Soil Water Content Research Articles

Effects of Soil Compaction Stress Combined with Drought on Soil Pore Structure, Root System Development, and Maize Growth in Early Stage

Soil compaction is a major environmental stress to root development and plant growth. Meanwhile, drought always results in increasing soil mechanical impedance, which in turn aggravates soil compaction stress. In this study, a column experiment with three levels of compaction stress (low, moderate, and severe) and two levels of soil water content (well-watered and drought,) was established to investigate the effects of soil compaction combined with drought on soil pore structure, root development, and maize growth properties. The results showed that soil compaction combined with soil water stress significantly affected the characteristics of soil pore structure. With the increase in soil compaction, the porosity, larger pores (>500 μm), and maximum pore diameter significantly decreased (p < 0.05) regardless of soil water status. Additionally, both pore morphology and network parameters also deteriorated under soil compaction with drought conditions. Soil compaction substantially affected the root length, root volume, root surface area, and root average diameter in the whole profile (p < 0.05). Compared to well-watered conditions, the effects of soil compaction on root characteristics under drought conditions were more obvious, which indicated that appropriate soil water content could alleviate compaction stress. The aboveground biomass and plant height showed a consistent trend with root traits under soil compaction stress regardless of water status. A Pearson’s correlation analysis showed that there were significant correlations between most soil pore parameters and maize growth traits. In addition, soil compaction showed a significant effect on both stomatal conductance and transpiration rate while soil water showed a significant effect on SPAD (Soil Plant Analysis Development).

Effects of different sand fixation plantations on soil properties in the Hunshandake Sandy Land, Eastern Inner Mongolia, China.

Planting forests is an effective way to improve desertification. In order to elucidate the impacts of different vegetation types on soil development and restoration of degraded lands, we compared the properties of soils at different depths in three plantation forests in the Hunsandak Sandy Land in the Chinese agro-pastoral ecotone (Ulmus pumila, Pinus sylvestris var. mongolica, and Populus simonii). The results show that all three plantation forests were able to significantly improve the soil properties, and they resulted in soil nutrient enrichment in the surface layer. As the soil depth increased, the soil became progressively poorer in nutrients, the fine particle content decreased, and the bulk density and water content increased. The orders of the fractal dimension characterization and soil improvement effects of the different tree species were as follows: U. pumila > P. sylvestris var. mongolica > P. simonii. Compared with the bare sand, the soil bulk density under the U. pumila plantation was 19% lower; the soil water content was 74% higher; the soil organic matter, total N, P, and K were 336%, 207%, 106%, and 31% higher; the available N, P, and K were 41%, 125%, and 21% higher; and the clay and silt contents were 498% and 387% higher, respectively. The ranges of the soil fractal dimension were 1.67-2.08 for the bare sandy land and 2.14-2.32 for the planted forests. The soil fractal dimension was strongly correlated with the soil physicochemical properties, especially with the soil nutrients and fine particle content, which exhibited highly significant correlations (p < 0.01), and the correlation coefficients were all greater than 0.8. Therefore, we believe that U. pumila is a suitable sand-fixing plant species in this area. In addition, the soil fractal dimension can be used as an important reference index for characterizing soil properties in sandy areas.

Low-Cost Sensors for the Measurement of Soil Water Content for Rainfall-Induced Shallow Landslide Early Warning Systems

Monitoring soil water content (SWC) can improve the effectiveness of early warning systems (EWSs) designed to mitigate rainfall-induced shallow landslide risk. In extensive areas, like along linear infrastructures, the adoption of cost-effective sensors is critical for the EWS implementation. The present study aims to evaluate the reliability of different low-cost SWC sensors (frequency domain reflectometry and capacitance-based) in capturing soil moisture conditions critical for EWS, without performing soil-specific calibration. The reliability of the low-cost sensors is assessed through a comparative analysis of their measurements against those from high-cost and well-established sensors (time domain reflectometry) over a two-year period in a shallow landslide-prone area of Oltrepò Pavese, Italy. Although no landslides are observed during the monitoring period, meteorological conditions are reconstructed and statistical analysis of sensor’s responses to different rainfall events is conducted. Results indicate that, despite differences in absolute readings, low-cost sensors effectively capture relative SWC variations and demonstrate sensitivity to rainfall events across both cold and warm periods. The presented low-cost sensors can serve as reliable indicators of soil infiltration and saturation levels, highlighting their potential for real-time monitoring within extensive networks for EWS.

