Monday, 10 July 2006

Technique of Detailed - Level-by-Level Definition of Soil Moisture with TDR TRIME-FM3.

Olga S. Ermolaeva and Anatoly Zeiliger. Moscow State University of Environmental Engineering, 19, Prjanishnikov Street, Moscow, Russia

Background. Accurate measurement of profile of soil water content is essential to many areas of environmental and agricultural research. Nowadays, Time Domain Reflectometry (TDR) is a widely used technique for measuring soil moisture. However, the design of probes doesn’t allow effective using of these devices for monitoring vertical distribution of moisture in thin soil layers. Device TRIME-FM3 created by IMKO company is based on TDR-technology and allows to do the rapid, routine and non-destructive measurements of water content profiles. The research which has been carried out by the producing company have shown, that the geometrical body of measurement of this probe represents the cylinder with height about 15-16 cm and the basis in the form of an ellipse with the greatest radius about 40 sm. In this case, direct using of this probe to monitor water content of layers thinker a hight of cylinder of measurement is not possible. The aim: To develop a method of detailed - level-by-level calculation of water content profiles scanning by TDR for boreholes such as TRIME-FM3. For achievement of the aim were solved the following tasks: 1) To carry out verification model TDR-probe of measurement throw soil layers with different moisture content; 2) To test a technique for detailed - level-by-level definition of results of soil moisture scanning.

Method: Verification of the additive model was carried out on the experimental data received on prepared in special case(with horizontal dimensions of 70x70 cm and height of 90 cm) an artificial soil monolith with different moisture content layers. All sides of this monolith have been coated by film getting them impervious for evaporation. Each layer of the soil was separated from another by the film to exclude mixing of soil water content on the boundary of layers. The soil material of a monolith has been selected from the top of aggregated horizons of dark-chestnut soil of Saratov Region. For exception of formation inside a monolith of significant air cavities and this soil material was exposed to preliminary processing (a choice of roots and crushing of large blocks), then the soil has been placed in a monolith, thus was made level-by-level (1 cm) compressing for obtaining homogeneous soil body and condensation up to the planned values (gravimetric moisture in a range from 0,08-0,30g/g, density from 1,1 up to 1,38 g/sm3). The plastic tube (1 m height) was installed in the middle of the box to measure the soil water content by TRIME tube probe. Series of scanning measurements of volumetric humidity have been done at various position of a probe on height of a monolith with step on 1 sm. With the purpose of reception of representative given measurements they were carried out several times during three days at four various horizontal positions of a TDR-probe. After the measurements the soil monolith has been disassembled, and from each created layer were selected samples for density and moisture definition by gravimetric method. The model and results: The model simulate measurements of volumetric soil moisture, contained in volume of probe approbation, is based on a hypothesis of additivity of the moisture content, of layers getting in this volume. On this model the program in language VBA was developed. This model provides us a curve of scanning with a set of entrance data and a step of scanning. Experimental values of volumetric and the density of soil layers received as a result of disassembly of a soil monolith, and also size of an active and inactive zone of a probe have been used as the entrance data for the developed program of calculations. Calculations have been carried out for various combinations of size of an active and inactive zone of a probe at a step of scanning 1 sm. As a result of comparison of modeling curves of scanning with experimental, it has been shown, that the best reproduction of first second (factor of pair correlation 0,994) corresponds(meets) to sizes of an active zone laying in a range 15-16 sm.

Back to 1.5B Soil Sampling in Space and Time - Theater
Back to WCSS

Back to The 18th World Congress of Soil Science (July 9-15, 2006)