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Ponding at the soil surface exerts profound impacts on infiltration. However, the effects of ponding depth on infiltration, especially the development of a saturated zone below the soil surface, have yet to be considered in present infiltration models. A new general Green‐Ampt model solution (GAMS) was derived for a one‐dimensional vertical infiltration problem under a uniform initial moisture distribution with ponding on its surface. An expression was included in the new solution for simulating the saturated layer developed below the soil surface as long as the pressure head at the surface is sufficiently high to saturate the soil. The GAMS simulates the infiltration processes closer to the numerical solution by HYDRUS‐1D than the traditional and the recently improved Green‐Ampt model. Moreover, an inversion method to improve the estimates of soil hydraulic parameters from one‐dimensional vertical infiltration experiments that is based on the GAMS was suggested. The effect of ponding depth (hp), initial soil moisture content, soil texture, and hydraulic soil properties (saturated hydraulic conductivity Ks, water‐entry suction hd and shape coefficient n of soil water retention curve) in the saturated zone was also evaluated. The results indicate that the saturated zone length increased at a comparable rate with the unsaturated wetted zone length during infiltration. Generally, a larger saturated zone was found for soils with higher initial soil moisture contents, coarser texture, higher Ks values, greater n, and lower −hd. Our findings reveal that including the saturated zone in the infiltration model yields a better estimate of the soil hydraulic parameters. The proposed GAMS model can improve irrigation design and rainfall‐runoff simulations. Key Points: An implicit expression was proposed for the development of saturated zone during infiltrationThe newly proposed formula improved the simulation accuracy in all stages of ponded infiltrationThe new approach eliminated the time‐dependency of the estimated soil hydraulic properties [ABSTRACT FROM AUTHOR]

The recognition of treated wastewater (TWW) as an alternative water resource is expanding in areas with a shortage of freshwater (FW). While many studies have been devoted to the effects of long-term irrigation with TWW on soil wettability and spatial flow variations in the soil profile, much less attention has been given to the spatial distribution of soil water repellency in the soil surface layer. This is the objective of the current study. Undisturbed soil samples (5 cm thick) were taken at 15-cm intervals parallel to a drip lateral in two adjacent plots of a commercial citrus orchard in central Israel. Each soil sample was sectioned into five consecutive 1-cm layers for which soil water repellency was determined by water drop penetration time method, and soil organic matter by loss-on-ignition method. Geostatistics and multivariate empirical mode decomposition were used to investigate the overall and scale-specific spatial variation of soil water repellency and its dependence on dripper intervals along the lateral. A high degree of soil water repellency with strong spatial variation was found in the surface soil after 4–6 years of TWW irrigation. Weak to moderate spatial dependence of soil water repellency with maximum autocorrelation distance of around 30 cm was discovered by geostatistical analysis. The spatial distribution of soil water repellency was considered to be greatly affected by the location of the drippers, being higher between adjacent drippers and lower underneath them. This soil water repellency distribution is presumed to result from ongoing lateral displacement of the amphiphilic substances in the TWW toward the outer edge of the wetted plume periphery. Multivariate empirical mode decomposition of the overall spatial variation of soil water repellency yielded three scale-specific variations with corresponding characteristic scales of 30 cm, 110 cm and 200 cm. Most of the soil water repellency variation was separated into the 30 cm and 110 cm spatial scales, which were correlated to processes related to the drippers and trees. Replacing TWW with FW for the reclamation of water-repellent soils partially alleviated the intensity of TWW irrigation-induced soil water repellency. Moreover, an inconsistency between the hot spots of water-repellency development between adjacent drippers and the areas that are effectively ameliorated by FW irrigation below the drippers could be developed and affect the spatial distribution of flow pattern in an a priori unpredictable way. [ABSTRACT FROM AUTHOR]

