Salinity and sodicity induced changes in dispersible clay and saturated hydraulic conductivity in sulfatic soils

Abstract

Irrigation is becoming a more commonly used practice on glacially derived soils of the Northern Great Plains. Threshold salinity and sodicity water quality criteria for soil‐water compatibility in these sulfatic soils are not well defined. This study was conducted to relate soil salinity and sodicity to clay dispersion and saturated hydraulic conductivity (K_sat) in four representative soils. Soil salinity (EC treatment levels of 0.1 and 0.4 S m^‐1) and sodicity (SAR treatment levels of 3, 9, and 15) levels were established to produce a range of conditions similar to those that might be found under irrigation. The response of each soil to changes in salinity and sodicity was unique. In general, as sodicity increased clay dispersion also increase, but the magnitude of the increase varied among the soils. In two of the soils, clay dispersion across a range of sodicity levels was lower under the 0.4 S m^‐1 treatment than under the 0.1 S m^‐1 treatment and in the other two soils, clay dispersion across a range of sodicity levels was similar between the two salinity treatments. Changes in K_sat were greatest in the finer textured soil (decreasing an order of magnitude across the range of sodicity levels), but was unchanged in the coarse textured soils. Results suggest that these sulfatic soils are more susceptible to sodicity induced deterioration than chloridic soils. These results and earlier field observations suggest that sustainable irrigation may be limited to sites with a water source having a SAR <5 and an EC not exceeding 0.3 S m^‐1 for these sulfatic glacially derived soils.     

Effect of zeolite on saturated hydraulic conductivity and crack behavior of silty clay paddled soil

The addition of zeolites to soil modifies soil physical and chemical properties. The objectives of this research were to study the effect of zeolite on saturated hydraulic conductivity, K _s, and crack behavior in a silty clay paddled soil. Soil samples were mixed with 0, 4, 8 and 12 g kg^?1 of zeolite for K _s determination, and 0, 2, 4, 8 and 12 g kg^?1 for soil crack measurements. Saturated hydraulic conductivity was measured using the constant head method. The results indicated that K _s was significantly increased at a zeolite application rate of 8 g kg^?1. Furthermore, an increase in zeolite content up to 8 g kg^?1 decreased soil crack area after paddling and first rewetting. Higher amounts of zeolite (e.g. 12 g kg^?1) increased crack density after the second rewetting. However, a 50% reduction in crack depth occurred with zeolite application rates of 8 and 12 g kg^?1 in comparison with controls. Thus, a zeolite application rate of 8 g kg^?1 is recommended for soil crack reduction in intermittent-flood irrigation. Furthermore, a relationship was obtained between crack area density (Ln), gravimetric soil water content and zeolite application rate. After the second irrigation, a relationship was also obtained between crack depth, gravimetric soil water content and zeolite application rate. Crack depth showed a positive and highly significant linear correlation with crack width.     

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     

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.     

苏打碱土盐分淋洗与饱和导水率的关系

土壤饱和导水率是土壤重要的物理性质之一,反映了土壤入渗和渗漏性质,是计算土壤剖面水通量和排水工程设计的一个重要土壤水力参数[1]。准确地估测农田饱和导水率,对于制定正确的水分和盐分、水分和养分的管理措施及有效地防止污染物对环境的影响,都有十分重要的意义。已有研究表明,饱和导水率受土壤质地、结构、盐分含量与组成、容重或孔隙度、土壤水分特征等诸多因素影响[2-7]。就碱土而言,饱和导水率低是其标志性特征之一[8-10],提高饱和导水率是有效淋洗碱土盐分的基本前提[11]。松嫩平原是国内仅次于黄淮海平原的第二大平原,其西部是中国五大盐渍土分布区域之一[12]。土壤盐分以NaHCO3和NaCO3为主[     

Effect of test solution composition on the hydraulic conductivity of normal and saline-sodic soils

Laboratory and field studies were conducted to find out the effect of test solution composition on the hydraulic conductivity of different soils. Results show that the nature and degree of permeability changes, differ with soil texture, nature of exchangeable cations and composition of the saturating solution. Hydraulic conductivity was more stable in a sodic-soil of heavier texture as compared to soils of lighter texture which underwent drastic changes in permeability. These differences were probably because of the ease with which dispersion or formation of floccules took place in different soils. The results bear out the possibility of using poor quality irrigation waters for the reclamation of saline-sodic soils. Application of a calcium amendment will, however, be most desirable to maintain reasonable permeability for removing excess salts.     

