Saturated Hydraulic Conductivity Research Articles

Hydraulic conductivity over a wide suction range of loess with different dry densities

Experimental research into the hydraulic conductivity curve (HCC) of unsaturated soil is limited due to the inherent challenge associated with labor, cost, and time. Typically, the HCC is estimated using the soil water characteristic curve (SWCC) based models and saturated hydraulic conductivity (SHC). However, the efficiency of the SWCC-based model is rarely assessed, and the influence of soil density and pore structure on HCC remains incomplete due to limited experimental data. To address this gap, this study employs an innovative filter-paper-based column method, which can measure the HCC over a wide suction range (e.g. 0−105 kPa), to capture the HCCs of both intact and compacted specimens with varying dry densities. The efficiency of two typical SWCC-based models is assessed using the measured data. Meanwhile, the mercury intrusion porosity (MIP) technique is employed to obtain the pore characteristic (i.e. pore size distribution (PSD)) and a method of predicting the HCC using the PSD data is proposed, emphasizing the dominant role of the pore structure in shaping the HCC. The results reveal that the dry density's influence on the HCC is primarily observed within the low suction range, corresponding to variations in the dominant and large pores. In the high suction range, the HCCs align along a linear trajectory when plotted in a log-log format. A notable finding is the overestimation of the HCC obtained from the SWCC-based models using the measured SHC. When the SHC is regarded as a fitting parameter, good agreement is achieved. The adjusted SHC value is typically 0-1 order of magnitude lower than the measured value, and this discrepancy diminishes as dry density increases. On the other hand, the proposed PSD-based model performs well with the measured SHC data. Caution is exercised when using the SHC to estimate the HCC for modeling water movement in partially saturated soil.

Spatial distribution of soil erodibility factors in erosion-prone areas in Umuahia, Southeast, Nigeria

This study evaluates the spatial distribution of soil erodibility factor (K) in Umuahia, Abia State, Nigeria using the Universal Soil Loss Equation (USLE) nomograph. The soils used for the study was sampled from 14 erosion prone areas in Umuahia, Southeast, Nigeria. The topsoil samples collected at depths of 0–10 cm, 10–20 cm, and 20–30 cm around the middle of each location identified with the aid of a GPS. The percentages of sand, silt, clay, moisture content, saturated hydraulic conductivity, and organic matter (OM) were all examined. The Gaussian ordinary kriging model for the determination of K-factor was compared with the Inverse Distance Weighting method. The K-factor’s coefficient of variation (CV) was 0.29 and the K-factor value of the nuggets to sill ratio (0.44) indicates a moderate spatial distribution. The Gaussian semi-variogram approach yielded the best estimate accuracy and model fitting effects, meaning that the Gaussian ordinary Kriging model is better for K-factor estimation. The root mean squared error (RMSE) was 0.0079 and the mean squared deviation ratio (MSDR) was 0.89, implying that the Gaussian model was unbiased and adequately captured the experimental variation. The K-factor values were lower in the north of the research region ranging from 0.0250 to 0.0197 Mg h MJ−1 mm−1 compared to east with the K-factor ranging from 0.0399 to 0.0423 Mg h MJ−1 mm−1. The estimated K-factor was relatively unbiased since the root mean square error was extremely small and the mean error was nearly equal to 0. The determination of soil erodibility (k-factor) influenced by factors such as soil texture, structure, and organic matter is crucial in assessing the vulnerability of land area to soil erosion. The spatial distribution of these factors affects the k-factor at different locations in a landscape, which enables accurate estimation of k-factor. Nutrient levels impact soil erodibility and distribution. Low nitrogen limits growth, favoring erosion. Phosphorus aids stability. Optimal potassium benefits growth and erosion control. Spatial distribution is vital, emphasizing precise nutrient management for effective soil health.

