Soil Hydraulic Conductivity Research Articles

Mid- and long-term effects of biochar on soil improvement and soil erosion control of sloping farmland in a black soil region, China

Biochar has been widely used as a soil conditioner, but research on the mid-and long-term effects of biochar on soil structure and soil erosion is still seriously lacking. To investigate the effects of mid- and long-term applications of biochar on soil improvement and soil erosion, a 4-year experiment was carried out on a field runoff plot of 3° sloping farmland in the black soil region of Northeast China. By examining the influence of different biochar application amounts (0, 25, 50, 75, and 100 t ha−1) on annual runoff, annual soil erosion, soil water retention curves, unsaturated hydraulic conductivity and unsaturated water diffusivity over four consecutive years, the optimal biochar application rate was determined. The results showed that the biochar application amount, year and their interaction imposed significant effects on soil structure, annual runoff, annual soil erosion, and moisture characteristic parameters. When the water content exceeded a certain value (0.28 cm3 cm−3), biochar improved the soil hydraulic conductivity. biochar inhibited the horizontal diffusion of water, while Pearson correlation analysis indicated that soil structure improvement encouraged soil water holding capacity enhancement and prevented soil erosion. Based on the analysis of the soil structure and soil erosion during the four-year period, the best biochar application rate for water and soil improvement of the sloping farmlands in the black soil area was proposed, namely, biochar application at 50 t ha−1 for two consecutive years. The research results provide practical application for combat soil erosion of sloping land.

Variation in root morphology amongst tree species influences soil hydraulic conductivity and macroporosity

Natural approaches to flood risk management are gaining interest as sustainable flood mitigation options. Targeted tree planting has the potential to reduce local flood risk, however attention is generally focused on the hydrological impacts of catchment afforestation linked to generic tree features, whilst the species-specific impacts of trees on soil hydrology remain poorly understood. This study compared effects of different tree species on soil hydraulic properties. Monocultures of Alnus glutinosa (common alder), Fraxinus excelsior (European ash), Fagus sylvatica (European beech), Betula pendula (silver birch), Castanea sativa (sweet chestnut), Quercus robur (English oak) and Acer pseudoplatanus (sycamore maple) were used to determine effects of tree species identity on soil hydraulic properties (near-saturated K and soil water retention) in a sandy loam soil, North Wales, United Kingdom. The interaction of F. excelsior root properties and soil class on hydraulic conductivity was also examined in four different soils (Rendzic Leptosol, Haplic Luvisol, Dystric Fluvic Cambisol and Dystric Gleysol) across England and Wales. Fine root biomass (FRB) and morphological characteristics were determined at three depths (0–0.1, 0.1–0.2 and 0.2–0.3 m) and complemented by in situ surface measurement of soil hydraulic conductivity. Root morphological traits were closely associated with species identity and pore-size distribution, and FRB was strongly correlated with soil hydraulic conductivity (R2 = 0.64 for 0–0.1 m depth FRB; R2 = 0.69 for 0.1–0.2 m depth FRB). Fine root biomass of F. excelsior was sixfold greater than C. sativa (p < 0.001), and the frequency of 0.01 mm radius soil pores under F. excelsior was twice that of Q. robur. Near-saturated hydraulic conductivity under F. excelsior was 7.91 ± 1.23 cm day−1, double the mean rate of the other species. Soil classification did not significantly influence FRB (p = 0.056) or near-saturated hydraulic conductivity (p = 0.076) in the 0.0–0.1 m depth soil, but soil water retention varied with depth. Species-specific traits of trees should be considered in landscape design to maximise the local hydrological benefits of trees.

