Water Potential Sensors Research Articles

In-situ water retention monitoring system of an operational dike

The severe droughts in recent decades and the lack of regular flooding have caused considerable fissures to develop on clay embankments. Previous surveys in Hungary have identified the examined dike section as prone to desiccation cracks. It is essential to determine the possible extent of these desiccation cracks, as they degrade the dikes’ resistance against several failure mechanisms. A representative dike cross-section was equipped with a unique water retention monitoring system comprising 17 sensors, including 14 soil moisture and 3 water potential sensors. These devices were validated with laboratory measurements to obtain accurate results. The gravimetric water content (w) ranged from 8.3 % to 31.3 %, and the matric potential was recorded between 0.1 kPa and 2350.7 kPa over one and a half years. The study examined the differences in soil behaviour under pavement and turf cover, identifying common moisture content distribution patterns and areas of the cross-section prone to desiccation cracking. The uniqueness of the monitoring system lies in the fact that it was established in an operational embankment, which regulates the flow of a river. Furthermore, it was instrumented along the Tisza River, which is among Europe’s most significant watercourses. The results may help better understand the moisture content change in clay embankments and the role of the crest pavement in the moisture content distribution.

Scheduling irrigation events in corn using three soil water potential strategies

AbstractScheduling irrigation events is important for high corn (Zea mays L.) yield, water use efficiency, economic returns, and water conservation. The use of shallow subsurface drip irrigation (S3DI) is cost effective for small irregular shaped field areas. Currently there are no irrigation scheduling recommendations for S3DI systems for corn production. The objective was to evaluate three water potential value strategies for scheduling irrigation events and the effect on corn yield, test weight, irrigation water use efficiency (IWUE), and value water use efficiency (VWUE). Corn was grown multiple years (2012–2013; 2019–2023) at two locations (Dawson and Shellman, GA) using soil water potential sensors to schedule irrigation events. Sensors were installed at 10 and 20 inches (25 and 50 cm) soil depth. Irrigation events were scheduled when the average water potential was between 40 to 60 cbar (I1), 60 to 80 cbar (I2), 80 to 100 cbar (I3), and compared to a dryland control (I0). There was no difference in corn yield, IWUE, or VWUE between irrigation treatments, but all irrigation treatments had greater yield than I0, except in high rainfall years. At the Shellman location, total water applied for I3 was 46% less than for I1. At Dawson, I2 applied 17% more water than either I1 or I3. Across both sites, I1 and I2 applied 1.5 and 1.3 times more water than I3, respectively. Therefore, irrigation events scheduled at 80 to 100 cbar can be a viable technique for irrigating corn using S3DI without yield reductions while promoting water conservation.

How does soil water retention change over time? A three‐year field study under several production systems

AbstractAgricultural practices and meteorological conditions affect soil structure and soil hydraulic properties. However, their temporal evolution is rarely studied, and even less in the field. Thus, their dynamics are rarely taken into account in models, often leading to inconsistent results and poor decision making. In this study, the temporal evolution of water retention properties and soil structure was monitored over a 3‐year period under several contrasting production systems. Soil Water Retention Curves (SWRCs) obtained directly in the field (with soil water content and potential sensors) were compared with theoretical SWRCs predicted by pedotransfer functions (PTFs) and laboratory SWRCs measured on undisturbed samples. Bulk densities were measured every 2 months. Results indicate a high degree of variability in SWRCs over time and between production systems. The results suggest that variations in the soil water retention behaviour can be induced by crop differentiation, weed control, crop residue management, compaction during harvest, or the introduction of temporary grassland. Contrasting climatic conditions between 2021 (water excess), 2022 (severe drought) and 2023 (intermediate) provided a unique opportunity to study the resilience of the crop systems to extreme climatic conditions. Different soil drying dynamics were observed and some agricultural practices were identified as influencing the soil water retention behaviour for at least 2 years. Comparison of SWRCs showed that the theoretical curves obtained from PTFs are not a good representation of the field SWRCs, especially for less conventional agricultural practices. The laboratory curves are closer with similar trends. However, these SWRCs are not optimal for investigating the temporal evolution of water retention properties. This research also shows that agricultural practices and crops can be levers for contributing to greater food resilience against future climatic conditions. Therefore, to assess the relevance of production systems for tomorrow's needs, studies should focus on the impact of multi‐cropping systems on water retention dynamics in the field.

