双环入渗仪的缓冲指标对测定土壤饱和导水率的影响

双环入渗仪在测定田间土壤饱和导水率时被广泛采用。本文采用不同直径的双环入渗仪(内环直径分别为20 cm、40 cm、80 cm和120 cm)和不同的内外环直径比,即不同的缓冲指标(0.2、0.33、0.5和0.71),进行了16组定水头积水入渗试验,研究了双环入渗仪缓冲指标对土壤饱和导水率测定的影响。结果表明:内环直径较小的入渗仪,其累积入渗过程曲线的分布较分散;随着入渗环直径逐渐增大,分散范围逐渐缩小。另外,随着缓冲指标的逐渐增大,测定的土壤饱和导水率并没有明显的增大或减小趋势,但内环直径20 cm的入渗仪测定的土壤饱和导水率的波动最大,而80 cm和120 cm内径的双环入渗仪测定的土壤饱和导水率最稳定,并且始终非常接近。因此,相对于双环入渗仪内环大小或土壤非均质性的影响,双环入渗仪的缓冲指标对于土壤饱和导水率测定的影响要小。     

4种土壤入渗测定方法的比较

入渗是土壤的基本物理性状,与降雨产流、侵蚀、非点源污染等过程密切相关,快速、准确测定土壤入渗速率具有重要的意义。以黄土高原沟壑区安塞水土保持综合试验站大豆地的黄土为测试土壤,利用双环、单环、圆盘入渗仪、Hood入渗仪4种方法测定了土壤入渗性能,并以双环法测定的稳渗速率、Hood仪测定的饱和导水率、单环/双环和圆盘测定的累积入渗量为基础,比较分析了4种方法各自的优劣。结果表明,单环、圆盘、Hood测定的稳渗速率分别为双环的116%,111%和225%,双环、单环、圆盘测定的饱和导水率分别为Hood的65.8%,75.1%和105%,双环、单环、圆盘达到稳渗时间分别为100,80和30min。说明圆盘测得的稳渗速率、饱和导水率最接近标准值,而且省时省力省水,更适合于野外实验。     

塔里木沙漠公路防护林带土壤入渗研究

为了探明塔里木沙漠公路防护林带咸水灌溉土壤入渗特性,在塔里木沙漠公路防护林带内选取5种不同种植年限的土壤,并取3种不同矿化度水,应用Guelph入渗仪测定土壤水分入渗过程,并进行模型拟合与分析。结果表明:不同种植年限对土壤初始入渗速率、饱和导水率有显著影响,尤其是0-10cm,10-15cm层土壤,随着种植年限增加土壤初始入渗速率、饱和导水率呈减小趋势。咸水灌溉条件下,土壤饱和导水率较淡水大。不同深度土壤入渗特性有差异,表现为25-40cm,40-60cm层土壤饱和导水率较其他层大。用常用的入渗模型对入渗过程进行模拟,可以发现通用经验模型对研究该区域土壤入渗有最好的适用性,Kostiakov模型也较适用,Horton模型在该区域土壤入渗研究中适用性相对较差。     

双环直径对土壤入渗速率的影响

双环法是测定土壤入渗速率最为广泛最为经典的方法,但双环直径可能影响土壤入渗速率测定结果,因其为地表积水有压入渗,在坡地上测定时,因整平地表时会产生很大扰动,从而产生测定误差。研究设计5组不同直径的双环入渗试验,分析双环直径对土壤初始入渗速率、稳定入渗速率、累计入渗量的影响。结果表明:当双环内环直径分别为15,20,25,30cm时,初始入渗速率分别是常规内环直径为35cm双环的88.3%,110.8%,119.9%,100.7%,稳定入渗率分别是54%,73%,85%,89%。对不同时刻入渗速率进行T值检验发现,用内环直径为20,25,30cm双环测定的入渗过程与常用内径为35cm的双环测定土壤入渗过程无显著差异。考虑地表扰动因素、试验需水量等多因素的影响,可用内环直径20cm、外环直径为35cm的双环替代目前常规内环直径为35cm,外环直径为50cm的双环,用于坡地土壤入渗速率测定,可以减少地表扰动,从而准确测定土壤入渗率,又能节约用水量。     

