘土矿物为主，因此其易受秸秆还田的影响。然而长期秸秆还田下土壤纳米和微纳米颗粒释钾特征尚不清楚。本项目利用长期（14年）定位试验,分离并提取纳米、微纳米和微米无机和有机无机复合体颗粒。通过现代仪器分析技术研究土壤颗粒中粘土矿物组成和晶体结构特征，结合各颗粒中钾素形态变化和缓效钾释放特性，阐明长期秸秆还田下土壤纳米、微纳米和微米颗粒供钾特征的异同。再通过模拟试验研究不同尺寸纯粘土矿物对钾的吸附与解吸特点，揭示不同粒径土壤颗粒的供钾机理。研究结果将丰富和发展秸秆还田下钾素养分转化基础理论和土壤供钾特性，为我国稻麦秸秆循环利用、土壤钾肥管理提供理论依据。

秆直接还田是补充土壤钾素的重要手段，研究秸秆还田下土壤供钾特征的变化对钾肥管理具有重要作用。然而长期秸秆还田下土壤纳米和微纳米颗粒释钾特征尚不清楚。本项目利用长期（14年）定位试验，分离并提取纳米（<100 nm）、微纳米(100-450 nm)和微米(450-2000nm)无机颗粒和有机颗粒。分析不同土壤颗粒的钾素形态变化和释放规律、粘土矿物类型和结构特征；以伊利石、蛭石和蒙脱石为对象，通过分析矿物颗粒钾素形态和钾素释放特点，探讨不同尺寸粘粒对钾供给的作用机制。结果表明：（1）秆秸秆的外源钾素能够补充土壤钾素，土壤钾素由亏缺转为盈余状态。长期秸秆还田主要提高粘土矿物层间和表面钾素库存，促进作物生育过程和钾素耗竭时土壤钾素供给能力。（2）土壤粘粒中各形态钾素随粒径降低而增加，主要分布在100-450和<100nm颗粒，长期秸秆还田主要促进纳米和微纳米颗粒非交换性钾的固定。（3）长期秸秆还田并未显著改变各土壤粘粒的粘土矿物组成和结构，粒径是影响粘土矿物组成的主要因素，随着粒径降低，土壤颗粒中蛭石和蒙脱石比重升高。（4）常见含钾矿物的钾素固持和释放能力依次表现为蛭石>蒙脱石>伊利石，蛭石微纳米颗粒和蒙脱石纳米颗粒对钾素具有更高固定和释放能力。（5）结合土壤无机和有机颗粒、矿物颗粒钾素形态、Q/I关系和有机碳组成特征，秸秆还田主要通过增加土壤100-450和<100 nm颗粒中活性有机碳与蛭石和蒙脱石的胶结，从而提升土壤粘粒中非交换性钾的固定及钾素释放。项目研究完善土壤钾素转化理论，对作物科学施肥具有重要实践意义。