Influence of dry density and wetting–drying cycles on the soil–water retention curve of compacted loess: experimental data and modeling

AbstractIn this paper, the EC-5 water sensor and the MPS-6 water potential sensor were used to measure water content and suction, respectively, to investigate the evolution of soil–water retention properties of compacted loess samples prepared at different dry densities and subjected to different numbers of wetting–drying cycles. The water retention data were integrated with a detailed microstructural investigation, including morphological analysis (by scanning electron microscopy) and pore size distribution determination (by nuclear magnetic resonance). The microstructural information obtained shed light on the double porosity nature of compacted loess, allowing the identification of the effects of compaction dry density and wetting–drying cycles at both intra- and inter-aggregate levels. The information obtained at the microstructural scale was used to provide a solid physical basis for the development of a simplified version of the water retention model presented in Della Vecchia et al. (Int J Numer Anal Meth Geomech 39: 702–723, 2015). The model, adapted for engineering application to compacted loess, requires only five parameters to capture the water retention properties of samples characterized by different compaction dry densities and subjected to different numbers of wetting–drying cycles. The comparison between numerical simulations and experimental results, both original and from the literature, shows that only one set of parameters is needed to reproduce the effects of dry density variation, while the variation of only one parameter allows the reproduction of the effects of wetting and drying cycles. With respect to the approaches presented in the literature, where ad hoc calibrations are often used to fit density and wetting–drying cycle effects, the model presented here shows a good compromise between simplicity and predictive capabilities, making it suitable for practical engineering applications.

Impact of Hillslope Agriculture on Soil Compaction and Seasonal Water Dynamics in a Temperate Vineyard

Major losses of agricultural production and soils are caused by erosion, which is especially pronounced on hillslopes due to specific hydrological processes and heterogeneity. Therefore, the aim of this study was to assess the impact of agricultural management on the compaction, infiltration, and seasonal water content dynamics of the hillslope. Measurements were made at the hilltop and footslope, i.e., soil water content and potential were measured using sensors, wick lysimeters were used to quantify water flux, while a mini-disk infiltrometer was used to measure the infiltration rate and calculate the unsaturated hydraulic conductivity (K_unsat). Soil texture showed differences between hillslope positions, i.e., at the hilltop after 50 cm depth, the soil is classified as silty clay loam, and from 75 cm onward, the soil is silty clay, while at the footslope, the soil is silt loam even at the deeper depths. The results show a higher K_unsat at the footslope as well as higher average water volumes collected in wick lysimeters compared to the hilltop. Average water volumes showed a statistically significant difference at p < 0.01 between the hilltop and the footslope. The soil water content and water potential sensors showed higher values at the footslope at all depths, i.e., 8.0% at 15 cm, 8.4% at 30 cm, and 27.3% at 45 cm. The results show that, even though the vineyard is located in a relatively small area, soil heterogeneity is present, affecting the water flow along the hillslope. This suggests the importance of observing water movement in the soil, especially today when facing extreme weather (e.g., short-term high-intensity rainfall events) in order to protect soil and water resources.

Toward Optimal Irrigation Management at the Plot Level: Evaluation of Commercial Water Potential Sensors.

Proper irrigation practice consists of applying the optimum amount of water to the soil at the right time. The porous characteristics of the soil determine the capacity of the soil to absorb, infiltrate, and store water. In irrigation, it is not sufficient to only determine the water content of the soil; it is also necessary to determine the availability of water for plants: water potential. In this paper, a comprehensive laboratory evaluation-accuracy and variability-of the world's leading commercial water potential sensors is carried out. No such comprehensive and exhaustive comparative evaluation of these devices has been carried out to date. Ten pairs of representative commercial sensors from four different families were selected according to their principle of operation (tensiometers, capacitive sensors, heat dissipation sensors, and resistance blocks). The accuracy of the readings (0 kPa-200 kPa) was determined in two soils of contrasting textures. The variability in the recordings-repeatability and reproducibility-was carried out in a homogeneous and inert material (sand) in the same suction range. The response in terms of accuracy and value dispersion of the different sensor families was different according to the suction range considered. In the suction range of agronomic interest (0-100 kPa), the heat dissipation sensor and the capacitive sensors were the most accurate. In both families, registrations could be extended up to 150-200 kPa. The scatter in the readings across the different sensors was due to approximately 80% of the repeatability or intrinsic variability in the sensor unit and 20% of the reproducibility. Some sensors would significantly improve their performance with ad hoc calibrations.

