Infiltration Curve Research Articles

Soil water repellency under Eucalyptus stands of different age and its relationship with soil hydrological function and soil organic matter

Eucalyptus stands can modify soil hydrological functioning, by several mechanisms including the effect of the growing root system, changes in soil organic matter (SOM) and the occurrence of soil water repellency (SWR). This effect is expected to evolve with time, as tree root system develop and SOM is formed from tree litter. SWR can prevent water from entering the soil, reducing infiltration, while the effect of roots and SOM can improve structure, favoring infiltration. The aims of this study were: i- to determine the influence of Eucalyptus stands of different ages on soil physical and hydraulic properties and SWR phenomena; ii- to evaluate the effects of SOM content and composition on SWR; iii- to determine the relationship between SWR and soil physical properties; iv- to compare different methodologies for SWR evaluation. The soil studied was a in a silty loam Typic Argiudoll with Eucalyptus stands of 3, 7, 11 and 32 years. Samples were taken to determine saturated and near saturation hydraulic conductivity, water retention curve, total organic carbon and different fractions of SOM, and SWR. Different parameters were used to estimate SWR, including the repellency index (RI), water repellency cessation time (WRCT), modified repellency index (RIm), and a qualitative analysis of the shapes of cumulative infiltration curves. As main results, a reduction in total porosity (TP) in the first years of Eucalyptus plantation was found, followed by a steep increased in TP, mainly due to an increase in microporosity. Hydraulic conductivity decreased with stand age, which was attributed to a decrease in macro and mesoporosity and porosity connectivity. SOM and most SOM fractions were not affected by stand age. RI was a consistent method to estimate SWR in Eucalyptus stands, while WRCT and RIm determination was more difficult when non classical shapes of infiltration curves were obtained.

Soil pore dynamics and infiltration characteristics as affected by cultivation duration for Mollisol in northeast China

Elucidating the effects of long-term cultivation on pore structure and infiltration characteristics is essential for understanding soil degradation mechanism and improving cropland sustainability. In this study, we evaluated a number of indicators regarding soil properties, pore structure, and water infiltration during long-term cultivation and the relationship of basic properties and pore structure with soil infiltration in northeast Mollisol region of China. The studied cropland involved four cultivation durations (20, 40, 60, and 100 years) and one forest (FR) as the control. X-ray computed tomography (CT) and mini disk infiltrometer were applied to assess the effects of long-term cultivation on soil pore structure and infiltration characteristics at soil depths of 0–100 cm. The pore properties including soil porosity (TP), pore number (PN), pore size distribution, mean shape factor (MSF), fractal dimension (FA), anisotropy (DA), and Euler number (EN), and infiltration properties including mean (IR), initial (IIR), stable infiltration rate (SIR), and saturated hydraulic conductivity (Ks) were planned to be measured in this study. The results showed that soil organic carbon (SOC) in cropland was significantly lower than that in FR, while bulk density (BD) and mean weight diameter (MWD) exhibited an opposite trend. Long-term cultivation altered the soil pore size and shape distribution, and decreased the macroporosity (>500 μm) and elongated porosity, which suggested that long-term cultivation results in a simpler pore network. FR took a longer time to reach a stable state in infiltration curve over time, while cropland had lower IR, IIR, SIR and Ks, indicating negative effects of cultivation on water infiltration. > 500 μm porosity and elongated porosity were positively correlated with infiltration characteristics (P<0.01). The infiltration parameters were mainly affected by soil pore properties (MSF, PN, and DA) and basic properties (SOC, MWD, and BD), highlighting the importance of pore morphology in the infiltration process. Our results provide new insights into the evolution of soil structure and properties and explanations for water infiltration dynamics under long-term cultivation from the microscale.

