Measurements Of Soil Moisture Content Research Articles

Review of research progress on soil moisture sensor technology

Soil moisture is directly related to the amount of irrigation in agriculture and influences the yield of crops. Accordingly, a soil moisture sensor is an important tool for measuring soil moisture content. In this study, the previous research conducted in recent 2-3 decades on soil moisture sensors was reviewed and the principles of commonly used soil moisture sensor and their various applications were summarized. Furthermore, the advantages, disadvantages, and influencing factors of various measurement methods employed were compared and analyzed. The improvements were presented by several scholars have established the major applications and performance levels of soil moisture sensors, thereby setting the course for future development. These studies indicated that soil moisture sensors in the future should be developed to achieve high-precision, low-cost, non-destructive, automated, and highly integrated systems. Also, it was indicated that future studies should involve the development of specialized sensors for different applications and scenarios. This review research aimed to provide a certain reference for application departments and scientific researchers in the process of selecting soil moisture sensor products and measuring soil moisture. Keywords: soil moisture sensor, measurement principle, influencing factor, improvement method, development direction DOI: 10.25165/j.ijabe.20211404.6404 Citation: Yu L M, Gao W L, Shamshiri R R, Tao S, Ren Y Z, Zhang Y J, et al. Review of research progress on soil moisture sensor technology. Int J Agric & Biol Eng, 2021; 14(4): 32–42.

Uncertainties in Measuring Soil Moisture Content with Actively Heated Fiber-Optic Distributed Temperature Sensing.

Actively heated fiber-optic distributed temperature sensing (aFO-DTS) measures soil moisture content at sub-meter intervals across kilometres of fiber-optic cable. The technology has great potential for environmental monitoring but calibration at field scales with variable soil conditions is challenging. To better understand and quantify the errors associated with aFO-DTS soil moisture measurements, we use a parametric numerical modeling approach to evaluate different error factors for uniform soil. A thermo-hydrogeologic, unsaturated numerical model is used to simulate a 0.01 m by 0.01 m two-dimensional domain, including soil and a fiber-optic cable. Results from the model are compared to soil moisture values calculated using the commonly used Tcum calibration method for aFO-DTS. The model is found to have high accuracy between measured and observed saturations for static hydrologic conditions but shows discrepancies for more realistic settings with active recharge. We evaluate the performance of aFO-DTS soil moisture calculations for various scenarios, including varying recharge duration and heterogeneous soils. The aFO-DTS accuracy decreases as the variability in soil properties and intensity of recharge events increases. Further, we show that the burial of the fiber-optic cable within soil may adversely affect calculated results. The results demonstrate the need for careful selection of calibration data for this emerging method of measuring soil moisture content.

An assessment of different methods to determine specific yield for estimating groundwater recharge using lysimeters

Estimation of groundwater recharge is considered crucial for the management of groundwater resources. The groundwater level fluctuation (GLF) method is a widely used approach to estimate groundwater recharge due to its simplicity and ease of implementation. However, the main source of uncertainty is the specific yield for the GLF method. Although there have been a lot of methods for determining specific yield, the performance of specific yield on the estimation of recharge remains unclear. We set up three lysimeters with different water table depths in the Guanzhong Basin, China. Soil moisture content along with the soil profile, water table depths, and rainfall data were measured continuously. These data provide us with accurately observed recharge and allow us to analyze the performance of specific yields from different methods in estimating recharge. The main results are: (1) The constant specific yield from the pumping tests, which is equal to the ultimate specific yield, significantly overestimated the observed recharge rates independent of water table depths. (2) The constant specific yield obtained from saturated soil moisture content minus field capacity tended to overestimate recharge under the shallow water table depths (less than 2 m), and vice versa; (3) The depth-dependent specific yield using the measured soil moisture content along with soil profile can obtain reliable recharge across all water table depths. (4) The accuracy of the depth-dependent specific yield obtained by the soil water retention curve relies on reliable parameters. The parameters α and n have to be taken into account carefully for determing the specific yield. Our results are important for the application of the GLF method to estimate recharge. More importantly, it is valuable for the sustainable management of groundwater recourses.