Mancozeb associated with water deficit: Physiological and biochemical responses of soybean plants

Can oxidative stress from xenobiotics be intensified under water deficit conditions? Based on the hypothesis that the exposure to a xenobiotic aggravates the oxidative damages induced by water deficit, soybean plants were cultivated in pots eqquipped with soil water potential sensors to continuously monitor soil moisture levels. The experiment was conducted in 2020, in a protected environment, using a randomized block design with three replications. To comprehensively evaluate physiological and biochemical responses of plants, we conducted a range of analyses, including measurements of stomatal conductance, leaf temperature, chlorophyll, chlorophyll fluorescence, relative water content, membrane damage, electrical conductivity, lipid peroxidation, concentration of reactive oxygen species – hydrogen peroxide and superoxide, activity of antioxidative enzymes – ascorbate peroxidase, superoxide dismutase, catalase, non-enzymatic compounds – non protein thiols, nitric oxide and proline. Plants that received the application of the fungicide mancozeb showed 1 °C higher temperature compared to the control plants. Irrigated soybean plants had higher nitric oxide content when treated with mancozeb, but under water deficit the higher content was observed in control plants. No deleterious effects of mancozeb as a xenobiotic were observed when applied at the recommended dose for soybean cultivation, even under water deficit conditions. The plants exhibited deleterious effects caused by water deficit, particularly in relation to oxidative stress induced by water shortage. The combination of two stresses (water deficit and xenobiotics) did not result in the maximization of negative effects caused by water stress. By refuting the working hypothesis, it becomes evident that the application of mancozeb to plants under water deficit conditions did not exacerbate the damage induced by this stress. Responses to this combination are contingent upon various factors, including the stress duration, its severity, the plant species involved, and, in the case of xenobiotics, their inherent properties and mode of action within the plant.

Effect of Plastic Membrane and Geotextile Cloth Mulching on Soil Moisture and Spring Maize Growth in the Loess–Hilly Region of Yan’an, China

In order to study the effect of a plastic membrane and geotextile cloth mulching on soil moisture and crop growth in the loess–hilly region, a one-year continuous field monitoring experiment was carried out in Ansai District, City of Yan’an, Shaanxi Province, China. The experimentation included three treatments: plastic membrane and geotextile cloth mulching on the ridge (MB), geotextile cloth mulching on the ridge (DB), and bare soil ridge (CK). Soil moisture and water potential sensors were installed to monitor the changes in soil moisture content and water potential at 5, 15, and 30 cm below the furrow surface and meteorological data above the soil surface, and the growth traits, yield, and quality of maize were analyzed. The results showed the following: (1) The soil water-storage capacity of the three treatments dropped to a minimum in the filling stage and gradually recovered in the mature stage. The average water-storage capacity for the MB treatment was 35.5% higher than that for the DB treatment and 85.1% higher than that for the CK treatment, significant throughout the whole growth period. (2) For four types of rainfall events, namely, light, medium, heavy, and storm rainfall, significant responses were observed at 5 cm below the ground for three treatments, and the fastest response was in MB due to its best rain-collection effect. A significant response was also observed at 15 and 30 cm below the surface of the furrow during medium, heavy, and storm rainfall, while no significant difference in response time was found between the three treatments due to the restriction of the soil infiltration capacity. (3) The differences between the three treatments in the agronomic traits of maize, except for plant height and stem thickness, were insignificant (p < 0.05). The seed moisture content and yield for the MB treatment were the highest, with values of 40.33% and 8366 kg/hm2, respectively, followed closely by the DB treatment, with values of 38.61% and 7780 kg/hm2, respectively, and the smallest values were observed in the CK treatment, with values of 35.80% and 6897 kg/hm2, respectively. Compared with those for the CK treatment, the average starch content and the average lipid content for the mulching treatments (MB, DB) decreased by 13.40% and 17.11%, respectively, while the average protein content of maize increased by 7.86%. Overall, a plastic membrane and geotextile cloth mulching could significantly increase soil moisture and spring maize yield due to their better rain-collection effect.

