Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    We will mail you new results for this query: keywords==time-domain reflectometry
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Resilience of roof-top Plant-Microbial Fuel Cells during Dutch winter
Helder, M. ; Strik, D.P.B.T.B. ; Timmers, R.A. ; Reas, S.M.T. ; Hamelers, H.V.M. ; Buisman, C.J.N. - \ 2013
Biomass and Bioenergy 51 (2013). - ISSN 0961-9534 - p. 1 - 7.
time-domain reflectometry - electricity production - temperature - performance - biofilm
The Plant-Microbial Fuel Cell (P-MFC) is in theory a technology that could produce sustainable electricity continuously. We operated two designs of the P-MFC under natural roof-top conditions in the Netherlands for 221 days, including winter, to test its resilience. Current and power densities are not stable under outdoor conditions. Highest obtained power density was 88 mW m-2, which is lower than was achieved under lab-conditions (440 mW m-2). Cathode potential was in our case dependent on solar radiation, due to algae growth, making the power output dependent on a diurnal cycle. The anode potential of the P-MFC is influenced by temperature, leading to a decrease in electricity production during low temperature periods and no electricity production during frost periods. Due to freezing of the roots, plants did not survive winter and therefore did not regrow in spring. In order to make a sustainable, stable and weather independent electricity production system of the P-MFC attention should be paid to improving cathode stability and cold insulation of anode and cathode. Only when power output of the Plant-Microbial Fuel Cell can be increased under outdoor conditions and plant-vitality can be sustained over winter, it can be a promising sustainable electricity technology for the future
Sensing soil properties in the laboratory, in situ, and on-Line: A review
Kuang, B. ; Mahmood, H.S. ; Quraishi, Z. ; Hoogmoed, W.B. ; Mouazen, A.M. ; Henten, E. van - \ 2012
Advances in Agronomy 114 (2012). - ISSN 0065-2113 - p. 155 - 223.
ground-penetrating radar - infrared reflectance spectroscopy - time-domain reflectometry - ion-selective electrodes - apparent electrical-conductivity - partial least-squares - gamma-ray spectrometry - complex dielectric permittivity - plant-available potassium
Since both the spatial and vertical heterogeneities in soil properties have an impact on crop growth and yield, accurate characterization of soil properties at high sampling resolution is a preliminary step in successful management of soil-water-plant system. Conventional soil sampling and analyses have shown mixed economical returns due to the high costs associated with labor-intensive sampling and analysis procedures, which might be accompanied with map uncertainties. Therefore, the conventional laboratory methods are being replaced or complemented with the analytical soil sensing techniques. The objective of this chapter is to review different soil sensing methods used to characterize key soil properties for management of soil-water-plant system. This will cover laboratory, in situ in the field, and on-line measurement methods. This review chapter is furnished with an overview of background information about a sensing concept, basic principle and brief theory, various factors affecting the output of the sensor, and justification of why specific soil properties can be related with its output. The literature review is succeeded with an integration and analysis of findings in view of application in the precision agriculture domain. Potentials and limitations of current sensor technology are discussed and compared with commonly used state-of-the-art laboratory techniques. As sensing is commonly addressed as a very technical discipline, the match between the information currently collected with sensors and those required for site-specific application of different inputs, and crop growth and development is discussed, highlighting the most accurate method to measure a soil property for a given application.
Soil moisture monitoring for climate research: evaluation of a low cost sensor in the framework of the Swiss soil Expperiment (SwissSMEX) campaign
Mittelbach, H. ; Casini, F. ; Lehner, I. ; Teuling, A.J. ; Seneviratne, S.I. - \ 2011
Journal of Geophysical Research: Atmospheres 116 (2011)D5. - ISSN 2169-897X - 11 p.