蓄水坑入渗表层土壤体积质量和饱和导水率的变化

表层土壤体积质量和导水率是影响土壤入渗及水分运动的重要物理参数。该文采用土壤切片技术和数字图像分析技术,分析了蓄水坑灌条件下入渗水头对砂壤土表层土壤体积质量的影响,进行了不同入渗水头、土壤体积质量对砂壤土表层土壤饱和导水率的试验研究,并对蓄水坑侧向水平入渗湿润锋变化的试验结果与数值模拟结果进行对比分析。结果表明：该研究试验条件下（土壤体积质量为1.345 g/cm3）,入渗水头对土壤体积质量和表层土壤饱和导水率有较明显的影响。随着入渗水头的增大,其作用下的表层土壤体积质量趋于增大,土壤结构趋于密实,表层土壤的饱和导水率趋于减小;表层土壤饱和导水率与入渗水头和土壤体积质量之间呈乘幂关系,且表层土壤饱和导水率对土壤体积质量的变化较为敏感,当土壤体积质量达到某一程度时（1.466 g/cm3）,入渗水头对表层土壤饱和导水率的影响甚微。研究成果揭示了入渗水头影响蓄水坑土壤入渗的微观机制,为进一步研究蓄水坑灌法提供了理论依据。     

自动双环入渗仪设计与试验

为克服传统双环入渗仪的供水不稳定、读取和记录数据工作量大的问题,该文基于定水头法测量导水率的原理,设计了一种高效的自动双环入渗仪。该入渗仪采用非接触式电容感应液位传感器来监测内环和外环内的水位（精度<1.5 mm）;将激光测距传感器（精度<1 mm）安装在圆柱形蓄水器的顶部,以连续自动监测供水量;高精度液位控制系统与电磁阀组合以保持恒定水头。通过理论分析,增大蓄水器中的液面与双环中的液面之间的压力差,可使自动双环入渗仪的初始供水速率远高于马氏瓶的初始供水速率。自动双环入渗仪的精度和可靠性试验于2019年7月至2019年10月在中国农业大学绿苑试验场进行,并进行了该自动双环入渗仪和传统双环入渗仪之间的比较。试验结果显示,在选定土壤的稳定入渗阶段,用马氏瓶测量的稳定入渗速率为0.068 5 cm/min,该自动双环入渗仪的稳定入渗速率为0.068 7 cm/min,自动双环入渗仪实测数据与Philip的理论入渗模型计算结果吻合（R2>0.99）。结果表明,该自动双环入渗仪的自动化测量结果可靠,对今后土壤水分入渗过程研究提供了更加高效的手段。     

多因素作用下浑水入渗对土壤导水特性的影响

浑水土壤入渗具有复杂的上边界变化过程,其上边界导水能力的变化规律是研究浑水土壤入渗特性的重要基础。为研究浑水入渗形成致密层过程中导水率的变化情况,该研究进行了17组（9组正交试验处理,8组用于模型验证）浑水饱和土柱入渗试验,通过对试验结果进行多元回归构建多因素（浑水含沙率、黏粒含量及入渗时间）影响下砂土导水率动态模型;并结合浑水饱和土柱入渗特性进行合理假设,分别建立浑水砂壤土和粉壤土饱和土柱导水率动态模型并进行验证。结果表明：浑水含沙率、黏粒含量及入渗时间对砂土导水率影响极显著（P<0.01）,入渗时间为砂土影响导水率变化的主要因素,其次为含沙率和黏粒含量;建立的砂土导水率动态模型决定系数为0.853,均方根误差为0.004 cm/min,表明该模型可客观反映各因素与导水率之间的关系;模型验证试验结果中均方根误差小于0.01 cm/min,相对误差绝对值均值小于7%,说明该导水率动态模型可靠性较高;砂壤土和粉壤土导水率动态模型决定系数分别为0.912和0.930,均方根误差分别为2×10^-3和5×10^-5 cm/min;模型验证中均方根误差小于0.01 cm/min,相对误差绝对值小于17%,表明模型计算值与实测值的一致性较好。研究结果有助于揭示浑水土壤入渗规律,为进一步探明浑水入渗过程及致密层阻渗机理提供理论依据。     

盘式吸渗仪测定土壤导水率的两种新方法

应用盘式吸渗仪测定田间土壤导水率具有快速简单的优点，但是测定结果的计算处理比较繁琐，寻求简单的计算方法是广泛应用盘式吸渗仪的关键问题。该文改变盘式吸渗仪测定土壤导水率的三维入渗过程为一维入渗过程，简化了测定结果的计算处理。结果显示：两种不同的一维入渗过程达到的稳定入渗率和导水率之间有很好的线性关系，但是三维过程计算的导水率大于一维过程。双套盘吸渗仪一维过程计算导水率与稳定入渗率一致性较好，但是和三维稳态、瞬态方法计算结果之间差异明显，因此在应用这些方法时需要适当调整参数，建议使用双套盘吸渗仪快速测定田间土壤导水率。     

