Method and device for determining the microbiological activity of soils

Abstract

The invention relates to a method and a device for determining the microbiological activity of a soil and is characterised by the following method steps: providing a main body (1) having the following features: a heating element (2) and a temperature sensor (3). On the main body (1), a bait (4) is furthermore arranged which covers the temperature sensor (3) and the heating resistor (2). The bait (4) is encased in a microbe concentrator (5). The microbiological activity of a soil is determined in the following steps: a. switching on the energy supply in order to heat the main body (1), b. switching off the energy supply, measuring the cooling speed and ascertaining the cooling curve, c. storing the first cooling curve as a reference curve (7), - carrying out steps a and b at predetermined time intervals, and - comparing the current cooling curves (8, 9) with the reference curve (7).

Description

[0001] Method and device for determining the microbiological activity of soils

[0002] The invention relates to a method and a device for determining the microbiological activity of an agricultural soil.

[0003] It is well known that a large number of soil organisms, such as bacteria and fungi of various kinds, decompose organic matter in the soil. A single handful of soil may contain billions of such organisms. Without them, the soil would be infertile and would be unable to retain much water. This soil property is referred to as microbiological activity.

[0004] Microbiological activity is a key parameter for assessing the quality of agricultural soils. Measuring microbiological activity has so far been complex and requires sophisticated instruments, such as those used to measure soil gases and microbiological analyses. Various attempts have been made to simplify the measurement process, but to date, no methods are known that could be used in practice.

[0005] The Swiss Federal Institute of Technology in Zurich, for example, has attempted to evaluate the movements and chewing sounds of springtails and other organisms by using highly sensitive microphones embedded in the soil. Another option is laboratory testing of soil samples. Gas chromatography can, in principle, be used to determine the proportion of organic components, although it is not possible to clearly distinguish between living and dead organisms.

[0006] Both methods are technically very complex and therefore practically unsuitable for use on large areas. Therefore, there is a need for a method to reliably determine the microbiological activity of agricultural soils using a cost-effective technique and in a relatively short time.

[0007] These objects are achieved by a method according to claim 1 and a device according to claim 2.

[0008] The inventive method according to claim 1 includes the following process steps:

[0009] A preferably rod-shaped base body with an upper and a lower end section is provided. At the lower end section of the base body, an arrangement with the following components and materials is provided: an electrical heating resistor for heating the lower section of the base body and a temperature sensor that measures the temperature of the base body in the vicinity of the heating resistor. Depending on the size of the base body, the distance between the heating element and the temperature sensor is approximately 1 mm to 15 mm. A bait is also arranged at the end section of the base body. The bait serves as food for the microorganisms in the soil. The bait is completely or predominantly surrounded by a microbial concentrator. The microbial concentrator consists of a material that absorbs water from the surrounding soil through capillary action.These capillary effects and concentration differences between the soil and the bait cause the microorganisms to penetrate the material and migrate to the bait. In other words, the microorganisms are attracted. Therefore, the material in which the bait is embedded is called a microbial concentrator. Open-pored sponges, felt, or other textiles with comparable properties are preferred.

[0010] The combination of base body, feeding bait, and microbial concentrator is referred to below as the "heat conduction system." The heat conduction system has a predetermined heat conduction property, which is determined by the volume of the individual materials and their specific heat conduction properties. The method according to the invention proceeds in the following steps when the heat conduction system is located in the soil:

[0011] The microorganisms are attracted by the effects described above, reach the food bait and decompose it. This also reduces the volume of the food bait. If the volume of the food bait decreases, the thermal conduction properties of the entire thermal conduction system change. If, for example, the food bait is still complete, i.e. has its original volume and composition, the thermal conduction system has different thermal conduction properties than if the food bait has been decomposed and / or eaten by the microbes. This changed thermal conduction property of the thermal conduction system is recorded by the temperature sensor and downstream evaluation electronics. To do this, the temperature of the thermal conduction system is first increased by a few degrees using the heating element. The heating element is then switched off. The cooling curve is determined using the temperature sensor and saved as a reference curve, for example in the evaluation electronics.The reference curve is generated immediately after the base body is inserted into the soil. At predetermined intervals, e.g., 6 to 48 hours or even several days, multiple cooling curves are generated and saved. Since the microorganisms have partially or later completely consumed or decomposed the bait in the meantime, the thermal conductivity of the thermal conduction system also continually decreases, i.e., the cooling curves become flatter. When a flat cooling curve no longer changes, the bait is no longer present. If the bait is consumed within just a few hours, the soil contains many microorganisms. The cooling curves are therefore an objective measure of the number of soil organisms per unit volume of soil, i.e., an objective measure of the microbiological activity of the soil.

[0012] To save energy, the heating cycles can be adapted to the rate of change of the cooling curves, i.e., if the cooling curve changes little, measurements are taken at longer intervals. If the cooling curve changes more significantly, measurements are taken more frequently. This measuring method can be implemented using a preferably rod-shaped device according to claim 2. A rod-shaped device is structurally expedient, but the skilled person, with knowledge of the technical teaching of method claim 1, can also develop other devices that also operate according to this measuring principle.