Retrieving Photometric Properties and Soil Moisture Content of Tidal Flats Using Bidirectional Spectral Reflectance

Moisture content in tidal flats changes frequently and spatially on account of tidal fluctuations, which greatly influence the reflectance of the tidal flat surface. Precise prediction of the spatial-temporal variation of tidal flats’ moisture content is an important foundation of surface bio-geophysical information research by remote sensing. In this paper, we first measured the multi-angle reflectance of soil samples obtained from tidal flats in the northeastern Dongtai, Jiangsu Province, China, in the laboratory. Then, based on the particle swarm optimization (PSO) algorithm, we retrieved the photometric characteristics of the soil surface by employing the SOILSPECT bidirectional reflectance model. Finally, the soil moisture content was retrieved by introducing the equivalent water thickness of the soil. The results showed that: (i) A significant correlation existed between the retrieved equivalent water thickness and the measured soil moisture content. The SOILSPECT model is capable of estimating soil moisture with high precision by using multi-angle reflectance. (ii) Retrieved values of single scattering albedo (ω) were consistent with the variation of soil moisture content. The roughness parameter (h) and the asymmetry factor (Θ) were consistent with the structure and particle composition of the soil surface in dry soil samples. (iii) When the soil samples were soaked with water, the roughness parameter (h) and the type of scattering on the soil surface both showed irregular changes. These results support the importance of using the measured soil particle size as one of the parameters for the retrieval of soil moisture content, which is a method that should be used cautiously, especially in tidal flats.

Response of rhizomes of the invasive Hedychium coronarium J. König (Zingiberaceae) to different soil moisture conditions

The ability to maintain high competitiveness under a wide range of conditions is common among successful invasive species. The performance of rhizomatous macrophytes in different habitats is closely related to morphological and physiological adaptations in the rhizome system. We investigated the effects of soil moisture conditions on the microstructure of rhizomes of Hedychium coronarium (Zingiberaceae), an aggressive invader of Neotropical riparian sites. We collected rhizome fragments of H. coronarium and soil samples in wet and dry regions of riparian areas dominated by this species in southeastern Brazil. We measured soil moisture content gravimetrically and rhizome fragments were fixed, sectioned, and stained for histological analysis. Only rhizomes from wet regions exhibited aerenchyma, whereas amyloplasts were much more abundant and larger in rhizomes from dry regions than in rhizomes from wet regions. Even though low starch content in wet soils indicates the occurrence of anaerobic metabolism, the presence of aerenchyma may contribute to the typically high performance of H. coronarium in waterlogged soils. Although further studies are needed to assess how responses at the rhizome level affect the competitive ability of H. coronarium, our findings show that they may play a role in the dominance of this species in Neotropical riparian sites.

Design and Development of Soil Moisture Sensor

Water is a very valuable and stimulating force for irrigation. The Optimum usage of water is an hourly requirement. Efficient irrigation helps to conserve water, increase plant yields, reduce fertilizer reliance, and improve the quality of crops. Various techniques are available to measure soil moisture content, both laboratory and field, including remote sensing, but the fastest and better one is with the use of soil moisture sensor electronic devices. The range of soil moisture sensors has its own benefits and drawbacks. The goal of this work is to design and develop a module for the measurement of soil moisture and temperature levels, as well as ambient temperature and humidity by using frequency concepts. The sensor is made of a corrosion resistant element and it is rugged, battery operated, low power and long range sensor using IoT. A “GND BLE Mobile Application (gSense100)” has been developed, which includes everything related to the BLE technology and soil moisture sensor, where the app uses BLE technology to transmit all sensor values to the consumer.

