TDR Probes Research Articles

An Integrated Hydrogeophysical Approach for Unsaturated Zone Monitoring Using Time Domain Reflectometry, Electrical Resistivity Tomography and Ground Penetrating Radar

Continuous measurements of soil moisture in the deeper parts of the unsaturated zone remain an important challenge. This study examines the development of an integrated system for the continuous and 3-D monitoring of the vadose zone processes in a cost- and energy-efficient way. This system comprises TDR, ERT and GPR geophysical techniques. Their capacities to adequately image subsurface moisture changes with continuous and time-lapse measurements are assessed during an artificial infiltration experiment conducted in a characteristic urban site with anthropogenic fills and much compaction. A 3-D array was designed for each method to expand the information of a single TDR probe and obtain a broader image of the subsurface. Custom spatial TDR probes installed in boreholes made with a percussion drilling instrument were used for soil moisture measurements. Moisture profiles along the probes were estimated with a numerical one-dimensional inversion model and a standard calibration equation. High conductivity water used during all infiltration tests led to the detection of the flow by all techniques. Preferential flow was present throughout the experiment and imaged sufficiently by all methods. Overall, the integrated approach conceals each method’s weaknesses and provides a reliable 3-D view of the subsurface. The results suggest that this approach can be used to monitor the unsaturated zone at even greater depths.

Impacts on Soil and Cowpea Plants Fertigated with Sanitary Sewage through Subsurface Drip Irrigation

The application of sanitary sewage using subsurface drip irrigation can mitigate current challenges related to water availability and food production. However, before implementing these techniques, it is crucial to conduct studies to assess their impacts on soil and plants. The objective of this study was to evaluate chemical changes in the soil and the development of cowpeas subjected to sanitary sewage applied by drippers with different flow rates and installation depths. Drippers were positioned at various depths (0 to 30 cm) and operated with flow rates of 1.6 and 3.8 L h−1. Cowpeas were cultivated in pots with clayey soil, using synthetic sanitary sewage based on the maximum limit of nitrogen fertilization. Irrigation management was controlled in terms of soil moisture, which was monitored using TDR probes. The results indicated that reducing the depth of the drippers positively affected grain production and the development of cowpeas. Fertigation with sanitary sewage at greater depths increased soil phosphorus concentrations and base saturation. Dripper depth also influenced soil concentrations of phosphorus, potassium, calcium, and magnesium, while sodium concentrations decreased with greater depth. It is concluded that dripper flow rates did not impact soil chemical parameters or the agronomic characteristics of cowpeas. However, despite nutrient supply at greater depths, the subsurface drip irrigation system proved unsuitable for cowpea production in clayey soil.

Characteristics of spring maize sap flow and its environmental influencing factors in typical mollisol area.

Clarifying the variations of sap flow rate of spring maize in the typical mollisol area and its main control factors is of great significance to explore water consumption from transpiration and regulate field water management. In this study, we installed the wrapped sap flow sensors and TDR probes to continuously monitor the sap flow rate of spring maize during filling-maturity stage and soil water and heat conditions of topsoil. In combination with meteorological data collecting from a nearby automatic weather station, we analyzed the correlation between the sap flow rate of spring maize and environmental factors at different time scales. The results showed that the sap flow rate of spring maize in typical mollisol area had an obvious fluctuation of high diurnal and low nighttime. The instantaneous sap flow rate peaked at daytime, with a value of 139.9 g·h-1, but being weak at nighttime. The starting time, closing time, and peak values of spring maize sap flow were significantly inhibited in cloudy and rainy days, compared with that in sunny days. On hourly scale, the sap flow rate was significantly correlated to solar radiation, saturated vapor pressure deficit (VPD), relative humidity, air temperature, and wind speed. On daily scale, only solar radiation, VPD, and relative humidity were significantly correlated with sap flow rate, with the absolute values of correlation coefficient being all above 0.7. Due to high soil water content during the observation period, the sap flow rate was not significantly correlated with soil water content and soil temperature of 0-20 cm layer, with the absolute values of correlation coefficient being less than 0.1. Under the condition without water stress, solar radiation, VPD, and relative humidity were the top three influencing factors of sap flow rate in this region, on both hourly scale and daily scale.

