A nitrogen precision control system and method based on multi-dimensional monitoring

Abstract

The present application relates to the technical field of plant cultivation, and particularly relates to a nitrogen precision control system and method based on multidimensional monitoring. The system is provided with a plant growth model, a substrate environment detection module, an irrigation module, and a data processing module. The data processing module is configured to control the irrigation amount and irrigation frequency of the irrigation module based on the nitrogen nutrition index and the substrate nitrate content. The above-mentioned effect is due to the establishment of the variety-specific nitrogen concentration gradient, the integration of the three-end collaborative monitoring system, the substrate nitrate content backstepping method based on the leaching fraction, and the construction of the "model-sensor-actuator" closed-loop control logic. The system forms a set of nitrogen precision regulation system covering monitoring, decision-making and execution, and has strong industrial applicability and promotion value. The system realizes the closed-loop control from nitrogen state monitoring, supply-demand model analysis to irrigation parameter dynamic adjustment.

Description

Technical Field

[0001] This invention relates to the field of plant cultivation technology, and in particular to a nitrogen precision control system and method based on multi-dimensional monitoring. Background Technology

[0002] Tomatoes are a core vegetable crop grown in hydroponics systems, with an annual output exceeding 50 million tons, of which over 50% are grown in greenhouses. Nitrogen, a key limiting factor for tomato growth and development, directly determines crop yield and quality through precise nitrogen supply. Traditional cultivation management often faces a dilemma: excessive nitrogen leads to non-point source pollution, while insufficient nitrogen causes growth stress. Especially in hydroponics systems, the dynamic balance of nitrogen concentration in the nutrient solution has a decisive impact on root absorption efficiency and aboveground physiological metabolism. Therefore, establishing a scientific nitrogen regulation theory and technology system is a core requirement for transforming greenhouse tomato production from extensive management to precision and high efficiency.

[0003] At the technological development level, existing nitrogen monitoring and regulation methods still have multiple limitations. Regarding monitoring methods, current methods mainly rely on leaf SPAD value measurement and destructive sampling of plants. SPAD values ​​are easily affected by variety, light intensity, and leaf aging; the absolute difference in SPAD values ​​between different tomato varieties can reach 10-15 units, severely impacting their universality. Furthermore, destructive sampling methods cannot achieve dynamic continuous monitoring; the time from sampling to laboratory analysis is typically 24-48 hours, making it difficult to provide data support for real-time regulation. In addition, existing monitoring methods mostly do not incorporate the core theory of "critical nitrogen concentration," only indirectly linking SPAD thresholds to yield and quality, lacking a systematic integration of nitrogen dilution effects and the dynamic needs of plants at different growth stages, resulting in limited regulation accuracy.

[0004] In terms of model construction, existing models are not well-suited for hydroponically grown tomatoes, especially lacking specific models for nitrogen-sensitive stages such as the seedling stage, making it difficult to accurately depict the coupling relationship between dry matter accumulation and nitrogen demand during the seedling stage. Furthermore, because a nitrogen nutrient index is not introduced for quantitative diagnosis, it is impossible to effectively distinguish between nitrogen excess, deficiency, or adequate conditions, still relying on retrospective indicators such as yield and quality for back-calculation, resulting in significant regulatory lag.

[0005] At the system integration level, although intelligent water and fertilizer systems, such as integrated water and fertilizer equipment based on fuzzy control or the Internet of Things, have been applied in practice, their designs generally prioritize execution over decision-making. The systems are not deeply integrated with critical nitrogen concentration models and nitrogen uptake models for hydroponics in tomato cultivation, and control parameters still rely on empirical settings. Furthermore, sensor accuracy is insufficient; for example, traditional nitrate sensors have detection errors as high as 10%-15% for nitrate nitrogen concentration differences of less than 1 mmol / L. In addition, the lack of unified communication protocols between sensors, controllers, and actuators makes it difficult to achieve a closed loop of "sensing-decision-execution," hindering the integration of the entire technology chain from "experimental data to model building to intelligent control."

[0006] It can be said that the current nitrogen regulation technology for hydroponically grown tomatoes has significant shortcomings in terms of monitoring dynamism, model adaptability, and system integration. There is an urgent need to build a nitrogen precision control system and method that is based on multi-dimensional real-time monitoring, adapts to the growth characteristics of hydroponically grown tomatoes, and can achieve seamless integration of sensing, decision-making, and execution.

[0007] Furthermore, on the one hand, there are differences in understanding among those skilled in the art; on the other hand, the inventors studied a large number of documents and patents when making this invention, but due to space limitations, not all details and contents were listed in detail. However, this does not mean that the present invention does not possess the features of these prior art. On the contrary, the present invention already possesses all the features of the prior art, and the applicant reserves the right to add relevant prior art to the background art. Summary of the Invention

[0008] This invention relates to the field of plant cultivation technology, and in particular to a nitrogen precision control system and method based on multi-dimensional monitoring.

[0009] To address the aforementioned technical problems, one objective of this invention is to provide a nitrogen precision control system based on multi-dimensional monitoring. The system includes: a plant growth model for acquiring the actual nitrogen concentration and dry matter accumulation of the aboveground parts of the plant; a substrate environment detection module for acquiring the nitrate nitrogen concentration in the leachate; an irrigation module for acquiring the leachate volume and nutrient solution volume after a single irrigation; and a data processing module configured to: confirm the nitrogen nutrient index based on the aboveground dry matter accumulation and actual nitrogen concentration obtained from the plant growth model; confirm the substrate nitrate content based on the nitrate nitrogen concentration in the leachate obtained from the substrate environment detection module and the leachate volume and nutrient solution volume after a single irrigation obtained from the irrigation module; and control the irrigation amount and frequency based on the nitrogen nutrient index and substrate nitrate content.

