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that stimulate the phenomena and processes observed in the soil-plant-atmosphere system. Monitoring of water status is accomplished using digital systems. The digital data acquisition systems react only on electric signals and the applied sensors must convert the measured value into the proportional electric signal. Water status of soil, as a porous material should be expressed by minimum five variables: amount of water in the soil (ie soil water content), soil potential, salinity, oxygenation and temperature (Malicki and Bieganowski [55]). The most difficult are the electric measurement of soil water potential and soil water content (soil water content), therefore they are the subject of permanent research. It is assumed here, that the method successfully verified for soils will be also applicable for other porous agricultural materials because their structure is not so complex as soil. 1.1.1. Minimal number of variables describing the water status The number of variables for water status description in the porous material depends on the specificity of the analysed problem and, up till now, is arbitrary chosen. In majority of practical cases the status of water is described by one variable: water content of the material. One variable - water content – is enough for wood as building material. Two variables are practically enough to describe the status of water in grain: water content and temperature. Soil is a material in which water status should be describes by minimum five variables: amount of water (soil water content), its potential, salinity, oxygenation and temperature. Soil is the most difficult biological material for water status monitoring because soil is diverse and its properties are not stable in time and space. Soil water content is the most challenging soil water status parameter for determination because the measurement results must be in the form of electric signal, while the current flow though the soil depends not only on its water content. Assuming that: − the methods effective for soil water content measurements are also effective for water content measurements of other biological materials − characterized by simpler construction, and sensors, methods and instrumentation requirements in soil water content monitoring are not stronger than in water content monitoring of other biological materials we can concentrate further discussion on soil water content measurement and monitoring. 9
2. REQUIREMENTS AND MEANS OF SOIL WATER STATUS MONITORING Monitoring of soil water status, ie temporal and spatial registration of its water content, potential, salinity, oxygenation and temperature, is the necessary condition for modelling of processes in soil-plant-atmosphere continuum, prediction of their consequences and control. The implementation of soil water status monitoring needs the application of automatic systems based on digital technique. The digital acquisition systems read only electrical signals; therefore the applied sensors must convert the measured quantity on the respective electrical signal. The sensors, methods and instrumentation requirements used for “electrical” monitoring of soil water status are: − automatic and continuous registration of data in situ ensuring non invasive actions affecting soil and the observed processes, − selectivity (the measurement method should not be sensitive on factors other than the selected one), − security and simplicity (application of inoffensive medium and minimum specialized knowledge of the operator) The actual means of agrophysical metrology gives diverse possibilities of soil water monitoring of the individual parameters: − electrical measurement of temperature is easy because electrical temperature sensors are commercially available, − electrical measurement of potential is possible for its matrix element in the range of 0-950 mbar with the application of electrical tensiometric converter , and above 950 mbar up to the value relating to the plant wilting point (about 1.5x10 4 mbar) with the use of capillary-porous blocs (Campbell and Gee [13]) and thermoelectric tensiometers (Mullins [69]), − oxygenation can be measured electrically or evaluated on the base of soil aeration, that is closely correlated with its water content, − the electrical method of soil water content (moisture) and salinity measurement and is the subject of continuous research. 2.1. Selectivity of the method The key feature of the applied method is the selectivity of the measurement, ie the lack of sensitivity of the conversion function (calibration) on the influence from the factors other than the measured one. Proper selectivity liberates the user from frequent, specific for each soil, in situ calibration measurements. 10