Automatic measurement of water infiltration into the soil

ABSTRACT In hydrological modeling and for the development of projects related to soil and water conservation and civil engineering, determination of water infiltration variables into the soil plays a key role. However, measuring infiltration with manual infiltrometers is work-intensive and requires several people, which casts doubts on the consistency of the process description. Our objective was to develop automated and compact systems for data acquisition by double-concentric-ring and Cornell infiltrometers. The systems are based on air differential pressure sensors and microcontrollers using open-source software and a simple construction. We developed ten sets of automatic infiltrometers for each method that were properly calibrated. The equipment was validated in the field, and the alignment of the automatically measured with the hand-measured infiltration data was considered satisfactory. The proposed systems make data records of infiltration and associated variables possible, with less operator dependence than manual measurement strategies. In addition, the enhanced resolution resulting from infiltrometer automation makes the infiltration curve more representative, especially in the initial infiltration stage.

The Infiltration characteristics of expansive soil subjected to drying-wetting cycles under surchage

This study investigates the infiltration characteristics of expansive soil subjected to drying-wetting cycles under surcharge. Infiltration tests are conducted on undisturbed expansive soil over four drying-wetting cycles. Additionally, the permeability coefficient under loading is determined prior to any drying–wetting cycles. Within the context of this study, the sample heights after drying and after wetting are monitored to determinethe natural swelling and shrinkage deformations. Experimental results show that the infiltration rate decreases asthe presssure increases. The sample’s swelling–shrinkage deformation decreases with each progressive drying–wetting cycle, whereas the infiltration rate consistently increases. The infiltration curve under the drying–wetting cycle can be divided into three stages according to the infiltration characteristics, which is significantly different from the infiltration curve of the sample without the drying–wetting cycle. Moreover, the proposed model can fit the infiltration curves well, and its fitting parameters are described using dimensionless pressure and the number of drying-wetting cycles.The drying of the expansive soil produces cracksthat are advantageous for infiltration. Additionally, the microscopic connection between aggregates reflects changes in the internal structure of the soil during successive drying–wetting cycles. As the number of drying–wetting cycle increases, small particles aggregate into large aggregates, and the contact relationship between the aggregate changes from face–face to point-point contact, reducing the swelling potential and increasing the porosity and infiltration capacity of the soil.

The time validity of Philip's two‐term infiltration equation: An elusive theoretical quantity?

AbstractThe two‐term infiltration equation is commonly used to determine the sorptivity, , and product, , of the dimensionless multiple and saturated soil hydraulic conductivity from cumulative vertical infiltration measurements (L) at times (T). This reduced form of the quasi‐analytical power series solution of Richardson's equation of Philip enjoys a solid physical underpinning but at the expense of a limited time validity. Using simulated infiltration data, Jaiswal et al. have shown this time validity to equal about 2.5 cm of cumulative infiltration. The goals of this work are twofold. First, we investigate the extent to which cumulative infiltration measurements larger than 2.5 cm bias the estimates of and . Second, we investigate the impact of epistemic errors on the inferred time validities and parameters. Partial infiltration curves up to 2.5 cm of cumulative vertical infiltration improve substantially the agreement between actual and least squares estimates of and . But this only holds if the data generating infiltration process follows Richardson's equation and experimental conditions satisfy assumptions of soil homogeneity and a uniform initial water content. Otherwise, autocorrelated cumulative infiltration residuals will bias the least squares estimates of and . Our findings reiterate and reinvigorate earlier conclusions of Haverkamp et al. and show that epistemic errors deteriorate the physical significance of the coefficients of infiltration functions. As a result, the parameters of infiltration functions cannot simply be used in storm water and vadose zone flow models to forecast runoff and recharge at field and landscape scales unless these predictions are accompanied by realistic uncertainty bounds. We conclude that the time validity of Philip's two‐term equation is an elusive theoretical quantity with arbitrary physical meaning.