Deep learning and data fusion to estimate surface soil moisture from multi-sensor satellite images

We propose a new architecture based on a fully connected feed-forward Artificial Neural Network (ANN) model to estimate surface soil moisture from satellite images on a large alluvial fan of the Kosi River in the Himalayan Foreland. We have extracted nine different features from Sentinel-1 (dual-polarised radar backscatter), Sentinel-2 (red and near-infrared bands), and Shuttle Radar Topographic Mission (digital elevation model) satellite products by leveraging the linear data fusion and graphical indicators. We performed a feature importance analysis by using the regression ensemble tree approach and also feature sensitivity to evaluate the impact of each feature on the response variable. For training and assessing the model performance, we conducted two field campaigns on the Kosi Fan in December 11–19, 2019 and March 01–06, 2022. We used a calibrated TDR probe to measure surface soil moisture at 224 different locations distributed throughout the fan surface. We used input features to train, validate, and test the performance of the feed-forward ANN model in a 60:10:30 ratio, respectively. We compared the performance of ANN model with ten different machine learning algorithms [i.e., Generalised Regression Neural Network (GRNN), Radial Basis Network (RBN), Exact RBN (ERBN), Gaussian Process Regression (GPR), Support Vector Regression (SVR), Random Forest (RF), Boosting Ensemble Learning (Boosting EL), Recurrent Neural Network (RNN), Binary Decision Tree (BDT), and Automated Machine Learning (AutoML)]. We observed that the ANN model accurately predicts the soil moisture and outperforms all the benchmark algorithms with correlation coefficient (R = 0.80), Root Mean Square Error (RMSE = 0.040 mathrm {m^3/m^3}), and bias = 0.004 mathrm {m^3/m^3}. Finally, for an unbiased and robust conclusion, we performed spatial distribution analysis by creating thirty different sets of training-validation-testing datasets. We observed that the performance remains consistent in all thirty scenarios. The outcomes of this study will foster new and existing applications of soil moisture.

Hydrodynamics of the Vadose Zone of a Layered Soil Column

Getting into the heart of the water movement into the vadose zone is essential due to the direct impact on the aquifer recharge, the flood hazards, the irrigation planning and the water resources management in general. Since soil profiles in nature appear in layers, the present study accomplishes a deep investigation of the water’s motion through soil layers with different hydraulic properties. A series of experiments were conducted in the laboratory where infiltration, tension, soil moisture and hydraulic conductivity data were collected and analyzed. In particular, a transparent column was filled with two soils (loamy sand over sand), and TDR probes, along with ceramic capsules connected to pressure transducers, were set to the column. Using the experimental data and the unsaturated zone modeling, hydraulic parameters were obtained, along with water motion simulation and prediction. An investigation into the drainage, imbibition, infiltration, soil water characteristic curves and, in general, the hydrodynamics of the vadose zone of the soil layers has been achieved. The results of the current study suggest a method to estimate the crucial hydraulic parameters that are involved in the soil-water interaction and have an impact on infiltration, runoff, aquifer horizon recharge, water management and water saving.