Identification of optimum scopes of environmental drivers for schistosome-transmitting Oncomelania hupensis using agent-based model in Dongting Lake Region, China.

Oncomelania hupensis (O. hupensis), the sole intermediate host of Schistosoma japonicum, greatly influence the prevalence and distribution of schistosomiasis japonica. The distribution area of O. hupensis has remained extensive for numerous years. This study aimed to establish a valid agent-based model of snail density and further explore the environmental conditions suitable for snail breeding. A marshland with O. hupensis was selected as a study site in Dongting Lake Region, and snail surveys were monthly conducted from 2007 to 2016. Combined with the data from historical literature, an agent-based model of snail density was constructed in NetLogo 6.2.0 and validated with the collected survey data. BehaviorSpace was used to identify the optimal ranges of soil temperature, pH, soil water content, and vegetation coverage for snail growth, development and reproduction. An agent-based model of snail density was constructed and showed a strong agreement with the monthly average snail density from the field surveys. As soil temperature increased, the snail density initially rose before declining, reaching its peak at around 21°C. There were similar variation patterns for other environmental factors. The findings from the model suggested that the optimum ranges of soil temperature, pH, soil water content and vegetation coverage were 19°C to 23 °C, 6.4 to 7.6, 42% to 75%, and 70% to 93%, respectively. A valid agent-based model of snail density was constructed, providing more objective information about the optimum ranges of environmental factors for snail growth, development and reproduction.

Forest soil CO2 emission in Quercus robur level II monitoring site

Abstract In this study, the soil CO2 emission was analysed at the level II ICP Forests monitoring plot in Serbia in the pedunculate oak forest. Two plots of pedunculate oak (Quercus robur L.) were selected for this study. The main question was to determine the differences in the impact of management (human impact) on CO2 emission. Different time periods were compared to identify the main factors affecting soil CO2 emission. Sampling was done by chambers. During the study period, climate indicators were quite different. A strong positive correlation between the soil temperature and soil CO2 emission, as well as a strong negative correlation between the soil moisture and soil CO2 emission, was found in the spring aspect (Plot). In other cases, a moderate to weak correlation was found. Multiple linear regressions showed that CO2 emission from soil was primarily controlled by soil moisture. Increasing soil water content had a positive effect on soil respiration (except in spring). The effect of soil temperature appeared in the multiple regressions as a secondary factor during the period studied, and an increase in temperature resulted in a decrease in soil respiration (except in spring).

Using stem water potential derived from continuous reading sensors for irrigation scheduling: nectarine as a test case

AbstractWe investigated on-site soil and plant based sensors translated to stem water potential for nectarine orchard irrigation control on heavy clay soil. Irrigation targeted predetermined stem water potential (SWP) thresholds for each phenological stage. Sensors were compared to SWP in six trees in a drying and wetting plot where irrigation was withheld periodically, allowing SWP to reach moderate water stress. Other sensor readings were regressed on SWP for those times, and the regressions were used for irrigation scheduling. The latter kept stage I and III SWP at ~ − 0.9 MPa, and moderate water stress in stage II (SWP ~ − 1.5 MPa). Weekly adjustments were made according to the thresholds. Results showed that tensiometers could be used for stages I and III, as they were very sensitive. However, when stress was applied soil water tension exceeded tensiometer range at 30 cm depth.Soil water content sensors had slower responses than the others, so they might be difficult to use for precise irrigation in heavy soils. Dendrometers responded quickly and therefore might be more useful for management even in moderate water stress, even with their sensitivity to climatic conditions. Analysis showed to maintain SWP within ± 0.1 MPa, 2 tensiometers, 10 soil water content sensors and 7 dendrometers stations are needed. Signal-to-noise (SNR) ranks were SWP &gt; 30 cm tensiometers &gt; 60 cm tensiometers &gt; dendrometers &gt; 30 cm soil water content &gt; 60 cm soil water content sensors for the full season. Nonetheless, in some stages tensiometer SNR was greater than that of SWP.

Enhancing streamflow prediction in a mountainous watershed using a convolutional neural network with gridded data.

