【作者】 仵峰；

【导师】 吴普特； 黄修桥；

【作者基本信息】 西北农林科技大学 ， 农业水土工程， 2010， 博士

【摘要】 为完善地下滴灌系统设计理论、提高系统运行管理水平,针对地下滴灌条件下土壤水分运动和系统水力性能交互影响的特点,以地下滴灌管网、土壤和作物这一连续的水流系统作为研究对象,采用田间定位观测、室内试验、理论分析和数学模拟相结合的方法,研究了地下滴灌条件下土壤水分的运动特征,探讨了地下滴灌系统灌水器流量、毛管间距与埋深等工程设计问题,提出了地下滴灌系统主要设计参数的计算方法,分析了地下滴灌系统管网的水力特性,并探索了田间监测和评价地下滴灌系统运行状况的新方法。取得的主要研究结论如下:(1)地下滴灌湿润峰随时间变化过程可概化为2个相对独立的线性过程。灌水过程中,在滴头附近形成了水分过饱和区,湿润峰的运移速度向下最大,水平次之,向上最小;土壤水再分布过程中,湿润峰的水平和向下运移速度趋于相同。不同方向上湿润峰运移距离存在一定的比例关系,该比例与土壤质地和灌水器流量有关。(2)地下滴灌条件下,灌水器额定流量和土壤的导水性直接影响灌水器出口处的土壤水能态。同一土壤条件下,灌水器出口稳定正压随灌水器额定流量的增大而增加,随土壤初始含水率的增大而降低。地下滴灌土壤水能态为非线性分布,以灌水器出口处的土壤水势为参数,给出了求解点源或线源入渗条件下土壤水势分布的数学方程。(3)地下滴灌土壤水运动是以水分运动为主、包含土壤中细小颗粒运动的两相流,不能直接用理查得方程进行描述。将地下滴灌土壤水分运动分为饱和渗透区和非饱和扩散区,分别用达西定律和理查得方程对其进行描述,建立了分区耦合模型;采用非线性函数对地下滴灌饱和区外边界进行描述,作为地下滴灌耦合模型的区界。(4)地下滴灌灌水过程中,灌水器的流量呈由大变小、最终趋于稳定的动态变化过程,其稳定流量与额定流量相比,减少5%~30%。灌水器额定流量越小,埋入地下后的稳定流量与其额定流量越接近,达到稳定流量的时间越长;土壤初始含水率越小,灌水器的稳定流量也越接近其额定流量。在选择地下滴灌灌水器流量时,可以参考灌水器的额定流量,并考虑一定的折减系数。对于砂壤土而言,折减系数的取值范围在0.70~ 0.95之间。(5)砂壤土条件下,地下滴灌适宜毛管铺设间距为90 cm。结合地下滴灌条件下土壤水势的分布,将地下滴灌的灌水影响区分为压力传导区、土壤水分扩散区和作物吸水影响区3个部分,以土水势为变量,给出了对应区域的计算公式,地下滴灌毛管间距等于3部分距离之和的2倍,并以作物与水关系为函数,建立了地下滴灌毛管间距计算公式。(6)地下滴灌毛管埋深受土壤质地、作物和犁底层的影响。与壤土和粉砂壤土相比,砂壤土毛管埋深可相对浅一些;考虑作物影响时,设计毛管埋深可适当加深。设计时,应考虑毛管铺设位置与犁底层相对位置间的关系,结合作物根系主要吸水区、农事作业等因素,选择适宜的毛管埋深。(7)冲洗管的加设,提高了地下滴灌系统工作稳定性。田间实测地下滴灌毛管的工作压力在额定工作压力的±30%之间,灌水器的流量偏差小于20%。毛管水头损失与距小区进口处的距离呈正相关;系统工作压力变化时,主要影响小区进口附近毛管的工况。将地下滴灌田间管网的支、毛管概化为多孔出流管道,采用尾端有出流的多孔管段计算公式,将环状管网化为树状管网,组成非线性方程组,对地下滴灌系统田间环状管网的水力要素进行了求解。(8)提出了2 L计时法对地下滴灌系统的工况进行监测。地下滴灌系统毛管流量降低率与使用年限有关,对应于1年、2年、3年、4年的地下滴灌系统,大于10%毛管流量降低率分别达到测试毛管条数的0、1/3、2/3、2/3。同一使用年限内,毛管性能变化与其所在的位置及滴灌带类型有关,靠近小区进口的毛管流量降低率较小,小流量、厚壁滴灌带的流量较稳定。(9)采用25点取样法,对大田地下滴灌灌水后土壤水分分布均匀度进行了评价。地下滴灌条件下,土壤水消耗以毛管为中心,其土壤水变幅最大;与上、下土层相比,灌水前毛管位置处的土壤水分均匀度较低,灌水后均匀度大幅提高,明显阻止了由于水分消耗而引起的土壤水分分布不均匀性。更多还原