Hydrological function of rewetted peatlands linked to saturated hydraulic conductivity in Kubu Raya, West Kalimantan, Indonesia

Hydrological function of rewetted peatlands linked to saturated hydraulic conductivity in Kubu Raya, West Kalimantan, Indonesia

Effect of super absorbent hydrogel on hydro-physical properties of soil under deficit irrigation

Due to water scarcity challenges, efficient management of irrigation water is becoming crucial. Water use efficiency (WUE) involves increasing crop productivity without increasing water consumption. This study was carried out to study the effect of hydrogel, deficit irrigation and soil type on WUE, soil hydro-physical properties and lettuce productivity. For this purpose, four irrigation treatments (100%, 85%, 70% and 60% of full irrigation requirements), four hydrogel concentrations (0, 0.1, 0.2 and 0.3% w/w) and three soil textural classes (clay, loamy sand, and sandy-clay soil) were conducted in pot experiment at open field during two consecutive seasons. The results revealed that crop growth parameters and soil hydro-physical properties were significantly affected by hydrogel application rates. Hydrogel addition significantly enhanced head fresh and dry weights, chlorophyll content, number of leaves and WUE. Application of hydrogel at 0.3% and 85% of irrigation requirements achieved the highest WUE without significant yield reductions. Changes in the studied hydro-physical properties of soil were more dependent on soil texture and hydrogel application rate than on the amount of irrigation water. The significant decrease in soil saturated hydraulic conductivity and bulk density confirms that super absorbent hydrogels could be recommended to improve soil water retention and enhance water use efficiency under deficit irrigation conditions.

Design of drainage channel for effective use of land on fully mechanized sugarcane plantations: A case study at Bone Sugarcane Plantation

Abstract Drainage in sugarcane cultivation in high-rainfall areas is of paramount importance because it affects sugarcane plants from planting, maintenance, and production. Poor drainage can damage plants and reduce productivity. This study was conducted at Bone Sugarcane Plantation, which typically has high annual rainfall; thus, drainage is necessary. The existing drainage channel cannot drain all surface runoff quickly and causes problems to sugarcane plants. Therefore, a study was conducted with the aim of designing the shape and size of drainage channels that can drain surface runoff quickly, have a strong structure, allows for an effective use of cultivated land by reducing headland for tractor turning, and maintains appropriate soil moisture. The research began by determining the saturated hydraulic conductivity of the soil using the Falling Head method. Surface runoff discharge was calculated using rational equations to determine the dimensions of the drainage channel. Rainfall intensity was determined from Intensity Duration Frequency curve which was constructed using Manonobe method. The results showed that the saturated hydraulic conductivity of the soil was 3.54 × 10−3 cm/s which is suitable with surface drainage. Rainfall intensity is estimated to be 201.33 mm/hour. The shape and dimensions of the drainage channel are parabolic with the largest width and depth of 1.70 m and 0.90, respectively. This study provides a practical method to solve drainage problems in sugarcane fields that apply full mechanization. In addition, the practical analysis used in this study can be adapted to analyze the design of drainage channel for other plantations or regions with similar constrains.

Assessment of Saturated Hydraulic Conductivity with Using Soil Particle Size Distribution: A Comparative Study of Constant Head and Falling Head Methods

<p>The purpose of soil hydraulic conductivity is to retain soil water contents, and soil water pressure. In this study investigates two different methods to understand the soil hydraulic conductivity of loam and clay soils. The present research conducted a laboratory experiment to measure the saturated hydraulic conductivity (Ksat) using two different methods: the constant head and falling head methods. The constant head method utilized a soil column with a length of 8.5 cm, and three soil columns were occupied with various soil texture classes (%). The study results demonstrate that the classification of soil texture was predominantly sandy loam with porosity varying between 35%, 43%, and 50% within the clay soil category. Furthermore, the average value of Ksat for the soil samples using the constant head method was 0.00142 cm/sec, while the falling head method provides average values of 0.00123, 0.00172, and 0.00144 for sandy loam and 0.0000146 cm/sec for clay soil. It is concluded that the falling head method indicates greater accuracy, particularly evident in the concurrent analysis of three samples. This study suggested that determination of Ksat through laboratory method is suitable due to cost effectiveness and simplicity.</p>

Hydraulic characterization of Pwales aquifer in Malta Island preparatory for planning managed aquifer recharge (MAR) pilot plant

