Soil Water Content Research Articles

Development and in situ application of actively heated fiber Bragg grating cable for soil water content measurement

The actively heated fiber-optic (AHFO) technology has emerged as a frontier and hotspot in soil water content measurement, offering advantages such as easy installation, large-scale distributed measurement capability, and resistance to electromagnetic interference. However, current AHFO water content sensors fail to simultaneously achieve high precision, applicability for deep soil, and automated real-time monitoring, thereby limiting their development and application. Therefore, this study introduces a novel actively heated fiber Bragg grating (AH-FBG) cable. Laboratory tests were conducted to assess the heating uniformity of the AH-FBG cable and to establish the temperature characteristic value (Tt) – soil water content (θ) calibration formula for water content measurement. Subsequently, AH-FBG cables were deployed for in situ soil water content monitoring in a test pit on the Loess Plateau. Through two-year monitoring data verified the accuracy of the AH-FBG cable and elucidated the spatiotemporal distribution of in situ loess water content. Laboratory results demonstrated superior heating uniformity of AH-FBG cable, with a Tt standard deviation of approximately 0.3 °C. In the field, the AH-FBG cable exhibited excellent performance in soil water content measurement, achieving a high accuracy of 0.023 cm3/cm3. Further analysis revealed that the θ fluctuation predominantly occurred within a 10 m depth from the soil surface, with an overall upward trend over the two-year monitoring period; the response of shallow θ to precipitation was significant but exhibited increasing hysteresis with depth; frequent precipitation significantly enhanced water infiltration depth. This study provides technical guidance for high-precision, quasi-distributed, automated and real-time water content measurement of deep soil.

Structural build-up of 3D printed earth by drying

In recent years, the potential of earth materials in construction has emerged as a sustainable pathway, offering environmental benefits compared to traditional methods. When used in raw form, earth materials can be recycled at the end of a building life, reducing construction waste. In parallel, integrating additive manufacturing into the architecture, engineering, and construction (AEC) sector has brought about a shift in construction dynamics, combining efficiency with precision. This paper bridges the study of 3D printing with earth-based fresh mortars, emphasising the capabilities of the “Forced Layer Drying” (FLD) technique in the additive manufacturing process to increase the mechanical performance of the printing mortar.This paper begins by defining the requisite rheological properties for successful 3D printing. A chosen material for this paper is speswhite kaolin. An instrumental aspect of our research is exploring an established model for the drying rate of saturated porous media, such as earth and concrete, and its application to predict the evaporation rate of saturated earth-based mortar in 3D printing with forced drying conditions. The Wind-Tunnel experiment was conducted to validate this model, examining the interplay of airflow speed and temperature on the evaporation rate. Further deepening this study, the soil water content and undrained shear strength are correlated, specifically based on models derived from oedometer geotechnical standard tests. This facilitated a comprehensive understanding of porous earth-based materials in various moisture scenarios. Our findings confirm that airflow, temperature, and the geometry of the printed object play instrumental roles in affecting evaporation rate, consequent mechanical performance, and structural build-up of the material. The paper wraps up by offering insights into the practical application of 3D printing using earth-based mortars, with a special focus on FLD technique.

Characteristics of forest understory herbaceous vegetation and its influencing factors in biodiversity hotspots in China

Forest ecosystems, especially within biodiversity hotspots, heavily rely on the often-overlooked understory herbaceous communities (USHC) for their structural integrity and ecological functions. Because of their modest stature, these communities have garnered insufficient attention from researchers. Therefore, in this study attention is focused on USHC, which attempts to fill this research gap. To achieve this, we established 105 sample plots in 2022 within forest ecosystems situated in the biodiversity hotspot of southwest China. Our investigation unveiled a rich biodiversity tapestry, identifying 424 plant species from 108 families and 284 genera. Notable were the 217 herbaceous species identified in the understory layer, representing 67 families and 163 genera. These understory herbaceous species accounted for 51.2 % of the overall species count. Through a detailed analysis, the sample plots were categorized into eight distinct communities using a two-way indicator species analysis. These communities exhibited diverse variations in species composition, diversity, biomass, and nutrient characteristics. Notably, community I (Eucalyptus robusta Smith + Rubus corchorifolius L. f. + Alternanthera philoxeroides (Mart.) Griseb.), V (Camptotheca acuminata Decne + Rubus parkeri Hance + Iris tectorum Maxim), VIII (Platycladus orientalis (L.) Franco + Viburnum dilatatum Thunb. + Cyclosorus interruptus (Willd.) H. Ito) stood out for their exceptional species diversity and productivity. Moreover, correlation analyses highlighted the substantial impact of topographic and soil factors on USHC. Altitude, soil water content, and total carbon content emerged as the primary determinants of species diversity. Biomass demonstrated close associations with total soil carbon and nitrogen. Furthermore, the nutrient characteristics displayed significant correlations with soil nutrient contents. These findings underscore the critical importance of prioritizing USHC attention in forest conservation and management strategies within biodiversity hotspots. The implications strongly advocate for the inclusion of these communities in planning and decision-making processes, emphasizing their pivotal role in maintaining structural and functional diversity in ecosystems.

