Variability Of Soil Water Content Research Articles

Spatiotemporal patterns of soil water replenishment and their seasonal origins in a subtropical red soil critical zone

Assessing the integration of precipitation and its isotopic signals in soil water is crucial for understanding the sensitivity of soil available water to precipitation variability. Here the investigations of water stable isotopes and in-situ soil water content were conducted for determining the spatiotemporal patterns of soil water replenishment and their seasonal origins in a subtropical red soil critical zone. Variations in soil water content provide valuable information regarding the quantity and depth of soil water replenishment in response to precipitation events. Soil water replenishment often penetrated to a depth of 100 cm or more from winter to early summer (from December to the next June), but the corresponding replenishment amounts were relatively low. However, most soil water replenishment events were generally limited to the upper 40 cm soil layers between midsummer and autumn (from July to November), with relatively large amounts in summer. The temporal and vertical variations in the seasonal origin index of soil water indicated that summer precipitation constituted the largest fractions (∼66 %) of soil water storage in the entire explored soil profile (thickness = 130 cm) during the study period. Winter precipitation was overrepresented in soil water only at the depth of 0–20 cm in spring, but it may vary slightly from year to year due to changes in winter precipitation patterns (amount and frequency). The findings of the current study broadly highlight how precipitation contributes to soil water storage over space and time, which has significant implications for plant water sources.

Water transfer mechanisms and vapor flow effects in seasonally frozen soils

In seasonally frozen soils, liquid water and water vapor movement are critical in numerous environmental and engineering areas. However, the process of soil water movement becomes complicated due to the coexistence of liquid water, water vapor, and ice, and the underlying mechanisms are not yet fully understood. Based on the theory of coupled water, vapor, and heat transport, the modified HYDRUS-1D freezing module was used to investigate the mechanisms of soil water transfer in a cold region. Compared with its previous version, the newly developed model overcomes the numerical instability caused by the phase transformation between liquid water and ice. The verification results showed that the modified model was numerically stable and highly accurate, indicating its suitability for the study region. The variations in soil temperature, water content, water storage, evaporation, and drainage displayed typical seasonal patterns during the analyzed period, reflecting the effects of freeze–thaw cycles and rainfall-infiltration processes. Liquid flow, driven by a water potential gradient, played a major role under most environmental conditions, except when the soil was frozen when it became negligible. In comparison, vapor flow, driven by a temperature gradient, dominated soil water flow when ice was present and accounted for a considerable proportion of the total water flux in dry conditions, proving its significance for affecting soil water transport. These results clarified the mechanisms of soil liquid water and water vapor transfers in seasonally frozen soils and provided more insights for deepening the hydrological cycle theory.

Daily and seasonal patterns of stem diameter micro-variations in three semiarid forest species in relation to water status and environmental factors

Understanding the relationship between stem diameter micro-variation (SDMV) and stem water status and revealing the mechanism regulating stem water are essential for elucidating environmental adaptation and water use strategies in forest trees. Here, we report the results of the year-round monitoring (November 2018–October 2019) of SDMV and xylem sap flow obtained using high-resolution dendrometers and Granier-type thermal dissipation probes, respectively, in mature trees of three species in the semiarid Loess Plateau region: Quercus liaotungensis, Platycladus orientalis, and Robinia pseudoacacia. The year-round trend for the variations in stem diameter can be divided into phases of a decreasing period and a relatively stable period in the non-growing season, and a progressive rise and fluctuating plateau throughout the growing season. The observed interspecific differences in the time to full recovery from the water deficit state corresponded to species phenology and soil moisture conditions. These differences were manifested as the responses of sap flux density (Fd) and tree water deficit (TWD) to variations in soil water content during the growing season. Q. liaotungensis implements stomatal regulation early to avoid drastic water loss in the trunk, P. orientalis maintains a relatively stable Fd at the expense of increased TWD under soil drought, and R. pseudoacacia maintains relatively low stomatal conductance under soil drought with an increase in TWD. The results revealed that SDMV is determined by the stem water status and species-specific strategies for water use, which could provide beneficial information for forestation practices in semiarid regions.