滨海盐渍土原土滴灌水盐调控对土壤水力性质的影响

为研究滨海盐渍土滴灌原土水盐调控不同处理对土壤导水率(K)、土壤孔隙大小分布常数(Gardnerα)、土壤孔隙对水流贡献率等水力性质的影响,在滨海盐渍土上进行滤层及基质势(-5、-10、-15、-20、-25kPa)处理的原土水盐调控试验。用圆盘入渗仪在-15、-6、-3、0cm4个连续增大的负压下进行入渗测定,并计算不同负压下导水率、土壤孔隙大小分布常数、孔隙级别对水流的贡献率。结果表明:经原土水盐调控后,各处理的饱和导水率、土壤孔隙大小分布常数较对照增大,在-6和-15cm水头下的导水率较对照减少,在-3cm水头下的导水率无明显变化规律。滤层处理下土壤的饱和导水率、-6cm水头下的导水率、土壤孔隙大小分布常数较无滤层处理有显著提高;各处理土壤大孔隙对水流的贡献率大于对照处理,中等孔隙2及小孔隙对水流的贡献率小于对照处理。滤层处理是不同级别土壤孔隙对水流贡献率大小的主要影响因素,其中滤层的土壤大孔隙、中等孔隙1对水流的贡献率显著高于无滤层。可见,经原土水盐调控后,土壤饱和导水率、-6cm水头下的导水率、土壤孔隙大小分布常数明显增加,土壤大孔隙增加,小孔隙减少,土壤结构得到改善。     

盘式入渗仪法测定喀斯特洼地土壤透水性研究

研究土壤水入渗有助于了解喀斯特地区表层岩溶带对降水资源的调蓄作用。该文利用盘式负压入渗仪(盘径d=20 cm,负压h0=-20 mm)研究了桂西北喀斯特洼地典型剖面各层次土壤透水性。结果表明:各层土壤透水性能差异较大,具有随土层深度增加而减小的趋势,但菜地50-80 cm层大于20-50 cm层;菜地剖面0-10 cm层土壤近似饱和导水率(1.85×10-3cm/s)是20-50 cm层的5.2倍,玉米地剖面0-16 cm层土壤近似饱和导水率(2.21×10-3cm/s)是55-70 cm层的3.1倍;土壤比重、初始含水率同土壤入渗性能关系密切,与近似饱和导水率的相关系数分别为-0.676*和-0.841**。     

土壤水力特性异质性对土壤排水影响的瞬态随机分析

土壤剖面水分入渗及再分布对生态和水文建模十分重要,而土壤异质性导致垂向的导水率值差异非常大。因此,该文假设在单位梯度下,用微扰法和运动波模型并结合随机分析研究一维瞬态土壤剖面排水的问题。采用Brooks-Corey模型,设饱和导水率和模型参数为随机变量。结果表明:1)饱和导水率方差增大对排水过程具有减缓的作用,有效饱和导水率较小;2)土壤导水率异质性越大,土壤蓄水能力越强;3)比较模型参数的波动与饱和导水率方差和模型参数的协方差,饱和导水率方差对排水影响更大;4)田间排水试验的结论与模型预测相一致。研究可为以长期自我维持的生态系统和高田间持水量为目标的土壤复垦提供依据。     

A method for automating data collection from a double-ring infiltrometer under falling head conditions

Estimating soil hydraulic properties, such as infiltration rate and hydraulic conductivity, is important for understanding hydrological processes such as rainfall and irrigation partitioning. Current infiltrometers can require considerable operator input to limit the number of readings that can be simultaneously performed. Therefore, the objective of this work was to develop a simple double-ring infiltrometer for automated data collection under falling head conditions. The design consisted of 15.2-cm tall inner- and outer-rings of 14.6 and 33.0 cm in diameter, respectively. The inner-ring was held in the centre of the outer-ring by a small pipe that also served as a handle. A small hole was drilled 3.8 cm from the bottom of each ring and a slightly larger hose passed through both holes. One hose end led into the inside of the inner-ring and the opposite end to the outside of the outer-ring. A pressure transducer was attached to the outside end of the hose. A datalogger was used to record the transducer output. This design was compared in-situ to a constant head method using a Mariotte bottle system on two distinct soils and tested on four different soil series ranging in textural class from a loamy sand to a clay. Soils had been fallow prior to this work for at least 2 years, except the loamy sand which had a 5-year-old Bahia grass ( Paspalum notatum ) stand. Although there were some differences between the two approaches, values estimated with the proposed method had less variability. This method allows a single user to collect multiple readings. Collected data can be used to estimate quasi-steady state and cumulative infiltration, and in situ hydraulic conductivity of saturated soil. The proposed procedure could be beneficial when multiple readings of soil hydraulic properties are required, such as when characterizing soil spatial variability.     