Whitin the aim to reduce the water demand by increasing water use efficiency and providing alternative water resources, and mainly to meet the demand of good quality irrigation water for agriculture, the Energy and Water Agency of Malta is planning to develop a Managed Aquifer Recharge pilot plant in Pwales Valley to improve the quantitative and qualitative status of the groundwater body. For this reason a detailed hydraulic characterization of the valley was carried out. Specifically, hydraulic properties of the rocks that constitute strata atop of the Pwales aquifer were determined by means of both laboratory measurements on samples and field test carried out in the studied area. The water retention and hydraulic conductivity functions, which relate the matric potential, ψ, and hydraulic conductivity, K, to the water content, θ, respectively, were measured using three experimental methods because each of them allows to obtain data points in a specific wet range. The water retention and hydraulic conductivity functions were measured on samples extracted from blocks of Upper Coralline Limestone formation, that hosts the aquifer, collected in three different quarries: Ghian Tuffieha, Mellieha and San Martin areas. The measured water retention and hydraulic conductivity data were fitted with LABROS SoilView Analysis software that allows to describe the functions and obtain the parameters which are crucial for modelling the water flow and transport processes in the critical zone. In addition, large ring infiltrometer test was carried out to determine the field saturated hydraulic conductivity, Kfs, and the average infiltration rate. Knowledge of the hydraulic characteristics of the Upper Coralline Limestone, completely missing in the scientific literature, allows developing a local groundwater-flow numerical model in order to better describe and understand how the water flows from the soil to the groundwater of the valley and visualize different environmental scenarios such as the potential effects of Managed Aquifer Recharge plant in the Pwales Coastal Groundwater Body.

Crop-livestock integration influenced soil profile organic carbon and hydro-physical properties in converted grasslands to row crops

Integrated crop-livestock systems (ICLS) can mitigate the impacts of cropping intensification by improving soil organic carbon (SOC) and associated hydro-physical properties. This study was conducted on three on-farm long-term (≥30 years) sites (Site 1, 2, and 3) and one short-term (4 years) experimental site (Site 4) to compare the SOC and hydro-physical properties to a depth of 40 cm for an intensive-cropland (CL), a native-grassland (NG) and cropland managed with ICLS. Data showed higher SOC, soil water retention (SWR), macroporosity, available water capacity (AWC), and saturated hydraulic conductivity (Ksat) for the NG than the CL indicating the degradation of soil physical quality because of intensive agriculture. However, for sites 1 and 2, the ICLS had 27% and 46% more SOC than the CL in the 0–10 cm depth. In addition, the ICLS decreased bulk density (ρb) (sites 1 and 3) and increased the Ksat (sites 1, 2, and 3) at 0–10 cm depth as compared to the CL. No differences in SOC or hydro-physical properties were observed for the short-term ICLS (site 4) when compared to the CL. The impacts of ICLS were most prominent at the surface soil (0–10 cm) and no difference was observed for the deeper soil. The AWC showed a linear increase with the increase in SOC, however, soils under ICLS and CL showed a higher increase in AWC with an increase in SOC as compared to the NG. This study highlighted the negative impacts of grassland to cropland conversion and suggested the implementation of ICLS to improve organic carbon and other associated hydro-physical properties of soils.

Effect of Freeze–Thaw and Wetting–Drying Cycles on the Hydraulic Conductivity of Modified Tailings

