三峡库区紫色土坡耕地-桑树系统农业面源污染控制机理研究

The system of slope land - mulberry of purple soil of Three Gorges Reservoir Area will be studied by using the methods of field investigation, experimental runoff plot, slope-surface observation, artificial rainfall experiment, environmental isotope tracing. Combining experimental observation, mathematical derivation and model simulation, the characteristics of soil habitat as well as the control effect of agricultural non-point source pollution of various configuration modes of the system of slope land - mulberry of purple soil will be quantitative researched. Afterwards, the optimum mode of system of slope land - mulberry of purple soil of controlling agricultural non-point source pollution will be chosen, the range and distance of critical band of various configuration modes of the system of slope land - mulberry of purple soil controlling agricultural non-point source pollution will be determined. Applying 4DAgro, the nutrient transportation model of farmland, to simulate the accumulation and migration of nutrients of various configuration modes of the system of slope land - mulberry of purple soil, the mechanism of system of slope land - mulberry of purple soil of Three Gorges Reservoir Area controlling agricultural non-point source pollution will be revealed. This project will provide a theoretical basis to promote the system of slope land - mulberry of purple soil of Three Gorges Reservoir which can prevent and control agricultural nonpoint source pollution.

本项目以三峡库区紫色土坡耕地-桑树系统为研究对象，采用野外调查、径流试验小区、坡面观测、人工降雨试验、环境同位素示踪等多种试验观测方法，将试验观测、数学推导和模型模拟相结合，定量研究不同紫色土坡耕地-桑树配置模式的土壤生境特征以及农业面源污染的控制效果，进行控制农业面源污染的紫色土坡耕地-桑树配置模式的优选，确定不同紫色土坡耕地-桑树配置模式控制农业面源污染的临界带间距范围，应用4DAgro农田营养迁移模型模拟不同紫色土坡耕地-桑树配置模式营养物质的积累和迁移，揭示三峡库区紫色土坡耕地-桑树系统控制农业面源污染的机理，为在库区推广紫色土坡耕地-桑树系统防控农业面源污染提供理论依据。

随着对点源污染控制技术和水平的提高，由非点源特别是农业面源造成的水环境问题已日益突出，三峡库区特殊的生态环境条件、人口资源、社会经济状况和三峡工程建设对生态环境的压力使农业面源污染问题十分尖锐。本项目以三峡库区紫色土坡耕地-桑树系统为研究对象，采用野外调查、径流试验小区、坡面观测、环境同位素示踪等多种试验观测方法，通过将试验观测、数学推导相结合，我们发现T3（地埂桑+一带等高桑树，带间距为4.25 m）模式能够显著减少地表径流和泥沙量，分别比对照（常规农作）减少72.04%和81.82%。径流中磷的流失与径流和泥沙息息相关，以颗粒态附着的形式为主。径流中氮的流失主要取决于径流，不受桑树植物篱种植方式影响，却受桑树种植密度影响，当桑树密度越大则拦截氮的效果越好。桑树植物篱的种植使耕层土壤全氮、全磷分别比对照增加10.1%和25.9%，T3和T5（两带纵坡桑树，带间距为1.6 m）效果显著。T5处理的> 0.25mm水稳性团聚体含量为806.33g kg-1，> 0.5mm水稳性团聚体是常用的土壤抗蚀性指标，其含量占水稳性总团聚体的76.20%，结构体破坏率仅为18.82%，水稳性团聚体的平均质量直径（EMWD）为4.48，由此表明随着桑树树龄的增大，坡耕地水稳性团聚体含量增多，稳定性好。T1处理（两带等高桑树，带间距为4.5 m）土壤微生物的PLFA总量（20.54 nmol g-1）显著高于对照；T1处理显著提高了土壤细菌含量，T5处理土壤中真菌的丰富度相对较高。T1的多样性指数(H')和均匀度指数(J)最高。综上所述，T1、T3和T5配置模式能够有效控制水土流失，提高土壤肥力，改善土壤颗粒组成，丰富土壤微生物群落结构，以达到有效农业面源污染的控制效果的目的，为在库区推广紫色土坡耕地-桑树系统防控农业面源污染提供理论依据。