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.     

Prediction of saturated hydraulic conductivity of compacted soils using empirical scaling factors

A new empirical-based scaling method is introduced to predict saturated hydraulic conductivity (K _s ) of compacted soils. This method is an improvement of the former non-similar media concept (NSMC) model that is generalized for tilled and untilled conditions. In this method, geometric mean particle size diameter (d_g ), geometric standard deviation (σ _g ) and saturated soil water content (total porosity) are successfully incorporated in the empirical-based scaling factor of K _s . Results showed that the scaled model overestimated K _s by ～18%, whereas the NSMC model underestimated K _s by ～21%. However, the scaled model based on the similar media concept (SMC) failed to predict K _s . Because of the complexity and high uncertainty in determining the shape factor parameter in the NSMC model, it is suggested that the new scaled model might be used reliably in practical cases to predict K _s in the various layers of compacted soils irrespective of the tillage condition. Further assessment of the new scaling model in other areas, in which new collected data are available, is recommended.     

Seasonal variation in field-saturated hydraulic conductivity in two swelling clay soils in Sweden

A simple method (the inversed auger hole method) for measuring field-saturated hydraulic conductivity (K_fs) was investigated. Measurements were carried out in the spring, summer and autumn at three depths in two Swedish clay soils (Ultuna and Limsta, with clay contents of 45–60%0 and 65–80%, under barley and grass/clover ley respectively). Seasonal fluctuations in K_fs at Limsta were more pronounced, and were observed deeper in the profile. This was attributed primarily to larger structural changes due to a higher capacity for swell/shrink (normal shrinkage over the available water range) and an earlier drying up of the soil under grass/clover ley. It was shown that the measured K_fs values were strongly correlated with the total inter aggregate (macro-) porosity (e_t), estimated from a simple model of soil shrinkage. Combining the data from both soils, a single power-law relation was adequate (r= 0.73) to describe the variations in K_fs with e_t     

Spatial scaling of saturated hydraulic conductivity of soils in a small watershed on the Loess Plateau, China

Purpose

Soil saturated hydraulic conductivity (K _S) is a key variable in hydrologic processes, the parameters of which have strong scale-dependency. Knowing the scaling dependency of K _S is important when designing an appropriate sampling strategy.

Materials and methods

Determinations of K _S were made for 4,865 undisturbed soil samples, collected from a grid with cells of 10?×?10?m in the Daye watershed (50?ha) on the Loess Plateau, China. The dataset was ??re-sampled?? to investigate the effect on K _S of scales that differed by two orders of magnitude in terms of spacing and support, and eight scales of extent. The variance, correlation length, and nugget?Csill ratio derived by analysis of the full dataset were taken to be the true values. Apparent values of variance, correlation length, and nugget?Csill ratio were those calculated for each re-sampled data sub-set.

Results and discussion

Comparing the parameter values at different scales showed that apparent variance increased with increasing extent (p?<?0.01), decreased with increasing support (p?<?0.01), but was not significantly affected by spacing (p?=?0.137). Apparent correlation length increased with increasing extent and support (p?<?0.01). As spacing increased below 1.1 times the true correlation length (i.e., below 80?m), the apparent correlation length decreased slightly but, as spacing increased above 80?m, it notably increased. Apparent nugget?Csill ratio decreased with increasing spacing and support (p?<?0.01), and increased with increasing extent (p?<?0.01). The scaling dependency for K _S was in the order of extent > support > spacing for all three parameters, with mean coefficient of determination values of 0.96, 0.88, and 0.53, respectively.

Conclusions

The statistical properties investigated for K _S were found to be scaling-dependent, which would benefit sampling strategy design.     

