RU2244296C1 - Method for electroosmotic measurement of soil moisture potential - Google Patents

Abstract

FIELD: agriculture and soil science; evaluating water-physics properties of soils.

SUBSTANCE: porous probe communicating with water-filled tank is driven into soil, cathode is inserted in probe and anode, in soil. Voltage is applied to electrodes from dc power supply and soil moisture potential preventing water transfer from tank to soil is determined by measuring current between them.

EFFECT: reduced single measurement time due to eliminating escape of significant amount of water from measuring instrument.

1 cl, 1 ex

Description

The invention relates to agriculture and soil science, and in particular to methods for determining the water-physical properties of soils.

A known method for determining the potential of soil moisture [1], based on the use of a membrane press. The soil is placed on a porous membrane that passes water, impervious to particles of soil and air. After that, excess pressure is created above the soil. Changing the pressure determines the onset of soil moisture.

The main disadvantage of this method is the inability to conduct experiments in natural conditions.

Closest to the claimed is a method for determining the potential of soil moisture [2], which consists in the use of a tensiometer. A tensiometer is a hydrophysical device for measuring capillary-sorption pressure of moisture in soil in the range from 0 to - 90 kPa. It consists of a glass tube filled with deaerated water, connected to a finely porous ceramic probe (pore size 1-2 microns) and a vacuum gauge. The device must be tight. The ceramic probe is immersed in the soil, and due to the difference in the thermodynamic potentials of the water in the device (free water) and in the soil, moisture is transferred from the device to the soil until equilibrium is established. A vacuum occurs in the device, which characterizes the suction power of the soil (potential of soil moisture), which is recorded by a vacuum gauge. Various tensiometer designs are known which differ from each other primarily by a manometric device.

The main disadvantage of this method is the length of the equilibrium between the tensiometer and the soil. For a vacuum to occur in the device, a certain amount of water must come out of it, and this water, once in the soil, should not significantly change the potential of soil moisture in the probe area. Consequently, the size of the soil sample must be large enough, and it is necessary to wait for the excess moisture of the tensiometer to leave the vicinity of the probe. The time to establish equilibrium takes hours, and for some soils poorly permeable to water, even a day.

In addition, the use of devices operating under reduced pressure is very inconvenient. The slightest violation of the tightness makes them inoperative.

The aim of the invention is to reduce the time of a single measurement and increase productivity in mass measurements, as well as the rejection of work at reduced pressure.

An object of the invention is to eliminate the release of significant amounts of water from the device.

The problem is solved by placing a porous probe connected to a tank filled with water in the soil. Introducing the cathode into the tank of water, and the anode into the soil and passing current between the electrodes. The value of the potential of soil moisture is determined by the magnitude of the current between them, not allowing water to pass from the tank to the soil. In this case, the water in the ceramic filter will move under the action of the resulting two forces. In the direction of the soil, the movement will be determined by the potential of soil moisture (soil suction force), and in the opposite direction, the water will move due to electroosmosis, since the ceramic filter is negatively charged. At a certain magnitude of the current, dynamic equilibrium sets in and the water will not move. By calibrating the device on the bench, we get the opportunity to measure the potential of soil moisture by the magnitude of the current.

The technical essence of the invention consists in placing a porous probe connected to a container filled with water in the soil, introducing a cathode into the container, and an anode into the soil, and determining the potential of soil moisture from the amount of current between them, preventing water from passing from the container to the soil.

The proposed method allows you to refuse to work under reduced pressure and significantly reduces the measurement time. In addition, it allows you to move from measuring pressure to measuring current, which is much more accurate and simpler.

The following examples reveal the essence of the invention.

Example 1

A porous probe connected to a container filled with water is placed in a glass of water. The cathode is located inside the probe, and the anode, which consists of several turns of copper wire with a diameter of 1 mm, is outside, adjacent to the outer surface of the probe. The water tank is connected to the probe using a flexible hose. It can be raised to different heights, creating a different, excess pressure inside the probe. A voltage is supplied from the DC source to the electrodes, and the device is calibrated - the pressure value is set to the value of the current strength that keeps the meniscus stationary. After calibration, the device is placed in the soil and the magnitude of the current is determined, which keeps the meniscus of fluid in a stationary state. According to the calibration graph, the correspondence of the pressure value to the current strength is found.

The experiments showed that the accuracy of measuring the potential of soil moisture is not lower than the accuracy of determination using conventional tensiometers, and the speed of determination increases many times, since you do not have to wait for the establishment of equilibrium (absorption of moisture through the soil) after it leaves the tensiometer. A decrease in the amount of water leaving the soil from the device determines a decrease in the measurement time. Moreover, the denser and less moisture-permeable soil, the more time is required to establish equilibrium, and, accordingly, the greater the gain in time during measurements. The proposed method allows one measurement in 3-5 minutes, which significantly increases productivity and reduces costs when conducting mass surveys of soils. In addition, the method has greater reliability, since if a conventional tensiometer is not tight enough, it will become clear only after measurements, which forces several parallel measurements to increase reliability. The proposed method is devoid of this disadvantage.

Thus, the proposed method reduces time, improves productivity and reliability of measurements.

Literature

1. Vadyunina A.F., Korchagina Z.A. Research methods for the physical properties of soils and soils. M .: Higher School, 1973. S.185-187.

2. Shein E.V., Kapinos V.A. Collection of problems in soil physics. M .: Moscow State University, 1994. P.48-50.

Claims (1)

The method of electroosmotic measurement of the potential of soil moisture, which consists in placing a porous probe connected to a container filled with water, into the soil, characterized in that a cathode is inserted inside the probe, and an anode adjacent to the surface of the probe, voltage is supplied to the electrodes from a constant source current and the potential value of soil moisture is determined by the magnitude of the current between them, not allowing water to pass from the tank to the soil.