不同土质中地下滴灌滴头流量敏感性因素分析

为研究不同土壤质地条件下地下滴灌滴头流量变化的敏感程度,分别对工作压力、土壤容重和土壤初始含水率这3个因素采用求偏导的方法作为滴头流量对各因素的敏感性指标进行计算分析.结果表明:工作压力的变化对滴头流量影响显著,但滴头流量对压力变化的敏感性在不同土壤质地之间的差异并不大,相同压力条件下,土壤质地越轻,滴头流量对压力变化...     

基于分形理论的地下滴灌灌水器水力特性研究

为了研究滴头工作压力和土壤物理特性对地下滴灌灌水器流量的影响,采用分形理论分析各种级配土壤的分形特征;以土壤颗粒质量分形维数、灌水器工作压力、土壤容积密度、土壤初始含水率为试验因素,运用混合水平均匀设计方法进行试验。结果表明,粘粒含量大小是土壤分形维数的主要影响因素,土壤分形维数随着粘粒含量的增加而增大;PLASSIM公司地下滴灌灌水器流量随土壤分形维数的增大而减小,即土壤质地越细地下滴灌滴头流量就越小;通过试验所建立的包含有土壤分形维数因素的地下滴灌灌水器流量计算经验公式的普适性较高。     

微润管出流特性和流量预报方法研究

为探明影响微润管流量的主要因素,确定微润管压力与流量关系,通过田间试验,研究不同土壤初始质量含水率(13.83%、15.49%、16.27%、17.72%)和不同土壤容重(1.18、1.21、1.24、1.26 g/cm~3)条件下不同压力水头(0、0.1、0.3、0.7、1.1、2.1 m)对微润管流量的影响。结果表明:微润管流量随土壤质量含水率变化有一定的自我调节作用,但微润管流量受土壤质量含水率变化影响较小,自我调节时间约为44 h。随着灌水时间增加,微润管流量呈先快速增加再减小后趋于稳定平缓的趋势,灌水后约48 h趋于稳定状态。工作压力、土壤容重和初始质量含水率均对微润管流量有显著影响,在一定工作压力范围内(0~2.1 m水头),压力与流量呈显著性线性关系(P0.05),模型决定系数R~2大于0.85,随土壤初始质量含水率与容重增加,微润管流量呈减小趋势,微润管流量变化对工作压力的敏感度逐渐下降;在压力与流量线性回归模型中微润管的流量系数和压力为零的流量b均非单纯由产品自身特性决定,土壤初始质量含水率和容重与流量系数呈显著负相关关系(P0.05),容重与压力为零的流量均存在显著负相关关系(P0.05),可用土壤初始质量含水率和容重确定流量系数和压力为零时的流量值,最终实现微润灌出流预报。通过灰色关联分析发现,压力是影响微润管流量的最主要因素,土壤容重次之,土壤初始质量含水率对微润管流量影响最小。     

滴灌点源入渗湿润锋影响因子的研究

以试验为基础,针对重壤土、中壤土、砂壤土研究滴灌点源入渗的湿润锋运移规律,分析土壤种类、土壤容重、土壤初始含水率、滴头流量、灌水量等主要因子对湿润锋运动的影响。通过试验发现,除了土壤质地和灌水量对湿润体形状有明显影响外,土壤容重和初始含水率的变化也将造成湿润锋和滴灌效果的不同。另外,滴头流量对湿润锋水平运移影响很大。     

不同初始土壤含水率和滴头流量下滴灌土壤湿润体特征及其有效性评价

【目的】研究滴灌条件下土壤湿润体水分分布。【方法】开展单点源入渗试验,探究了不同初始土壤含水率和滴头流量对滴灌土壤湿润体特征及湿润体内含水率分布的影响。【结果】灌溉结束24 h后,湿润体内的含水率达到相对稳定的状态,湿润体体积基本保持稳定;随灌水及再分布时间增加,湿润体宽深比逐渐降低,再分布过程中,宽深比随初始含水率减小而增大,随滴灌流量减小而减小;各处理湿润体体积与入渗时间呈良好的线性函数关系,灌水结束24 h后,各处理实际湿润体积均已超出计划湿润体积;计划湿润体内含水率60%θFC～80%θFC区间占比随初始含水率增大而减小,随滴头流量的增大而增大,其余各区间占比变化规律与之相反,相同滴头流量下,50%θFC初始含水率处理超出计划湿润体的体积最少。【结论】再分布后的湿润体体积主要受灌水量的影响,可以选择较小的初始含水率及较大的滴头流量以提高湿润体内水分有效性。     

