Soil Hydraulic Properties Research Articles

A Generalized Framework to Describe Unimodal and Bimodal Soil Hydraulic Properties Over Full Water Saturation Range

A Generalized Framework to Describe Unimodal and Bimodal Soil Hydraulic Properties Over Full Water Saturation Range

Biochar Amendment as a Mitigation Against Freezing–Thawing Effects on Soil Hydraulic Properties

Seasonal freeze–thaw cycles compromise soil structure, thereby increasing hydraulic conductivity but diminishing water retention capacity—both of which are essential for sustaining crop health and nutrient retention in agricultural soils. Prior research has suggested that biochar may alleviate these detrimental effects; however; further investigation into its influence on soil hydraulic properties through freeze–thaw cycles is essential. This study explores the impact of freeze–thaw cycles on the soil water retention and hydraulic conductivity and evaluates the potential of peanut shell biochar to mitigate these effects. Peanut shell biochar was used, and its effects on soil water retention and unsaturated hydraulic conductivity were evaluated through evaporation tests. The findings indicate that freeze–thaw cycles predominantly affect clay’s ability to retain water and control hydraulic conductivity by generating macropores and fissures; with a notable increase in conductivity at high matric potentials. The impact lessens as matric potential decreases below −30 kPa, resulting in smaller differences in conductivity. Introducing biochar helps mitigate these effects by converting large pores into smaller micro- or meso-pores, effectively increasing water retention, especially at higher content of biochar. While biochar’s impact is more pronounced at higher matric potentials, it also significantly reduces conductivity at lower potentials. The total porosity of the soil increased under low biochar application rates (0% and 1%) but declined at higher application rates (2% and 3%) as the number of freeze–thaw cycles increased. Furthermore, the characteristics of soil deformation during freeze–thaw cycles shifted from frost heaving to thaw settlement with increasing biochar application rates. Notably, an optimal biochar application rate was observed to mitigate soil deformation induced by freeze–thaw processes. These findings contribute to the scientific understanding necessary for the development and management of sustainable agricultural soil systems.

Concentration‐ and Size‐Dependent Influences of Microplastics on Soil Hydraulic Properties and Water Flow

ABSTRACTExtensive usage of agricultural plastic film correspondingly leads to excessive residues of microplastics (MPs). MP accumulation alters soil hydraulic properties and water flow. However, little is known about the combined effects of concentration and particle size on soil hydrological properties, and a numerical approach for modelling infiltrated flow has not been well developed. Hence, we determined soil hydraulic properties and infiltrated flow affected by MP concentration and particle size and established a water flow model suitable for MP‐contaminated soils. Quantitative findings indicated that the saturated conductivity for soil–MP mixture was 10.8%–50.0% smaller than that for pure soil, which decreased and increased with the increase in MP concentration and size, respectively. The MP concentration always had significant influences on saturated conductivity; in contrast, the MP particle size always generated significant influences under the condition of small particle size. Besides, higher concentration or size of MPs led to weaker soil water‐holding capacity, and the saturated and residual water content decreased by 0.6% – 41.5% and 0.2% – 11.6%, respectively. Furthermore, the presence of MPs inhibited water infiltration, with the wetting front migration rate and cumulative infiltration decreased by 7.1% – 29.4% and 4.7% – 21.7%, respectively, with the increase in the MP concentration and size. Correlation analysis indicated that MP particle size was negatively correlated with saturated/residual moisture, wetting front migration and cumulative infiltration; in addition, MP concentration was negatively correlated with saturated conductivity, residual moisture, wetting front migration and cumulative infiltration; compared with the MP particle size (15.63%), the MP concentration (46.28%) played a major role in the response of soil hydraulic properties and water movement to changes in the external environment. A two‐dimensional numerical approach was proposed by considering the Richards equation and hydraulic parameters of soil–MP mixture, and a model based on finite element theory was further employed and validated through comparing experimental observations with numerical simulations, which indicated that the proposed model had a high accuracy in simulating the infiltration process in MP‐contained soils. Our findings elucidate the influence of MP concentration and size on soil hydraulic properties and water flow and confirm the potential of using simulations to predict water infiltration in MP‐contained soils.