Modeling the effect of slope aspect on temporal variation of soil water content and matric potential using different approaches by HYDRUS-1D

Slope aspect affects microclimate and soil moisture conditions, and thus has an important effect on the hydrological cycle. Given the lack of precise field data on this effect, two soil temperature, moisture and matric potential monitoring sites on north- and south-facing slopes have been established since 2017 in sandy loam soil under beech forest in a small valley near Ebergötzen, central Germany. HYDRUS-1D software was used with different approaches (including Rosetta, RETC, and RETC–measured θs approaches) for deriving soil hydraulic parameters of the van Genuchten model, to simulate temporal variability of soil water content and matric potential in the two slope aspects. Due to different microclimatic conditions, the south-facing slope was warmer and drier than the north-facing slope (two-years average temperatures 9.71 and 9.36 °C, and two-years average soil water contents 0.17 and 0.26 cm3 cm-3, respectively). The model was satisfactorily calibrated and validated on the two slopes. The calibration for the wet period was better on the south-facing slope (R2 = 0.772) than on the north-facing slope (R2 = 0.690). The simulation performance by HYDRUS-1D was better in the wet period than in the dry period. In the dry period, the model was better calibrated for the north-facing slope (R2 = 0.880) than for the south-facing slope (R2 = 0.691). The better calibration results for the wet period of south-facing slope can be explained by the location of the majority of measured soil water retention data which were in the near-saturation zone on the north-facing slope, and discontinuity of second-order derivative of the van Genuchten equation at saturation point when shape parameter (n) is smaller than 2. According to the model ability and different datasets used for the model validation, the north-facing plot was validated better than the south-facing plot for both wet and dry periods. Given that Rosetta was developed based on a soil hydraulic dataset from temperate climates, and the shortcomings of the hydraulic model, our results indicated that the Rosetta–derived approach was a reliable source for soil hydraulic parameters in both slope aspects for the wet period. However, the RETC–derived parameters were more accurate than Rosetta for the dry period on the north-facing slope.

Soil Moisture Distribution and Time Stability of Aerially Sown Shrubland in the Northeastern Margin of Tengger Desert (China)

Considering the importance of soil moisture in hydrological processes, it is crucial to understand the water distribution and time stability of different aerial shrub soils. There are few studies on the soil moisture of aerial vegetation in the northeastern margin of the Tengger Desert. Based on long-term monitoring data from the aerial seeding area in the northeastern margin of the Tengger Desert, the distribution characteristics of soil moisture and the temporal stability of soil moisture were studied. From June to October 2022, the soil moisture monitoring instrument WatchDog was used to monitor the long-term soil moisture changes (0–200 cm) in the four aerial afforestation plots of Hedysarum scoparium, mixed forest land (Hedysarum scoparium dominant species), mixed forest land (Calligonum mongolicum dominant species), and Calligonum mongolicum. The Spearman rank correlation coefficient was used to study the temporal stability of soil moisture in the four plots. Rainfall data were collected through small weather stations. The results show that the average soil water storage of four kinds of aerial shrub land in the study area was the highest in August, and the average soil water storage of different forest lands was different. The soil water content of the surface layer (0–30 cm) fluctuated the most in different months. The variation in soil water content in the shallow layer (30–100 cm) was smaller than that in the surface layer. The fluctuation of soil water content in the middle layer (100–150 cm) and deep layer (150–200 cm) was relatively stable. There was no strong variability in soil moisture content, and the temporal variation coefficient of surface soil moisture was the highest (31.44–39.8%), which showed moderate variability. The temporal variation coefficient of soil moisture in the shallow, middle and deep layers of all kinds of plots was significantly reduced, and the soil moisture stability of different aerial shrub land was the same. Spearman rank correlation analysis showed that the spatial pattern of soil water content in the surface layer (0–30 cm) and deep layer (150–200 cm) was more stable over time, that is, the temporal stability of soil water content was higher, and the temporal stability of soil water content in the middle and shallow layers of different types of shrub land was different. The research results help us to understand the soil hydrological process in the aerial seeding afforestation area in the northeastern margin of Tengger Desert, rationally arrange soil moisture monitoring points, efficiently manage and utilize water resources in the aerial seeding area, and provide a theoretical basis for local vegetation restoration and the optimization of the ecological environment.