[0010] According to a preferred embodiment, the data processing module is configured as follows: When NNI is not greater than the first threshold and Csubstrate is less than the third threshold, the irrigation module is adjusted to increase the concentration of nutrient liquid nitrogen and increase the amount of irrigation per session, while the irrigation frequency remains unchanged.

[0011] According to a preferred embodiment, the data processing module is configured as follows: When NNI is greater than the first threshold but not greater than the second threshold and Csubstrate is greater than the third threshold but not greater than the fourth threshold, the irrigation control module maintains the current nutrient liquid nitrogen concentration and irrigation parameters.

[0012] According to a preferred embodiment, the data processing module is configured as follows: When NNI is greater than the second threshold and Csubstrate is greater than the fourth threshold, the irrigation module is adjusted to reduce the concentration of nutrient solution nitrogen and reduce the amount of irrigation per cycle.

[0013] According to a preferred embodiment, the substrate environment detection module includes a nitrate sensor probe placed in a cultivation pot exudate collection device, the cultivation pot exudate collection device comprising an inner layer for placing the substrate and cultivated plants and an outer layer for collecting the exudate from the inner layer.

[0014] One of the objectives of this invention is to provide a method for precise nitrogen control based on multi-dimensional monitoring, comprising the following steps: collecting the actual nitrogen concentration of the aboveground parts of the plant, the dry matter accumulation of the aboveground parts of the plant, the nitrate nitrogen concentration in the leachate, the leachate volume of the plant after a single irrigation, and the nutrient solution volume of a single irrigation; confirming the nitrogen nutrient index based on the dry matter accumulation of the aboveground parts of the plant and the actual nitrogen concentration of the aboveground parts of the plant obtained from the plant growth model; confirming the substrate nitrate content based on the nitrate nitrogen concentration in the leachate obtained from the substrate environment detection module and the leachate volume of the plant after a single irrigation and the nutrient solution volume of a single irrigation obtained from the irrigation module; and controlling the irrigation amount and irrigation frequency based on the nitrogen nutrient index and the substrate nitrate content.

[0015] According to a preferred embodiment, when NNI is not greater than a first threshold and Csubstrate is less than a third threshold, the irrigation module is adjusted to increase the concentration of nutrient liquid nitrogen and increase the amount of irrigation per session, while the irrigation frequency remains unchanged.

[0016] According to a preferred embodiment, when NNI is greater than a first threshold but not greater than a second threshold and Csubstrate is greater than a third threshold but not greater than a fourth threshold, the irrigation module is adjusted to maintain the current nutrient liquid nitrogen concentration and irrigation parameters.

[0017] According to a preferred embodiment, when NNI is greater than a second threshold and Csubstrate is greater than a fourth threshold, the irrigation module is adjusted to reduce the nutrient solution nitrogen concentration, thereby reducing the amount of water required for a single irrigation. Preferably, if LF is greater than a fifth threshold, the irrigation module is adjusted to extend the irrigation interval.

[0018] This invention addresses the problems in hydroponics of tomatoes, such as the lack of nitrogen concentration gradients, insufficient synergy in monitoring nitrogen levels in the substrate-exudate-plant system, and weak correlation between nutrient solution dosage and plant nitrogen absorption. By setting variety-specific nitrogen concentration gradients, constructing a multi-dimensional nitrogen monitoring system, and establishing a correlation model between nutrient solution dosage and nitrogen supply and demand, it effectively solves the problems of plant growth stress, resource waste, and non-point source pollution caused by nitrogen supply and demand imbalances. It achieves precise control of nitrogen levels in the hydroponics of target varieties, with specific beneficial effects including: (1) Regarding nitrogen use efficiency, by introducing six specific nitrogen concentration gradients (22, 18, 14, 9, 6, and 3 mmol / L) for the "Ruifen 882" tomato variety, and combining them with a nitrogen monitoring network that coordinates the plant, substrate, and exudate, the accuracy and variety suitability of nitrogen supply were significantly improved, avoiding the problems of nitrogen over- or under-nitrogen in traditional fertilization. Experimental verification showed that the nitrogen use efficiency of this scheme was 25%-30% higher than that of traditional fertilization methods, while effectively reducing nitrogen leaching and lowering the risk of agricultural non-point source pollution.

[0019] (2) In terms of planting economic benefits, based on the critical nitrogen concentration model and real-time sensor data, the precise control of nutrient solution dosage and nitrogen concentration has been achieved, which not only reduces the ineffective input of nitrogen fertilizer, but also reduces the yield loss caused by nitrogen stress. The overall planting cost is 15%-20% lower than the traditional model.

[0020] (3) In terms of crop growth performance, the dynamic response mechanism and dual-threshold triggering control strategy effectively avoided the impact of nitrogen nutrient stress on plant physiology. The experimental results showed that the coefficient of variation of key growth indicators of tomatoes (plant height, stem diameter, number of leaves) decreased by 10%-12%, the fruit quality indicators (soluble sugar, vitamin C content) increased by 8%-10%, the plant growth was more uniform and stable, and the yield and quality were improved in synergy.

[0021] (4) In terms of system response performance, the real-time monitoring of nitrate nitrogen concentration in the exudate is achieved by using a nitrate sensor, and the matrix nitrogen content is quantitatively calculated by the back-calculation method of leaching fraction. This realizes the transformation from the traditional lag mode (24-48 hours) that relies on laboratory testing to the in-situ rapid response (2-4 hours), which significantly enhances the system's dynamic adaptability to the nitrogen requirements of tomatoes at different growth stages.

