Search

Abstract Many forests suffer increased drought stress due to climate change, particularly impacting Central Europe. However, our understanding considering drought stress and resulting tree mortality remains incomplete. For addressing this issue, fine-scale water balance assessment as well as robust and spatially integrating measures on large scales are necessary for forest ecosystem monitoring. The latter is particularly important to provide reliable data sets for verifying remote sensing and hydrological modelling products. Various traditional in-situ methods exist for assessing the water balance in forest ecosystems as for instance measuring the water content or matric potential. However, the spatial limitations of these methods have led to an increased importance of Cosmic Ray Neutron Sensing (CRNS) in the last two decades whose measuring signal is integrated over a larger area. We equipped two forest monitoring plots with ECH2O probes, Tensiomark soil systems, and installed a CRNS station at one site to measure soil water content and matric potential at different soil depths and distances to trees from November 2020 till November 2023. The results indicate distinct temporal and spatial variations influenced by meteorological conditions and soil properties, but also forest characteristics. The year 2022 is identified as exceptionally dry, causing high drought stress at one of the forest sites. The comparison between CRNS and traditional methods reveals a strong correlation, highlighting CRNS' potential in forest monitoring as a promising tool for an area wide assessment of water availability in forest ecosystems. Our study further advocates for the need of tree species-specific thresholds to assess matric potential in relation to drought stress in order to better assess the impact of climate change on our forest ecosystems.

Many forests suffer increased drought stress due to climate change, particularly impacting Central Europe. However, our understanding considering drought stress and resulting tree mortality remains incomplete. For addressing this issue, fine-scale water balance assessment as well as robust and spatially integrating measures on large scales are necessary for forest ecosystem monitoring. The latter is particularly important to provide reliable data sets for verifying remote sensing and hydrological modelling products. Various traditional in-situ methods exist for assessing the water balance in forest ecosystems as for instance measuring the water content or matric potential. However, the spatial limitations of these methods have led to an increased importance of Cosmic Ray Neutron Sensing (CRNS) in the last two decades whose measuring signal is integrated over a larger area. We equipped two forest monitoring plots with ECH2O probes, Tensiomark soil systems, and installed a CRNS station at one site to measure soil water content and matric potential at different soil depths and distances to trees from November 2020 till November 2023. The results indicate distinct temporal and spatial variations influenced by meteorological conditions and soil properties, but also forest characteristics. The year 2022 is identified as exceptionally dry, causing high drought stress at one of the forest sites. The comparison between CRNS and traditional methods reveals a strong correlation, highlighting CRNS' potential in forest monitoring as a promising tool for an area wide assessment of water availability in forest ecosystems. Our study further advocates for the need of tree species-specific thresholds to assess matric potential in relation to drought stress in order to better assess the impact of climate change on our forest ecosystems.Article Highlights : Soil moisture monitoring using soil water content, matric potential, and neutron activity at one, respectively two forest sites. Very high correlation between the water content based on soil probes and the water content based on the CRNS. CRNS offers high potential in forest monitoring for assessing the soil water content on a larger scale. [ABSTRACT FROM AUTHOR]

The heat generated by high-level radioactive waste can pose numerical and physical challenges to subsurface flow and transport simulators if the liquid water content in a region near the waste package approaches residual saturation due to evaporation. Here, residual saturation is the fraction of the pore space occupied by liquid water when the hydraulic connectivity through a porous medium is lost, preventing the flow of liquid water. While conventional capillary pressure models represent residual saturation using asymptotically large values of capillary pressure, here, residual saturation is effectively modeled as a tortuosity effect alone. Treating the residual fluid as primarily dead-end pores and adsorbed films, relative permeability is independent of capillary pressure below residual saturation. To test this approach, PFLOTRAN is then used to simulate thermal-hydrological conditions resulting from direct disposal of a dual-purpose canister in unsaturated alluvium using both conventional asymptotic and revised, smooth models. While the two models have comparable results over 100 000 years, the number of flow steps required is reduced by approximately 94%. [ABSTRACT FROM AUTHOR]

Peat-based casings have been used for button mushroom (Agaricus bisporus) cultivation for decades but there is environmental pressure to find sustainable alternatives. This work aimed to characterise the physicochemical properties of peat and peat-substituted casings and to determine their influence on mushroom cropping to enable alternatives to be identified. British milled peat and German wet-dug peat casings produced smaller mushrooms than Irish wet-dug peat casing although yield was unaffected. Substitution of milled or wet-dug peat casings with 25% v/v bark, green waste compost or spent mushroom casing, except Irish wet-dug peat casing with spent peat mushroom casing, caused reductions in mushroom yield and/or size. These poorer results of casings compared with Irish wet-dug peat casing corresponded with lower water retention volumes at matric potential (Ψ m) −15 kPa but not after drainage from saturation or at −1 kPa. Air-filled porosity (17–22% v/v), compacted bulk density after drainage (670–800 g L−1) and electrical conductivity (0.30–0.54 mS cm−1) of casings were unrelated to their mushroom cropping performance. In-situ casing measurements with electronic tensiometers confirmed laboratory casing physical analysis: at the same casing Ψ m , Irish wet-dug peat casing had a higher water content than German wet-dug peat casing and produced larger mushrooms for the same yield. Solid-state foam-based tensiometers were more robust than water-filled tensiometers but they did not detect the full decrease in casing Ψ m during a flush of mushrooms. The results indicate that if sustainable materials are to replace wet-dug peat casing with the same mushroom yield and size quality performance, they should have equivalent water retention volumes at Ψ m −15 kPa. Measurement of casing Ψ m with electronic tensiometers to control mushroom crop irrigation should assist in this transition. [ABSTRACT FROM AUTHOR]

As climate change continues, forests are increasingly suffering from drought stress, which is leading to widespread forest dieback, but also to increased mortality of individual trees. In this regard, the impact of small-scale differences in water availability on individual trees has not yet been sufficiently studied to determine possible responses of different tree species to future droughts. Since conventional soil moisture monitoring and sampling methods only consider single points or small volumes, Electrical Resistivity Tomography (ERT) is becoming increasingly important to cover a larger survey area and to detect small-scale heterogeneities with regard to soil properties and soil moisture.The current study describes the application of a combined two- and three-dimensional geoelectrical monitoring approach with daily measurements over two years (May 2021 – April 2023) in a forest ecosystem in Lower Franconia (northwestern Bavaria, Germany), which is strongly affected by climate change. Soil water content, soil matric potential, throughfall, and stem flow are also measured at the forest site as well as precipitation at an adjacent forest clearing.The seasonally (long-term) and precipitation-driven (short-term) temporal change of soil resistivity is correlated strongly with the measured soil water content and matric potential. The applied 3D-ERT approach also allowed a first three-dimensional monitoring of the subsurface below a European beech located in the middle of the measuring grid with a daily resolution. The corresponding results also provide first indications that besides soil moisture changes also chemical processes in the subsurface may influence temporal resistivity changes in the soil of forest sites.The results of this study show that daily 3D-ERT is very suitable for investigating small-scale as well as short- and long-term variations in soil moisture, which is becoming increasingly important for understanding the causal relationships considering tree mortality and the subsurface.

