Measuring near‐saturated hydraulic conductivity of soils by quasi unit‐gradient percolation—2. Application of the methodology

Sarkar et al. (this issue) proposed a laboratory measurement method for obtaining the hydraulic conductivity of soil at near‐saturated moisture conditions, bridging the gap between measurements that can be obtained with the evaporation method in the medium dry region, and measurements of the saturated conductivity by traditional methods. The method is based on a tension infiltration on a limited part of the surface of a soil sample and drainage of the sample at the same tension, leading to a divergent flow field. Despite equal tensions at top and bottom of the sample (“unit gradient”), the water flux in the sample is smaller than the corresponding value of the soil hydraulic conductivity at the applied tension. From numerical analysis of the flow problem, they concluded that unsaturated conductivity can be obtained with an accuracy of 10% for all texture classes of the USDA soil texture triangle. In this paper, we test the methodology for three different soil types using an appropriate apparatus. The results match well with independent saturated conductivity measurements on the wet side, and with unsaturated conductivity measurements in the medium moisture range that were obtained with the evaporation method.     

Estimation of saturated hydraulic conductivity from double‐ring infiltrometer measurements

This research aims to determine soil vertical saturated hydraulic conductivity (K_s) in situ from the measured steady infiltration rate (I), initial soil properties and double‐ring infiltrometer (DRI) test data. Characterizing the effects of these variables on the measured steady infiltration rate will enable more accurate prediction of K_s. We measured the effects of the ring diameter, head of ponding, ring depth, initial effective saturation and soil macroscopic capillary length on measured steady infiltration rates. We did this by simulating 864 DRI tests with the finite element program HYDRUS‐2D and by conducting 39 full‐scale in situ DRI tests, 30 Mini‐Disk infiltrometer experiments and four Guelph Permeameter tests. The M5′ model trees and genetic programming (GP) methods were applied to the data to establish formulae to predict the K_s of sandy to sandy‐clay soils. The nine field DRI tests were used to verify the computer models. We determined the accuracy of the methods with 30% of the simulated DRI data to compare I/K_S values of the finite element models with estimates from the suggested formulae. We also used the suggested formulae to predict the K_s values of 30 field DRI experiments and compared them with values measured by Guelph Permeameter tests. Compared with the GP method, the M5′ model was better at predicting K_S, with a correlation coefficient of 0.862 and root mean square error (RMSE) of 0.282 cm s^?1. In addition, the latter method estimated K_svalues of the field experiments more accurately, with an RMSE of 0.00346 cm s^?1.     

Effect of long‐term swine‐manure application on soil hydraulic properties and heavy metal behaviour

This study evaluated the effect of 13 years of swine‐manure application on the changes in soil hydraulic properties, and as associated physicochemical properties, with a focus on heavy metal mobility. Various soil hydraulic properties were measured, including soil water retention (SWR), saturated field hydraulic conductivity (K_fs) and unsaturated field hydraulic conductivity (K_funsat) using a disc infiltrometer. Heavy metal mobility was evaluated with a sequential extraction procedure. At 0–30 cm soil depth in the heavily manured plot (SMhigh plot), SWR at 0 to ?100 kPa was significantly larger than in plots amended with a standard amount of manure (SMstd plot) or with chemical fertilizer (CF plot). K_fs and K_funsat values in both manure‐amended plots were less than in the CF plot under dry soil conditions but greater than those of the CF plot under wet soil conditions. Furthermore, K_fs and K_funsat did not necessarily increase with manure application rates. On the other hand, high‐mobility metal fractions, such as the exchangeable fraction of Zn, and the CH₃CO₂Na‐extractable fraction of Zn and Mn, and the metal–organic complex fractions of Zn, Cu and Mn, increased with the greater manure application rate. In addition, low‐mobility metal fractions, the organically bound fractions of Zn, Cu and Mn in the high SM plot and the easily reducible metal oxide fraction of Mn in both manure‐amended plots were probably affected and released into high‐mobility fractions. This indicated that manure application changed the soil redox conditions by improving the soil structure, depending on the water content of soil pores. Despite the reduction of K_fs and K_funsat by heavy manure application, the transport of high‐mobility metal fractions with either surface water flow or infiltration water flow could be controlled by soil water content at the beginning of a rain or irrigation event.     