[0022] The above-mentioned effects are due to the establishment of variety-specific nitrogen concentration gradients, the integration of a three-terminal collaborative monitoring system, the matrix nitrate content back-calculation method based on leaching fraction, and the construction of a "model-sensor-actuator" closed-loop control logic. The system forms a set of nitrogen precision regulation system covering monitoring, decision-making, and execution. The system realizes closed-loop control from nitrogen status monitoring and supply and demand model analysis to dynamic adjustment of irrigation parameters, and has strong industrial applicability and promotion value. Attached Figure Description

[0023] Figure 1 This is a diagram showing the relationship between the various modules of the present invention; Figure 2 This is a schematic diagram of the experimental planting and monitoring system layout. The image shows the greenhouse dimensions, the distribution of planting pots, the location of sensors, and the connection between irrigation pipes and electromagnetic flow valves. Figure 3 The image shows a comparison of tomato plants under different treatments, illustrating the differences in plant growth status among the six nitrogen concentration gradient treatment groups. Figure 4 A comparison chart of leaf area of ​​tomato plants under different treatments at different stages is shown. The horizontal axis represents the number of days after transplanting, and the vertical axis represents the leaf area. Different growth stage nodes are marked. Figure 5 A comparison chart of aboveground dry weight of tomato plants at different stages and under different treatments. The horizontal axis represents the number of days after transplanting, and the vertical axis represents the dry weight, reflecting the pattern of dry matter accumulation. Figure 6 A comparison chart of the aboveground fresh weight of tomato plants at different stages and under different treatments. The horizontal axis represents the number of days after transplanting, and the vertical axis represents the fresh weight, reflecting the plant growth rate. Figure 7 The dilution curve for the critical nitrogen concentration obtained from the experiment is shown. The horizontal axis represents the aboveground dry matter accumulation (DW), and the vertical axis represents the critical nitrogen concentration (Nc). The values ​​are labeled ac=3.65, b=0.16, and the fitted R value is shown. 2 =0.95; Figure 8 This is a diagram illustrating the theory of nitrogen regulation, used to show the closed-loop logic of "plant monitoring - model calculation - sensor feedback - implementation of regulation".

[0024] Figure Labels 100: Plant growth model; 200: Substrate environment detection module; 210: Cultivation pot exudate collection device; 2101: Inner layer; 2102: Outer layer; 220: Nitrate sensing unit; 300: Irrigation module; 310: Data acquisition unit; 320: Irrigation unit; 400: Data processing module. Detailed Implementation

[0025] In the description of this invention, terminology is used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0026] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the materials, reagents or instruments used, unless otherwise specified by the manufacturer, are all commercially available reagents and materials; the conditions not specified in the examples are all carried out according to conventional conditions or conditions recommended by the manufacturer. At the same time, the present invention does not limit the source of the raw materials used. Unless otherwise specified, the raw materials used in the present invention are all commercially available products in this technical field.

[0027] The first threshold (the lower limit of the nitrogen nitrogen index) is used to determine whether a plant has begun to enter a nitrogen deficiency state. When the nitrogen nitrogen index is below or equal to this value, it indicates that the nitrogen concentration in the plant is below the level required for ideal growth. For example, the first threshold for tomatoes is 0.85-0.95. More specifically, during the reproductive growth stage of tomatoes, the first threshold is 0.85-0.9. More specifically, during the vegetative growth stage of tomatoes, the first threshold is 0.9-0.95.

[0028] The second threshold (the upper limit of NNI) is used to determine whether a plant has entered a state of nitrogen excess. When the NNI is higher than this value, it indicates that the nitrogen concentration in the plant has exceeded the ideal growth requirements, and there may be a risk of excessive absorption or excessive vegetative growth. For example, the second threshold for tomatoes is 1.05-1.15. More specifically, during the reproductive growth stage of tomatoes, the first threshold is 1.05-1.1. More specifically, during the vegetative growth stage of tomatoes, the first threshold is 1.1-1.15.

[0029] The third threshold (the lower limit of Csubstrate) is used to determine whether the concentration of nitrate nitrogen in the substrate that is directly available to plants is insufficient. When the nitrate nitrogen concentration in the exudate is below this value, it indicates that the immediate nitrogen supply level in the substrate is low. For example, the third threshold for tomatoes is 80-150 mg / kg. More specifically, during the reproductive growth stage of tomatoes, the third threshold is 80-100 mg / kg. More specifically, during the vegetative growth stage of tomatoes, the third threshold is 100-150 mg / kg.

[0030] The fourth threshold (the upper limit of Csubstrate) is used to determine whether nitrate nitrogen has accumulated excessively in the substrate. Excessive concentration can lead to salt stress, root damage, and increase the risk of leaching into the environment. For example, the third threshold for tomatoes is 300-500 mg / kg. More specifically, during the reproductive growth stage of tomatoes, the fourth threshold is 300-400 mg / kg. More specifically, during the vegetative growth stage of tomatoes, the fourth threshold is 400-500 mg / kg.

[0031] The fifth threshold (the leaching fraction (LF) threshold) is used to determine whether irrigation is excessive, leading to water and fertilizer waste and environmental pollution. Leaching fraction (LF) is a key indicator of irrigation efficiency; an excessively high LF means that most irrigation water is discharged unused. For example, the fifth threshold for tomatoes is 0.15-0.25. More specifically, during the reproductive growth stage of tomatoes, the fifth threshold is 0.15-0.2. More specifically, during the vegetative growth stage of tomatoes, the fifth threshold is 0.2-0.25.

[0032] It should be noted that the settings for each threshold can be determined based on past planting experience, reference to crop models of the same family and genus, or small-scale experimental data. For example, the parameters for tomatoes, which belong to the Solanaceae family and the Solanum genus, can also be applied to other Solanaceae plants such as eggplants, peppers, and potatoes.

