测定尺度对所测土壤导水参数及其空间变异性的影响

用 3种盘径 (14.4,2 0 ,30cm)的负压入渗仪在 2个供水负压 (1和 10cm)下 ,在 65个测点测定了田间水分入渗。基于入渗数据 ,计算了宏观毛管上升高度和 2个基模吸力的导水率。导水率和宏观毛管上升高度的值呈对数正态分布。用大盘径负压入渗仪测定获得的导水率和宏观毛管上升高度的空间连续性最好。当供水负压为 1cm ,盘径为 14.4cm(小盘径 ) ,导水率和宏观毛管上升高度的空间连续性没有表现出来。导水率的均值随测定尺度增加而趋于减少 ,宏观毛管上升高度的均值和标准偏差均随测定尺度增加而趋于减小。导水率和宏观毛管上升高度的样本半方差 ,半方差金砖方差 (nugget)和平台方差 (sill)随测定尺度增加而减少     

应用土壤质地预测干旱区葡萄园土壤饱和导水率空间分布

田间表层土壤饱和导水率的空间变异性是影响灌溉水分入渗和土壤水分再分布的主要因素之一,研究土壤饱和导水率的空间变化规律,有助于定量估计土壤水分的空间分布和设计农田的精准灌溉管理制度。为了探究应用其他土壤性质如质地、容重、有机质预测土壤饱和导水率空间分布的可行性,试验在7.6 hm2的葡萄园内,采用均匀网格25 m×25 m与随机取样相结合的方式,测定了表层(0～10 cm)土壤饱和导水率、粘粒、粉粒、砂粒、容重和有机质含量,借助经典统计学和地统计学,分析了表层土壤饱和导水率的空间分布规律、与土壤属性的空间相关性,并对普通克里格法、回归法和回归克里格法预测土壤饱和导水率空间分布的结果进行了对比。结果表明:1)土壤饱和导水率具有较强的变异性,平均值为1.64 cm/d,变异系数为1.17;2)表层土壤饱和导水率60%的空间变化是由随机性或小于取样尺度的空间变异造成;3)土壤饱和导水率与粘粒、粉粒、砂粒和有机质含量具有一定空间相关性,而与土壤容重几乎没有空间相关性;4)在中值区以土壤属性辅助的回归克里格法对土壤饱和导水率的预测精度较好,在低值和高值区其与普通克里格法表现类似。研究结果将为更好地描述土壤饱和导水率空间变异结构及更准确地预测其空间分布提供参考。     

重庆市四面山典型林分土壤饱和导水率研究

采用恒定水头法测定了重庆市四面山地区典型人工林和天然次生林剖面土壤饱和导水率(Ks),并运用多元回归和通径分析方法探讨了其与土壤物理因子和有机质的相关性。结果表明,土壤饱和导水率从表层到深层呈现出负指数形式的递减规律。各林分对饱和导水率均有显著提高,由高到低的顺序为:天然针阔混交林>天然阔叶林、楠竹林、针叶林>人工阔叶林、混交林、针叶林>荒地。土壤黏粒、容重、非毛管孔隙度和大于0.25 mm水稳性团聚体含量是影响该地区饱和导水率的主要因子。各林分对土壤有机质含量均有提高作用,有机质含量与饱和导水率符合二次曲线的关系。在植被经营过程中,建议营造针阔复层混交类型的树种配置模式。     

土柱尺寸对扰动黏壤土饱和导水率的影响

土壤饱和导水率Ks是最基本的水力参数之一,而已知实验室内其值的确定受土柱尺寸的影响.以关中的塿土为研究对象,在室内,采用定水头法,研究5～30 cm内6个不同土柱尺寸对扰动黏壤土Ka测定的影响.结果表明：随着时间的延伸,Ks逐渐减小,其值最初降幅较大,其后趋于稳定,且在5 ～ 30 cm土柱直径范围内,Ks随着土柱直径的变大,扰动黏壤土的Ks递增,二者线性相关,y=0.000 4x＋0.003 7（R2=0.965 1）.研究结果可为测定Ks合理测定时间段及合理尺寸的选择提供参考.     