Athelia rolfsii, causal agent of "southern blight" disease, is a soilbome fungal pathogen with a wide host range of more than 500 species. This study's objectives were to (i) quantify the effects of two environmental factors, temperature and soil moisture, on germination of A. rolfsii inoculum (sclerotia), which is a critical event for the onset of disease epidemics and (ii) predict the timing of sclerotial germination by applying populationbased threshold-type hydrothermal time (HTT) models. We conducted in vitro germination experiments with three isolates of A. rolfsii isolated from peanuts, which were tested at five temperatures (7), ranging from 17 to 40°C, four matric potentials (W) between -0.12 and -1.57 MPa, and two soil types (fine sand and loamy fine sand), using a factorial design. When Mm was maintained between -0.12 and -0.53 MPa, T from 22 to 34°C was found to be conducive to sclerotial germination (>50%). The HTT models were fitted for a range of T (22 to 34°C) and Mm (-0.12 to -1.57 MPa) that accounted for 84% or more of variation in the timing of sclerotial germination. The estimated base T ranged between 0 and 4.5°C and the estimated base Mm between -2.96 and -1.52 MPa. The results suggest that the HTT modeling approach is a suitable means of predicting the timing of A. rolfsii sclerotial germination. This HTT methodology can potentially be tested to fine-tune fungicide application timing and in-season A. rolfsii management strategies. [ABSTRACT FROM AUTHOR]

The lack of long‐term reliable in‐situ soil moisture data sets creates unique drought monitoring challenges for the semi‐arid Southwestern United States ("Southwest"). Land managers use multiscalar meteorological drought indices, like the Standardized Precipitation Index (SPI) and Standardized Precipitation‐Evapotranspiration Index (SPEI), as proxies for soil water availability; however, objectively identifying the index and timescale that best represents soil water availability in semi‐arid environments remains a significant gap for applying available climate information to land management action. Here, we couple site‐specific soil modeling with high resolution, spatially continuous meteorological data sets to define the relationship between index timescale length and soil water availability of different depths. By creating new matric potential indices (MPI) from 0 to 200 cm, we correlate MPI time series with the SPI and SPEI at different timescale lengths to identify the best index‐timescale combination for each depth. Results indicate the general relationship between highest correlating index‐timescale and MPI‐depth operates roughly on a 1‐month:5 cm step progression at shallow depths (<80 cm). Analysis by soil texture class shows that soils with higher clay content produce shallower sloped relationships (>1‐month:5 cm) than sandy soils (<1‐month:5 cm). Overall, the SPI produced higher correlations and less error with the MPI compared to the SPEI across all texture classes and depths. Thus, the SPI is a good indicator of soil water availability at shallow depths (<80 cm) and should be considered for soil drought monitoring on Southwestern drylands. However, land managers should consult local soils information, if available, given the impacts of texture class on timescale‐depth relationships. Plain Language Summary: Vegetation productivity in the semi‐arid Southwestern United States ("Southwest") is adapted to the seasonal timing and magnitude of precipitation for soil water recharge. However, a lack of soil moisture data sets creates unique drought monitoring challenges. Many land managers utilize the variable timescale lengths of multiscalar drought indices, like the Standardized Precipitation Index (SPI) and Standardized Precipitation‐Evapotranspiration Index (SPEI), to approximate the time lag associated with water movement through a soil profile. However, objectively identifying the index and timescale length that best represents soil water availability in the Southwest remains a significant gap for applying available climate information to land management action. In this study, we conduct a regional analysis of the Southwest to define the relationship between index timescale length and soil water availability at different depths. Results show this relationship generally operates in a linear fashion for both indices but changes by depth and soil texture—with clay soils producing shallower sloped relationships compared to sandy soils. Additionally, the SPI more closely matches soil water variability through time compared to the SPEI. Thus, the SPI should be considered for Southwestern drought monitoring; however, land managers should consult local soils information, if available, given the impacts on timescale‐depth relationships. Key Points: The Standardized Precipitation Index is a good indicator of shallow soil water availability for the semi‐arid Southwestern United StatesThe general index‐timescale to soil‐water‐depth relationship operates on a 1‐month to 5 cm step progression at shallow depths (<80 cm)Clay loam soils produce shallower sloped timescale‐depth relationships and higher correlations with drought indices compared to sandy soils [ABSTRACT FROM AUTHOR]

Introduction Drought stress is one of the most common environmental stresses that limits agricultural production through disruption of physiological processes and reduces plant performance. Since in most parts of the world, including in Iran, melon plants and generally pumpkins are cultivated in hot and dry areas, and in these areas the main challenge is due to the limitation of suitable water for agriculture, the possibility of various types of stress, including water deficit stress (partial or severe) in the cultivation of these plants is relatively high. From this point of view, it seems necessary to study and know the tolerant cultivars and masses and ways to improve water management. Among the physiological characteristics, leaf water status, membrane stability, photosynthesis changes and related factors are of special importance in relation to tolerance of stressful conditions and especially dehydration. A review of scientific sources shows that due to the relative importance of melons among fruit vegetables, no comprehensive research has been done on the effect of water stress on the yield and stress level evaluation indicators in Garmak and Dudaim groups. This research has tried to investigate and evaluate this issue in some products of this group of vegetables that have been less studied. Materials and Methods This experiment was carried out in the form of a split plot design in the form of randomized complete blocks and in four replications in the Mahan greenhouse complex located 25 km from Kerman province. Experimental treatments include; There were three plants (Shahdad and Isfahan cantaloupe (Garmak) and Birjand dudaim (Cucumis melo group dudaim)) and three levels of irrigation in order to apply stress (starting irrigation at matric potentials of -45 (control), -55 and -65 kPa). The parameters of net photosynthesis rate, stomatal conductance, leaf transpiration rate, leaf chlorophyll index, water potential, osmosis and turgor potential of leaves, water use efficiency and leaf relative humidity were measured and evaluated. Results and Discussion Based on the results of the first and third tables, the three population were different in the changes in the net rate of photosynthesis under different levels of dehydration stress, but the change process in them was largely similar. The highest rate of net photosynthesis and leaf stomatal conductance was obtained in Isfahan cantaloupe population plants under control irrigation (-45 kPa), which, of course, did not have a significant difference with plants under -55 kPa dehydration stress, and the lowest rate of these traits in Birjand dudaim under irrigation at matric potential -65 kPa was measured. A more severe level of dehydration stress (starting irrigation at matric potential of -65 kPa) reduced the net photosynthetic rate in all three plants compared to control irrigation (-45 kPa). It seems that under the conditions of this experiment, the reduction of the relative humidity of the leaves occurs following the reduction of the water potential in the leaves and leads to the closing of the stomata in order to increase the resistance of the mesophyll cells against the dehydration stress and parallel to these changes, the reduction it happens in the amount of stomatal conductance and as a result the rate of net photosynthesis. The rate of leaf transpiration in matric potentials of -55 and -65 kPa has decreased significantly compared to control irrigation. The decrease in transpiration rate in plants under stress is probably due to stomatal closure and reduction of stomatal conductance. Plants under stress prevent excessive water loss through transpiration by regulating stomata. Based on the results of the second and fourth tables, by measuring the water potential, osmosis and turgor potential of the leaves of the three population used, it was shown that the water potential of the leaf decreased with the increase in the water stress levels. The slope of this decrease is such that the potential values are equal to the osmotic potential values of the leaf and the turgor potential, which is the result of the difference between the osmotic and water potentials of the leaf, also decreases, but it is the turgor pressure that has increased and in a more positive way. even at the end of the stress period and at the most extreme level of stress, it reaches zero. This same turgor pressure maintains the normal state of the membrane in cells under dehydration stress. In fact, the extreme level of water stress in this experiment significantly reduced the osmotic potential of the leaf. The highest amount of osmotic potential (8.5 Bar) for these plants was obtained in the usual or control irrigation treatment and the lowest (22 Bar) in the more severe level of dehydration stress treatment (watering as soon as the matric potential reaches -65 kPa) was obtained. At matric potentials of -45 and -55, there was no significant difference between the three population in terms of leaf relative humidity percentage, but in Garmak and Dudaim populations, the relative humidity of leaves was significantly reduced by applying stress at the matric potential of -65 kPa. This is despite the fact that in the Isfahan cantaloupe, the decrease in the relative humidity of the leaf was not significant. The existence of this difference in the reduction of the relative humidity of the leaves in the conditions of stress between the three plants may be due to the genetic differences in the ability of the stomata of the plants to lose water. In fact, more drought tolerant population (Isfahan Garmak) compared to Shahdad Garmak and Birjand dudaim have better maintained relative humidity until the end of the stress. Conclusion Plants with the ability to regulate osmosis can be considered as drought tolerant plants. This adjustment in the plants of this experiment occurred in the condition that in all three population, the osmotic potential decreased by -19 to -22 Bar. This event is to some extent guaranteeing the performance of pure photosynthesis, although at a low rate in these plants, in the condition that the water potential of the cell has become negative at the level of severe water deficit stress, at the end of growth.

