Soil Water Transport Research Articles

Simulating coefficient of soil moisture content uniformity of sprinkler irrigation systems using a COMSOL-3D model

Water distribution uniformity is important for assessing the hydraulic performance of sprinkler nozzles and designing sprinkler irrigation systems. However, current studies rarely consider the redistribution abilities of sprinkler water in the soil and judge whether a sprinkler system is qualified based only on the coefficient of uniformity on the ground (CUg), which leads to a serious underestimation of the actual irrigation effect of sprinkler irrigation projects. Hence, this study establishes and validates a COMSOL-3D model to simulate the movement of soil water during sprinkler irrigation. Moreover, the effects of the soil hydraulic and irrigation parameters on the coefficient of soil moisture content uniformity (CUs) were explored. The results showed that 1) the Nash-Sutcliffe efficiency coefficient (NSE) of the vertical wetting front (VWF) and soil moisture content (SMC) in the two sets of validation experiments was 0.965 and 0.862 and 0.867 and 0.900, respectively. 2) Owing to the differences in soil saturated hydraulic conductivity, after the end of irrigation, the VWF transport rates in vertical direction differed among the three textured soils, with loam exhibiting the highest rate, followed clay loam and silty clay. However, their CUs increased with increasing water transport time, indicating that the water distribution within the sprinkler-wetted zone became increasingly homogeneous as the sprinkler irrigation water was transported and diffused from the top to bottom in the soil. 3) Dimensional analyses showed that CUs were strongly influenced by the initial soil moisture content, irrigation time, and water transport time. 4) In Case 4, when CUg was reduced from 81.9% to 60%, CUs only decreased from 83.2% to 81.4% after 48h of irrigation, indicating that the sprinkler irrigation water had good redistributive ability. This study provides a reference for rationally reducing the CUs of sprinkler irrigation projects and maximising project investments and planting interest.

Employing stable isotopes to reveal temporal trajectories of water travelling through the soil–plant-atmosphere continuum

The spatiotemporal patterns of water travelling through the soil–plant-atmosphere continuum (SPAC) have received much attention due to the frequency of extreme weather and water scarcity. However, the interconnections and transboundary transport of specific compartments within the hydrologic cycle are poorly understood. We portrayed the propagation paths of water isotope signals by analyzing isotopes of precipitation, soil water, and xylem water. The isotope sine curves analysis method was improved to quantify water transfer efficiency, mean transmission time from precipitation to soil (MTT1), mean transmission time from soil to trees (MTT2), mean residence time within soil (MRTSW), and mean residence time within tree xylems (MRTXY). The temporal trajectory of water traveling through SPAC was depicted, and its influencing factors and intrinsic mechanisms were explored. Our results showed that (1) water isotopes were blocked when crossing water pools (precipitation, soil water, and xylem water) and the transfer efficiency was progressively weaker (85.5 %→13.5 %). (2) The MTT1 was significantly and positively correlated with soil porosity (Spearman correlation coefficient, 0.551). Its spatiotemporal pattern (0.8–15.9d) indicated that the transport and mixing of soil water involved two modes: displacement flow and bypass flow. The MTT2 (−13.2d–4.3d) of Platycadus orientalis was in general smaller than that of Quercus variabilis (−4.7d–11.5d). (3) The MRT (35.2d–343.8d) was influenced by a combination of soil physicochemical properties, root distribution, and tree morphological traits. Our study shows that connectivity between pools is better reflected with transfer efficiency. Comparing MTT and MRT of P. orientalis and Q. variabilis, tree hydrodynamic processes were quantified, and P. orientalis was more sensitive to seasonal moisture variability. Additionally, our study improved the understanding of the “black box” within the hydrological interface of plant-soil interactions.

