团聚体解聚与重聚过程中水合铁氧化物转化及其调控措施对水稻土肥力的影响

Paddy soil is one of the most important resources for food production in China. Researches on paddy soil fertility improvement are of great significance in terms of enhancing yield potential of paddy fields with middle and low productivity, reducing chemical fertilizer use and promoting eco-environmental satisfaction as well as dealing with global climate change. This program establishes a field experiment with altering seasonal application of phosphorus and inputting ferrihydrite and organic fertilizers at a typical region of paddy soil in the Mid-low Reaches of Yangtze River. Intensive analysis of soil fertility indicators, aggregate composition and size distribution, aggregate C and N, hydrous ferric oxides (HFOs) of 0-10 cm surface soil and 10-20cm subsurface soil from 5 sampling periods will be done annually while characterization of mineral and surface chemical states is performed by using X-ray diffraction, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Our aims are to clarify dynamic changes of soil aggregates under different tillage, moisture, fertilization and rotation, to interpret the roles of hydrous ferric oxides in transformation of plant nutrients, aggregation of soil particles and improvement of soil fertility, and to raise new strategies for paddy soil fertility improvement though comprehensive incorporation of the field management of rice/wheat rotation with meaningful application of phosphorus, HFOs and organic fertilizers.

水稻土是我国粮食生产最重要的土壤资源之一，研究水稻土肥力培育问题对于挖掘中低产稻田增产潜力、减少化肥用量、改善生态环境和应对全球气候变化等具有重大生产实践意义。本项目在我国长江中下游地区典型稻麦轮作水稻土上进行改变施磷季节、施用水铁矿和有机肥的田间试验。分析每年5个不同时期0-10cm表层和10-20cm亚表层土壤样品的肥力指标、团聚体粒径组成与分布及不同粒级碳氮含量、土壤和团聚体中水合氧化铁(HFOs)含量，并采用X射线衍射法、高分辨透射电镜和X射线光电子能谱等技术表征HFOs的矿物学特征和表面化学状态。旨在揭示稻麦轮作水稻土在不同耕作、水分管理和施肥条件下土壤团聚体变化特征，解析HFOs在水稻土养分转化、团聚体形成过程和土壤肥力培育中的作用，提出综合稻麦轮作田间管理与合理施用磷、外源HFOs和有机肥的水稻土肥力培育新途径。

传统土壤学中所谓的无定型或弱晶型铁、铝硅和锰氧化物是土壤中天然存在的纳米矿物，这些纳米矿物对全球碳、氮和磷循环及重金属的迁移具有重要影响。采用先进的研究方法有利于定量化揭示纳米矿物在土壤中形成、变化及其对土壤性质和作物生长的影响机制。本项目研究了田间条件下水稻-小麦轮作下土壤团聚体解聚与重团聚过程中土壤纳米铁氧化物与有机碳的形成、转化和积累特征及其相互作用，并通过温室试验和实验室试验研究了外源添加纳米铁氧化物（水铁矿）土壤有效磷以及对玉米、水稻和小麦生长的影响。研究结果表明，施有机肥促进了晶型铁氧化物和晶型硅铝氧化物向纳米铁氧化物和纳米硅铝氧化物的转变和纳米矿物在土壤中的积累；土壤纳米铁氧化物含量与土壤有机质含量呈良好的正相关关系，而与土壤有机质分解速率呈良好的负相关关系；在厌氧条件下部分水铁矿发生了还原和溶解，但却增大了残留水铁矿的比表面积和吸附能力。我们发现，土壤纳米矿物在提高旱地红壤有机质含量、阻止红壤酸化和钝化重金属活性也起重要作用。我们认为矿物纳米颗粒（如碳酸钙纳米颗粒）在半干旱地区褐土中也可能起重要作用。而在作物生产上，施用低浓度水铁矿对玉米、水稻和小麦种子萌发和生长具有显著的促进作用。本项目从土体土壤、不同粒径土壤团聚体和土壤胶体尺度系统地阐明了土壤纳米矿物对提高土壤有机质含量的促进作用，研究结果在培肥土壤、减少土壤温室气体排放和提高作物产量中具有良好的应用前景。