The Dynamics of Soil Moisture and Temperature—Strip-Till vs. Plowing—A Case Study

The dynamics of soil moisture and its temperature is an important criterion for evaluating soil tillage technology in terms of achieving plant production stability. Understanding changes in soil moisture and temperature depending on rainfall and air temperature is necessary to develop application models for agriculture 4.0. A hypothesis was adopted assuming that the dynamics of soil moisture and its thermal properties will depend on the technology of cultivation. Hence, the aim of the research was to learn the dynamics of soil moisture and temperature during a growing season using strip and conventional tillage. Soil moisture was monitored using TDR probes in the row and inter-row of winter barley using plowing and strip-till techniques. Soil temperature was also monitored. Measurements were made every 5 min. In the most important period for the growth and development of barley vegetation, the soil in the strip-till was characterized by greater moisture (3.6% v/v on average) and greater stability than was the case with plowing. The soil in the strip-till was cooler (an average of 0.64 °C), but more stable than in plowing—temporary temperature differences in ST vs. PT reached even more than 5 °C. Strip-till therefore mitigates weather extremes to a greater extent than plowing.

From point to field scale - indirect monitoring of soil moisture variations at the DWD test site in Falkenberg

Information regarding the spatial distribution of soil water content is key in many disciplines and applications including soil and atmospheric sciences, hydrology, and agricultural engineering. Thus, within the past decades various experimental methods and strategies have been developed to map spatial variations in soil moisture distribution and to monitor temporal changes. Our study examines the combination of electrical resistivity mapping and point observations of soil moisture to infer the spatial and the temporal variability of soil moisture. Over a period of around two years, we performed field measurements on six days to collect repeated electrical resistivity mapping data for a nine-hectare test site south-east of Berlin, Germany. Permanently installed TDR probes, temporary TDR measurements within permanently installed tubes, and gravimetric measurements using soil samples provided soil moisture data at various selected points. In addition, soil analysis and classification results are available for 132 regularly distributed positions up to depths of 1.2 m. We compare and link three-dimensional resistivity models obtained via data inversion to soil composition and soil moisture as provided by our point data. Both the soil samples and the resistivity models indicate a two-layer medium characterized by a sandy top layer with varying thickness and a loamy bottom soil. For all six field campaigns, we observe similar resistivity patterns reflecting the temporally stable influence of soil texture. While the overall patterns are stable, the range of resistivity values changes with soil moisture. Finally, to estimate spatial models of soil moisture, we link our soil moisture and resistivity data using empirical petrophysical models relying on a second order polynomial function. We observe a mean prediction error for soil moisture of +/- 0.034 m3 • m−3 using all observation points while we notice that point-specific models further reduce the error. Thus, we conclude that our experimental and data analysis strategies represent a reliable approach to establish site-specific models and to estimate three-dimensional moisture distribution including temporal variations.

Hydrological monitoring of a slope covered by stratified pyroclastic deposits and analysis of infiltration processes

AbstractIn addition to the duration and intensity of rainfall, infiltration processes are strongly affected by the hydraulic properties of the soil. In the case of heterogeneous and stratified soil profiles, the analysis of the infiltration process becomes more complex, since conflicting hydraulic properties of adjacent layers can induce locally diverted flow. Soils of volcanic origin present these characteristics, because during the various eruptive phases, layers with very different textures are deposited. In this article, data are analysed which have been recorded by a monitoring station installed on a slope made up of volcanic deposits. The station consists of a rain gauge to measure rainfall and seven tensiometers and eight TDR probes installed at different depths to measure suction and volumetric water content, respectively. The slope is made up of alternating volcanic ash (silt‐sandy‐clay paleosoils) interspersed with pumice (sandy‐gravel), due to the different eruptive phases of the volcanic complexes in the area. The analysis of the data established that the layers of coarser material (pumices), depending on the initial moisture conditions, may hinder or even favour the infiltration of water into the deeper layers. In particular, when water content is low, the pumices presented a low unsaturated conductivity which hindered infiltration. By contrast, in wetter conditions, they favoured the flow of water. Therefore, the initial moisture conditions of the soil layers must be taken into account for a correct prediction of the infiltration phenomena. Dry conditions of the pumice layers can hinder drainage into the lower layers, thus favouring the rapid accumulation of soil water during rainfall events, which could eventually lead to slope failure.