非饱和水分运动参数空间变异的研究

田块尺度土壤特性的空间变异性对水分与溶质运移具有明显的影响。该研究在野外30m×30m面积、土壤类型为砂壤土的田块的100个空间点上,分别利用张力计和取土样室内测定的方法测定了30cm土层深处土壤水张力、土壤容重ρ、饱和含水率θ_s,与初始含水率θ_i,同时利用圭尔夫仪,测定了该田块同样深度108个空间点上的饱和水力传导度K_s与孔隙大小分布参数α。利用经典统计分析与地质统计分析方法分析上述参数的空间变异特征,研究结果表明:ρ,θ_i,θ_s,K_s和容水度C遵从正态分布,而α具有对数正态分布;K_s,α和C具有较大的空间变异性,而ρ和θ_s的空间变异性则较小;K_s和logα是空间统计相关的;土壤水张力的空间变异具有时不变特征,且土壤水张力方差是其均值的二次函数     

Comparison of experimentally Determined and Calculated Hydraulic Conductivities for two alluvial sandy loam Profiles

The dynamic water conductivity characteristics of two alluvial sandy loam profiles (Typic Ustochrepts) were determined following the ?instantaneous profile method”? by monitoring the temporal variation in soil moisture content and potential at different depths in the profile, as the downward movement of water in the nearly saturated profile continued with evaporation prevented. The experimental sites differed in bulk density, moisture retention functions as well as dynamic water conductivity characteristics K(O). The unsaturated hydraulic conductivities were also calculated from moisture retention functions following the methods suggested by Campbell(1974) and Ghosh (1977). The calculated conductivity values agreed fairly well with the field data for the light-textured soils studied and the calculated values can be used for all practical purposes.     

Effect of degree of fluid saturation on transport coefficients in disturbed soils

To improve the predictive capability of transport models in soils we need experimental data that improve their understanding of properties at the scale of pores, including the effect of degree of fluid saturation. All transport occurs in the same soil pore space, so that one may intuitively expect a link between the different transport coefficients and key geometrical characteristics of the pores such as tortuosity and connectivity, and pore‐size distribution. To understand the combined effects of pore geometry and pore‐size distribution better, we measured the effect of degree of water saturation on hydraulic conductivity and bulk soil electrical conductivity, and of degree of air saturation on air conductivity and gaseous diffusion for a fine sand and a sandy loam soil. To all measured data were fitted a general transport model that includes both pore geometry and pore‐size distribution parameters. The results show that both pore geometry and pore‐size distribution determine the functional relations between degree of saturation, hydraulic conductivity and air conductivity. The control of pore size on convective transport is more for soils with a wider pore‐size distribution. However, the relative contribution of pore‐size distribution is much larger for the unsaturated hydraulic conductivity than for gaseous phase transport. For the other transport coefficients, their saturation dependency could be described solely by the pore‐geometry term. The contribution of the latter to transport was much larger for transport in the air phase than in the water phase, supporting the view that connectivity dominates gaseous transport. Although the relation between effective fluid saturation and all four relative transport coefficients for the sand could be described by a single functional relation, the presence of a universal relationship between fluid saturation and transport for all soils is doubtful.     

Properties of soils from the Swedish long-term fertility experiments: VI. Mapping soil electrical conductivity with different geophysical methods

Abstract

Swedish long-term soil fertility experiments were used to investigate the effect of texture and fertilization regime on soil electrical conductivity. In one geophysical approach, fields were mapped to characterize the horizontal variability in apparent electrical conductivity down to 1.5 m soil depth using an electromagnetic induction meter (EM38 device). The data obtained were geo-referenced by dGPS. The other approach consisted of measuring the vertical variability in electrical conductivity along transects using a multi-electrode apparatus for electrical resistivity tomography (GeoTom RES/IP device) down to 2 m depth. Geophysical field work was complemented by soil analyses. The results showed that despite 40 years of different fertilization regimes, treatments had no significant effects on the apparent electrical conductivity. Instead, the comparison of sites revealed high and low conductivity soils, with gradual differences explained by soil texture. A significant, linear relationship found between apparent electrical conductivity and soil clay content explained 80% of the variability measured. In terms of soil depth, both low and high electrical conductivity values were measured. Abrupt changes in electrical conductivity within a field revealed the presence of ‘deviating areas’. Higher values corresponded well with layers with a high clay content, while local inclusions of coarse-textured materials caused a high variability in conductivity in some fields. The geophysical methods tested provided useful information on the variability in soil texture at the experimental sites. The use of spatial EC variability as a co-variable in statistical analysis could be a complementary tool in the evaluation of experimental results.     

