CN2854559Y - Device for measuring water-holding capacity of farm - Google Patents

Abstract

The utility model discloses a field water holding capacity measuring device, which belongs to the fields of farmland irrigation and crop water management. The technical solution includes a water dispenser (1), a water supply container (6) that can communicate with a water source, a water supply pipe (4), an air intake control pipe (7), and a soil drilling cylinder (10), wherein the water supply container (6) is located Above the lower port of the device (1) and the intake control pipe (7), the upper end of the water supply pipe (4) communicates with the water supply container (6), and its lower end communicates with the sprinkler (1); the intake control pipe (7) The upper end is connected with the water supply container (6), and its lower end is placed in the soil drilling cylinder (10), between the air inlet (11) at the lower end of the air intake control pipe (7) and the cylinder wall of the soil drilling cylinder (10) There is a gap. The device has the following advantages: it is more suitable for measuring soil with fine texture, and the measurement time is short; it is closer to the actual situation under modern water-saving irrigation technology; it saves measurement water, and is easy to carry and easy to measure in the field.

Description

A field water holding capacity measuring device

technical field

The utility model relates to a device for quickly measuring the field water holding capacity of a characteristic constant of soil moisture, which belongs to the fields of farmland irrigation and crop water management.

Background technique

Soil moisture status in farmland is an important factor affecting crop growth. Field water holding capacity is an important index to measure soil water retention, and is also an important parameter for farmland irrigation and crop water management. It is usually regarded as the upper limit of crop available water. A long time ago, it was believed that the flow of water and the change of water content in the soil after irrigation decreased with time, and the water flow rate generally decreased to a negligible level within a few days, or even stopped completely, and the water content of the soil after the internal drainage was completed called field capacity. For a long time afterwards, field water holding capacity has been considered as the highest soil water content that the soil can maintain stably. It is an actual physical property of soil and a characteristic constant of every soil.

With the research on the movement process of unsaturated soil moisture and the further development of experimental measurement techniques, many studies have shown that the concept of field water holding capacity is artificial, arbitrary, and even misleading. It is a soil physical property affected by the measurement method. After irrigation or rainfall, when the groundwater table is deep, the drainage is good, and there is no surface evaporation, although the water flow rate continues to decrease, the internal drainage process of the soil actually continues, there is no "change point", and there is no static state. water content; even if there is, the time to reach equilibrium is very long. The size of the field water capacity is not only affected by soil factors such as soil texture and structure, but also by human factors such as measurement methods, balance duration, and measurement depth.

Currently, there are three main methods for measuring field water holding capacity. The first is the frame flood irrigation method, which is used for field measurement. The basic principle is: in the field, the frame or soil ridge is irrigated to saturate the soil at an appropriate depth, and then the soil surface is covered to avoid surface evaporation, and the soil begins to drain into the soil. In the process of soil water redistribution, when the gravitational water in the soil is "completely" removed, the water reaches a basic balance, and soil samples are taken to measure the soil water content. The water content at this time is the field water capacity. When reporting the measurement results, the depth of the groundwater table, the depth of the soil layer and the equilibrium duration should be indicated. This method is more suitable for soil with coarse texture, because the hydraulic conductivity of this soil decreases sharply with the increase of soil suction (decrease of water content), the flow rate of soil water decreases rapidly, and the soil profile can be shortened after irrigation. The basic equilibrium is reached within a period of time (1 ~ 2d), and the reproducibility is good. However, for soils with finer soil texture and higher clay content, the measurement accuracy of this method is poor, and some are even unavailable, mainly because there is no significant reduction in soil water movement in cohesive soils, and it takes several days or even several days. After ten days, the soil water movement is still going on, so it is difficult to select the equilibrium duration. For cohesive soil, if the "balance duration" (actual unbalanced) is selected to be short, the measured value will be too large, which has been proved by many studies. Therefore, Hillel (1998) believed that the soil moisture content should be continuously observed until the difference between the two times before and after is very small. At this time, the measured value is the field water capacity, rather than the randomly assumed measurement after a few days (such as 2 days) of irrigation. value. This improved method seems to be feasible, but for soil with heavy viscosity, it is bound to greatly increase the workload and measurement time.