Improving Field Moisture Monitoring of Recycled and Virgin Aggregates

The structural capacity of pavement foundation is altered by moisture conditions. Reliable moisture monitoring of geomaterials throughout pavement service life is critical for asset management by transportation agencies. Improved moisture sensing enables transportation officials and practitioners to better understand performance of complex recycled materials under frequent extreme rain events. Although moisture sensing for geomaterials has improved significantly, there are still challenges when using sensors in recycled materials that may contain unhydrated cement, aged asphalt, or both. Challenges include the development of calibration functions that account for the presence of recycled materials and robust installation procedures, as technology was developed mostly for agricultural practices. In this study, a series of experiments were conducted to suggest improvements for installation techniques and data interpretation of soil moisture and water potential sensors. Suggested installation guidelines minimize wash-out and erosion potential at the soil–sensor interface. Experimental results indicate a strong bilinear relation between dielectric of recycled materials and water content, with a region of relatively small change governed by dielectric permittivity of air and a region of rapid change controlled by dielectric permittivity of water. Moreover, it was found that dielectric permittivity is not significantly affected by aggregate internal structure as dielectric for a specific moisture content for different compaction degrees is relatively similar. Furthermore, soil water characteristic curves obtained using the water potential sensor and improved installation technique compare reasonably well with laboratory results obtained with traditional equipment. Reliability of both moisture and water potential sensors was improved with the suggested guidelines.

Evaluating the performance of three sensor types for long-term measurement of suctions in gold tailings

A key aspect of the stability of a tailings dam is the pore pressure regime within the dam. Although gold tailings can exist in an unsaturated state in the field, the measurement of negative pore pressures (matric suctions) in active gold tailings dams is not common. One of the reasons for this may be the uncertainty regarding the ideal sensor type that should be used due to the shortcomings of various types of sensors. To investigate this, a long-term Drying Box experiment was conducted in the geotechnical laboratory at the University of Pretoria. Three sensor types were assessed: a commercially available water potential sensor and two versions of the TUKS tensiometer – a high capacity tensiometer designed and constructed at the University of Pretoria. Gold tailings was deposited in a slurry form and allowed to desiccate. The response from the three sensor types as a result of the change in suctions due to drying and subsequent re-wetting were observed. It was found that the TUKS tensiometer with the steel casing provided rapid, reliable, long-term suction readings. This sensor type is therefore recommended for long-term measurement of suction in gold tailings.

Probability Distribution of Soil Suction of Engineered Turf Cover and Compacted Clay Cover

It is unlikely to predict the distribution of soil suction in the field deterministically. It is well established that there are various sources of uncertainty in the measurement of matric suction, and the suction measurements in the field are even more critical because of the heterogeneities in the field conditions. Hence it becomes necessary to probabilistically characterize the suction in the field for enhanced reliability. The objective of this study was to conduct a probabilistic analysis of measured soil suction of two different test landfill covers, compacted clay cover (CC) and engineered turf cover (ETC), under similar meteorological events. The size of the two test landfill covers was 3 m × 3 m (10 ft. × 10 ft.) and 1.2 m (4ft.) in depth. The covers were constructed by excavating the existing subgrade, placing 6-mil plastic sheets, and backfilling the excavated soil, followed by layered compaction. Then the covers were instrumented identically with soil water potential sensors up to specified depths. One of the covers acted as the CC, and the other cover was ETC. In ETC, engineered turf was laid over the compacted soil. The engineered turf consisted of a structured LLDPE geomembrane overlain by synthetic turf (polyethylene fibers tufted through a double layer of woven polypropylene geotextiles). The sensors were connected to an automated data logging system and the collected data were probabilistically analyzed using the R program. There were significant inconsistencies in the descriptive statistical parameters of the measured soil suction at both covers under the same climatic conditions. Soil suction measured in the field ranged between almost 12 to 44 kPa in ETC, while it was in the range of almost 1 to 2020 kPa in the CC. The histogram and quantile-quantile (Q-Q) plot showed the data to be non-normally distributed in the field. A heavy-tailed leptokurtic (Kurtosis=13) distribution of suction was observed in the ETC with substantial outliers. In contrast, the suction distribution in CC was observed skewed to the right containing a thinner tail indicating an almost platykurtic distribution. The distribution of suction in the field under engineered turf was observed to be reasonably consistent with time compared to bare soil under the same meteorological events. The results obtained from this study revealed the engineered turf system to be an effective barrier to inducing changes in soil suction against climatic events.