Mine tailings have shown viability as the fine–grained layer in a capillary barrier structure for controlling acid mine drainage in a circular economy. Their saturated hydraulic conductivities (ksat) under wetting–drying cycles and freeze–thaw cycles remain unexplored. In this study, modified tailings with a weight ratio of 95:5 (tailings/hydrodesulfurization (HDS) clay from waste–water treatment) and an initial water content of 12% were used. The ksat of specimens was measured after up to 15 wetting–drying cycles, each lasting 24 h, with a drying temperature of 105 °C. The ksat for wetting–drying cycles decreased from 3.9 × 10−6 m/s to 9.5 × 10−7 m/s in the first three cycles and then stabilized in the subsequent wetting–drying cycles (i.e., 5.7 × 10−7 m/s–6.3 × 10−7 m/s). Increased fine particles due to particle breakage are the primary mechanism for the ksat trend. In addition, the migration of fines and their preferential deposition near the pore throat area may also promote this decreasing trend through the shrinking and potentially clogging–up of pore throats. This could be explained by the movement of the meniscus, increased salinity, and, subsequently, the shrinkage of the electrical diffuse layer during the drying cycle. Similar specimens were tested to measure ksat under up to 15 freeze–thaw cycles with temperatures circling between −20 °C and 20 °C at 12 h intervals. Compared to the untreated specimen (i.e., 3.8 × 10−6 m/s), the ksat after three freeze–thaw cycles decreased by 77.6% (i.e., 8.5 × 10−7 m/s) and then remained almost unchanged (i.e., 5.6 × 10−7 m/s–8.9 × 10−7 m/s) in subsequent freeze–thaw cycles. The increased fine grain content (i.e., 3.1%) can be used to explain the decreased ksat trend. Moreover, the migration of fines toward the pore throat area, driven by the advancing and receding of ice lens fronts and subsequent deposition at the pore throat, may also contribute to this trend.

Effect of Biostimulant, Manure Stabilizer, and Manure on Soil Physical Properties and Vegetation Status.

Food production sustainability is one of contemporary agriculture's fundamental challenges. Farmers are currently facing high input prices in crop production and declining organic matter in the soil. For this reason, a field experiment was established to assess the effect of the biostimulant NeOsol (NS), the manure stabilizer Z'fix (ZF), farmyard manure (FM), and their combination in farm practice. In situ measurements provided information on the change in bulk density (BD), unit draft (UD), saturated hydraulic conductivity (SHC), and cone index (CI). Furthermore, the vegetation status was investigated via vegetation indices, and the yield and quality parameters were assessed. Management of the experimental field resulted in an overall decrease in BD over time for the treated variants compared to the control (CL). The decrease with time was also verified in the case of UD and CI at the depth zone of 10-20 cm. Variants FM (by 8.0%), FM_NS (by 7.3%), and FM_ZF_NS (by 3.8%) proved to have lower UD values than CL. An overall increase in SHC and in yield was observed over time. Concerning SHC, only FM (by 58.5%) proved different from CL. The yield of all the treated variants, i.e., NS (by 8.2%), FM (by 10.8%), FM_NS (by 14.1%), FM_ZF (by 17.8%), and FM_ZF_NS (by 20.1%), surpassed CL. Simultaneously, none of the examined treatments proved to have any adverse effect either on soil or on plant-related variables.

Flow through and Volume Change Behavior of a Compacted Expansive Soil Amended with Natural Biopolymers

Natural biopolymers offer a sustainable alternative for improving soil behavior due to their inert nature, small dosage requirement, and applicability under ambient temperatures. This research evaluates the efficacy of natural biopolymers for ameliorating an expansive soil by using a 0.5% dosage of cationic chitosan, charge-neutral guar gum, and anionic xanthan gum during compaction. The results of laboratory investigations indicate that the flow through and volume change properties of the expansive soil were affected variably. The dual porosity, characterized by low air entry due to inter-aggregate pores (AEV1 of 4 kPa) and high air entry due to the clay matrix (AEV2 of 200 kPa) of the soil, was healed using chitosan and guar gum (AEV of 200 kPa) but was enhanced by the xanthan gum (AEV1 of 100 kPa and AEV2 of 200 kPa). The s-shaped swell–shrink path of the soil comprised structural (e from 1.23 to 1.11), normal (e from 1.11 to 0.6), and residual stages (e ranged from 0.6–0.43). This shape was converted into a j-shaped path through amendment using chitosan and guar gum, showing no structural volume change, with e from about 1.25 to 0.5, but was reverted to a more pronounced form by xanthan gum, with e from 1.5 to 1.32, 1.32 to 0.49, and 0.49 to 0.34 in the three stages, respectively. The consolidation behavior of the soil was largely unaffected by the addition of biopolymers such that the saturated hydraulic conductivity decreased from 10−9 m/s to 10−12 m/s over a void ratio decrease from 1.1 to 0.6. At a seating stress of 5 kPa, the swelling potential (7.8%) of the soil slightly decreased to 6.9% due to the addition of chitosan but increased to 9.4% and 12.2% with guar gum and xanthan gum, respectively. The use of chitosan and guar gum will allow the compaction of the investigated expansive soil on the dry side of optimum.