Soil thermal properties play crucial roles in governing heat storage and conduction across soil profiles and affect various soil processes by determining soil microclimate. Biochar has gained wide attention as a soil amendment to affect a series of soil physiochemical properties. However, little information is available on the integrated effects of biochar application on soil thermal properties. Disturbed soil columns with consistent bulk density (1.3 g cm −3 ) were packed using clayey red soil and wheat straw biochar at application rates (w/w) of 0%, 0.5%, 1.0%, 1.5%, 2.0% and 2.5%. Besides, a 2-year field experiment of biochar application at the same application rates with crop rotation was performed in a red soil region in south China. Soil thermal properties, i.e. thermal capacity, conductivity and diffusivity, were measured with heat pulse method for disturbed soil columns and undisturbed soil cores from the field at controlled soil water contents ranging from 0% to 40% at an interval of 5%. Furthermore, soil thermal properties were measured in situ for different biochar treatments under field conditions. For the disturbed soil columns, no significant effect of biochar application on soil thermal properties was detected at most of the soil water content levels. Additionally, it indicated that biochar application cannot directly affect soil thermal properties by changing soil solid substances composition at application rates up to 2.5% w/w. The results from undisturbed soil cores showed significant decreasing effects of biochar application on soil thermal capacity and diffusivity at most of the soil water content levels. The results from in situ measurement showed significant decreasing effect of biochar application on soil thermal capacity, conductivity and diffusivity. Two main underlying mechanisms were identified for the effects of biochar application on soil thermal properties. One is the negative effect of biochar application on soil thermal capacity and conductivity by increasing the soil total porosity, mainly by increase in the meso- and macro-porosity. The other is the positive effects of biochar application on soil thermal properties by increasing the soil water content through improved soil water retention ability. The negative effects through change in the soil structure were the dominant effect under field condition. [ABSTRACT FROM AUTHOR]

Spatial heterogeneity of soil water retention curves (SWRC) plays an important role in modelling the movement of water and solutes in soils. To characterize the spatial variability of SWRC parameters fitted by the van Genuchten (VG) equation, and then identify factors that closely correlated with the VG parameters, we collected undisturbed and disturbed soil samples from the upper 0-5 cm soil layer at 382 sampling sites across the entire Loess Plateau of China (~620 000 km2). We determined the SWRC and six other soil properties as well as nine environmental factors for each site. Results showed that the saturated water content ( θs) and a curve-shape parameter that is related to soil pore size distribution ( n) were weakly spatially variable (coefficient of variation (CV) = 15%), and that the residual soil water content ( θr) and a scaling parameter that is related to the inverse of the air entry pressure ( α) were moderately (CV = 96%) and strongly variable (CV = 136%), respectively. Semivariograms of [ABSTRACT FROM AUTHOR]

• Biochar produced at low temperature is hydrophobic. • Hydrophobic biochar induces water repellency. • Water repellency in biochar–soil mix is mainly physically, not chemically induced. • Internal finger-like plumes develop within primary plumes in biochar–soil mix. Despite the known benefits of biochar application to soils, little is known about its effect on soil wettability and the consequences on soil water movement across the soil profile. Focusing on the latter, three types of commercial biochar derived from wheat, corn, and rice straw produced under low temperature (350–450 ℃) were mixed with a wettable sandy soil at rates of 0%, 2%, 5%, and 10% w/w. Soil water repellency (SWR) of the biochars and biochar–soil mixtures was determined by water drop penetration time (WDPT) test and sessile-drop contact angle (CA) measurement. The WDPT results (< 5 s) showed complete wettability for the biochar–soil mixtures, whereas CA results indicated some water repellency. The mean initial CA of the three biochars varied between 105.3° and 113.9°, with ∼ 30° for the pure sand, and between 56.8° and 75.7° for the biochar–soil mixtures. SWR increased with biochar-application rate, whereas biochar particle size (< 1 mm and > 1 mm) had no significant effects on SWR. A 2-D flow chamber experiment with point source water application at the surface was used to continuously monitor the flow pattern and soil water content (SWC) distribution across the soil profile during infiltration and redistribution periods. Biochar–soil mixtures (2% and 5% w/w) with the three biochar types were studied. Flow chamber results showed substantial differences in plumes shape and internal SWC distribution in the biochar–soil mixtures compared to the untreated sand during the wetting and drainage. The plumes' shape and nonmonotonic spatial SWC distribution suggested unstable flow in the biochar–soil mixtures. The internal fingers developed in the biochar treated sand indicate that SWR induced by biochar addition seemed to be physically induced via the blending of the biochar and soil particles, rather than chemically induced, via coating of the soil particles with amphiphilic molecules. Under field conditions, the primary and inner finger-like plumes may eventually form preferential flow paths that will affect the spatial distribution of water and fertilizer in soil profiles and their availability to plant roots. [ABSTRACT FROM AUTHOR]