渗灌用黏土基微孔陶瓷灌水器入渗性能研究

针对3种孔径相同开口孔隙率和渗流面积不同的黏土基微孔陶瓷灌水器,进行了水力性能和土壤入渗试验研究。结果表明,相同条件下微孔陶瓷开口孔隙率和渗流面积越大,灌水器渗流量越大;灌水器入渗性能受灌水时间、土壤类型和进口压力的影响。随着灌水时间延长土壤含水率增加,入渗速率减小;在无压条件下,黄绵土入渗速率较砂土大,随着进口压力增大,砂土入渗速率大于黄绵土入渗速率;同时随着进口压力增大灌水器入渗速率增大且稳定时间缩短。     

残膜土壤对点源入渗湿润体特性的影响

为探明含残膜污染土壤对点源入渗湿润体特性的影响,选取360 kg/hm~2残膜量,采用室内土箱模拟的方法,以不同土壤初始含水率、土壤容重和滴头流量等3个因素进行试验,研究相应土壤入渗湿润锋过程及不同滴头流量下横纵比特征。结果表明:在相同入渗时间内,湿润锋运移距离随土壤初始含水率和滴头流量的增大而增大;不同土壤容重下,水平运移距离随土壤容重的增大而增大,垂直运移距离随土壤容重的增大而减小。土壤入渗湿润体特征值与时间呈幂函数关系,并以此为基础分别建立了湿润锋水平和垂直向运移距离的预测模型。横纵比与流量呈负相关,随着灌水历时增加,横纵比逐渐减小,不同滴头流量下,横纵比与入渗时间也呈幂函数关系,决定系数R~2在0.98以上。     

地下滴灌灌水器出口正压试验研究

通过试验 ,研究了灌水器类型、流量、工作压力和土壤初始含水量对地下滴灌灌水器出口正压的影响规律。结果表明 :灌水器埋入土壤后 ,其出流由于受土壤等因素的限制 ,在灌水器出口处产生了一定的正压 ,该正压随着灌水历时的延长而增大。影响地埋灌水器出口正压的主要因素是灌水器的额定流量和土壤初始含水量     

滴头流量对风沙土滴灌湿润锋运移影响的试验研究

为了在风沙土地区更为合理的利用滴灌技术,通过室内试验模拟了单点源和双点源滴灌条件下风沙土土壤水分运移过程,研究了不同滴头流量下土壤湿润锋时空动态分布规律。结果表明灌水时间相同时,滴头流量越大,湿润锋运移距离越大;灌水量相同时,滴头流量增大对湿润锋水平运移距离影响较小,但可增大垂直方向运移距离。大流量滴头增大了湿润锋初始运移速度,随着灌水时间的增加,湿润锋运移速度迅速减小并趋于稳定,且不同流量处理之间差异较小。双点源滴灌时,入渗交汇前水分运动规律与单点源入渗规律相同;滴头流量越大,湿润体交汇时间越短,交汇处湿润锋运动速度越快;但滴头正下方含水量高,土壤含水量径向变化较大,增加了土壤含水量空间分布的不均匀性。     

微孔陶瓷渗灌与地下滴灌土壤水分运移特性对比

以微孔陶瓷灌水器为研究对象,在0 m工作水头下进行土壤水分运移特性试验,并以10 m额定工作水头下工作的地下滴灌灌水器作为对照。通过对比分析2种灌溉方式下累计入渗量、流量、湿润体特征和土壤含水率变化,结果表明:相同灌溉时间下微孔陶瓷渗灌的累计入渗量、湿润锋运移距离、湿润体截面面积均明显小于地下滴灌。微孔陶瓷渗灌的流量随时间逐渐减小,直至接近于零;试验后期,微孔陶瓷渗灌湿润体内整体土壤含水率变化较小;由于微孔陶瓷渗灌为无压连续灌溉,因此在其工作过程中可为作物提供一个恒定的水分环境。而地下滴灌的流量则会维持稳定,使得土壤含水率一直增大,停止灌溉后由于土壤水分再分布而减小。地下滴灌为被动恒压灌溉,因此其灌溉条件下作物生长的水分环境处于干湿交替的循环变化状态。     