Método sobol para análise de sensibilidade do modelo hydrus na simulação de infiltração de água em depósito aluvionar no semiárido brasileiro

ABSTRACT Simulation of water flow in the soil in semiarid regions is fundamental for managing scarce water resources. Aiming for more accurate results, the sensitivity analysis (SA) of the hydrodynamic parameters involved in the simulations is very relevant. This study aims to evaluate the influence of hydrodynamic parameters on the hydrological response of an alluvial deposit in the dry bed of the Capibaribe River using the Hydrus-1D. A global sensitivity analysis method proposed by Sobol was chosen to evaluate the sensitivity of the soil water infiltration curve. A convergence analysis was carried out to investigate the evolution of the indices with increasing sample size. Values of the sensitivity indices showed gross variations at the beginning of the simulations for the different parameters, but they converged within the set of 10,000 samples. For parameters whose sensitivity indices are closer to 0, it is noted that 1,000 samples (14,000 simulations) were sufficient for the index to converge to their final value. The total and first-order sensitivity index calculated with 10,000 samples present the parameters n and Ks as the most important, being expressly more influential than the others.

Modelling Soil Water Infiltration and Wetting Patterns in Variable Working-Head Moistube Irrigation

Moistube irrigation is an efficient method that accurately irrigates and fertilizes agricultural crops. Investigation into the mechanisms of infiltration behaviors under an adjusted working head (WKH) benefits a timely and artificially regulating moisture condition within root zones, as adapted to evapotranspiration. This study explores the laws of Moistube irrigated soil water movement under constant and adjusted working heads. Lysimeter experiments were conducted to measure Moistube irrigation cumulative infiltration, infiltration rate, and to observe wetting front area and water content distribution using digital image processing and time domain reflectometry, respectively. Treatments of constant heads (0, 1, and 2 m), increasing heads (0 to 1, 0 to 2 and 1 to 2 m) and deceasing heads (1 to 0, 2 to 0 and 2 to 1 m) were designed. The results show that (1) under constant heads, the cumulative infiltration increases linearly over time. The infiltration rate and cumulative infiltration are positively correlated with the pressure head. When WKH is increased or decreased, the infiltration rate and cumulative infiltration curves significantly change, followed by a gradual stabilization. The more the head is increased or decreased, the more evident this tendency will be. (2) When WKH is increased, the wetting front migration rate and the wetted soil moisture content marked increase; when WKH is decreased, the wetting front migration rate sharply decelerates, and the water content of the wetted soil slowly grows. They both tend to equilibrium with time. (3) By regarding the same cumulative infiltration of increased WKH and constant WKH treatments as a similar initial condition, we proposed a cumulative infiltration empirical model for Moistube irrigation under variable working head. Additionally, we treat the Moistube as a clayey porous medium and construct a HYDRUS-2D numerical model to predict the infiltration behaviors under variable WKH. The validity of the two models were well proven, with MRE and NRMSE close to 0 and NSE greater than 0.867, indicating good agreements with the experimental results. This model breaks through the limitation of constant boundary of traditional numerical model and applies variable head boundary to the boundary of the Moistube pipe, which can also effectively simulate the response mechanism of Moistube irrigation to variable WKH. The research results further confirmed the feasibility of manually adjusting the WKH to regulate the discharge of the Moistube pipe and soil moisture state. Based on the HYDRUS-2D numerical model simulation results and the root distribution and water demand of typical facility crops, the selection range of placement depth and the adjustable range of WKH of Moistube irrigation were proposed. The research results provide a theoretical reference for manual adjustment or automatic control of Moistube irrigation WKH to adapt to real-time crop water demand in agricultural production.

Hydraulic characterization of earthworm macropore surfaces using miniaturized infiltration data

