A computer controlled 36-channel time domain reflectometry system for monitoring soil water contents

1990 ◽  
Vol 26 (10) ◽  
pp. 2311-2316 ◽  
Author(s):  
Timo Heimovaara
Keyword(s):  
Soil Water ◽  
Time Domain ◽  
Time Domain Reflectometry ◽  
Computer Controlled ◽  
Water Contents ◽  
Soil Water Contents

Comparing Heat-Pulse and Time Domain Reflectometry Soil Water Contents from Thermo-Time Domain Reflectometry Probes

2005 ◽  
Vol 4 (4) ◽  
pp. 1080-1086 ◽  
Author(s):  
Tusheng Ren ◽  
Zhaoqiang Ju ◽  
Yuanshi Gong ◽  
Robert Horton
Keyword(s):  
Soil Water ◽  
Time Domain ◽  
Heat Pulse ◽  
Time Domain Reflectometry ◽  
Water Contents ◽  
Soil Water Contents

Assessing corn seedbed conditions for emergence

2000 ◽  
Vol 80 (1) ◽  
pp. 53-61 ◽  
Author(s):  
L. M. Dwyer ◽  
B. L. Ma ◽  
R. de Jong ◽  
M. Tollenaar
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Time Domain ◽  
Time Domain Reflectometry ◽  
Planting Date ◽  
Stand Establishment ◽  
Soil Temperatures ◽  
Water Contents ◽  
Soil Water Contents

Seedbed temperature and moisture conditions affect crop emergence rate and stand establishment. A 4 × 4 factorial experiment arranged in a split plot design with four replications was conducted for 3 yr at four sites to measure corn emergence rate and stand establishment while monitoring seedbed temperature and soil water content in situ. Four planting dates, beginning as early as the soil could be worked and every 10 d thereafter, were the main plots and four corn (Zea mays L.) hybrids the subplots. Volumetric soil water content in the top 0.10 m was measured a minimum of two times per week using time domain reflectometry (TDR) and estimated daily using a budget model. Measured and estimated soil water contents were similar (R2 = 0.73) and daily estimated values were used in the analysis. Stand establishment for most planting date-site-years ranged from 80 to 99%. Less than 15% of planting date-site-years had stands below 80%, and they were characterized by soil temperatures at or below 12.5°C combined with high soil water contents (>90% available water). Rate of emergence was not associated with stand establishment (P > 0.10) and could not be predicted from soil temperatures below 12.5°C. Results suggest that reduction in stand establishment under conditions of low (12.5°C) soil temperature and high (>field capacity) soil water content may be a factor in corn yield reductions associated with reduced or no tillage. Key words: Time domain reflectometry, soil water content, soil temperature, maize

scholarly journals Simulation of Long-Term Soil Hydrological Conditions at Three Agricultural Experimental Field Plots Compared with Measurements

Water ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 989 ◽  
Author(s):  
Martin Wegehenkel ◽  
Karin Luzi ◽  
Dieter Sowa ◽  
Dietmar Barkusky ◽  
Wilfried Mirschel
Keyword(s):  
Soil Water ◽  
Measurement Errors ◽  
Goodness Of Fit ◽  
Time Domain Reflectometry ◽  
Hydrological Conditions ◽  
Experimental Field ◽  
Precise Knowledge ◽  
Field Plots ◽  
Water Contents ◽  
Soil Water Contents

Soil hydrological conditions influence crop growth and groundwater recharge and, thus, precise knowledge of such conditions at field scale is important for the investigation of agricultural systems. In our study, we analyzed soil hydrological conditions at three agricultural experimental field plots with sandy soils and different crop rotations using a 22-year period from 1993 to 2014 with daily volumetric soil water contents measured by the Time Domain Reflectometry with Intelligent MicroElements (TRIME)-method and pressure heads determined by automatic recording tensiometers. These measured data were compared with soil water contents and pressure heads simulated by a process-based agroecosystem model. Within this 22-year period, time spans with a better model performance and periods with a lower goodness of fit between simulations and observations were observed. The lower goodness of fit in the summer periods was attributed to inadequate calculations of root water uptake. Measurement errors of the TRIME-probes and differences between soil water contents measured by TRIME and pressure heads observed by tensiometers due to different measurement volumes, precision and measuring principles were identified as further reasons for mismatches between simulated and measured model outputs.

scholarly journals Assessing AquaCrop model to simulate soil water contents under semi arid climate of Central Tunisia

2019 ◽  
Vol 6 (12) ◽  
pp. 203-221
Author(s):  
Hiba Ghazouani ◽  
Basma Latrech ◽  
Mguidich Belhaj Amel ◽  
Cherni Amani ◽  
Boutheina M. Douh ◽  
...  
Keyword(s):  
Soil Water ◽  
Goodness Of Fit ◽  
Field Measurements ◽  
Time Domain Reflectometry ◽  
Growth Duration ◽  
Data Set ◽  
Aquacrop Model ◽  
The Time Domain ◽  
Water Contents ◽  
Soil Water Contents

The objective of the present study was to preliminary calibrate and validate AquaCrop model based on crop conservative parameters from the literature for plant growth and water stress thresholds. In addition, physical soil characteristics, root growth, duration of plant stages and atmospheric demands were introduced according to field measurements. Based on this preliminary calibration, simulated water contents were compared to a measured data set of water contents retrieved from deficit and full irrigation treatments on a potato cropped field during an experimental year of 2015. Statistical indexes were computed and finally this performance in simulating water contents were validated under independent measurements carried out during an experiments campaign on the same field on 2014. Moreover, the paper presents the experimental protocol followed for soil characterization, considered as a milestone component for this soil water contents prediction. Results showed, that under the followed preliminary calibration, the model was able to simulate water contents (0v). In general, values of Root Mean Square Error were lower than 0.03 cm3.cm-3 representing the magnitude of error of the time domain reflectometry probe. Moreover values of Nash coffecients were close to 1 confirming the goodness of fit between measured and estimated water contents. Once assessed, the model could be used to study effects of different irrigation strategies on dynamic of water contents aiming to increase water use efficiency.