In order to overcome this problem caused by soil texture, people try to find a way from the state of soil water energy, which leads to another field water holding capacity measurement method: pressure film (plate) method, the measuring device is pressure film (plate) )instrument. The basic principle is: Assume that different soils have the same soil matric potential although they have different water contents in the field water holding capacity, which is a constant, denoted as Ψ _fc , and the water content under the suction value measured by the pressure membrane instrument is the field water holding capacity. However, the values of Ψ _fc obtained by different scholars are quite different. Colman's (1947) test result was -33kPa, while Zhang Yulong et al. (1996) believed that the range of soil suction in the 10-70cm soil layer was 3.3-5.6kPa. There is a big difference between the two, and the main influencing factors are soil depth, ground temperature, and surface cover. wait.

In addition, the Wilcox method is also commonly used to determine the field water holding capacity indoors. The method is: after the undisturbed soil sample is soaked and saturated, it is placed on the air-dried soil, and the gravity water in the soil sample is discharged under the action of the air-dried soil suction. After a period of time, the water content of the soil sample is measured to obtain the field water holding capacity of the soil. This method also involves the selection of water absorption time of air-dried soil, that is, when gravity water is completely discharged, and the length of drainage time (usually 8 hours) directly affects the measurement results.

To sum up, the existing methods and measuring devices all use the method of saturating the soil sample first, and then removing the gravity water to measure the field water holding capacity, and the measurement process is a dehumidification process. Therefore, the most critical issue involved in all methods and measuring devices is to judge when the gravity water is completely eliminated. However, since the internal drainage or redistribution of soil is a continuous process, especially for soil with heavy viscosity, it is difficult to determine when gravity water is completely or basically eliminated. This is the main "controversy" of existing methods and measurement devices. . Therefore, if there is a measuring device that can make the water content of the measured soil reach the maximum water capacity that the soil capillary can absorb, that is, the field water capacity without generating gravity water, this kind of controversy will be avoided.

Contents of the invention

The purpose of the present invention is to provide a field water holding capacity measuring device which is convenient to carry, saves time and water.

The technical solution adopted in order to achieve the purpose of this utility model includes an emitter 1, a water supply container 6 that can be communicated with a water source, a water supply pipe 4, an air intake control pipe 7, and a soil drilling cylinder 10, wherein the water supply container 6 is located at the emitter 1 And above the lower port of the air intake control pipe 7, the upper end of the water supply pipe 4 communicates with the water supply container 6, and the lower end of the water supply pipe 4 communicates with the water dispenser 1; the upper end of the air intake control pipe 7 is connected with the water supply container 6, and the air intake control pipe The lower end of 7 is placed in the soil drilling cylinder 10, and a gap is provided between the air inlet 11 at the lower end of the air intake control pipe 7 and the cylinder wall of the soil drilling cylinder 10.

In the above field capacity measuring device, the material of the emitter 1 includes clay or fiber or foam.

In the above-mentioned field water holding capacity measuring device, the water supply container 6 is a Marsh bottle.

In the above field water holding capacity measuring device, the lowest point o of the emitter 1 is 1-2 cm higher than the air inlet 11 at the lower end of the air inlet control pipe 7 .

In the above-mentioned field water holding capacity measuring device, the soil drilling cylinder 10 is conical.

In the above-mentioned field capacity measuring device, the bottom of the water supply container 6 has a base 2 .

In the above field water holding capacity measuring device, the soil drilling cylinder 10 and the water supply container 6 are integrally structured, and the soil drilling cylinder 10 is located at the bottom of the water supply container 6 or fixed on the lower part of the base 2 .

In the above-mentioned field water holding capacity measuring device, the water supply pipe 4 and the air intake control pipe 7 can be hard pipes or soft pipes.

In the above-mentioned field capacity measuring device, a water filling port 5 is opened on the upper end of the water supply container 6 .

In the above-mentioned field water holding capacity measuring device, a valve 8 is installed on the air intake control pipe 7 to adjust the height of the air inlet 11 of the air intake control pipe 7 to provide a stable water supply head.

In the above-mentioned field water holding capacity measuring device, the basic principle of measurement is different from the existing method, that is, the soil matrix suction (soil matrix potential) is used to "actively" suck water into the soil, so that the water content of the soil sample reaches the level that the soil capillary can absorb. The maximum amount of water held is the field water holding capacity, and there is no gravity water.

Compared with the existing measuring method and its measuring device, the above-mentioned new rapid field water holding capacity measuring device has the following advantages:

(1) The basic principle of the utility model is to use the suction force of the matrix, which is more suitable for measuring the soil with fine texture, and the measurement time is short.

