Water vapor balance-based space planting substrate moisture control method and system

Abstract

The application provides a space planting substrate moisture control method and system based on water-gas balance, constructs a water use efficiency model between transpiration rate of unit area leaf and photosynthesis rate and substrate moisture content, obtains substrate moisture content from the water use efficiency model, and when the substrate moisture content is lower than a set threshold, a controller controls a water tank to start irrigation, and stops irrigation until the water use efficiency is equal to the maximum water use efficiency of the plant. The application solves the problem that the substrate moisture content cannot be directly and accurately measured by a sensor in a space microgravity environment, and realizes efficient management and utilization of water in the space microgravity environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of agricultural equipment, in particular to a water-gas balance-based water content control method and system for space planting substrates. BACKGROUND

[0002] In space planting, watering is needed to ensure the normal growth of crops. In the existing water solution based on the substrate growth method, a passive orbit nutrient delivery system supplies water to the plants when the sensors detect that the plants lack water. However, in a space environment, water droplets will adhere to the sensors due to the influence of microgravity, causing the sensors to malfunction; the sensors may show sufficient water content although the substrate is lacking water. If watering is not timely, the growth rate of the plants will be affected, and if the watering is excessive, the humidity in the incubator will be too high, algae and microorganisms will easily breed, the workload of astronauts will be increased, and water resources will be wasted, which has a profound impact on long-term deep space missions. SUMMARY

[0003] In view of the deficiencies in the prior art, the present application provides a water-gas balance-based water content control method and system for space planting substrates, which solves the problem that the water content of the substrate under space microgravity cannot be directly and accurately measured by sensors, and realizes efficient utilization and management of water under a space microgravity environment.

[0004] The present application achieves the above technical objectives through the following technical means.

[0005] The water-gas balance-based water content control method for space planting substrates comprises the following steps:

[0006] The water use efficiency model is used to evaluate the substrate water content state of the space planting plants in actual application; the water use efficiency model is as follows:

[0007]

[0008] In the formula, D is the water use efficiency, and Pn and Tr are the photosynthesis rate and transpiration rate per unit area of leaves obtained by a CO2 / H2O analyzer; D max is the maximum water use efficiency of the plants, which is obtained in advance through a water experiment; i is the number of data collection times in an irrigation period, and Tr i represents the crop transpiration rate at the i th data collection time in the irrigation period; and a is a to-be-determined coefficient, the value of which is different for different plants, and is obtained through least squares fitting by setting different substrate water content gradients through experiments before evaluating the substrate water content state of the space planting plants in actual application.

[0009] The substrate moisture content I is obtained from the water use efficiency model, and when the substrate moisture content is lower than a set threshold value, the controller controls the water tank to start irrigation until the water use efficiency D = D max ;

[0010] In the above process, the method for obtaining the photosynthesis rate Pn and the transpiration rate Tr of the leaf per unit area is as follows:

[0011] The cultivation box is sealed, and when the CO2 / H2O analyzer determines that the CO2 and H2O contents in the cultivation box reach stability, the air pump in the water vapor analysis module is opened to draw air, and the water vapor analysis module records the changes of CO2 and H2O in the interval Δt, which is denoted as The transpiration rate and the photosynthesis rate in the cultivation box are calculated by using the formula The transpiration rate and the photosynthesis rate in the cultivation box are calculated by using the formula

[0012] Further, the plant leaf is scanned by using a depth camera, the three-dimensional point cloud data of the leaf is obtained and preprocessed, then the leaf segmentation and surface reconstruction are performed, and the surface area of the reconstructed surface is calculated, that is, the plant leaf area;

[0013] The specific method for obtaining the plant leaf area is as follows: each leaf is divided into triangular facets by using a greedy projection triangle algorithm, a triangular mesh model of the surface is generated, the area of each triangle is calculated by using the Heron formula, and then the surface areas of all the triangular meshes are added to obtain the surface area of each leaf.

[0014] Further, the maximum plane angle of the triangular facet is set to 50°, the maximum angle of each triangle is 120°, and the minimum angle is 10°, that is, the leaf point cloud can be triangularly divided.

