四川紫色土区耕作机具与坡面要素的配适机制

Tillage erosion results from the combined actions from tillage activities and landscape elements, and tillage erosion rates depend on the combination of two kinds of elements. To prevent and control tillage erosion at this stage, the key is to adjust human behavior which should guide to stimulate the coordination of tillage activities and landscape elements, and to prompt the advancement of soil conservation. Yet little is known about the mechanism of tillage activities matching landscape elements. This study will start with determining tillage translocation and tillage erosion rates of main implements (manual hoe, animal-powered plough, rotary cultivator) in purple soil regions using magnetic tracing and simulation tillage experiments. We will quantify the tillage erosivity and determine the relationships of tillage erosion and tillage operations for tillage implements. We will reveal the susceptibility of cultivated soil to be eroded by tillage operations under different soil and landform conditions. Then we will put forward the tuning parameters for matching among tillage implements, tillage operations and soil erodibility, landform erodibility using optimization methods. Finally, we will illuminate alignment mechanism between tillage implements and landscape elements. This study will provide the foundation for a deeper appreciation of mechanism of tillage erosion and thus for an adoption of appropriate tillage measures on the steep land of purple soil.

耕作侵蚀的发生是耕作人为要素与坡面自然要素综合作用的结果，其强度大小取决于两种要素的组合状况。现阶段耕作侵蚀防治的关键在于人类自身行为的调控，通过引导耕作活动与坡面要素相协调，与土壤保持相一致，然而两种要素的协调机制有待研究。本项目采用磁性示踪、模拟耕作试验定量确定紫色土区人工锄、家畜犁、旋耕机3种动力耕作机具的土壤耕作位移和侵蚀速率，查明不同耕作机具的耕作侵蚀力，明确耕作方式与耕作侵蚀的关系，揭示土壤和地形坡面要素对耕作侵蚀土壤的敏感性；通过最优化方法，提出耕作机具和耕作方式与坡面要素的配适优化参数，阐明耕作机具与耕作侵蚀坡面影响要素的配适机制，为深入认识紫色土耕作侵蚀的机制和采取适宜的耕作措施提供依据。

耕作侵蚀的过程机制和防治技术研究是我国现阶段水土保持科学与技术的重点研究领域。本项目主要开展了耕作机具的耕作侵蚀力、耕作方式、坡面要素对耕作侵蚀的影响、耕作机具与坡面要素的配适参数研究。对于人力锄耕：宽锄和空心锄的耕作位移与坡度显著相关(P<0.01)，而坡度与窄锄和双齿锄的耕作位移无显著相关性(P>0.05)，相比宽锄，窄锄、空心锄和双齿锄的耕作侵蚀速率分别减小12.4%，11.0%，16.3%，表明锄头形式的变化如减小锄头、开孔等减弱了耕作侵蚀强度；耕作深度对锄耕耕作位移影响显著，当耕作深度从0.26m减小为0.14m，耕作侵蚀速率减小了64%。对于牛拉犁耕作：上下坡交替犁耕和等高向下犁耕引起的土壤位移量分别为0.68—34.58kg/m和15.62—70.42kg/m，等高向上犁耕土壤净位移量为-10.91—8.23kg/m，土壤净位移方向随着坡度的增大由向上坡转为向下坡，临界坡度为14%；等高向下犁耕15次后坡顶侵蚀深度是原土层深度的132%，等高向上犁耕15次后坡顶土层深度增加了12.7%，表明等高向上犁耕具有保护坡顶土层深度的作用。对于旋耕机耕作：不同耕作方向下旋耕机单次耕作过程中均引起土壤同时发生向上坡和向下坡移动，且均导致土壤发生向下坡净位移；快档时上下坡交替耕作的耕作侵蚀速率小于等高耕作，但慢档时两者相当；土壤力学性质和土壤物理性质对旋耕机耕作侵蚀有显著影响，土壤抗剪强度、土壤紧实度和土壤容重可以作为评价耕作侵蚀的土壤可蚀性指标；耕作深度由8cm增加为10cm耕作侵蚀速率增大了77%，由10cm增加为12cm耕作侵蚀速率增大了49%。向上锄耕在不同坡度条件下都非常适宜，但陡坡较难实施，等高锄耕对不同坡度适宜性较好，不同形式的锄头顺坡耕作都表现为不适宜；等高向下犁耕在耕作深度较浅时对不同坡度都适宜，等高向上犁耕和上下交替犁耕特别适合缓坡(<15%)，但不适宜陡坡(>30%)；旋耕机对不同坡度适宜性较强，但陡坡(>30%)坡地不适宜旋耕机快档耕作。研究成果有利于深入认识紫色土坡地耕作侵蚀的过程机制，并为因地制宜地优化耕作防治土壤退化提供基础数据。