[0033] Example 1 like Figure 1 As shown, the nitrogen precision control system based on multi-dimensional monitoring of the present invention includes a plant growth model 100, a substrate environment detection module 200, an irrigation module 300, and a data processing module 400. The plant growth model 100, the substrate environment detection module 200, the irrigation module 300, and the data processing module 400 are interconnected by signal connection.

[0034] The plant growth model 100 is used to obtain the actual nitrogen concentration and dry matter accumulation of the aboveground parts of the plant. Preferably, the plant growth model 100 can be a mechanism-based virtual plant growth model, for example, by constructing a plant structure-function coupling model to simulate the transport and distribution process of photosynthetic assimilates within the plant, thereby dynamically predicting changes in aboveground dry matter accumulation and nitrogen concentration. The plant growth model 100 can also employ an empirical or semi-empirical model based on measured data, for example, by periodically performing destructive sampling of the plant to measure the dry matter weight and nitrogen content of the aboveground and underground parts, thereby establishing a functional relationship between dry matter accumulation and nitrogen absorption over time.

[0035] Specifically, when using a virtual growth model, the plant growth process can be simulated by inputting environmental factors (such as light, temperature, water, and nitrogen fertilizer application rate) and plant physiological parameters (such as specific leaf nitrogen content, photosynthetic rate, and allocation coefficient), thereby outputting aboveground dry matter and nitrogen concentration.

[0036] When using destructive sampling methods, representative plant samples can be selected during key growth periods, the aboveground and underground parts can be separated, dried and weighed separately to obtain dry matter weight, and the total nitrogen content of the tissue can be determined by Kjeldahl nitrogen determination method or near-infrared spectroscopy, thereby calculating the nitrogen accumulation per unit area or per plant aboveground part and the dry matter accumulation.

[0037] Both methods can achieve quantitative characterization of plant growth and nitrogen uptake, and the appropriate model can be selected based on the actual application scenario and data availability.

[0038] The matrix environment detection module 200 is used to acquire the nitrate nitrogen concentration in the exudate in real time or periodically. The core of this module is the nitrate sensing unit 220, which can be implemented in ways including, but not limited to, an ion-selective electrode sensor or an optically based ultraviolet absorption spectroscopy sensor. During setup, the sensor body can be directly embedded or inserted into a dedicated matrix exudate collection device, or it can be designed as a flow-through detection pool, allowing the nutrient solution exuding from the bottom to flow through the detection area to ensure the representativeness of the measurement. Preferably, as... Figure 8 As shown, the substrate environment detection module 200 includes a nitrate sensor probe placed in the cultivation pot exudate collection device 210. The cultivation pot exudate collection device 210 includes an inner layer 2101 for placing the substrate and cultivated plants, and an outer layer 2102 for collecting the exudate from the inner layer 2101. A leakage hole is provided at the bottom of the inner layer 2101. The inner layer 2101 and the outer layer 2102 are not in contact with each other.

[0039] To ensure accurate parameter acquisition, this module typically integrates signal conversion and data processing units. An ion-selective electrode generates a potential signal by detecting the ion activity in the leachate, while an ultraviolet spectral sensor measures nitrate nitrogen concentration by measuring the light absorption intensity in a specific ultraviolet band. This optical method effectively reduces interference from colored substances in the leachate. The acquired concentration data, after temperature compensation calibration, is converted into a standard nitrate nitrogen concentration value by a built-in algorithm and transmitted to the system's central control unit via wired or wireless means. This setup enables continuous, in-situ monitoring of nitrogen residue in the substrate environment, providing direct data for precise control of nitrogen fertilizer supply.

[0040] The irrigation module 300 is used to perform precise water and fertilizer application operations and acquire key irrigation parameters. The irrigation module 300 includes a data acquisition unit 310 and an irrigation unit 320. According to a preferred embodiment, the data acquisition unit 310 is used to acquire the volume of exudate from the plant after a single irrigation and the volume of nutrient solution used in a single irrigation. Preferably, the data acquisition unit 310 is used to accurately measure the volume of nutrient solution consumed in a single irrigation event, and the volume of exudate seeping from the bottom of the cultivation substrate after irrigation. More preferably, the data acquisition unit 310 typically acquires the irrigation liquid volume using a high-precision flow meter or level sensor integrated into the irrigation pipeline; for measuring the exudate volume, a level gauge or weighing sensor can be installed in a dedicated collection container.

[0041] According to a preferred embodiment, the irrigation unit 320 serves as the system's execution terminal. The irrigation unit 320 can periodically and quantitatively irrigate plants with water and / or nutrient solution based on instructions from the data processing module 400. Preferably, the irrigation unit 320 comprises a nutrient solution storage tank, a water pump, a solenoid valve, a mixing device, and irrigation pipelines. The irrigation unit 320 can receive and execute control instructions from the data processing module 400, precisely controlling the start-stop duration of the water pump and the opening and closing state of the solenoid valve according to the plant's water and fertilizer requirements, thereby achieving timed, quantitative, and pre-selective irrigation of the plant root zone with water or nutrient solution, and supporting various irrigation strategies such as continuous and intermittent irrigation.

[0042] According to a preferred embodiment, the data processing module 400 serves as the control core of the system, and its specific implementation can be an embedded microprocessor, a programmable logic controller, an industrial computer, or a cloud server, etc., as an intelligent terminal. Preferably, the data processing module 400 can be physically deployed locally in the field control box of the cultivation system, or it can work collaboratively with a remote cloud platform as an edge computing node. The data processing module 400 acquires multiple parameters in real time from the plant growth model 100 (theoretical nitrogen requirement), the substrate environment detection module 200 (nitrate nitrogen concentration in the exudate), and the irrigation volume and exudate volume recorded by the irrigation module 300, through integrated analog / digital input interfaces and communication units (such as RS485, CAN, or Ethernet).