time-domain reflectometry - water-content - global-models - calibration - land - variability - atmosphere - dynamics - europe - system
Soil moisture measurements are essential to understand land surface–atmosphere interactions. In this paper we evaluate the performance of the low-cost 10HS capacitance sensor (Decagon Devices, United States) using laboratory and field measurements. Measurements with 10HS sensors of volumetric water content (VWC, Vol.%), integrated absolute soil moisture (millimeters) over the measured soil column, and the loss of soil moisture (millimeters) for rainless days are compared with corresponding measurements from gravimetric samples and time domain reflectometry (TDR) sensors. The field measurements were performed at two sites with different soil texture in Switzerland, and they cover more than a year of parallel measurements in several depths down to 120 cm. For low VWC, both sensor types present good agreement for laboratory and field measurements. Nevertheless, the measurement accuracy of the 10HS sensor reading (millivolts) considerably decreases with increasing VWC: the 10HS sensors tend to become insensitive to variations of VWC above 40 Vol.%. The field measurements reveal a soil type dependency of the 10HS sensor performance, and thus limited applicability of laboratory calibrations. However, with site-specific exponential calibration functions derived from parallel 10HS and TDR measurements, the error of the 10HS compared to the TDR measurements can be decreased for soil moisture contents up to 30 Vol.%, and the day-to-day variability of soil moisture is captured. We conclude that the 10HS sensor is appropriate for setting up dense soil moisture networks when focusing on medium to low VWC and using an established site-specific calibration function. This measurement range is appropriate for several applications in climate research, but the identified performance limitations should be considered in investigations focusing on humid conditions and absolute soil moisture
Polymer tensiometers with ceramic cones: direct observations of matric pressures in drying soils
Ploeg, M.J. van der; Gooren, H.P.A. ; Bakker, Gerben ; Hoogendam, C.W. ; Huiskes, C. ; Koopal, L.K. ; Kruidhof, H. ; Rooij, G.H. de - \ 2010
Hydrology and Earth System Sciences 14 (2010)10. - ISSN 1027-5606 - p. 1787 - 1799.
time-domain reflectometry - hydraulic-properties - osmotic tensiometer - tensile-strength - water-content - suction - performance - sensor
Measuring soil water potentials is crucial to characterize vadose zone processes. Conventional tensiometers only measure until approximately -0.09 MPa, and indirect methods may suffer from the non-uniqueness in the relationship between matric potential and measured properties. Recently developed polymer tensiometers (POTs) are able to directly measure soil matric potentials until the theoretical wilting point (-1.6 MPa). By minimizing the volume of polymer solution inside the POT while maximizing the ceramic area in contact with that polymer solution, response times drop to acceptable ranges for laboratory and field conditions. Contact with the soil is drastically improved with the use of cone-shaped solid ceramics instead of flat ceramics. The comparison between measured potentials by polymer tensiometers and indirectly obtained potentials with time domain reflectometry highlights the risk of using the latter method at low water contents. By combining POT and time domain reflectometry readings in situ moisture retention curves can be measured over the range permitted by the measurement range of both POT and time domain reflectometry
Root Zone Sensors for Irrigation Management in Intensive Agriculture
Pardossi, A. ; Incrocci, L. ; Incrocci, G. ; Marlorgio, F. ; Battista, P. ; Bacci, L. ; Rapi, B. ; Marzialetti, P. ; Hemming, J. ; Balendonck, J. - \ 2009
Sensors 9 (2009)4. - ISSN 1424-8220 - p. 2809 - 2835.
soil-water content - time-domain reflectometry - moisture sensor - tensiometer - conductivity - performance - calibration - texture - network - suction
Crop irrigation uses more than 70% of the world’s water, and thus, improving irrigation efficiency is decisive to sustain the food demand from a fast-growing world population. This objective may be accomplished by cultivating more water-efficient crop species and/or through the application of efficient irrigation systems, which includes the implementation of a suitable method for precise scheduling. At the farm level, irrigation is generally scheduled based on the grower’s experience or on the determination of soil water balance (weather-based method). An alternative approach entails the measurement of soil water status. Expensive and sophisticated root zone sensors (RZS), such as neutron probes, are available for the use of soil and plant scientists, while cheap and practical devices are needed for irrigation management in commercial crops. The paper illustrates the main features of RZS’ (for both soil moisture and salinity) marketed for the irrigation industry and discusses how such sensors may be integrated in a wireless network for computer-controlled irrigation and used for innovative irrigation strategies, such as deficit or dual-water irrigation. The paper also consider the main results of recent or current research works conducted by the authors in Tuscany (Italy) on the irrigation management of container-grown ornamental plants, which is an important agricultural sector in Italy.