烟台棕壤土饱和导水率的初步研究

该文利用单环入渗的概化解,对不同土地利用方式下烟台棕壤土的饱和导水率进行了研究,同时分析了不同单环直径对求解饱和导水率产生的影响。研究结果表明：草地、裸地和道路的入渗速率、累积入渗量和饱和导水率呈现依次降低的变化趋势,利用直径为20、30和45 cm的入渗环得到的饱和导水率具有明显的差异性。根据求解的饱和导水率计算的累积入渗量非常接近实测值,整体相对误差很小,草地、裸地和道路,在5、7和40 m in后浮动在5%以内;在15、43和55 m in后变化幅度小于1%。20、30和45 cm入渗环累积入渗量计算值的相对误差初始阶段波动较大,随后逐渐趋于平稳。     

Using boosted regression trees to explore key factors controlling saturated and near‐saturated hydraulic conductivity

Hydraulic conductivity at and near saturation is difficult to predict. We investigated, for the first time, the potential of boosted regression trees to identify the key factors that determine saturated and near‐saturated hydraulic conductivities in undisturbed soils with a global meta‐database of tension infiltrometer measurements. Our results demonstrate that pedotransfer functions developed from meta‐databases may strongly over‐estimate prediction performance unless they are validated against each individual data source separately. For such a source‐wise cross‐validation, we estimated the hydraulic conductivity at a tension of 10 cm (K₁₀) and the saturated hydraulic conductivity (K_s) with coefficients of determination of 0.36 and 0.15, respectively. The most important predictors for K₁₀ were the average annual precipitation and temperature at the measurement location, which are key variables for pedogenesis and constrain soil management. More research is required for the in‐depth interpretation of their influence on hydraulic conductivity. The soil clay and organic carbon contents were also important predictors of K₁₀, with hydraulic conductivity decreasing as organic carbon contents increased up to 1.5% and as clay contents increased between about 10 and 40%. The direction of the tension‐sequence with which the infiltrometer data were collected was also a significant predictor. Land use and bulk density were the most important predictors for K_s. The direction of the tension‐sequence and the soil texture class were also important, with both coarse and fine‐textured soils generally having larger K_s values than medium‐textured soils.     

设计流量和土壤质地对微孔陶瓷灌水器入渗特性的影响

为探明微孔陶瓷灌水器土壤中入渗流量变化的原因,明确微孔陶瓷灌水器的出流原理,该研究基于土桶模拟试验,研究3种设计流量(0.72、1.87和4.40 L/h)的微孔陶瓷灌水器下2种土壤(黄绵土、塿土)的渗流特性。结果表明,使用不同灌水器灌溉后,短时间内入渗流量均迅速减小,而后缓慢减小趋于稳定。设计流量与土壤质地均影响灌水器的出流。灌水器周围土壤水势的变化是造成入渗流量变化的直接原因,土壤含水率的变化是入渗流量变化的根本原因。在没有淹没出流的情况下,土壤含水率越高,入渗流量越小。设计流量为1.87 L/h灌水器应用于塿土中,当土壤含水率由13%增大至40%时,入渗流量由1.4 L/h下降至0.3 L/h左右。灌水器周围土壤含水率对入渗流量具有反馈调节作用。采用微孔陶瓷灌水器作为灌溉系统的核心部件,在内部水头适宜(微压或零压)的情况下,通过灌水器入渗流量与土壤含水率的耦合作用,可实现土壤水分的自动调控,达到主动灌溉的目的。该文可为微孔陶瓷灌水器的推广应用提供参考。     