Water repellency related to organic matter (OM) of coatings along the earthworm burrows (EB) walls can facilitate preferential flow due to limiting the water exchange with the soil matrix. The objectives of this work were (i) to characterize the hydraulic behavior of EB wall and the surrounding matrix using a miniaturized infiltrometer; (ii) to compare standard infiltration analyses with BEST-WR algorithm; and (iii) to determine the local spatial distribution of water repellency at the EB wall surface in relation to that of the OM composition. Infiltration experiments were carried out on intact sample surfaces, including the EB wall and the surrounding matrix. Soil samples were collected from Bt and C horizons in a characteristic Haplic Luvisol. Hydraulic conductivity (K) at different water pressure heads (h) and water and ethanol sorptivity (Sw and Se, respectively), water repellency index (RI) and water repellency cessation time (WRCT) were determined from infiltration data. The adapted Beerkan Estimation of Soil Transfer parameters (BEST) algorithm for water-repellent soils (BEST-WR) was used for analysing infiltration data. The potential water repellency index (PWRI), relating C-H with CO functional groups in OM, was determined at the same locations using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Lower values of K and Sw in the coatings as compared to the soil matrix were found related to higher PWI values. Water repellency was also reflected in the shape of the cumulative infiltration curves and in the RI-values. The latter were significantly higher for EB as compared to matrix surfaces. The fittings provided by the BEST-WR algorithm characterizing the hydraulic properties of the macropore surfaces were comparable to those obtained with standard method. The tested methods could help to improve the estimation of parameters for macropore-matrix mass exchange in two-domain models.

Infiltration Measurements during Dry Conditions in an Urban Park in Ljubljana, Slovenia

A thorough understanding of the hydrologic mechanisms that control the movement of water through the soil is essential for developing effective stormwater management strategies. Infiltration is critical for determining the amount of water entering the soil and controlling surface runoff. Spatial and temporal variations in soil properties strongly affect infiltration rates, which underscores the importance of evaluating field-specific values for hydraulic conductivity, which are also highly dependent on the chosen measurement and evaluation methods. The objective of this study is to determine and compare soil hydraulic conductivity under dry conditions using two field measurement techniques, namely the double-ring infiltrometer (DRI) and the mini-disk infiltrometer (MDI). The results demonstrate the importance of performing multiple replicates of infiltration tests, especially during the dry season, as the initial dry surface caused deviations in hydraulic conductivity estimates for both methods used (DRI and MDI). Significant spatial variability was observed within the radius of the test replicates over short distances (&lt;1 m). In addition, experimental infiltration curves for a selected site were used to evaluate and compare soil hydraulic parameters through infiltration modeling. In general, the Philip, Green-Ampt, and Smith-Parlange theoretical models showed a better fit to the experimental DRI data than the semi-empirical Horton model.

New procedure to estimate soil field capacity based on double ring infiltration data

Many models have been proposed to explain the water infiltration curve in soil, but according to the studies we have done so far, no model can simultaneously estimate the field capacity (FC) and soil hydraulic conductivity (K). The aim of this research is to present a new model that is defined based on the dynamic balance of water-soil-time and is able to estimate FC and soil hydraulic conductivity using cumulative field infiltration data. The studies were carried out in Varamin region with an area of 1370 square kilometers. For the penetration test, first, seven sides (A, B, C, D, E, F and G) were selected in 7 areas of agricultural land and with a double ring with an outer diameter (70 cm) and an inner diameter (30 cm) became. Also, to determine the soil texture, apparent specific gravity, PWP and FC, soil sampling was done at the depths of 0–10 and 20–30 cm. To determine FC moisture, pressure (−10 kPa) was used in a pressurized membrane device, and to determine volumetric moisture in PWP, sieved samples were placed on ceramic plates. Using a spray, the samples were wetted, so that they reached the saturation level, and the pressure was set to 1500 kPa. Examining the FC values showed that the maximum value of FC in site F (clay loam texture) is equal to 14.73 cm and the lowest value in site G (sandy clay loam texture) is equal to 6.8 cm by the model estimated by the results obtained in Laboratory confirmed. Meanwhile, the minimum saturated hydraulic conductivity of soil at site A was estimated to be 0.06 cm/min and the maximum at sites D and F was 0.28 cm/min. Time constant (Ksh) has shown completely different water infiltration rate in the first term of the model (Rfksh) compared to the second term of it (K), and no obvious relation has detected between them. But, their summation (k+Rfksh) was always equal to the maximum infiltration instantaneous rate (T→0). The research results showed that using the new model, the FC value varies between 6.8 and 14.73 cm. Also, the minimum and maximum instantaneous speed of water infiltration occurred in the site. An equal to 0.621 and in site D equal to 1.735 cm/min. The results of fitting the penetration model on cumulative penetration data showed that R2 varies between 0.994 and 0.999 and RMSE between 0.116 and 1.197. Therefore, the model is able to describe the penetration data well.