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• MASCP considers the effect of ponding by introducing a developing saturated zone. • MASCP reveals scaling relations of infiltration for sloping and horizontal surfaces. • New numerical algorithm can model slope infiltration with non-uniform initial SWC. Slope rainfall infiltration is a critical component of the Earth's hydrologic processes. Although various infiltration models have been proposed to simulate rainfall infiltration, simple and accurate ones are still scarce. This work developed a non-integral infiltration model for sloping surfaces, called modified approximate solutions under constant pressure conditions (MASCP). New expressions were proposed to improve slope infiltration simulation by introducing a developing saturated zone in soil water content (SWC) profile to quantify the role of ponding water during infiltration. The MASCP was then extended to simulate the infiltration with uniform and non-uniform initial SWC distributions under complex rainfall patterns. The model performance was evaluated by comparing with Hydrus-1D and the sloping Green-Ampt model for four distinct textured soils. The results demonstrated that the ponding time and infiltration rate simulated by the MASCP agreed well with those by Hydrus-1D at all given conditions. Besides, the MASCP yielded higher simulation accuracy than the sloping Green-Ampt model, especially for coarse-textured soils, low rainfall intensity, and long rainfall hiatus. In conclusion, the MASCP is a simple and accurate computation tool for slope rainfall infiltration modeling. [ABSTRACT FROM AUTHOR]

• The comprehensive utilization of solar light frequency division and Even-lighting technologies are deployed to reduce the rate of soil water evaporation. • The mechanism of water evaporation reduction was analysed. • Cumulative evaporation from soil and pan surfaces decreased by 21% and 14% under Concentrated-lighting Agrivoltaic System. • Cumulative evaporation from soil and pan surfaces decreased by 33% and 19% under Even-lighting Agrivoltaic System. The triple benefits of the AgriVoltaic Systems Development (AVSD) have been well demonstrated, not only for the PV electricity generation but also for reduced water evaporation, enhancing further the benefits of simultaneously crop growth on the same land area. However, the reduction rate of the water evaporation of AVSD has not been investigated in a quantitative way. Therefore, this study conducted experiments to measure water evaporation reduction under the Concentrated-lighting Agrivoltaic System (CAS) and the Even-lighting Agrivoltaic System (EAS). Evaporation containers and pans were placed in the bare soil (CK) under the CAS and the EAS. Our results showed a significant reduction in water evaporation under CAS and EAS. Cumulative soil surface evaporation of CK, CAS, and EAS for 45 days was 80.53 mm, 63.38 mm, and 54.14 mm. The cumulative water evaporation from soil and pan surfaces decreased by 21 % and 14 % (under CAS), 33 %, and 19 % (under EAS), respectively. The slope β 1 ≠ 0 of simple linear regression showed a significant positive relationship between evaporation time and cumulative water evaporation. The correlation coefficient in all treatments was more than 0.91, suggesting a robust linear relationship. The feasibility of AVSD could significantly reduce irrigation water, enhance crop growth, and generate electricity simultaneously on the same agricultural land. [ABSTRACT FROM AUTHOR]