Mapping barrier island soil moisture using a radiative transfer model of hyperspectral imagery from an unmanned aerial system

The advent of remote sensing from unmanned aerial systems (UAS) has opened the door to more affordable and effective methods of imaging and mapping of surface geophysical properties with many important applications in areas such as coastal zone management, ecology, agriculture, and defense. We describe a study to validate and improve soil moisture content retrieval and mapping from hyperspectral imagery collected by a UAS system. Our approach uses a recently developed model known as the multilayer radiative transfer model of soil reflectance (MARMIT). MARMIT partitions contributions due to water and the sediment surface into equivalent but separate layers and describes these layers using an equivalent slab model formalism. The model water layer thickness along with the fraction of wet surface become parameters that must be optimized in a calibration step, with extinction due to water absorption being applied in the model based on equivalent water layer thickness, while transmission and reflection coefficients follow the Fresnel formalism. In this work, we evaluate the model in both field settings, using UAS hyperspectral imagery, and laboratory settings, using hyperspectral spectra obtained with a goniometer. Sediment samples obtained from four different field sites representing disparate environmental settings comprised the laboratory analysis while field validation used hyperspectral UAS imagery and coordinated ground truth obtained on a barrier island shore during field campaigns in 2018 and 2019. Analysis of the most significant wavelengths for retrieval indicate a number of different wavelengths in the short-wave infra-red (SWIR) that provide accurate fits to measured soil moisture content in the laboratory with normalized root mean square error (NRMSE)< 0.145, while independent evaluation from sequestered test data from the hyperspectral UAS imagery obtained during the field campaign obtained an average NRMSE = 0.169 and median NRMSE = 0.152 in a bootstrap analysis.

Spatial‐Temporal Simulations of Soil Moisture Content in a Large Basin of the Loess Plateau, China

Soil moisture is a crucial factor limiting the growth and survival of plants on the Loess Plateau. Its level has a severe impact on plants’ growth and development and the type and distribution characteristics of communities. This study area is the Jihe Basin in the Loess Plateau, China. Multiple linear regression models with different environmental variables (land use, topographic and meteorological factors, etc.) were developed to simulate soil moisture’s spatial and temporal changes by integrating field experiments, indoor analysis, and GIS spatial analysis. The model performances were evaluated in the Jihe Basin, with soil moisture content measurements. The result shows that soil moisture content is positively correlated with soil bulk density, monthly rainfall, topographic wetness index, land use coefficient, and slope aspect coefficient but negatively correlated with the monthly‐averaged temperature and the relative elevation coefficient. The selected variables are all related to the soil moisture content and can account for 75% of the variations of soil moisture content, and the remaining 25% of the variations are related to other factors. Comparing the simulated and measured values at all sampling points shows that the average error of all the simulated values is 0.09, indicating that the simulation has high accuracy. The spatial distribution of soil moisture content is significantly affected by land use and topographic factors, and seasonal variation is remarkable in the year. Seasonal variation of soil moisture content is determined by the seasonal variation of rainfall and the air temperature (determining evaporation) and vegetation growth cycle. Therefore, the proposed model can simulate the spatial and temporal variation of soil moisture content and support developing the soil and water loss model on a basin scale.

Moisture sensitive electrical property measurement in concrete slab with step graded antenna

The step graded antenna is designed for the measurement of electrical property inside the concrete samples. This paper designs, simulates and fabricates the single band microstrip antenna at the frequency of 2.76 GHz. The simulated results are compared and analysed with measured results for the designed antenna. It has been noted that the measured and simulated values corresponding to reflection coeffcieints results in offset of 0.02 GHz. The designed antenna is tested on two different composition of concrete samples. The disparity in the reflectivity of both the samples is observed due to the variance in the composition of the concrete structure. The operating frequency of the proposed antenna changes from 2.76 to 2.72 GHz when applied to both concrete samples. Thus the designed antenna can be used for the soil moisture content measurement for structural health monitoring.