Hydraulic characterization and modeling of hydrophobic substrates

The hydraulic characterization of hydrophobic substrates, which strongly depends on the water content, is an understudied topic in the field of soil physics. Based on laboratory experiments, this work presents a physically-based model, denoted as Soil Water Repellency Infiltration Model (SWRIM), to describe the double-slope cumulative infiltration curves commonly observed in hydrophobic substrates, whose behavior is conditioned by the dual hydraulic behavior (under dry and saturated conditions) of the water repellency materials. The experimental setup consists of 1D infiltration tests on hydrophobic substrates and tension of 0 cm, following by a free drainage. The SWRIM model assumes that water flow in the hydrophobic substrate is gravity driven, representing the pore system as a set of disconnected pathways or capillaries with dual behavior. Each capillary is governed by two hydraulic conductivity values corresponding to dry or partially saturated and saturated conditions, Kd and Ks respectively. During infiltration, water flow within each pathway is regulated by Kd, but once the pathways are filled and the substrate is fully saturated, the water flow is governed by Ks, whose value is directly measured from the slope of the drainage curve. In order to incorporate the variability of the pore system, unimodal and bimodal probability distributions of Kd values were considered. The application of the SWRIM model allowed determining the distribution of Kd and the percentage of water-conducting pores, δ, of the hydrophobic layer. Additional determinations of the soil hydraulic conductivity, K, and sorptivity under water repellent conditions were also obtained from the inverse analysis of the initial times of the infiltration test. The proposed model was validated on experimental soil columns of 5 cm internal diameter and 1.0 and 2.5 cm height filled with pine forest organic material, Pine, rosemary leaf litter, RS, and, blond peat, Peat. Overall, convex-to-linear curves with a monotonously increasing infiltration, typical of hydrophobic substrates, were obtained. SWRIM model allowed robust fits of the infiltration curves, showing in all cases a distribution of Kd with a bimodal shape. Pine and Peat presented the largest values of δ. The estimated average Kd was within the same order of magnitude as K values. Overall, the results showed that the proposed physically-based model allows to satisfactory describe and characterize the dynamic hydraulic behavior of hydrophobic soil substrates.

Soil‐dependent β and γ shape parameters of the Haverkamp infiltration model for 3D infiltration flow

AbstractEstimating of soil sorptivity () and saturated hydraulic conductivity () parameters by field infiltration tests are widespread due to the ease of the experimental protocol and data treatment. The analytical equation proposed by Haverkamp et al. (1994) allows the modelling of the cumulative infiltration process, from which the hydraulic parameters can be estimated. This model depends on both initial and final values of the soil hydraulic conductivity, initial soil sorptivity, the volumetric water content increase () and two infiltration constants, the so‐called and parameters. However, to reduce the number of unknown variables when inverting experimental data, constant parameters such as and are usually prefixed to 0.6 and 0.75, respectively. In this study, the values of these constants are investigated using numerical infiltration curves for different soil types and initial soil water contents for the van Genuchten‐Mualem (vGM) soil hydraulic model. Our new approach considers the long‐time expansions of the Haverkamp model, the exact soil properties such as , and initial soil moisture to derive the value of the and parameters for each specific case. We then generated numerically cumulative infiltration curves using Hydrus‐3D software and fitted the long‐time expansions to derive the value of the and parameters. The results show that these parameters are influenced by the initial soil water content and the soil type. However, for initially dry soil conditions, some prefixed values can be proposed instead of the currently used values. If an accurate estimate of and is the case, then for coarse‐textured soils such as sand and loamy sand, we propose the use of 0.9 for both constants. For the remaining soils, the value of 0.75 can be retained for . For constant, 0.75 and 1.5 values can be considered for, intermediate permeable soils (sandy loam and loam) and low permeable soils (silty loam and silt), respectively. We clarify that the results are based on using the vGM model to describe the hydraulic functions of the soil and that the results may differ, and the assumptions may change for other models.