• A concise soil water content profile expression was obtained by an analytical method. • An approximate solution was derived for one-dimensional upward infiltration. • A method with a standard ring was proposed to determine BC model parameters. Soil hydraulic properties quantify soil pore structure and are essential input parameters for simulating soil hydrological processes in the vadose zone. Although methods have been proposed to estimate soil hydraulic properties, efficient and applicable ones are still scarce. In this study, we derived an approximate solution for a one-dimensional upward infiltration process with initially uniform soil water content distribution. Founded on our solution, a nonlinearly constrained optimization method was developed to simultaneously estimate the parameters K s and n , h d of the Brooks-Corey model by measuring the upward infiltration process in a 5-cm high soil column. Numerical experiments simulated with Hydrus-1D were performed on six theoretical soils to evaluate the accuracy of the new method. The results indicate that the approximate solution can accurately simulate the upward infiltration process at the low initial soil water content range, with a relative error (Re) of 2.85% to 5.47% for soil water content distribution in space and time. For the cumulative infiltration curve, the Re ranges from 0.2% to 1.01%. The estimated parameters K s and n , h d of the Brooks-Corey model are close to the actual parameter values, with a Re of 0.59% to 4.68% for n , 0.00% to 7.91% for h d , and 0.50% to 8.83% for K s , respectively. It is concluded that the new method provides a simple and valuable tool for the accurate estimation of soil hydraulic properties. [ABSTRACT FROM AUTHOR]

Summary: Saturated hydraulic conductivity (Ks ) is an important soil property that shows a high degree of spatial heterogeneity. There is a lack of research that investigates and determines Ks at a regional scale, due to the challenges associated with the required intensive sampling. To determine the closely correlated factors affecting Ks at a regional scale and to then generate a regional distribution map of Ks , we selected 382 sampling sites across the Loess Plateau of China (620,000km2) and collected undisturbed and disturbed soil samples from two soil layers (0–5 and 20–25cm). We found that both surface Ks and subsurface Ks had log(base 10)-normal distributions, and demonstrated strong spatial variability (CV=206% and 135%, respectively). Surface LogKs was most closely correlated with LogSand, LogSilt, LogSG (slope gradient), LogSSWC (saturated soil water content), vegetation coverage and land use; while subsurface LogKs was correlated with LogClay, SSWC, LogSG, LogAltitude, LogGY (growth year) and land use. Geostatistical analysis indicated that semivariograms of surface and subsurface Log Ks could be best fitted by an isotropic exponential model, with effective ranges of 204km and 428km, respectively. Distribution maps of Ks produced by kriging indicated a pronounced spatial pattern and demonstrated an obvious spatial depth gradient. The spatial distribution patterns of Ks at a regional scale in the loessial soils of China comprehensively reflected soil hydraulic properties and the combined effects of soil texture, vegetation, topography and human activities. [Copyright &y& Elsevier]

Abstract: In arid and semiarid regions that have deep soils, plant root systems can extract soil water to a depth of 20m or more. An accurate evaluation of soil water conditions in such regions is essential in order to improve the understanding of the role of soils as a water pool and to design scientifically based water management strategies. However, the vertical distribution of soil water and its storage in deeper layers are unclear due to the shortage of field data. In this study, soil water content (SWC) and related soil (i.e., soil organic carbon, soil particle composition) and plant (i.e., root depth, root mass) properties were determined to a depth of 21m at 11 sites across the Loess Plateau of China. Soil water storage (SWS) and available soil water storage (AWS) were calculated for each 1-m thick soil layer in the profile as well as for the whole profile. Mean values for SWC, SWS, and AWS in the soil layers had a similar distribution pattern down the profile, which could be divided into three statistically significant different sub-layers where the parameter decreased (0–2.5m), then increased (2.5–5m), and increased with fluctuations (5–21m). The amount of SWS and AWS in the 21-m profiles varied from 1639mm to 5669mm and from 831mm to 2953mm, respectively. In the root zone, the vertical distribution and quantity of soil water were significantly influenced by land use and plant characteristics (i.e., root mass); while below the root zone, soil texture became a more important factor. Compared with the upper soil layers, the deeper soil layers provided a larger water pool and thus potentially had a stronger buffering capacity, which could mitigate the effects of seasonal or inter-annual drought on plants. Understanding this information is important to regional water budgets, sustainable land management and the restoration of the ecological environment on the Loess Plateau and possibly in other water-limited ecosystems around the world. [Copyright &y& Elsevier]