Verification on the mode of moisture transfer in the vadose zone of thick loess

AbstractPrecipitation is the only source of groundwater recharge in the Chinese loess region. However, rainfall has been the main driver of geological disasters and engineering challenges in China, such as landslides, slope collapse and sinking of foundations. The roles of preferential flow and piston flow in moisture transfer in the thick loess vadose zone remain controversial. This study used a 100‐m thick loess shaft to monitor soil moisture content and soil temperature over 5 years, whereas climate indices were monitored on the Earth surface. The soil water characteristic curves and hydraulic conductivity function of the loess and the palaeosol collected in the profile were measured in a laboratory. The soil profile moisture transfer process was simulated based on the climatic boundary conditions and measured hydraulic parameters. The monitored and simulated results suggest that loess moisture transfer is dominated by piston flow. The thick loess vadose zone above the groundwater level could be divided into two sub‐zones, namely the active and steady zones. The active zone has a thickness of ~7 m and shows a direct response to climate change, with soil moisture content regulated by rainfall infiltration, evaporation and transpiration and soil moisture moving as transient flow. Although preferential flow can move in the active zone along joints, fissures and holes when water accumulates in the lower ground during heavy rainfall, piston flow remains the main mode of water movement. The steady zone has a thickness of &lt;7 m and is above the groundwater level. Soil moisture content and soil temperature in the steady zone show temporal stability and soil moisture moves as a steady flow. Piston flow is the only mode of water movement in the steady zone. Since percolation velocity in the steady zone is estimated to be 73.3 mm/year, 1330 years of rainfall infiltration through the 97.5 m thick vadose zone would be required to recharge groundwater.

Large‐scale lateral saturated soil hydraulic conductivity as a metric for the connectivity of subsurface flow paths at hillslope scale

AbstractLateral saturated soil hydraulic conductivity, Ks,l, is the soil property governing subsurface water transfer in hillslopes, and the key parameter in many numerical models simulating hydrological processes at the hillslope and catchment scales. Likewise, the hydrological connectivity of the lateral flow paths plays a significant role in determining the rate of the subsurface flow at various spatial scales. This study investigates the relationship between Ks,l and hydrological connectivity at the hillslope spatial scale. Ks,l was determined by the subsurface flow rates intercepted by drains and water table depths observed in a well network. The hydrological connectivity was evaluated by the synchronicity among water table peaks, and between these and the peaks of the drained flow. Rainfall and soil moisture were used to investigate the influence of the transient hydrological soil condition on connectivity and Ks,l. As the synchronicity of the water table response between wells increased, the lag times between the peaks of water levels and those of the drained subsurface flow decreased. Moreover, the most synchronic water table rises determined the highest drainage rates. The relationships between Ks,l and water table depths were highly non‐linear, with a sharp increase in the values for water table levels close to the soil surface. Estimated Ks,l values for the full saturated soil were in the order of thousands of mm h−1, suggesting the activation of macropores in the root zone. The Ks,l values determined at the peak of the drainage events were correlated with the indicators of synchronicity. The sum of cumulative rainfall and antecedent soil moisture was correlated with the connectivity indicators and Ks,l. We suggest that, for simulating realistic processes at the hillslope scale, the hydrological connectivity could be implicitly considered in hydrological modelling through an evaluation of Ks,l at the same spatial scale.

Multistep optimization of HyPix model for flexible vertical scaling of soil hydraulic parameters

Efficient simulation of water-flow processes in the vadose zone is crucial to increase agricultural productivity within environmental limits. This requires deriving detailed soil hydraulic parameters of the soil profile that is highly challenging, particularly for heterogeneous soils. We therefore developed an alternative indirect methodology to calibrate the hydraulic parameters from soil water content time series measured at multiple depths by using the new physically based hydrological model HyPix.We propose a novel, efficient, multistep optimization algorithm for layered soils that derives an optimal set of hydraulic parameters for a desired number of soil layers. For each selected soil layer, HyPix derives five physical, bimodal, Kosugi hydraulic parameters that describe the soil water retention and hydraulic conductivity by using a novel algorithm that reduces the degree of sensitivity and freedom of the parameters. The optimization algorithm upscales the soil hydraulic parameters by gradually incorporating the soil heterogeneity. This method overcomes the problems associated with optimization of the hydraulic parameters of each layer individually, which leads to poor results because it does not represent the cohesive soil water dynamics across the unsaturated zone.We tested the method using soil water content measurements at different depths at five heterogeneous experimental sites in New Zealand. We show how the accuracy of the simulated water balance components increases with the number of soil layers. The multistep optimization upscales a detailed, layered profile of soil hydraulic parameters into a model with fewer layers. The methodology developed provides an estimate of the uncertainty of using a reduced number of soil layers. We also show that a pedological description can provide an indication of the minimum soil layers of vertical discretization required to accurately compute the soil water balance components.