Historical soil compaction impairs biogeochemical cycling in restored tidal marshes through reduced groundwater dynamics.

Tidal marshes are often restored on compact agricultural soil that limits tidally induced groundwater dynamics and soil aeration after restoration. We hypothesized that impaired soil aeration affects biogeochemical cycling and leads to altered porewater nutrient concentrations in restored tidal marshes. We studied soil hydraulic properties, groundwater dynamics and porewater nutrient concentrations (nitrogen, phosphorus and dissolved silica) over the course of one year in a natural and a restored freshwater tidal marsh in the Scheldt estuary, Belgium. From measured groundwater levels, we calculated the soil saturation index (the proportion of time the soil is saturated at a certain depth). The aerated zone generally extends over a deeper soil profile in the natural marsh compared to the restored marsh, where the former agricultural subsoil has a higher compaction rate and lower hydraulic conductivity. The soil saturation index was negatively correlated with nitrate (ρ=-0.21, p<0.001) and positively correlated with ammonium (ρ=0.32, p<0.001). Concentrations of phosphate (ρ=0.43, p<0.001) and dissolved iron (ρ=0.44, p<0.001) were positively correlated to the soil saturation index, suggesting retention of phosphate on iron oxides in well aerated zones, which are more abundant in the natural marsh. The depth profile of soil hydraulic properties and soil aeration is very site specific, even within the same marsh, suggesting the need for a pre-restoration assessment of soil hydraulic properties to determine where and which design measures are required to optimize nutrient cycling in newly restored tidal marshes.

Leaching of pollutant metals (Pb, Zn) from abandoned mine tailings: A multicomponent reactive transport model of a pilot-scale experiment.

Mine tailing deposits pose a global problem, as they may contain metal contaminants in various geochemical forms and are likely to be leached from the surface into the underlying groundwater, which can result in health and/or environmental risks. Unfortunately, little is currently known regarding the water flow and mass balance related to leaching in the vadose zone as these factors are still difficult to measure at the field scale. A pilot-scale experiment was run in a 1 m3 instrumented column for 6months to address this issue. This 70cm high column was filled with highly Pb-contaminated tailings and then watered regularly. The top half remained unsaturated while the bottom half was kept saturated. Continuous water flow and water saturation measurements were recorded and the physico-chemical properties of the soil solutions were monitored weekly at different levels in the column. A 1D multicomponent reactive transport model was built to simulate the fate and transport of Pb as well as other elements. The variably saturated water flow was simulated using the Richards equation, while the van Genuchten analytic form was used to describe the unsaturated soil hydraulic properties. The main processes considered to simulate the reactive transport were advection-dispersion, thermodynamic equilibrium, and kinetically-controlled dissolution-precipitation reactions. The most reactive Pb-bearing phases accounted for in the simulation were anglesite (PbSO4) and plumbojarosite Pb0.5Fe3(SO4)2(OH)6. The simulations accurately reproduced the water flow and mass balance as well as the drop of 2 pH units experimentally measured in the pore solution. This trend resulted from plumbojarosite dissolution followed by ferrihydrite precipitation. The increased Pb concentration in the soil solution induced by the dissolution of Pb-bearing phases was partially offset by Pb-sorption onto newly formed iron oxides and the precipitation of secondary mineral phases, e.g. anglesite. The modeling results could be used to assess potential risks of groundwater contamination by mine tailings.