In this research, we demonstrate the effectiveness of a convolutional neural network (CNN) model, integrated with the ERA5-Land dataset, for accurately simulating daily streamflow in a mountainous watershed. Our methodology harnesses image-based inputs, incorporating spatial distribution maps of key environmental variables, including temperature, snowmelt, snow cover, snow depth, volumetric soil water content, total evaporation, total precipitation, and leaf area index. The proposed CNN architecture, while drawing inspiration from classical designs, is specifically tailored for the task of streamflow prediction. The model's performance, assessed during both the training and testing phases, demonstrates high accuracy, reflected quantitatively in metrics such as RMSE, MAPE, R2, and NSE. Notably, the model exhibits enhanced accuracy in predicting lower flow rates, particularly in autumn and winter, as evidenced by an average RMSE of 2.02 m3/s for flows below 13.8 m3/s. In contrast, the model's precision decreases in high flow rate scenarios, predominantly in spring and early summer. The implementation of forward feature selection (FFS) has further optimized the model, pinpointing total evaporation and volumetric soil water as key parameters, thus enabling a more efficient model with accuracy comparable to the initial, more complex version. This research underscores the practical utility of an image-based approach using CNN models for streamflow prediction. Moreover, the adoption of the freely available and universally accessible ERA5-Land dataset highlights its effectiveness as a valuable and cost-efficient tool for streamflow prediction.

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).

Modeling tree responses to soil water variability guides irrigation to account for soil winter reserves

AbstractHigh‐yield almond (Prunus amygdalus) production requires irrigation to support soil water availability throughout the summer. We aimed to develop tools that project almond trees’ water requirements and then integrate them into irrigation management. We postulated that deficit irrigation would limit root allocation and reduce irrigation efficiency. Thus, we monitored soil water availability (soil water content and potential evapotranspiration) and tree physiology (transpiration and trunk circumference) under 600, 900, or 1250 mm summer irrigations. A soil‐tree model was trained to predict trees’ transpiration as the soil dried between irrigation events. The model included an empirical function for tree transpiration at variable soil water potentials (50% loss by −1 MPa). Field records corroborated the soil‐tree model projections that 600 mm irrigation reduces soil water potential to −1 MPa and limits transpiration after winter soil water reserves deplete. Trees at deficit irrigation did grow deep roots to extract soil winter reserves, thus disputing our original notion. A 900 mm irrigation matched transpiration and maintained soil at −0.6 MPa. The 1250 mm irrigation exceeded transpiration and narrowed trees’ water uptake to the upper 50 cm. The reciprocity between soil water and transpiration dictates that predetermined irrigation would limit or exceed transpiration. The soil‐tree model could project transpiration responses to soil water variability, thereby supporting irrigation by trees’ transpiration. The model uses soil water dynamics, rather than insular water potential measures, to account for spatial discrepancies between water application and uptake depths. Hence, the soil‐tree model lays a computational framework for precision irrigation by automated sensory.

A centrifuge modelling setup for dewatering, rewetting, and characterizing soil deposits

Dewatering in soils serves various purposes in the field of geotechnical engineering as well as other disciplines. In geotechnical engineering, dewatering is effective for improving stability, reducing settlements, and limiting seepage of contaminated pore fluid. This study details the development of an experimental setup that enables dewatering and rewetting soil deposits in-flight in a geotechnical centrifuge while the pore pressures/suctions and moisture contents are measured. Cone penetration tests and shear wave velocity measurements are also used to characterize the material in-flight. Detailed discussion is provided regarding the construction of the tensiometers and calibration of the moisture content probes. Tests are performed on two coal combustion products (CCPs) to exemplify the capabilities of the equipment. Illustrative test results provide time histories and profiles of soil suction and water content at different depths, agreeing well with measurements from laboratory soil-water retention curves. The results also show that dewatering of the CCP deposits leads to significant increases in strength and stiffness, and that after subsequent rewetting, the material maintains a permanent increase in stiffness. The developed system enables an economical and reliable study of the impacts related to dewatering and rewetting cycles to fulfill research purposes in a broad range of engineering disciplines.

Optimizing plastic film mulch to improve the yield and water use efficiency of dryland maize in the Loess Plateau, China.