Snowmelt-Driven Seasonal Infiltration and Flow in the Upper Critical Zone, Niwot Ridge (Colorado), USA

The hydrology of alpine and subalpine areas in the Colorado Front Range (USA) is evolving, driven by warming and by the alteration of precipitation patterns, the timing of snowmelt, and other components of the hydrologic budget. Field measurements of soil hydraulic conductivity and moisture along 30-m transects (n = 13) of representative soils developed in surficial deposits and falling head slug tests of shallow groundwater in till demonstrate that hydraulic conductivity in the soil is comparable to hydraulic conductivity values in the shallow aquifer. Soil hydraulic conductivity values were variable (medians ranged from 5.6 × 10−7 to 4.96 × 10−5 m s−1) and increased in alpine areas underlain by periglacial deposits. Hydraulic conductivities measured by a modified Hvorslev technique in test wells ranged from 4.86 × 10−7 to 1.77 × 10−4 m s−1 in subalpine till. The results suggest a gradient from higher hydraulic conductivity in alpine zones, where short travel paths through periglacial deposits support ephemeral streams and wetlands, to lower hydraulic conductivity in the till-mantled subalpine zone. In drier downstream areas, streambed infiltration contributes substantially to near-channel groundwater. As summer temperatures and evapotranspiration (ET) increase and snowmelt occur earlier, alpine soils are likely to become more vulnerable to drought, and groundwater levels in the critical zone may lower, affecting the connectivity between late-melting snow, meltwater streams, and the areas they affect downstream.

Evaluation of Soil Hydraulic Parameters Calculation Methods Using a Tension Infiltrometer

In the present work, a review for the methodologies that have been proposed to calculate the main soil hydraulic properties, hydraulic conductivity (K) and sorptivity (S), at negative pressure heads near to saturation of the soil using a tension infiltrometer is presented. These hydraulic properties can be calculated either from the analysis of steady flow or from early time observations. In particular, the main steady state methods described here are those of Ankeny et al., Reynolds and Elrick, and White and Sully, which are all based on Wooding’s equation. As for the transient flow, the approaches of Haverkamp et al. (complete, two-, three-, four-, five-terms expansions), Zhang and two different linearization methods are examined for the estimation of S and K. Generally, in steady state methods studied, a sequence of pressure heads is applied on the same disc (Ankeny et al., Reynolds and Elrick) or a unique pressure head is applied on a single disc radius (White and Sully), while in transient methods, a unique pressure head is applied on a single disc radius (Zhang and Haverkamp et al.). The conditions of their application and the way of calculating the soil parameters included into each method are critically commented. This gives to the researchers the opportunity to choose the appropriate method and a way to analyze the experimental data.

Ensemble HYDRUS-2D modeling to improve apparent electrical conductivity sensing of soil salinity under drip irrigation

Monitoring and mapping soil salinity are valuable for irrigation management and reclamation of salt-affected agricultural soils in arid and semi-arid regions. Proximal measurements of apparent soil electrical conductivity (ECa) can help characterize soil salinity spatial distributions. However, ECa is not solely a function of salinity. ECa is strongly influenced by soil salinity, water content, and edaphic properties such as texture and bulk density. Consequently, monitoring and mapping salinity based on geospatial ECa measurements is challenging in fields with dynamic and spatially complex patterns of salinity and water content, such as occurs under drip irrigation. We conducted a numerical modeling study to evaluate protocols for using proximal ECa sensing in drip irrigated systems, focusing specifically on the measurement distance from the drip-line that consistently identifies areas of high salinity in the rootzone. The measurement distance was evaluated as a function of six irrigation management parameters: soil hydraulic conductivity, irrigation discharge, irrigation interval, solute concentration, root-zone volume, and leaching fraction. HYDRUS-2D was used to run a 729 member ensemble of drip irrigation simulations of water and solute dynamics under different irrigation management scenarios. Two case studies were simulated for clay loam soil: (1) low salinity soil irrigated with high salinity irrigation water and (2) high salinity soil irrigated with low salinity water. Depth-averaged ECa measurements down to the 75 and 150 cm depths, such as can be obtained using an electromagnetic induction (EMI) sensor, were evaluated in the simulations. According to the ensemble results, a reliable EMI measurement distance from the drip-line was about 100 cm for the case of low salinity irrigation in saline soil and adjacent to the drip-line for the high salinity irrigation. The ensemble ECa and EC of saturated paste extract (ECe) distributions were twice as sensitive to the irrigation water salinity level as compared to the other irrigation management parameters. The probabilistic ensemble approach can be extended to a variety of case studies to aid soil scientists and agricultural consultants monitoring and mapping soil salinity with ECa-directed soil sampling for micro-irrigation systems.