Capillary rise quantification improves irrigation performance in pear orchards

The shallow water table in Río Negro and Neuquén valley causes a capillary rise (CR) that modifies the water content in soil profile. Therefore, irrigation performance is expected to be affected by the capillary water input into the root zone. The aim of this study was to evaluate the effect of CR on surface irrigation performance during 2020-2021 growing season in a pear orchard. In a Bartlett pear orchard planted in 2003, three irrigation moments were evaluated, and irrigation sheets were calculated to obtain efficiency. Water table level (WTL) was measured monthly in an open aquifer piezometer. CR was calculated with the software UPFLOW. Soil water content was measured with a Frequency Domain Reflectometry (FDR) sensor at: 0.20 m, 0.40 m, and 0.60 m. Water use efficiency (WUE) and water productivity were calculated using pear crop yield and the irrigation sheets applied and the crop water demand, respectively. WTL was shallower in spring than in the rest of the season. The mean depth fluctuated between 0.70-1.20 m during spring, affecting irrigation performance. Data of FDR deepest sensor showed an increase of soil moisture due to CR. Capillary contribution negatively affects irrigation efficiency if it is not included in the water balance. Irrigation schedules can be re-arranged considering soil moisture and CR. In this way, the necessary water sheets could be applied in each crop development stage adjusted to water demand. Improving irrigation performance and WUE enables a sustainable water management strategy in pear production.

Coupled simulation of percolation and evapotranspiration in semi-mobile and semi-fixed dunes

Accurately describing the important components of the water balance, such as precipitation (P), deep percolation (D), and evapotranspiration (ET) and their relationships is crucial for understanding the water cycle and eco-hydrological processes in arid and semi-arid regions. This study coupled the dual crop coefficient model (Dualkc) with the HYDRUS-1D model to simulate D and ET processes in the semi-mobile and semi-fixed dune ecosystem in China’s Horqin Sandy Land during the growing seasons from 2015 to 2022. The results indicated that the improved HYDRUS-1D model achieved high simulation accuracy at a daily scale, with the R2 of 0.83, RMSE of 0.392, NSE of 0.714, and b of 0.828, representing increases of 15.27%, 20.16%, 16.01%, and 5.6%, respectively, compared to the original model. ET and D constituted the primary water dissipation processes in semi-mobile and semi-fixed dunes, accounting for 97% to 99% of P during the growing season. The evaporative ratio (ET/P) ranged from 46.7% to 79.3%, averaging 65.67% over multiple years, and the deep percolation ratio (D/P) varied between 16.1% and 53%, averaging 31.02%. The distribution of precipitation events, soil water content, and vegetation conditions are critical factors affecting ET and D in arid and semi-arid dune ecosystems. This study is of great significance for a deep understanding of the eco-hydrological processes in the dune ecosystem, and it can provide important support in developing water management strategies in the desertification region.

Characteristics of deep soil layer water deficit under different artificial vegetation types of the Loess Plateau, China