Evaluating soil water and nitrogen transport, nitrate leaching and soil nitrogen concentration uniformity under sprinkler irrigation and fertigation using numerical simulation

Evaluating soil water and nitrogen transport, nitrate leaching and soil nitrogen concentration uniformity under sprinkler irrigation and fertigation using numerical simulation

Straw incorporation: A more effective coastal saline land reclamation approach to boost sunflower yield than straw mulching or burial

In coastal lands, soil salinity greatly impedes crops growth and severely affects the agricultural productivity. Returning the crop straw and residual to soil was considered an important land reclamation method; however, the approach of straw return varied, including mulching (SM), burial (SB), and incorporation (SI). This study aimed to determine which approach was most effective to ameliorate coastal saline land and boost crop yield. Field experiments were conducted under different straw amelioration treatments on dry farming sunflowers (Helianthus annuus Linn.) in Bohai coastal land of Northern China. The results indicated that SM and SB changed the soil salt profile and significantly reduced the topsoil (0–0.2 m) salt content mainly by their direct effects on soil water transport, with little impacts on soil structure changes. Differently, SI significantly increased 21.8 % soil organic carbon and 52.3 % soil mean weight diameter in straw incorporated layer. The improvement on soil aggregates and porosity reduced 24.1–38.9 % of topsoil salt content, by limiting soil salt accumulation and promoting salt leaching. Furthermore, SI significantly boosted the sunflower fine root (d< 1.0 mm) growth and resulted in the highest sunflower yield (4.7 t/ha in 2020 and 4.6 t/ha in 2021) among those straw treatments. Compared to SM and SB, the net revenues of two-years sunflower cultivation under SI were improved by 40.68 % and 31.22 %, respectively. Therefore, it concluded that straw incorporation was more effective to reclaim coastal saline soil than straw mulching or burial. In addition, a back propagation artificial neural network model was developed to predict the dynamic of sunflower yield. This outcome provides an insight into the management of coastal farmland by establishing an easily desalinized and fertile topsoil profile structure.

Compound effects of biochar application and irrigation on soil water and temperature transport

The issue of soil salinization poses a significant barrier to sustainable agricultural development, particularly in arid and semi-arid regions. Finding methods to enhance the quality of salinized soils while conserving water resources has become a pressing challenge. In arid and semi-arid environments, conserving water resources while maintaining soil health is a critical challenge. This study, conducted from 2021 to 2023, aimed to explore the combined effects of irrigation and biochar application on soil physicochemical properties, such as bulk density, porosity, and pH, as well as on Weighted Plane Soil Water Storage (WPSWS), soil temperature, and soil water evaporation. The experimental design included four irrigation levels, based on actual crop evapotranspiration (ETc): I1 (0.6 ETc), I2 (0.8 ETc), I3 (1.0 ETc), and I4 (1.2 ETc), coupled with four amounts of biochar application (AOBA) of 0, 10, 20, and 30 t ha−1, designated as C0, C10, C20, and C30, respectively. Through binary quadratic regression analysis, we sought to identify the optimal combination of irrigation amount and AOBA for enhancing soil quality. The results revealed that as AOBA increased from 10 to 30 t ha−1, soil bulk density decreased by 1.31–8.58% and soil pH by 0.23–1.31%. However, higher levels of AOBA adversely affected WPSWS, with the C10 treatment showing the maximum improvement in WPSWS, registering an average increase of 6.77, 7.49, and 11.16% compared to the C0, C20, and C30 treatments, respectively. We observed that an increase in irrigation amount significantly elevated accumulated soil evaporation (ASE) and WPSWS but led to a reduction in accumulated soil temperature (AST). The most notable soil quality improvements were recorded when irrigation levels were between 340 and 380 mm and AOBA ranged from 10 to 25 t ha−1. This study provides insights into the effective combination of biochar application and irrigation for optimizing soil resilience, thereby offering a sustainable approach to soil management in water-limited environments.