Jatropha curcas plant is known for its soil tolerance and ability to thrive in low humidity conditions; however, there is a lack of systematic reports documenting the impact of limited water availability on its growth and development. This work aimed to analyze the development of J. curcas cultivated with daily supplementation of limited amounts of water. Five daily irrigation treatments were established to simulate varying annual rainfall levels: 250, 750, 1250, 1750 mm and 2250 mm. In each treatment, we used 16 seedlings of J. curcas MAP-08. The seedlings were sown in pots containing loam soil substrate mixed with vermicompost (19: 1 weight to weight). After 60 weeks of cultivation, plants receiving irrigation of 2250 mm per year exhibited growth rates 1.28, 1.51, 1.95 and 1.95 times higher, with respective increases in stem diameter of 15.6, 22.2, 41.9% and 47.7%, as well as 1.2, 1.4, 1.8, and 1.8 more leaves compared to those receiving 1750, 1250, 750, and 250 mm. There was no statistical difference in the number of branches (3.86 branches per plant) between the plants of the treatment with irrigation of 2250, 1750 mm and 1250 mm per year or between the plants belonging to the 750 and 250 mm per year (2.90 branches per plant) treatments. The plants of treatments 1750 and 2250 were the only ones that produced flowers. Although J. curcas typically functions as a succulent deciduous bush, with its stem serving to regulate leaf water potential and acting as a shock absorber against soil water potentials, its morphological and reproductive characteristics were recorded to be negatively affected when subjected to reductions of 22, 44, 67% and 89% in water availability compared to the maximum annual level recorded in the work area (2250 mm).

Soil pore structure and soil water content are critical regulators of microbial activity and associated carbon dioxide (CO2) emissions. This study evaluated the impacts of soil bulk density and matric potential on carbon dioxide (CO2) emissions through modifications of total porosity, air-filled porosity, water retention, and gas diffusivity. Soil samples were manipulated into four bulk densities (1.0, 1.1, 1.2, and 1.3 Mg m−3) and ten matric potential levels (−1, −2, −3, −4, −5, −6, −7, −8, −9, and −10 kPa) in controlled soil cores. The results showed that lower bulk densities enhanced while higher densities suppressed CO2 emissions. Similarly, wetter matric potentials decreased fluxes, but emission increased with drying. Correlation and regression analyses revealed that total porosity (r = 0.28), and gravimetric water content (r = 0.29) were strongly positively related to CO2 emissions. In contrast, soil bulk density (r= −0.22) and matric potential (r= −0.30) were negatively correlated with emissions. The results highlight that compaction and excessive water content restrict microbial respiration and gas diffusion, reducing CO2 emissions. Proper management of soil structure and water content is therefore essential to support soil ecological functions and associated ecosystem services. [ABSTRACT FROM AUTHOR]

Copyright of Revista de Ciencias Agricolas is the property of University of Narino, Faculty of Agricultural Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Direct soil water retention curve (SWRC) measurement is laborious, time-consuming, and expensive. To estimate its parameters, mathematical models and optimization approaches are applied. In this study, an improved alternative method to solve the optimization problem was introduced and developed. To evaluate the efficiency of this method, 12 soil samples with 6 different textures from 9 different regions of the world were used. The optimization equations were solved using a genetic algorithm (GA) and standard mathematical models, and the best model was chosen based on Taylor diagrams, R2, and computing time. The Bimodal versions of Fredlund-Xing (FX-b) and Brooks-Corney (BC) mathematical models represented the best and poorest findings of this stage, with R2 values of 0.913 and 0.825, respectively. Then, the optimization problem is solved with differential evolution (DE), Salp Swarm Algorithm (SSA), Jaya, and improved Jaya (I-Jaya) method, and the mean values of R2 were obtained 0.919, 0.931, 0.921, and 0.958, respectively. The results indicated a 16% improvement in the average R2, by selecting the suitable mathematical model and also using the I-Jaya.

Soil unsaturated hydraulic conductivity (K), which depends on water content (θ) and matric potential (ψ), exhibits a high degree of variability at the field scale. Here we first develop a theoretical hydraulic‐electrical conductivity (σ) relationship under low and high salinity cases based on the capillary bundle model and Waxman and Smits model which can account for the non‐linear behavior of σ at low salinities. Then the K‐σ relationship is converted into a K(θ, ψ) model using the Brooks‐Corey model. The model includes two parameters c and γ. Parameter c accounts for the variation of the term (λ + 2)/(λ + 4) where λ is the pore size distribution parameter in the Brooks‐Corey model, and the term m‐n where m and n are Archie's saturation and cementation exponents, respectively. Parameter γ is the sum of the tortuosity factor accounting for the differences between hydraulic and electrical tortuosity and Archie's saturation exponent. Based on a calibration data set of 150 soils selected from the UNSODA database, the best fitting log(c) and γ values were determined as −2.53 and 1.92, −4.39 and −0.14, −5.01 and −1.34, and −5.79 and −2.27 for four textural groups. The estimated log10(K) values with the new K(θ, ψ) model compared well to the measured values from an independent data set of 49 soils selected from the UNSODA database, with mean error (ME), relative error (RE), root mean square error (RMSE) and coefficient of determination (R2) values of 0.02, 8.8%, 0.80 and 0.73, respectively. A second test of the new K(θ, ψ) model using a data set representing 23 soils reported in the literature also showed good agreement between estimated and measured log10(K) values with ME of −0.01, RE of 9.5%, RMSE of 0.77 and R2 of 0.85. The new K(θ, ψ) model outperformed the Mualem‐van Genuchten model and two recently published pedo‐transfer functions. The new K(θ, ψ) model can be applied for estimating K under field conditions and for hydrologic modeling without need for soil water retention curve data fitting to derive a K function. Key Points: A new unsaturated hydraulic conductivity model was developed in terms of independent θ and ψ valuesBest fitting values of two parameters in the new unsaturated hydraulic conductivity model were determined from 150 soils in the calibration data setThe new model provided reliable estimates of hydraulic conductivity for 72 soils from two independent data sets [ABSTRACT FROM AUTHOR]