Comparison of soil moisture content measurement between Internet of Things (IoT) and traditional methods

Soil is a composition of Sand, Silt and Clay. From three phase concept, it is clear that the soil consists of solids, water and air. The ratio of weight of water to weight of solids for a given soil mass is known as water content of soil. In other words, the water content (w) also known as natural water content or natural moisture content. Water content is used in a wide range of scientific and technical areas, and is expressed as a ratio, which can range from zero to the value of the soil porosity at saturation. Traditionally, the water content is measured by pycnometer or oven dry methods which would generally take 24 hours to determine the water content soil. As the time is important these days, several smart advances are occurred in determining the moisture content through Internet of Things (IoT). In this project, the water content of soil is measured through IoT sensors and traditional methods. Present work involves in which different soil samples are taken along the road construction site and classifying them with the help of sieve analysis, Atterberg limits and plasticity chart and moisture content measurement using internet of things (IoT) and traditional methods are compared. Also, find a possible correlation developed between the soil moisture content by traditional methods and through IoT.

Numerical evaluation of the thermal performance of a near-surface earth-to-air heat exchanger with short-grass ground cover: A parametric study

Abstract High energy consumption and increasing energy cost have encouraged investment in energy efficiency. In hot areas, like the Middle East, the share of space cooling accounts for most of the total energy use in buildings. Earth-to-air heat exchangers represent an energy-efficient and environmentally friendly cooling technique. An earth-to-air heat exchanger buried near the ground surface with short-grass cover, which lowers the soil temperature by evapotranspiration, is an alternative to conventional deep buried types. In this study, a steady three-dimensional numerical model of this earth-to-air heat exchanger was developed by considering the conservation of mass, momentum, energy, and species. Soil temperature and moisture content measurements were used as boundary conditions for the model. In addition, the variations of soil temperature and thermal conductivity with depth were considered in the model. Numerical predictions of temperature matched experimental measurements within ±0.5 °C. Using the validated numerical model, the effect of inlet air temperature, airflow rate, tube length, material, wall thickness, and soil thermal conductivity on the earth-to-air heat exchanger thermal performance was investigated. Increasing the airflow rate and tube length resulted in an asymptotic increase and decrease in the earth-to-air heat exchanger outlet temperature, respectively. By increasing the tube wall thickness from 1 to 10 mm, the outlet temperature for an aluminum tube remained unchanged, while for PE and PVC tubes, the outlet temperature increased by about 1.1 and 2.2 °C, respectively. By increasing the soil thermal conductivity from 1 to 5 W m−1 K−1 the outlet temperature decreased by about 4.4 °C.

Effect of Intermittent Water Application from Trickle Source on The Water Movement and Moisture Distributionin Layered Soil

Efficient design of trickle irrigation system depends on the shape and volume of wetted soil, which are affected by many factors. Among these factors are water application rate, soil profile type, initial soil moisture, and continuous or intermittent water application. The aim of this research is to study the effect of intermittent water application on the wetting pattern and soil moisture distribution for homogeneous and layered soils under trickle source. Thirty experiments were conducted to monitor the advance of the wetting front in the soil profiles. Measurements of soil moisture content were also made at selected locations to evaluate the moisture distribution in soil. A rectangular box with inside dimensions of 147 cm*90 cm*5 cm was used to build the soil profile. One of the faces of the box is transparent. Two different soils were used; a sandy loam and a silty clay loam. The soils were air dried, sieved, and packed inside the box in accordance with their apparent densities which have been measured in the field. Four types of soil profiles were built; the first was sandy loam soil, the second was silty clay loam soil, the third was (silty clay loam/ sandy loam) layered soil, and the fourth was (sandy loam/ silty clay loam) layered soil. Three water application rates were used for each soil profile. Three continuous or intermittent applications were used; continuous applications, equally intermittent applications (120 minutes ON with 120 minutes OFF), and different intermittent applications ([1]20 minutes ON with 240 minutes OFF). In addition, several cylindrical infiltration tests were conducted to describe some characteristics of each soil. Empirical relations to predict each of vertical (under trickle source) and horizontal (at soil surface) wetting front advance were found in this study. Empirical relations to predict the percentage of applied water volume in horizontal strips as a function of soil depth and in vertical strips as a function of horizontal distance from the trickle emitter were also found. The study showed that the wetted soil volume increases as either the water application rate increases, or the intermittent application ratio increases. Also, it showed that the ratio of horizontal advance to vertical advance of wetting front increases as either the water application rate increases, or the intermittent application ratio decreases. The study demonstrated that the accumulated ratio of water application volume at a certain soil depth from trickle source increases as the intermittent application ratio decreases. Also, it demonstrated that the accumulated ratio of water application volume at a certain horizontal distance from trickle source decreases as the intermittent application ratio decreases.