Two-Phase Conceptual Framework of Phosphatase Activity and Phosphorus Bioavailability.

The activity of extracellular phosphatases is a dynamic process controlled by both plant roots and microorganisms, which is responsible for the mineralization of soil phosphorus (P). Plants regulate the availability of soil P through the release of root mucilage and the exudation of low-molecular weight organic acids (LMWOAs). Mucilage increases soil hydraulic conductivity as well as pore connectivity, both of which are associated with increased phosphatase activity. The LMWOAs, in turn, stimulate the mineralization of soil P through their synergistic effects of acidification, chelation, and exchange reactions. This article reviews the catalytic properties of extracellular phosphatases and their interactions with the rhizosphere interfaces. We observed a biphasic effect of root metabolic products on extracellular phosphatases, which notably altered their catalytic mechanism. In accordance with the proposed conceptual framework, soil P is acquired by both plants and microorganisms in a coupled manner that is characterized by the exudation of their metabolic products. Due to inactive or reduced root exudation, plants recycle P through adsorption on the soil matrix, thereby reducing the rhizosphere phosphatase activity. The two-phase conceptual framework might assist in understanding P-acquisition (substrate turnover) and P-restoration (phosphatase adsorption by soil) in various terrestrial ecosystems.

Exploring the Role of Ash on Pore Clogging and Hydraulic Properties of Ash-Covered Soils under Laboratory Experiments

Fires can alter the hydraulic properties of burned soils through the consumption of organic matter on the ground surface. This study examined the effects of rainfall on the presence of soil pore clogging with varying ash layer thickness using laboratory rainfall simulator experiments. The image analysis with resin impregnation showed that rainfall impact caused plugging of soil pores at 22.2% with soil particles and 14.3% with ash particles on near surface soils (0–5 mm below). High rainfall intensities enhanced soil pore clogging by ash particles, particularly at shallow soil depths (0–10 mm). Ash deposits on the soil surface increased the water-absorbing capacity of ash-covered soils compared with that of bare soils. The rainfall simulation experiments also showed that ash cover led to a reduction in soil hydraulic conductivity, owing to the combined effects of surface crust formation and soil pore clogging. The complementary effects of soil pore clogging and water absorption by ash cover could hamper the accurate understanding of the soil hydrologic processes in burned soils.

Assessment of Uncertainty in Grid-Based Rainfall-Runoff Model Based on Formal and Informal Likelihood Measures

Damage prevention from the local storms and typhoons in Korea, the development of a rainfall-runoff model reflecting local geological, meteorological and physical characteristics is necessary. The accuracy of the rainfall-runoff model is influenced by the various uncertainty factors that can occur in the modeling processes, including input data, model parameters, modeling simplification, and so on. Thus, the objectives of this study are (1) to estimate runoff for two rainfall events using Grid Rainfall-Runoff Model (GRM); (2) to quantify the uncertainty of the GRM model using the Generalized Likelihood Uncertainty Estimation (GLUE) method, and (3) to assess the uncertainty ranges of the GRM based on different likelihood functions. For this, two rainfall events were implemented to the GRM in the Cheongmicheon watershed, and informal likelihood functions (LNSE, LPBIAS, LRSR, and LLOG) based on the fitness indices (NSE, PBIAS, RSR, and Log-normal) were used for uncertainty analysis and quantification using GLUE method. As a result, the GRM parameters varied according to the different rainfall patterns even in the same watershed. In addition, among the GRM parameters, the CRC (Channel Roughness Coefficient) and CSHC (Correction factor for Soil Hydraulic Conductivity) characteristics are the most sensitive. Moreover, this study showed that the uncertainty range of the GRM model can be changed with the subjective selection of likelihood functions and thresholds. The GRM model is open source and has good accessibility. Especially, this open-source model allows various approaches to disaster prevention plans such as flood forecasting and flood insurance policies. In addition, if the parameter range of GRM is quantified and standardized at domestic watersheds, it is expected that the reliability of the rainfall-runoff simulation can be increased by the reduction of the uncertainty factors.