Soil moisture content and matric potential are two important parameters for determining soil water characteristic curve (SWCC), which has significant differences for different types of soils. The common method to determine SWCC under field condition is using two separated sensors to measure moisture content and matric potential of the tested soils. However, measurement error may occur due to soil spatial heterogeneity around two sensors. In this study, a novel composite sensor was designed to simultaneously measure soil moisture content, matric potential, and temperature. The composite sensor consists of a 32-bit MCU main control chip, relay switching module, dielectric measurement module for determining soil moisture content and matric potential, and temperature measurement module. The main MCU control chip measures soil moisture content, matric potential, and temperature through controlling the relay switching, and performs temperature correction as well. The performances of the composite sensor were tested for soil moisture content and soil matric potential measurements including monotonicity, calibration, volume of sensitivity, response time, etc. To test the monotonicity of the dielectric mode, the length of high frequency transmission line was gradually increased and the sensor output was recorded when the probes of soil moisture content and soil water potential were moistened from dry to saturation. The three modes, soil moisture content, soil matric potential and temperature were calibrated respectively using forest soil, farmland loam and sandy soil. To determine the volume of sensitivity of the soil moisture content mode, the probe of soil moisture content was installed in a soil sample. The soil sample was gradually removed layer by layer and meanwhile the output of the soil moisture content was recorded. When the output started to decrease, the radius of volume of sensitivity was determined by measuring the thickness of residual soil layer from surface to the probe. To determine the response time of soil moisture content and soil matric potential modes, the composite sensor probe was firstly dried and then put into a saturated soil sample. Meanwhile, the output of the soil moisture content and soil matric potential was recorded as time elapse. When the recorded output of each mode did not remarkedly change, the elapsed time was the response time. Experiments for sensor observation were conducted using forest soil, farmland loam and sandy soil under laboratory condition at 25 °C. The experimental results were compared with those measured using commercial instruments. The results showed that the composite sensor had a good monotonicity when measuring soil moisture content and matric potential in the range from dry to near saturation. After calibration, the composite sensor can determine soil moisture content, matric potential and temperature with high accuracies, achieving the determination coefficients larger than 0.98. The measurement ranges of volumetric soil water content and soil matric potential were 0%-40% and -1 500--15 kPa, respectively, which is feasible for most soil textures. The response time of the soil moisture content and soil matric potential was 450 ms and 150 s, respectively. The temperature coefficient of the circuit board of the composite sensor was yielded to correct the temperature induced output variation. The SWCCs of forest soil, farmland loam and sandy soil were determined using both the commercial instruments and the composite sensor during wetting and drying processes. The hysteresis between soil drying and wetting processes was also observed as expected. The Pearson correlation coefficients between the SWCCs measured by the two methods were larger than 0.96 during wetting and drying processes, i.e., 0.962 and 0.983 for the forest soil, 0.993 and 0.995 for the farmland loam, and 0.979 and 0.998 for the sandy soil. The composite sensor developed in this study can accurately determine soil water characteristic curves of different types of soils. [ABSTRACT FROM AUTHOR]

Soil pore structure and soil water content are critical regulators of microbial activity and associated carbon dioxide (CO2) emissions. This study evaluated the impacts of soil bulk density and matric potential on carbon dioxide (CO2) emissions through modifications of total porosity, air-filled porosity, water retention, and gas diffusivity. Soil samples were manipulated into four bulk densities (1.0, 1.1, 1.2, and 1.3 Mg m−3) and ten matric potential levels (−1, −2, −3, −4, −5, −6, −7, −8, −9, and −10 kPa) in controlled soil cores. The results showed that lower bulk densities enhanced while higher densities suppressed CO2 emissions. Similarly, wetter matric potentials decreased fluxes, but emission increased with drying. Correlation and regression analyses revealed that total porosity (r = 0.28), and gravimetric water content (r = 0.29) were strongly positively related to CO2 emissions. In contrast, soil bulk density (r= −0.22) and matric potential (r= −0.30) were negatively correlated with emissions. The results highlight that compaction and excessive water content restrict microbial respiration and gas diffusion, reducing CO2 emissions. Proper management of soil structure and water content is therefore essential to support soil ecological functions and associated ecosystem services.

Extreme weather phenomena are on the rise due to ongoing climate change. Therefore, the need for irrigation in agriculture will increase, although it is already the largest consumer of water, a valuable resource. Soil moisture sensors can help to use water efficiently and economically. For this reason, we have recently presented a novel soil moisture sensor with a high sensitivity and broad measuring range. This device does not measure the moisture in the soil but the water available to plants, i.e., the soil water potential (SWP). The sensor consists of two highly porous (>69%) ceramic discs with a broad pore size distribution (0.5 to 200 μm) and a new circuit board system using a transmission line within a time-domain transmission (TDT) circuit. This detects the change in the dielectric response of the ceramic discs with changing water uptake. To prove the concept, a large number of field tests were carried out and comparisons were made with commercial soil water potential sensors. The experiments confirm that the sensor signal is correlated to the soil water potential irrespective of soil composition and is thus suitable for the optimization of irrigation systems. [ABSTRACT FROM AUTHOR]

Pore-water pressure in soil is caused by three physically distinguishable sources: ambient (environmental) pressure, surface tension–induced capillary pressure, and the soil's electromagnetic potential–induced adsorptive pressure. The former two form the conventional concept of pore-water pressure, which is considered a constant within a soil-water-air representative elementary volume and can be directly measured by piezometer (under saturated and compressive states) or tensiometer (under unsaturated and tensile states). The third one can be called adsorption-induced pore-water pressure and is localized within a certain distance to the particle surface of soil or intercrystalline surface of swelling clay. The adsorption-induced pore-water pressure is always compressive and dictates the water phase transition in soil by altering water's freezing point, density, and viscosity, among other physical properties. A framework of quantifying the adsorption-induced pore-water distribution via the measured soil water isotherm is presented for any soil type under any given water content. It is demonstrated that the adsorption-induced pore-water pressure can be up to 1.6 GPa in the first few layers of hydration, but will diminish to zero at a distance equivalent to the gravimetric water content >1% for sandy soil and greater than a few percent for silty soil. In clayey soil, the adsorption-induced pore-water pressure can sustain tens of megapascals even at much farther distance, equivalent to ∼30% water content. In expansive clay, the adsorption-induced pore-water pressure inside the crystalline lamellae can exceed 800 MPa. The soil water density functions of a silty soil and a bentonite clay predicted by the proposed framework matched well with that measured independently from the conventional consolidation testing, validating the framework to determine the spatial distribution of the adsorption-induced pore-water pressure in soil. [ABSTRACT FROM AUTHOR]