Estimation of soil saturated hydraulic conductivity by artificial neural networks ensemble in smectitic soils

The saturated hydraulic conductivity (K_s) of the soil is one of the main soil physical properties. Indirect estimation of this parameter using pedo-transfer functions (PTFs) has received considerable attention. The Purpose of this study was to improve the estimation of K_s using fractal parameters of particle and micro-aggregate size distributions in smectitic soils. In this study 260 disturbed and undisturbed soil samples were collected from Guilan province, the north of Iran. The fractal model of Bird and Perrier was used to compute the fractal parameters of particle and micro-aggregate size distributions. The PTFs were developed by artificial neural networks (ANNs) ensemble to estimate K_s by using available soil data and fractal parameters. There were found significant correlations between K_s and fractal parameters of particles and microaggregates. Estimation of K_s was improved significantly by using fractal parameters of soil micro-aggregates as predictors. But using geometric mean and geometric standard deviation of particles diameter did not improve K_s estimations significantly. Using fractal parameters of particles and micro-aggregates simultaneously, had the most effect in the estimation of K_s. Generally, fractal parameters can be successfully used as input parameters to improve the estimation of K_s in the PTFs in smectitic soils. As a result, ANNs ensemble successfully correlated the fractal parameters of particles and micro-aggregates to K_s.     

The use of air-filled porosity and intrinsic permeability to air to characterize structure of macropore space and saturated hydraulic conductivity of clay soils

Intrinsic permeability to air of macropore space (k_a) is related to macroporosity (?) and organization of macropore space (O). Organization is defined as k_a/?. The use of k^a for estimating saturated hydraulic conductivity (K^a) is also considered. The relationship between Log (O) and ? (O? characteristic) can be used to describe changes to the macropore space of clay soils by amelioration and compaction. The effects of dominant macropore shape can also be identified and calculated as an empirical index of the efficiency of the pore organization E (E=log (O)/?). Intrinsic permeability can then be related to E in a E:k_a characteristic. Intrinsic permeability is the parameter most sensitive to structural change and E is mainly influenced by the dominant shapes of the macropores. Thus, the E:k^a characteristic is suggested as a basis for studying differences in macropore space as may occur in response to external and internal stresses upon the soil and different systems of soil management, for example increases of packing pores by cultivation or of fissures by gypsum application and loss of packing pores by compaction. Empirical data indicate that K^s of the B horizons of Australian red-brown earths can be estimated from k^a of macropore space at a standard potential.     

Evaluation of different methods for the prediction of saturated hydraulic conductivity in tilled and untilled soils

The larger the bulk density of the soil, the smaller the saturated hydraulic conductivity (K_s), however, the relationship between K_s and dry bulk density for tilled and untilled conditions is different. K_s is lower in tilled soil than in untilled soil with the same texture at the same bulk density. The purpose of this study was to compare different models for the prediction of K_s for two soil textures under both tilled and non-tilled conditions. We compred two models based on the non-similar media concept (NSMC-0, NSMC-1), a model based on the similar media concept (SMC) and a model based on the Kozeny equation and Poiseuille law for prediction of K_s (KC-1 and KC-2). This study was conducted at two areas with loam and silty clay loam soils under tilled and untilled conditions. It is concluded that the SMC model is not able to predict K_s under either tilled or untilled conditions. Further, the NSMC-0 model, along with an equation to estimate the shape factor, was able to predict K_s versus dry bulk density for tilled soils. According to our study, under untilled conditions, the KC-1 and NSMC-1 models, and under tilled conditions, the NSMC-1 and NSMC-0 models, predicted K_s accurately. It is concluded that the NSMC models together with the optimized Kozeny–Carman models could reliably be used to predict K_s in different soil textures.     

土壤饱和导水率的田间测定

本文简述了圆盘渗透仪(disc permeameter) 在田间条件下测定土壤饱和导水率的原理及方法.该方法在测定时田间土壤饱和导水率附加了一个负压Ψo,因而可以控制土壤入渗孔隙的孔径大小、排除土壤裂缝和蚯蚓孔洞对测定的影响,具有操作简便,测定精度高等优点.     

秸秆-膨润土-PAM改良材料对砂质土壤饱和导水率的影响

为改善砂质土壤持水状况,设计了由作物秸秆、膨润土和聚丙烯酰胺（PAM）配制的改良材料,以重庆市分布面积较大的冷沙黄泥为研究对象,采用恒定水头入渗双环法,研究了秸秆改良材料对砂质土壤饱和导水率的影响。结果表明,施用秸秆改良材料能增加砂质土壤的饱和导水率,并且随着施用剂量的增大,土壤饱和导水率逐渐增加;随土培时间的延长土样饱和导水率均出现了先增大后减小的趋势,当土培时间为60 d时土样饱和导水率达到最大值;添加麦秆改良材料（质量分数为10 g/kg,配方中PAM质量分数为2%）的土样,在培养60 d后其饱和导水率是对照组的4.97倍,对砂质土壤改良效果最明显。可见,秸秆改良材料可以改善砂质土壤持水状况,对砂质土壤具有改良作用。     