Emitter discharge variability of subsurface drip irrigation in uniform soils: effect on water-application uniformity

Emitter discharge of subsurface drip irrigation (SDI) decreases as a result of the overpressure in the soil water at the discharge orifice. In this paper, the variation in dripper discharge in SDI laterals is studied. First, the emitter coefficient of flow variation CV _q was measured in laboratory experiments with drippers of 2 and 4 L/h that were laid both on the soil and beneath it. Additionally, the soil pressure coefficient of variation CV _hs was measured in buried emitters. Then, the irrigation uniformity was simulated in SDI and surface irrigation laterals under the same operating conditions and uniform soils; sandy and loamy. CV _q was similar for the compensating models of both the surface and subsurface emitters. However, CV _q decreased for the 2-L/h non-compensating model in the loamy soil. This shows a possible self-regulation of non-compensating emitter discharge in SDI, due to the interaction between effects of emitter discharge and soil pressure. This resulted in the irrigation uniformity of SDI non-compensating emitters to be greater than surface drip irrigation. The uniformity with pressure-compensating emitters would be similar in both cases, provided the overpressures in SDI are less than or equal to the compensation range lower limit.     

黄土高原重力式地下滴灌水分运动模型与分区参数研究

建立了重力式地下滴灌条件下的土壤水分运动模型,分析地下滴灌土壤水分入渗规律.对黄土高原不同分区的4种典型土壤、不同灌水技术要素条件下的地下滴灌土壤湿润体形态、滴孔处出流量及土壤土水势进行数值模拟得出:榆林紧砂土土壤导水率较大,向下渗漏过多,不适宜地下滴灌;安塞砂壤土、洛川中壤土、武功重壤土在相同灌水量下,供水压力与滴孔孔径对地下滴灌湿润体形态影响微弱,但对滴孔出流量有较大影响,因此在地下滴灌工程设计时,只需根据田块长度和渗水管损失设计孔径和供水压力,并采用较小供水压力,降低供水水池高度,减小工程量;对武功重壤土,孔径和供水压力较大时地下滴灌滴孔处土壤易饱和板结,宜采用较小的孔径和供水压力.     

重力式地下滴灌土壤水分运动规律的模拟研究

基于非饱和土壤水运动理论,建立了重力式地下滴灌条件下土壤水分运动数学模型,用Galerkin有限元法推导了重力式地下滴灌土壤水分运动有限元方程,并通过试验进行了验证,在此基础上模拟分析了中壤土条件下的滴灌管道埋深、出水孔孔径、供水压力对简易重力式地下滴灌土壤湿润特征和滴孔出水量的影响。结果表明所建模型可以分析地下滴灌土壤水分入渗规律,在中壤土条件下,不同供水压力、滴孔孔径虽对重力式地下滴灌的滴孔出流量有较大影响,但对土壤湿润特征影响微弱,地下滴灌管道埋深对土壤水分湿润特征影响较大,这些结论可为重力式地下滴灌合理的设计及运行提供理论依据。     

地下滴灌中毛管水力计算的数学模型与试验

为了研究地下滴灌毛管水力特性与水力计算方法,用较短毛管并通过毛管末端泄流的方式,在室内利用地下滴灌毛管水力要素试验测试系统,分别测试了2种滴灌管在轻黏土中毛管上每个滴头的流量和毛管首末两端的压力水头．结果表明：在灌水持续2min之后,地下滴灌毛管上各滴头流量均趋于恒定值;在稳定的压力水头差下,滴头流量沿程依次减少．根据毛管沿程压力变化规律,结合考虑土壤质地、土壤体积质量和初始含水率的地下滴灌滴头流量计算公式,提出了毛管水力计算数学模型．利用该模型计算的滴头流量值与其实测值之间的相对误差在1．0％左右;并计算出考虑毛管局部水头损失的加大系数约为1．20．将该模型推广应用于一般情况下的地下滴灌毛管水力计算,可求解均匀坡、均质土、均匀管径与滴头等间距时的地下滴灌毛管水力特征值．     

