A karst region crop precision irrigation method based on trunk sap flow early warning

Abstract

The application discloses a kind of karst region crop precision irrigation methods based on stem sap flow early warning, comprising: step 1, layout underground infiltration irrigation system drip irrigation pipeline and surface water retaining layer;Step 2, install heat pulse sap flow sensor on healthy planting pearl stem;Step 3, according to the early warning signal generated by heat pulse sap flow sensor sap flow rate, as the starting signal of infiltration irrigation system;Step 4, after starting infiltration irrigation system, start underground infiltration irrigation system to carry out targeted water replenishment, when the monitored real-time average sap flow rate falls to normal level, close irrigation valve, complete closed-loop irrigation;Realize the combination of karst mountainous area drought early warning and root closed-loop targeted irrigation, effectively avoid the death of plant due to catastrophic hydraulic failure in xylem, significantly improve water resource utilization efficiency and crop drought survival rate;Solve the technical problems such as irrigation timing lag and low water resource utilization efficiency in karst region.

Description

Technical Field

[0001] This invention belongs to the field of precision irrigation technology in agriculture and forestry, and specifically relates to a precision irrigation method for crops in karst areas based on tree trunk sap flow early warning. Background Technology

[0002] Karst topography is characterized by a highly heterogeneous "dual soil and water structure." Its topsoil is extremely shallow (typically less than 50 cm) and discontinuous, underlying highly permeable carbonate rock. Because precipitation easily seeps through cracks, the topsoil is extremely depleted of moisture, making it highly susceptible to severe drought. In the hot and dry karst valleys, pioneer plants with high economic and ecological value, such as *Zanthoxylum bungeanum*, are widely cultivated. However, during extreme drought events, some plants, unable to adjust transpiration in time to reduce soil moisture, experience continuous sap flow driven by high temperatures and radiation, leading to a severe breach of the embolism threshold (e.g., P0.05). 50 (At -2.2 MPa), a catastrophic hydraulic failure occurred, ultimately leading to its demise.

[0003] Traditional agricultural irrigation methods, such as timed and quantitative irrigation or surface flooding, are not only difficult to implement in rugged karst mountainous areas, but also fail to accurately grasp the physiological critical point of water depletion in plants, resulting in low water resource utilization efficiency and an inability to effectively save crops subjected to extreme drought stress. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a precision irrigation method for crops in karst areas based on tree trunk sap flow early warning, so as to solve the technical problems in the existing technology, such as delayed irrigation timing, low water resource utilization efficiency, and inability to effectively prevent crop hydraulic failure and death under extreme drought.

[0005] The technical solution of this invention is:

[0006] A method for precision irrigation of crops in karst areas based on early warning of tree trunk sap flow, the method comprising:

[0007] Step 1: Lay out the underground infiltration irrigation system drip irrigation pipes and surface water-retaining layer;

[0008] Step 2: Install a thermal pulse flow sensor on the trunk of a healthy beaded tree;

[0009] Step 3: Generate an early warning signal based on the dry flow rate of the thermal pulse flow sensor, which serves as the start signal for the drip irrigation system;

[0010] Step 4: After starting the seepage irrigation system, start the pre-drip irrigation system for targeted water replenishment. When the monitored real-time average liquid flow rate drops back to the normal level, close the irrigation valve to complete the closed-loop irrigation.

[0011] Drip irrigation pipes were laid horizontally at soil depths of 15 cm, 30 cm, and 45 cm.

[0012] Inoculate 0-15 cm of *Moss sphaeroides* to construct a bio-soil crust as a surface water-retaining layer.

[0013] The method for installing the thermal pulse flow sensor is as follows: Select a healthy plant and peel off the surface phloem to expose the xylem; use a drill to drill a hole on the north side of the trunk according to the positioning template, and insert the thermal pulse flow sensor probe into the middle sapwood to the depth; seal the pores with medical silicone; and wrap the outside with a heat insulation film for heat insulation and radiation protection.

[0014] The method for generating early warning signals includes: during drought, if the plant sap flow fails to decrease normally (i.e., the plant sap flow is greater than or equal to 0.17 L·h⁻¹ and the value remains between 0.17 L·h⁻¹ and 0.63 L·h⁻¹), an early warning signal is generated.

[0015] The criterion for closing the irrigation valve is: when the monitored real-time average liquid flow rate drops to ≤0.17 L•h -1 And maintain a fluctuation range of ≤10% for more than 2 hours.