[0043] After acquiring the aforementioned parameters, the module's built-in or dedicated control algorithm (e.g., judgment logic or optimization model based on preset thresholds) will perform data fusion and decision analysis. Specifically, by comparing the plant's nitrogen requirements with the nitrogen supply in the rhizosphere, the module dynamically calculates the triggering time for the next irrigation operation, the amount of nutrient solution injected, and the amount of nitrogen fertilizer stock solution added. Finally, the module sends precise control commands to the actuators of the irrigation unit 320 (e.g., drippers, water pumps, solenoid valves, fertilizer injection pumps) through its digital output interface or communication bus, thereby achieving precise water and fertilizer integration regulation based on the actual needs of the plant.

[0044] The data processing module 400 establishes stable signal connections with the irrigation module 300, plant growth model 100, and substrate environment detection module 200 through its integrated multiple input / output interfaces and communication units, forming a complete monitoring and control system. Specifically, the data processing module 400 connects with the plant growth model 100 via a data interface to obtain predicted data such as the theoretical nitrogen requirement and dry matter accumulation of the aboveground parts of the plant, calculated by the model. Simultaneously, the data processing module 400 connects with the substrate environment detection module 200 via an analog signal interface or a digital communication bus to receive in real-time electrical signals of nitrate nitrogen concentration in the leachate collected and converted by a nitrate sensor. Furthermore, the data processing module 400 connects with the data acquisition unit 310 of the irrigation module 300 via a pulse counter or digital communication link to obtain irrigation liquid volume and leachate volume data reported by sensors such as flow meters and level gauges.

[0045] In terms of signal flow, the data acquisition unit 310 of the plant growth model 100, substrate environment detection module 200, and irrigation module 300 mainly acts as a signal source, providing unidirectional data input to the data processing module 400. After receiving and analyzing all the data, the data processing module 400 sends a digital or analog control signal containing switching commands and adjustment parameters to the irrigation unit 320 of the irrigation module 300, driving the actuators such as water pumps and solenoid valves to operate, thereby achieving precise regulation of water and fertilizer supply. The entire process constitutes a closed-loop feedback system based on data flow and executed by control signals.

[0046] Example 2 In terms of information interaction, the data processing module 400 is configured to: confirm the nitrogen nutrition index based on the dry matter accumulation of the aboveground parts of the plant and the actual nitrogen concentration of the aboveground parts of the plant obtained from the plant growth model 100.

[0047] The nitrate content of the substrate is determined based on the nitrate nitrogen concentration in the exudate obtained by the substrate environment detection module 200 and the exudate volume of the plant after a single irrigation and the nutrient solution volume of a single irrigation obtained by the irrigation module 300.

[0048] The irrigation amount and frequency of irrigation module 300 are controlled based on the nitrogen nutrient index and the nitrate content of the substrate.

[0049] (I) Calculation method for matrix nitrate content The matrix nitrate content is calculated using the "leaching fraction (LF) back-calculation method". The specific steps are as follows: S1 Calculation of Leaching Fraction (LF): The leaching fraction is the ratio of the volume of infiltrate to the volume of irrigation fluid, and the formula is: LF = Vleach / Virrigate Where Vleach is the volume of seepage fluid after a single irrigation (unit: L); Virrigate is the volume of nutrient solution after a single irrigation (unit: L).

[0050] The irrigation module 300 reads Vleach and Virrigate values ​​and calculates the LF value in real time. The LF value range is usually 0.1-0.3 (if it is below 0.1, the irrigation amount needs to be increased; if it is above 0.3, the irrigation amount needs to be reduced to avoid the substrate being too dry or too wet).

[0051] S2 Determination of nitrate nitrogen concentration in exudate (Cleach): The nitrate nitrogen concentration in the exudate (unit: mg / L) is read by a nitrate sensor, and the data is calibrated to ensure an error of ≤5%.

[0052] S3 Calculation of matrix nitrate content (Csubstrate): Based on the principle of mass balance, the nitrate content in the matrix is ​​positively correlated with the nitrate nitrogen concentration and leaching fraction of the exudate, as shown in the formula: Csubstrate = Cleach / LF × K Where K is the matrix adsorption coefficient, ranging from 0.8 to 1.2, in mg / kg; Cleach is the nitrate nitrogen concentration in the exudate, in mg / L.

[0053] If this value is higher than the appropriate nitrate content threshold of the substrate, the result indicates that there is excessive residual nitrogen in the substrate, and the concentration of nutrient solution nitrogen in the next irrigation needs to be reduced.

[0054] (ii) Nitrogen Nutrition Index a. Critical nitrogen concentration Collect plant dry matter accumulation (DW) and actual nitrogen concentration (Nt) data from at least three samplings. Use a nonlinear regression method to fit a critical nitrogen concentration model. The fitting formula is: Nc=ac×DW ^(-b) Where DW is the dry matter accumulation of the aboveground parts of the plant, in g / plant; Nc is the critical nitrogen concentration, in g / plant.

[0055] Based on the above fitting, the parameter values ​​of ac and b are determined.

[0056] b. Nitrogen Nutrition Index Collect DW and Nt, and calculate the nitrogen nutrient index NNI. The calculation formula is as follows: NNI = Nt / Nc, Wherein, Nt represents the actual nitrogen concentration in the aboveground parts of the plant, in units of %.

[0057] The data processing module 400 is configured to: when NNI is not greater than the first threshold (i.e. nitrogen deficiency) and Csubstrate is less than the third threshold, regulate the irrigation module 300 to increase the nitrogen concentration of the nutrient solution, while increasing the amount of irrigation per irrigation, and keeping the irrigation frequency unchanged.

[0058] When NNI is greater than the first threshold but not greater than the second threshold (nitrogen is suitable) and Csubstrate is greater than the third threshold but not greater than the fourth threshold, the irrigation module 300 maintains the current nutrient solution nitrogen concentration and irrigation parameters (irrigation amount and irrigation frequency).

