Vertical variation of near-saturated hydraulic conductivity in three soil profiles (original) (raw)
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Variation of hydraulic conductivity in a tilled soil
European Journal of Soil Science, 2002
619 possible de relier une description morphologique de la structure de la couche de sol travaille e aÁ des valeurs de conductivite hydraulique pour, aÁ terme, e laborer un modeÁ le spatialise d'infiltration de l'eau prenant en compte les variations spatiales de la structure induites par le labour, les ope rations de pre paration du lit de semence et les roulages.
Soil tillage is one of the key soil management practices in agricultural land use. The farming concepts are based on understanding of soil physical and hydrological characteristics under different tillage treatments. Hydraulic conductivity of the surface layer determines water infiltration into the soil profile and possible runoff formation. The treatment of the surface layer affects the soil pore system (distribution and connectivity of macroscopic cracks, voids, holes, etc.). The aim of this study was to evaluate the changes in hydraulic conductivity at and near saturation under the field conditions for soil with different tillage treatments (reduced tillage – RT, no tillage – NT, and conventional tillage – CT). The field experiments were carried out in four phases (June 2008, September 2008, April 2009, and July 2009) in order to characterise also the seasonal changes in hydraulic conductivity of the soil. Pressure ring infiltrometer (Matula and Kozáková, 1997) was employed to carry out the infiltration tests to determine hydraulic conductivity at saturation, Ks. The infiltration time was allowed long enough to obtain steady state infiltration data, which were analysed based on the equations formulated by Philip (1985) and Reynolds and Elrick (1990). To determine hydraulic conductivity near saturation K(h), Mini Disk infiltrometer (Decagon Devices, Inc.) was used. The transient infiltration data obtained from Mini Disk infiltrometer were analysed by HYDRUS 2D software (Šimůnek et al., 1999). Analysis of variance identified significantly lower Ks values for NT plots, while CT and RT plots did not differ from each other. When comparing the K(h) values measured at three consecutive water pressure heads (-5, -3, and -1 cm) the statistically significant differences were found between all three treatments (CT > RT > NT). The seasonal changes in hydraulic conductivity were reflecting the changes in structure of the surface layer (caused for example by tillage operation, winter frost, and wetting and drying circles). In contrast to some published studies, this study showed no improvement in soil structure of soil under NT after certain time period, resulting in significantly lower values of hydraulic conductivity during each of the experimental phase.
Hydraulic Conductivity Related to Porosity and Swelling of Soil1
Soil Science Society of America Journal, 1969
The hydraulic conductivity factor in Darcy's equation for viscous flow is analyzed in terms of a modified Kozeny equation. The modifications include a correction for swelling, and the replacement of the cubic exponent of the porosity term by an exponent varying between O and 3. The choice depends on the interplay between surface and volume of soil pores, as determined by flocculation-dispersion conditions. Swelling is calculated from the theory of the diffuse double layer. A theoretical analysis of experimental results on the hydraulic conductivity of two soils for percolants of variable concentration and composition showed that a single value for the electrical potential parameter sufficed to match theoretical with experimental data when the concentration of the percolant ranged from 10 to 100 meq/Iiter. Taking into account effects of pore size, pore density, effective porosity, and flow matrix on the hydraulic conductivity, the above has been explained in terms of expansive swelling of smaller pores at the expense of larger ones. A number of published studies have been analyzed in the light of the theory proposed. The relevance of the theory with regard to the alleged contrast between grain and pore models of soil has been considered.
European Journal of Soil Science, 2017
Agricultural expansion in the Kharga Oasis, in the western desert of Egypt, depends strongly on irrigation. Soil hydraulic conductivity is therefore a key property for reclaiming desert land and planning irrigation schemes. Soil samples collected at 10-m intervals in a 120 m by 120 m plot were analysed for hydraulic conductivity together with 12 other basic physical and chemical soil properties. The resulting data were analysed statistically using Pearson correlation, principal component analysis and linear regression. The hydraulic conductivity values varied over four orders of magnitude and, because of the saline-sodic nature of the soil, were about two orders of magnitude smaller than what is generally reported in the literature for similar soil textures. Results showed that the hydraulic conductivity was correlated significantly with soil variables that relate to soil structure, such as wilting point, field capacity and SAR, and less to variables that relate to soil texture, such as silt and clay fractions. Pedotransfer functions for hydraulic conductivity were derived by stepwise multiple linear regression and fitted by residual maximum likelihood. The first model was based directly on soil properties, whereas the second model was based on principal components. Both models showed that part of the variation in hydraulic conductivity encountered in the field could be explained, but with large uncertainty probably resulting from sampling and measurement errors, randomness and soil heterogeneity, or other soil properties that were not observed. The most significant predictors for the first model were wilting point, SAR and silt fraction. The second model used the first two principal components of the soil variables as predictors, the first one related to soil structure and the second to soil texture. Highlights • We analysed relations between saturated hydraulic conductivity and other basic soil properties. • Principal component analysis showed that the variation in hydraulic conductivity is related to soil structure. • A pedotransfer function predicted hydraulic conductivity from wilting point, sodium adsorption ratio and silt fraction. • A pedotransfer function was derived from principal components one and two related to structure and texture, respectively.