Biochar‐Amended Soils: A Water‐Saving Strategy for Quinoa Cultivation in the Andes

ABSTRACTIntroductionPrevious studies showed that biochar amended soils significantly enhanced the growth and yield of quinoa under water limitations. So it becomes an emerging agronomic strategy to consider for sustainable quinoa production. Biochar can specifically be considered for the area particularly receiving low annual rainfall and more vulnerable to current climate change conditions.Materials and MethodsA field experiment was conducted using the quinoa variety INIA 415 Pasankalla, employing a factorial design to assess the effects of different application rates of biochar made of municipal pruning waste and agricultural waste (0, 1, 2, and 3 t·ha⁻¹), and three irrigation intervals (irrigation every 5 days, irrigation every 10 days, and irrigation every 15 days). The volumetric soil moisture content, the soil hydraulic properties, and quinoa's biometric characteristics and yield components were evaluated.ResultsThe results indicated that the longest irrigation intervals (10 and 15 days) resulted in soil moisture levels between 19% and 40% below the wilting point (soil matric potential: −1.5 MPa), creating water stress conditions. However, biochar application increased the field capacity from 0.31 to 0.38 g H₂O g⁻¹ soil, raised soil air content from 22% to 29% at irrigation, and promoted the quinoa's soil water absorption below the wilting point. Furthermore, the application of 3 t·ha⁻¹ of biochar significantly enhanced quinoa yield, increasing it from 3.18 to 4.22 t·ha⁻¹, along with improvements in leaf area, total biomass, root length, and panicle length by 70.74%, 76.54%, 14.34%, and 16.55%, respectively.ConclusionsIt was concluded that a 3 t·ha⁻¹ biochar application mitigated the negative effects of water stress caused by prolonged irrigation intervals. This biochar treatment improved the soil's physical properties and enabled the quinoa variety INIA 415 Pasankalla to achieve yields close to its theoretical productive potential.

MANAGEMENT OF USING SALINE IRRIGATION WATER AND TILLAGE SYSTEMS ON THE SOIL MECHANICAL AND HYDRAULIC

A field experiment was carried out within the Shanafiyah - Nasiriyah project / Iraq during the autumn season 2022-2023 to evaluate the performance of the different tillage systems in some soil physical and hydraulic properties when irrigated with salt water and 25% Leaching factor throughout the growing season. In addition to evaluating its performance in mechanical technical properties before sowing. The experiment included three systems: A. minimum tillage with a disc harrow b. Tillage with Chisel Plow and Spring Tooth Harrows c. Tillage with Mold Plow and Spring Tooth Harrows. The study results showed that the Mini Tillage with (Disk Harrow) treatment was superior in giving the best values ​​for the mechanical and technical properties and the soil’s physical and hydraulic properties compared to other systems.

Modeling and Application of the Hydrus-2D Model for Simulating Preferential Flow in Loess Soil Under Various Scenarios

Soil hydraulic properties are mainly governed by the soil’s heterogeneity, anisotropy, and discontinuous structural characteristics, primarily when connected soil macropores characterize the structures. Therefore, researchers must document reliable hydrological models to elucidate how the soil medium affects the movement of soil water. This study, utilizing a field-scale staining tracer test, distinguishes between matrix flow and preferential flow areas in the seepage field of Xi’an loess. The Xi’an loess’s soil water characteristic curve (SWCC) was explored through field investigations and laboratory analyses. A dual-permeability model that couples matrix and macropore flow was developed using the Hydrus-2D model, enabling simulations of water migration under varying initial soil water content, rainfall intensity, and crack width. The results showed that (1) The SWCC of macropores in the preferential flow area exhibits a bimodal distribution, and the Fredlund &amp; Xing model is applied for sectional fitting to obtain the corresponding soil water characteristic parameters. (2) Initial soil water content and rainfall intensity significantly influence water distribution, while crack width has a relatively minor effect. (3) The cumulative flux under the preferential flow is significantly higher than in the matrix area, and the wetting front depth increases with higher initial water content and rainfall intensity. This study reveals the key characteristics of preferential flow and moisture migration in the matrix zone and their influencing factors in loess. It constructs a two-domain infiltration model by integrating loess’s diverse structural characteristics and pore morphology. This model provides a theoretical basis and technical support for simulating preferential flow and studying the moisture dynamics of loess profiles.