[0015] Further, the initial point values of the are kept the same when the CO2 concentration in the cultivation box is determined.

[0016] The space planting substrate moisture control system based on water vapor balance comprises a cultivation box, a cultivation bag is arranged in the cultivation box, a small rooting bag is arranged in the cultivation bag, and the cultivation bag is connected with a water tank;

[0017] A circulating fan A and a circulating fan B are respectively arranged on the upper and lower sides of the inside of the cultivation box, an LED light source and a depth camera are arranged on the top of the cultivation box, and a measurement hole is reserved on the box body of the cultivation box to facilitate the measurement and calibration of the photosynthesis and transpiration rate of the plant in the cultivation box by using a CO2 / H2O analyzer;

[0018] ​​​The inside of the cultivation box is also provided with a wind speed sensor, a light sensor, a temperature and humidity sensor, a micro air conditioner and a steam humidifier.

[0019] The data collected by the depth camera, the wind speed sensor, the light sensor, the temperature and humidity sensor and the CO2 / H2O analyzer are transmitted to the controller; the controller controls the working of the LED light source, the circulation fan A, the circulation fan B, the micro air conditioner, the steam humidifier and the water tank.

[0020] In the technical scheme, the substrate in the small rooting bag is selected from diatomite.

[0021] In the technical scheme, the box body of the cultivation box is made of high-transmittance acrylic plate.

[0022] In the technical scheme, the CO2 / H2O analyzer measures and calibrates the photosynthesis and transpiration rate of the plants in the cultivation box, specifically: the CO2 / H2O analyzer monitors the gas exchange in the cultivation box, according to the characteristics of the water-gas balance in the semi-closed system, the change of the molar ratio of water and carbon dioxide in the in-out gas in the cultivation box is calculated to calibrate the photosynthesis and transpiration rate measurement of the plants.

[0023] The beneficial effects of the present application are:

[0024] (1) The present application aims at the problem that the water content of the substrate cannot be directly measured by sensors in the space microgravity environment, and uses the water-gas balance relationship of the cultivation system to construct an estimation model of the transpiration rate and photosynthesis rate of the plants, so as to realize indirect estimation and control of the water content of the substrate;

[0025] (2) The present application obtains the leaf area of different plants through point cloud technology, and then calculates the transpiration rate and photosynthesis rate of unit area of leaves, and uses the transpiration rate and photosynthesis rate of unit area of leaves to construct a water use efficiency model, which can more accurately reflect the physiological characteristics and water demand of different sizes of plants;

[0026] (3) The present application uses the water use efficiency model to replace the conventional model which only considers transpiration, comprehensively considers the relationship among the water content of the substrate, the photosynthesis rate and the transpiration rate, can more accurately evaluate the water content of the substrate, so as to realize efficient management and utilization of water in the space microgravity environment, and improve the utilization efficiency of water resources. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 It is a space planting substrate water content control system based on water-gas balance according to the present application;

[0028] Figure 2 It is a space planting substrate water content control flow chart based on water-gas balance according to the present application;

[0029] Fig. 1-LED light source, 2-depth camera, 3-wind speed sensor, 4-illumination sensor, 5-temperature and humidity sensor, 6-circulating fan A, 7-CO2 / H2O analyzer, 8-cultivation bag, 9-micro air conditioner, 10-circulating fan B, 11-water tank, 12-controller, 13-cultivation box, 14-steam humidifier. DETAILED DESCRIPTION

[0030] The application will be further described below in conjunction with the drawings and specific examples, but the scope of protection of the application is not limited thereto.

[0031] Transpiration and photosynthesis as a plant physiology index, can characterize the change of plant in different water conditions. According to the principle of gas exchange measurement, the photosynthesis and transpiration intensity of the plant can be estimated by the change of CO2 concentration and H2O in unit time. And the space planting box is a closed space, so the photosynthesis and transpiration rate of the whole plant can be estimated by analyzing the water vapor change in the cultivation box.

[0032] As shown in Figure 1 , the water vapor balance-based space planting substrate moisture control system includes LED light source 1, depth camera 2, wind speed sensor 3, illumination sensor 4, temperature and humidity sensor 5, circulating fan A 6, CO2 / H2O analyzer 7, cultivation bag 8, micro air conditioner 9, circulating fan B 10, water tank 11, controller 12, cultivation box 13 and steam humidifier 14.