A Numerical Investigation of the Dispersion Law of Materials by Means of Multi-Length TDR Data

In this paper, we propose a method for retrieving the dispersion law of a material under test from multi-length TDR measurements in reflection mode, repeated at several frequencies. By replacing the multi-frequency measurements with measurements using multi-length TDR probe, it is possible to retrieve the complex equivalent permittivity of the material in a frequency band of interest. The proposed procedure does not require a priori knowledge of the type of dispersion law of the material, which instead can possibly be inferred from the measured data. The algorithm is validated using numerically simulated data obtained with the commercial code CST Microstudio®.

Preferential solute transport under variably saturated conditions in a silty loam soil: Is the shallow water table a driving factor?

A shallow water table might enhance preferential solute movement by modifying both the water flow and solute dynamics. In this study, we estimated soil hydraulic and solute transport parameters through a tracer experiment in lysimeters comparing different water table levels. In a set-up of 12 lysimeters, the bottom boundary condition was set as a water table depth of 120 cm, or 60 cm, or as free drainage. A tracer solution of bromide (250 mg l−1, 40 mm) was added to each lysimeter and soil water was sampled with suction cups at different depths for the following 174 days. Soil water content and matric potential were monitored using TDR probes and electronic tensiometers at the same depths. Soil hydraulic and solute transport parameters in different soil layers were estimated by inverse modeling using HYDRUS 1D. Soil hydraulic parameters were estimated from the Mualem-van Genuchten equations, while both the advection–dispersion (ADE) and physical non-equilibrium mobile-immobile water (MIM) models were used to describe the solute transport. Moreover, the soil pore network was analyzed by means of 3D X-ray microtomography. Results showed different solute dynamics between contrasting water table managements. With free drainage, solute in the immobile domain was negligible, and its transport was fully associated with the mobile water flow. In contrast, a shallow water table affected the tracer transport, by modifying a) the soil pore network, with an increase of the macropores and a reduction of the pore connectivity; b) the flow field, with an increase of immobile water and a reduction of αMIM, indicating slow exchange between mobile and immobile regions, in turn promoting preferential pathways. Hence, groundwater pollution might be worsened by preferential solute transport of agrochemicals occurring with shallow water table conditions.

Assessment of spatial and temporal variability in soil moisture using multi-length TDR probes to calibrate Aquaflex sensors

Assessment of spatial and temporal variability in soil moisture using multi-length TDR probes to calibrate Aquaflex sensors

Modelling Shallow Groundwater Evaporation Rates from a Large Tank Experiment

A large tank (1.4 m x 4.0 m x 1.3 m) filled with medium-coarse sand was employed to measure evaporation rates from shallow groundwater at controlled laboratory conditions, to determine drivers and mechanisms. To monitor the groundwater level drawdown 12 piezometers were installed in a semi regular grid and equipped with high precision water level, temperature, and electrical conductivity (EC) probes. In each piezometer, 6 micro sampling ports were installed every 10 cm to capture vertical salinity gradients. Moreover, the soil water content, temperature and EC were measured in the unsaturated zone using TDR probes placed at 5, 20 and 40 cm depth. The monitoring started in February 2020 and lasted for 4 months until the groundwater drawdown became residual. To model the groundwater heads, temperature, and salinity variations SEAWAT 4.0 was employed. The calibrated model was then used to obtain the unknown parameters, such as: maximum evaporation rates (1.5-4.4 mm/d), extinction depth (0.90 m), mineral dissolution (5.0e-9 g/d) and evaporation concentration (0.35 g/L). Despite the drawdown was uniformly distributed, the increase of groundwater salinity was rather uneven, while the temperature increase mimicked the atmospheric temperature increase. The initial groundwater salinity and the small changes in the evaporation rate controlled the evapoconcentration process in groundwater, while the effective porosity was the most sensitive parameter. This study demonstrates that shallow groundwater evaporation from sandy soils can produce homogeneous water table drawdown but appreciable differences in the distribution of groundwater salinity.