Knowledge on the variation of yield and water use efficiency under different mulching methods is important for guiding rained maize production in the Loess Plateau area. In this study, eight different plastic film mulching methods was established to analyze the maize growth, soil water content and soil temperature changes of dryland maize, and increase yield and water use efficiency (WUE). The field experiment was conducted in 2019, and eight treatments were set up, including a traditional flat planting without mulching (CK), ridge-furrow with ridges mulching black plastic film and furrows mulching straw (HJ), ridge-furrow with ridges mulching black plastic film and furrows bare (HL), ridge-furrow with ridges mulching liquid plastic film and furrows mulching straw (YJ), ridge-furrow with ridges mulching liquid plastic film and furrows bare (YL), ridge-furrow with ridges mulching biodegradable plastic film and furrows mulching straw (SJ), ridge-furrow with ridges mulching biodegradable plastic film and furrows bare (SL) and ridge-furrow with ridges bare and furrows mulching straw (NJ). Furthermore, the AHP-TOPSIS was employed to evaluate the optimal mulching method for maize. The results showed that compared with CK and NJ treatment, the soil water content and soil storage were significantly changes with other treatments in the reproductive period of maize. Among the six mulching methods, maize yield in HJ, HL, YJ, YL, SJ, and SL treatments were 46.28%, 61.95%, 70.30%, 51.02%, 52.02% and 53.53% significantly greater than CK treatment. In addition, dryland maize WUE was 66.53% and 84.01% higher in the YJ and YL treatments with ridges mulching liquid plastic film than in the CK treatment, respectively. The optimal treatments of economic benefits were YL and HJ. Through AHP-TOPSIS comprehensive analysis, the optimal mulching methods were YL and HJ treatment. Current field trials indicate that YL treatment could serve as a promising option to improve dryland maize yield, WUE, and reducing environmental risks in the Loess Plateau of China.

Long-term alfalfa planting mediates the coupling of soil water and organic carbon storage in a semi-arid area of the Loess Plateau, China.

The key to restoring arid and semi-arid ecosystems is maintaining soil water and organic carbon contents. Alfalfa (Medicago sativa L.) is a high-yield perennial forage crop and performs ecological functions as a drought-resistance leguminous herb. It has been widely planted for reconstruction of degraded soils in the Loess Plateau in northwestern China, but long-term planting may affect soil carbon-water coupling and lead to crop yield reduction. To maximize the benefits of reconstructed grassland, this study explored the couplings of soil water, organic carbon, and alfalfa productivity along a reconstruction chronosequence in a semi-arid area of the Loess Plateau. Space-for-time substitution approach was used to select different-aged stands of reconstructed grassland (1, 5, 7, 10, 15, 20, 30 years old). Alfalfa above-ground biomass (AGB), soil water storage (SWS), organic carbon storage (SOCS), and carbon-water coupling coordination degree (D) were measured in the 0-100 cm soil profile. Alfalfa AGB reached a peak in the 7th year, and the degradation began in the 10th year. Both SWS and SOCS varied nonlinearly with stand age. The greatest loss of SWS occurred in the 15th year (80-100 cm depth), whereas the largest increase of SOCS occurred in the 30th year (0-20 cm depth). There was a negative feedback relationship between AGB and SWS over the 30-year study period (Pearson r = -0.835, P = 0.098). AGB and SOCS initially showed a trade-off within the first 10 years (Pearson r = -0.7431, P = 0.2569), in contrast to their positive feedback in the 20-30th years (Pearson r = 0.9978, P = 0.0421). A decoupling between SWS and SOCS (D < 0.6) was observed after 12 years of alfalfa planting. For agricultural production, a greater supply of water and organic fertilizer is required from the 7th year of alfalfa planting, and reseeding may be needed around the 10th year to prolong the life of alfalfa community. Alfalfa should be planted for no more than 12 consecutive years in the study area for ecological protection.