This 20-month study of a prairie hillslope seep system builds upon and extends the soil moisture record from a previous study conducted during the most extreme drought ever recorded in Texas. We seek to improve understanding of how prolonged drought impacts seep-headwater hydrology, and to determine how well dominant vegetation reflects changes in volumetric soil moisture (θv). Results show the entire hillslope saturates after storm events, but due to severe drought, no surface runoff or channel flow was recorded. We documented changes in soil moisture, with the highest θv occurring along the deeper footslope soils. We hypothesize hyperseasonal environments, or seasonal waterlogging/desiccation of upland vegetation in poorly drained soils, exist in the study area and are the first to quantify hyperseasonality, or % change in magnitude of θv throughout a hydrologic year. The seep and riparian plots aligned with lower hyperseasonality, indicating seasonal hypoxia, but not complete desiccation. High hyperseasonality occurred along the midslope barrens, indicative of a true hyperseasonal environment. We suggest a ≥ 90% threshold would likely indicate true hyperseasonal cyclicity of anaerobic and xeric regimes. Our results provide insight to how extreme drought impacts seep-headwater systems, and how predicted hotter, drier conditions may alter their hydrologic regime. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study developed and evaluated an electronic irrigation system controlled by soil water matric potential. The controller uses tensiometers and pressure transducers as a reading mechanism, integrated with an Arduino microcontroller board that drives the solenoid valves and a 1/3 hp single-phase motor. Four electronic tensiometers were installed in plastic containers filled with 6 kg of Red-Yellow Latosol (RYL) with a clayey texture, and another four in plastic containers filled with 7 kg of Regolitic Neosol (RN) with a sandy texture. Irrigation automation components were activated autonomously at the critical potentials of -20, -25, -30, and -35 kPa for RYL, and -10, -15, -20, and -25 kPa for RN, with a 20% variation tolerance. The entire system is able to monitor and control irrigation based on soil water matric potential. Components were deactivated when the soil water potential reached the field capacity of each soil type. Irrigation automation performance was considered satisfactory, as it kept critical potentials within the pre-established thresholds in both soil types. Automation control was set for matric potentials between -10 kPa and -35 kPa in RYL, and between -5 kPa and -25 kPa in RN.

A soil's elastic modulus is a fundamental property defining the soil's reversible stress-strain relation under mechanical and environmental loadings. It has been observed that a soil's elastic modulus can increase up to several orders of magnitude from fully saturated to dry conditions due to two distinct soil water retention mechanisms: adsorption and capillarity. Adsorption affects interparticle stress through van der Waals and electrostatic attraction and interparticle friction coefficient through water film retained by soil sorptive potential. Capillarity governs interparticle stress through capillary pressure and surface tension. The onset and scaling laws of the two mechanisms depend on the soil properties of specific surface area, pore-size distribution, cation exchange capacity, and soil mineralogy. These mechanisms are unified by a proposed elastic modulus characteristic curve (EMCC) equation. It is demonstrated that the proposed EMCC equation can well describe the moisture-dependent elastic modulus of a wide array of soils. Further, an interrelation among the EMCC equation, suction stress and soil shrinkage curves is established, which can greatly facilitate predicting suction stress from soil shrinkage curves and vice versa, further validating the EMCC equation in capturing soil's hydromechanical behavior. The practical importance of the EMCC equation is demonstrated through prediction of ground heave of various soils due to a hypothetical flooding event. [ABSTRACT FROM AUTHOR]

Copyright of Investigación e Innovación en Ingenierías is the property of Universidad Simon Bolivar and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Carbon (C) substrates are critical for regulating denitrification, a process that results in nitrous oxide (N2O) and dinitrogen (N2) emissions from soil. However, the impacts of C substrates on concomitant soil emissions of carbon dioxide (CO2) and N2O under varying soil types and soil water contents are not well studied. Three repacked Pallic grassland soils, varying in texture and phosphorus (P) status, containing NO3−‐15N were held at three levels of matric potential (ψ, −3, −5 and −7 kPa), while receiving daily substrate additions (acetate, glucose and water control) for 14 days. The CO2 and N2O emissions were measured daily. Additionally, the N2O:(N2 + N2O) ratios were determined using 15N on days 3 and 14. Results showed that N2O emissions increased exponentially as soil gas diffusivity declined, and N2O peak emissions were higher with glucose than with acetate addition, with a range (± standard deviation) of 0.1 ± 0.0 to 42.7 ± 2.1 mg N m−2 h−1. The highest cumulative N2O emission (2.5 ± 0.2 g N m−2) was measured following glucose addition with a soil ψ of −3 kPa. In comparison with added glucose, acetate resulted in a twofold increase in N2 emissions in soils with relatively low gas diffusivities. The N2O:(N2O + N2) emissions ratios varied with substrate (glucose, 0.91; acetate, 0.81) on day 3, and had declined by day 14 under substrate addition (≤0.10). Cumulative CO2 emissions were enhanced with increasing soil gas diffusivity and were higher for soils amended with glucose (ranging from 22.5 ± 1.3 to 36.6 ± 1.8, g C m−2) than for those amended with acetate. Collectively, the results demonstrate that the increase of N2O, N2 and CO2 emissions and changes in the N2O:(N2 + N2O) ratio vary over time in response to C substrate type and soil gas diffusivity. Highlights: Co‐regulation of CO2 and N2O emissions was assessed for varying soil types and C substrates.Soil diffusivity explained concurrently cumulative N2O and CO2 emissions.Acetate enhanced N2O reduction to N2 in three grassland soils more than glucose.C substrate effects on soil N2O, N2 and CO2 emissions were soil type specific. [ABSTRACT FROM AUTHOR]

Frost heave damage is caused by the in situ freezing of pore water and segregated ice due to moisture migration. Previous studies have shown that in freezing soil, moisture migration is related to the pore water pressure gradient, and moisture migration is the dominant reason for the formation of an ice lens. However, the essential relationship between ice segregation and the matric potential is still controversial. Using a pF meter sensor, a 5TM volume water content sensor, and a digital image capture system, the relationship between the matric potential and the unfrozen water in saturated freezing soil was monitored in real time, and digital images of the formation of segregated ice were collected. Furthermore, the time space coupling relationships between the unfrozen water, the matric potential, the frost-heaving amount, the moisture migration, and the formation of an ice lens were systematically analyzed during soil freezing. The results demonstrate that there is an internal relationship between the moisture migration driven by the matric potential (from the micro-perspective) and the segregated ice layer effect (from the macroscopic perspective). In addition, the unfrozen water and the matric potential in the frozen area have a significant impact on the distribution of the segregated ice lenses. [ABSTRACT FROM AUTHOR]