[0013] Furthermore, it is clear to the expert that certain microorganisms prefer certain bait. Thus, by selecting predetermined bait materials, it is possible to estimate which microorganisms are predominantly present in the soil.

[0014] Preferably, a ring-shaped bait made of gelatin, agar-agar, or a similar material is used. If an attractant such as sugar is added, the microorganisms will quickly find their way to the "food source" because they follow the gradient of the food concentration.

[0015] The device with its components described above is hereinafter referred to as the sensor.

[0016] Once the sensor is inserted into the soil, the input heat energy is absorbed by the water-containing gelatin ring during the initial measurement, and the sensor tip cools down rapidly. If the soil contains microorganisms, these migrate into the microbial concentrator and begin to decompose the gelatin ring. Since the ring is only 1-3 mm thick, this process occurs quickly. In organically healthy soils, the gelatin can be decomposed by the microorganisms after just a few hours, significantly reducing the original heat conduction at the sensor tip. This decomposition thus leads to a significant change in the thermal conductivity between the heating element and the temperature sensor. Since the temperature change over time can be determined easily and inexpensively, a very cost-effective sensor is available for determining the microbiological activity of agricultural soil.The rate at which decomposition occurs depends on the concentration of microorganisms. In so-called "dead" soils, no decomposition will occur. The thickness of the gelatin ring can be very small, since even a thin gap between the sensor and the microbial concentrator, such as a felt pad, significantly interrupts heat conduction. The sensor therefore responds very quickly.

[0017] The sensor and the process are explained below using schematic drawings.

[0018] Fig. 1 shows a schematic diagram of the sensor in a cross section Fig. 2 shows a further embodiment of the sensor according to Fig. 1

[0019] Fig. 3 shows a temperature-time curve at the sensor

[0020] List of reference symbols

[0021] 1 - rod-shaped base body

[0022] 2 - Heating element

[0023] 3 - Temperature sensor

[0024] 4 - Food bait

[0025] 5 - Microbial concentrator

[0026] 6 - Cable for the power supply of the heating resistor and detection of the

[0027] Temperature measurements

[0028] 7 - Temperature curve for unused bait

[0029] 8 - Temperature curve with partially consumed bait

[0030] 9 - Temperature curve when the bait is completely consumed

[0031] Figure 1 shows the device of the invention, Figure 3 shows temperature-time curves which reveal the basic method of the invention.

[0032] Figure 1 shows a rod-shaped base body (1), preferably made of plastic, including any type of plastic composite material. However, metal can also be used in principle. Plastic, however, has the advantage of being electrochemically neutral and has no effect on the microorganisms. The base body (1) has an arrangement of the following components and materials at its lower end:

[0033] A heating resistor (2) for heating the base body (1) in the immediate spatial vicinity of the heating resistor (2) to a temperature which is a few degrees, preferably 2 - 4 degrees, above the ambient temperature, ie the earth temperature.

[0034] Furthermore, a temperature sensor (3) is arranged next to the heating resistor (2), which measures the temperature of the base body (1) in the vicinity of the heating resistor (2). The distance between the heating resistor (2) and the temperature sensor (3) is preferably 1 to 3 mm.

[0035] In this embodiment of the invention, a gelatin ring is arranged on the base body (1) as a feeding bait (4), which covers the temperature sensor (3) and the heating resistor (2). The gelatin ring is thus also in thermally conductive contact with the heating resistor (2) and the temperature sensor (3). The area of ​​the heating resistor (2), the temperature sensor (3), and the gelatin ring is covered with a textile ring that acts as a microbial concentrator (5). The microbial concentrator (5) is in contact with the surrounding soil. The textile ring is a fiber composite with a highly hydrophilic effect, meaning the material is very absorbent towards water. This property leads to two effects that are essential to the invention. The water content of the soil causes the textile ring to also absorb water.The gelatin ring, to which sugar is preferably added, is slightly dissolved by the water, creating a feed concentration gradient within the volume of the textile ring (5). The feed concentration is thus lower at the outer area of ​​the textile ring (5) than in the immediate vicinity of the gelatin ring (4). This creates the desired effect of attracting microbes via the relatively large outer surface of the textile ring (5) and then migrating into the hydrophilic textile material. There, they follow the feed concentration gradient. This directs the microorganisms specifically to the gelatin ring (4). The hydrophilic textile material thus has a desired concentrating effect. Therefore, any material that exhibits the functionality described above is suitable as a microbe concentrator (5).

[0036] The microbial concentrator (5) also has a positive additional effect: The feeding bait (4), such as a gelatin ring, is often a soft material that could be damaged by direct mechanical contact with soil. Therefore, the microbial concentrator (5) also acts as mechanical protection for the feeding bait (4).