Study on Spatiotemporal Transport Characteristics of Soil Moisture in Layered Heterogeneous Vadose Zone Based on HYDRAS-3D

The heterogeneity of layered soils affects the transport processes of water in the vadose zone. However, the mechanism of soil moisture transport in the vadose zone under heterogeneous media conditions, especially the three-dimensional transport mechanism, is a frontier problem to be studied. In order to reveal the law of soil water transport in the vadose zone under heterogeneous media, this paper constructs a three-dimensional model of water transport using HYDRAS-3D (V 2.x) software through in situ tests of water transport in 3 × 3 × 4 m sample and verifies and analyzes the model. The vertical distribution and variability of soil water content and the temporal and spatial rules of soil water transversal transport at the soil–layer interface were analyzed. The results indicate that after adjusting the parameters in the HYDRAS-3D model using measured values, the simulation results are reasonable, and the model has high reliability. To represent the water content variability characteristics of the test tube profile, water movement in the vadose zone was classified as follows: (I) steady period (April–September, less affected by rainfall), (II) slow change period (January–March), and (III) rainfall rapid change period (June, when the impact of rainfall on the test cylinder was greater). The two largest values of the soil water potential variation gradient, 19.9 and 17.8 cm/d, were observed in the silty clay layer of the test cylinder, and the influence of evaporation and infiltration in the silty clay layer was most notable at the interface. The lateral transport of soil water at the interface was influenced to a certain degree by the layered heterogeneity, wherein the fine sand layer exhibited the most pronounced impact. This was followed by silt and silty clay layers, with the silt layer showing the lowest degree of influence. The research results can provide scientific reference for the rational planning of water resources in the Yinchuan Plain.

Close-to-nature management effects on tree growth and soil moisture in Mediterranean mixed forests

Given the rising frequency of drought events, close-to-nature principles appear to be a suitable management option for promoting more adapted forests by increasing diversity and vitality (e.g., enhancing tree growth), while preserving soil moisture. In this study, we evaluate individual tree growth from selected trees (including future crop trees) and soil moisture responses to close-to-nature silvicultural treatments in sub-humid Mediterranean mixed forests in Catalonia (Northeastern Spain). We relied on 18 permanent sample plots (i.e., 9 paired-plots: managed / control) representing a competition intensity gradient and different forest types (dominated by either Quercus ilex, Castanea sativa, Quercus pubescens/petraea, Pinus pinea and Pinus sylvestris). From them, 8 plots were subject to intense monitoring in terms of intra-annual tree radial growth, monitored by manual band dendrometers, and hourly soil water content. Basal area increment, and annual and seasonal (May, June, July) radial increment rates were computed as a proxy of tree growth for all plots and for those plots with dendrometers, respectively. We conducted Spearman correlation analyses between tree growth, competition intensity, soil water content and climatic variables to detect significant relations between forest management and variables of interest (e.g., basal area increment, radial increment rates, soil water content). To investigate further into the effect of this silviculture on tree growth, we used mixed-effects models using as predictors variables related to competition intensity and forest management (dummy variable) in combination with monthly soil water content variables. We observed that basal area increment and radial increment rates had a positive (albeit weak) correlation with forest management, while competition intensity had a negative correlation with both variables. The models were not capable of detecting clear species-specific tree growth responses to competition. Compared to control plots, on average, the treatments boosted soil water content by about a 10% in managed plots in Q. ilex, P. sylvestris and P. pinea stands, and this increase was particularly significant during the growing season. Moreover, the best-fitted model predicted seasonal radial increment rates using not only forest management and competition variables, but also monthly soil water content factors. Our results suggest that close-to-nature-forest management may reduce the vulnerability to drought by increasing tree vitality and soil moisture, at least in the short term (<3 years).