Effect of desiccation cracking on the hydraulic conductivity of a compacted clay liner

Despite our best efforts to reduce the waste stream, there will always remain some residues which cannot be further treated and must be disposed in landfills. One critical aspect of landfill construction is the integrity of the landfill liner. Current landfill liner technology includes a composite liner which consists of a FML component and a compacted soil component. The primary characteristic for selecting a soil for use in composite liner construction is that the soil have a saturated hydraulic conductivity of 1 × 10^?7 cm s^?1 or less. In the present study the effects of desiccation cracks on the hydraulic conductivity of the compacted soil were measured. Two soils of diverse mineralogy and typical of soils used for clay liner construction were selected for use. Each was tested in its native state plus after the addition of 30% sand. Laboratory measurements were made of the volumetric shrinkage of each soil. In addition, the hydraulic conductivity was determined using 10 cm diameter fixed wall permeameters. Additional conductivity measurements were made using 60 cm diameter fixed wall double ring permeameters which had been exposed to 0, 1, and 2 periods of desiccation prior to hydraulic conductivity determinations. The data show that laboratory measurements using 10- cm diameter fixed wall permeameters underestimate the hydraulic conductivity of the same soils when packed in large diameter permeameters. It was also found that exposure to two cycles of desiccation resulted in large increases in hydraulic conductivity. The time required to reach a steady outflow volume decreased as the amount of desiccation increased. The hydraulic conductivities of soils which had been allowed to dry were greater than those which were not allowed to dry prior to measurement. The relationship between volumetric shrinkage and the increase in hydraulic conductivity after desiccation indicates that soils which exhibit less than 11% shrinkage in the laboratory, exhibit increases in K of less than a factor of 2 upon desiccation. Clay soils with greater than 11% shrinkage can potentially be amended with sand to decrease the volumetric shrinkage and their response to desiccation.     

热融湖塘对青藏高原土壤饱和导水率的影响及因素分析

为研究多年冻土区热融湖塘对湖岸生态水文过程的影响,该文基于湖岸不同迹地植被发育、导水性及土壤理化性质的分析,并结合土壤转换函数(pedo-transfer functions,PTFs),对土壤导水性及其影响因素进行研究。结果表明:热融湖塘的形成使土壤环境发生了重要演变,其中湖岸死根区土壤饱和导水率相比于未影响区域(110.88 cm/d)增加了70.1%之多,而其在盐渍化区域相比于未影响区域减少了33.8%,同时土壤饱和导水率随着坡度的增加而增强;通过比较ROSETTA、CAMPBELL和VAUCLIN 3种土壤转换函数的预测能力,发现VAUCLIN模型更适合于模拟青藏高原高寒草甸土壤饱和导水率。热融湖塘影响迹地对土壤饱和导水率的变化,是植被盖度、有机质含量、颗粒组成等因素耦合影响作用的结果,运用土壤转换函数对其进行预测时,须综合考虑以上因子。对热融湖塘不同迹地土壤水力参数的研究可为区域土壤侵蚀,产流模式及水文过程的研究提供理论基础。     

Soil structure and the saturated hydraulic conductivity of subsoils

The saturated hydraulic conductivity, K_sat, was measured on soil samples collected from the plough layer and the subsoil. A range of naturally occurring soil bulk densities was obtained by sampling in different years, with different crops and within and without wheel-tracks, etc. It was found that, for the plough layer, quite good linear relationships exist between the logarithm of K_sat and the bulk density. However, for the subsoils, the value of K_sat usually lies above the regression line for found for the corresponding plough layer. This “excess” hydraulic conductivity of subsoils is attributed to the presence of biopores, especially root channels. The lower hydraulic conductivity of the plough layer, relative to the subsoil, is attributed to the destruction of these biopores by tillage. A simple model for the separate contributions of soil texture and root channels to the overall value of K_sat is presented. It is concluded that subsoil tillage could cause significant reductions in K_sat with potentially serious environmental consequences unless it is repeated periodically.