Soil hydraulic properties of two loess soils in China measured by various field-scale and laboratory methods

Knowledge of hydraulic properties is essential for understanding water movement in soil. However, very few data on these properties are available from the Loess Plateau of China. We determined the hydraulic properties of two silty loam soils on agricultural land at sites in Mizhi and Heyang in the region. Undisturbed soil cores were collected from seven layers to one meter depth to determine saturated hydraulic conductivity, soil water retention curves and unsaturated hydraulic conductivity (by the hot-air method). Additional field methods (internal drainage and Guelph permeameter) were applied at the Heyang site to compare differences between methods. Soil water retention curves were flatter at Mizhi than at Heyang. Water contents at saturation and wilting point (1500 kPa) were higher at Heyang than at Mizhi. However, unsaturated hydraulic conductivity was lower at Heyang than at Mizhi, with maximum differences of more than six orders of magnitude. Nevertheless, the two soils had similar saturated hydraulic conductivities of about 60 cm day^− 1. Comparison between the methods showed that soil water retention curves obtained in the laboratory generally agreed well with the field data. Field-saturated conductivities had similar values to those obtained using the soil core method. Unsaturated hydraulic conductivities predicted by the Brooks–Corey model were closer to field data than corresponding values predicted by the van Genuchten model.     

六盘山华北落叶松坡面土壤饱和导水率空间异质性及其影响因素

为深入理解森林坡面土壤饱和导水率的空间变异,利用经典统计学和地统计学的方法研究六盘山华北落叶松人工林坡面不同土层土壤饱和导水率的空间异质性,并基于相关性分析揭示其空间变异的主要因素。结果表明:(1)随土层的加深,土壤饱和导水率逐渐增加,不同土层土壤饱和导水率的空间变异程度存在差异,表现为40—60 cm土层土壤饱和导水率为强变异,其他土层均为中等变异。(2)不同土层土壤饱和导水率的空间结构也存在差异,20—40,40—60,60—80 cm土层土壤饱和导水率表现为强烈的空间自相关性,0—20,80—100 cm土层土壤饱和导水率表现为中等空间自相关性。(3)坡面土壤饱和导水率与石砾含量、非毛管孔隙度、毛管持水量、田间持水量和毛管孔隙度显著相关。综上,研究坡面土壤饱和导水率具有较强的空间变异,石砾含量和土壤物理性质是影响研究坡面土壤饱和导水率空间分布的主要因素。     

Effect of raindrop impact and its relationship with aggregate stability to different disaggregation forces

A soil surface exposed to rainfall is subjected to processes of wetting and drop impact which can lead to the formation of a seal during the rainfall, reducing infiltration and increasing erosion by increasing runoff. The objective of this research was to evaluate the relationship between the effect caused by the drop impact and the aggregate stability of the soils when they are subjected to different disaggregation forces. The aggregates were subjected to cracking (by slow wetting), slaking (by fast wetting) and mechanical breakdown (by mechanical stirring after pre-wetting in ethanol). The effect of each process was evaluated by measuring the mean weight diameter (MWDsl, MWDf and MWDst, respectively) calculated as the sum of the mass fraction of soil left in the sieve after fractionation into four size classes, ranging from <0.25 to 2 mm, multiplied by the mean aperture of the sieve meshes and divided by the initial soil weight. The effect of water impact plus wetting was quantified by the saturated hydraulic conductivity of the seal (Ks) and the time necessary to reach this value. A relative sealing index (RSI) that measured the reduction of water intake caused by sealing was defined as the relationship between the minimum value of saturated hydraulic conductivity of the seal and that reached when the drop impact was avoided. The air-dry material rupture was evaluated with a penetrometer. The main soil characteristics that determine all these processes for the study soils were analysed. Most of the studied soils were very sensitive to slaking and mechanical breakdown, while they were stable when they were subjected to slow wetting. A significant relationship was found between the minimum saturated hydraulic conductivity (Ks) and the MWDst (R²=0.40, p<0.005), and between Ks and the MWDf (R²=0.69, p<0.05). In both treatments, slaking and mechanical stirring, the percentage of aggregates retained in the larger sieve mesh was also significantly correlated with Ks. This result could indicate that both processes are implicated in the disaggregation produced by drop impact, which contribute to seal formation process. The less stable soils had the lowest Ks value (<1 mm h⁻¹), which was reached in a short period of time (<10 min). The high silt content and the low organic matter control the loss of aggregation by mechanical breakdown and the formation of the seal. The RSI values indicated a 200-fold reduction in water infiltration for some soils, caused by the formation of a seal.     