Surface and subsurface runoff generation processes and their influencing factors on a hillslope in northern China

Runoff processes are essential to the hydrological cycle in mountainous areas. However, many aspects of surface and subsurface runoff generation mechanisms and their influencing factors remain to be fully understood. In this study, rainfall simulation experiments were conducted in micro runoff plots in different slope positions on a typical hillslope to explore runoff processes and their influencing factors in the Taihang Mountain region in northern China. The surface and subsurface runoff and soil water content (SWC) variation processes were analyzed. Moreover, the impact of the soil properties, such as soil saturated hydraulic conductivity (Ks), bulk density (BD), capillary porosity (CP), non-capillary porosity (NCP), and soil organic matter (SOM), on these processes were investigated. The results revealed that the response of the SWC to rainfall was significantly different in different soil layers and slope positions. The response time was slower and the period was longer on the lower slope. However, the middle and upper slopes had a faster response time and shorter period. The surface runoff was the dominant type in the lower slope (67.26 % of the total runoff), while the subsurface runoff was the dominant type in the middle (78.83 %) and upper (83.67 %) slopes. The subsurface runoff was mainly generated in the 40 cm layer on the lower slope, 20 and 30 cm layers on the middle slope, and 30 and 40 cm layers on the upper slope. These layers exhibited good correspondence with the Ks' vertical distribution, but were inconsistent with the other soil properties. These results indicate that the Ks was the most critical factor influencing the runoff generation process. The ratio of the upper layer's horizontal Ks to the lower layer's vertical Ks controlled the subsurface runoff generation process in the hillslope. These findings provide useful information for understanding the hydrological processes in mountainous areas.

Analysis of Spatial and Temporal Variability and Coupling Relationship of Soil Water and Salt in Cultivated and Wasteland at Branch Canal Scale in the Hetao Irrigation District

The Hetao Irrigation District is a typical salinized irrigation district in China, and soil salinization restricts agricultural development. To explore the spatial and temporal variability of soil water and salt and the coupling relationship in the Hetao Irrigation District, a field experiment was carried out at the scale of the Yichang Irrigation District branch canal in the downstream of the Hetao Irrigation District. Fifty-three soil sampling points were established to analyze the spatial and temporal variability of soil water content and total salt content and the coupling relationship using geostatistics and the coupling degree model. The results showed that soil water content in the study area belonged to medium variability and weak variability, and soil total salt content belonged to strong variability and medium variability. The theoretical models of soil water content and total salt content semi-variance function in the study area following the Gaussian model, with the block-base ratio less than 25%, with strong spatial autocorrelation, and the spatial correlation gradually increased with the increase of soil depth. The total salt content of the soil in the study area was interpolated with higher accuracy using radial basis functions as compared to ordinary kriging interpolation. In terms of temporal changes in salinity, the average salt accumulation rate of the 0–100 cm soil layer in the study area was 20.17% when salinity increased from May to June; the average desalination rate was 16.37% when salinity decreased from June to August. The main factors affecting soil salinity in cultivated land during the growing period were irrigation, precipitation, and planting crops, and the main factors affecting soil salinity in wasteland were precipitation and topography. The average coupling degree of soil water and salt in wasteland in the study area was lower than that of cultivated land, ranging from 65.15% to 86.59% of that of cultivated land. The level of coordination is marginal coordination for cultivated land and marginal disorder for wasteland. The study provides a theoretical basis for the prevention and control of soil salinization in arid areas.