Numerical evaluation of subsurface trickle irrigation with brackish water

In this study, an assessment for a proposed irrigation system in the El-Salam Canal cultivated land, Egypt, was conducted. A numerical model (HYDRUS-2D/3D) was applied to investigate the effect of irrigation amount, frequency, and emitter depth on the wetted soil volume, soil salinity levels, and deep percolation under subsurface trickle irrigation (SDI) of tomato growing with brackish irrigation water in three different soil types. The simulations indicated that lower irrigation frequency increased the wetted soil volume without significant increase in water percolates below the plant roots. Deep percolation decreased as the amount of irrigation water and emitter depth decreased. With the same amount of irrigation water, the volume of leached soil was larger at lower irrigation frequency. The salinity of irrigation water under SDI with shallow emitter depth did not show any significant effect on increasing the soil salinity above tomato crop salt tolerance. Based on the results, it appears that the use of SDI with brackish irrigation water is an effective method for growing tomato crop in El-Salam Canal cultivated land especially with shallow emitter depth.     

Yield, water-use efficiencies and root distribution of soybean, chickpea and pumpkin under different subsurface drip irrigation depths and oxygation treatments in vertisols

Most trickle irrigation in the world is surface drip yet subsurface drip irrigation (SDI) can substantially improve irrigation water use efficiency (IWUE) by minimizing evaporative loss and maximizing capture of in-season rainfall by the soil profile. However, SDI emitters are placed at depths, and in many soil types sustained wetting fronts are created that lead to hypoxia of the rhizosphere, which is detrimental to effective plant functioning. Oxygation (aerated irrigation water) can ameliorate hypoxia of SDI crops and realize the full benefit of SDI systems. Oxygation effects on yield, WUE and rooting patterns of soybean, chickpeas, and pumpkin in glasshouse and field trials with SDI at different emitter depths (5, 15, 25, and 35 cm) were evaluated. The effect of oxygation was prominent with increasing emitter depths due to the alleviation of hypoxia. The effect of oxygation on yield in the shallow-rooted crop vegetable soybean was greatest (+43%), and moderate on medium (chickpea +11%) and deep-rooted crops (pumpkin +15%). Oxygation invariably increased season-long WUE (WUE_sl) for fruit and biomass yield and instantaneous leaf transpiration rate. In general, the beneficial effects of oxygation at greater SDI depth on a heavy clay soil were mediated through greater root activity, as observed by general increase in root weight, root length density, and soil respiration in the trialed species. Our data show increased moisture content at depth with a lower soil oxygen concentration causing hypoxia. Oxygation offsets to a degree the negative effect of deep emitter placement on yield and WUE of SDI crops.     

Simulation of point source wetting pattern of subsurface drip irrigation

Laboratory experiments and calculations were carried out to analyze the effect of subsurface drip irrigation (SDI) design features on soil wetting patterns for a point source. Experimental and simulated soil wetting patterns, using the SWMS-2D (simulating water movement and solute transport in two-dimensional) Galerkin finite element model, were investigated to maximize the efficiency of water saving. The analysis addressed the influence of water pressure head, back pressure and emitter diameter on wetting patterns. Predictions of water content distributions in the soils made with SWMS-2D were found to be in good agreement with the observed data. Results showed that this model provides confidence that model predictions are not too sensitive to back-pressure effects.     

Analysis of trickle irrigation with application to design problems

Summary Designing trickle irrigation systems involves the selection of a proper combination of trickle discharge rate, spacing between emitters, diameter and length of the lateral system for any given set of soil, crop and climatic conditions. Trickle irrigation is treated as transient and steady axisymmetric infiltration processes. An existing numerical solution to nonsteady state infiltration is used to quantify the effect of soil hydraulic properties and trickle discharge rates on emitter spacing (Fig. 2). The results of the analysis suggest the possibility of controlling the wetted volume of a soil by regulating the emitter discharge according to soil properties (Figs. 3 and 4). The surface distribution of a transformed soil water content (or pressure) function (Fig. 5) is derived from a linearized solution to steady infiltration. The analysis of steady and non-steady infiltration is employed to estimate the spacing between emitters as a function of discharge and water pressure conditions between emitters using hydraulic soil data (Fig. 6). Hydraulic conductivity parameters are given for 17 different soils (Table 1) to be used for design purposes. Theoretical analysis of soil water is combined with hydraulic principles to derive lateral diameter and length for engineering design requirements.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. 1977 Series, No. 134-E