Assessing field scale spatiotemporal heterogeneity in salinity dynamics using aerial data assimilation

Soil moisture and salinity shifts within the root zone can significantly alter crop yields. Thus, spatiotemporal dynamics of these parameters are essential for precision crop management. Airborne or spaceborne earth observation methods based on vegetation and soil observations have sometimes been used with limited success to indirectly understand parameters like soil salinity. These datasets lack spatiotemporal resolution to discern field-scale heterogeneities, and estimates’ accuracy is poor. A Metropolis-Hasting Markov Chain-Monte Carlo (MCMC) based method was developed to estimate field-scale soil salinity by assimilating estimated evapotranspiration (ET) data obtained from aerial canopy temperature sensing with ET outputs from a one-dimensional soil-water transport model. By aligning the two estimated ET values, we inferred anticipated soil salinity levels in a mature pecan orchard (28,951 m2). Our results aligned closely with in-situ measurements with a spatial cross-correlation more than 0.86 and highlighted the expected heterogeneities and nonlinearities. This research offers an approach to refine the current state-of-the-art crop models by accounting for field scale heterogeneities using remotely sensed data. This assimilation method will pave the way for a more inclusive agricultural system modeling that can infer critical but hard-to-measure soil properties from easier-to-obtain remotely sensed datasets. Though this paper concentrates on aerial observations, we anticipate similar methods can be used for satellite-based imagery, especially those with high spatial, temporal, and spectral resolutions.

Effect of Plow Pan on the Redistribution Dynamics of Water and Nutrient Transport in Soils

Plow pans are an essential part of the agricultural soil structure. By adjusting the soil bulk density and plow pan height, the water and nutrient transport are dynamically redistributed. Plow pans play a crucial role in promoting crop growth, increasing yields, and supporting sustainable land management. In this study, a column experiment was conducted to investigate the effects of plow pan height (10 cm and 15 cm) and bulk density (1.2, 1.4, and 1.6 g cm⁻3) on soil nutrient and water leaching under high-volume (HV) and low-volume (LV) fertilizer applications. The results reveal that the leachate volume decreased by 61.9% at a plow pan height of 10 cm and by 96.2% at a plow pan height of 15 cm when the bulk density was increased from 1.2 to 1.4 g cm⁻3 under HV conditions. There was no leachate when the plow pan bulk density was 1.6 g cm−3. The reserved concentration of alkali-hydrolyzable N in the plow pan soils was the highest when the plow pan had a bulk density of 1.4 g cm−3 and a height of 15 cm. However, when the plow pan height was 15 cm, the available P content in the plow pan soils decreased by 27.0% and 21.0% at bulk densities of 1.4 g cm⁻3 and 1.6 g cm⁻3, respectively, when compared with 1.2 g cm⁻3. Furthermore, the available P concentrations in the plow pan and subsoil layers decreased with an increase in the plow pan height. The available K concentrations in the topsoil decreased by 26.8% and 24.0% when the plow pan bulk density was increased from 1.2 to 1.4 g cm−3 at heights of 10 and 15 cm, respectively. Thus, the optimal plow pan height and bulk density are closely related to the types of soil nutrients. However, it is clear that excessively high bulk densities (e.g., 1.6 g cm−3) negatively impact soil properties. For different nutrient requirements, a bulk density of 1.2 or 1.4 g cm−3 can be chosen, with each providing suitable options based on the specific nutrient needs. This research offers practical insights into changes in nutrient adsorption and fixation in agricultural production associated with alterations in plow pan bulk density.

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 &lt; 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 &lt;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.

An adaptive and fast emulsion separation Janus membrane

Inspired by the capillary effect in nature (such as water transport in soils) and droplet-drive performance of Nepenthes, a new driving strategy for emulsion separation membrane based on the synergistic effect of capillary force and progressive wettability-induction force was proposed. It is prepared by a one-step, simple continuous, electrospinning process. By adjusting solutions and spinning parameters, the membrane obtains its capillary structure and progressive oleophilicity in one-step preparation. Attractively, the membrane shows separation efficiency and excellent permeability, with a flux of 384801 L m−2 h−1 bar−1 for the oil-water mixture, and the little water content of less than 18 ppm. And for emulsions, the flux even reaches 50000 L m−2 h−1 bar−1 and the separation efficiency reaches 99.95%. Furthermore, the membrane has excellent mechanical-stability: at 80 kPa transmembrane pressure, it can still effectively prevent water's penetration. Drawing inspiration from nature, the incorporation of capillary force and progressive wettability-induction force into the separation membrane as an additional dual emulsion separation driving force proves to be a highly effective and versatile approach. This method provides a way to solve the general flux-efficiency balance problem of oil-water separation and also provides a new strategy for the preparation of separation membranes for various purposes.