To Investigate the Impact of Land Use Change on the Potential Groundwater Recharge on Hillslope With Deep Loess Deposits

ABSTRACTAccurately estimating groundwater recharge in hilly areas with limited water and thick vadose zones is challenging. This study investigated the impact of land use changes on groundwater recharge at a hillslope scale of Yuanzegou Watershed in China's Loess Plateau. Three adjacent hillslopes were selected for three different land uses: arbor (jujube, Ziziphus jujuba Mill.), subshrub (native grass, Artemisia gmelinii), and crop (millet, Setaria italica). Soil cores (as deep as 10–16/18 m) were collected at each of the three landscape positions on a hillslope. Reported tritium profiles in the watershed were used to estimate the net chloride input into vadose zone on hillslope associated with inverse chloride mass balance (CMB) method/chloride accumulation method (CAM). Soil water content and chloride profiles in the study were measured to determine recharge rates at each landscape position beneath different vegetation types. For the first time, we evaluated the actual chloride input into vadose zone on hillslopes as 540.2 ± 23.8 mg m−2 yr.−1, excluding the impact of runoff. Then, estimated recharge rates ranged from 42.7 ± 3.5 to 62.4 ± 4.7 mm yr.−1, consistent with nearby studies. Results showed that groundwater recharge does not change with landscape position except for higher value on upslope beneath subshrub hillslope. In contrast, groundwater recharge did significantly reduce by 12.9% ± 5.4% and 26.5% ± 4.5% after conversion from cropland to subshrub/arbor on the hillslope, respectively. Our findings contribute to understanding the ecohydrological effects of land use changes on groundwater recharge on hillslope and help to select suitable afforested vegetation for greening efforts in water‐limited hilly areas, with a priority on groundwater safety.

Experimental investigation on treatment of high-water-content dredged slurry with vacuum preloading-airbag pressurization

This paper offers valuable insights for advancing the consolidation of dredged slurry, alleviating blockage, and the application of vacuum preloading-airbag pressurization (VP-AP) technology in engineering practice. This study conducted laboratory model tests on the consolidation of sludge using prefabricated vertical drains-vacuum preloading, prefabricated horizontal drains-vacuum preloading, and VP-AP methods to further investigate the effectiveness of the VP-AP technique in strengthening the consolidation of dredged slurry. Comparative analysis was conducted on the macroscopic and microscopic differences in soil drainage characteristics, settlement, water content, shear strength, and soil particle morphology under the three treatment methods. The results show that the VP-AP method surpasses traditional vacuum preloading techniques in soil consolidation, effectively guaranteeing the consolidation of deep soil layers and enhancing the uniformity and stability of foundation strength. In addition, the microstructural analysis reveals that the VP-AP method can effectively mitigate the decrease in drainage efficiency caused by the clogging of the PVD and improve the structure of the soils, allowing a significant increase in the mechanical properties of the soils. In conclusion, the VP-AP technology demonstrates significant advantages in drainage efficiency, consolidation effectiveness, thus it has a widespread application potential in engineering practices for treating soft ground and deserves further in-depth study.

Intercropping increases plant water availability and water use efficiency: A synthesis

Intercropping, involving the incorporation of annual crops with alternative crops or non-crop cash crops, has the potential to enhance water conservation and stabilize agroecosystems. However, few studies have comprehensively explored the effects of intercropping on water cycling. Here, we investigated the impacts of intercropping on five crucial water cycle processes (states): soil water content (SWC), runoff (RO), soil evaporation (E), leaf transpiration (LT), and water use efficiency (WUE). To this end, a meta-analysis was carried out utilizing a global dataset comprising 1285 paired observations from 64 publications. We found that intercropping reduced SWC (1.31 %), RO (29.17 %), and E (10.30 %), but increased LT (9.85 %) and WUE (29.46 %). The effects of intercropping on SWC, E, and RO did not exhibit significant fluctuations over the course of a year, but SWC initially decreased then increased in multi-year planting durations. Moreover, the intercropping effect was contingent upon climatic conditions (mean annual precipitation and temperature), soil characteristics (organic matter content, bulk density, and total nitrogen content), and agricultural practices (crop type, fertilization, and irrigation). We determined that resource complementarity, abiotic facilitation, and biotic feedback mechanisms may underlie the effect of intercropping on the water cycle. This research underscores the potential of using intercropping to improve plant water usage and the sustainability and productivity of cropping systems.