Temporal variation of saturated and near‐saturated soil hydraulic conductivity and water‐conducting macroporosity in a maize‐wheat rotation under conventional and conservation tillage practices

AbstractKnowledge of temporal variation of soil hydraulic properties (SHPs) is crucial to understand soil physical behaviour under different tillage practices. The objective of this study was to assess the variation of saturated and near‐saturated soil hydraulic conductivity (NSHC) and water‐conducting macroporosity (Ɛ) under long‐term (09 years) tillage regimes viz. zero tillage (ZT), conventional tillage (CT), and minimum tillage (MT) in a rain‐fed maize‐wheat crop rotation (RMWC) in the North‐West Himalayas, India (NWHI). A hood infiltrometer (HI) was used to measure the steady‐state water flux (q) at 0, −10, and −30 mm pressure head (PH) after harvesting of maize and over two wheat cropping seasons for each treatment. The infiltration data were analyzed in terms of unsaturated hydraulic conductivity k(h), field saturated hydraulic conductivity (ks), water‐conducting macroporosity (Ɛ). The results showed that the seasonal effects on ks, k(h), and Ɛ values were significantly different (p ≤0.05) for tilled treatments (CT and MT). In contrast, no significant difference (p ≤0.05) was found for untilled treatment (ZT). Significantly higher (p ≤0.05) ks, k(h), and Ɛ values were observed in ZT than CT and MT, associated with higher SOC and lower ρb values. A multivariate analysis of variance of the ks showed a highly significant difference (p ≤0.01) with both time and tillage treatments. Overall, a significant improvement of hydraulic conductivity characteristics was observed during the wheat‐growing seasons compared with the maize harvest season. The temporal dynamics of SHPs under different tillage regimes indicate that ZT can be a suitable tillage practice for reducing runoff and soil loss in monsoon maize and winter wheat cropping system.

A multiscale finite element method for coupled heat and water transfer in heterogeneous soils

Large-scale modeling of coupled heat and water transfer (CHWT) is challenging due to the spatial variabilities of soil hydraulic and thermal properties. A multi-scale finite element method (MsFEM) has been designed for simulating liquid water fluxes in unsaturated soils. In this study, the MsFEM approach is expanded as a new scheme that can handle CHWT in soils. Two groups of MsFEM basis functions are constructed to incorporate the heterogeneities in soil hydraulic conductivity and thermal conductivity, and a Petrov-Galerkin formulation is adopted to implement the proposed MsFEM scheme. The MsFEM scheme is also exploited as a sequential solver when heat transfer and water transfer are expressed in a partially coupled formulation (Wang et al., 2022a). Numerical examples illustrate that, without essentially increasing the computing load, the MsFEM scheme can improve the accuracy by up-to 30% compared to the standard finite element method (FEM), especially for thermally driven water transfer. Some fine scale spatial variations in soil temperature can only be revealed with the MsFEM scheme. If the MsFEM sequential solver is applied, the coupled heat and water transfer model can be rewritten into a sequence of modules, where liquid water transfer, heat transfer and vapor transfer are solved step-by-step, but the thermally driven liquid water is omitted due to its relatively small value (Wang et al., 2022a). With the MsFEM sequential solver, a flexible modeling architecture can be achieved at the cost of a relatively small increase of error (<5%). Therefore, the MsFEM scheme presented in this study is an effective numerical approach to simulating CHWT in heterogeneous soils.

