长期施用石灰红壤性水稻土酸性特征变化过程与机制

Reddish paddy soil is one of the most important soil types in tropical and subtropical region of southern China. Acidification of reddish paddy soil has become the main restrictive factor for agricultural crops growth in recent years. Liming is an effective method to amend acid soils, but the changing process and the mechanisms of soil acidity under long-term liming in reddish paddy soils are unclear. This study is to clarify the changing process and response mechanisms of soil acidity under long-term liming condition in reddish paddy soils based on a long-term experiment which was established in 1981 year. Study contents include changing processes of contents and ration of soil active acidity, exchangeable acidity and hydrolytic acidity and its relationship with soil pH under long-term liming; changing processes of soil cation exchange capacity, effective cation exchange capacity, exchangeable cation(Ca2+, Mg2+, Na+, K+), exchangeable H+, Al3+ and the content of CaCO3, degree of based saturation, degree of exchangeable H+, Al3+ saturation and its relationship with soil pH; comprehensively analyze the relationship between soil acidity forms, based saturation and soil pH and their relative contribution rate, and elaborate the formation mechanisms of soil acidity during different stage under long-term liming condition in reddish paddy soil. Our results will provide scientific basis for scientific application of lime to ameliorate soil acidity and impede soil acidification processes.

红壤性水稻土是我国南方最主要的水稻土类型，近年来酸化问题日益突出。施用石灰是改良酸性土壤的重要措施，但目前尚缺乏长期施用石灰红壤性水稻土酸性特征变化过程的监测及机理研究。本项目以连续33年施用石灰的长期定位试验为平台，主要探明长期施用石灰红壤性水稻土酸性特征变化过程，包括土壤活性酸、交换性酸、水解性酸的变化特征；分析长期施用石灰红壤性水稻土酸性变化过程中土壤酸性形态的比例和转化及其与pH的关系；研究酸性变化过程中盐基离子的变化特征，阐明盐基离子的变化特征在土壤酸化中作用；从酸碱动态平衡角度分析长期施用石灰条件下盐基离子交换、迁移特征；综合分析酸性形态及阳离子饱和度与土壤pH变化的关系及其相对贡献率，揭示长期施用石灰红壤性水稻土酸性变化过程的机制。本研究结果将为施用石灰阻控南方红壤性水稻土酸化和改良酸性土壤提供理论依据。

土壤酸化是土壤质量退化的重要形式，近几十年来，由于工业化飞速发展导致酸沉降增加对土壤酸化加速起到重要作用，化肥的大量施用也加速了农田土壤酸化过程，农田土壤酸化问题对我国粮食安全和生态环境已造成严重威胁。红壤性水稻土分布区农业集约化种植程度高、化肥施用量大，且与我国酸雨分布区重叠，土壤酸化问题尤为严重。施用石灰是改良酸性土壤的重要措施，通过施用石灰可以提高土壤pH和交换性Ca2+含量，降低土壤交换性H+、Al3+含量，由于土壤是一个由多种物质和组分组成的多相复杂体系，同时土壤处于水、大气和作物整个物质能量循环系统之中，土壤中的物理化学反应十分复杂，长期施用石灰下土壤在不同阶段呈现的酸性特征及其机制并不明确。项目以开始于1981年的红壤性水稻土施用石灰的长期定位试验为平台，研究了长期施用石灰红壤性水稻土酸性特征变化规律，分析土壤活性酸、交换性酸、水解性酸的变化及比例和它们与土壤pH值的关系，测定土壤阳离子交换量（CEC）、交换性盐基离子（Ca2+、Mg2+、Na+、K+）、交换性阳离子H+、Al3+含量及CaCO3含量，探讨不同施肥模式对土壤盐基离子、水稻产量效应和植株阳离子吸收积累的影响，及土壤盐基离子和植株带出阳离子量与土壤酸度的关系。研究结果表明，长期氮磷钾肥配施石灰显著提高了红壤性水稻土交换性Ca2+含量、交换性盐基离子和盐基饱和度，可缓解稻田土壤的酸化。本项目研究结果可以为红壤性水稻土长期合理施用石灰调节土壤酸度、改良土壤质量和促进农业的可持续发展提供理论依据和技术支撑。