[0059] When NNI is greater than the second threshold (excess nitrogen) and Csubstrate is greater than the fourth threshold, the irrigation module 300 is adjusted to reduce the nitrogen concentration of the nutrient solution and reduce the amount of irrigation per cycle. At the same time, if LF is greater than the fifth threshold, the irrigation module 300 is adjusted to extend the irrigation interval.

[0060] Test case This experimental example uses tomatoes as an example to illustrate the setup and application of the system in this invention.

[0061] (1) Experimental materials and basic conditions (1-1) Test varieties "Ruifen 882" pink tomato (produced by Rijkswagen in the Netherlands).

[0062] (1-2) Planting substrate The mixture is prepared by mixing peat moss, coconut coir, and perlite in a volume ratio of 2:1:1.

[0063] (1-3) Cultivation environment The artificial greenhouse (7.3 m long, 4.3 m wide) adopted a substrate-based pot cultivation method. The planting pots were circular open containers (0.3 m in diameter and 0.3 m deep), with 4 tomato plants planted in each pot, totaling 288 plants in the experimental area. Six nutrient solution irrigation tanks were provided, connected to pipes via pumps, and individual plant irrigation was carried out using insert-type drip irrigation systems. Figure 8 As shown.

[0064] Place the nitrate sensor probe (substrate environment detection module 200) in the exudate collection device 210 of the cultivation pot, and debug the sensor data transmission function to ensure that real-time data can be collected and stored normally.

[0065] Select uniformly growing "Ruifen 882" tomato seedlings (3 leaves and 1 heart), wash the roots and substrate, and transplant them into planting pots with 4 seedlings per pot. After transplanting, water them with clean water to help them recover. During this period, maintain a greenhouse temperature of 25-28℃ and a humidity of 60%-70%.

[0066] (1-4) Experimental design: such as Figure 2As shown, the experimental area was divided into 18 small regions, and each nitrogen concentration treatment was repeated 3 times. The repeated regions were not distributed continuously to reduce the interference of environmental factors.

[0067] (2) Nitrogen concentration gradient setting Prepare your own nutrient solution and set up 6 nitrogen concentration gradients (based on NH4+). 4+ NO 3- Total molar concentration: T1 (22 mmol / L), T2 (18 mmol / L), T3 (14 mmol / L), T4 (9 mmol / L), T5 (6 mmol / L), T6 (3 mmol / L). See Table 1-6 for the nutrient solution formulas for each gradient.

[0068] (3) Timing of treatment and monitoring methods Treatment timing: Transplant tomato seedlings when they have grown to 3 leaves and 1 heart. After 3 days of seedling establishment, start nitrogen concentration gradient treatment until the nitrogen regulation cycle from seedling stage to early fruiting stage is completed.

[0069] a. Plant monitoring: Regularly perform destructive sampling of plants to measure nitrogen accumulation in the aboveground and underground parts.

[0070] Specifically, destructive sampling of plants was carried out every 7 days. Four tomato plants were randomly selected from each treatment group, and the above-ground parts (stems and leaves) and underground parts (roots) were separated. After washing, they were dried to constant weight, and the dry matter weight was measured. The nitrogen content of each part was determined by the Kjeldahl method, and the nitrogen accumulation was calculated.

[0071] b. Matrix monitoring: Simultaneously collect matrix samples and detect the residual nitrogen content in the matrix.

[0072] Specifically, while sampling the plants, substrate samples were collected from the corresponding planting pots, and the nitrogen content of each part was determined using the Kjeldahl method. The residual nitrogen data in the substrate were recorded.

[0073] c. Exudate monitoring: The nitrate nitrogen concentration in the exudate from the cultivation pots was monitored in real time using a nitrate sensor.

[0074] Specifically, exudate data were collected and recorded weekly, including the volume of the exudate and the nitrogen content of the exudate measured using a nitrate sensor.

[0075] d. Nutrient solution usage statistics: Record the amount of nutrient solution used in each irrigation for each treatment group and establish the correlation between usage and nitrogen absorption.

[0076] c. Irrigation operation: Irrigate with nutrient solution at a fixed time every day (e.g., 9:00 am). Adjust the irrigation amount according to the growth stage of tomatoes (50-100 mL per plant per time during the seedling stage, and 100-150 mL per plant per time during the early fruiting stage). Record the irrigation amount of each treatment group each time.

[0077] (4) Construction of nitrogen regulation model Based on monitoring data, combined with the critical nitrogen concentration theory (Nc=ac×DW) ^(-b) By combining the nitrogen nutrient index (NNI=Nt / Nc), a nitrogen supply and demand model specifically for "Ruifen 882" tomatoes is constructed. The nitrogen concentration of the nutrient solution and the irrigation amount are adjusted in real time through model calculation to achieve precise nitrogen regulation.

[0078] Specifically, plant dry matter accumulation (DW) and nitrogen concentration (Nt) data were collected from at least three samplings, and a nonlinear regression method was used to fit the critical nitrogen concentration model (Nc=ac×DW). ^(-b) The ac (3.65) and b (0.16) parameter values ​​of “Ruifen 882” tomatoes were determined, and the nitrogen nutrient index (NNI) was calculated.

[0079] (5) Calculation method for matrix nitrate content The matrix nitrate content is calculated using the "leaching fraction (LF) back-calculation method". The specific steps are as follows: S1 Calculate the leaching fraction (LF): The leaching fraction is the ratio of the volume of leached liquid to the volume of irrigation liquid, calculated using the formula: LF = Vleach / Virrigate. The LF value is calculated in real-time, typically ranging from 0.1 to 0.3. If the LF is below 0.1, the irrigation rate needs to be increased. If the LF is above 0.3, the irrigation rate needs to be decreased. Adjusting the LF value helps prevent the substrate from becoming too dry or too wet.