Estimation of soil water content using electromagnetic induction sensors under different land uses

The complex nature of podzolic soils makes investigating their subsurface challenging. Near-surface geophysical techniques, like electromagnetic induction (EMI), offer significant assistance in studying podzolic soils. Multi-coil (MC-EMI) and multi-frequency (MF-EMI) sensors were selected to maximize soil water content (SWC) prediction in this study. The objectives were to (i) compare apparent electrical conductivity (ECa) measurements from the MC and MF-EMI sensors under different land use conditions, (ii) investigate the spatial variation of ECa, SWC, texture, soil organic matter (SOM), and bulk density (BD) under different land use conditions, and (iii) use statistical and geostatistical analysis to evaluate the effectiveness of ECa measurements in characterizing SWC under different land use conditions, considering the texture, SOM, and BD contents. The study found that MC-EMI had statistically significant relations (p-value < 0.05) with SWC relative to the MF-EMI. Multiple linear regression (MLR) models were also shown to be more effective in representing SWC variations (higher coefficient of determination and lower root mean square error) than simple linear regression models. MC-EMI sensor provided better SWC predictions compared to the MF-EMI sensor, possibly due to larger sampling depths differences between time domain reflectometry measured SWC (SWCTDR) and MF-EMI sensor than those between SWCTDR and MC-EMI sensor. Lastly, cokriging of measured SWC was found to offer more accurate maps than cokriging of predicted SWC obtained from MLR across different land use conditions. The study has shown that EMI may not be highly effective for shallow depths, and ECa can be affected by various soil properties, making it difficult to extrapolate other parameters. However, EMI still shows promise as a reliable method for predicting SWC in boreal podzolic soils. Research into EMI’s usefulness for this purpose has yielded promising results, as indicated in this study. Further investigation is needed to fully harness the potential of this promising technique.

Spatiotemporal Variability of Soil Water Content and Its Influencing Factors on a Microscale Slope

In order to enhance food security and promote sustainable agricultural development, there is extensive utilization of sloping land in China. However, soil and water loss are severe in sloping lands. Understanding the spatiotemporal variability of soil water content (θ) is therefore important for determining suitable soil and water conservation strategies. Nevertheless, there exists a dearth of current research that focuses on the spatiotemporal variability of θ in microscale sloping lands. This study used statistical and temporal stability (TS) analyses to explore the characteristics of the spatiotemporal variability of θ on slopes. Furthermore, this study aimed to quantify the impacts of soil depth, slope position, air temperature, and hydrological conditions on the TS of θ. The average θ increases with depth, and it follows a logarithmic increase above 1.3 m and a linear increase below 1.3 m. The spatial variability of θ is higher in shallow soils and wet seasons compared with deep soils and dry seasons. The temporal stability of θ is higher on the upper and lower slopes compared with the middle slope. Day-MRD is more effective at capturing the temporal stability of θ than all-MRD. The diurnal variation of the TS of θ on slopes is primarily influenced by soil depth, slope position, air temperature, and hydrological conditions. We found that soil depth had a greater impact on the TS of θ than the slope position and that air temperature has a greater influence than the hydrological conditions. This study accurately describes the spatiotemporal variability of θ at the microscale slope, which helps solve the problems of soil and water conservation and water resource management on slopes.

Similarities and Differences in the Earth’s Water Variations Signal Provided by Grace and AMSR-E Observations Using Maximum Covariance Analysis at Various Land Cover Data Backgrounds

ABSTRACT The study presents a compatibility analysis of gravimetric observations with passive microwave observations. Monitoring the variability of soil water content is one of the essential issues in climate-related research. Total water storage changes (ΔTWS) observed by Gravity Recovery and Climate Experiment (GRACE), enables the creation of many applications in hydrological monitoring. Soil moisture (SM) is a critical variable in hydrological studies. Advanced Microwave Scanning Radiometer (AMSR-E) satellite products provided unique observations on this variable in near-daily time resolutions. The study used maximum covariance analysis (MCA) to extract principal components for ΔTWS and SM signals. The analysis was carried out for the global area, dividing the discussion into individual continents. The amplitudes of gravimetric and microwave signals were computed via the complex empirical orthogonal function (EOF) and the complex conjugate EOF* to determine the regions for detailed comparison. Similarities and differences in signal convergence results were compared with land cover data describing soil conditions, vegetation cover, urbanization status, and cultivated land. Convergence was determined using Pearson correlation coefficients and cross-correlation. In order to compare ΔTWS and SM in individual seasons, ΔTWS observations were normalized. Results show that naturally forested areas and large open spaces used for agriculture support the compatibility between GRACE and AMSRE observations and are characterized by a good Pearson correlation coefficient &gt;0.8. Subpolar regions with permafrost present constraints for AMSR-E observations and have little convergence with GRACE observations.