Continuous and Real-Time Measurement of Plant Water Potential Using an AAO-Based Capacitive Humidity Sensor for Irrigation Control

Water potential measurement is an essential factor in determining water consumption management and recycling in the agricultural field. We report the development of a continuous water potential measurement system using sensors for water stress analysis in tomato plants with better irrigation plan feedback. The water potential sensor uses the capacitive sensing principle which measures humidity inside an anodic aluminum oxide (AAO) layer. An analog to digital converter with a wireless communication module system records the capacitance data of the sensing system. Calibration data of sensors derived from superabsorbent polymer (SP) and deionized water (DIW) mixtures can represent their water potential value. The method showed good matching of capacitance and water potential values above −7 MPa, matching the result obtained in tomato stem. The measurements were conducted for a few days with the sap flow and water potential sensors connected in series on a tomato stem. When sunlight is sufficient, sap flow increases; meanwhile, water potential decreases. The opposite phenomenon could be observed during the nighttime. With irrigation restricting conditions, both sap flow and water potential signal decrease, triggering the emergency watering signals. This continuous water potential sensing system can quantitatively monitor the plant stem’s water stress and set irrigation schedules to achieve high-quality products in the agricultural field.

Robust Soil Water Potential Sensor to Optimize Irrigation in Agriculture.

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.

A novel frequency-domain integrated sensor for in-situ estimating unsaturated soil hydraulic conductivity

Unsaturated soil hydraulic conductivity (Ku) plays a significant role in agricultural, hydrological and ecological applications. However, the existing measurement technologies are failed to consecutively measure soil hydraulic conductivity in-situ, high cost or destructive to soil structure. Here we designed a novel frequency-domain integrated sensor that is combined with Richards’ equation to in-situ estimate Ku. The novel sensor has three perforated cylinder coaxial (PCC-1, PCC-2, PCC-3) probes and a stainless steel pin to measure soil water potentials at up (PCC-1), middle (PCC-2) and bottom (PCC-3) layers and soil water content at middle layer, respectively. After sensor calibration, drying experiments were conducted with sandy loam and clay loam. The Richards’ equation was used to in-situ estimate dynamics of Ku combining finite difference method with measurements of the novel sensor under certain assumptions, and thus neither additional parameters nor boundary condition was required. In order to assess the accuracy of the in-situ estimated Ku, the actual Ku were determined in laboratory using van Genuchten and Campbell hydraulic models as references. Then, a field experiment was conducted at an experimental farm to test the performance of the novel integrated sensor. The results showed that the in-situ estimated Ku in unsaturated range had a good agreement with the model calculated Ku in laboratory. The RMSEs (in log10) were 0.707 cm h−1 (van Genuchten) and 0.426 cm h−1 (Campbell) for sandy loam and 0.749 cm h−1 (van Genuchten) and 0.587 cm h−1 (Campbell) for clay loam. In near-saturated range, the in-situ estimated Ku were somewhat underestimated in comparison with the model calculated Ku. This may attribute to the limitation of accuracy of soil water potential sensor (TEROS 21) used for calibration, the insensitivity of drying method to the estimation of Ku or the effect of structural macropores or discontinuity of soil intrinsic hydraulic characteristics in near-saturated range. The overall trend of in-situ estimated Ku in the field is similar to that in laboratory. The consistent between the in-situ estimated and model calculated Ku in laboratory verified the availability and feasibility of the novel integrated sensor and the estimation of Ku in the field was achieved. In addition, the novel integrated sensor is low cost and reduces sensor-to-sensor uncertainties when multiple sensors were used, which has distinct advantages and potential application under field conditions.