[0080] S2 Determination of nitrate nitrogen concentration in exudate (Cleach): The nitrate nitrogen concentration in the exudate (unit: mg / L) is read by a nitrate sensor, and the data is calibrated to ensure an error of ≤5%.

[0081] S3 Calculation of matrix nitrate content (Csubstrate): Based on the principle of mass balance, the nitrate content in the matrix is ​​positively correlated with the nitrate nitrogen concentration and leaching fraction of the exudate. The formula is: Csubstrate=Cleach / LF×K.

[0082] For example, in this test case, when Cleach is 200 mg / L and LF is 0.2, Csubstrate is 200 / 0.2×0.92, which is 920 mg / kg. If this value is higher than the suitable nitrate content threshold of the substrate (800 mg / kg), it is determined that the substrate nitrogen residue is excessive, and the concentration of nutrient solution nitrogen in the next irrigation needs to be reduced.

[0083] (6) System control logic and intelligent irrigation scheme A closed-loop control system consisting of a critical nitrogen concentration model, a nitrate sensor, and an electromagnetic flow valve was constructed. Through algorithm optimization, intelligent irrigation of tomatoes at different growth stages was achieved.

[0084] (6-1) Data acquisition and preprocessing The control system collects four types of data in real time, including: plant model data (DW, Nt, NNI), sensor data (leachate Cleach, substrate temperature), irrigation data (Virrigate, LF), and environmental data (greenhouse temperature, humidity, light intensity). During data preprocessing, outliers are removed (such as sensor data exceeding the measurement range, LF > 0.5 or < 0.05), and the moving average method (average of 5 data points) is used for smoothing to ensure data stability. The detection of environmental parameters is for the content displayed on the panel to provide reference for operators and can also provide guidance for system regulation. The EC is automatically adjusted based on temperature and humidity, reducing the EC in hot weather when the plant's water requirement is greater than its fertilizer requirement, and vice versa.

[0085] (6-2) Algorithm optimization and regulation decision-making The "dual-threshold trigger" algorithm is adopted, and combined with the critical nitrogen concentration model and nitrate data, the data processing module 400 generates regulation instructions: a. When NNI ≤ 0.8 (nitrogen deficiency) and Csubstrate < 600 mg / kg: The data processing module 400 automatically increases the nitrogen concentration of the nutrient solution by 8% - 10% (for example: if the current is 14 mmol / L, it is increased to 15.1 - 15.4 mmol / L), and at the same time increases the single irrigation amount by 10% (such as from 80 mL / plant to 88 mL / plant at the seedling stage), and the irrigation frequency remains unchanged (once a day); b. When 0.8 < NNI ≤ 1.2 (suitable nitrogen) and 600 mg / kg ≤ Csubstrate ≤ 800 mg / kg: The data processing module 400 maintains the current nitrogen concentration of the nutrient solution and irrigation parameters (irrigation amount, irrigation frequency), and复测 the data every 3 days; c. When NNI > 1.2 (nitrogen excess) and Csubstrate > 800 mg / kg, the data processing module 400 reduces the nitrogen concentration of the nutrient solution by 5% - 8% (for example: if the current is 18 mmol / L, it is reduced to 16.6 - 16.9 mmol / L), and reduces the single irrigation amount by 15% (such as from 150 mL / plant to 127.5 mL / plant at the initial fruiting stage); In addition, if LF > 0.3, the data processing module 400 additionally extends the irrigation interval (from once a day to once every 2 days); d. Execution and feedback: According to the regulation decision, the data processing module 400 sends instructions to the irrigation module 300 (such as adjusting the opening of the flow valve to control the irrigation volume, switching the valve of nutrient solution barrels with different nitrogen concentrations); after the execution is completed, the system records the execution parameters (such as the actual irrigation volume, nitrogen concentration), and re-collects the sensor data after 2 hours to verify the regulation effect. If the NNI or Csubstrate does not return to the appropriate range, the above decision-making process is repeated until the indicators reach the standard.

[0086] Preferably, c. Adjust the nitrogen concentration of the nutrient solution according to the NNI value. That is, when NNI > 1.2 (nitrogen excess), reduce the nitrogen concentration of the nutrient solution by 5% - 10%; when 0.8 < NNI ≤ 1.2 (nitrogen suitable), keep the current concentration; when NNI ≤ 0.8 (nitrogen deficiency), increase the nitrogen concentration of the nutrient solution by 5% - 10%. At the same time, combined with the nitrate nitrogen concentration in the leachate and the nutrient solution usage data, optimize the irrigation frequency and single usage.

[0087] The results are as Figures 3-6 shown, and the results illustrate the influence of different concentration settings on tomato indicators. At the same time, through subsequent experimental measurements, Figure 7 the critical nitrogen concentration curve model is obtained. By controlling the nitrogen supply in each period through this curve model, the optimal comprehensive benefit can be achieved.

[0088] Aiming at the problems existing in the soilless cultivation of "Ruifen 882" tomatoes, such as the lack of exclusive nitrogen concentration gradient, insufficient coordination of nitrogen monitoring in substrate - leachate - plant, and weak correlation between nutrient solution usage and nitrogen absorption, the present invention solves the problems of growth stress, resource waste and non-point source pollution caused by nitrogen supply - demand imbalance by setting an exclusive nitrogen concentration gradient, constructing a multi-dimensional monitoring system, and establishing an association model between nutrient solution usage and nitrogen supply - demand, and realizes the precise control of nitrogen in the soilless cultivation of this variety.