[0033] As shown in Figure 2 , the water vapor balance-based space planting substrate moisture control method specifically includes the following processes:

[0034] (1) Build a semi-closed plant cultivation system:

[0035] Choose a suitable site to ensure a clean, dry and well-ventilated environment;

[0036] Build a semi-closed cultivation box 13, the box body material is selected from high light transmittance acrylic plate, the size is 500*500*700mm;

[0037] Set up cultivation bag 8 in the cultivation box 13, put small rooting bags containing substrate, fertilizer and germination core into the cultivation bag 8, and ensure that the attached seeds can grow normally, select diatomite as the growth substrate; connect the cultivation bag 8 to the water tank 11 through the water pipe, when the water content of the substrate is low, the water tank 11 is controlled by the controller 12 to supplement the water for the substrate;

[0038] An air circulation fan (specifically air circulation fan A6 and air circulation fan B10 in the figure) is installed on the upper and lower sides inside the cultivation box 13, respectively, and the two air circulation fans are oppositely arranged to ensure that the air circulation fans can normally operate to provide stable air flow for the system, so as to solve the problem of insufficient water diffusion in the microgravity environment of the cultivation system.

[0039] The LED light source 1 is installed inside the cultivation box 13, and the LED light source 1 is located at the top of the cultivation box 13 and is arranged opposite to the plants; according to the growth needs of the plants, the light intensity and light time of the LED light source 1 are adjusted to provide sufficient light for the plants.

[0040] A miniature air conditioner 9 and a steam humidifier 14 are installed inside the cultivation box 13, and the heating, cooling and dehumidifying functions of the miniature air conditioner 9 and the humidifying function of the steam humidifier 14 are used to regulate the temperature and humidity environment inside the cultivation box 13.

[0041] (2) Build a plant physiological information monitoring system:

[0042] A measurement hole is left on the box body of the cultivation box 13 to facilitate the measurement and calibration of the photosynthesis and transpiration rate of the plants in the cultivation box 13 by the CO2 / H2O analyzer 7; specifically, the CO2 / H2O analyzer 7 monitors the gas exchange in the cultivation box 13, and according to the characteristics of the water-gas balance in the semi-closed system, the change in the molar ratio of water and carbon dioxide in the incoming and outgoing gas in the cultivation box 13 is calculated to calibrate the photosynthesis and transpiration rate determination of the plants.

[0043] The wind speed sensor 3, the light sensor 4 and the temperature and humidity sensor 5 are installed inside the cultivation box 13 to detect the environmental information in the cultivation box 13 in real time, send it to the controller 12, and control the wind speed, light and temperature and humidity in the cultivation box 13 through the controller 12; specifically, the wind speed in the cultivation box 13 is set by the controller 12 to control the wind speed of the two air circulation fans, the light in the cultivation box 13 is set by the controller 12 to control the LED light source 1, and the temperature and humidity in the cultivation box 13 are set by the controller 12 to control the miniature air conditioner 9 and the steam humidifier 14;

[0044] A depth camera 2 is installed on the top of the cultivation box 13 to obtain the growth state information of the plants and send it to the controller 12.

[0045] (3) Measure the leaf area of the plants:

[0046] The depth camera 2 is used to scan the leaves of the plants planted in the small rooting bags to obtain three-dimensional point cloud data of the leaves;

[0047] The obtained point cloud data is preprocessed, including removing noise and filtering abnormal points, to improve the quality of the data;

[0048] Leaf segmentation is performed to separate the leaves from the background so as to accurately calculate the leaf area;

[0049] Surface reconstruction is performed to calculate the surface area of the reconstructed surface, i.e., the leaf area of the plant: each leaf is divided into triangular facets using a greedy projection triangle algorithm to generate a triangular mesh model of the surface; in the process of triangulation, considering that the maximum plane angle, the maximum and minimum angles of the triangle, and other parameters affect the effect of triangular facetization, combined with the spatial distribution characteristics of the plant leaves, the maximum plane angle of the triangular facet is set to 50°, the maximum angle of each triangle is 120°, and the minimum angle is 10°, triangular division of the leaf point cloud is realized, the area of each triangle is calculated by the Heron formula, and the surface area of each leaf is obtained by adding up the areas of all the triangular meshes, and the calculation formula is:

[0050]

[0051] In the formula, p is half of the perimeter of the triangular facet, a, b, and c are the lengths of the edges of the triangular facet, l is the number of all triangular facets, and S is the surface area of the leaf. i i i i leaf

[0052] (4) Based on the change of the molar ratio of CO2 and H2O in the cultivation box 13, the photosynthesis and transpiration of the plant are estimated:

[0053] The cultivation box 13 is closed;

[0054] When the CO2 / H2O analyzer 7 measures the CO2 and H2O contents in the cultivation box 13 to be stable, the air pump in the water vapor analysis module of the CO2 / H2O analyzer 7 is opened;

[0055] The water vapor analysis module records the changes of CO2 and H2O in the interval Δt, denoted as and In order to avoid the influence of the CO2 concentration in the cultivation box 13 on the photosynthesis and transpiration rate of the plant, the initial point values of the and should be kept the same as the CO2 concentration in the cultivation box 13 when measured;

[0056] The transpiration rate and photosynthesis rate in the cultivation box 13 are calculated by the formulas and , and the photosynthesis rate Pn and transpiration rate Tr per unit area of the leaf are calculated according to the obtained leaf area of the plant.

[0057] (5) Construct a water use efficiency model: ​​​​​

[0058] Before evaluating the substrate moisture state of the plants grown in space in practical applications, the plants in the cultivation box 13 are cultivated in the laboratory, and different substrate water content gradients are set;

[0059] The wind speed sensor 3, the light sensor 4, and the temperature and humidity sensor 5 simultaneously record the wind speed, light, and temperature and humidity data in the cultivation box 13 at present, and the method in (2) is used to control the environmental parameters to remain stable;

[0060] Through the methods of (3) and (4), the transpiration rate and photosynthesis rate of the unit area of the leaf of the plant under different substrate water contents are obtained;

[0061] Through least square fitting analysis, the water use efficiency model between the transpiration rate / photosynthesis rate of the unit area of the leaf and the substrate water content is constructed:

[0062]

[0063] In the formula, D is the water use efficiency, D max is the maximum water use efficiency of the plant, that is, the water use efficiency of the plant under the optimum substrate water content, which is inherent to each substrate and can be obtained through a water experiment; i is the number of data collection in the irrigation period, Tr i represents the crop transpiration rate (obtained by the CO2 / H2O analyzer 7) at the i th data collection in the irrigation period; I is the substrate water content; a is a to-be-determined coefficient, and the value of different plants is obtained through the following method: according to the water use efficiency model, the least square fitting is performed on the corresponding substrate water content and water use efficiency when the different substrate water content gradients are set.

[0064] (6) The water use efficiency model is used to evaluate the substrate moisture state of the plants grown in space in practical applications: the transpiration rate and photosynthesis rate of the unit area of the leaf of the plant are obtained through the methods of (3) and (4), and D is calculated; the a value corresponding to the plant and the D max corresponding to the substrate used for planting are determined through the method in (5), and then the substrate water content I is obtained through the water use efficiency model; when the substrate water content is lower than the set threshold value, the controller 12 controls the water tank 11 to start irrigation until the water use efficiency D = D max is measured, and the irrigation is stopped.

[0065] The embodiments are preferred embodiments of the present application, but the present application is not limited to the above embodiments, and any obvious improvements, replacements, or modifications made by those skilled in the art without departing from the essential content of the present application shall fall within the protection scope of the present application.