Efficacy of Arduino based low-cost Resistive Sensor in evaluating Soil Moisture from different Soil types collected in the Kelantan-Terengganu plain of Malaysia

This paper presents an experimental study on the effectiveness of using Arduino based low-cost resistive sensors to measure soil moisture content from five different soil types. In this experiment, the soil samples were filled in the vases and arranged in a completely randomized design with three replications. The soil samples from the vases were taken for soil moisture evaluation for 28 days. The experiment began with soil samples at fully saturation condition followed by field capacity condition and finished at the dry condition. The sensors used in this study were calibrated with a gravimetric method by using an oven. The results reveal that the Arduino based low-cost resistive sensor is highly capable of measuring suitable soil moisture content of fine sand, loamy soil, and sandy clay loam soil types. However, this type of sensor has poor performance for sandy loam and clay loam soil types due to the high content of organic matter and low bulk density. The performance of this sensor on peat and wetland soil can be further enhanced by using a distinctively developed empirical formula. The system developed in this work allows employing large-scale soil moisture measurement network for irrigation monitoring and controlling in future research due to its low-cost and great simplicity.

Quantitative Estimation of Soil-Ground Water Storage Utilization during the Crop Growing Season in Arid Regions with Shallow Water Table Depth

Water storage in unsaturated and saturated zones during the crop non-growing season is one of the important supplementary water resources to meet crop water requirements in arid areas with shallow water table depth. It is necessary to analyze utilization of the soil-ground water storage during the crop growing season and its attribution to irrigation during the non-growing season. To facilitate the analysis, a new method based on measurements of soil moisture content and water table depth is developed. The measurements used in this study include (1) 15-year data of soil moisture content within a depth of 1 m from the land surface and water table depth measured in Jiefangzha, including its four subareas and (2) 4-year data of the same kind in Yonglian, located in arid northern China. The soil-ground water storage utilization is calculated as the difference of water storage between the beginning and end of the crop growing season in the whole computational soil profile. The results of average soil-ground water storage utilization in Jiefangzha and its four subareas and Yonglian are 121 mm, 126 mm, 113 mm, 124 mm, 185 mm and 117 mm, and the corresponding average utilization efficiencies in the non-growing season are 32.2%, 32.5%, 31.5%, 31.6%, 57.3% and 47.6%, respectively. Further, the water table fluctuation method was used to estimate the variation in water storage. The coefficients of soil-ground water storage utilization, soil-ground water storage utilization below 1 m soil depth and ground water utilization are defined, and their average values are 0.271, 0.111 and 0.026 in Jiefangzha, respectively. Then, the contribution of soil-ground water storage utilization to actual evapotranspiration is evaluated, which are over 23.5% in Jiefangzha and Yonglian. These results indicate that the soil-ground water storage plays an important role in the ecological environment in arid areas with shallow water table depth.