Effect of mixed plant roots on saturated hydraulic conductivity and saturated water content of soil in the loess region

Soil hydraulic properties are essential for understanding soil hydrological and erosion processes. The importance of roots on soil hydraulic parameters has been widely recognized, but current studies have focused mainly on the root effect of a single plant species. However, few studies have been carried out to investigate the effect of mixed plant roots on soil hydraulic parameters. Undisturbed soil samples were collected from three natural sampling sites with single plant types and four sites with mixed plant types. Both soil hydraulic parameters were measured: soil saturated hydraulic conductivity (Ks) and soil saturated water content (SW). Then the root effects on Ks and SW were subsequently evaluated. The results showed that the Ks and SW at the sites with mixed plants were higher than those at the sites with a single plant species. At all the sites, Ks and SW both exhibited a decreasing-increasing-decreasing trend with increasing root density. The critical root density for the above change was quantified. When fibrous roots were mixed with tap roots, Ks was mainly affected by tap roots, while SW was mainly affected by fibrous roots. The influence of roots on Ks and SW was mainly achieved by affecting soil organic matter, not by directly affecting Ks and SW. Based on the root density, the herbaceous coverage with optimal saturated hydraulic conductivity and water content was estimated to be 66.71%.

Water dispersible clay and micro-structure of soils from coastal plain sands, shale and false-bedded sandstones

Information regarding water-dispersible clays in soils of contrasting textures is needed to evaluate soil qualities that influence susceptibility of soils to slaking in water. Water-dispersible clays (WDCs), plastic limits, and basic properties of soils on Coastal Plain Sands (CPS), Shale (Shale), and False-Bedded Sandstones in southern Nigeria were quantified for use in evaluating management options of some tropical soils. Results revealed that WDCs, micro-aggregate indices, and plastic limits differed significantly amongst the parent materials. At 0–15 cm depth, clay content was 29.7%, 11.2 and 3.8%, for Shale, CPS and False-Bedded sandstones, respectively, indicating significant high clay content in Shale. The highest SOC of 29.8 g kg−1., and very slow saturated hydraulic conductivity (Ksat) of 6.33 cm h−1 were found in Shale. False-Bedded Sandstone had the lowest SOC content of 7.7 g kg−1 and highest Ksat value of 31.10 cm h−1 at 0–15 cm topsoil. Micro-aggregate stability indices measured by aggregated silt+clay (ASC) and clay flocculating index (CFI) were significant in CPS at 0–15 cm, whereas water-dispersible clay (WDC) was significantly higher (p < 0.05) in Shale at 8.32%, compared to very low value of 0.76% in False-Bedded Sandstone. Plastic limit (PL) of 16.5%, was significantly higher (p < 0.05) in Shale, indicating its high sensitivity to mechanical deformation when wet. There was a significant positive correlation between clay content and WDC (r = 0.815, p < 0.01), indicating the positive influence of clay content on WDCs and micro-structural indices, and the tendencies for quick degeneration of the soils.

Interactive effects of environmental factors and fertilization practices on soil nitrate leaching and tea productivity in Tianmu Lake Basin, China