Abstract: A dried soil layer (DSL) is generally formed in the soil profile at a particular depth owing to serious soil desiccation in water-limited ecosystems. The occurrence of DSLs potentially limits the development and sustainability of the ecological environment on the Loess Plateau of China. There is a need to address the spatial variations in DSL thickness (DSLT) and the DSL depth of formation (DSLFD) in this region. We pre-selected 382 sampling sites across the entire Loess Plateau region (620000km2) based on mapped information using an intensive sampling design. A total of 17906 disturbed soil samples from various soil depths were collected. Using classical statistics, principal component analysis, residual maximum likelihood (REML), and geostatistical methods, we investigated and characterized DSLs and their spatial distribution. There was strong spatial variation in DSLs, which had a mean thickness of 160cm occurring at a mean soil depth of 270cm. DSLT was highly correlated with a topographical factor (i.e., slope gradient) that dominated the first principal component (PC), which explained 39% of the variance. Geographical position (i.e., longitude) was important in the second PC. REML analysis demonstrated that land use, rainfall, soil type and slope gradient had a significant impact on DSLT, while only land use, rainfall, and soil type influenced DSLFD significantly. Semivariograms of DSLT indicated weak spatial dependence while DSLFD had moderate spatial dependence. The DSL was generally thicker (>170cm) in the western Loess Plateau region and in a central area (170 to 220cm). Where irrigation was used along parts of the Yellow River and near rivers in the interior, DSLT was considerably thinner or non-existent due to the higher water inputs. Management practices utilizing knowledge of the spatial distribution of DSLs and the factors influencing them can improve land use management to improve the efficiency of vegetation restoration, water management, and to control or reclaim DSLs. [Copyright &y& Elsevier]

• Ground cover management (GCM) overall increased soil moisture content (SMC) by 9.2% in orchards. • Effects of GCM on SMC change varied with management and environmental factors. • Climate and tree age were the dominant drivers of SMC responses to GCM. • High soil bulk density (greater than 1.4 g cm−3), full cover, and mowing could constrain the GCM-induced positive effect. Ground cover management (GCM) is an important practice for sustainable agricultural development, which has been garnering popularity in numerous orchards worldwide. It can effectively improve soil health, reduce soil erosion, and enhance carbon sequestration. However, the effects of GCM on soil moisture content (SMC) dynamics vary with management and environmental factors, and it remains unclear how these factors affect GCM-induced SMC. In addition, it remains unknown how SMC and influencing factors such as climatic, edaphic, and agronomic factors are inter-related in responding to mulching practices. Therefore, we performed a meta-analysis to identify the effect of these factors on SMC accumulation and elucidate the potential mechanisms involved under different environmental and management conditions. Results revealed that GCM practices significantly enhanced SMC (9.2%) compared with the effects of traditional clean tillage. The maximum benefits of SMC were observed when the average annual temperature was smaller than 8 ℃, initial soil organic carbon was 20 g kg−1, and tree age was greater than 20 yr. Further analysis using a random forest model revealed that sampling time, tree age, and soil depth were the predominant drivers of SMC change. Overall, these findings highlight the critical importance of GCM in increasing SMC in orchards worldwide. In addition, the results show that the corresponding changes are controlled by specific climatic, soil, and management factors. These findings provide insights and guidance that can assist practitioners and policy-makers to establish and manage site-specific GCM practices to maximize SMC benefits and promote sustainable agricultural development. [ABSTRACT FROM AUTHOR]