Remote sensing vs. field-based monitoring of agricultural terrace degradation

The degradation of agricultural terraces is considered a major challenge to soil and water conservation in steep-slope viticulture. Although terracing is a widespread conservation practice, its sustainability is threatened by adverse climatic and man-made conditions. Previous studies have shown the impact of terrace designs on the formation of runoff pathways, causing degradation processes on terrace platforms (e.g. sheet erosion) and walls (e.g. piping, landslides, collapse). This study evaluates a remote sensing versus a field-based approach to monitor hydrological processes responsible for terrace degradation, as tested in a north-Italian vineyard. The field-based approach was based on spatially measured Soil Moisture Content (SMC) using a Time Domain Reflectometry (TDR) instrument, which clearly revealed saturation hotspots around two damaged terraces in the study area. Moreover, these zones showed a particular cross-sectional SMC profile, with the highest saturation close to the terrace platform edges. The remote sensing approach was based on aerial imagery acquired by an Unmanned Aerial Vehicle (UAV) and photogrammetric reconstruction of the vineyard geomorphology, allowing terrain-based analysis and physical erosion modelling. In this approach, simulations indicated that terrace damages could be partly explained by the formation of preferential runoff pathways caused by the terrace design. This parallel methodology allowed a comparison of the merits and limitations of either approach, as done in light of published work. The occurrence of two SMC hotspots at terrace edges (and their non-typical cross-sectional profiles) could be better understood from simulated surface flow paths. While the causal relationship between heterogeneous soil saturation and terrace instability has been previously reported in literature, the novelty of the presented study is the use of topsoil SMC as an indicator of potential damages, favouring the scalability compared to fixed, local and often intrusive terrace sub-surface experiments. Remote sensing based approaches, however, tend to offer the most time-efficient solution on larger scales, and aerial acquisition of SMC distribution could thus potentially offer a powerful integrated methodology.

The spatial pattern of the belowground bud bank and its responses to soil water status in the interdune lowlands of active sand dunes of Inner Mongolia, China

Bud bank composition in interdune lowlands plays a key role in population colonization and vegetation restoration in active sand dune ecosystems. However, no studies have explicitly explored the spatial pattern of belowground bud banks in the interdune lowlands of active sand dune ecosystems and their response to soil moisture conditions. Therefore, this study investigated belowground bud banks and measured soil moisture contents in four interdune lowlands in the Horqin Sandy Land of northeastern Inner Mongolia. The density of total buds, rhizome buds, and tiller buds decreased significantly at the windward slope‐interdune and leeward slope‐interdune transitional zones (p &lt; 0.05), while the densities of both root‐collar buds and root‐sprouting buds were the highest at the edge of the interdune lowland. Rhizome buds (60–100%) were predominant over tiller buds in the windward slope transitional zone, while root‐collar buds (57–62%) and tiller buds (60–79%) were prominent in the leeward slope transitional zone. Furthermore, all bud types except the root‐collar bud had obvious water dependence. It was concluded that there is a significant difference in bud density between the different interdune lowland positions, and root‐collar buds were more resistant to water stress than the other bud banks. These survival strategies and responses may be important in the recovery of both artificial and sand‐fixing vegetation in semiarid regions of China.

Measurement and zonation of soil surface moisture in arid and semi-arid regions using Landsat 8 images

Monitoring of soil surface moisture is an imperative factor in water and energy cycle. Due to the variability of soil characteristics such as topography, vegetation, and climate dynamics, this important factor varies with respect to time and place. Measuring methods can provide soil moisture information in a wide range of short intervals with reasonable accuracy. In present research, Landsat 8 satellite data with various soil moisture content estimation methods were tested. In order to evaluate the accuracy of each method, the real-field data used 80 samples of volumetric soil moisture content in suburban areas of Semnan city that were collected at the time of satellite passage of the area. Some of the indicators used in this study are normalized vegetation index, NDTI index, NDMI index, PSMI index (use full form of these indices), surface temperature, and SMSWIR index. The SMSWIR index with correlation coefficient was 0.78, and the correlation coefficient of regression model was 0.61, and RMSE was 3.69. The results of the regression model and real data were estimated to be 3.69, which are recommended for assessing surface soil moisture in arid and desert regions. Three indicators of SMSWIR index, NDTI index, and NDMI index with a small difference are not suitable indices for measuring soil moisture content in desert areas with vegetation cover. By employing multivariable regression models, soil moisture model was also prepared by using the studied indices. The findings of this research indicate that the simultaneous correlation model is superior to the surface soil moisture mapping.