Reclaiming histosols in Montéregie region, Québec, Canada, increases peat decomposition and compaction rate and decreases the effectiveness of subsurface drainage. The objective of this paper was to use HYDRUS-2D to model the behavior of subsurface drainage systems, in order to evaluate the compaction effect on drain depth and spacing, and to determine the compact layer thickness and saturated hydraulic conductivities (Ksat) resulting in an improvement of subsurface drainage]. The drainage model was calibrated [Nash-Sutcliffe efficiency coefficient (NSE) = 0.958, percent bias (PBIAS) = −0.57%] using Ksat, meteorological data, and matric potential (h) data measured on the project site from June 10 to July 19, 2017. The calibrated and validated model was used to analyze the variation of h values (Δh in cm d−1) as a function of drain spacing (2–7 m) and drain depth (1 and 1.2 m) and to identify the response surface of Δh to various compact layer thickness and Ksat combinations. The results showed that Δh was on average 58% greater below the compact layer than above it and that reducing drain spacing or increasing drain depth does not improve the drainage rate. The analysis of the compact layer thickness and Ksat effect on Δh showed that for a Δh of 40 cm d−1, Ksat actual values in the two uppermost layers should be multiplied by 50 for compact layer thickness varying from 12 to 35 cm. Water percolation in the soil is reduced by the compact layer. Soil management methods for improving Ksat should therefore be better than deepening the drains or and reducing the spacing.

The soil‐water characteristic curve (SWCC) is a key input to many hydrological and water‐quality models that simulate water movement and solute transport in the vadose zone. Over the past four decades a considerable number of pedotransfer functions (PTFs) have been developed to predict SWCC. The goal of this study was to conduct a comprehensive evaluation of 30 PTFs, 11 discrete functions and 19 continuous functions. The SWCC predicted by different PTFs was statistically compared to SWCC measured for 2046 United States soils. The performance of each function was evaluated for soils of different textural classes and at four matric potentials: −4, −10, −33 and − 1,500 kPa. The results showed that for point PTFs, the PTF developed by Adhikary et al. (2008), was the best function to predict SWCC in very fine soils, whereas the PTF developed by Fooladmand (2011), showed the best performance in fine, medium fine, medium and coarse soils. For continuous PTFs, the PTF developed by Saxton et al. (1986), showed the best performance in very fine soil; the PTF developed by Cosby et al. (1984), showed the best performance in fine soil; the PTF developed by Rawls and Brakensiek (1985) showed the best performance in medium fine soil; and the PTF of Zacharias and Wessolek (2007), showed the best performance in medium and coarse soils. With respect to matric potentials, the PTFs of Gupta and Larson (1979), Dashtaki et al. (2010), and Hua et al. (2011), were the best performing point PTFs to predict SWCC at −4, −10, −33 and − 1,500 KPa, respectively. The continuous PTFs developed by Mayr and Jarvis (1999), Rosetta SSC (Schaap et al. 2001), Cosby et al. (1984), and Al Majou et al. (2007), showed the best performance to predict SWCC at −4, −10, −33 and − 1,500 kPa, respectively. The results of this study may be useful to hydrologic modelling as it identifies the most accurate PTF for each soil textural class and across the matric potential ranges. Highlights: Performances of 30 pedotransfer functions of SWCCs were evaluated using soil database from the USA.The pedotransfer functions were classified into 11 point functions and 19 continuous functions.The pedotransfer functions were evaluated at five soil texture classes and four matric potentialsBest‐performing pedotransfer functions were identified for each texture class and matric potential. [ABSTRACT FROM AUTHOR]

Accurate determination of the water retention curve (WRC) of a soil is essential for the understanding and modelling of the subsurface hydrological, ecological, and biogeochemical processes. Volcanic ash soils with andic properties (Andosols) are recognized as important providers of ecological and hydrological services in mountainous regions worldwide due to their large fraction of small size particles (clay, silt, and organic matter) that gives them an outstanding water holding capacity. Previous comparative analyses of in situ (field) and standard laboratory methods for the determination of the WRC of Andosols showed contrasting results. Based on an extensive analysis of laboratory, experimental, and field measured WRCs of Andosols in combination with data extracted from the published literature we show that standard laboratory methods using small soil sample volumes (≤300 cm3) mimic the WRC of these soils only partially. The results obtained by the latter resemble only a small portion of the wet range of the Andosols' WRC (from saturation up to −5 kPa, or pF 1.7), but overestimate substantially their water content for higher matric potentials. This discrepancy occurs irrespective of site‐specific land use and cover, soil properties, and applied method. The disagreement limits our capacity to infer correctly subsurface hydrological behaviour, as illustrated through the analysis of long‐term soil moisture and matric potential data from an experimental site in the tropical Andes. These findings imply that results reported in past research should be used with caution and that future research should focus on determining laboratory methods that allow obtaining a correct characterization of the WRC of Andosols. For the latter, a set of recommendations and future directions to solve the identified methodological issues is proposed. [ABSTRACT FROM AUTHOR]

Tropical regions such as Java, Indonesia, still lack publication of soil water retention (SWR) information, particularly at upper Citarum watershed. The SWR is one of the critical elements in water storage and movement in the soil and very important to solve ecological and environmental problems. However, getting the access requires a lot of laboratory measurement that is time-consuming and expensive. Therefore, utilizing pedotransfer functions (PTFs) to estimate the water in the soil is needed. This study aims to define soil properties related to the SWR and to evaluate the performance of existing PTFs in predicting SWR. The study was carried out at agroforestry land system soil at upper Citarum watershed, Indonesia. Ten point and two continuous existing PTFs developed for tropical regions were applied in this study. Pearson's correlation (r), mean error (ME), root mean square error (RMSE), and modelling efficiency (EF) were used for evaluation. Cation exchange capacity (CEC), organic carbon (OC), bulk density (BD), and clay were considered as potential soil properties for soil water retention prediction. The performance of PTFs by MINASNY, HARTEMINK [2011] at matric potential of –10 kPa and BOTULA [2013] at matric potential of –33 kPa and –1500 kPa were recommended for point PTFs, while PTFs by HODNETT, TOMASELLA [2002] was for continuous PTFs in predicting SWR. The accuracy of the point PTFs is almost better than the continuous PTFs in predicting SWR in agroforestry land system soil at upper Citarum watershed, Indonesia. [ABSTRACT FROM AUTHOR]

In recent years, Mongolia has witnessed an increase in not only wheat fields, which have been present for a long time, but also rapeseed fields. This has led to increasing concerns about soil degradation due to inappropriate cultivation. This study aims to determine the impacts of rapeseed production on soil water storage in Mongolia. The soil water content and matric potential were measured in wheat and rapeseed fields and adjacent steppe rangeland for five years, including crop production and fallow years, and the soil water storages in the fields were compared. The results demonstrated that the matric potential below the root zone in the rapeseed field and both rangelands was drier than the wilting point, whereas the potential in the wheat field was usually almost the same or wetter than this point. The comparison of the amount of soil water storage during the fallow year with that of the adjacent rangeland showed it to be 5–10% higher for the wheat field and almost equal for the rapeseed field. Field management must consider the fact that rapeseed fields use more water than is required by wheat fields and that less water is stored during fallow periods.