Claims

1. A water vapor balance-based space planting substrate moisture control method, characterized in that: a water use efficiency model is used to evaluate the substrate moisture state of the space planting plant in actual application; the water use efficiency model is: where D is water use efficiency, and Pn, Tr are the photosynthetic rate and transpiration rate per unit area of leaf obtained by CO2 / H2O analyzer (7); D max is the maximum water use efficiency of the plant, obtained in advance by water experiment; i is the number of data collection times in the irrigation period, Tr i represents the crop transpiration rate at the i th data collection time in the irrigation period; a is a to-be-determined coefficient, the value of which is different for different plants, and in actual application, before the matrix moisture state of the space planting plant is evaluated, the least square fitting is performed through experimental setting of different matrix water content gradients according to the water use efficiency model; The water use efficiency model is used to determine the substrate water content I, and when the substrate water content is below a set threshold, the controller (12) controls the water tank (11) to start irrigation until the water use efficiency D = D max ; In the above process, the method for obtaining the photosynthesis rate Pn and the transpiration rate Tr of the unit area leaf is: The cultivation box (13) is closed, and when the CO2 / H2O analyzer (7) determines that the CO2 and H2O contents in the cultivation box (13) are stable, the air pump in the water vapor analysis module is opened to draw air, and the water vapor analysis module records the changes of CO2 and H2O in the Δt interval, denoted as and The transpiration rate and photosynthetic rate in the cultivation box (13) are calculated by the formula and The photosynthetic rate Pn and the transpiration rate Tr per unit area of the leaf are calculated by combining the leaf area of the plant.

2. The space planting medium moisture control method of claim 1, wherein, The plant leaf is scanned by using a depth camera (2), three-dimensional point cloud data of the leaf is obtained and preprocessed, then leaf segmentation and surface reconstruction are performed, and the surface area of the reconstructed surface is calculated, that is, the area of the plant leaf; The specific method for obtaining the area of the plant leaf is: each leaf is divided into triangular facets by using a greedy projection triangle algorithm, a triangular mesh model of the surface is generated, the area of each triangle is calculated by using the Heron formula, and then all the triangular mesh areas are added to obtain the surface area of each leaf.

3. The space planting medium moisture control method of claim 2, wherein, The maximum plane angle of the triangular facet is set to 50°, the maximum angle of each triangle is 120°, and the minimum angle is 10°, so that the leaf point cloud can be triangularly divided.

4. The space planting medium moisture control method of claim 1, wherein, The and The starting point values of the CO2 concentration in the cultivation box (13) were kept the same when the measurements were taken.

5. A control system for the method of controlling water in a space planting medium according to any one of claims 1 to 4, characterized in that, A cultivation box (13) is provided, a cultivation bag (8) is arranged in the cultivation box (13), a small rooting bag is placed in the cultivation bag (8), and the cultivation bag (8) is connected with a water tank (11); A circulation fan A (6) and a circulation fan B (10) are respectively arranged on the upper and lower sides of the inside of the cultivation box (13), an LED light source (1) and a depth camera (2) are arranged on the top of the cultivation box (13), and a measurement hole is reserved on the box body of the cultivation box (13) to facilitate the measurement and calibration of the photosynthesis and transpiration rate of the plant in the cultivation box (13) by a CO2 / H2O analyzer (7); A wind speed sensor (3), a light sensor (4), a temperature and humidity sensor (5), a miniature air conditioner (9), and a steam humidifier (14) are further arranged in the cultivation box (13); The data collected by the depth camera (2), the wind speed sensor (3), the light sensor (4), the temperature and humidity sensor (5), and the CO2 / H2O analyzer (7) are transmitted to a controller (12); and the controller (12) controls the working of the LED light source (1), the circulation fan A (6), the circulation fan B (10), the miniature air conditioner (9), the steam humidifier (14), and the water tank (11).

6. The control system of claim 5, wherein, The substrate in the small rooting bag is selected from diatomite.

7. The control system of claim 5, wherein, The box body material of the cultivation box (13) is selected from a high-transmittance acrylic plate.

8. The control system of claim 5, wherein, The CO2 / H2O analyzer (7) measures and calibrates the photosynthesis and transpiration rate of the plant in the cultivation box (13), specifically: the CO2 / H2O analyzer (7) monitors the gas exchange in the cultivation box (13), according to the characteristics of the water vapor balance in the semi-closed system, the change of the molar ratio of water and carbon dioxide in the in-out gas of the cultivation box (13) is calculated, and the photosynthesis and transpiration rate determination of the plant is calibrated.

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