An ice correction model for dielectric sensor to improve accuracy of soil water potential measurement in frozen soils

Soil water potential is a key variable that determines water flow and indicates water availability and content. Although diverse techniques and methods have been developed for water potential measurement in unfrozen soils, most commercial techniques such as dielectric soil water potential (DSWP) sensors are not applicable for frozen soils due to potential errors of the dielectric measurement caused by ice formation within the sensor probes. Rather than directly recording sensor readings, these commercial DSWP sensors have to indirectly estimate soil water potential under equilibrium conditions by temperature measurement and the Clapeyron equation. Here we develop a mathematical model to correct the ice induced measurement error of the DSWP sensor in frozen soils. The DSWP sensor tested in this research was self-developed with a perforated cylinder coaxial (PCC) probe filled with a porous medium (gypsum). The central electrode was a temperature sensor (Pt100) replacing the usual steel pin. Sensor performance was demonstrated in a non-saline, loamy soil, by installing one sensor (DSWP-1) in a wetted soil sample prior to soil freezing, with two additional sensors (DSWP-2 and DSWP-3) installed later in frozen soil, prior to stepwise thawing. The results show that ice formed in the porous gypsum of the DSWP-1 sensor during soil freezing, as would be expected in the field with liquid water initially present to enter the probe. In comparison, no ice formed in the porous gypsums of the DSWP-2 and DSWP-3 sensors during the stepwise thawing process, allowing directly measurement of soil water potential in frozen soils and acting as a reference to develop an ice correction model based on a dielectric mixing model for the ice-formed DSWP-1 sensor to improve accuracy of soil water potential measurement. With the ice correction model, the RMSE between the readings of the DSWP-1 sensor and the reference values determined by the DSWP-3 sensor was decreased from 1.065 MPa to 0.491 MPa. In general, the ice correction model developed here can be used to improve accuracy of soil water potential measurement during soil freeze-thaw process using the DSWP sensor or other dielectric sensors and may extend application of the DSWP sensor to frozen soils under non-equilibrium conditions in the field.

Investigation of Effective Irrigation Strategies for High-Density Apple Orchards in Pennsylvania

Irrigation helps grow agricultural crops in dry areas and during periods of inadequate rainfall. Proper irrigation could improve both crop productivity and produce quality. For high density apple orchards, water relations are even more important. Most irrigation in tree fruit orchards is applied based on grower’s experience or simple observations, which may lead to over- or under-irrigation. To investigate an effective irrigation strategy in high-density apple orchard, three irrigation methods were tested including soil moisture-based, evapotranspiration (ET)-based and conventional methods. In soil moisture-based irrigation, soil water content and soil water potential sensors were measured side by side. In ET-based irrigation, daily ET (ETc) and accumulated water deficit were calculated. Conventional method was based on the experience of the operator. The experiment was conducted from early June through middle of October (one growing season). Lastly, water consumption, fruit yield and fruit quality were analyzed for these irrigation strategies. Results indicated that the soil moisture-based irrigation used least water, with 10.8% and 4.8% less than ET-based and conventional methods, respectively. The yield from the rows with the soil moisture-based irrigation was slightly higher than the other two, while the fruit quality was similar. The outcome from this study proved the effectiveness of using soil moisture sensors for irrigation scheduling and could be an important step for future automatic irrigation system.

Miniaturized, Field-Deployable, Continuous Soil Water Potential Sensor

Soil water potential is a significant factor in determining the dynamics of water in the soil. However, few soil water potential sensors are available to conduct long-term, continuous measurements with full automation, due to cavitation formation inside the sensors while interacting with the soil. This paper presents a miniature, field-deployable soil water potential sensor capable of real-time measurement with a wide dynamic range from 0 to −800 kPa, a minimum detectable change of water potential of ~40 Pa, and a high sensitivity of $\sim 0.248~\mu \text{A}$ /kPa. The sensor consists of a shallow water reservoir sandwiched between a nanoporous ceramic plate and a thin silicon diaphragm with thermal oxide. The nanoscale pores of the ceramic plate allow for the increase of air entry tension, while the smooth and hydrophilic interior surfaces of the water reservoir help to minimize the trapping of air bubbles in the reservoir. When the sensor is embedded in unsaturated soils, the pre-filled water in the reservoir tends to leave the reservoir through the nanopores of the ceramic plate, until an equilibrium in water potential is achieved between the reservoir and the soil. The loss of water leads to bending of the silicon-based diaphragm toward the reservoir. The displacement of the diaphragm is quantified by a miniature optical displacement detector assembled with the sensor, which corresponds to the soil water potential. The presented soil sensor has been validated through both greenhouse and field experiments to monitor dynamic changes in soil water potential in real-time over multiple days.