The basic measurement principles of the traditional three methods are to saturate the soil to be tested first, and then perform the internal drainage (dehumidification) process until the soil moisture is basically balanced. For soil with rough texture, due to the process of significantly weakening soil moisture movement, the soil moisture content changes little after a short period of time (such as 1-2d), and the reproducibility is good. At this time, the measurement results of the three methods are valid of. For cohesive soil, due to the high soil suction, the internal drainage process is longer, and the soil moisture takes a longer time to reach the basic balance, so the measurement time is longer, and even the measurement accuracy is affected. On the contrary, the utility model utilizes the soil matrix suction (matrix potential). The heavier the soil viscosity, the greater the suction, and the faster the "water absorption", so that the measurement time is shorter, and the process of soil saturation to be measured (usually 24 hours is required) ).

(2) The process measured by the utility model is a moisture absorption process, which is closer to the actual situation under the modern water-saving irrigation technology.

The basic measurement principles of the existing three methods are to saturate the soil to be measured first, and then perform internal drainage, and the soil water content is dehumidified from saturation to field water holding capacity; and the soil water content in the measurement process of the utility model is determined by As small as the field water holding capacity, it is a hygroscopic process.

Compared with surface irrigation, sprinkler irrigation and other comprehensive irrigation, with the development of modern water-saving irrigation technology drip irrigation, especially subsurface drip irrigation and other local irrigation methods, after irrigation, only a part of the soil surface is wetted, not the entire plan wetted layer. After irrigation, for the dry soil outside the wet area, the subsequent redistribution of soil water is a moisture absorption process rather than a dehumidification process. Therefore, the field water holding capacity measured by the utility model is closer to the actual situation of soil water under these irrigation methods, so as to better guide the formulation of irrigation systems under such water-saving irrigation methods.

(3) When the utility model works, it saves measuring water, is easy to carry, and is easy to measure in the field.

The existing three methods all need to saturate the soil to be tested, especially the enclosing frame flood irrigation method used for field measurement, which consumes a lot of water; while using the utility model to measure, the maximum water content of the soil to be tested can be the maximum water content in the field. Water holding capacity, so the water consumption in the measurement process is very small, just fill it with a martens bottle, it is easy to carry for field measurement, and the operation is simple.

(4) when utilizing the utility model to measure, the lowest point o point of the bottom of the dispenser 1 is higher than the air inlet 11 of the Marsh bottle 6, but it cannot be too much higher, just slightly higher (1～2cm), thereby The potential of the soil matrix can be fully utilized.

Description of drawings

Fig. 1 is a schematic diagram of a field water holding capacity measuring device of the present invention.

Example

Below in conjunction with accompanying drawing, the utility model is further described.

As shown in Figure 1, 1 is an emitter, and its material includes at least one of the three materials of clay, fiber, and foam; 2 is the base of the water supply container 6; 3 is the hole on the right side of the base 2; 4 is the water supply pipe , 5 is the water filling port of the water supply container 6, and 6 is the water supply container. The hole on the left side on the base 2, 10 is the soil drilling tube connecting the base 2, 11 is the air inlet of the air intake control pipe 7, and 12 is the soil to be measured. Of course, in actual production, the water supply container 6 may not be provided with the base 2 .

In this field water holding capacity measurement device, the upper end of the water supply pipe 4 is connected to the Martens bottle 6, and the other end extends downwards through the hole 3 to communicate with the sprinkler 1; Through the hole 9, placed in the soil drilling cone 10, a gap is provided between the air inlet 11 at the lower end of the air intake control pipe 7 and the wall of the drill pipe 10; a valve 8 is installed on the air intake control pipe 7 , adjusting the height of the air inlet 11 of the air intake control pipe 7 can provide a stable water supply head.

In this embodiment, the soil drilling cylinder 10 is conical, and it is integrated with the water supply container 6 , and the soil drilling cylinder 10 is fixed on the bottom of the base 2 . As shown in the figure, the soil drilling cylinder 10 is connected with the base 2 of the water supply container, and inserted into the soil for fixing, especially when measuring on a slope, this structure is more stable. The soil drilling barrel 10 can also be other shapes, such as a pyramid, or be replaced by other things, as long as it has the characteristics of being easy to insert into the soil, and can accommodate the lower part of the air intake control pipe 7 and keep the air inlet 11 at the lower end of it in contact with the atmosphere. The shape of the martensitic bottle can also be various, and its main feature is to provide a constant water head, and the water head position is at the lower end of the air intake control pipe. In actual production, the water supply pipe 4 and the air intake control pipe 7 can be hard pipes or soft pipes.