Temperature and soil moisture control CO2 flux and CH4 oxidation in urban ecosystems

Climate-driven shifts in soil temperature and soil moisture are crucial factors that control the ecosystem-atmosphere greenhouse gas (GHG) balance. In the present study, the relationship between CO2, CH4 fluxes and soil moisture content and temperature sensitivity was examined in three dominating types of urban ecosystems: grassland, city park and arable land. The analysis was based on the field measurements at biweekly intervals over a year using a static closed chamber method in Wroclaw urban area, Poland. The observed patterns of land-atmosphere CO2 and CH4 exchange varied across land cover types and were strongly influenced by seasonal variations in temperature and soil water content. Emission of CO2 from grassland and the city park was two times higher than from the arable land. The calculated CH4 oxidation rate was one and half times higher (p < 0.05) under grassland and the city park as compared to arable land.The estimated Q10 values ranged between 1.68 and 1.79 for CO2 and from 1.26 to 1.49 for CH4, depending on the ecosystem type. The temperature sensitivity of soil respiration decreased when the temperature was above 24.5 °C across the moisture gradient from 20 to 25 % m/v. Results suggest that despite the urban areas with agricultural land use revealed the lowest CO2 fluxes compared to grassland and city park, the former showed the lowest seasonal mean CH4 oxidation. This indicates that with ongoing warming, the higher Q10 of CO2 production vs. CH4 oxidation will further shift the carbon balance towards the source and this shift will be especially critical for arable lands in urban areas.

Advanced monitoring of soil-vegetation co-dynamics reveals the successive controls of snowmelt on soil moisture and on plant seasonal dynamics in a mountainous watershed

Evaluating the interactions between above- and below-ground processes is important to understand and quantify how ecosystems respond differently to atmospheric forcings and/or perturbations and how this depends on their intrinsic characteristics and heterogeneity. Improving such understanding is particularly needed in snow-impacted mountainous systems where the complexity in water and carbon storage and release arises from strong heterogeneity in meteorological forcing and terrain, vegetation and soil characteristics. This study investigates spatial and temporal interactions between terrain, soil moisture, and plant seasonal dynamics at the intra- and inter-annual scale along a 160 m long mountainous, non-forested hillslope-to-floodplain system in the upper East River Watershed in the upper Colorado River Basin. To this end, repeated UAV-based multi-spectral aerial imaging, ground-based soil electrical resistivity imaging, and soil moisture sensors were used to quantify the interactions between above and below-ground compartments. Results reveal significant soil-plant co-dynamics. The spatial variation and dynamics of soil water content and electrical conductivity, driven by topographic and soil intrinsic characteristics, correspond to distinct plant types, with highest plant productivity in convergent areas. Plant productivity in heavy snow years benefited from more water infiltration as well as a shallow groundwater table depth. In comparison, low snowpack years with an early first bare-ground date, which are linked to an early increase in plant greenness, imply a short period of saturated conditions that leads to lower average and maximum greenness values during the growing season. Overall, these results emphasize the strong impact of snowpack dynamics, and terrain and subsurface characteristics on the heterogeneity in plant type and seasonal dynamics.

Spatiotemporal variability of soil physical properties and water, salt, nitrogen, and phosphorus contents for farm level

