【作者】 刘刚才；

【导师】 林三益；

【作者基本信息】 四川大学 ， 水文学及水资源， 2002， 博士

【摘要】 摘要紫色土是世界上一种特殊的土类，集中分布于四川盆地，以其易成土性和富盐基性(自然肥力高)养育着500人以上／平方公里的人口而著称于世，但是它分布的区域存在严重的季节性干旱和时有发生的洪灾等水问题。综观国内外有关研究，我们认识到对紫色土土壤产流和水分变化特征的认识，是认识该区土壤侵蚀与保护、农田水量平衡、非点源污染等的机理和规律的基础，也是解决该区水患问题、实施径流调节而提高旱地的雨水利用程度，以及水肥管理等的基本科学依据。因此，以水文学原理为基础，采取水文学与土壤学、地理学、水土保持学等相结合的途径，研究紫色土坡耕地的降雨产流机制与产流后土壤水分的变化特征，是具有新的科学价值和现实意义的。经近几年的观测和理论分析，取得了以下结果和创新的认识： 1)在降雨强度较大的情况下，保护性耕作制——聚土免耕的产沙强度明显较常规耕作制——顺坡耕作的小，说明聚土免耕耕作制防治土壤流失是有效的；但当土壤达到饱和后，聚土免耕的径流强度与常规耕作的差异较小，产沙强度也增大，因此，聚土免耕防治水土流失的能力是有限的。 2)耕作制下紫色土的产流主要机制是：1)当雨前土壤含水量未达到饱和状态时，表面产流起始时间有明显滞后现象，这与紫色土的快吸水性和较多非毛管孔隙密切相关；当雨前土壤较干燥，降雨初期雨强较大时，易形成临时相对不透水表层，表面产流峰也有明显滞后现象。2)表面径流的产流方式主要是超渗产流，当土壤达到饱和状态后，有 四川大学博士学位论文 小部分回归流发生，但主要是饱和超渗产流发生，因为紫色土的相对 不透水层和其它透水障碍层不明显。3）壤中流主要是饱和产流，与降 雨过程有明显的滞后，而且雨停后的壤中流产流历时与降雨特征无 关。4）耕作层（0—20cm）的壤中流是很明显的，如当雨强达120 mlllirl时，其产流强度可达到3 5 mlllirl。当土壤达饱和后，壤中流强度 与雨强有一定的联系，说明耕作层的大孔隙介质流和管流是存在的。 因此，应特别注意防止施肥和灌水在此层的流失。 3）同一块紫色土坡耕地内，土壤水分的时空变化有较明显的差异。地块 上部，耕层土壤含水量递减较快，因此，表现出较易受旱的情况，应 采取少量多次的灌溉原则。据观测，土壤接受一定降雨后，耕层在雨 后一定时期内，能保持基本稳定的含水量，可称之为“紫色土耕层持 水平台期”。这种平台期因土壤产流机制不同而异。若有降雨使土壤 饱和（产流）发生，Zwt天后，在无外界水源条件下，土壤含水量大 约有一周的稳定期，这一时期是施肥的有益时期。这与以往的一些研 究结果不同。过去研究认为土壤接纳降水后，土壤水分含量要么一直 递减，要么稳定一段时间再递减。我们提出的土壤接纳降水后的土壤 水分的变化模式是“递减——稳定——再递减”，特别是紫色土坡耕 地的耕作层土壤水分明显符合此模式变化。 4）表面径流的数值模拟能揭示表面产流的一般趋势，而且有一定的有效 性，通过调整模拟输入参数，能使模拟达较理想程度。土壤水分变化 的数值模拟结果——坡耕地的上、中、下各部位的模拟土壤水分变化 过程基本一致，这与实际观测结果差异较大，因此，还不能准确反映 坡耕地不同部位的水分变化特征，但通过对模拟参数的调整，可获得 一定可靠性的模拟结果，尽管未达到很理想的程度。同时也提示我 们，在进行数值模拟时，如何把土壤水势和作物根水势融合起来（不 是简单的迭加），以及其它参数的合理定量化，才能更好地模拟有作 物生长条件下的土壤水的复杂运动。 5）把产流机制与土壤水分变化过程紧密结合起来研究，认识到了紫色 土不同机制的产流发生后，其土壤水分的变化过程不一致，尤其是 土壤养分的流失差异明显；而且认识到“紫色土耕层持水平台期” — —2—— 四川大学博士学位论文 长短与土壤产流机制密切相关，因而进一步完善和弥补了以往土壤 学和农艺学的不足认识，为旱地农田的水利建设（径流调节设施） 和水肥管理提供了可靠科学依据。比如：根据当地坡耕地的产流机 制和土壤水分变化规律，可拦蓄和利用含土壤养分较多的壤中流来 调节土壤的需水量，等等。 6）认识到目前我们布设的水土流失观测小区设置的局限性：坡脚有渗漏 阻碍面（墙），不能将表面径流和壤中流分开。当有饱和产流发生 时，坡脚处的部分壤中流成为地面径流（包括表面径流和壤中流）， 使所测得的结果与实际的差异较明显。这一点，对指导水土更多还原