The Link between Surface Visible Light Spectral Features and Water–Salt Transfer in Saline Soils—Investigation Based on Soil Column Laboratory Experiments

Monitoring soil salinity with remote sensing is difficult, but knowing the link between saline soil surface spectra, soil water, and salt transport processes might help in modeling for soil salinity monitoring. In this study, we used an indoor soil column experiment, an unmanned aerial vehicle multispectral sensor camera, and a soil moisture sensor to study the water and salt transport process in the soil column under different water addition conditions and investigate the relationship between the soil water and salt transport process and the spectral reflectance of the image on the soil surface. The observation results of the soil column show that the soil water and salt transportation process conforms to the basic transportation law of “salt moves together with water, and when water evaporates, salt is retained in the soil weight”. The salt accumulation phenomenon increases the image spectral reflectance of the surface layer of the soil column, while soil temperature has no effect on the reflectance. As the water percolates down, water and salt accumulate at the bottom of the soil column. The salinity index decreases instantly after the addition of brine and then tends to increase slowly. The experimental results indicate that this work can capture the relationship between the water and salt transport process and remote sensing spectra, which can provide theoretical basis and reference for soil water salinity monitoring.

Insight into the initiation and propagation mechanism of desiccation cracking in clayey soil from DEM simulations

Desiccation cracking, a common natural phenomenon, significantly affects the mechanical and hydraulic properties of clayey soils. This study employs 3D Discrete Element Method (DEM) to investigate the initiation and propagation mechanisms of soil desiccation cracking. By integrating water evaporation at the soil surface and water transportation between soil grains into a traditional DEM model, we unveil a sequential and hierarchical pattern in the development of desiccation cracks. Initially, micro cracks proliferate and coalesce in regions of soil defects characterized by the lowest coordination numbers, leading to the genesis of primary cracks. Subsequently, a complex network of cracks propagates, governed by the interplay between cracking and the redistribution of the tensile stress field. As desiccation advances, the detachment of soil from the bottom wall and an increase in soil strength contribute to the stabilization of the crack network. Notably, the hierarchical nature of desiccation cracking is predominantly shaped by initial soil defects and subsequently refined by stress concentration within the soil clods, correlating with changes in the length-to-height ratio of the soil clods.

Coupled Efficacy of Magneto-Electric Water Irrigation with Foliar Iron Fertilization for Spinach Growth

The lack of trace element iron has become a key factor restricting vegetable yield and quality improvement. To address the low production efficiency of water–fertilizer coupling in agricultural production, we used a combination of experimental research, theoretical analysis, and mathematical modeling to systematically determine the effects of magneto-electric water irrigation with iron application on spinach growth and physiology, its yield and quality, and soil water transport characteristics. Compared with conventional water irrigation, under magneto-electric water irrigation, the water volume and applied iron concentration average increased the total accumulation of nitrogen, carbon, and iron in the aboveground part of spinach by 3.71%, 10.16%, and 14.14%, respectively, and the aboveground part of spinach had the highest total accumulation of nitrogen and carbon when irrigation water was 3300 m3 ha−1 and iron fertilizer application at 0.15%. Additionally, magneto-electric water irrigation increased spinach aboveground fresh weight and soluble sugar and protein content by an average of 13.34, 18.26, and 11.61%, respectively. Based on a comprehensive quantitative evaluation and analysis of aboveground nutrient accumulation in spinach, aboveground fresh weight, water use efficiency, and soluble sugar and protein content, we determined the optimal irrigation water and iron fertilizer application for spinach growth.

Super absorbent polymer (SAP) on water‐salt transport in saline alkali soil: Effects of dosage, height and thickness

AbstractSoil salinisation is a pervasive form of land degradation posing a significant threat to the global environment. Saline soil, covering roughly 10% of the total land area, represents a crucial reserve of land resources. The use of super absorbent polymer (SAP) impacts capillary water movement through the soil because of its exceptional water absorption and retention capabilities. SAP is expected to influence the intricate water‐salt migration processes and their redistribution within soil. This study employed soil column experiments to investigate the impacts of varying SAP dosages (A), heights (B) and thicknesses (C) on soil water and salt transport in the Tianjin Binhai New Area, China. The main findings showed that: (1) average capillary water rise rate decreased with SAP dosage increase. The groundwater recharge trend in time was like that of capillary water rise height; (2) SAP usage increased water and salt content on the application layer and reduced surface soil salt accumulation; (3) the best SAP combination for application was 1.1% SAP at 17–18 cm from the groundwater level. This study provides basic effective SAP application strategies for preventing soil salinisation.