Regional pattern of the mobile water fraction in soils as determined by disc infiltrometer experiments

In order to characterize the partitioning of solutes into the mobile and the immobile fraction of pore water at the soil surface, field measurements of infiltration in unsaturated loamy sands were carried out using a disc infiltrometer in a region of about 10 km² at the Lüneburger Heide, Germany. The aims of these measurements were to obtain the mobile water fraction and the hydraulic properties of the soil, to relate them to other measured soil properties like the soil texture, and to assess their spatial variability in the region. From the infiltration results we obtained the hydraulic conductivity K₀ and the sorptivity S₀ using a three-dimensional infiltration analysis and the two-term infiltration equation, respectively. The mobile water fraction θ_m/θ of the soil was estimated from the infiltration results of a second disc infiltrometer filled with bromide solution. The estimated values of K₀ and S₀ were in good agreement with those reported in the literature as typical for loamy sands. The average value of θ_m/θ was calculated to be 71 % under the experimental conditions. Neither the horizontal spatial distribution of water and bromide concentration beneath the disc infiltrometer nor the change of the infiltrometer during the experiment had a notable influence on the experimental results. The spatial variability of the data was analyzed by means of variograms. All variograms were spatially structured and indicated a high small scale variation of the variables. In conclusion, the technique applied is suitable for the estimation of the hydraulic and solute transport properties of soils, especially at larger scales.     

推求土壤水分运动参数的简单入渗法──Ⅱ.实验验证

预报土壤中水分流动需要的土壤导水特性可通过观察水平土柱的入渗过程来确定,这一观测过程的分析是基于对Ｒｉｃｈａｒｄｓ方程求积分解。土壤水分特征曲线中的参数由观测的水平土柱和特征湿润长度和吸力为确定,非饱和土壤导水率由已确定的特征曲线中的参数和测定的饱和导水率导出。供试土壤有三种,它们的质地从砂壤到粘壤。由这种方法所确定的这三种土壤的水分特征曲线与实测的特征曲线符合良好,所确定的砂壤的非饱和导水率与实     

含岩屑紫色土水力特性及饱和导水率传递函数研究

紫色土中存在的岩石碎屑会对土壤的水力性质如饱和导水率、水分特征曲线产生显著影响。以两种不同母质发育的土壤(紫色页岩和紫色泥岩)为研究对象,设置0.25~2、2~5、5~10 mm三个岩屑粒径水平,0、30%、50%、70%、100%五个岩屑含量水平,采用压力膜仪法和定水头法分别测定水分特征曲线和土壤饱和导水率。利用BP神经网络,选择特定输入变量建立土壤饱和导水率传递函数PTF1和PTF2(PTF1的输入变量为岩屑含量、岩屑粒径、初始土壤容重和机械组成,PTF2的输入变量为岩屑含量、岩屑粒径、初始土壤容重、机械组成、进气压力值和S指数(土壤水分特征曲线拐点处斜率的绝对值))。结果表明:添加岩屑极大提高了土壤饱和导水率和S指数,并且随岩屑含量的增加而增加,相比之下,进气压力值随岩屑含量增加而减小,饱和导水率也随岩屑粒径的增加而增加,岩屑粒径从0.25~2 mm增加至5~10 mm,饱和导水率平均提高了2.3倍。岩屑粒径对进气压力值和S指数影响较小。PTF1和PTF2的几何平均数、几何标准偏差、均方根误差以及AIC指数分别为1.27、5.57、0.16、2.94和1.17、1.70、0.06、–53.28,PTF2的相关值均小于PTF1,表明PTF2模型的预测效果更好。综上所述,岩屑的存在显著影响了紫色土的水力特性,使饱和紫色土导水能力增加而保水能力减弱,利用神经网络所构建的传递函数PTF2可很好地实现含岩屑土壤饱和导水率的预测。     

不同含盐土壤圆盘入渗特征试验

不同含盐土壤水分入渗特征是获得准确的土壤水力参数的基础。该文通过圆盘入渗试验,分析了4种土壤在5个（-1、-3、-6、-9和-12 cm）负水头下的入渗特征。结果表明,随着水头的减小,4种土壤的吸湿率线性减小,稳定入渗率和非饱和导水率呈不同程度减小。随土壤含盐量增加稳定入渗率和导水率呈增大规律。根据实测资料确定了不同负水头下非饱和导水率的Gardner指数模型参数,为盐渍化土壤水力参数的确定提供理论参考。     