Exploring the Hydraulic Properties of Unsaturated Soil Using Deep Learning and Digital Imaging Measurement

This work aims to improve the accuracy of traditional models for analyzing the hydraulic properties of unsaturated soil by integrating digital imaging measurement with deep learning techniques. The work first reviews current research on the basic characteristics of unsaturated soil and the applications of deep learning in this field. Next, it examines the impact of soil specimens’ physical properties on their hydraulic properties. This includes acquiring hydraulic parameters and the soil-water characteristic curve through full-surface digital imaging measurements. Finally, a soil hydraulic property model based on the backpropagation neural network (BPNN) is implemented, trained, and validated. Results indicate that the model’s predicted soil-water characteristic curve aligns closely with the experimental findings from previous studies. Moreover, the proposed BPNN-based unsaturated soil hydraulic property model uses the Levenberg–Marquardt algorithm, which reduces computational time and noise compared to alternative algorithms. Meanwhile, analysis of the model parameters suggests that ten neurons in the hidden layer provide optimal performance. By incorporating correlations between physical parameters, such as soil particle size and soil hydraulic properties, the model demonstrates lower error rates compared to other literature models. Overall, this BPNN model effectively represents the relationship between soil’s physical and hydraulic parameters, streamlining traditional soil correlation coefficient estimation.

Assessing Roles of Aggregate Structure on Hydraulic Properties of Saline/Sodic Soils in Coastal Reclaimed Areas

During coastal reclamation processes, land use conversion from natural coastal saline/sodic soils to agricultural land changes the soil’s physicochemical properties. However, the impact of soil structure evolution on soil hydraulic properties (SHPs, e.g., hydraulic conductivity and soil water retention curves) during long-term reclamation has rarely been reported. In this study, we aimed to evaluate the effect of reclamation duration and land use types on the soil aggregate stability and SHPs of coastal saline/sodic soils and incorporate the aggregate structures into the SHPs. In this study, a total of 90 soil samples from various reclaimed years (2007, 1960, and 1940) and land use patterns (cropland, grassland, forestland, and wasteland) were taken to analyze the quantitative effects of soil saline/sodic characteristics and the aggregate structure on SHPs through pedotransfer functions (PTFs). We found that soil macroaggregate contents in the old reclaimed areas (reclaimed in 1940 and 1960) were significantly larger than those in the new reclamation area (reclaimed in 2007). The soil saturated hydraulic conductivity (Ks) of forestland was larger than that of grassland in each reclamation year. Soil structure contributed to 22.13%, 24.52%, and 23.93% of the total variation in Ks and soil water retention parameters (α and n). The PTFs established in our study were as follows: log(Ks) = 0.524 − 0.177 × Yk3 − 0.093 × Yk1 + 0.135 × Yk4 − 0.054 × Yk2, 1/α = 477.244 − 91.732 × Yα2 − 81.283 × Yα4 + 38.106 × Yα3, and n = 1.679 − 0.086 × Yn2 + 0.045 × Yn1 − 0.042 × Yn3 (Yareprincipalcomponents). The mean relative errors of the prediction models for log(Ks), 1/α, and n were 79.30%, 36.1%, and 9.89%, respectively. Our findings quantify the vital roles of the aggregate structure on the SHPs of coastal saline/sodic soils, which will help us understand related hydrological processes.

Salinity Effects on Soil Structure and Hydraulic Properties: Implications for Pedotransfer Functions in Coastal Areas