Model Test Analysis of Groundwater Level Fluctuations on Karst Cover Deformation Taking the Monolithic Structure of Guilin as an Example

Engineering practice and real-life cases show that the geological conditions of the Guilin overlying karst site are complex. In particular, the groundwater, which drives the accelerated formation of soil cavities, and the thickness of the overlying soil layer, which affects the speed of the groundwater subsidence process. Therefore, this paper is based on a physical model to evaluate the effects of groundwater level changes caused by different factors on the deformation of karst cover. The model tests are simulated for different cover thicknesses (6 cm, 9 cm, 12 cm, 15 cm, 18 cm) under rainfall and other recharge, cavity supply, and drainage conditions at the same density (1.40 g/cm3) and initial water content (30%), respectively. The results show that with the increase of rainfall and other recharge time, the basic change trend of different cover thicknesses is that the infiltration curve changes faster at the beginning and slows down at the end, but the thicker the cover, the slower the overall deformation; at a certain rate of cavity recharge and drainage, the thicker the cover, the smaller the deformation caused by the fluctuation of groundwater level. The cavity recharge makes the cover displacement obvious, in the order of 0.304 cm, 0.173 cm, 0.118 cm, 0.068 cm, and 0.056 cm. After the formation of the cavity, the rainfall, other recharge, and the cavity supply and drainage accelerate the destruction and deformation of the soil body and the upward development of the cavity. The research results provide theoretical support for the subsequent prevention and control of karst collapse in covered karst areas, and have certain practical engineering significance.

Tight gas fracturing productivity calculation model based on gas-water permeability curve

Measuring well production per well can not only simplify the process flow, improve economic efficiency, but also reduce the development cost of the oil field. In this paper, a single-well measurement of oil well production is carried out by establishing a capacity calculation model for fracturing straight wells in tight gas reservoirs by means of gas-water phase infiltration curve. According to different permeability and porosity, several representative relative permeability curves are selected for normalization treatment, and then the angle-preserving transformation principle is used, considering the formation stress sensitivity effect and gas slip effect, as well as the stress sensitivity effect in the fracture and the effect of high-speed non-Daxi effect on gas seepage, the quasi-pressure function is introduced, and the capacity calculation model of the fracturing straight well of the tight gas reservoir is established, so as to achieve the calculation of the yield.

Investigating the Spatial Structure of Soil Hydraulic Properties in a Long-Term Field Experiment Using the BEST Methodology

Understanding the spatial structure of soil properties at field scale and introducing this information into appropriate data analysis methods can help in detecting the effects of different soil management practices and in supporting precision agriculture applications. The objectives of this study were: (i) assessing the spatial structure of soil physical and hydraulic properties in a long-term field experiment; (ii) defining a set of spatial indicators for gaining an integrated view of the studied system. In seventy-two georeferenced locations, soil bulk density (BD), initial volumetric soil water content (θi) and cumulative infiltration curve as function of the time (I(t)) were measured. The soil water retention curve (θ(h)) and the hydraulic conductivity function (K(h)) were then estimated using the Beerkan Estimation of Soil Transfer parameters (BEST) methodology. The volumetric soil water contents at soil matrix (h = −10 cm), field capacity (h = −100 cm) and wilting point (h = −15,300 cm) were considered. In addition, a set of capacitive indicators—plant available water capacity (PAWCe), soil macroporosity (PMACe), air capacity (ACe) and relative field capacity (RFCe)—were computed. The data were first analyzed for overall spatial dependence and then processed through variography for structural analysis and subsequent spatial interpolation. Cross-correlation analysis allowed for assessing the spatial relationships between selected physical and hydraulic properties. On average, optimal soil physical quality conditions were recorded; only PMACe values were indicative of non-optimal conditions, whereas mean values of all the other indicators (BD, Ks, PAWCe, ACe, RFCe) fell within optimal ranges. The exponential model was found to be the best function to describe the spatial variability of all the considered variables, except ACe. A good spatial dependence was found for most of the investigated variables and only BD, ACe and Ks showed a moderate autocorrelation. Ks was confirmed to be characterized by a relatively high spatial variability, and thus, to require a more intensive spatial sampling. An inverse spatial cross-correlation was observed between BD and Ks up to a distance of 10 m; significant cross-correlations were also recorded between Ks and PMACe and ACe. This result seems to suggest the possibility to use these soil physical quality indicators as covariates in predictive multivariate approaches.