Assessment of spectral indexes for estimating soil water content in the Brazilian Pantanal

The Pantanal is the largest floodplain of the globe occupying 138,183 km2 in Brazil. The fundamental ecological factor of interaction between the Pantanal ecosystems is the flooding regime. Connected to properties of the soil-plant-atmosphere system, knowledge on the soil water content becomes increasingly necessary. The high temporal and spatial variability of water content in the soil caused by the vast heterogeneity of soil texture, vegetation, topography and climate makes it a difficult physical variable to be measured. However, its spatial and temporal variability can be determined by recent modern techniques of remote sensing based on data obtained by microwave or infrared sensors. Thus, the aim of this study was to evaluate the accuracy of vegetation and soil water indexes through satellite images from Landsat 5 in the northern Brazilian Pantanal. The study was conducted in a pasture, experimental site in the Northern Pantanal in Mato Grosso state. Soil moisture was measured using a TDR probe installed at 10 cm depth in the period from 2009 to 2011. For comparison, spectral indexes and the surface temperature provided by Geological Survey (USGS) were used, these indexes are derived from bands ratios of satellite reflectance products Landsat 5 TM. The data evaluation was performed using some indicators: accuracy - Willmott index, Root Mean Square Error and the Mean Absolute Error. This study demonstrated that the application of remote sensing in the management of water resources is very promising. The indexes correlated with soil moisture measurement. Among the soil water indexes the NBR-2 showed related to soil moisture measurement. For both types of soils EVI had the highest determination coefficient, lowest errors and highest Willmott’s index of agreement.

DEFICIT IRRIGATION OF SUBSURFACE DRIP-IRRIGATED GRAPE TOMATO

ABSTRACT Agriculture is one of the segments that most uses water and developments have been made to save irrigation water. Deficit irrigation is a technique that can contribute to production and water saving in agriculture. This study aimed to evaluate the viability of deficit irrigation in tomato production irrigated by subsurface drip in a greenhouse and estimate water saving. The experiment was conducted at the CCA/UFSCar, in Araras, Sao Paulo, Brazil, with grape tomato cultivation. It consisted of three treatments, 100 % water depth and deficit irrigation (75 and 50 % of water depth), with a randomized block design. Irrigation management was performed using mean soil moisture data collected through TDR probes installed in each treatment. Tomato plants were cultivated for 137 days and conducted vertically with one stem and six bunches. Fruit size, number and mass of fruits per plant, fruit pH and soluble solids were attributes measured and analyzed weekly. The deficit irrigation of 50 % treatment presented lower values in all attributes evaluated and 90.6 % of water saving. The 75 % treatment showed lower value only for pH and fruit diameter and 70.4 % of water saving. Deficit irrigation of 75 % was viable for tomato cultivation in greenhouse and for water saving in crop cycle.

MONITORING XYLEM SAP IN SUGARCANE THROUGH TDR

The TDR can be used to measure water content and nutrients in several media with a potential to monitor the xylem sap flow in plants. The objective of this study was to determine whether there is a correlation between the xylem sap content and water available in the soil for sugarcane cultivation using TDR. The study was conducted in a protected environment with eight boxes (500 L). The boxes were divided into two treatments with different water application rates (1.6 and 3.4 L h-1) through subsurface irrigation. In each box TDR probes were inserted in the medium part of sugarcane stalk, totaling three probes per box to monitoring the sap flow. The soil water content was monitored using 20 net-placed probes. Therefore, the simultaneous monitoring of xylem sap and soil water content occurred for five months. As a result, it was obtained that the xylem content monitoring through TDR is moderately related to soil moisture, with a response to the absorption and translocation of the solution in the stem of sugarcane plants as a consequence of irrigation applications and/or fertirrigation. Thus, it was concluded that there is a weak relations between water contents in the soil and plant, especially for the treatment that used the highest flow rate (3.4 L h-1).