AbstractSoil water is a crucial factor for the growth of vegetation and sustainable development in water‐limited areas. After large‐scale vegetation restoration on the Chinese Loess Plateau, understanding the relationship between vegetation and deep soil moisture has become a crucial focus in current research. In this study, artificial forest (Pinus tabulaeformis [PT], Robinia pseudoacacia [RP] and Platycladus orientalis [PO]), apple orchard (AO), secondary forest (SF) and farmland (FL) were selected as the research objects, and grassland (GL) as the control, using soil‐drilling techniques. We systematically monitored the soil water content of 0–10 m soil layer over two hydrological years, and explored the effects of different vegetation types on soil water deficiency. The results showed that: (1) The deep soil water various significantly among different vegetation types. Compared with GL, the soil water content in all forest land was generally lower, and this difference became more pronounced in deeper soil layer (>7 m), which indicating the depth of the influence of vegetation on soil water has reached 10 m. (2) The mean soil water deficit size (SWDS) values of PT (0.14), RP (0.17), PO (0.07), AO (0.15), SF (0.10) and FL (0.27) in 0–1 m were all positive, indicating that surface soil water had accumulated during more than half of the sampling periods. In the 2–10 m soil layer, mean SWDS was negative in all vegetation types except in FL, leading to soil desiccation. SWDS was found to fluctuate with soil depth. (3) SWDS was affected by a combination of soil properties and vegetation growth. Our results indicate that the current afforestation model could lead to the deficiency of deep soil water. Therefore, it is imperative to make reasonable vegetation structure according to the available local soil and water resources in future vegetation allocation and management.

Droughts Amplify Soil Moisture Losses in Burned Forests of Southeastern Amazonia

AbstractSoil moisture is a crucial variable mediating soil‐vegetation‐atmosphere water exchange. As climate and land use change, the increased frequency and intensity of extreme weather events and disturbances will likely alter feedbacks between ecosystem functions and soil moisture. In this study, we evaluated how extreme drought (2015/2016) and postfire vegetation regrowth affected the seasonality of soil water content (0–8 m depth) in a transitional forest in southeastern Amazonia. The experiment included three treatment plots: an unburned Control, an area burned every three years (B3yr), and an area burned annually (B1yr) between 2004 and 2010. We hypothesized that (a) soil moisture at B1yr and B3yr would be higher than the Control in the first years postfire due to lower transpiration rates, but differences between burned plots would decrease as postfire vegetation regrew; (b) during drought years, the soil water deficit in the dry season would be significantly greater in all plots as plants responded to greater evaporative demand; and (c) postfire recovery in the burned plots would cause an increase in evapotranspiration over time, especially in the topsoil. Contrary to the first expectation, the burned plots had lower volumetric water content than the Control plot. However, we found that droughts significantly reduced soil moisture in all plots compared to non‐drought years (15.6%), and this effect was amplified in the burned plots (19%). Our results indicate that, while compounding disturbances such as wildfires and extreme droughts alter forest dynamics, deep soil moisture is an essential water source for vegetation recovery.

In situ soil moisture and thermal properties estimated using a dual-probe heat-pulse

In situ monitoring of the temporal and spatial distribution of soil moisture and thermal properties are important for studying the water and energy transport in the vadose zone. The single-probe heat-pulse method based on fiber Bragg grating technology (SPHP-FBG) has become a research focus in field monitoring because of its capability to realize quasi-distributed and real-time monitoring. However, the SPHP-FBG method can only obtain thermal conductivity. This study developed a dual-probe heat-pulse method based on FBG (DPHP-FBG). The DPHP-FBG method can measure thermal conductivity (λ), volumetric heat capacity (Cv), and thermal diffusivity (k). Consequently, volumetric soil water content (θ) can be estimated from its linear relationship with Cv. The accuracy of the DPHP-FBG method in the estimation of Cv, λ, and θ was tested under different heating duration and various soil moisture conditions. In addition, Monte Carlo simulation was performed to investigate the impact of FBG measurement errors on accuracy. Finally, a field test was conducted to verify the effectiveness of the developed DPHP-FBG system. The results show that the DPHP-FBG method allows accurate soil moisture and thermal properties estimation without soil-specific calibration. The mean errors of the Cv and θ decrease with the extended heating duration. When the heating lasts 20 s, the measured Cv and θ have mean errors of 0.02 MJ m−3 K−1 and 0.01 m3/m3, respectively, for various moisture conditions. In the field test, the spatio-temporal distribution of soil moisture and thermal properties can be obtained in real time. Thereby, the proposed DPHP-FBG monitoring system is potential to conduct in situ coupled heat and soil moisture measurements at a large scale.