【Abstract】 There is an interaction characteristic between system hydraulic properties and soil water movement under Subsurface Drip Irrigation system (SDI). To improve the design theory and management method of SDI, field positioned observations, laboratory experiments, theoretical analysis and mathematical models were conducted for studying the continuous system from pipe network of SDI, soil to crops. Characteristics of soil water movement under SDI were studied. Emitter flow, drip line spacing and depth were discussed, and such main designning parameters of SDI system were proposed. Hydraulic of pipe networks were analyzed. A new method was explored for the monitoring and evaluation of SDI system in the field. The main conclusions obtained as follows:(1) Process of the Soil Water Front (SWF) can be summarized into two independent linear. Process under SDI. There is a saturated zone near the emitter during irrigation. Migration rates of SWF vary with directions. Form downward, level to upward, migration rates of SWF decrease. Different directions of SWF distance trend to a same value during the redistribution process. There is a certain ratio among the migration distance at different directions, and this ratio related to the emitter flow and the soil texture.(2) The potential energy near the outlet of emitter were directly affected by the emitter’s flow and soil water conductivity under SDI. The stability pressure near the emitter’s outlet increases with the nominal emitter flow rate’s increasing, and decreased with the increasing of initial soil moisture for a same soil. The distribution of soil water potential was nonlinear. Using the soil water potential as parameters, equations were given to solute the soil water potential distribution under the infiltration from point and line source(3) For the soil water movement under SDI contains fine soil particles’movement,it couldn’t be described directly with Richard equation. Soil water movement under SDI were divided into saturated and unsaturated infiltration diffusion zone, and described by Darcy Law and Richard equations, respectively. A coupled regional model was established. A nonlinear function was used to describe the outside boundary of saturation range, and it was used as the boundary of the coupled ranges of SDI.(4) the emitter flow was a dynamic decreasing process and tended to a stable rate during the process of SDI. The steady flow rate reduced by 5% to 30% compared with the nominal emitter flow. Lesser of the nominal emitter flow, the flow rate of buried emitter closer to its nominal value and longer time to its stable status. So as to smaller initial soil water content. It is suggested that the designed emitter discharge could be discounted on it’s nominal discharge. The reduction coefficient is from 0.70 to 95 for the sandy loam.(5) The suitable Drip Line Spacing (DLS)for sandy loam soil is 90 cm. The affected zone of SDI was divided into pressure conduction, soil moisture diffusion zone and crop water uptake zone, based on soil water potential distribution. The formulas were given to calculate the length of corresponding regions, with soil water potential as the variable. DLS equals to 2 times of above 3 parts sum. And formula of drip line spacing, as the function of crops and water relations, was given under SDI, too.(6) The drip line buried depth of SDI were affected by soil texture, crop, and plow pan. The drip line buried depth could be shallower for sandy loam compared with the loam and silt loam, and be deeper with crops. It should be considered that relative position of drip line and plow pan, combined with the main root water uptake areas, agricultural operations and other factors, for selecting of drip line depth.(7) The stability of SDI system was improved with flushing pipes. Field observions show that the drip line working pressure were±30% of nominal pressure. and the difference of emitter flow is less than 20%. Drip line head loss has a positive correlation to the distance from the plot entrance. The drip line working status near the entrance of plot varies with the system working pressure. Field pipes can be analyzied as multi-outlet with outflow at its end, ring pipe networks could be changed into the tree pipe networks. Composed of nonlinear equations to calculate hydraulic of pipe network in SDI.(8) 2 L timing method was proposed to monitor the status of SDI. Reducing drip line flow rate varied with using years. Corresponding to 1, 2, 3 and 4 years, more than 10% of drip line flow decreased rates are 0, 1/3, 2/3, 2/3, respectively. For a same service year, drip line properties changes with their location and their types. Near to inlet of plot, the decreased drip line flow rate is smaller. It is stable for lower flow and thicker drip wall.(9) 25-point sampling method was used to evaluate soil water distribution uniformity under SDI. Results show that soil water consume is as the drip line of center in the space under SDI. Compared with the upper and lower layers, uniformity of the soil moisture vicinity of drip line lower before irrigation; it increase obviously after irrigation.更多还原