Understanding the effects of salinity on soil structure and hydraulic properties is critical for addressing environmental challenges in coastal saline and sodic areas. In this study, soil samples were collected from a coastal region in eastern China to investigate how salinity affected the soil structure and hydraulic properties based on lab experiments. A comprehensive soil dataset was also compiled from the experimental results to develop a salinity-based pedotransfer function (PTF-S) tailored to the coastal environment. The results showed that salinity significantly altered the soil aggregate size distribution and hydraulic properties. Higher salinity promoted the formation of larger aggregates (0.25–2 mm), particularly in silty clay soil. Salinity positively correlated with the saturated hydraulic conductivity (Ks) in sandy loam soil, regardless of the cation type (Na⁺ or Ca2⁺). By comparison, Na+ increased the Ks of silty clay soil up to a certain threshold, while Ca2+ enhanced the Ks regardless of the soil texture. Increased salinity also reduced the soil water retention of sandy loam soil; however, Na+ increased the soil water retention of silty clay soil and Ca2+ had different effects depending on the suction levels. The newly developed PTF-S model, which included the electrical conductivity (EC) and cation exchange capacity (CEC), showed better predictions for the volumetric water content (R = 0.886 and RMSE = 0.057 cm3/cm3) and log Ks (R = 0.991 and RMSE = 0.073 mm/h) than the traditional model that excludes the salinity variables EC and CEC (PTF-N) (R = 0.839 and RMSE = 0.066 cm3/cm3 for the volumetric water content, and R = 0.966 and RMSE = 0.140 mm/h for the log Ks). This study highlights the importance of developing salinity-based PTFs for addressing soil salinization challenges.

Exploring the physical properties of Australian alpine soils to inform ecosystem restoration

Alpine soils are globally threatened and are particularly vulnerable to the impacts of climate change. In Australia, development and grazing put further pressure on alpine ecosystems. Consequently, land managers and restoration practitioners are increasingly interested in understanding how to tailor revegetation approaches to enhance their success in mountain environments. Because of the intrinsic role of soils in plant-water relationships, the aim of this study was to quantify and compare the physical and hydraulic properties of soils in the Australian Alps. We investigated four common soils that occur across the Australian Alps bioregion: peat soils (organosols), alpine humus soils, skeletal mountaintop soils, and disturbed soils (anthroposols). We quantified and compared soil bulk density, particle density, porosity, water content, infiltration, hydraulic conductivity, and wilting point between soils. We found significant differences in soil properties both within and among each soil, highlighting the importance of understanding local edaphic conditions to improve revegetation outcomes. We recommend that direct measurements of plant establishment, growth, and survival are linked with soil physical, chemical, and hydraulic properties in future research, to build upon these findings.

Wildfire burn severity and post-wildfire time impact mechanical and hydraulic properties of forest soils

Vegetation contributes to the overall slope stability and is recognized as an environmentally friendly nature-based solution. Wildfires burn and denude vegetated slopes, thus increasing the risk of shallow landslides and debris flows. However, little attention has been given to assessing the effects of burn severity and the time elapsed since a wildfire on the hydro-geomechanical properties of burned slopes. This study performed a series of standard laboratory tests to evaluate the shear strength and saturated hydraulic conductivity (ksat) of forest soils collected from moderate-low (ML) burned, moderate-high (MH) burned, and unburned (UB) test plots. The plots were sampled one, four, and six months after the March 2022 wildfire in Uljin County, South Korea. The results show that the continuous deterioration of roots highly depended on the burn severity. The root biomass of ML- and MH-burned soils was consistently lower than those of the UB soils. The root deterioration reduced the shear strength of the soils temporally. The burned soil's cohesion intercept was 1.80–2.30 times lower than that of the UB soil six months post-wildfire, with the friction angle unaffected. One- and four-months post-wildfire, ksat of the burned soils was 1.22–3.15 times lower than the UB soil. Such lowered ksat was due to the fine ash-clogged pores and hydrophobic layers beneath the soil surface. However, six months post-wildfire, the burned soils' ksat increased by approximately twice that of the pre-wildfire condition because of macropore flow passages formed by impoverished roots. The appreciation of sand fraction, depreciation of fines content, and weakening of hydrophobicity over time have also emphasized their role in the temporal shifts in the properties of the ML- and MH-burned soils. The documented results herein can be incorporated into rainfall infiltration and stability analyses of wildfire-affected slopes, landslide susceptibility mapping, and mitigation measures design.