Nitrogen addition alleviates the negative effects of reduction in precipitation on soil multifunctionality in a typical steppe

The increasing frequency of drought events and nitrogen deposition have fundamentally changed soil microbial functions in terrestrial ecosystems. However, most studies have mainly concentrated on the impact of a single environmental factor on ecosystem functions; how drought and nitrogen enrichment interactively affect soil multifunctionality remains largely unknown. In this study, the effects of different drought scenarios [intense drought (ID), chronic drought (CD), and reduced rainfall frequency (RF)] and nitrogen addition on soil microbial biomass, and soil multifunctionality (determined using soil enzyme activity) were examined in the fourth year of a field manipulative experiment conducted in a typical steppe in northern China. The results demonstrated that both ID and CD significantly reduced soil multifunctionality, microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN). The CD treatment also decreased the ratio of MBC to MBN, while RF had less impacts on soil multifunctionality and the biomass of soil microbes. In contrast, nitrogen addition enhanced soil multifunctionality, MBC and MBN. Structural equation modeling analysis demonstrated that drought decreased soil multifunctionality directly and indirectly by reducing MBN and soil water content, whereas nitrogen addition increased soil multifunctionality mainly by increasing MBN and soil inorganic nitrogen. This study provides the first experimental evidence of the opposing impacts of reduction in precipitation and nitrogen enrichment on soil microbial biomass and soil multifunctionality in a semiarid typical steppe, and suggests that nitrogen fertilization could be an effective measure to alleviate the negative effects of climate drought on soil functions in nitrogen- and water-limited grassland ecosystems.

Understanding and simulating of three-dimensional subsurface hydrological partitioning in an alpine mountainous area, China

AbstractCritical zone (CZ) plays a vital role in sustaining biodiversity and humanity. However, flux quantification within CZ, particularly in terms of subsurface hydrological partitioning, remains a significant challenge. This study focused on quantifying subsurface hydrological partitioning, specifically in an alpine mountainous area, and highlighted the important role of lateral flow during this process. Precipitation was usually classified as two parts into the soil: increased soil water content (SWC) and lateral flow out of the soil pit. It was found that 65%–88% precipitation contributed to lateral flow. The second common partitioning class showed an increase in SWC caused by both precipitation and lateral flow into the soil pit. In this case, lateral flow contributed to the SWC increase ranging from 43% to 74%, which was notably larger than the SWC increase caused by precipitation. On alpine meadows, lateral flow from the soil pit occurred when the shallow soil was wetter than the field capacity. This result highlighted the need for three-dimensional simulation between soil layers in Earth system models (ESMs). During evapotranspiration process, significant differences were observed in the classification of subsurface hydrological partitioning among different vegetation types. Due to tangled and aggregated fine roots in the surface soil on alpine meadows, the majority of subsurface responses involved lateral flow, which provided 98%–100% of evapotranspiration (ET). On grassland, there was a high probability (0.87), which ET was entirely provided by lateral flow. The main reason for underestimating transpiration through soil water dynamics in previous research was the neglect of lateral root water uptake. Furthermore, there was a probability of 0.12, which ET was entirely provided by SWC decrease on grassland. In this case, there was a high probability (0.98) that soil water responses only occurred at layer 2 (10–20 cm), because grass roots mainly distributed in this soil layer, and grasses often used their deep roots for water uptake during ET. To improve the estimation of soil water dynamics and ET, we established a random forest (RF) model to simulate lateral flow and then corrected the community land model (CLM). RF model demonstrated good performance and led to significant improvements in CLM simulation. These findings enhance our understanding of subsurface hydrological partitioning and emphasize the importance of considering lateral flow in ESMs and hydrological research.

Spatial variability of hydraulic parameters of a cropped soil using horizontal crosshole ground penetrating radar

AbstractSoil hydraulic parameters (SHP) play a crucial role controlling the spatiotemporal distribution of water in the soil–plant continuum and thus affect water availability for crops. To provide reliable information on the SHP at different scales, measurement techniques with a good spatial resolution and low labor costs are required. In this study, we used crosshole ground penetrating radar (GPR)‐derived soil water contents (SWCs) measured along horizontal rhizotubes under a controlled experimental test site cropped with winter wheat to estimate the unimodal and dual‐porosity soil hydraulic characteristics with different soil layer setups. Therefore, sequential inversion of the GPR‐derived SWCs was performed using the hydrological model HYDRUS‐1D, whereby the SWC data were either averaged prior inversion or used in a spatially distributed way. To analyze if the time‐lapse gathered GPR data contain enough information to estimate the SHP, additional synthetic studies were performed increasing the data resolution to daily GPR measurements. The results showed that the time‐lapse data contained enough information to estimate the SHP accurately. Additionally, spatially distributed soil hydraulic characteristics differed from the one estimated based on averaged SWCs derived from spatially distributed GPR data. Finally, we derived spatially resolved SHP, which can be used for 3D process rhizosphere processes and root–soil interaction modeling.