Soil water, salt, and nutrient variability are essential factors that impact crop productivity in agriculture systems. However, effective management of small farms requires access to fine-scale data on soil water, salt, and nutrients. Large-scale assessments of spatial variability using classical statistics and geostatistical methods can help identify nutrient-deficient zones. In Xinjiang, China, inadequate water and nutrient management has resulted in low crop productivity in agriculture systems. To address this issue, this study evaluated the mechanical composition, bulk density, and contents of water, salt, ammonium nitrogen ([Formula: see text]), nitrate nitrogen ([Formula: see text]), and available phosphorus (A-P) in soil at the farm level in the Xinjiang region. Results showed low variability in soil bulk density, medium variability in soil water content, mechanical composition, [Formula: see text], and A-P, and high variability in soil salt content and [Formula: see text]. Mechanical composition and A-P showed a small range of variation across different soil depths, while soil water content and [Formula: see text] in the surface layer varied significantly more than in other soil layers. [Formula: see text] variability increased with soil depth. Soil properties showed minimal differences over time. Multi-factor deficiencies, particularly in nitrogen, were observed throughout the study area. The generated maps offer a useful tool for farm managers and policymakers. In summary, this study highlights the significance of evaluating the spatial variability of soil properties for identifying zones deficient in water and nutrients, as well as those with salt accumulation. This information can be utilized to develop effective strategies for site-specific nutrient management.

Zeolite and Ascophyllum nodosum-Based Biostimulant Effects on Spinach Gas Exchange and Growth

Among the innovative practices of dry-farming in recent years, the possibility of the combined use of biostimulants and soil conditioners is assuming an important role. In a preliminary pot experiment, this study aimed to verify the combined effects of Ascophyllum nodosum-based biostimulant and zeolite applied to the soil on gas-exchange and spinach growth. We also monitored the soil water content to study the effect on spinach soil water uptake. Pots were filled with soil to which zeolite and an Ascophyllum nodosum-based biostimulant were added. Spinach plants grew into pots and were subjected to four treatments: (1) soil plus zeolite at a percentage of 1%, (2) soil plus the biostimulant, (3) soil plus zeolite at 1% and biostimulant, (4) bare soil as control. The use of the zeolite and the A. nodosum-based biostimulant led to a higher (+10%) soil water content, highlighting the positive role in allowing a good water uptake by the spinach plant. Plant growth was not changed, while only photosynthesis showed an increase equal to 6% in spinach plants. These results are discussed with the soil water content variation according to modification induced by treatments. The combined use of zeolite and A. nodosum-based biostimulant can be considered a strategy to improve water storage and, at the same time, improve spinach cultivation in terms of sustainability.

Stand structure of Central European forests matters more than climate for transpiration sensitivity to VPD

Abstract Temperature rise and more severe and frequent droughts will alter forest transpiration, thereby affecting the global water cycle. Yet, tree responses to increased atmospheric vapour pressure deficit (VPD) and reduced soil water content (SWC) are not fully understood due to long‐term tree adjustments to local environmental conditions that modify transpiration responses to short‐term VPD and SWC changes. We analysed sap flux density (SFD) of Fagus sylvatica, Picea abies, Pinus sylvestris and Quercus ilex from 25 sites across Europe to understand how daily variation in SWC affects the sensitivity of SFD to VPD (βVPD) and the maximum SFD (S95). Furthermore, we tested whether long‐term adjustments to site climatic conditions and stand characteristics affect βVPD and S95. The studied species showed contrasting βVPD and S95 with the largest values in F. sylvatica, followed by Q. ilex, which surpassed the two conifers that showed low βVPD and low S95. We observed that βVPD and S95 dropped during days of low SWC in F. sylvatica, P. sylvestris and Q. ilex, but not in P. abies. Both βVPD and S95 were driven by tree height, and the temperature and precipitation at the sites. However, stand basal area was the most important driver of βVPD and S95, explaining 30% of their total variance. Synthesis and applications: A future warmer and drier climate will restrict tree transpiration and thereby heavily affect the soil–plant‐atmosphere coupling. However, the effect of basal area, being the largest driver of tree transpiration sensitivity to vapour pressure deficit across a broad range of conditions, provides the opportunity to pre‐adapt European forests to future climate conditions. While stand thinning can increase the soil water availability for remaining trees, it also increases transpiration sensitivity to high air temperatures and may thereby amplify tree vulnerability to heat and drought.