黄土区小流域土壤容重和饱和导水率的时空动态特征

土壤水力性质是评估降水入渗、径流发生以及土体可蚀性的重要参数。研究小流域尺度土壤水力性质的时空动态特征,对于以小流域为基本单元的黄土高原综合治理具有直接意义,有助于加深对相关生态水文过程的理解。以陕西省神木县六道沟老叶满渠小流域为对象,进行50 m×50 m网格布点(共73个样点),2014年8-10月期间每月测定1次表层土壤容重和饱和导水率,结合经典统计学与地质统计学的方法研究容重和饱和导水率的时空变化规律。结果表明:1)小流域尺度容重的月际变化趋势较为一致,整体呈正态分布规律,饱和导水率的月际变化强烈,呈偏态分布;容重较饱和导水率变化范围较小,变异程度较低;2)小流域尺度容重和饱和导水率在8-10月的半方差可用指数模型进行最优拟合,两者均表现出中等程度的空间依赖性;Kriging插值图表明小流域容重总体差异性较小,而饱和导水率差异显著;8-10月,西坡局部区域、坡顶的容重呈逐月增大趋势,而饱和导水率呈减小趋势;3)Pearson相关性分析表明,8-10月单次测定的容重和饱和导水率之间的相关性不明显;在同一土壤类型下(干润砂质新成土)表现出极显著的负相关关系(P0.01)。     

植被群落演替对土壤饱和导水率的影响

土壤饱和导水率是表征土壤入渗能力的重要参数,对不同土地利用类型反应敏感。为了揭示植被演替对土壤剖面上饱和导水率的影响规律,采用恒定水头法测定了天童林区155 a植物群落演替序列60 cm深土壤剖面上的饱和导水率。结果表明,不同演替阶段饱和导水率均随土壤深度增加迅速降低,在0～20 cm土层内,各演替阶段饱和导水率均存在极显著差异,0～60 cm土层内饱和导水率的平均值从裸地、石栎+檵木灌丛、马尾松林、木荷+马尾松林、木荷林到栲树林升高极为显著,植物群落演替到灌丛阶段,平均饱和导水率已与裸地存在显著差异,演     

黄河三角洲暗管排水土工布外包滤料的试验研究

黄河三角洲地区多为近代黄河泥沙淤积形成的粉细砂土,其质地均一、结构松散,在农田排水明沟建设中边坡不稳定的问题突出。近年来该地区大力开展了暗管排水系统建设,但当地砂滤料来源不足,因此,迫切需要筛选出适合当地土壤特点的土工布外包滤料。该文在对研究区土壤特性分析的基础上,利用自制水力渗透仪,通过理论计算和渗透试验观测,研究了所选择土工布的反滤、透水以及防淤堵性能。结果发现,在满足测试条件的2种型号土工布中,Typar 3201G能够满足防淤堵与透水要求,但是有一定的淤堵风险;另一型号土工布(Typar SF20)则能较好的满足研究区暗管排水外包滤料的反滤、透水与防淤堵要求。研究结果表明,满足研究区特殊土壤类型的土工布外包滤料厚度不宜过大,土工布的开孔直径应符合选择标准。研究成果可为黄河三角洲地区暗管排水土工布外包滤料的选择提供技术支撑。     

Hydraulic energy indices reveal spatial dependence in a subtropical soil under maize crop in Southern Brazil

Soil physical quality (SPQ) assessment is an important part in the evaluation of soil use, management, and conservation. It can be assessed using several physical properties, hydraulic indices, and functions. Soils from tropical and temperate regions represent different physical behaviors, and the quantification of their physical properties is important to support soil evaluation and modelling. The objective of this study was to evaluate the SPQ in a subtropical field under maize crop cultivation according to its physical properties, hydraulic indices, and functions in an attempt to infer the spatial variability and to determine the behavior of soil physical structure across a spatial domain. Commonly used soil key physical variables, such as texture, bulk density, total porosity, saturated hydraulic conductivity, and organic carbon content, were measured in a regular grid with a soil sampling density of 30 points per hectare, covering an area of 0.5 ha. Saturated hydraulic conductivity varied strongly between subsamples and in the field, suggesting the heterogeneity of the soil structure regarding water drainage. The physical variables were combined with other indicators, which were based on the soil water retention curve and the pore size distribution (PSD) function. Correlation analysis was performed to verify the relationship between the measured and calculated variables, and some strong linear correlations were revealed, such as between aeration energy index and microporosity (r = 0.608) and water retention energy index with microporosity (r = 0.532) and with bulk density (r = 0.541). For most sampled locations, the shape and location parameters of PSD showed results outside of the optimum ranges, whereas the hydraulic energy indices and cumulative hydraulic energy functions presented values that were similar to those found for some tropical soils described in the literature. The spatial variability of these indices was described using semivariograms and kriged maps, indicating the variability of the SPQ in this field.