Evaluación de la productividad primaria en un gradiente de precipitación, en un pastizal patagónico

La disponibilidad de agua es el factor principal que determina la producción primaria de los pastizales en zonas áridas y semiáridas. En noviembre de 2018, en el sur de Patagonia, Estepa Magallánica Seca, se instaló un ensayo de disponibilidad hídrica, con el fin de evaluar la productividad primaria aérea neta (PPAN) de gramíneas altas y bajas frente a distintos niveles de ingreso de agua. Los tratamientos fueron: sequía con interceptores de lluvia (reciben 50% menos de la precipitación anual), tratamiento húmedo (60mm de agua agregados en el periodo seco) y testigo, tres parcelas por tratamiento excluidas del pastoreo. En estas parcelas se instalaron sensores de potencial hídrico de suelo a 10cm de profundidad y un pluviómetro conectados a un logger con frecuencia de medición de una hora. La productividad anual se estimó por cosecha de biomasa en marcos de 0,6m2 y separación de material en verde y seco, los cortes se realizaron al final de la estación de crecimiento (marzo 2019). Los tratamientos de disponibilidad hídrica no afectaron la PPAN, pero si mostraron diferencias en los valores de humedad de suelo, el suelo en el tratamiento de riego estuvo más húmedo. Posiblemente se requiera de un periodo más extenso para que la sequía se manifieste en el suelo y en la vegetación.

Factory-Calibrated Soil Water Sensor Performance Using Multiple Installation Orientations and Depths

Abstract. The use of soil water sensors is commonly advocated to aid and improve irrigation management in crop production systems. However, there are concerns about how sensor type, installation technique, sensor orientation, and soil texture may affect sensor accuracy. A field study was conducted to compare the performance of three commercially available soil water sensors (Acclima 315L, Decagon GS1, and Campbell Scientific 655) and a soil water potential sensor (Watermark 200SS) using different installation orientations of horizontal insertion, laid horizontal placement, and vertical insertion at depths of 15, 46, and 76 cm (6, 18, and 30 in.) in an irrigated clay loam soil field. Results indicated all sensors demonstrated similar trends of soil water content in response to wetting events (precipitation and irrigation) at the 15 cm depth following a 4-month settling period prior from the start of the growing season. Comparatively, the Acclima 315L performed well using horizontal insertion compared to calibrated neutron moisture meters (NMMs) at depths of 46 and 76 cm with R2 of 0.73 and 0.96 and slopes of 1.36 and 1.47, respectively. In addition, water storage in the 0.9 m soil profile integrated using the horizontally inserted Acclima 315L across the three depths matched closely with profile water storage determined by the NMMs with a mean difference (MD) and root mean square error (RMSE) of 25.7 and 36.4 mm. However, site-specific corrections or calibrations for each sensor type are required for accurate soil water content estimations with this clay loam soil for irrigation management applications. Keywords: Corn, Irrigation management, Neutron moisture meter, Soil water content, Soil water sensors, Semi-arid region.

Straw Removal Effects on Soil Water Dynamics, Soil Temperature, and Sugarcane Yield in South-Central Brazil

The use of sugarcane straw as bioenergy feedstock has been encouraged in recent years due to its potential to mitigate greenhouse gases emissions. Nevertheless, the indiscriminate straw removal causes soil damages, impairing crop development and productivity. Experiments in three sugarcane growing locations (Quata-SP, Chapadao do Ceu-GO, and Quirinopolis-GO) were conducted over 2 years to evaluate soil water dynamics, soil temperature, and sugarcane yield under diverse edaphoclimatic conditions. Straw removal of 0%, 50%, and 100% was arranged in a randomized block design with four replications. Dielectric water potential sensors were used to record soil water potential (ψ, kPa) and soil temperature (°C) every 6 h at a 0.15-m depth. Sugarcane yields were measured annually using an instrumented truck equipped with load cells. In general, the complete and partial straw removals were detrimental to water storage and therefore to plant available water causing an increase in soil temperature during sprouting and tillering phases, which are extremely important periods for a good crop establishment and, consequently, for yield increase. For the experimental sites presenting high fertility, greater water holding capacity, high sugarcane yield potential, and considering an extended water deficit in early stages of crop development, the complete straw removal resulted in yield losses of up to 16 and 40 Mg ha−1, respectively. For the experimental site presenting low sugarcane yield potential, even with low water deficit at the beginning of crop seasons, straw removal had no significant influence on sugarcane yield in the short term, since straw did not produce enough improvements to soil in order to enable benefits for water retention.