Specific cation effects on soil water infiltration and soil aggregate stability–Comparison study on variably and permanently charged soils

Improving soil hydraulic properties is one of important purposes of soil tillage. Recent studies on permanently charged soil have shown specific cation effect on soil water infiltration. In this study, specific cation effects on soil water infiltration and soil aggregate stability of both variably and permanently charged soils were comparatively examined. It was found that, specific cation effects on soil water infiltration and soil aggregate stability are quite different for permanently and variably charged soils. For the permanently charged soil, the sequence of specific cation effects on soil water infiltration was Li+ << K+ < Cs+, which was in accordance with the cation polarizability sequence of Li+ (0.029 Å3) << K+ (0.88 Å3) < Cs+ (2.56Å3); but for the variably charged soil, the sequence changed to Cs+ > Li+ > K+. Moreover, the sequence of cation concentration effect on permanently charged soil water infiltration rate (SWIR) was SWIR (0.0001 mol/L) < SWIR (0.001 mol/L) < SWIR (0.01 mol/L) < SWIR (0.1 mol/L) whereas that for the variably charged soil changed to SWIR (0.1 mol/L) < SWIR (0.0001 mol/L) ≈ SWIR (0.01 mol/L) < SWIR (0.001 mol/L). The differences of specific cation and cation concentration effects on soil water infiltration for the two soils came from those on soil aggregate stability. For permanently charged soils, soil electric field determined soil aggregate stability. However, for variably charged soils, besides soil electric field, osmotic pressure, positively charged colloids and surface reaction of metal cation may possibly play critical role in soil aggregate stability.

A comprehensive approach to building a continuous hydrologic model with Soil Moisture Accounting using Earth Observation data

ABSTRACT In recent years, both availability and interest in Earth Observations (EO) have increased due to their ability to provide information with extensive spatial coverage, which is valuable for data-scarce regions. This study provides a roadmap to exploit EO/satellite data (EO-based model) for continuous hydrological simulation using the Hydrologic Engineering Center–Hydrologic Modelling System model with a soil moisture accounting (SMA) component. As a case study, we consider the Boeotikos Kephisos River basin, in Greece. The SMA component is calibrated using the HiHydroSoils dataset, to map its parameters to the regionally varying soil hydraulic properties and a comparison is made to an alternative parameterization, following the standard literature approach (literature-based model). The effectiveness of satellite data in enhancing model performance is further assessed, by comparing three different satellite precipitation datasets, as model drivers, and by using satellite-based soil moisture for model initialization. The discussion extends to the potential for integration of EO/satellite data at the operational level, by simulating a significant precipitation event. Yet, the most promising result pertains to the opportunity to exploit satellite-derived estimates of soil hydraulic properties to base the calibration of the data-intensive SMA scheme, with the EO-based model significantly outperforming the literature-based model parameterization.

Analytical solution for rainwater infiltration in monolithic soil covers under heavy rainfall and its implications for practice

This study established an analytical solution for rainwater infiltration in MSCs during heavy rainfall assuming that the soil hydraulic properties follow exponential forms. The analytical solution was used to calculate the factor of safety (FOS) of MSCs after the verification with numerical simulations. It is found that the FOS for the potential slip surface at the cover bottom remined the lowest during and after heavy rainfall. The percolation and FOS might present pronounced “lag effects”, meaning that the maximum percolation rate and minimum FOS occurred after heavy rainfall. A parametric study was conducted to reveal the influencing factors on the hydraulic response and slope stability of MSCs based on the analytical solution. Relevant results demonstrate that the hydraulic performance and slope stability could be improved by decreasing soil saturated hydraulic conductivity, increasing soil desaturation coefficient and lowering water level in landfills. The results also reveal the existence of a threshold of soil saturated hydraulic conductivity (1×10&lt;sup&gt;-8&lt;/sup&gt; m/s for this study) for controlling the hydraulic performance and slope stability of MSCs. Furthermore, the analytical solution was applied to determine the rainfall intensity-duration threshold curves of MSCs. The results indicate that the obtained curves of MSCs satisfied exponential forms.