Spatial variability of soil water content at the crop row scale with and without straw mulch inside a corn field in semi-humid Northeastern China

Soil water content (SWC) is an important but highly variable element of hydrological cycle. Understanding SWC spatial variability at the crop row-scale is critical for improving management of water, soils, and crops. This study investigated the SWC spatial variability at the row scale in corn (Zea mays L.) after the fields were treated with straw mulch (FPM) or without straw mulch (FP) in 2013 and 2014. The spatial variability in SWC was assessed from five horizontal measurement points (MPs), at 10-, 30-, 50-, and 70-cm depths using time domain reflectometry. The spatial variability in SWC among the five MPs was statistically significant for 19–75% of sampling dates and was most often different between the two treatments at 10- and 30-cm depths. Straw mulch most strongly affected the spatial variability of SWC at a 10-cm depth, but this effect differed between the two years. With respect to SWC, the FP treatment exhibited a higher range and lower maximum standard deviation and coefficient of variation compared to those of the FPM treatment. In the majority of sampling dates (more than 60%), the most representative SWC estimates were obtained at MPs positioned at one-quarter into the inter-row gap.

Estimation of Precipitation Fraction in the Soil Water of the Hillslope Vineyard Using Stable Isotopes of Water

This paper presents research related to the estimation of the precipitation fraction in the soil water of a sloped vineyard at the SUPREHILL Critical Zone Observatory (CZO) in Zagreb, Croatia. Numerous investigations have shown that exploration of hillslope soils can be very challenging due to the existence of heterogeneity and different soil properties, as well as due to anthropogenically induced processes, which can affect precipitation infiltration and soil water flow. Within this research, physicochemical soil properties, soil water content (SWC), and isotopic composition of soil water and precipitation (δ2H and δ18O) have been examined. The isotopic signature of soil water was monitored in 24 points, at 4 depths, throughout the hillslope vineyard. Soil water isotopic composition from all monitoring points coincided with the Local Meteoric Water Line (LMWL), with almost no variability at 100 cm depth, which was consistent with the smallest variation of SWC at 80 cm depth and indicated that most of water mixing takes place in the shallower part of the hillslope. Results suggested the existence of heterogeneity, uneven erosion processes in the footslope of the observed vineyard, and different infiltration patterns. Fractions of precipitation varied significantly depending on the depth and position in the vineyard, from approximately 1% up to 98%, where more precipitation fraction has been determined in the surface and subsurface runoff. Additionally, statistical analysis and a more detailed evaluation of precipitation fractions at the 40 cm depth, where wick lysimeters are installed, have shown that Corg content is related to the silt fraction, while the first results indicate that the infiltration patterns were dependent on the common influence of all observed physicochemical properties.

Assessment of soil water content variability using electrical resistivity imaging in an Oxisol under conservation cropping systems

Agricultural systems are increasingly challenged of achieving high yields while optimizing plant water consumption. Soil conservation practices are preponderant in rain-fed agriculture for increasing water infiltration, water storage in the soil, and for promoting root development. This study aimed to assess the spatial-temporal soil water content (θ) dynamics identified by the application of electrical resistivity tomography (ERT) surveys in an Oxisol under grain production systems in the Brazilian Cerrado. The utilized cropping systems were: soybean monoculture (SS); maize monoculture (MM); maize/soybean rotation (MS); maize/soybean rotation with intercropped brachiaria (MBSB); maize/soybean rotation with high fertilizer investment (MS-HI), and MBSB and high fertilizer investment (MBSB-HI). ERT measurements were performed at field conditions using different time-steps during the rainy (March, 2019) and dry seasons (July 2018 and 2019). Logarithmic and power models were tested for evaluating the relationships between θ and the electrical resistivity (ρ). Results showed ERT was adequate for monitoring the spatial-temporal θ variation and for inferring soil-plant related processes (i.e., water uptake and macro-porosity due to roots development). The power model was more suitable in depicting the θ - ρ relationship, and for imaging the water unavailability for plants during the dry periods. Intercropped brachiaria positively affected the θ dynamics due to its aggressive root systems. MBSB-HI showed the highest θ values in the rainy season, demonstrating that ecological intensified cropping systems can help overcome severe dry spells, in the Brazilian Cerrado.