Although the effects of fertilization practices and environmental factors on tea yield and NO3−–N leaching have been acknowledged, the interactive effects of these influencing factors remain unknown. These effects were investigated in this study using the denitrification–decomposition (DNDC) model, which was validated using field data collected from a typical tea garden hillslope in the Tianmu Lake Basin, China. Environmental factors such as temperature, precipitation intensity, slope, saturated hydraulic conductivity (Ksat), and fertilization practices (fertilizer amount and type) were combined to construct 1080 scenarios. The results revealed that DNDC achieved acceptable performance in simulating NO3−–N leaching under the application of a compound fertilizer (CF) and a slow-release fertilizer (SF). During the calibration period, the Nash–Sutcliffe efficiency (NSE) values were 0.48 and 0.24. During the validation period, the NSE values were 0.71 and 0.67. Scenario analysis indicated that precipitation intensity (p < 0.001), saturated soil hydraulic conductivity (Ksat) (p < 0.001), fertilizer amount (p < 0.001), and fertilizer type (p < 0.001) significantly influenced the leaching flux of NO3−–N and tea yield. The interactive effects of different factors also varied across the different types of fertilizers. The amount of fertilizer had the most significant impact on NO3−–N leaching, with relative contribution rates of 70% and 53% for compound and SFs, respectively. As CF application increased, there was a significant increase (93%) in the average flux, whereas SF application resulted in an increase of only 76%. The highest contribution rate in terms of tea yield was observed for the amount of fertilizer under CF application at 44%. However, the highest contribution rate under SF application was attributed to Ksat at 51%. The application of SFs resulted in a higher yield improvement rate than that of CFs as the fertilizer amount increased, with respective rates of 15% and 8%. Additionally, environmental factors, excluding temperature, exerted opposite effects on tea production and NO3−–N leaching flux. These findings contribute to optimizing fertilization management in tea plantations by integrating multiple environmental factors to control nonpoint nitrogen loss. Future research should conduct long-term monitoring of tea garden yield and nitrogen loss to accurately assess the impact of SF application on the ecological and economic benefits of tea gardens.

Prediction of atrazine degradation in soil based on XGBoost model.

We established the optimal model by using the automatic machine learning method to predict the degradation efficiency of herbicide atrazine in soil, which could be used to assess the residual risk of atrazine in soil. We collected 494 pairs of data from 49 published articles, and selected seven factors as input features, including soil pH, organic matter content, saturated hydraulic conductivity, soil moisture, initial concentration of atrazine, incubation time, and inoculation dose. Using the first-order reaction rate constant of atrazine in soil as the output feature, we established six models to predict the degradation efficiency of atrazine in soil, and conducted comprehensive analysis of model performance through linear regression and related evaluation indicators. The results showed that the XGBoost model had the best performance in predicting the first-order reaction rate constant (k). Based on the prediction model, the feature importance ranking of each factor was in an order of soil moisture > incubation time > pH > organic matter > initial concentration of atrazine > saturated hydraulic conductivity > inoculation dose. We used SHAP to explain the potential relationship between each feature and the degradation ability of atrazine in soil, as well as the relative contribution of each feature. Results of SHAP showed that time had a negative contribution and saturated hydraulic conductivity had a positive contribution. High values of soil moisture, initial concentration of atrazine, pH, inoculation dose and organic matter content were generally distributed on both sides of SHAP=0, indicating their complex contributions to the degradation of atrazine in soil. The XGBoost model method combined with the SHAP method had high accuracy in predicting the performance and interpretability of the k model. By using machine learning method to fully explore the value of historical experimental data and predict the degradation efficiency of atrazine using environmental parameters, it is of great significance to set the threshold for atrazine application, reduce the residual and diffusion risks of atrazine in soil, and ensure the safety of soil environment.

Evaluation of Soil Hydraulic Properties in Northern and Central Tunisian Soils for Improvement of Hydrological Modelling

The hydrological cycle is strongly affected by climate changes causing extreme weather events with long drought periods and heavy rainfall events. To predict the hydrological functioning of Tunisian catchments, modelling is an essential tool to estimate the consequences on water resources and to test the sustainability of the different land uses. Soil physical properties describing water flow are essential to feed the models and must therefore be determined all over the watershed. A simple but robust ring infiltration method combined with particle size distribution (PSD) analysis (BEST method) was used to evaluate and derive the retention properties and the hydraulic conductivities. Physically based and statistical pedotransfer functions based on PSD were compared to test their potential use for different types of Tunisian soils. The functional sensitivity of these parameters was assessed by employing the Hydrus-1D software (PC Progress, Prague, Czech Republic) for water balance computations. This evaluation process involved testing the responsiveness and accuracy of the parameters in simulating various water balance components within the model. The evaluation of soil hydraulic parameters across the three used models highlighted significant variations, demonstrating distinct characteristics in each model. While notable differences were evident overall, intriguing similarities emerged, particularly regarding saturated hydraulic conductivity between BEST and Rosetta, and the shape parameter (n) between Arya–Paris and Rosetta. These parallels indicate shared hydraulic properties among the models, underscoring areas of agreement amid their diverse results. Significant differences were shown for scale parameter α for the various methods employed. Marginal differences in evaporation and drainage were observed between the BEST and Arya–Paris methods, with Rosetta distinctly highlighting a disparity between physically based models and statistical models.