Time Domain Reflectometry (TDR) technique – A solution to monitor moisture content in construction materials

Measuring moisture content in building materials is crucial for the correct diagnosis of buildings’ pathologies and for the efficiency evaluation of the treatment solution applied. There are several different techniques available to measure the moisture content in construction materials. However, perform long-term minor-destructive measurements is still a great challenge. The TDR – Time Domain Reflectometry – technique is commonly used for moisture content measurements in soils, but is considered a relatively new method with regard to its application in construction materials. In the present state of research, the current use of the TDR technique for monitoring moisture content in all types of consolidated porous building materials is not possible yet. Indeed, the empirical conversion functions proposed for soils are mostly not suitable for building materials. Furthermore, to successfully use the TDR technique, a good contact between the TDR probe and the material under study is required, which may be difficult to achieve in hard materials. In this paper, the TDR technique was implemented in two limestone walls constructed in the lab to test experimentally the efficiency of a wall-base ventilation channel to speed up drying after a flood. Each wall was equipped with four two-rod TDR probes for continuous monitoring the moisture content in both situations: with and without the ventilation channel. All the equipment used, procedures followed during the drilling until the probes’ final installation, as well as the individual calibration required for each probe are explained in detail. Instead of using unsuitable functions proposed for soils, the evaluation of the moisture content from the apparent relative dielectric permittivity measured was established using as reference method the gravimetric method. The results obtained suggest that the TDR technique is suitable for moisture content monitoring in consolidated porous building materials.

Non-invasive time domain reflectometry probe for transient measurement of water retention curves in structured soils

Transient evaporation method is promising for rapid measurement of soil water retention curve (WRC). Existing apparatuses of transient evaporation method are not ideal for measuring the WRC of structured soils because of the sample disturbance induced by invasive water content probes used. In this study, non-invasive TDR probes with different waveguide layouts (i.e., different number of conductors and waveguide length) were developed to measure the WRC of loess during transient evaporation, while the soil suction is recorded through a tensiometer. Results show that the WRCs of undisturbed and remolded loess measured by a three-conductor non-invasive TDR probe are in good agreement with the results of pressure plate tests. The differences in the air entry value (AEV) and desorption rate between the WRCs measured by the transient evaporation method and the pressure plate measurement are less than 10 %. On the other hand, the WRCs measured by a two-conductor non-invasive TDR probe underestimate the water content for a given suction. The AEV of undisturbed and remolded loess determined by the transient evaporation method is 66.7 % and 112.9 % smaller than the results of pressure plate measurements, respectively. The underestimation of the two-conductor non-invasive TDR probe in measuring the WRC of loess can be attributed to the fact that the vertical sampling range of two-conductor non-invasive TDR probe is two times greater than that of the tensiometer. The results in this study show the effectiveness of using the non-invasive TDR probe along with a tensiometer for measuring the WRC. More importantly, great caution should be taken on compliant sampling volume of the non-invasive TDR probe and tensiometer to obtain accurate WRC measurements.

Laboratory Calibration of TDR Probes for Simultaneous of Measurements Soil Water Content and Electrical Conductivity