Characteristics of Soil Hydraulic Conductivity in Natural Forest, Agricultural Land, and Green Open Space Area

Soil hydraulic conductivity is one of the important soil characteristics that determines the amount and proportion of water that will be infiltrated into the soil column and flowing as surface runoff. It is strongly influenced by soil porosity and soil characteristics that affect the soil porosity such as soil texture and structure and soil organic matter content (internally factors) as well as land management and the intensity of plant canopy cover (external factors). This research is aimed to identify the character of soil hydraulics conductivity in different landuse that consist of forest, agricultural land (moor land, cacao plantations, intensive and conservation annual crops), and green open space areas. The results showed that: a) forest conversion into agricultural land led to the decline of soil quality such as decreased levels of soil organic matter, soil porosity and distribution of soil pores so that the conversion of forest land into agricultural land decreases the soil hydraulic conductivity of both for the initial value and saturated hydraulic conductivity; b) forets canopy cover density affects the soil quality and soil hydraulics conductivity, where high canopy cover has the higher value of soil hydraulics conductivity compared to medium and low canopy forest; c) Situgede tourism forest has the lowest soil hydraulics conductivity compared to other forest types; d) soil hydraulics conductivity in conservation annual crops is higher than intensive annual crops land and Situgede tourism forest and it’s not significantly different from the soil hydraulics conductivity in low canopy forest; and e) soil hydraulics conductivity in green open spaces area were strongly determined by the naturalness of landscape and human intervention level on its formation and management, where the UI city forest and Lembah Gurame city park which were function as ecotourism areas has the lower soil hydraulics conductivity compared to great forest park.

A bimodal extension of the ARYA&amp;PARIS approach for predicting hydraulic properties of structured soils

• Bimodal Arya&Paris hydraulic properties were developed based on soil structure. • The bimodal PTF provides better prediction of un/saturated hydraulic conductivity. • The bimodal PTF predicts well the spatial variability of the hydraulic properties. The main purpose of this paper is to develop a bimodal pedotransfer function to obtain soil water retention (WRC) and hydraulic conductivity (HCC) curves. The proposed pedo-transfer function (PTF) extends the Arya and Paris (AP) approach, which is based on particle size distribution (PSD), by incorporating aggregate-size distribution (ASD) into the PTF to obtain the bimodal WRC. A bimodal porosity approach was developed to quantify the fraction of each of the porous systems (matrix and macropores) in overall soil porosity. Saturated hydraulic conductivity, K 0 , was obtained from WRC using the Kozeny-Carman equation, whose parameters were inferred from the behaviour of the bimodal WRC close to saturation. Finally, the Mualem model was applied to obtain the HCC. In order to calibrate the PTF, measured soil physical and hydraulic properties data were used, coming from field infiltration experiments from an irrigation sector of 140 ha area in the “Sinistra Ofanto” irrigation system in Apulia, southern Italy. The infiltration data were fitted by using both bimodal and unimodal hydraulic properties by an inverse solution of the Richards equation. The bimodal “measured” hydraulic properties were then used to calibrate the scaling parameter (α AP ) of the proposed bimodal AP ( bimAP ) PTF. Similarly, for the sake of comparison with the bimodal results, the unimodal hydraulic properties were used to calibrate the α AP of the classical unimodal AP ( unimAP ) PTF. Compared to the unimAP PTF, the proposed bimAP significantly improves the predictions of the mean WRC parameters and K 0 , as well as the prediction of the shape of the whole HCC. Moreover, compared to the unimodal approach, it also allows to reproduce statistics of the hydraulic parameters (for example, variance) similar to those observed in the calibration dataset. Multiple linear regression (MLR) was also applied to analyse the sensitivity of the bimodal α AP parameter to textural and structural features, confirming significant predictive effects of soil structure.