Reducing drought vulnerability of forest soils using Xanthan gum-based soil conditioners

Climate change increases the frequency and severity of droughts in many parts of Europe, thereby affecting the availability of water resources. Therefore, preserving the soil water content is essential for maintaining forest diversity and plant vitality. To improve soil hydraulic properties and reduce drought vulnerability, three xanthan-gum-based soil conditioners (SC_R, SC_CG, and SC_ZZC) were developed under the European ONEforest project. These soil conditioners (SCs), including oxide ash and cellulose fibres of different lengths, differ in their filler properties. This study evaluated the performance of these soil conditioners in forest soils in Slovenia (S1), Spain (S2), and Germany (S3). Water absorption, water retention, hydraulic conductivity, seed germination, and plant growth in the untreated soils and mixtures were analysed.The results showed a 53% to 100% increase in water absorption with high dosage of SCs (1.7% of dry SC per dry soil mass). The addition of SCs also significantly improved the water retention capacity of the treated soils within a suction range of 0-100 kPa, which is advantageous for maintaining adequate water availability for plant growth. The effect of SCs on unsaturated hydraulic conductivity varies depending on the soil type. For example, at a similar suction, the unsaturated hydraulic conductivity of mixtures with soils S2 and S3 can be more than an order of magnitude lower than that of untreated soils S2 and S3. In contrast, mixtures with soil S1 showed unsaturated hydraulic conductivity similar to that of the untreated soil. In the seeding experiment, plants in treated soils survived for up to 8 d without watering compared to those in untreated soils, with survival linked to the initial water content of the mixtures. These findings suggest that soil conditioners reduce drought vulnerability by improving water retention and regulating water loss. However, the optimal dosage should be adjusted according to different soil types and local environmental conditions.

The application of organic mulch and chicken manure for improving soil water availability and yield of turmeric (Curcuma domestica Val) in an Inceptisol of Jambi, Indonesia

Turmeric (Curcuma domestica Val) is one of the agricultural commodities being developed by the Jambi Province of Indonesia. However, despite the high value of turmeric, its productivity in Jambi Province is low. This is because the crop is mostly cultivated in marginal lands dominated by Inceptisol, which has low fertility and low water availability. Organic mulch and chicken manure have the potential to be used to improve soil water availability and crop yield. This research aimed to evaluate the effect of organic mulch cover and chicken manure on soil water availability and turmeric yield. The treatments tested were combinations of various percentages of organic mulch cover (30%, 60%, and 90%, and chicken manure dosage (0, 5, 10, and 15 t ha-1). The twelve treatment combinations were arranged in a randomized block design with three replications. The results showed that the combination of the percentage of organic mulch cover and chicken manure dosage affected soil organic matter content, soil bulk density, soil pore size distribution, soil water availability, and turmeric yield. The application of 30% cover of organic mulch and 10 t ha-1 of chicken manure was found to be the best combination to improve soil available water and turmeric yield. The regression analysis results showed that soil bulk density, organic carbon, fast-drainage pores, and slow-drainage pores simultaneously affected the soil water content, with an R2 value of 0.85. The results of this study proved that soil available water is also closely correlated with turmeric yield.

Improvement Effect of Straw Interlayer Thickness on Saline-Alkali Soil

In order to evaluate and optimize the application effect of straw interlayer technology in improving soil quality and crop production in saline-alkali soil, and to understand the synergistic relationship between soil water and nutrient distribution, crop roots and above-ground growth in saline-alkali soil, the improvement effect of straw interlayer thickness on saline-alkali soil was studied. Through the indoor root box control experiment combined with the field micro-zone verification experiment, four corn straw interlayer thickens were set (CK: no straw interlayer; S3: Straw layer thickness is 3 cm; S5: The straw layer thickness is 5 cm; S7: straw interlayer thickness is 7 cm), and the effects of straw interlayer thickness on soil water and salt transport and nutrient distribution are simulated. The results showed that straw interlayer could enhance the water retention and salt leaching capacity of 0–40 cm soil layer after irrigation, and S5 treatment had the best effect, with soil water content increased by 11.0% and salt content decreased by 4.0% compared with CK (P < A0.05). Compared with CK, straw separation treatment decreased the soil nutrient content in 0–40 cm soil layer (except alkali-hydrolyzed nitrogen and available potassium), and increased the soil nutrient content in 40–60 cm soil layer, and S5 treatment had the largest increase, in which available potassium was significantly increased by 15.0% compared with CK (P <0.05). Therefore, it shows that the straw interlayer can play a role in preventing water and reducing permeability, and can reduce the salt content of the soil above the interlayer, and has a good effect on the improvement of saline-alkali soil.

Migration patterns of phthalic acid esters from mulch plastic film in the soil-plant-atmosphere continuum system.