A percolation model of unsaturated hydraulic conductivity using three-parameter Weibull distribution

Accurate estimation of unsaturated hydraulic conductivity, K(Sw), is crucial for modeling water and solute transport in variably-saturated soils. In this study, a new model for the estimation of K(Sw) based on percolation theory and critical path analysis is presented, in which the pore-throat size distribution is described by the three-parameter Weibull probability density function. To evaluate the performance of the proposed K(Sw) model, two datasets including more than three hundred samples are analyzed. The first dataset includes 240 pore-network simulations, while the second dataset consists of 101 soil samples from the UNSODA database. For the pore-network simulations, for which both pore-throat size distributions and capillary pressure curves are available, we estimate K(Sw) from the capillary pressure curve with RMSLE = 0.54 slightly better than the estimations obtained from the pore-throat size distribution with RMSLE = 0.6. For the soil samples, since only the capillary pressure curve is measured, we estimate K(Sw) from the capillary pressure curve and evaluate three previously proposed approaches for determining the exponent, α, in Poiseuille's law. We find that RMSLE = 0.98 for α = 3, RMSLE = 0.87 for α = 2(4 − D) − (3 − D)/(2D − 3), and RMSLE = 1.06 for α = 4 − 0.74D, in which D is the fractal dimension characterizing the pore space. Comparing the results with previous studies in which the power-law probability density function was used to characterize capillary pressure curve and pore sizes shows that the proposed three-parameter Weibull distribution, in conjunction with the CPA analysis, may more accurately estimate K(Sw) for a wide variety of soils ranging from very fine to very coarse textures.

Carbon to nitrogen stoichiometry of organic amendments influences the improvement of aggregate stability of a cropping vertisol

AbstractSoil aggregation is one of the key processes controlling air, water and gas transport in soil. Long‐term cropping without returning organic matter in the soil can reduce the water stability of the aggregates. Microbial decomposition of organic matter plays a significant role in aggregate formation and hence can reverse the decline in the water stability of the aggregates. The inoculation of soil with beneficial microbes can improve the aggregate stability of cropping soil, potentially restoring its condition to healthy soil. However, the restoration of the aggregate stability may also be dependent on the C:N ratio of added organic matter. We hypothesize that a higher C:N ratio of added organic matter and microbial inoculation can trigger a more persistent improvement in aggregates. We treated pasture (aggregates were water‐stable) and cropping (aggregates were unstable in water) vertisols with sugarcane (C:N = 104) and lucerne (C:N = 23) residues with and without microbial inoculant that had both bacteria and fungi. After 4 months of incubation, we found that the slaking index dropped by 46% in sugarcane‐treated cropping soils, whereas the reduction was 27% in lucerne treatment. A similar reduction in the slaking index was also observed in the pasture soil but the magnitude of the reduction was lower than in the cropping soils. However, microbial inoculation did not show a statistically significant influence on reducing the slaking of cropping or pasture soils in this study. The reduction of slaking in both soils was supported by an increase in mean weight diameter (MWD), macro‐aggregates and the aggregate‐associated soil organic carbon. Our results demonstrated that organic carbon input with a high C:N ratio facilitates the restoration of water stability of the structurally unstable cropping soils.