SOIL HYDRAULIC PROPERTIES OF A CHROMIC LUVISOL IN KATUMANI, KENYA

&lt;p&gt;&lt;strong&gt;Background:&lt;/strong&gt; Soil hydraulic parameters in non-saturated conditions are crucial for explaining soil water dynamics in the field. It is therefore necessary to understand the link between soil water potential and hydraulic conductivity in the soil in order to estimate plant available water and hence simulate its movement within the soils. However, measurement of such hydraulic properties in the field and laboratory is somehow difficult, laborious and costly. &lt;strong&gt;Objective&lt;/strong&gt;: To determine soil hydraulic properties of Ferro-chromic Luvisols in Katumani using the RETC code based on pedo-transfer functions; % sand, silt, clay and soil bulk density. &lt;strong&gt;Methodology:&lt;/strong&gt; Undisturbed soil samples were collected from a profile pit at 0-15, 16-30, 31-45 and 46-60 cm depths using core rings for bulk densities and texture determination. Soil water retention curves and saturated hydraulic conductivities (Ksat) were estimated for all the samples using standard suction apparatus and the constant head method, respectively. The air entry suction (α) and pore size distribution (n) were generated using the RETC code. &lt;strong&gt;Results:&lt;/strong&gt; The permanent wilting point and field capacity were at 0.081, 0.102, 0.107 and 0.121 and 0.188, 0.225, 0.241, 0.262 m&lt;sup&gt;3&lt;/sup&gt;m&lt;sup&gt;-3 &lt;/sup&gt;H&lt;sub&gt;2&lt;/sub&gt;O, whilst its soil water diffusivity ranged from a low of 6.39, 6.94, 9.03 to a high of 12.5 cm&lt;sup&gt;2&lt;/sup&gt;min&lt;sup&gt;-1&lt;/sup&gt; in the 0-15, 16-30, 31-45 and 46-60 cm depth, respectively. Ksat values from RETC code ranged from 29 - 48 cm day&lt;sup&gt;-1&lt;/sup&gt;, while the total and readily available water within the soil profile were 330.4 and 214.7 mm H&lt;sub&gt;2&lt;/sub&gt;O, respectively. &lt;strong&gt;Implication:&lt;/strong&gt; The air entry value (α) and pore size distribution (n) implied an almost even distribution from the top and subsequent horizons. The soils ‘field capacity was achieved at pF 2.0 whilst PWP was arbitrary indicated at pF 4.2 reducing the time it takes to calculate irrigation cycles based on the amount of water available to the crops. &lt;strong&gt;Conclusion:&lt;/strong&gt; The data indicates that pedo-transfer functions; especially high bulk densities negatively impact on soil hydraulics conductivity.&lt;/p&gt;

Influence of land-use systems on hydraulic properties of soils in Yenagoa and Amassoma, Bayelsa State, Nigeria

This research aimed to determine the effect of different land-use systems on the matric potential, and hydraulic conductivity of the soils of Yenagoa and Amassoma communities. Soil samples were collected from four respective land-use types namely: Fallow land, Oil Palm Plantation, Plantain Plantation, and Virgin land. A total of 12 samples were bulked from three replicates at each land use type and were collected at depths of 0-15cm, 15-30cm, and 30-45cm respectively. The samples were taken to the laboratory to analyze their physical, chemical, and hydrological properties. The result showed that the different land use had a significant effect (P&lt;0.05) on some soil physical, chemical, and hydraulic characteristics. The different land-use systems had a significant effect on the soil hydraulic conductivity with the highest in virgin (13.6 cm/hr) and lowest in the plantain plantation (7.6 cm/hr). The virgin land recorded the highest Soil Water Holding Capacity (SWHC) of 2.85 cm with a range of 1.55 – 2.85cm and Plant Available Water Capacity (PAWC) of 0.19 cm3cm-3, with a range of 0.10 - 0.19 cm3cm-3, while the plantain plantation recorded the lowest (1.55 cm and 0.10 cm3cm3). Based on the study, it is recommended that soils with high Plant Available Water Capacity (PAWC) and Soil Water Holding Capacity (SWHC) be used to cultivate crops that are non-tolerant to water stress while organic amendments are used on soils with low fertility.

Role of Cover Crop, Irrigation Systems and Different Tillage on Soil Physical Properties

The central and southern regions of Iraq are located within the arid and semi-arid regions. The deterioration of the physical properties of the soil due to the low content of organic matter that is less than 1%. The high temperatures, low rainfall and the absence of vegetation cover, as well as the poor use of land and the absence of proper management of irrigation and tillage operations have negative effects on the physical, chemical and biological properties of the soil, which in turn will negatively affect the growth and production of agricultural crops. The experiment was conducted in the Nile district, located within the Babil Governorate, 86 km south of the capital, Baghdad, in a silty clay loam in the fall season 2020, aimed to examine the role of cover crop, irrigation systems and different tillage systems in some physical properties of soil (bulk density, porosity, mean weight diameter, soil resistance to penetration, and saturated soil hydraulic conductivity). The experiment was designed according to the strip-split plot arrangement according to a complete randomized block design. The experiment included three factors, the first that occupied the main plots is the cover crop (C) and included on two levels: without cover crop (C ), and the presence of cover crop (C ), and the second factor was the tillage systems (T) and included on four levels: Zero tillage (T ), 0 1 0minimum tillage (T ), medium tillage (T ) and deep tillage (T ), and the third factor is irrigation systems (I) with three levels: surface drip irrigation 1 2 3 (I ), subsurface drip irrigation (I ) and surface irrigation in basins. (I ) The results showed the superiority of treatment C T I in obtaining the 1 2 3 1 1 2lowest value of bulk density, soil resistance to penetration, highest porosity, mean weight diameter rate, and soil hydraulic conductivity saturated while treatment C T I gave the highest bulk density, soil resistance to penetration, less porosity, mean weight diameter and soil 0 3 3 hydraulic conductivity saturated.