Plastic film mulching is an important agricultural practice, but its release of phthalic acid esters (PAEs) poses threats to soil and human health. However, the migration patterns of PAEs during the lifecycle of mulch plastic film (MPF) remain unclear. This study aims to explore the temporal patterns of release of PAEs during the MPF's lifecycle and evaluate the migration patterns of PAEs from MPF in the soil-plant-atmosphere continuum (SPAC) system through pot experiments and model simulations. The results reveal that during the mulching period, 44.90-56.71% of the PAEs released went into the atmosphere and 14.97-18.90% into the soil, while during the residual film period, 24.39-40.13% were slowly released into the soil. Elevated soil water content increased maize transpiration rates, leading to higher concentrations of PAEs in roots, stems, and fruits, but lower concentrations in leaves. In 2020, the estimated total release of PAEs from MPF in northwest China amounted to 35.42 tons. Notably, PAEs predominantly accumulated in the soil, with minimal accumulation in plant tissues. Moreover, PAEs were primarily removed through degradation. Our results elucidate the migration patterns of PAEs from MPF in the SPAC system, facilitating the evaluation of PAE pathways into the human food chain.

Vegetation Restoration Increases the Drought Risk on the Loess Plateau.

The extensive implementation of the 'Grain for Green' project over the Loess Plateau has improved environmental quality. However, it has resulted in a greater consumption of soil water, and its overall hydrological effects remain highly controversial. Our study utilized a coupled land-atmosphere model to evaluate the effects of vegetation changes resulting from revegetation or reclamation on the hydrology of the Loess Plateau. Revegetation was found to stimulate an increase in precipitation, evapotranspiration, and atmospheric water content. However, the increase in precipitation was insufficient to compensate for soil water loss driven by intensified evapotranspiration, resulting in a decrease in both runoff and soil water content. In contrast to revegetation, reclamation would reduce precipitation, although the reduction was less than the decrease in evapotranspiration. This could lead to an increase in both runoff and soil water content. The results provide an important scientific basis for the hydrological effects of vegetation changes on the Loess Plateau, which is particularly important for guiding current and future revegetation activities toward sustainable ecosystem development and water resources management.

Decadal warming-induced changes in abiotic factors and multitrophic diversity drive soil multifunctionality in an alpine meadow

Climate warming can be detrimental to biodiversity and ecosystem multifunctionality. Numerous studies have examined the effect of warming on ecosystem multifunctionality; however, little is known about how long-term warming affects ecosystem multifunctionality and its seasonal dynamics. Here, we determined the effects of long-term (10 years) in-situ soil warming on multitrophic diversity (plants, soil bacteria, soil fungi, arthropods, and nematodes) and soil multifunctionality in an alpine meadow. The effects of warming on multitrophic diversity were inconsistent, showing a positive effect on soil microbial diversity, including bacterial diversity and fungal diversity, in the upper layer (0–10 cm), a negative effect on plant diversity, and no effect on soil fauna diversity in either the upper (0–10 cm) or lower soil layers (10–20 cm). Warming had a minor effect on soil multifunctionality, and reduced seasonal differences in soil multifunctionality in upper soil layers, but expanded the differences in the lower soil layers. Based on structural equation models, both abiotic factors (soil water content and soil pH) and biotic factors (microbial diversity and fauna diversity) jointly influenced soil multifunctionality, with abiotic factors having a greater effect than biotic factors. The findings provide insights in the important effects of long-term warming on seasonal dynamics of soil multifunctionality, and the crucial role of multitrophic diversity for maintaining the sustainable development of the alpine ecosystem under climate warming.

Effects of different mulching technologies on rainfed maize field energy exchange and evapotranspiration partitioning in northwest China