祁连山区不同尺寸双环入渗仪对比试验

设计7组不同内外径的双环入渗仪,在位于祁连山区的黑河上游平坦草地开展多次野外土壤入渗试验,对比分析双环入渗仪内外环尺寸对土壤入渗率和饱和导水率的影响。结果表明,双环入渗仪内径相同时,外径越大则稳定入渗率和饱和导水率越小;外径相同时,内径越小则稳定入渗率和饱和导水率越小。初始入渗率与双环入渗仪尺寸关系不显著,但稳定入渗率和饱和导水率与入渗仪缓冲指数呈显著负相关。综合考虑安装简便,用水条件,试验可靠等多方面因素,推荐山区使用内径20cm,外径40cm的双环入渗仪。     

Effect of sodium adsorption ratio and electrolyte concentrations on the saturated hydraulic conductivity of clay–sand mixtures

We did flow experiments under saturated conditions on homoionic (Na⁺) kaolin–sand and illite–sand systems, containing 5, 10, and 15% clay, to validate a drainage model, and evaluate the effect of the different chemical composition of the percolating solutions on the hydraulic properties of the systems. Column drainage experiments, under a constant hydraulic head, were carried out using solutions with two sodium adsorption ratios (SAR 0 and ∞) and three electrolyte concentrations (10^?2, 10^?3, and 10^?4 m ). We calculated the saturated hydraulic conductivity, K_sat, of the systems using Darcy's law when these showed linear relationships between effluent volume and time. The drainage model was applied to characterize the flow of non‐steady‐state drainage of solutions through the porous systems. This model describes and characterizes quantitatively the drainage of solutions from soil columns that vary in intrinsic permeability, k, because of structural modifications that occur within the solid matrix of the systems. For both the systems investigated we always observed a decrease in the flow rate as electrolyte concentration decreased, or clay percentage increased. Under the same conditions the flow was faster for the kaolin system than the illite system, even though kaolin dispersed more than illite. Non‐linear relations were also observed at the smallest electrolyte concentration (10^?4 m ). In all cases, the equations proposed correlated well with the experimental data, confirming the soundness of the model. The flow rates observed in the experiments at SAR ∞ were unexpectedly greater than those observed at SAR 0, for the two systems, when leaching with solutions at 10^?3 and 10^?4 m . The values of pH and electrical conductivity of the eluates support the idea that the clay hydrolysis occurred during the saturation and, to a lesser extent, during the leaching phase of the flow.     

Impact of land‐use changes on soil hydraulic properties of Calcaric Regosols on the Loess Plateau,NW China

Vegetation restoration efforts (planting trees and grass) have been effective in controlling soil erosion on the Loess Plateau (NW China). Shifts in land cover result in modifications of soil properties. Yet, whether the hydraulic properties have also been improved by vegetation restoration is still not clear. The objective of this paper was to understand how vegetation restoration alters soil structure and related soil hydraulic properties such as permeability and soil water storage capacity. Three adjacent sites with similar soil texture, soil type, and topography, but different land cover (black locust forest, grassland, and cropland) were selected in a typical small catchment in the middle reaches of the Yellow River (Loess Plateau). Seasonal variation of soil hydraulic properties in topsoil and subsoil were examined. Our study revealed that land‐use type had a significant impact on field‐saturated, near‐saturated hydraulic conductivity, and soil water characteristics. Specifically, conversion from cropland to grass or forests promotes infiltration capacity as a result of increased saturated hydraulic conductivity, air capacity, and macroporosity. Moreover, conversion from cropland to forest tends to promote the creation of mesopores, which increase soil water‐storage capacity. Tillage of cropland created temporarily well‐structured topsoil but compacted subsoil as indicated by low subsoil saturated hydraulic conductivity, air capacity, and plant‐available water capacity. No impact of land cover conversion on unsaturated hydraulic conductivities at suction > 300 cm was found indicating that changes in land cover do not affect functional meso‐ and microporosity. Our work demonstrates that changes in soil hydraulic properties resulting from soil conservation efforts need to be considered when soil conservation measures shall be implemented in water‐limited regions. For ensuring the sustainability of such measures, the impact of soil conversion on water resources and hydrological processes needs to be further investigated.     