Estimating hydraulic conductivity values from ring infiltrometer measurements

Infiltration from ring infiltrometers of different radii was measured into four soil materials contained in laboratory tanks. The infiltration per unit area was larger the smaller the ring size, coming to a steady state at an earlier time. Scaling based on similar media theory was applied to the results using a microscopic characteristic length defined in terms of the hydraulic conductivity of the saturated soil and a macroscopic characteristic length taken as the radius of the ring. The relationships between scaled cumulative infiltration and scaled time merged into a single relationship at small scaled times for all soil materials and for all sizes of ring, but were different for the different soils and for the various ring radii at large scaled times. The relationship at small times was used as a type curve to interpret in situ measurements with ring infiltrometers on three field soils in terms of the hydraulic conductivity of the saturated soil. These estimates of hydraulic conductivity pertained to the small volume of soil near the surface which was wetted during the measurement. Large variations in hydraulic conductivity values were found from experiments with small sized rings, but little variation was found for large sized rings. The technique provides a simple method of investigating soil structural changes near the surface.     

Measuring near‐saturated hydraulic conductivity of soils by quasi unit‐gradient percolation—1. Theory and numerical analysis

The saturated and near‐saturated hydraulic conductivity of soils, k_u, is a sensitive indicator of soil structure and a key parameter for solute transport and soil aeration. In this contribution, we present and numerically investigate a double‐disk method to determine k_u in the laboratory by steady‐state percolation at different suction steps. Tension infiltration of water takes place at the top of a soil column through a porous disk with a smaller diameter than the soil sample. This leaves part of the soil surface open and ensures a proper soil ventilation. Drainage takes place at the base through a porous disk with the full diameter of the soil column at exactly the same tension as applied to the top boundary. Since the infiltration area is less than the percolation area, the water flow diverges and the equality of steady flow rate and hydraulic conductivity, which characterizes the standard unit‐gradient experiment, is no longer valid. To develop a general relationship between observed steady flow rate and unsaturated hydraulic conductivity, the experiment was simulated with the Richards‐equation solver HYDRUS 2D/3D, for twelve different soil classes. We found for tensions in the range 1 cm < 10 cm, an infiltration disk diameter of 4.5 cm diameter and a sample diameter of 8 cm diameter that the flux rate at any given tension was about 0.7 times the respective hydraulic conductivity, with an error of less than 10%.     

利用圆盘入渗仪测定不同土地利用类型土壤吸渗率

探讨利用圆盘入渗仪测定不同利用类型土壤吸渗率的适用性,该文选用盘径分别为10和20 cm的圆盘入渗仪对3种利用土壤(菜地、草地和茶园)在0、-3、-6、-9 cm 4个压力水头下的吸渗过程进行测定。研究以Vandervaere法为参考方法,对Philip法、Haverkamp三维吸渗法、Haverkamp三维吸渗改进法的适用性进行比较分析。结果表明:吸渗率的不同计算公式所适应的吸渗过程时间尺度不同,且Haverkamp三维吸渗法所得吸渗率值与参考方法最接近。盘径对吸渗率测定差异的影响不显著。除0 cm压力水头外,不同利用类型土壤吸渗率差异显著,且不同压力水头下测得3种土壤吸渗率大小排序不同。当压力水头为-9和-6 cm时,菜地吸渗率(0.0104和0.0119 cm/s0.5)显著高于茶园(0.0017和0.0025 cm/s0.5)(P0.05);当压力水头为-3 cm时,茶园吸渗率(0.0370 cm/s0.5)显著高于菜地和草地(0.0147和0.0132 cm/s0.5)(P0.05)。该研究可为南方丘陵区土壤水力参数的测定提供理论依据。