Artificial mulching, a prevalent water-saving tool in arid and semiarid agroecosystems, complicated energy exchange and water transport process between land surface and atmosphere. The field energy and evapotranspiration (ET) partitioning within a soil-mulch-plant-atmosphere continuum have not been comprehensively examined, which limited cognition of the underlying mechanisms that control hydrological processes and achieve yield improvement. Here, a four-season experiment in a rainfed summer maize field with four mulching treatments (NM: non-mulching, SM: straw mulching, RPBF: plastic-mulched ridge with bare furrow, and RPSF: plastic mulched ridge with straw-mulched furrow) was conducted to study the dynamics of surface energy and ET components and their regulation mechanisms. Results indicated that the effects of mulching on field energy partitioning were most evident at the maize initial stage, during which net radiation was significantly decreased under PM treatments (RPBF and RPSF), while soil heat flux was significantly reduced in SM treatments (p < 0.05). The average latent heat flux (LE) was 3.55 and 5.65 MJ·d−1 for NM maize at sowing and seedling stages, but decreased by 9.01 %, 27.04 %, 29.58 % at sowing, and 7.08 %, 9.56 % and 16.46 % at seedling stages for SM, RPBF and PRSF, respectively. The energy component differences among different treatments were minimal during the middle and late stages with high leaf coverage, and total LE and sensible heats were not significantly different. Mulch exerted a notable impact on soil evaporation (E) and crop transpiration (T), characterized by the average E of 0.96, 0.82, 0.57 and 0.46 mm·d−1 in NM, SM, RPBF and RPSF, while the value for T was 1.67, 1.88, 2.03 and 2.10 mm·d−1, respectively. PM conserved soil water by reducing E during the initial growing season and in dry periods, but also enhancing T and deepening the depth of soil water consumption under higher leaf cover. Energy exchange and ET partitioning were found to be more sensitive to soil water content (SWC) during periods characterized by lower leaf coverage, while the role of underlying canopy coverage characteristics overwhelmed soil properties in controlling energy and ET partitioning along with the leaf expansion. These findings contributed to a more comprehensive understanding of different mulching management on rainfed maize energy exchange and water use in Northwest China.

Effect of In Situ Polymerization of Super Absorbent Polymers on the Protection of Earthen Heritage Sites in Semi-Arid Regions

As precious cultural heritage, earthen sites are susceptible to various natural factors, leading to diverse forms of degradation. To protect earthen sites, the effects of super absorbent polymers (SAPs) on soil water retention, physical properties, and color compatibility at different concentrations were studied. After applying SAP treatment to an earthen site with different degrees of weathering, we drew the following conclusions. SAP-2 improved soil water retention capacity, increased soil water content, and slowed down the precipitation of soluble salts. At the same time, SAP-2 had the least effect on soil color difference and reduced the development of cracks by filling soil pores and enhancing the cohesion between soil particles, thus giving the earthen sites better weathering resistance. Therefore, the results provide a useful reference for the surface cracking of earthen sites in semi-arid areas and the degradation caused by flaking and block spalling.

Investigating soil properties and their effects on freeze-thaw processes in a thermokarst lake region of Qinghai-Tibet Plateau, China

Soil parameters form the foundation of hydrogeological research and are crucial for studying engineering construction and maintenance, climate change, and ecological environment effects in cold regions. However, the soil properties in the permafrost region of the Qinghai–Tibet Plateau (QTP) remain unclear. Hence, in this study, soil temperature (Ts), volumetric specific heat capacity (C), thermal conductivity (K), thermal diffusivity (D), soil water content (SWC), electric conductivity (EC), vertical (Kv) and horizontal (Kh) saturated hydraulic conductivity, bulk density (ρb), and soil texture near the Qinghai-Tibet Railway were measured, and their effects on the freeze-thaw process were evaluated. The results revealed a predominantly sandy loam soil texture, with Kh and Kv showing strong spatial variability, while the other parameters presented moderate spatial variability. Thermokarst lake had a limited influence on D, C, K, and ρb but significantly reduced Kh and Kv. Groundwater affected SWC, Ts, and EC. The model results showed that all parameters indicated small sensitivities to the maximum thawing depth (MTD), with MTD positively responding to all parameters except for Kv and porosity (ρp). Except for Kh and Kv, all parameters showed high sensitivities to the time from starting to complete freezing (TSCF). TSCF responded positively to C, ρp, and density (ρd) and negatively to K and Kh. This study expanded the quantification of soil properties in the QTP, which can help improve the accuracy of cryohydrogeologic models, thus guiding the construction and maintenance of infrastructure engineering.