Afforestation Reduces Deep Soil Carbon Sequestration in Semiarid Regions: Lessons From Variations of Soil Water and Carbon Along Afforestation Stages in China's Loess Plateau

AbstractAfforestation represents an effective approach for ecosystem restoration and carbon (C) sequestration. Nonetheless, it poses notable challenges concerning water depletion and soil drought in (semi)arid regions. The underlying mechanisms regulating the influence of afforestation on soil carbon‐water dynamics, particularly how deep soil C reacts to afforestation‐induced soil drying, remain largely unclear. This study examined the variations of soil water content (SWC), soil organic carbon (SOC), and soil inorganic carbon (SIC) in 500 cm depth along four afforestation stages: abandoned grasslands, shrublands, and 20‐year and 40‐year Robinia pseudoacacia forests (RP20 and RP40) in the semiarid Loess Plateau, China. The results indicated that afforestation has significantly increased SWC (+26.6%), SOC (+44.5%), and SIC (+6.5%) in the shallow layer (0–100 cm) but caused evident soil drying (−60.8%), decrease in SOC (−37.8%), and slight reduction in SIC (−0.3%) in the deep layer (300–500 cm) when compared with grasslands. The seriously decline in the coupling coordination between soil C and SWC in the middle and deep layers indicates the unsustainability of afforestation especially for RP40. Structural equation model showed that the negative impact of afforestation on deep SOC through soil water depletion (−0.38) outweighed the direct positive impact of increased aboveground biomass (AGB) (+0.33). The negative impacts of decreased SWC and increased pH on deep SIC was close to the positive impacts of AGB. Afforestation has different effects on SOC and SIC across shallow and deep layers, and its negative effects on deep soil C should be fully integrated into future forest ecosystem restoration and management efforts.

Estimation and Restoration of Dried Soil Layers in a Slope‐Gully Unit of the Chinese Loess Plateau

ABSTRACTDried soil layer (DSL) is a phenomenon of deep soil desiccation caused by soil water content (SWC) deficiency. Relevant studies in the fragmented terrain of Chinese Loess Plateau (CLP) remain limited. In a typical slope‐gully unit near the Liudaogou catchment, SWC was measured using neutron probes on 19 occasions at 15 observational locations. In order to reveal the temporal stability and elimination degree of DSLs, available soil moisture (ASM) and DSL were estimated by representative sites which were determined through the temporal stability method, and the reliability of simulating mean condition of the study area via representative locations was assessed. Results show that: (1) the dynamics of DSL was characterised by complexity and diversity. The ASM within the DSL (DSL‐ASM), ASM within the sandwiched DSL (SDSL‐ASM) and quantitative index (QI) varied within the range of 2.75%–3.11%, 2.98%–4.22% and 0.254–0.356, respectively. (2) The possibility of development and recovery for DSL and SDSL in deep layers were less than that in shallow layers. The maximum depth of DSL (DSLMD) was significantly and negatively related to the standard deviation of relative difference (SDRD) of DSL‐ASM, the maximum depth of SDSL (SDSLMD) was negatively related to the SDRD of SDSL‐ASM. (3) The prediction results of ASM above 300 cm depth were more accurate than other layers (R2 = 0.89). The DSL‐ASM had more accurate ability of prediction than SDSL‐ASM and QI. On the analysis of time stability characteristics of ASM and DSLs, the locations of A2 and C3 can better represent the mean conditions of ASM at three and four soil layers, respectively. C2, A1 and A1 can better represent the average levels of DSL‐ASM, SDSL‐ASM and QI, respectively (R2 = 0.43, 0.14 and 0.18). (4) The restoration degrees of DSLs mainly showed no elimination and slight elimination, the DSLs cannot be completely eliminated within a short time. We proposed that scientific regulation of SWC can alleviate the formation and development of DSLs at a certain extent, and provide the possibility for DSLs nonoccurrence.