[0037] At the upper end of the hollow base body (1) there is a cable connection (6) which is electrically connected to an electronic circuit for temperature measurement and to a power supply for the heating resistor (2).

[0038] When the heating resistor (2) is switched on, the temperature in the area of ​​the heating resistor (2) rises and thus the gelatin ring (4) is also heated by a few degrees above the original ambient temperature. The heating resistor (2) is then switched off and the temperature drops back to the original ambient temperature. The cooling process is measured using the temperature sensor (3) and corresponds to the curve (7) shown in Fig. 3. This curve (7) is characteristic of a complete gelatin ring (4) and is saved as a reference curve. If a curve (8) is present after a predetermined time, e.g. a few days or hours, it can be concluded that microbiological decomposition of the gelatin ring (4) has begun. An even stronger or complete decomposition can be seen from curve (9). The curve (9) remains constant because the thermal conduction behavior in the thermal conduction system no longer changes.

[0039] It is clear to those skilled in the art that the material of the base body (1) could also be a metal, such as stainless steel, which also has poor thermal conductivity like a plastic. It is also possible to use a material with particularly good thermal conductivity; in this case, it may be expedient to increase the distance between the heating resistor (2) and the temperature sensor (3). The teaching of the invention is that the thermal conductivity of the above-defined thermal conduction system changes as soon as the bait (4) is consumed and / or decomposed by microorganisms.

[0040] To increase measurement accuracy, familiar methods can be used by measurement technicians. For example, the reference curve can be determined multiple times at short intervals, and an average reference curve can be calculated from this. The same applies to measurements used to monitor microorganism activity. Since the sensor is very inexpensive to manufacture, a variety of sensors can be used as needed.

[0041] By carefully selecting gelatin or similar substances that microbacteria prefer as "food," it is also possible to estimate, to a certain extent, the type of microorganisms present in the soil. This requires the deployment of several sensors in close proximity.

[0042] Fig. 2 shows a device according to claim 2, wherein another, similarly constructed sensor is arranged on the base body (1) as a reference sensor, but without a bait (4). This arrangement has the following advantage: The reference sensor provides a reference measurement value, which can be used to correct the measurement value of the sensor with the bait. This can be advantageous when the soil moisture changes, because soil moisture and temperature also influence the decomposition rate of the bait (4).

Claims

Claims 1. Method for determining the content of living microorganisms in soils, characterized by the following process steps: - Providing a base body (1) with the following features: the base body is rod-shaped and an arrangement of the following components and materials is provided at its lower end: - a heating resistor (2) for heating the base body (1) to a temperature which is a few degrees, preferably 2 to 5 degrees, above the ambient temperature, - a temperature sensor (3) which measures the temperature of the base body (1) in the vicinity of the heating element (2), preferably at a distance of 1 to 3 mm from the heating element (2), - a feeding bait (4) is arranged on the base body (1), which covers the temperature sensor (3) and the heating element (2) and is in thermal contact with the covered area of the base body (1), - the bait (4) is surrounded by a microbe concentrator (5) permeable to water and microbes, - at the upper end of the hollow base body (1), electrical lines (6) are provided, by means of which electrical energy is supplied to the heating element (2) and the temperature at the temperature sensor (3) can be determined, the method comprising the following steps: a. switching on the power supply in order to heat the base body (1) in the area of the heating element (2) and the temperature sensor (3) to a temperature which is 2 to 6 degrees above the ambient temperature, b. switching off the power supply, measuring the cooling rate and determining the cooling curve, c. storing the first cooling curve as a reference curve (7) for a still complete, non-decomposed bait (4), - Carrying out steps a and b at predetermined intervals of 2 hours to 14 days and - Compare the current cooling curves (8, 9) with the reference curve (7) to determine the soil microbiological activity.

2. Device for carrying out the method according to claim 1 with a sensor having the following features: - a rod-shaped base body (1) at the lower end of which an arrangement of the following components and materials is provided: - a heating element (2) for heating the base body (1) to a temperature which is a few degrees, preferably 2 to 5 degrees, above the ambient temperature when the base body (1) is inserted into the ground, - a temperature sensor (3) which measures the temperature of the base body (1) in the vicinity of the heating element (2), the distance between the temperature sensor (3) and the heating element (2) preferably being 1 to 7 mm, - a feeding bait (4) which serves as food for the microorganisms of the soil, whereby the feeding bait (4) covers the temperature sensor (3) and the heating resistor (2) and is thus also in thermal contact with the covered area of the base body (1), - a microbe concentrator (5) made of a textile-like or sponge-like material which is permeable to water and microbes, wherein the microbe concentrator (5) encloses the bait (4) and - an electrical cable (6) with electrical lines is provided for supplying energy to the heating element (2) and for detecting the temperature at the temperature sensor (3).

3. Device according to claim 2, wherein a further sensor of similar construction is arranged on the base body (1) as a reference sensor, which, however, does not have a feeding bait (4).

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