Water use efficiency and its influencing factors following plantations restoration with Caragana korshinskii and Robinia pseudoacacia in the loess hilly region

Water use efficiency (WUE) as an indicator reflecting plant drought resistance, is crucial for plant survival adaptation and forestland sustainability especially in water scarce areas during revegetation. The understanding of WUE characteristics of major tree species at different ages and the key factors influencing WUE in the loess hilly region is currently lacking. The study selected Caragana korshinskii (CK) and Robinia pseudoacacia (RP) plantations, two species widely planted in different plantation ages (16, 30, and 47 years), in the loess hilly region. The instantaneous water use efficiency (WUEt) and short-term water use efficiency (WUEs) of these plantations were calculated to investigate the factors influencing both WUEt and WUEs. The results showed that the WUEt and WUEs of CK plantations showed an increasing trend with increasing plantation age, while the RP plantations was lowest at 30 years. The soil water content (SWC) in CK and RP plantations demonstrated an upward trend as the age of the plantations increased, while the pH showed a decreasing trend. Older CK plantations had high porosity of soil (Ps) and saturated hydraulic conductivity (Ks), coupled with a low bulk density (BD). Unlike CK plantations, the maximum value of Ps in RP plantations was observed at 30 years. The soil organic carbon (SOC), dissolved organic carbon (DOC), total nitrogen (TN), and dissolved organic nitrogen (DON) contents of RP and CK plantations increased with the increase of restoration years. Except for net photosynthetic rate (An), the 16-year RP and CK showed strong photosynthesis. During the revegetation process, soil and leaf factors explained 85.31% and 90.52% of the differences in WUEt and WUEs under plantations at different stand ages. Among them, DON and intercellular CO2 concentration (Ci) were the most sensitive factors to WUE in soil physicochemical and leaf physiological properties, respectively. The interaction between soil physicochemical and leaf physiological properties significantly influences variations in WUEt and WUEs. These variations were primarily constrained by the synergistic effects of DON, SWC and, Ci. In conclusion, our study underscores the importance of soil and leaf factors in affecting WUE, contributing to improved understanding of water utilization capacity and stand growth strategies during vegetation restoration.

Converted paddy to upland in saline-sodic land could improve soil ecosystem multifunctionality by enhancing soil quality and alleviating microbial metabolism limitation

Soil salinization is one of the major soil degradation threats worldwide, and parameters related to soil quality and ecosystem multifunctionality (EMF) are crucial for evaluating the success of reclamation efforts in saline-sodic wasteland (WL). Microbial metabolic limitation is also one of the main factors that influences EMF in agricultural cropping systems. A ten-year localization experiment was conducted to reveal the key predictors of soil quality index (SQI) values, microbial metabolic characteristics, and EMF in different farmland cropping systems. A random forest model showed that the β-glucosidase (BG), cellobiosidase (CBH) and saturated hydraulic conductivity (SHC) of the SQI factors were the main driving forces of soil EMF. Compared to monoculture models, such as paddy field (PF) or upland field (UF), the converted paddy field to upland field (CF) cropping system was most effective at improving EMF in reclaimed saline-sodic WL, increasing this metric by 275.35 %. CF integrates practices from both PF and UF planting systems, improved soil quality and relieves microbial metabolic limitation. Specifically, both CF and PF significantly reduced soil pH (by 16–23 %) and sodium adsorption ration (SAR) (by 65–83 %) and significantly reduced the abundance of large macroaggregates. Moreover, CF significantly improved soil saturated hydraulic conductivity relative to PF and UF (p < 0.05), indicating an improvement in soil physical properties. Overall, although reclamation improved SQI compared to WL (0.25), the EMF of CF (0.56) was significantly higher than that of other treatments (p < 0.05). Thus, while increasing SQI can improve soil EMF, it was not as effective alone as it was when combined with more comprehensive efforts that focus on improving various soil properties and alleviating microbial metabolic limitations. Therefore, our results suggested that future saline-sodic wasteland reclamation efforts should avoid monoculture systems to enhance soil EMF.