Soil water percolation and nutrient fluxes as a function of topographical, seasonal and soil texture variation in Central Amazonia, Brazil

AbstractUnderstanding soil water dynamics and transport of nutrients is challenging in tropical rainforests due to the uniqueness of several properties related to soils, vegetation and seasonality that make relating patterns found in temperate environments to tropical sites difficult. We address the need for better edaphic characterization in tropical environments by investigating soil water percolation rates and chemistry across topographic, soil texture and seasonal gradients in a mature tropical rainforest in Central Amazonia, Brazil. We utilized a passive wick flux meter (e.g., drainage lysimeter) to directly measure real‐time percolation fluxes at 60‐cm depth, and to sample a suite of chemical species across plateau, slope and valley topographic positions. We found percolation flux volume and chemical exports generally increase with decreasing elevation and clay content, which was lowest in the valley. Daily percolation flux was observed to be 2.39 ± 0.44 in plateau, 3.01 ± 0.50 in slope and 6.16 ± 0.83 mm in valley. Most solutes were present in small amounts of &lt;1 mg L−1, such as PO₄3−, Fe2+/Fe3+ and Mn2+; however, NO3− concentrations were &gt;20 mg L−1, even exceeding 100 mg L−1 in the valley. Based on additional isotopic analysis, we speculate high NO3− concentrations are partially an artefact of root decomposition following installation of the flux meters. The empirical relationships we show among percolation volume and nutrient exports under varying topographies and soil textures can improve Earth System Model performance by better constraining ecohydrological relationships to nutrient fluxes, which can in‐turn better illuminate the important factors that govern their behaviour.

How residual plastic film affects the soil water–salt and cotton growth at the seeding stage

AbstractCotton holds a significant position among cash crops in China, with Xinjiang serving as the primary cotton‐growing region within the country. Agricultural practices involving plastic mulching have gained importance. However, the presence of residual plastic film affects the growth of cotton seedlings as well as the soil environment. Our study aimed to explore the impact of residual plastic film accumulation on the growth of cotton seedlings and the associated soil water‐salt environment. This was done through a barrel planting experiment, utilizing soil from cotton fields with varying durations of mulching. The study showed that when the mulching period exceeded 12 years (residual plastic film content of 260.77 kg hm−2), residual plastic film had a significant impact on cotton seedling growth and the soil environment. Residual plastic film reduces the seedling germination rate of cotton by up to 11.11% (7 days after irrigation, 15 years of film mulching, residual plastic film content of 309.88 kg hm−2). It also impedes the growth of cotton seedlings; plant height, stem thickness, and leaf area were reduced by 34.52%, 10.73%, and 37.18%, respectively (19 days after irrigation, 15 years of film mulching, residual plastic film content of 309.88 kg·hm−2). Compared with the treatment without residual plastic film, the shallow soil water content in the T5 treatment decreased by 1.19% (10 days after irrigation, 15 years of film mulching, residual plastic film content of 309.88 kg·hm−2). Residual plastic film in cotton fields subjected to long‐term mulching obstructs the normal growth and development of cotton seedlings while also impacting the transport of soil water and salt. Therefore, we recommend adopting biodegradable mulch or regularly recycling residual plastic film within mulched areas to prevent its accumulation and subsequent negative impacts.

Effect of salt types on salt precipitation and water transport in saline sandy soil

AbstractSalt precipitation on the surface of porous media significantly affects water transport processes. Most studies on salt precipitation mainly focused on single salts, but in nature, salt precipitation usually occurs as mixtures. Consequently, information on the crystallization of salt mixtures and its effect on water transport remains scarce. This study investigated the precipitation of mixtures (the mass ratios of NaCl:Na2SO4 were 3:7, 5:5, and 7:3, respectively) of NaCl (typical efflorescence) and Na2SO4 (typical subflorescence) in the initially saturated sandy soil columns and its effect on evaporation and compared it with the cases of the two salts individually. The results showed that salt mixtures exhibited a mixed pattern of crystals including both efflorescence and subflorescence, and the efflorescence showed granular aggregation, unlike the mono‐salts. The crystallization coverage of the salt mixtures was smaller than that of NaCl mono‐salt; high (7:3) and low (5:5 and 3:7) proportions of NaCl led to larger and smaller crystallization coverage than that of Na2SO4 mono‐salt, respectively. While the salt mixtures had less crystallization coverage than the mono‐salts, they showed lower evaporation because the salt mixtures formed a denser crystallization structure of efflorescence‐subflorescence‐soil layer, this crystallization structure exhibited greater inhibition of water vapour diffusion, thus reducing evaporation. In addition, the crystallization of the salt mixtures with higher NaCl proportion afforded greater resistance of evaporation. The mixed crystallization pattern formed by the salt mixtures significantly enhances the crystallization resistance to evaporation.