Drainage is important to golf and athletic facilities trying to avoid lost play time. Native soil containing clay is sometimes incorporated into sand profiles with the intent to increase water and nutrient holding capacities. However, mixes high in silt and/or clay often have drainage problems. Research was conducted on soil physical properties from incremental 10% v/v additions of silt and clay (fines) to a U.S. Golf Association (USGA)- specification sand. Soils were evaluated based on volumetric water retention from 0 to 50 cm matric potential, saturated hydraulic conductivity (Ksat), porosity, and bulk density. The soil water characteristic (SWC) for 100:0 (sand:fines) had lower volumetric water content (θv) throughout the profile than any other mixture. Addition of 10% fines increased θv to more than 0.17 cm3·cm-3 throughout the 0- to 50-cm matric potential range, whereas 20% fines increased θv to more than 0.26 cm3·cm-3. The 70:30 mixture had greater θv throughout the profile than mixtures containing more than 70% sand. Mixtures with less than 70% sand produced similar SWCs. Increasing sand content increased bulk density, which altered saturated volumetric water content. Ksat was reduced from more than 265 cm·h-1 in 100:0 mixtures to 43 cm·h-1 for 90:10 mixtures, and to less than 5 cm·h-1 with -20% fines. The addition of -20% by volume of fines to a USGA sand increased water content in the soil to the point it was rendered unacceptable for trafficked turf sites. This research illustrates the influence fine particles, even in small amounts, can have on a USGA sand, and why they should not be added without prior evaluation. [ABSTRACT FROM AUTHOR]

In order to cope with water scarcity, improved water management should be implemented to reduce water inputs without affecting production. A better quantifying of the heat and water vapour transfers in response to water restriction is thus needed. Distributed climate models, with the addition of transfers through the substrate-plant-atmosphere continuum calculation is a useful tool. However, such models have generally been established for plants grown in well-watered conditions. This study aimed to simulate the transpiration of plants grown in pots and the resulting microclimate in a greenhouse compartment under different irrigation regimes. An experiment was conducted on New Guinea impatiens grown in containers on shelves, in a 100-m2 greenhouse compartment. A 2D transient CFD model was implemented, including a specific sub-model taking into account the water transport in the substrate-plant-atmosphere continuum, as well as the resulting crop interactions with the greenhouse climate for both well-watered and restricted water conditions. The substrate water content was calculated from the water balance. Special care was paid to model the stomatal resistance. Simulation results showed the model ability to correctly predict transpiration, air and leaf temperatures, as well as greenhouse air humidity for both irrigation conditions. Different irrigation scenarios were then tested by reducing the water supply from 100 to 50% of the substrate retention capacity. Simulations allow assessing the model responses on plant transpiration, growing media water potential and climate distribution inside the greenhouse. Consequently, the CFD model could be useful to define an irrigation strategy for a better water input management. • Transpiration of water-restricted plants was added to a transient CFD model. • The model was validated against experimental data for a New Guinea Impatiens crop. • A stress function was added to depict stress effect on stomatal resistance model. • Irrigation could be reduced by 30% without affecting plants transpiration. [ABSTRACT FROM AUTHOR]

The fraction of pollutant converted to CO 2 versus biomass in biofiltration influences the process efficacy and the lifetime of the bed due to pressure drop increases. This work determined the relative quantitative importance and potential interactions between three critical environmental parameters: toluene concentration (Tol), matric potential (ψ) and temperature (T) on % CO 2 , elimination capacity (EC) and the production rate of non-CO 2 products. These parameters are the most variable in typical biofilter operation. The data was fit to a non-linear model of the form y = a (T o l) b T c ψ d . A rigorous carbon balance (100.5 ± 7.0%) tracked the fate of degraded toluene as CO 2 and non-CO 2 carbon endpoints. The % CO 2 mineralization varied from (34–91%) with environmental parameters: temperature (20–40 °C), matric potential, (−10 to −100 cm H2O) and residual toluene, (20–180 ppm). The highest conversion to CO 2 was at the wettest conditions (−10 cm H2O) and lowest residual toluene concentration (18 ppm). Matric potential had twice the impact of toluene concentration on % CO 2 , while temperature had less impact. The elimination capacity varied from 11 to 50 g C ⋅m−3h−1 and was highest at 40 °C, the wettest conditions with limited impact by toluene concentrations. Temperature increased the EC and non-CO 2 production rates strongly while matric potential and toluene concentration had less influence (4x - 10x less). This study illustrated the quantitative significance and simultaneous interaction between critical environmental parameters on carbon endpoints and biofilter performance. This kind of multivariable parameter study provides valuable insights which can address performance and clogging issues in biofilters. Image 1 • Robust carbon balance closure accounting for CO 2 and non-CO 2 carbon endpoints(EPS). • Impact of environmental parameters on %CO 2 , EC and non-CO 2 fraction. • Matric potential had a greater impact (2x) on %CO 2 than toluene concentration. • Temperature strongly influenced EC and non-CO 2 production rates. • Multivariable investigations are key to decipher impact on vital response variables. [ABSTRACT FROM AUTHOR]

Root‐induced changes of soil hydraulic properties, that is soil water retention curve (SWRC) and unsaturated hydraulic conductivity (K(ψ)), depend on plant species and root density. This study aimed to investigate the effects of wheat roots and okra roots on both SWRC and K(ψ) of soil within an extended range of matric potential (−300 ~ 0 kPa) and to investigate the effects of root density of wheat (i.e. grass species) and okra (i.e. shrub species) on SWRC and K(ψ) of a loamy soil. The SWRC and K(ψ) of soil planted with wheat and okra were measured by the simplified evaporation method. Soil matric potential was measured directly by high‐capacity tensiometers. Different root densities were obtained by establishing different seeding densities in the soil. Meanwhile, root characteristics in planted soil were obtained using image analysis. The results showed that wheat‐ and okra‐planted soil had significantly larger volumetric water content (VWC) within the range of matric potential from −90 to 0 kPa than that of unplanted soil. Within the range of matric potential from around −300 to −90 kPa, the effects of wheat and okra roots on SWRC were not significant. The effects of wheat and okra roots on K(ψ) were not significant within the range of matric potential from around −300 to −10 kPa. Wheat‐planted soil with a root length density (RLD) of 10.04 cm cm−3 had larger values of VWC (ψ = 0, −33, −50 kPa) than those of wheat‐planted soil with RLD of 2.69 cm cm−3. The difference in hydraulic properties between okra‐planted soil and the two RLDs, 0.89 and 2.96 cm cm−3, was not significant. Okra roots were more effective in increasing saturated water content (θs) and field capacity (θfc) than wheat roots. This might be because okra roots are relatively coarser than wheat roots. Highlights: Effect of root density of wheat and okra on SWRC and K(ψ) was investigated.The K(ψ) of soil planted with wheat and okra was measured at matric potentials less than −100 kPa.Okra roots were more effective in increasing θs and θfc than wheat roots.Effect of wheat and okra roots on K(ψ) was not significant at matric potentials from −300 to −10 kPa. [ABSTRACT FROM AUTHOR]