Would delineation of nitrate vulnerable zones be improved by introducing a new parameter representing the risk associated with soil permeability in the Land Use–Intrinsic Vulnerability Procedure?

Most methods for mapping groundwater vulnerability are based on the excessively simplistic approach that aquifer recharge is produced by vertical infiltration. The novel Land Use–Intrinsic Vulnerability (LU–IV) procedure assesses groundwater vulnerability to nitrate pollution over the entire territory, including aquifers catchment areas. In this research, it was analysed if the delineation of nitrate vulnerable zones (NVZs) would be improved by introducing a new parameter representing the risk associated with soil permeability (parameter S) in the procedure. Different versions of parameter S were tested: S_HC (risk associated with soil hydraulic conductivity), S_St+G+S (risk associated with the stone, gravel and sand fraction of the soil) and S_C (risk associated with the clay fraction). The study was undertaken in the catchment areas of the Oja and Tirón alluvial aquifers (Spain). The efficacy of the following six models was compared: Model 1 (original LU–IV procedure), Model 2 (LU–IV’ procedure using parameter S_HC), Model 3 (LU–IV’ procedure using parameter S_St+G+S), Model 4 (LU–IV’ procedure using parameter S_C), Model 5 (LU–DRASTIC–COP procedure, based on DRASTIC–COP method), and Model 6 (designated NVZ).Catchment scale validations of the six models showed similar, highly significant correlations between the percent coverages of the estimated NVZs and those of the alluvial areas polluted by nitrate for Models 1 to 4. Models 5 and 6 did not show any significant results. In light of these results, Models 1 to 4 were considered the best predictors of nitrate pollution and the best methods for NVZ delineation. Results support the idea that including a parameter S in the LU–IV’ procedure is not essential since equivalent results were obtained from the original LU–IV procedure. So, the LU–IV procedure should be considered the best and simplest method of those tested for accurately delineating NVZs.

Poly‐γ‐glutamic acid application rate effects on hydraulic properties of sandy soil under wetting‐drying cycles conditions

AbstractWhen amending soil to increase sandy soil water holding capacity, amendment application rate and environment need consideration. Recently, poly‐γ‐glutamic acid (γ‐PGA) as a soil amendment has been increasingly applied in agricultural development. The purpose of this study was to determine the effect of γ‐PGA on soil water retention and soil hydraulic conductivity under wetting‐drying (W‐D) conditions. Specifically, this study investigated the influence of different γ‐PGA application rates (wt%: 0, 0.4, 0.8, 1.2, and 1.6%) on the soil water characteristic curve, saturated hydraulic conductivity (Ks), and the other hydraulic characteristic parameters (saturated water content [θs], field capacity [FC], permanent wilting point [PWP], and available water content [AWC]). Results showed that γ‐PGA significantly increased sandy soil water retention by increasing θs, FC, PWP, and AWC. Poly‐γ‐glutamic acid could decrease the proportion of large pore size (2–15 μm) and Ks and enhance the proportion of particles with small pore size (0.2–2 μm). Nevertheless, the effect of γ‐PGA on hydraulic properties of sandy soil depended on γ‐PGA application rate and the number of W‐D cycles. Under 8‐W‐D and 12‐W‐D, there was no significant difference on soil water retention among all treatments. Increasing the application rate of γ‐PGA was not more effective; P3 (1.2%) and P4 (1.6%) treatments had little difference in soil water holding capacity. This study quantitatively investigated effects of γ‐PGA on soil water retention under different W‐D cycles. Our results suggest that 1.2% might be recommended as an appropriate γ‐PGA application amount.