Watershed scale soil moisture estimation model using machine learning and remote sensing in a data-scarce context

Soil moisture content can be used to predict drought impact on agricultural yield better than precipitation. Remote sensing is viable source of soil moisture data in instrument-scarce areas. However, space-based soil moisture estimates lack suitability for daily and high-resolution agricultural, hydrological, and environmental applications. This study aimed to assess the potential of the random forest machine learning technique to enhance the spatial resolution of remote soil moisture products from the SMAP satellite. Models were built using random forest for spatial downscaling of SMAP-L3-E, then visually and statistically evaluated for disaggregation quality. The impact of topography, soil properties, and precipitation on the downscaled soil moisture was examined. The relationship between downscaled soil moisture and in-situ soil moisture was analyzed. The results indicate that the proposed method demonstrated spatial and hydrological coherence, along with a satisfactory downscaling quality. Statistical validation indicated suitable generalization error for scientific and practical use (RMSE &lt; 0.05 cm3 cm-3). Random forest effectively achieved spatial downscaling of SMAP-L3-E in the study area. Principal component and spatial analysis revealed dependence of downscaled soil moisture on elevation, soil organic carbon content, clay content, and saturated hydraulic conductivity, mainly under near-saturation conditions. Regarding validation against in-situ data, downscaled soil moisture explained in-situ soil moisture well under low soil water content ( = 0.624). Downscaling performance deteriorates for water contents between 0.40 to 0.50 cm3 cm-3, suggesting inadequacy under near saturation conditions at a daily temporal frequency. However, coarser temporal aggregations (7 to 10 days) yielded an average 0.98 correlation coefficient, regardless of saturation conditions. These results could potentially be applied in irrigation planning, soil physics studies and hydrology monitoring, to forecasting the occurrence of droughts, leaching of contaminants, surface runoff modeling, carbon cycle studies, soil's capacity to store and provide nutrients.

Numerical estimation of the equivalent hydraulic conductivity for canal concrete lining with cracks

The equivalent saturated hydraulic conductivity of concrete lining (Ksce) is a key parameter to estimate seepage loss, while few studies have quantified the effect of cracks on Ksce, potentially leading to significant errors in canal seepage estimation. A three-dimensional numerical model is employed to simulate seepage loss from canals lined with concrete, and then to obtain the value of Ksce by an equivalent method. A total of 58,400 scenarios are simulated for different concrete lining and crack conditions (e.g., crack length, crack width, crack location, hydraulic conductivity of concrete (Ksc), and underlying soil (Ksoil)), and the corresponding Ksce values are estimated. Results show that the Ksce value determined by the equivalent method is reliable in calculating seepage loss from concrete lined canals. Ksce increases linearly with crack length with a slope Ck, and Ck exhibits a power function relationship with crack width, reaching a maximum value when the crack width surpasses the critical threshold, which ranges from 0.424 to 0.435 mm. When the crack width follows a log-normal distribution, the logarithmic value of Ck increases linearly with the mean value of the logarithmic crack width. The influence of crack location and Ksc on Ksce can be negligible. The maximum increment of Ksce of a crack is proportional to Ksoil. Considering the variation of Ksce with crack parameters and Ksoil, equations to determine the value of Ksce are established by adding the increment of Ksce caused by cracks to Ksc. This study establishes a quantitative relationship between Ksce and crack parameters, thereby enhancing the accuracy of seepage loss calculations in lined canal under different damage status.