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12. SOIL WATER STATUS MONITORING DEVICES The Institute of Agrophysics introduces field and laboratory meters for the determination of: − water content by means of Time-Domain Reflectometry (TDR) method, − salinity (bulk electrical conductivity) of soils by means of TDR, − temperature of the soil, − soil water capillary pressure (suction force). There are three types of meters available: − Field Operated Meter (FOM), − field operated Data LOGger (D-LOG) and − Laboratory Operated Meter (LOM). Also adequate kinds of probes are offered: − Field Probe (FP) and − Laboratory Probe (LP) respectively. FOM is a portable, battery operated, microprocessor-controlled device designed for in situ field measurements of soil water content, temperature and salinity. It is particularly suitable for periodic measurements at random and/or fixed locations, where water content, temperature and salinity distribution is to be determined by readings taken at various levels of the soil profile. FOM provides a Mineral/Organic option switch for soils originated from mineral or organic parent material, thus no user calibration is needed to read the soil water content directly. FP is a probe for momentary or for semi-permanent installation. Through a pre-augered pilot hole it can reach any depth down to 4 m without destroying either the soil structure or disturbing heat and mass transport in the soil. It can be left then intact for as long period of time as needed. A single, mobile probe may also be used for momentary measurements in shallow layers of the soil profile by walking over the field and inserting the probe in chosen sites. For semi-permanent installation, when deeper layers are to be monitored, several FPs can be inserted from the soil surface or horizontally through a sidewall of a soil pit. A probe installed once may be left intact in the soil for as long as necessary and then drawn out at the end of the experiment. FOM and FP from the Institute of Agrophysics are offered in two versions: • FOM/m, field operated meter for soil water content measurements, • FOM/mts, field operated meter for simultaneous measurements of the soil water content, temperature and salinity (bulk electrical conductivity). FOM/m is equipped with a 3.5 digit LCD, whereas 119
FOM/mts is provided with a 256 by 64 dot matrix graphic LCD to display data and TDR trace simultaneously. Also adequate probes are offered: − − FP/m, field probe for measurements of soil water content, FP/mts, field probe for simultaneous measurements of soil water content, temperature and salinity. LOM is an IBM PC compatible aided device working under control of special software. It has been designated mainly to control long term laboratory experiments which require monitoring of water, salt and heat transport by means of periodic recording of instantaneous soil water content, capillary tension, temperature and electrical conductivity profiles in chosen time intervals. To read water content a factory installed conversion equation for mineral or organic soils can be chosen and/or user determined calibration functions could be applied as well. To switch between probes LOM is provided with a Single-Pole-f-Throw multiplexer (SPfT, where 2 ≤ f ≤ 15) for first level multiplexing and a special port to control second level multiplexers. Up to 15 of SPsT second level multiplexers can be incorporated, where 2 ≤ s ≤ 8. This makes it possible to scan up to 120 LP/ms, 120 LP/t and 120 LP/p probes. LOM works with the following probes: • LP/ms, Laboratory miniProbe for recording instantaneous profiles of water content and salinity in soil columns or in undisturbed soil cores, • UP/ms, User-made Probe for water content and salinity, • LP/p, Laboratory Probe (minitensiometer) for measurements of soil water capillary pressure (suction force, matrix potential), • LP/t, Laboratory Probe for temperature measurement. Several LP-probes of a selected kind or of all types can be inserted through the wall of a soil column or a steel sampling cylinder, thus allowing vertical scanning of the instantaneous water content, capillary tension (matrix potential, suction force), temperature and electrical conductivity profiles. This makes it possible to collect a set of corresponding water content, water potential, electrical conductivity and temperature data from drying or wetting front transition, from which, after further processing, one can obtain a complete set of the unsaturated water flow characteristics of the soil ie water retention (PF) curve, unsaturated water conductivity (k-function), differential water capacity and unsaturated water diffusivity as well as the solute transport data. Also heat transport coefficients (as the thermal conductivity, thermal diffusivity, specific heat) can be determined if a heat flux meter is installed in the experimental column. 120
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TDR METHOD FOR THE MEASUREMENT OF W
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PREFACE The importance of water for
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CONTENTS 1. Status of water as an s
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12.2. New prototype version of FOM/
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that stimulate the phenomena and pr
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The solution to the problem of elec
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3. ELECTRICAL MEASUREMENTS METHODS
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v = c 1 2L = = ( θ ) n ∆t ε (2)
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The TDR probe consists of two waveg
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ε a =1 and φ=0.5 the Eq. (10) has
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The experiment description is given
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Results obtained with the discussed
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Notice that at C s = 0, ie when dis
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water orientation polarization [s],
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Fig. 8. Frequency dispersion of the
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The measurements were performed in
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5. EVALUATION OF DIELECTRIC MIXING
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ε α = ∑V α iε i (29) i where
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where SAND and CLAY are percents of
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Below the transition value, the soi
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To verify the observations concerni
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6. TEMPERATURE EFFECT ON SOIL DIELE
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chamber and the freezer, only one w
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The user interface on the main comp
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soil sample volumetric water conten
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close vicinity of the analyzed obje
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process of measurement is non-destr
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dielectric permittivity change caus
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The values of the refractive index
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The relative, ∆n/∆T, and absolu
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Fig. 25. The temperature effect on
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The temperature effect of TDR soil
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The purpose of the above discussion
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( ,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 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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