The amendment value of pulp and paper mill sludges in Finnish coarse-textured soil

As a source of exogenous organic matter, pulp and/or paper mill sludges (PPMS) may have beneficial effects on crop productivity and soil chemical and physical properties. This study's aim was to assess the impacts of two different PPMS materials on crop yields, the quality of percolation water, and soil chemical and hydraulic properties in a three-year field experiment on a silt loam soil in East Central Finland. Fresh (FPMS) and lime-stabilized (LPMS) sludges were applied once at rates of 21–28 fresh-Mg ha−1 in the spring prior to the sowing of grass ley under barley as a cover crop and incorporated into the upper 7 cm soil layer. Supplemental nitrogen (N) was applied at levels of 40 and 80 kg ha−1. A decrease of barley grain yield due to N immobilization was observed at the N level 40 kg ha−1, but the standard N application rate (80 kg ha−1) connected with a moderate C:N ratio (FPMS 27:1, LPMS 24:1) was adequate to avoid significant yield losses. In the second and third year following the PPMS applications, there was a tendency for positive residual effects on the total dry matter yield of grass ley, which could be attributed to slow mineralization of sludge-N. The application of LPMS increased the pH in surface soil by 0.5–0.7-units and Ca concentration by 240–660 mg L−1 of soil relative to the non-amended control over the study period. In the year of PPMS applications, the amendments produced a significant increase (about 2.0 g kg−1) in the total carbon (C) concentrations in the uppermost 10 cm soil layer relative to the non-amended soil. During the following years, the change in soil C was no longer measurable, indicating relatively fast decomposition of sludge-C. Saturated hydraulic conductivity tended to be 1.4 to 2.3 times higher in the PPMS-treated soils than in the non-amended soil. Except for the decline in readily plant-available water, the other common water retention parameters were not significantly affected by the PPMS amendments. There were significant positive treatment effects on the amount of water retained between −13 and − 316 kPa matric potentials, suggesting an increase in medium-sized pores contributing to water storage in the soil. To maintain or enhance the beneficial direct and indirect effects of PPMS on crop yields and soil physico-chemical properties, repeated applications of PPMS are required, possibly combined with the use of organic fertilizers, especially during grass ley years.

Acidified biochar one-off application for saline-alkali soil improvement: A three-year field trial evaluating the persistence of effects

Salinization is a global soil degradation issue threatening agricultural productivity and environmental sustainability. Native biochar is a promising soil amendment, but its high alkalinity limits its use in saline-alkali lands. Acidified biochar, with a lower pH, is theoretically more suitable. This study aims to evaluate the persistence of effects of acidified biochar one-off application on soil particle size distribution, physicochemical properties, water retention, temperature regulation, and evaporation conditions of saline-alkali soil, thereby verifying its feasibility and exploring the optimal application range. We conducted a three-year cotton field experiment using palm fruit branch biochar as the raw material, acidified with ferrous sulfate, which involved four biochar applications (0, 10, 20, and 30 t ha−1) and four irrigation quotas (60 %, 80 %, 100 % and 120 % ETc). The results indicated that the initial acidified biochar application slightly increased surface soil (0–20 cm) pH by 0.1 %–3.9 %, this negative effect was nearly eliminated by the third year. Biochar application significantly altered surface soil particle size distribution, increasing sand content by 1.6 %–8.4 %, and persistently improved soil hydraulic properties, with water holding capacity still showing a 6.5 %–16.7 % increase in the third year. Biochar enhanced soil thermal insulation and suppressed soil evaporation, but these benefits gradually diminished with increasing cultivation years. Acidified biochar effectiveness was closely linked to irrigation quota. Significant differences in soil water and heat indicators were observed between the 20 and 30 t ha⁻¹ biochar treatments only under low irrigation quotas. Under sufficient irrigation (100 % and 120 % ETc), the optimal biochar application range was 15–20 t ha⁻¹, while under low irrigation (60 % and 80 % ETc), the optimal range was 20–25 t ha⁻¹. This study demonstrated that acidified biochar one-off application has significant multi-year benefits in improving soil structure and hydrothermal properties, providing a scientific basis for the improvement and sustainable utilization of saline-alkali soil.