【Abstract】 Purple soil classified as Regosols in FAO soil taxonomy and Pup-Cambols in china soil taxonomy, is one of well known soil types with the particularities such as weathering easily, high natural fertility, etc., and feeding population of 500/km2. However, it often meets the water disasters (sporadic flooding and serious seasonal drought). For this reason, our objective is the research of the mechanism of runoff generation and characteristics of moisture changing process of slope farming purple soil, accordding to the theory of hydrology and the intergrated-means of compined the hydrology with the peodology, because it is the basis of the studies: soil erosion and protection, farming-land water balance, Non-point pollute, etc., and the direction gist of runoff arrange implement, solving water hazard and management of irrigation and fertilizer. And the major results and some new viewpoints were presented as follow:1) Sediment content of CN tillage system in runoff process is substantially low compared to ST under rainfall with high intensity, showing CN bear the efficient capacity of control soil loss. Nevertheless, when soil is saturated, the runoff intensity of both tillage systems is near, implicating CN has the limited function of reducing runoff.2) Based on the case analysis of observed all rainfall-runoff generation processes, A) the initiation time hysteresis of surface runoff generation isnotable when rainfall fall upon the unsaturated purple soils, which is attributed to the property of rapid water sorption and much non-capillary porosity. When soil antecedent condition is dry and the initial rainfall intensity is high, peak surface runoff also considerably lag behind that of rainfall, because of the formation of temporary relative impermeable top layer; B) Surface runoff is controlled primarily by infiltration-excess runoff mechanism under unsaturated condition; the major fraction of surface runoff are dominated by saturated infiltration-excess runoff response, only a small fraction by return flow mechanism when soil is saturated; C) Subsurface flow is dominated by saturated runoff mechanism, and the duration of subsurface post the rainfall end is dependent upon rather the soil properties than the rainfall characteristics; D) Subsurface flow intensity in cultivated soil layer (0~20cm) is high up to 35mm/h when rainfall intensity is up to 120mm/h, indicating the existing of macropores and pipe flow in cultivated layer. Therefore, throughflow rate is, in somewhat, rely upon the intensity of rainfall.3) The moisture changing processes at various location of a slope purple soil are obvious different: at up-location, soil moisture reduce more rapidly, therefore, drought will easily response to it at which the principle of often and little irrigation should be adopted. After a rainfall end, soil moisture content of cultivated layer is nearly stable within a certain period that is one week if rainfall leads to saturated runoff generation and is the optimal duration of fertilization. And we found the model of moisture changing is "reduction---stabilization---reduction" while the former researchers’ result is linearly reduction or reduction after a steady period.4) Numerical simulation running of surface runoff shows simulation results presented the general features of surface runoff generation, and certain efficiency. After adjusting the input parameters, the simulation results show a good meet to the observed data. The numerical simulation of moisture varying processes have not shown a good fit to the measured, showing amoisture varying model of simple reduction, and not revealed the distinct courses at various slope locations. However, after simulating by the selected parameters shown the difference between various slope locations, the the coefficient of efficacy (CE) was increased obviusly and reached over 0.6, that is to say, the simualted results is reliable in a certain. These results prompt us the satisfied fit simulation can be reached only when we scientifically tre更多还原