Effects of charcoal production on soil physical properties in Ghana

Charcoal production, widespread in Ghana like in other W African countries, is a major driver of land‐cover change. Effects of charcoal production on soil physical, including hydrological, properties, were studied in the forest–savannah transition zone of Ghana. Core and composite samples from 12 randomly selected sites across the width of Kotokosu watershed were taken from 0–10 cm layer at charcoal‐site soils and adjacent field soils (control). These were used to determine saturated hydraulic conductivity (K_sat), bulk density, total porosity, soil texture, and color. Infiltration rates, surface albedo, and soil‐surface temperature were also measured on both sites. The results showed that the saturated hydraulic conductivity of soils under charcoal kilns increased significantly (p < 0.01) from 6.1 ± 2.0 cm h^–1 to 11.4 ± 5.0 cm h^–1, resulting to a relative increase of 88%. Soil color became darkened under charcoal kilns with hue, value, and chroma decreasing by 8%, 20%, and 20%, respectively. Bulk density on charcoal‐site soils reduced by 9% compared to adjacent field soils. Total porosity increased from 45.7% on adjacent field soils to 50.6% on earth kilns. Surface albedo reduced by 37% on charcoal‐site soils while soil‐surface temperature increased up to 4°C on average. Higher infiltration rates were measured on charcoal‐site soils, which suggest a possible decrease in overland flow and less erosion on those kiln sites.     

A dual‐porous,inverse model of water retention to study biological and hydrological interactions in soil

The deterministic modelling of bio‐hydrological processes in soil requires a void structure model that is explicitly dual‐porous containing fully and separately characterized macroporosity and microporosity. It should also contain information that relates the positioning of microporosity relative to macroporosity. An example of such a process is the production of nitrous oxide, in which bacteria in microporous ‘hot‐spots’ are supplied with nutrients and gases through a macroporous pathway. We present a precision void‐structure model that satisfies these two criteria, namely explicit macroporosity and microporosity, and their positional relationship. To demonstrate the construction of the model, we describe the modelling of a single soil, namely Warren soil from Rothamsted Research's Woburn Experimental Farm in Bedfordshire, UK, although the modelling approach is applicable to a wide range of soils and other dual porous solids. The model is capable of fitting several fundamental properties of soil, namely water retention, aggregate size distribution, and porosity of the microporous and macroporous zones. It comprises a dendritic critical percolation path, around which are clustered the microporous regions. The saturated hydraulic conductivity of the dual‐porous network is of the correct order of magnitude for a soil of the same density and texture as the Warren sample. Finally, we demonstrate how the preferential flow pathway in the resulting structure differs from the critical percolation pathway, and that only 4.6% by volume of the unclogged macroporosity contributes to the fluid flow through the structure.     

Anisotropy of pore functions in structured Stagnic Luvisols in the Weichselian moraine region in N Germany

In order to determine if soil hydraulic properties present a direction‐dependent behavior, undisturbed samples were collected at different horizons and orientations (vertical, diagonal [45°], and horizontal) in structured soils in the Weichselian moraine region in northern Germany. The water‐retention curve (WRC), the saturated hydraulic conductivity (k_f), and the air permeability (k_a) were measured. The air‐filled porosity (?_a) was determined, and pore‐continuity indices (k_a/?_a, k_a/?_a², N) and blocked porosities (?_b) were derived from the relationship between k_a and ?_a. The development of soil structures with defined forms and dimensions (e.g., platy by soil compaction or prismatic up to subangular‐blocky by swelling–shrinkage processes) and the presence of biopores can induce a direction‐dependent behavior of pore functions. Although the pore volume as a scalar is isotropic, the saturated hydraulic conductivity and air permeability (as a function of air‐filled porosity) can be anisotropic. This behavior was observed in pore‐continuity indices showing that the identification of soil structure can be used as a first parameter to estimate if hydraulic properties present a direction‐dependent behavior at the scale of the soil horizon.     