Effects of Different Modified Corn Straw Biochar on Soil Hydraulic Properties in Hilly Loess Areas

In order to investigate the influence of modified corn straw biochar on the hydraulic properties of water infiltration, evaporation, and water holding, corn straw biochar was prepared by pyrolysis at 500 ℃ for 2 hours in an N2 environment. Three solvents （H3PO4, NaOH, and NH4Cl） were selected, and different modified corn straw biochars were obtained by immersion modification at two concentrations （1 mol·L-1 and 3 mol·L-1）. The physical and chemical properties of all biochars, such as elemental composition, pore structure, functional groups, and surface morphology, were systematically characterized. Each type of corn straw biochar was selected to perform soil hydraulic properties tests under three different additions （1%, 2%, and 3%）. The influence of different corn straw biochar on the soil saturated hydraulic conductivity, water accumulation evaporation, and volume water content were analyzed by constant head method, soil evaporation test, and soil moisture characteristic curve. The results showed that the addition of modified corn straw biochar can significantly reduce the soil saturated hydraulic conductivity by 5.74%-46.69%, improve the soil volume water content by 0.74%-37.33%, and promote the soil water evaporation, while reduce the soil water accumulation evaporation by 0.63%-8.46% before the modification. With the increase in biochar addition, the saturated hydraulic conductivity of the soil decreased significantly, the cumulative evaporation gradually increased, and the volume water content showed a trend of first increasing and then decreasing. There was no correlation between the modified solution concentration and the soil saturated hydraulic conductivity, accumulated evaporation, and volume water content. This study can provide theoretical basis and technical support for improving the water retention performance of soil in the loess arid region of Shaanxi and Gansu.

Characterization and prediction of hydraulic properties of traffic-compacted forest soils based on soil information and traffic treatments

Key messageThe hydraulic properties of compacted and rutted soils were evaluated through in-situ infiltration experiments and predicted based on soil texture class and traffic treatments. A significant decrease in saturated soil water content and soil hydraulic conductivity at saturation was observed. The resulting soil hydraulic parameters, when integrated into a soil water transfer model, effectively simulated water dynamics in these impacted forest soils, providing a crucial first step toward developing decision support tools for real-time trafficability. This approach can assist forest managers in minimizing the extent of soil compaction.ContextTo overcome trafficability issues of forest soils induced by heavy logging machinery, planning support tools are needed to determine suitable soil moisture conditions for traffic.AimsThis study aimed to identify the soil properties that differ significantly between undisturbed and compacted soils and to provide several estimation tools to predict the hydraulic properties of compacted soils beneath the skid trails.MethodsFour hundred seventeen water infiltration tests were conducted on 19 forest sites, mostly in North-eastern France, and analysed with the BEST method to estimate the hydraulic properties of the skid trails and undisturbed soils. The hydraulic properties of the skid trails were predicted thanks to linear mixed effect models using a bulk treatment effect, a site effect, or a skid trail degradation score. The predicted hydraulic properties were tested using a water flow model to assess their relevance regarding the prediction of water dynamics in skid trails.ResultsThe compaction effect was only significant for the logarithm of the hydraulic conductivity at saturation (log10(Ksat)) and the soil water content at saturation (θsat). For the skid trails, θsat was reduced by - 0.02 and − 0.11 m3m−3 in the 0 − 10 cm and 15 − 25 cm layers respectively, compared to undisturbed topsoil (0 − 10 cm). log10(Ksat) was reduced by − 0.38 and − 0.85 for skid trails in the 0 − 10 and 15 − 25 cm soil layers respectively, compared to undisturbed topsoil. The use of a pedotransfer function, in replacement of water infiltration tests, and their combination with the same correction coefficients proved to efficiently simulate the difference in water dynamics between skid trails and undisturbed forest soils.ConclusionEstimation of soil hydraulic properties based on in situ water infiltration experiments proved efficient to simulate water dynamics in compacted and rutted forest soils. Yet, further studies are needed to identify the most adapted pedotransfer function to forest soils and to test the generalisation of our findings in different conditions, especially deeply rutted soils (rut depths > 12 cm).