Page 2 and 3: TDR METHOD FOR THE MEASUREMENT OF W
Page 4 and 5: PREFACE The importance of water for
Page 6 and 7: CONTENTS 1. Status of water as an s
Page 8 and 9: 12.2. New prototype version of FOM/
Page 12 and 13: The solution to the problem of elec
Page 14 and 15: 3. ELECTRICAL MEASUREMENTS METHODS
Page 16 and 17: v = c 1 2L = = ( θ ) n ∆t ε (2)
Page 18 and 19: The TDR probe consists of two waveg
Page 20 and 21: ε a =1 and φ=0.5 the Eq. (10) has
Page 22 and 23: The experiment description is given
Page 24 and 25: Results obtained with the discussed
Page 26 and 27: Notice that at C s = 0, ie when dis
Page 28 and 29: water orientation polarization [s],
Page 30 and 31: Fig. 8. Frequency dispersion of the
Page 32 and 33: The measurements were performed in
Page 34 and 35: 5. EVALUATION OF DIELECTRIC MIXING
Page 36 and 37: ε α = ∑V α iε i (29) i where
Page 38 and 39: where SAND and CLAY are percents of
Page 40 and 41: Below the transition value, the soi
Page 42 and 43: To verify the observations concerni
Page 44 and 45: 6. TEMPERATURE EFFECT ON SOIL DIELE
Page 46 and 47: chamber and the freezer, only one w
Page 48 and 49: The user interface on the main comp
Page 50 and 51: soil sample volumetric water conten
Page 52 and 53: close vicinity of the analyzed obje
Page 54 and 55: process of measurement is non-destr
Page 56 and 57: dielectric permittivity change caus
Page 58 and 59: The values of the refractive index
Page 60 and 61:
The relative, ∆n/∆T, and absolu
Page 62 and 63:
Fig. 25. The temperature effect on
Page 64 and 65:
The temperature effect of TDR soil
Page 66 and 67:
The purpose of the above discussion
Page 68 and 69:
( ,25 + T )( 45 + T ) 49 9 f rel =
Page 70 and 71:
8. THE ACCURACY OF SOIL WATER CONTE
Page 72 and 73:
gravimetric method and the soil ref
Page 74 and 75:
where: a 0 ÷ a 6 are coefficients
Page 76 and 77:
values of p F calculated for the re
Page 78 and 79:
eason of this is the fact that wate
Page 80 and 81:
9 ∆θ = 0,2 ⋅10 ⋅ ∆t = 0.00
Page 82 and 83:
values of θ rel for lower values o
Page 84 and 85:
9. COMPARISON OF OPEN-ENDED COAX AN
Page 86 and 87:
ε" = EC ε d " + (82) 2π fε wher
Page 88 and 89:
dielectric permittivity, the dielec
Page 90 and 91:
The applied lumped capacitance mode
Page 92 and 93:
stainless steel wires soldered to t
Page 94 and 95:
ε’ Open Coax and ε b-TDR , exce
Page 96 and 97:
− − The difference of the imagi
Page 98 and 99:
Integrated Circuit) recently introd
Page 100 and 101:
10.2. Electromechanical microwave s
Page 102 and 103:
RF1. Two PIN diodes in series in ea
Page 104 and 105:
The significant aspect of the proto
Page 106 and 107:
visible for lower values of soil el
Page 108 and 109:
In the TDR method the signal propag
Page 110 and 111:
description of functional and techn
Page 112 and 113:
MASTER modules are wireless transce
Page 114 and 115:
time the Real Time Clock module wak
Page 116 and 117:
ase station distinguishes A SLAVE d
Page 118 and 119:
sensor, format the data received fr
Page 120 and 121:
12. SOIL WATER STATUS MONITORING DE
Page 122 and 123:
D-LOG/mpts is a moisture/pressure/t
Page 124 and 125:
For compatibility reasons it uses t
Page 126 and 127:
D-LOG/mts (Fig. 59) is a TDR (Time-
Page 128 and 129:
12.4. FP/m, FP/mts - Field Probe fo
Page 130 and 131:
inside of a separate polyethylene b
Page 132 and 133:
differential water capacity and the
Page 134 and 135:
− maximum number of LP/p probes t
Page 136 and 137:
12.7. LP/t - Laboratory Probe for s
Page 138 and 139:
From the collected data set, after
Page 140 and 141:
25. de Loor G.P.: Dielectric proper
Page 142 and 143:
TDR. Symposium on Time Domain Refle
Page 144 and 145:
100. Whalley W.R.: Considerations o
Page 146 and 147:
Fig. 14. Fig. 15. Fig. 16. Fig. 17.
Page 148 and 149:
Fig. 38. The three-rod TDR probe -
Page 150 and 151:
Fig. 67. A set of LP/ms and LP/p LO
Page 152:
Table 17. An example of the executa
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