Structure and hydraulic properties of the boreal clay soil under differently managed buffer zones

Vegetated buffer zones (BZs) between arable fields and bodies of water are commonly established to reduce erosion and run‐off of particle‐bound nutrients. Functioning of a BZ depends on soil structure, as it is important for water infiltration. Therefore, it is vital to understand how varying management practices affect soils of BZs. We studied the structural and hydraulic properties of three differently managed BZs established in a boreal Vertic Stagnic Cambisol (clay, 51%). The three management practices for vegetation were as follows: natural with no treatment, harvested yearly and grazed by cattle. We used bulk density and macroporosity, together with a pore geometry index (air permeability per unit air‐filled porosity), to describe the soil structural properties. Hydraulic properties were measured at different length scales by means of an aggregate sorptivity test, saturated hydraulic conductivity of the core samples and field‐saturated hydraulic conductivity. Vegetation management markedly affected the physical properties in the top 5 cm of the soil. Properties were least favourable for infiltration at the grazed site, with the greatest bulk density, least macroporosity and hydraulic conductivity or greatest pore tortuosity. In general, spatial variation in zones with restricted and good hydraulic conductivity together with reduced aggregate sorptivity in the deeper horizons made the soil prone to preferential flow when initially dry. Prolonged wetness, on the other hand, reduced saturated hydraulic conductivity significantly, resulting in surface run‐off. Harvesting was considered the best management practice due to its inherent capacity for reducing the soil nutrient content and because it has minor implications for soil physical properties.     

Effect of Soil Sample Size on Saturated Soil Hydraulic Conductivity

Saturated hydraulic conductivity (K_sat) is regarded as a key soil physical variable to determine soil infiltration rate, percolation depth and other hydrological processes. The purpose of this study was to determine the best soil sampling’s ring size for measuring K_sat. For this purpose, 25 rings with five different diameters (2, 3, 4, 5 and 6 inch) and with the same depth of 20 cm (five replicates) were hammered in close vicinity to each other into the ground of undisturbed loess deposits of a small farm to measure K_sat and bulk density. Hydraulic conductivity was measured at three constant loads of 22, 27 and 32 cm. The results showed that the ring with the internal diameter of 6 inches had the minimum variation coefficient and maximum K_sat for all the three hydraulic heads. In addition, the bulk density of this ring size was less than the other rings.     

黄土丘陵区典型植被土壤物理性质差异及其对导水特性影响

选取黄土丘陵区12种典型植被样地,通过测定各样地不同土层植物残体生物量、土壤容重、毛管孔隙度、非毛管孔隙度及饱和导水率,研究各指标随土层深度和植被类型的变化规律及其对土壤饱和导水率的影响。结果表明:(1)除容重随土层深度增加外,植物残体、毛管孔隙度、非毛管孔隙度和饱和导水率均随土层深度减少,其中植物残体大多集中于表层土壤(0—10 cm),占总残体生物量的51.4%～85.7%。(2)不同植被类型其植物残体及土壤物理性质存在显著差异,乔木林地植物残体、农耕地土壤容重、灌木林地非毛管孔隙度及饱和导水率均最大,而毛管孔隙度与不同土地利用类型间无显著差异。(3)饱和导水率随植物残体生物量密度(0—10 cm)和土壤容重呈幂函数减小,随毛管孔隙度和非毛管孔隙度呈幂函数增大;土壤容重(BD)和非毛管孔隙度(NCP)是影响土壤饱和导水率(K_s)的主要因素,且土壤饱和导水率可表示为两者的综合非线性方程(K_s=0.6BD~(-4.717)NCP~(0.203),P0.01,R~2=0.63,NSE=0.50)。此外,沙棘灌木林地平均饱和导水率最大,有利于降雨过程中土壤水分入渗,具有较强的水土保持功能。本研究结果可为黄土高原植被恢复生态水文效益评价提供理论依据。     

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。     

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...     