The dielectric behaviour of clay soils and its application to time domain reflectometry

Soil Research ◽  
1996 ◽  
Vol 34 (6) ◽  
pp. 825 ◽  
Author(s):  
BJ Bridge ◽  
J Sabburg ◽  
KO Habash ◽  
JAR Ball ◽  
NH Hancock
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Time Domain ◽  
Time Domain Reflectometry ◽  
Clay Soils ◽  
Dielectric Behaviour ◽  
Swelling Clay ◽  
Network Analyser ◽  
Water Contents

The dielectric behaviour of 3 soils, a sandy loam (Red Chromosol), a highly structured non-swelling clay (Red Ferrosol), and a self-mulching swelling clay (Black Vertosol), was investigated using a waveguide and network analyser technique in the frequency range 3.0 GHz to 4.5 GHz. Curves relating the real part of the relative permittivity to water content are presented and compared with the general Topp curve. The Chromosol generally followed the Topp curve, but the Ferrosol and Vertosol both had curves below the Topp curve. The Ferrosol showed a maximum horizontal offset of 0.05 m3/m3 from the Topp curve in the mid soil-water content range of 0.2–0.3 m3/m3 offset from the Topp curve of 0.10 m3/m3, with a maximum of 0.12 m3/m3 occurring at a soil water content of 0.4 m3/m3. Similar dielectric curves were obtained for the Chromosol and Vertosol using time domain reflectometry (TDR). With this method, the Chromosol showed very close agreement with the Topp curve, but the Vertosol again gave a curve below the Topp curve, similar to the one obtained using the waveguide and network analyser, but with a smaller maximum horizontal offset of 0.08 m3/m3. The difference between the waveguide and TDR Vertosol curves was mainly attributed to low bulk densities in the waveguide where packing was difficult. Some was also attributed to the wider spectrum of frequencies used by TDR. Use of the Topp curve for TDR measurements in the Vertosol would underestimate its water content by at least 0.06 m3/m3. These results are in good agreement with others obtained from similar soils. Deviations from the Topp curve are attributed to bound water associated with the clay particles and this depends on clay mineralogy and clay content. The presented calibration curves improve the accuracy of TDR measurements in these types of clay soils. A field comparison between water contents measured by TDR and gravimetric sampling in a similar Black Vertosol is presented. This calibration showed that soil water contents can be severely overestimated by using TDR with long probes and cables. This unexpected and opposite result is discussed in terms of attenuated high frequencies in the 15-m-long connecting cable used, errors in depth of probe placement, and changes in bulk density and DC conductivity.

Soil texture and salinity effects on calibration of TDR300 dielectric moisture sensor

Soil Research ◽  
2013 ◽  
Vol 51 (4) ◽  
pp. 330 ◽  
Author(s):  
George Kargas ◽  
Nikolaos Ntoulas ◽  
Panayiotis A. Nektarios
Keyword(s):  
Porous Media ◽  
Water Content ◽  
Soil Water ◽  
Time Domain ◽  
Soil Texture ◽  
Time Domain Reflectometry ◽  
Bulk Soil ◽  
The Relationship ◽  
Calibration Equations ◽  
Water Contents

Newly developed sensors have simplified real-time determination of soil water content (θm). Although the TDR300 is one of the most recent dielectric sensors, little is known with regard to the accuracy and dependency of its measurements of soil type and other environmental factors. In this study, the performance of TDR300 was investigated using liquids of known dielectric properties and a set of porous media with textures ranging from sandy to clayey. The experiments were conducted in the laboratory by mixing different amounts of water with each soil to obtain a sufficient range of soil water contents. For sand, the calculated permittivity values (εr) correlated adequately with Topp’s equation derived for time domain reflectometry. However, for the remaining inorganic porous media, εr values were overestimated compared with those resulting from Topp’s equation, especially for water contents exceeding 0.2 cm3/cm3. The results suggested that the relationship between θm and √εr was strongly linear (0.953< r2 <0.998). The most accurate results were provided by soil-specific calibration equations, which were obtained by the multi-point calibration equation. However, two-point calibration equations determined water content in all tested soils reasonably well, except for clay soil. A linear regression equation was developed that correlated the slope of the relationship θm–√εr with bulk soil electrical conductivity (EC). The regression slope was influenced more by soil EC than by soil texture. Also, TDR300 response was investigated in bi-layered systems (liquid–air and saturated porous media–air). In a bi-layered sensing volume characterised by strongly contrasting dielectric values, the appropriate bulk permittivity values for water and loam soil were determined by arithmetic rather than refractive index averaging, while for butanol and sand these values remained somewhere between the two averaging schemes, indicating that the upward infiltration calibration technique is inappropriate for the TDR300 sensor. Soil solute EC, as determined by measurements conducted in liquids and sand, significantly affected permittivity values at much lower levels than the limit of EC <2 dS/m, as suggested by the manufacturer. However, the relationship θm–√εr remained linear up to EC 2 dS/m, which corresponded to a bulk soil EC value of 0.6 dS/m. By contrast, for EC values >2 dS/m, the relationship θm–√εr was not linear, and, thus the TDR300 device calibration became increasingly difficult. Therefore, rather than operating as a time domain device, TDR300 operates as a water content reflectometer type device.

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