Field-Obtained Soil Water Characteristic Curves and Hydraulic Conductivity Functions
Journal of Irrigation and Drainage Engineering, 2018
A compacted clay liner (test pad) was constructed and instrumented with volumetric water content and soil matric potential sensors to determine soil water characteristic curves (SWCC) and hydraulic conductivity (k) functions. Specifically, the compacted clay liner was subjected to an infiltration cycle during a sealed double ring infiltrometer (SDRI) test followed by a drying cycle. After the drying cycle, Shelby tube samples were collected from the compacted clay liner and flexible wall permeability (FWP) tests were conducted on sub-samples to determine the saturated hydraulic conductivity. Moreover, two computer programs (RETC and UNSAT-H) were utilized to model the SWCCs and k-functions of the soil based on obtained measurements including the volumetric water content ( v), the soil matric potential (), and the saturated hudraulic conductivity (k s). Results obtained from the RETC program (θ s , θ r , α, n and k s) were ingested into UNSAT-I would like to express the deepest appreciation to my thesis director, Dr. Richard A. Coffman for giving me the opportunity to conduct this research and guiding me along the way. Without his guidance, mentorship and persistent help this thesis would not have been possible. I would also like to thank my committee members, Dr. Norman D. Dennis and Dr. Michelle Bernhardt for being extraordinary committee members who showed me the road and helped to get me started on the path to this degree. I would also like to thank Cyrus Garner for assisting me to collect and reduce data for the research presented in this document. Also, a special thanks goes out to the students:
Technical note: Saturated hydraulic conductivity and textural heterogeneity of soils
Hydrology and Earth System Sciences
Saturated hydraulic conductivity (K sat) is an important soil parameter that highly depends on soil's particle size distribution (PSD). The nature of this dependency is explored in this work in two ways, (1) by using the information entropy as a heterogeneity parameter of the PSD and (2) using descriptions of PSD in forms of textural triplets, different than the usual description in terms of the triplet of sand, silt, and clay contents. The power of this parameter, as a descriptor of ln K sat , was tested on a database larger than 19 000 soils. Bootstrap analysis yielded coefficients of determination of up to 0.977 for ln K sat using a triplet that combines very coarse, coarse, medium, and fine sand as coarse particles; very fine sand, and silt as intermediate particles; and clay as fine particles. The power of the correlation was analysed for different textural classes and different triplets using a bootstrap approach. Also, it is noteworthy that soils with finer textures had worse correlations, as their hydraulic properties are not solely dependent on soil PSD. This heterogeneity parameter can lead to new descriptions of soil PSD, other than the usual clay, silt, and sand, that can describe better different soil physical properties, that are texture-dependent.
Hydraulic Conductivity Variability for Two Sandy Soils
Soil Science Society of America Journal, 1998
Reliable estimates of saturated hydraulic conductivity are a prerequisite for accurate estimations of water flow and chemical transport through soil profiles. While informative, mean estimates of flow and transport have been shown to be inadequate for modeling purposes. Distributions and variances along with mean predictions provide a better form of model input. The spatial variability of field-measured saturated hydraulic conductivity (A' r J was investigated on a transect across a 1-ha field in west-central Georgia. The field includes two soil types, a Pine Flat loamy sand (coarse-loamy, siliceous, thermic Typic Paleudult) and a Troup sand (loamy, siliceous, thermic Grossarenic Kandiudult). Estimates of K t , were calculated using data collected with a constant-head permeameter. Mean, variance, and distribution data were determined for each soil and four selected horizons. Calculated values in the top 2 m of the soil profiles ranged from 0.07 to 117 mm h ' for the Pine Flat loamy sand and from 23 to 406 mm h ' for the Troup sand. Statistical differences between A' ts data calculated for the lower soil profiles coincide with soil textural differences observed with depth and across the plot. Semivariances for In A fs data were calculated and models fit to the semivariograms. Random behavior, with little spatial correlation, dominated the In A" fs data for the upper 0.5 m of the Pine Flat soil and the 2.0-m measurement for the Troup soil. Observed correlation ranges varied from 2 to 166 m. Large statistical differences in K,, were observed for the adjacent soils.
Comparison of Saturated Hydraulic Conductivity Measurement Methods for a Glacial-Till Soil
Soil Science Society of America Journal, 1994
Hydraulic conductivity is the single most important hydraulic parameter for flow and transport-related phenomena in soil, but the results from different measuring methods vary under different field conditions. To evaluate the performance of four in situ saturated hydraulic conductivity (K s ) measuring methods, K s measurements were made at four depths (15, 30, 60, and 90 cm) and five locations on a glacial-till soil of Nicollet (fine-loamy, mixed, mesic Aquic Hapludoll)-Clarion (fine-loamy, mixed, mesic Typic Hapludoll) association. The four in situ methods were: (i) Guelph permeameter, (ii) velocity permeameter, (iii) disk permeameter, and (iv) double-tube method. The K s was also determined in the laboratory on undisturbed soil cores collected from all the five sites and four depths. The Guelph permeameter method gave the lowest K s values, possibly because of small sample size, whereas the disk permeameter and double-tube methods gave maximum values for K s with minimum variability, possibly because of large sample size. Maximum variability in K s values for soil cores at shallow depths may have occurred because of the presence or absence of openended macropores. Estimates of K s , however, are most comparable for the velocity permeameter and the laboratory method using a constant-head permeameter.
Journal of Applied and Natural Science
hree soil profiles from Regional Research Station of Bidhan Chandra Krishi Viswavidyalaya, Gayeshpur situated in New Alluvial zone of Nadia district, West Bengal were studied to assess the predictability of the hydraulic conductivity of the soil as influenced by different physical and chemical and properties of cultivated and forest land. The various statistical procedures were employed on the measured laboratory based data for comprehensive agree-ment of dependent hydraulic conductivity of soils as a model function of independent soil variables that is likely to be useful for different land cover systems. Soils are neutral in reaction, silty clay to silty clay loam in nature. Forest soil contained greater organic carbon (OC) (5.9 ± 0.16 g kg-1) compared to cultivated soil (4.4 ± 0.34 g kg-1). Jhau plan-tation recorded the highest value (6.8 g kg-1) of OC due to soil texture and cation exchange capacity (CEC). Soil hydraulic conductivity was greater in soil for cabbage and Sagun tre...