Bemerkungen zur Ermittlung der ungesättigten Wasserleitfähigkeit unter nichtstationären Bedingungen

On the Determination of Capillary Conductivity at Unsteady-State Conditions . Therefore it is stated that for obtaining the effective k_u-values. Considering the importance of capillary conductivity for the soil water regime the large differences up to 2 orders of magnitude between determinations on core samples from the same soil using the double-membrane-method (Henseler and Renger 1969) and the evaporation-method (Becher 1971a) initiated a study concerning the error caused by a possible nonlinearity of suction changes between two measuring levels using the latter method. The study was carried out on disturbed and undisturbed core samples from the three textural classes sand, silt and clay and with modified evaporation method. Comparing the geometric means of the obtained k_u-values calculated at unsteady-state and quasisteady-state conditions for different suctions resulted in that with usual application of the method the measured k_u-values must be diminished for obtaining the effective k_u-values. This correction factor increased with suction and is considered to be more important in laboratory than in field use.

• 1 For sandy soils a correction factor of 2 at 150 cmH₂O increasing to 6 at 1000 cm H₂O must be applied. The coarser the sand would be, at the lower suction nonlinearity will start and the more rapidly the correction factor will increase;.
• 2 For silty soils a correction factor of 2–4 must be applied for suctions > 300 cm H₂O;.
• 3 For clayey soils a correction factor of 2 rapidly increasing to 10 must be applied for suctions > 150 cm H₂O, but depending on soil cracks.

. The overestimation of water through-put resulting from the uncorrected k_u-values amounts to 1.5–4.0 [l/m² · d] at 100 cm H₂O, but these values are within the variation of the effective k_u-values. For 800cm H₂O the overestimation amounts to 0.002–0.065 [l/m² · d], but this makes up 300–1000 % of the effective water through-put.     

Suitability of a hydraulic‐conductivity model for predicting salt effects on swelling soils

Many empirical approaches have been developed to analyze changes in hydraulic conductivity due to concentration and composition of equilibrium solution. However, in swelling soils these approaches fail to perform satisfactorily, mainly due to the complex nature of clay minerals and soil–water interactions. The present study describes the changes in hydraulic conductivity of clay (Typic Haplustert) and clay‐loam (Vertic Haplustept) soils with change in electrolyte concentration (TEC) and sodium‐adsorption ratio (SAR) of equilibrium solution and assesses the suitability of a model developed by Russo and Bresler (1977) to describe the effects of mixed Na‐Ca‐Mg solutions on hydraulic conductivity. Four solutions encompassing two TEC levels viz., 5 and 50 mmol_c L^–1 and two SAR levels viz., 2.5 and 30 mmol^1/2 L^–1/2 were synthesized to equilibrate the soil samples using pure chloride salts of Ca, Mg, and Na at Ca : Mg = 2:1. Diluting 50 mmol_c L^–1 solution to 5 mmol_c L^–1 reduced saturated hydraulic conductivity of both soils by 66%, and increasing SAR from 2.5 to 30 mmol^1/2 L^–1/2 decreased saturated hydraulic conductivity by 82% and 79% in clay and clay‐loam soils, respectively. Near saturation, the magnitude of the change in unsaturated hydraulic conductivity due to the change in TEC and SAR was of 10³‐ and 10²‐fold, and at volumetric water content of 0.20 cm³ cm^–3, it was of 10¹⁴‐ and 10⁶‐fold in clay and clay‐loam soils, respectively. Differences between experimental and predicted values of saturated hydraulic conductivity ranged between 0.6% and 11% in clay and between 0.06% and 2.1% in clay‐loam soils. Difference between experimental and predicted values of unsaturated hydraulic conductivity widened with drying in both soils. Predicted values were in good agreement with the experimental values of hydraulic conductivity in clay and clay‐loam soils with R² values of 0.98 and 0.94, respectively. The model can be satisfactorily used to describe salt effects on hydraulic conductivity of swelling soils in arid and semiarid areas, where groundwater quality is poor.     

利用圆盘入渗仪推求含碎石土壤饱和水力传导度(英)

在模拟土柱中，利用圆盘入渗仪对碎石对土壤饱和水力传导度的影响进行了分析。结果表明：含碎石土壤饱和水力传导度可以通过对不同负压下土壤稳定入渗速率进行非线性回归获得。含碎石土壤饱和水力传导度与去除碎石后的土壤饱和水力传导度及碎石形状指数密切相关。试验中含碎石土壤的饱和水力传导度随碎石含量的增加而呈指数降低趋势。