An approximate solution to one-dimensional upward infiltration in soils for a rapid estimation of soil hydraulic properties

Soil hydraulic properties quantify soil pore structure and are essential input parameters for simulating soil hydrological processes in the vadose zone. Although methods have been proposed to estimate soil hydraulic properties, efficient and applicable ones are still scarce. In this study, we derived an approximate solution for a one-dimensional upward infiltration process with initially uniform soil water content distribution. Founded on our solution, a nonlinearly constrained optimization method was developed to simultaneously estimate the parameters Ks and n, hd of the Brooks-Corey model by measuring the upward infiltration process in a 5-cm high soil column. Numerical experiments simulated with Hydrus-1D were performed on six theoretical soils to evaluate the accuracy of the new method. The results indicate that the approximate solution can accurately simulate the upward infiltration process at the low initial soil water content range, with a relative error (Re) of 2.85% to 5.47% for soil water content distribution in space and time. For the cumulative infiltration curve, the Re ranges from 0.2% to 1.01%. The estimated parameters Ks and n, hd of the Brooks-Corey model are close to the actual parameter values, with a Re of 0.59% to 4.68% for n, 0.00% to 7.91% for hd, and 0.50% to 8.83% for Ks, respectively. It is concluded that the new method provides a simple and valuable tool for the accurate estimation of soil hydraulic properties.

Long-term effects of barley residue managements on soil hydrophysical properties in north-western Iran

The cold semi-arid cropping system is facing soil degradation, climate variability, and drought. For this reason, crop residue management is critical to soil and water conservation and the sustainability of farmers' livelihood. This study was conducted to test the hypothesis that in a cold semi-arid climate, the hydraulic properties of soil can be significantly affected by long-term crop residue management. To test this hypothesis, we investigated the changes in soil hydraulic properties (saturated hydraulic conductivity (Ks), soil water retention (SWR), cumulative infiltration (CI), parameters of van Genuchten SWR (θs, θr, α, and n), and Philip's equation indices (sorptivity and A) following long-term (five years) crop residue management. There were three treatments: (i) complete removal of crop residue from the soil surface (T1), (ii) incorporation of crop residue into the soil after harvest (T2), and (iii) burning of crop residue on the field (T3). The results showed that the Ks value was higher (p ≤ 0.05) in T2 (incorporation, 0.36 cm min−1) than in T1 (removal, 0.30 cm min−1) or T3 (burning, 0.26 cm min−1). Also, the α value was lower (p ≤ 0.05) in incorporation treatment (0.032 cm−1) than in removal treatment (0.042 cm−1) or burning treatment (0.048 cm−1). The value of S (1.72 cm min-0.5) in incorporation treatment differed significantly (p ≤ 0.05) from that of removal (1.09 cm min-0.5) and burning (1.31 cm min-0.5) treatments. Noticeable differences in soil water retention were greater at low soil water suction heads in the SWR. The differences between the SWR of treatments at low suction heads grew over time. A little difference was observed between the SWR of treatments in high suction heads. The cumulative infiltration curve for incorporation treatment differed from that obtained for removal and burning treatments, with no sizable differences observed between removal and burning over five years. The results of this study indicated that the increase in soil organic matter (SOM) for burning reduced the negative effects of burned barley residue on soil hydraulic properties to some extent. Thus, burning residues may have a little negative impact on a sustainable cropping system. The results revealed that the incorporated barley residue increased the infiltration of water into the soil more than other residue management practices in the cold semi-arid region.