A comprehensive study of deep learning for soil moisture prediction

Abstract. Soil moisture plays a crucial role in the hydrological cycle, but accurately predicting soil moisture presents challenges due to the nonlinearity of soil water transport and the variability of boundary conditions. Deep learning has emerged as a promising approach for simulating soil moisture dynamics. In this study, we explore 10 different network structures to uncover their data utilization mechanisms and to maximize the potential of deep learning for soil moisture prediction, including three basic feature extractors and seven diverse hybrid structures, six of which are applied to soil moisture prediction for the first time. We compare the predictive abilities and computational costs of the models across different soil textures and depths systematically. Furthermore, we exploit the interpretability of the models to gain insights into their workings and attempt to advance our understanding of deep learning in soil moisture dynamics. For soil moisture forecasting, our results demonstrate that the temporal modeling capability of long short-term memory (LSTM) is well suited. Furthermore, the improved accuracy achieved by feature attention LSTM (FA-LSTM) and the generative-adversarial-network-based LSTM (GAN-LSTM), along with the Shapley (SHAP) additive explanations analysis, help us discover the effectiveness of attention mechanisms and the benefits of adversarial training in feature extraction. These findings provide effective network design principles. The Shapley values also reveal varying data leveraging approaches among different models. The t-distributed stochastic neighbor embedding (t-SNE) visualization illustrates differences in encoded features across models. In summary, our comprehensive study provides insights into soil moisture prediction and highlights the importance of the appropriate model design for specific soil moisture prediction tasks. We also hope this work serves as a reference for deep learning studies in other hydrology problems. The codes of 3 machine learning and 10 deep learning models are open source.

Water Uptake Characteristics of Stipa bungeana Trin: Affected by Subsidence in the Coal Mining Areas of Northwest China

Revealing the water use pattern of plants influenced by coal-mining-caused land subsidence is crucial to understand plant–water interactions and guide ecological restoration. However, available information on herbaceous plants, the dominant species in most arid and semi-arid regions with abundant coal resources, remains inadequate. We investigated the water use patterns of Stipa bungeana Trin. by measuring soil water content, root distribution, and stable isotopes of hydrogen (δ2H) and oxygen (δ18O) of soil water and plant stem water both before and after a rainfall event. The results revealed that prior to rainfall, both areas exhibited a low soil water content with no discernible difference in soil drought. However, the soil waters δ2H and δ18O were found to be more enriched at varying depths within the subsidence area, indicating a heightened level of soil evaporation. Both soil water content and soil water isotopic composition responded sensitively to rainfall, with rainfall primarily replenishing the shallow layer (0–20 cm), thereby reflecting an infiltration mode dominated by piston flow. More water seeped into deeper soil layers in the subsidence area compared to the non-subsidence area, with more preferential flow. Before rainfall, the sources of plant water uptake were consistent both at shallow and deep soil layers, implying that the proportion of water uptake gradually decreased with increasing depth. After rainfall, the sources of plant water uptake differed slightly between the two soil layers. The plants in non-subsidence and subsidence areas dominantly extracted soil water at depths greater than 10 cm and 20 cm, respectively. The root system in the subsidence area was more developed than that in the non-subsidence area. Plant water uptake was primarily influenced by the spatial distribution of roots, as well as the post-rainfall water distribution, regardless of whether they were in the subsidence area or not. Although land subsidence affected soil water transport, the water uptake pattern of Stipa bungeana Trin. was similar before and after rainfall, indicating the adaptive growth of plants through their roots in the subsidence area. The high adaptability of herbs such as Stipa bungeana Trin. makes them a viable option for vegetation restoration in subsidence areas. This study has significant implications for evaluating plant–water relationships in subsidence areas due to coal mining, thereby providing a fundamental basis and valuable reference for ecological restoration and management strategies within such affected regions.