Soil nematode communities and their functions are simultaneously influenced by abiotic factors such as temperature and soil moisture. However, the complex interaction effects of these factors have not been clearly demonstrated, limiting our understanding of soil biodiversity and functions under different climate scenarios. Here, we conducted a short-term microcosm experiment, implementing three temperature treatments (20 °C, 25 °C, and 30 °C) combined with two soil moisture treatments (50% and 80% water-holding capacity). We comprehensively assessed the changes in abundance, diversity, composition, and functions (carbon footprints) of soil nematode communities under these different treatments. Our findings revealed that temperature and moisture did not have significant effects on the richness or Shannon diversity of nematodes, while they did have significant impacts on other properties. We found that the interaction effect between temperature and moisture had a greater influence on total abundance compared to their independent effects. Moisture emerged as the primary driver of nematode community composition, followed by the interaction term, while temperature exhibited the least influence. Contrary to expectations, increasing temperature did not cause a shift in the community towards small-bodied genera when considering intraspecific variability in body mass. However, elevating moisture level led to an increase in community-weighted mean body mass, irrespective of intraspecific variability. Consequently, the body-mass-related footprints varied among treatments when considering intraspecific variability, with the dominant influence arising from the interaction effect. Overall, our study highlights the dominant interaction effect of temperature and soil moisture on multiple ecological properties of nematode communities. Additionally, we underscore the importance of incorporating intraspecific trait variability when assessing the responses and functions of nematodes under distinct environmental conditions. [ABSTRACT FROM AUTHOR]

Abstract: A dried soil layer (DSL) formed in the soil profile is a typical indication of soil drought caused by climate change and/or poor land management. The responses of a soil to drought conditions in water-limited systems and the impacts of plant characteristics on these processes are seldom known due to the lack of comparative data on soil water content (SWC) in the soil profile. The occurrence of DSLs can interfere in the water cycle in soil–plant–atmosphere systems by preventing water interchanges between upper soil layers and groundwater. Consequently, a DSL may limit the sustainability of environmental restoration projects (e.g., revegetation, soil and water conservation, etc.) on the Loess Plateau of China and in other similar arid and semiarid regions. In this study, we investigated and compared the impacts of soil type, land use and plant characteristics within each of the three climatic regions (arid, semiarid, semihumid) of the Loess Plateau. A total of 17,906 soil samples from 382 soil profiles were collected to characterize DSLs across the Plateau. Spatial patterns of DSLs (represented by four indices: (1) DSL thickness, DSLT; (2) DSL forming depth, DSLFD; (3) mean SWC within the DSL, DSL-SWC; and (4) stable field water capacity, SFC) differed significantly among the climatic regions, emphasizing the importance of considering climatic conditions when assessing DSL variations. The impact of land use on DSLs varied among the three climatic regions. In the arid region, land use had no significant effect on DSLs but there were significant effects in the semiarid and semihumid regions (P <0.05). The development of DSLs under trees and grasses was more severe in the semiarid region than in the semihumid region. In each climatic region, the extent of DSLs depended on the plant species (e.g., native or exotic, tree or grass) and growth ages; while only in the semiarid region, the DSL-SWC and SFC (P <0.001) were significantly influenced by soil type. The DSL distribution pattern was related to the climatic region and the soil texture, which both followed gradients along the southeast–northwest axis of the Plateau. Optimizing land use can mediate DSL formation and development in the semiarid and semihumid regions of the Loess Plateau and in similar regions elsewhere. Understanding the dominant factors affecting DSLs at the regional scale enables scientifically based policies to be made that would alleviate the process of soil desiccation and sustain development of the economy and restoration of the natural environment. Moreover, these results can also be useful to the modeling of the regional water cycle and related eco-hydrological processes. [Copyright &y& Elsevier]