ABSTRACTAccurate measurement of water content (θ), apparent electrical conductivity (ECa) of soils, and soil solution electrical conductivity (ECw) is critical for a better management of irrigation water and the effective monitoring and control of soil salinity. In this paper, we demonstrate the design and validation of an identical time domain reflectometry (TDRWO) probe for accurate and non-destructive measurements of ECw. Two calibration functions were used to determine the soil-water content by TDR. Theses relations were verified by laboratory experiment over a wide range of θ and bulk density (BD) for dune sand. The exact length and the impedance of all TDR-probes were calibrated using the WinTDR procedure. Estimates of ECw were based on θ and the bulk ECa using a special modeling approach which applies long-time TDR waveform analysis. The geometrical disposition of the matrix phase factors (τ and β) was calculated by immersing the TDR probe in sodium chloride (NaCl) solutions of different electrical conductivities in pressure cells wetted and drained with each of these NaCl solutions. The reliability of the TDRWO was validated/proven under laboratory conditions. The laboratory experiment consisted in inserting the TDR probe into a pressure cell packed with mixed sand and 2-mm sieved loam soil that was subsequently wetted and drained with different NaCl solutions at various pressure heads. The ECw estimated by TDRWO was compared to the ECw measured in the draining solutions after they stabilized in the soil porous system. The τ and β factors calculated for the ceramic disks sets were 1.991 and 4.312, respectively. In the laboratory experiments, high and therefore significant correlations (R2 = 0.986; P < .001) were found between the ECw estimated by the TDRWO and the corresponding ECw values measured in the column-drainage. These results demonstrate that the TDRWO is an instrument which allows researchers to accurately estimate soil solution salinity independently of the soil water content and the porous medium in which the TDR probe is installed. Test results showed that the TDR method has high accuracy for monitoring soil water content but is less accurate in monitoring soil electrical conductivity across a water content range of about ≤0.03cm3/cm3. Regression analysis between TDR-Volumetric water content (ϴv) and weighing method – ϴv showed good correlation with an R2 of 0.97 and 0.98 during two laboratory experiments.

Time Stable Representative Position determination as affected by the considered part of an irrigation cycle

A recurrent issue in irrigation management refers to the number and optimal positioning of water content sensors in the root zone of a crop. In the field, the definition of the number and location of sensor installation is still arbitrary. How many sensors and where to install them has been studied using the Time Stable Representative Positions (TSRP) concept introduced by Soulis and Elmaloglou (2016). However, the effect of the period of the soil water content data used for the determination of the TSRP is not usually considered. The main objectives of this work are to analyze how the soil water content data collection period within an irrigation cycle affects the determined optimal sensor positioning based on TSRP; and, to evaluate if the sensors positioning affects the prediction of crop evapotranspiration (ETc) by numerical modeling. Over 60,000 soil water content data were obtained during 36 days from 12 TDR probes installed at different monitoring positions in the root zone of an irrigated banana plant. The optimal position of sensors was determined based on the concept of TSRP, considering soil water content data obtained during the entire and during the second part of the irrigation cycles. The SWAP hydrological model was also used to investigate the effect of sensors positioning in prediction of ETc by numerical modeling. It was verified that the use of soil water content data obtained at the beginning of an irrigation cycle - at times when infiltration occurs and there is a high intensity of redistribution of water in the soil - increases the uncertainties regarding the estimation of temporal stability for purposes of irrigation management. The result of the determination of the optimal positioning for sensors installation varies according to the part of the irrigation cycle from which water content measurements are considered. This variation affects the prediction of ETc by numerical modeling. As values of soil water content obtained at the beginning of the irrigation cycle increase the uncertainty of the statistical indicators and are not of practical interest for irrigation management, it is recommended that in the determination of optimal positioning of sensors, only soil water content values obtained after the infiltration and cessation of high rates of irrigation water redistribution are considered.

Water extraction and implications on soil moisture sensor placement in the root zone of banana

The knowledge on spatial and temporal variations of soil water storage in the root zone of crops is essential to guide the studies to determine soil water balance, verify the effective zone of water extraction in the soil and indicate the correct region for the management of water, fertilizers and pesticides. The objectives of this study were: (i) to indicate the zones of highest root activity for banana in different development stages; (ii) to determine, inside the zone of highest root activity, the adequate position for the installation of soil moisture sensors. A 5.0 m3 drainage lysimeter was installed in the center of an experimental area of 320 m2. Water extraction was quantified inside the lysimeter using a 72 TDR probe. The concept of time stability was applied to indicate the position for sensor installation within the limits of effective water extraction. There are two patterns of water extraction distribution during the development of banana and the point of installation of sensors for irrigation management inside the zone of highest root activity is not constant along the crop development.