Matric potential measurements by polymer tensiometers in cropped lysimeters under water-stressed conditions
Ploeg, M.J. van der; Gooren, H.P.A. ; Bakker, G. ; Rooij, G.H. de - \ 2008
Vadose Zone Journal 7 (2008). - ISSN 1539-1663 - p. 1048 - 1054.
time-domain reflectometry - root water - soil - extraction - responses - drought - systems - maize
In many regions of the world, plant growth and productivity are limited by water deficits. As a result of more frequent and intense droughts, the area of land characterized as very dry has more than doubled since the 1970s. Consequently, understanding root water uptake under water-stressed conditions is gaining importance. The performance of a recently developed polymer tensiometer (POT) designed to measure matric potentials down to ¿1.6 MPa was evaluated and compared with volumetric moisture content measurements in dry soil. Three irrigation intensities created severe, intermediate, and no water stress conditions in lysimeters with growing maize (Zea mays L.) plants. By monitoring matric potentials using POTs, levels of local water stress in our experiments were better defined. When the defined stress levels were reached, volumetric moisture measurements for this particular loam soil were below 0.1, thus less informative compared with matric potential measurements. The observed matric potential profiles indicate significant root water uptake between 0.3- and 0.5-m depth in the later growth stages under water-stressed conditions. The temporal pattern of matric potential profiles reflected changing root water uptake behavior under dry conditions. As the total soil water potential is a direct indication of the amount of energy required by plants to take up water, POTs may contribute to quantifying root water uptake in dry soils.
Calibration of capacitance probe sensors using Electric Circuit Theory
Kelleners, T.J. ; Soppe, R.W.O. ; Robinson, D.A. ; Schaap, M.G. ; Ayars, J.E. ; Skaggs, T.H. - \ 2004
Soil Science Society of America Journal 68 (2004)2. - ISSN 0361-5995 - p. 430 - 439.
time-domain reflectometry - soil-water content - moisture measurement - dielectric permittivity - field calibration - model
Capacitance probe sensors are an attractive electromagnetic technique for estimating soil water content. There is concern, however, about the influence of soil salinity and soil temperature on the sensors. We present an electric circuit model that relates the sensor frequency to the permittivity of the medium and that is able to correct for dielectric losses due to ionic conductivity and relaxation. The circuit inductance L is optimized using sensor readings in a modified setup where ceramic capacitors replace the sensor's capacitance plates. The three other parameters in the model are optimized using sensor readings in a range of nonconductive media with different permittivities. The geometric factor for the plastic access tube gp is higher than the geometric factor for the medium gm, indicating that most of the electromagnetic field does not go beyond the access tube. The effect of ionic conductivity on the sensor readings is assessed by mixing salts in three of the media. The influence is profound. The sensor frequency decreases with increasing conductivity. The effect is most pronounced for the medium with the lowest permittivity. The circuit model is able to correct for the conductivity effect on the sensors. However, as the dielectric losses increase, the frequency becomes relatively insensitive to permittivity and small inaccuracies in the measured frequency or in the sensor constants result in large errors in the calculated permittivity. Calibration of the capacitance sensors can be simplified by fixing two of the constants and calculating the other two using sensor readings in air and water.
Calibration of capacitance probe sensors in a saline silty clay soil
Kelleners, T.J. ; Soppe, R.W.O. ; Ayars, J.E. ; Skaggs, T.H. - \ 2004
Soil Science Society of America Journal 68 (2004)3. - ISSN 0361-5995 - p. 770 - 778.
time-domain reflectometry - solution electrical-conductivity - water-content probe - fine sand soils - field calibration - dielectric-constant - porous-media - moisture - anisotropy - diffusion
Capacitance probe sensors are a popular electromagnetic method of measuring soil water content. However, there is concern about the influence of soil salinity on the sensor readings. In this study capacitance sensors are calibrated for a saline silty clay soil. An electric circuit model is used to relate the sensor's resonant frequency F to the permittivity () of the soil. The circuit model is able to account for the effect of dielectric losses on the resonant frequency. Dielectric mixing models and empirical models are used to relate the permittivity to the soil water content (). The results show that the electric circuit model does not fit the F¿() data if the calibrated bulk electrical conductivity (EC) model is used. The dielectric losses are overestimated. Increasing the exponent c in the tortuosity factor of the bulk EC model and thereby lowering the bulk EC and the dielectric losses improves the performance of the model. Measured and calculated volumetric water contents compare reasonably well (R2 = 0.884). However, only 73 out of 88 data points can be described. The rejected points are invariably at high water contents where the high dielectric losses result in the sensor frequency being insensitive to ().
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