Abstract Crop yield reductions are common in drought-stressed agroecosystems and are likely to become more frequent with climate change. To combat this, soil amendments are often used to enhance soil moisture retention but typically only lead to marginal improvements. Moreover, even as concern over agricultural water use mounts, a large fraction of food is wasted. Diverting more food waste and byproducts back to agricultural fields could reduce waste issues while ameliorating critical water limitations. We evaluated lactobionate, a lactose derivative and major dairy industry byproduct, as a potential soil amendment for enhancing both soil moisture and soil organic carbon (SOC). Lactobionate (LB) is a hydrophilic compound consisting primarily of cations and simple sugar acids. These combined properties could synergistically modify numerous controls on soil-water balances. In a laboratory setting, we compared LB stabilized with various cations (K+, NH 4 +, and Ca+) across a range of soil types to determine LB effects on soil moisture and SOC retention. All LB amendments increased soil water content relative to unamended soil across a range of soil matric potentials and raised available water content by 37%. Additionally, LB amended soils had on average 70 times more microbial biomass and decreased soil inorganic nitrogen content compared to unamended soils. We found that K+-LB, the most effective amendment, increased soil water content by 100–600% compared to unamended soils and as much as 87% of the increased SOC following LB additions was retained after 2 months. Our results suggest that tapping into novel sources of organic inputs such as LB may be an effective approach for simultaneously enhancing soil moisture and carbon stocks while increasing the economic and energetic value of food production byproducts. Highlights • Lactobionate was evaluated for increases in soil carbon and water retention. • Lactobionate increased available water content by 37%. • Elevated soil carbon concentrations with lactobionate persisted for two months. • Soils amended with lactobionate had 70 times more microbial biomass. • Lactobionate is an effective soil amendment for carbon and moisture-limited soils. [ABSTRACT FROM AUTHOR]

Knowing the components of a soil water balance—for example, evapotranspiration, soil water content, and precipitation—is the basis for agricultural water management. Weighing lysimeters and soil water sensors are commonly used to quantify these components. Data can be used to validate common models to estimate evapotranspiration based on meteorological data, for instance. As every measurement device has its own characteristics, it is helpful to assess and improve the performance of a system to obtain best possible data. Recent developments in the processing of lysimeter data allow determining both evapotranspiration and precipitation directly from lysimeter data. Resulting datasets are characterized by a proper accuracy, completeness, and a high temporal resolution. Soil water sensors usually measure a physical property that is related to soil water content or matric potential via a specific calibration function. Hence, measurement accuracy depends not only on this calibration but also on basic physical principles and material properties. Knowing the performance of a device is, therefore, essential for the selection of an adequate sensor arrangement and truthful data interpretation. Advanced soil water monitoring sites combine different sensor types that are integrated into a wireless network to enable real-time data availability and provide a basis for large-scale monitoring.

The soil water retention curve (SWRC) shows the relationship between soil water (θ) and water potential (ψ) and provides fundamental information for quantifying and modeling soil water entry, storage, flow, and groundwater recharge processes. While traditionally it is measured in a laboratory through cumbersome and time-intensive methods, soil sensors measuring in-situ θ and ψ show strong potential to estimate in-situ SWRC. The objective of this study was to estimate in-situ SWRC at different depths under two different soil types by integrating measured θ and ψ using two commercial sensors: time-domain reflectometer (TDR) and dielectric field water potential (e.g., MPS-6) principles. Parametric models were used to quantify θ—ψ relationships at various depths and were compared to laboratory-measured SWRC. The results of the study show that combining TDR and MPS-6 sensors can be used to estimate plant-available water and SWRC, with a mean difference of −0.03 to 0.23 m3m−3 between the modeled data and laboratory data, which could be caused by the sensors’ lack of site-specific calibration or possible air entrapment of field soil. However, consistent trends (with magnitude differences) indicated the potential to use these sensors in estimating in-situ and dynamic SWRC at depths and provided a way forward in overcoming resource-intensive laboratory measurements.

The measurement of soil moisture in agriculture is currently dominated by a small number of sensors, the use of which is greatly limited by their small sampling volume, high cost, need for close soil–sensor contact, and poor performance in saline, vertic and stony soils. This review was undertaken to explore the plethora of novel and emerging soil moisture sensors, and evaluate their potential use in agriculture. The review found that improvements to existing techniques over the last two decades are limited, and largely restricted to frequency domain reflectometry approaches. However, a broad range of new, novel and emerging means of measuring soil moisture were identified including, actively heated fiber optics (AHFO), high capacity tensiometers, paired acoustic / radio / seismic transceiver approaches, microwave-based approaches, radio frequency identification (RFID), hydrogels and seismoelectric approaches. Excitement over this range of potential new technologies is however tempered by the observation that most of these technologies are at early stages of development, and that few of these techniques have been adequately evaluated in situ agricultural soils.

ABSTRACT: The soil water retention curve is one of the main instruments to assess the soil physical quality and to improve soil management. Traditionally, the equipment most used in the laboratory to determine the retention curve has been Haines funnels and Richards chambers. An important factor to which little attention has been given in the use of these equipaments is the height of the undisturbed soil sample. This work proposes to evaluate the influence of different heights of undisturbed samples for the determination of the retention curve. For this, undisturbed soil samples were collected in aluminum cylinders of three different heights (S1 = 75 mm; S2 =50mm; S3 =25 mm) and with the same internal diameter (70 mm) from the diagnostic horizons of a Typic Hapludox and a Kandiudalfic Eutrudox (Latossolo Vermelho amarelo distrófico típico and Nitossolo Vermelho eutrófico latossólico, respectively) in experimental areas of “Escola Superior de Agricultura Luiz de Queiroz” (ESALQ/USP), Piracicaba (SP), Brazil. The soil physical characterization was done based on granulometric analysis, bulk density, particle density, porosity, and organic carbon. The retention curves were determined for each sample size using Haines funnels for the tensions of 0.5, 1, 4, 6, and 10 kPa and Richards chambers for 33, 100, and 500 kPa. Data of the curves were estimated, fitted to a model and then the distribution of the soil pore radius was evaluated, differentiating the soil water retention curve. The Typic Hapludox showed a not so remarkable difference between the retention curve with the S3 samples and the retention curve with the S1 samples, in the range 0-1 kPa of tensions, and also between the retention curve with S1 samples and both retention curves with the S2 and S3 samples, in the range 100-500 kPa of tension. This led to a slight difference in the pore distribution curves for the sample heights of this soil. The Kandiudalfic Eutrudox, however, presented not only a remarkable difference of the smaller sample retention curve (S3) in relation to the larger ones (S1 and S2) in the range 0-10 kPa of tension, but also a notable difference in the pore distribution curves, with a reduction of mesopores and increase of micropores with the increase of sample height. Finally, from the results obtained and with the methodology used to determine the soil retention curve, it is not recommended to use undisturbed samples with a height greater than 25 mm.