Drip irrigation systems controlled by soil moisture sensors and a soil water balance model for cassava grown in soils of two different textures

Cassava (Manihot esculenta Crantz) yield could be improved by drip irrigation if irrigation scheduling is correctly organized. Soil moisture content is an important factor for controlling irrigation. It can be directly monitored by soil moisture sensors or predicted by soil water balance (SWB) models. Field experiments were conducted to investigate cassava production under drip irrigation and to determine the relationship between soil moisture content predicted from SWB models and actual measurements from soil moisture sensors. Treatments were carried out in a randomized complete block design with four replications including: T1: rainfed; T2: drip irrigation controlled by soil moisture sensors; T3: drip irrigation controlled by a SWB model. The results showed that cassava yield and water use efficiency in irrigated treatments were higher than in rainfed treatments but there were no significant differences between T2 and T3. The predicted soil moisture content (SMCp) was slightly higher than the measured soil moisture content (SMCm). The difference between SMCp and SMCm was consistently the same throughout the measuring period. The overall results confirmed that the SWB model can be accurately used to predict soil moisture content. Drip irrigation controlled by the SWB model achieved a high cassava yield and WUE values similar to those produced using drip irrigation controlled by a soil moisture sensor.

Influences of deficit irrigation on soil water content distribution and spring wheat growth in Hetao Irrigation District, Inner Mongolia of China

Abstract In order to develop a water-saving irrigation system for spring wheat, field experiments were conducted on the deficit irrigation of spring wheat in Hetao Irrigation District, Inner Mongolia. Through measurement of soil moisture content, the spring wheat growth and yield index, the influences of deficit irrigation on soil moisture distribution and spring wheat growth were studied. Results showed that, in the soil layers 0–100 cm below the ground, the soil moisture content under full irrigation at 100% ETc (ETc denotes actual water demanded by crops) and that under deficit irrigation at 80% ETc increased with the increase of soil layer depth; specifically, soil moisture under deficit irrigation at 60% ETc was mainly distributed in the subsurface layer (20–40 cm) and the middle layer (40–60 cm). The spring wheat yield was not greatly influenced by the deficit irrigation at 80% ETc, showing a decrease of merely 5–13% compared with that under full irrigation, while deficit irrigation at 60% ETc had greater impact on the growth and yield of spring wheat, cutting the yield by 10–37% in comparison with that under full irrigation. In the study area, the deficit irrigation treatment at 80% ETc was adopted, wherein the irrigation norm in the growth period was 288 mm. This irrigation system had little adverse impact on spring wheat growth and yield, and therefore, water-saving irrigation could be realized.

High‐Resolution Measurement of Soil Thermal Properties and Moisture Content Using a Novel Heated Fiber Optics Approach

AbstractHydrological parameters are scale dependent. Efficient monitoring techniques capable of measuring hydrological parameters, such as soil moisture content (θ), over a wide range of spatial scales are essential for understanding the complexity of water and energy movement across the landscape. Techniques to measure θ over spatial scales in the range from centimeters to thousands of meters, however, are sorely lacking. Recent improvements in the distributed temperature sensing (DTS) technology supported the development of novel techniques to fill that gap. However, improvements in the accuracy and applicability of DTS techniques are still needed. This study investigates the possibility of improving the accuracy of the fiber optics dual‐probe heat‐pulse (FO‐DPHP) DTS technique by using a new design to maintain the spacing between the FO‐DPHP probes and by introducing a novel data interpretation approach. The accuracy of the novel FO‐DPHP design was tested at different θ in a sand column experiment. The FO‐DPHP measurements obtained using traditional and novel data interpretation approaches were compared against independent measurements from several calibrated soil water content (EC5) sensors. Monte‐Carlo analyses were also performed to assess the impact of DTS measurement errors on the accuracy achieved using the data interpretation approaches. The novel design and data interpretation approach allowed for accurate measurements of soil thermal properties and θ without the need to perform a hard‐to‐achieve soil‐specific calibration. Measured θ had mean errors and standard deviations &lt;0.03 and &lt;0.01 m3 m−3, respectively, for moisture conditions ranging from dry to near saturation. The standard deviation in the measured heat capacity was &lt;0.01 MJ m−3 K−1.