[0089] Table 1. Nutrient solution formula (NH 4+ , NO 3- molar concentration 22 mmol•L -1 )

[0090] Table 2. Nutrient solution formula (NH 4+ , NO 3- molar concentration 18 mmol•L -1 )

[0091] Table 3. Nutrient solution formula (NH 4+ , NO 3- molar concentration 14 mmol•L -1 )

[0092] Table 4. Nutrient solution formula (NH4+) 4+ NO 3- molar concentration 9 mmol•L -1 )

[0093] Table 5. Nutrient solution formula (NH4+) 4+ NO 3- molar concentration 6 mmol•L -1 )

[0094] Table 6. Nutrient solution formula (NH4+) 4+ NO 3- molar concentration 3 mmol•L -1 )

[0095] It should be noted that the specific embodiments described above are exemplary, and those skilled in the art can devise various solutions inspired by the disclosure of this invention. These solutions all fall within the scope of this invention and its protection. Those skilled in the art should understand that this specification and its accompanying drawings are illustrative and not intended to limit the scope of the claims. The scope of protection of this invention is defined by the claims and their equivalents.

Claims

1. A nitrogen precision control system based on multi-dimensional monitoring, characterized in that, The system is configured with: A plant growth model (100) was used to obtain the actual nitrogen concentration and dry matter accumulation of the aboveground parts of plants. The matrix environment detection module (200) is used to obtain the nitrate nitrogen concentration in the exudate; An irrigation module (300) is used to acquire the volume of exudate from the plant after a single irrigation and the volume of nutrient solution after a single irrigation; and a data processing module (400) is configured to: Based on the aboveground dry matter accumulation and actual nitrogen concentration of the plant obtained from the plant growth model (100), the nitrogen nutrient index is calculated according to the critical nitrogen concentration model; based on the nitrate nitrogen concentration in the leachate obtained from the substrate environment detection module (200) and the volume of leachate and nutrient solution of the plant after a single irrigation obtained from the irrigation module (300), the substrate nitrate content is calculated according to the leaching fraction back-calculation method. Based on the nitrogen nutrient index and the nitrate content of the substrate, the irrigation amount and frequency of the irrigation module (300) are controlled and the nitrogen concentration of the nutrient solution is adjusted.

2. The nitrogen precision control system based on multi-dimensional monitoring according to claim 1, characterized in that, The data processing module (400) is configured as follows: When the nitrogen nutrient index is not greater than the first threshold and the substrate nitrate content is less than the third threshold, the irrigation module (300) is adjusted to increase the nitrogen concentration of the nutrient solution and increase the amount of irrigation per irrigation while keeping the irrigation frequency unchanged.

3. The nitrogen precision control system based on multi-dimensional monitoring according to claim 1, characterized in that, The data processing module (400) is configured as follows: When the nitrogen nutrient index is greater than the first threshold but not greater than the second threshold and the substrate nitrate content is greater than the third threshold but not greater than the fourth threshold, the irrigation control module (300) maintains the current nutrient solution nitrogen concentration and irrigation parameters.

4. The nitrogen precision control system based on multi-dimensional monitoring according to claim 1, characterized in that, The data processing module (400) is configured as follows: When the nitrogen nutrient index is greater than the second threshold and the substrate nitrate content is greater than the fourth threshold, the irrigation module (300) is adjusted to reduce the nitrogen concentration of the nutrient solution and reduce the amount of irrigation per cycle.

5. The nitrogen precision control system based on multi-dimensional monitoring according to claim 1, characterized in that, The substrate environment detection module (200) includes a nitrate sensor probe placed in the cultivation pot exudate collection device (210), which includes an inner layer (2101) for placing the substrate and cultivated plants and an outer layer (2102) for collecting the exudate from the inner layer (2101).

6. A method for precise nitrogen control based on multi-dimensional monitoring, characterized in that, Includes the following steps: The actual nitrogen concentration of the aboveground parts of the plant, the amount of dry matter accumulated in the aboveground parts of the plant, the nitrate nitrogen concentration in the exudate, the volume of the exudate after a single irrigation, and the volume of the nutrient solution after a single irrigation were collected. The nitrogen nutrient index was confirmed based on the dry matter accumulation of the aboveground parts of the plant and the actual nitrogen concentration of the aboveground parts of the plant obtained from the plant growth model (100). The nitrate content of the substrate is determined based on the nitrate nitrogen concentration in the exudate obtained by the substrate environment detection module (200) and the volume of the plant's exudate and the volume of the nutrient solution after a single irrigation obtained by the irrigation module (300). The irrigation amount and frequency are controlled based on the nitrogen nutrient index and the nitrate content of the substrate.

7. The nitrogen precision control method based on multi-dimensional monitoring according to claim 6, characterized in that, When the nitrogen nutrient index is not greater than the first threshold and the substrate nitrate content is less than the third threshold, the irrigation module (300) is adjusted to increase the nitrogen concentration of the nutrient solution and increase the amount of irrigation per irrigation while keeping the irrigation frequency unchanged.

8. The nitrogen precision control method based on multi-dimensional monitoring according to claim 6, characterized in that, When the nitrogen nutrient index is greater than the first threshold but not greater than the second threshold and the substrate nitrate content is greater than the third threshold but not greater than the fourth threshold, the irrigation control module (300) maintains the current nutrient solution nitrogen concentration and irrigation parameters.

9. The nitrogen precision control method based on multi-dimensional monitoring according to claim 6, characterized in that, When the nitrogen nutrient index is greater than the second threshold and the substrate nitrate content is greater than the fourth threshold, the irrigation module (300) is adjusted to reduce the nitrogen concentration of the nutrient solution and reduce the amount of irrigation per cycle.

10. The nitrogen precision control method based on multi-dimensional monitoring according to claim 9, characterized in that, If the rinsing fraction is greater than the fifth threshold, the irrigation module (300) is adjusted to extend the irrigation interval.

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