Estimation of hydrodynamic properties of a sandy-loam soil by two analysis methods of single-ring infiltration data

Abstract Beerkan infiltration runs could provide an incomplete description of infiltration with reference to either the near steady-state or the transient stages. In particular, the process could still be in the transient stage at the end of the run or some transient infiltration data might be loss. The Wu1 method and the BEST-steady algorithm can be applied to derive soil hydrodynamic parameters even under these circumstances. Therefore, a soil dataset could be developed using two different data analysis methods. The hypothesis that the Wu1 method and BEST-steady yield similar predictions of the soil parameters when they are applied to the same infiltration curve was tested in this investigation. For a sandy-loam soil, BEST-steady yielded higher saturated soil hydraulic conductivity, Ks, microscopic pore radius, λm, and depth of the wetting front at the end of the run, dwf, and lower macroscopic capillary length, λc, as compared with the Wu1 method. Two corresponding means differed by 1.2–1.4 times, depending on the variable, and the differences appeared overall from moderate to relatively appreciable, that is neither too high nor negligible in any circumstance, according to some literature suggestions. Two estimates of Ks were similar (difference by &lt; 25%) when the gravity-driven vertical flow and the lateral capillary components represented the 71–89% of total infiltration. In conclusion, the two methods of data analysis do not generally yield the same predictions of soil hydrodynamic parameters when they are applied to the same infiltration curve. However, it seems possible to establish what are the conditions making the two methods similar.

A new application of the upward infiltration method to quantify preferential flow hydraulic conductivity on undisturbed soil cores

Soil water preferential flow, PF, is the phenomenon where water moves along certain pathways, while bypassing a fraction of the porous matrix. This work presents a laboratory procedure to estimate the hydraulic conductivity of the soil water preferential flow, KPF. Using an upward infiltration curve followed by an over-pressure step, KPF is calculated as the difference between the total hydraulic conductivity, KT, measured with the constant head method, and the soil matrix hydraulic conductivity, Ks, calculated from the inverse analysis of the transient upward infiltration curve. Previous to this analysis, a new approach to detect and remove the effect of possible overpressures due to the soil core placement on the sorptivimeter on the hydraulic properties estimate was presented. This consisted on searching the best fitting between the experimental infiltration curve after removing successive early time steps and the corresponding simulated function. The method to estimate KPF was validated on four different 5-cm height soil columns packed with 2-mm sieved clay loam and loam soils traversed longitudinally by a closed/opened pipe of 1.5 mm and 2.5 mm internal diameter, respectively. This same experiment was also repeated on the same soils without artificial preferential channel. Next, the method was applied on 20 undisturbed soil cores collected from two fields with different grazing intensity and soil tillage management (conventional, CT, reduced, RT and no-tillage, NT, practices). Results showed that correction made to remove the infiltration curve jump due to an overpressure step allowed more accurate and realistic estimates of the soil matrix hydraulic properties. On the other hand, both KT and Ks, which could be satisfactorily calculated from a single upward infiltration curve followed by an overpressure step, where satisfactorily employed to quantify KPF. While no significant effect of grazing intensity on KPF was observed, the CT KPF was significantly larger than those obtained in RT and NT.

Effects of enset-based land use system on infiltration rate and curve number of the soil in Meki river watershed, Western Lake Ziway Sub-Basin, Central Rift Valley of Ethiopia

Effects of enset-based land use system on infiltration rate and curve number of the soil in Meki river watershed, Western Lake Ziway Sub-Basin, Central Rift Valley of Ethiopia