Regulatory mechanism of soil and water conservation measures on understorey erosion in a subtropical hilly region

Vegetation restoration affects soil erosion by altering near soil-surface characteristics and hydrodynamic mechanisms. However, the regulatory mechanisms of vegetation restoration in reducing soil erosion under forests are not fully clear. Five soil and water conservation measures (SWCM) with different vegetation structures and characteristics were used in the pure forest of Pinus massoniana which included the grass and shrub, grass, grass and shrub + level furrow, grass, shrub and trees and grass + fish-scale pits, to analyze the impact of vegetation restoration on near soil-surface characteristics and soil erosion. The data were analyzed using Structural Equation Modeling (SEM) to find the key indicators affecting soil erosion under forest. The findings revealed that, as opposed to the control plots (CK), there were significant alterations in the near soil-surface attribute following the application of SWCM. These changes were characterized by an increase in soil porosity, soil water content, soil nutrient content, root biomass, litter, and vegetation cover, and a decrease in soil compaction, disintegration coefficient, and bulk density, with the most significant improvement occurring in 0–10 cm soil layer. The SWCM significantly reduced soil erosion, with runoff and soil loss reduction ranging from 60.46 % to 74.09 % and 67.62 % to 79.99 %, respectively. Structural equation models revealed the influence of SWCM on soil erosion. Specifically, soil water content and litter had a favourable influence on reducing soil erosion, root biomass had a direct positive impact on soil erosion, and vegetation cover directly leads to a reduction in soil erosion. Soil physical properties primarily influenced soil erosion through their effect on vegetation cover. Combining bioengineering and vegetation measures is superior at enhancing soil structure, improving nutrient content, and decreasing soil erosion compared to single vegetation measures. It is recommended to combine bioengineering with vegetation strategies to effectively curb understory forest erosion and enhance soil quality in pine forests.

Disentangling the Impacts of Environmental Factors on Evaporative Fraction Across Climate Regimes

AbstractEvaporative fraction (EF) is a useful measure for quantifying land surface energy partitioning processes and determining evaporative regimes; however, its influencing factors remain highly uncertain. Here, global data sets were compiled to disentangle the effects of environmental variables on EF variations along climate and land surface gradients. We found that (a) at annual timescales, ecosystem‐level EF could be expressed as a power law function of aridity index. The relationships of mean annual soil water content (SWC) and leaf area index (LAI) with mean annual EF resembled the traditional evaporative regime theory; (b) at daily timescales, the boosted regression tree method quantitatively revealed that the impacts of environmental variables (including meteorological variables) on EF showed equal importance, especially at humid sites, primarily due to the different response direction and magnitude of latent heat (LE) and sensible heat (H) fluxes to environmental changes. Particularly, the contrasting responses of LE (positive) and H (negative) to SWC, LAI, and relative humidity enhanced the positive effects of those influencing variables on EF; whereas, the correlations between EF and energy‐related factors (i.e., net radiation‐Rn and air temperature‐Ta) deteriorated as both LE and H showed positive response patterns to those variables; (c) meteorological factors were also found to have nonlinear effects on daily EF, further modified by climatic conditions. Rn near 150 W/m2 and Ta near 15°C appeared to be important energy‐partitioning thresholds at drier and humid sites, respectively. Moreover, changing interactions among environmental variables with climates were demonstrated to be important for better explaining EF variations.

Model ensemble techniques of machine learning algorithms for soil moisture constants in the semi‐arid climate conditions

AbstractIn recent years, the use of prediction models based on intelligent algorithms has become widespread in soil science. However, each algorithm has advantages and disadvantages, and variable results can occur on different datasets. The evaluation of ensemble techniques for solving these problems is the current approach. Water problems will arise due to global warming, and soil water will become more important. This study aims to evaluate the predictive accuracy of different machine learning algorithms (support vector machine regression (SVR), random forest (RF), artificial neural network (ANN), and multivariate linear regression (MLR)) and ensemble techniques (equal weight [EQ], Bates–Granger‐BG), Granger–Ramanathan (GR), Akaike information criterion (AIC), and Bayesian information criterion (BIC)) on the field capacity (FC), wilting point (WP) and available water content (AWC) of soils. As a result, higher prediction accuracy was obtained with the RF algorithm than with the value machine learning algorithm in the estimation of moisture constants. The coefficients of determination (R2) obtained for the prediction of FC, WP, and AWC via the RF algorithms were 0.624, 0.759 and 0.641, respectively. MLR had the highest error rate. Among the ensemble techniques, GR was the most successful. Lin's concordance correlation coefficient (LCCC) values obtained from the estimation of FC, WP, and AWC with the GR model were 0.801, 0.894, and 0.801, respectively. The root mean squared error (RMSE) and mean absolute error (MAE) values obtained in the estimation of the available water content with the MLR algorithm were 1.905 and 1.435, respectively, whereas these values were 1.173 and 0.767, respectively, when the GR model was used. As a result of the present study, better predictive results were obtained with ensemble techniques instead of evaluating the algorithms individually.