紫色土坡耕地耕层质量对侵蚀/管理响应机制试验研究

Serious soil and water loss from the slope farmland in Purple hilly area would cause cultivated-layer shallowing and soil quality degradating, which have directly threatened the regional food safety and ecological security. However, few study have focused on the influencing mechanism of the soil erosion and soil management on cultivated-layer quality for slope farmland at the slope scale. Therefore, the subject of cultivated-layer quality of slope farmland in Purple hilly area will be carried out by sequence analysis between the erodent cultivated-layer simulated by a modified artificial topsoil removal and the recovery cultivated-layer with different erosion level and soil management measures, and by adopting such comprehensive methods as location test, field survey, in-situ monitoring, lab analysis and water-sensitivity simulating experiment.The specific objectives of the study are: (1)to clarify the general trend of cultivated-layer quality and its obstacle performance of slope farmland under different erosion degree and soil management;(2)to identify the quantitative effect of the infiltration difference and the degradation-recovery effect of soil shear strength with different dry-wet alternatingt intensity on cultivated-layer quality of slope farmland in order to reveal the dominant degradating process and its role of micro-erosion environment; (3)to quantify the response mechanism and its restoration effect & time-susceptibility of the cultivated-layer quality for slope farmland to the interaction of soil erosion and soil management measures so as to clarify the formatting mechanism and its recovering process of the rational cultivated-layer; (4)to confirm the diagnostic criteria of the rational cultivated-layer and its regulation approach for slope farmland in Purple hilly area, based on the crop-cultivated-layer coordination model and to propose a minimum data set for rational cultivated-layer according to field survey and its verification at small watershed scale. The project has important academic significance for realizing the sustainable utilization of soil and water resources of farmland, confirming the standards for slope farmland management and ensuring the regional food security in Purple hilly area.

紫色丘陵区坡耕地严重水土流失导致耕层变薄、土壤质量退化，直接威胁区域粮食安全和生态安全，而土壤侵蚀与土壤管理影响坡耕地耕层质量的机理尚不明晰。本项目以紫色土坡耕地耕层质量为研究对象，基于铲土侵蚀模拟法建立不同侵蚀程度和土壤管理措施的侵蚀耕层和恢复耕层序列，采取定位试验、野外调查、田间原位监测与室内分析模拟等综合手段，辨识紫色土坡耕地耕层质量垂直变化、年际变化及障碍类型；构建坡耕地耕层质量与入渗性能、土壤抗剪强度衰减—恢复效应定量关系，阐明耕层质量退化主控过程及微侵蚀环境；定量分析坡耕地耕层质量对土壤侵蚀与土壤管理交互作用响应机制、恢复效应及响应时间敏感性，阐明合理耕层形成机理及恢复过程；根据农作物—耕层耦合模型，确定紫色土坡耕地合理耕层诊断标准，调查验证提出合理耕层最小数据集及调控途径。项目结果对于紫色丘陵区坡耕地水土资源高效利用、治理标准拟定和粮食安全保证具有重要科学意义。

土壤侵蚀是导致紫色土坡耕地耕层质量退化和土地生产力不稳定的关键驱动因素，直接影响坡耕地持续利用。本项目采用铲土侵蚀模拟法建立了五种侵蚀程度（S-0、S-5、S-10、S-15、S-20）和三种管理措施（CK、化肥F、生物炭+化肥BF）的坡耕地侵蚀/恢复耕层序列小区，系统研究了坡耕地耕层质量变化特征、退化主控过程及障碍耕层类型，阐明了坡耕地耕层质量对侵蚀/管理的响应机制及恢复效应，提出基于耕层质量诊断最小数据集的坡耕地合理耕层调控途径。主要结论有：（1）紫色土坡耕地耕层质量指数在0.410~0.686间变化，剖面上表现为耕作层＞心土层＞底土层，障碍耕层为有效土层厚度限制型、耕层厚度限制型、田面坡度限制和土壤养分限制型。（2）土壤侵蚀可显著降低坡耕地耕层质量指数，S-20仅为0.393；随侵蚀程度加剧，耕层土壤容重、抗剪强度和砂粒含量增加、土壤渗透性能降低，S-20条件下土壤抗剪强度、砂粒含量最大可增加13.99%和43.18%，稳定入渗率、饱和导水率和有机质则分别降低27.42%、34.88%和29.03%。（3）土壤管理措施能明显提升坡耕地耕层质量，BF措施下耕层质量较CK提升15.3%，玉米产量提高24.23%，生物炭对0-20cm耕层改良效果为20-40cm土层的1~3倍，对侵蚀10cm以下的坡耕地改良效果最佳。（4）坡耕地耕层土壤抗剪强度和土壤有机碳对侵蚀/管理的交互作用有显著响应且对土壤管理的响应更为敏感，土壤有机碳在自然条件下年均损失12.52%，BF措施下年均增加9.31%，而土壤抗剪强度则随侵蚀程度加剧分别增大3.44%~8.19%和1.73%~9.73%。（5）紫色土坡耕地农作物与耕层适宜性存在协调发展类和失调衰退类2种状态和同步型、滞后型、损益型、共损型4种表现形式，在同样地力条件下耕层质量衰退较农作物具有滞后性，耦合关系为I类（0.4820）和II类（0.5207）的耕层属于基本协调发展类农作物耕层同步型、农作物生长勉强适宜。（6）地块尺度的坡耕地耕层质量诊断最小数据集为有效土层厚度、耕层厚度、土壤容重、土壤有机质、土壤粘粒含量、土壤抗剪强度、土壤饱和导水率，合理耕层剖面构型为上虚下实型或虚实并存型，主要调控途径有增厚耕层、添加生物炭和聚土免耕等。研究结果对于深入认识坡耕地耕层质量侵蚀性退化过程及其区域性治理标准拟定都具有重要科学意义和应用价值。