Before the measurement starts, close the valve 8, fill up the entire measuring device from the water filling port 5 of the Marlson bottle 6 to the water dispenser 1 with water, then put a rubber stopper on the water filling port 5, and open the valve 8. Atmospheric pressure is maintained at the position of the air inlet 11. Embed the emitter 1 into the soil 12 to be tested, and press into the soil-drilling cone 10 at the same time, so that the lowest point o at the bottom of the emitter 1 is slightly higher than the air inlet 11 of the Martens jar 6, such as 1-2 cm. Before measurement starts, when adding water in the water supply container 6 martensitic flasks, valve 8 is closed, and water will flow out from air intake control pipe 7 when adding water like this.

Assuming that Ψ _mo is the matric potential of soil water at the outer contact surface of the emitter, and its value should not be greater than 0 in any case, then -Ψ _mo is the matric suction. Taking point o as the reference point, the orientation is positive. Since the wall thickness of the emitter 1 and the elevation difference between the air inlet 11 and the emitter 1 are small and negligible, the potential energy difference inside and outside the emitter is -Ψ _mo , which is the matrix suction. The soil matrix suction is the only driving force for water to enter the soil through the emitter, which is the fundamental principle of the measuring device of the utility model. At the initial stage of measurement, under the action of matrix suction, the water content at the contact point between soil 12 and emitter 1 increases rapidly, so _Ψmo increases and the potential energy difference decreases. With the progress of infiltration, the matric potential and water content of the soil near the emitter 1 will also increase. After a certain range of wetting, the matric potential gradient of the soil around the emitter will decrease until it reaches zero, and the soil content around the emitter The amount of water reaches the maximum amount of water that the soil can absorb, and there is no gravity water. At this time, the field water holding capacity of the soil under the condition of moisture absorption is obtained by measuring the water content of the soil around the emitter 1 at this time.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the utility model without limitation. Although the utility model has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the utility model can be Modifications or equivalent replacements of the technical solutions of the new utility model without departing from the spirit and scope of the technical solutions of the utility model shall be covered by the claims of the utility model.

Claims (10)

1. A field water holding capacity measuring device, characterized in that it includes a sprinkler (1), a water supply container (6) that can communicate with a water source, a water supply pipe (4), an air intake control pipe (7), and a soil drilling cylinder (10), wherein, the water supply container (6) is located above the water dispenser (1) and the lower port of the air intake control pipe (7), the upper end of the water supply pipe (4) communicates with the water supply container (6), and the water supply pipe (4) The lower end of the air intake control pipe (7) is connected to the water supply container (6), and the lower end of the air intake control pipe (7) is placed in the soil drilling cylinder (10). (7) There is a gap between the air inlet (11) at the lower end and the cylinder wall of the soil drilling cylinder (10). 2. The field capacity measuring device according to claim 1, characterized in that the material of the emitter (1) includes clay or fiber or foam. 3. The field water holding capacity measuring device according to claim 1 or 2, characterized in that the water supply container (6) is a Marsh bottle. 4. The field water holding capacity measuring device according to claim 1 or 2, characterized in that the lowest point o of the sprinkler (1) is 1 higher than the air inlet (11) at the lower end of the air inlet control pipe (7). ~2cm. 5. The field water holding capacity measuring device according to claim 3, characterized in that the lowest point o of the sprinkler (1) is 1-2 cm higher than the air inlet (11) at the lower end of the air inlet control pipe (7) . 6. The field water holding capacity measuring device according to claim 5, characterized in that the soil drilling cylinder (10) is conical. 7. The field water holding capacity measuring device according to claim 4, characterized in that, the bottom of the water supply container (6) has a base (2); The soil drilling barrel (10) is positioned at the bottom of the water supply container (6) or is fixed on the bottom of the base (2). 8. The field water holding capacity measuring device according to claim 4, characterized in that the water supply pipe (4) and the air intake control pipe (7) can be hard pipes or soft pipes. 9. The field water holding capacity measuring device according to claim 4, characterized in that a water filling port (5) is opened on the upper end of the water supply container (6); 10. The field water holding capacity measuring device according to claim 4, characterized in that a valve (8) is installed on the air intake control pipe (7).