[0016] The beneficial effects of this invention are:

[0017] This invention offers precise early warning timing: it is the first to propose using abnormally high-frequency fluctuating sap flow rates of 0.17–0.63 L·h⁻¹ as an early warning signal for karst-suitable crops nearing death. Compared to relying solely on soil moisture monitoring, this method directly reflects the hydraulic imbalance state of the plant itself, greatly improving the survival rate of emergency irrigation.

[0018] This invention offers highly efficient targeted water supply: Scientific research shows that the sap flow of surviving plants is primarily driven by soil moisture in the 30-45 cm layer. This invention directly buries drip irrigation pipes in the 15-45 cm soil layer, achieving precise, targeted water replenishment to the roots. This avoids the severe evaporation waste associated with surface irrigation, making it extremely suitable for karst regions with severe water scarcity.

[0019] This invention constructs a micro-ecological water-saving system: by planting moss in the 0-15 cm surface layer, it can effectively block shallow soil evaporation and quickly alleviate the contradiction of water supply and demand imbalance in karst arid environments.

[0020] This invention combines drought early warning in karst mountainous areas with closed-loop targeted irrigation of the root system, effectively preventing plant death due to catastrophic hydraulic failure of the xylem, significantly improving water resource utilization efficiency and crop drought resistance survival rate; it solves the technical problems of delayed irrigation timing, low water resource utilization efficiency, and inability to effectively prevent crop hydraulic failure and death under extreme drought in existing technologies in karst areas. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the drip irrigation pipeline layout for a specific implementation method. Detailed Implementation

[0022] A method for precision irrigation of crops in karst areas based on early warning of tree trunk sap flow, the method comprising the following steps:

[0023] Step 1, System layout of underground drip irrigation and surface water retention: The underground drip irrigation system (device) adopts a multi-layer layout, with drip irrigation pipes laid horizontally at three depths of 15 cm, 30 cm and 45 cm respectively. The design basis is that the soil thickness in karst areas often exhibits extremely high heterogeneity and discontinuity. The advantages of the three-layer equally spaced layout are: (1) Constructing a three-dimensional root water supply barrier: In order to adapt to drought in the karst rocky desertification environment, crops often evolve a layered root structure. The multi-layer layout can ensure that regardless of the depth at which the main root or lateral root of the crop is distributed, it can obtain precise water replenishment. (2) Alleviating soil moisture gradient loss: Experiments show that the shallow layer (0–15 cm) water in this area is easily affected by evaporation, while the deep layer (30–45 cm) is the core water acquisition area for surviving plants. The three-layer layout can maintain activity through shallow water replenishment in the early stage of drought, and ensure core hydraulic safety through deep water replenishment during severe drought, thus forming a comprehensive drought resistance closed loop. Meanwhile, inoculating sphagnum moss at 0-15 cm to construct a biological soil crust, the advantages of the crust layer are: (1) Enhanced water retention efficiency: It improves the instant infiltration efficiency of water in traditional drip irrigation and reduces evaporation loss through water retention performance; (2) Smooth monitoring signals: It stabilizes the surface soil moisture through physical covering, thereby reducing non-biological noise interference of plant sap flow data and improving the accuracy of early warning triggering; (3) Soil and water stability: It strengthens the water retention and soil stabilization capacity of dry and hot river valley slopes, forming a closed-loop coupling system of 'irrigation-water retention-early warning'.

[0024] Step 2: Monitoring Equipment Installation and Data Acquisition: Select healthy plants and peel off a small amount of phloem to expose the xylem. Using a miniature drill, drill a hole on the north side (shaded side) of the trunk according to the positioning template. Insert the probe of the thermal pulse sap flow sensor (model: SFM-5) into the middle sapwood. After insertion, seal the hole with medical-grade silicone to prevent sap leakage or external moisture interference, and wrap it with a heat-insulating film (aluminum foil) for heat insulation and radiation protection. Connect the sensors to the data acquisition unit to continuously acquire plant sap flow data at fixed time intervals (e.g., every 30 minutes). Installation advantages: North-side installation effectively avoids thermal interference from direct sunlight on the temperature sensor, ensuring the stability of thermal pulse velocity calculation; sealing and heat insulation greatly reduce measurement reference drift caused by ambient background temperature fluctuations, ensuring high-fidelity data acquisition.

[0025] Step 3: Sap Flow Dynamics Analysis and Early Warning Determination: Real-time analysis of sap flow dynamics is conducted, with the dry sap flow rate serving as the core trigger threshold for initiating irrigation. During drought, if the plant sap flow fails to decrease normally (normally not exceeding 0.17 L·h⁻¹), but instead exhibits drastic fluctuations and remains abnormally high between 0.17 L·h⁻¹ and 0.63 L·h⁻¹ for an extended period, it is determined that the xylem faces a severe risk of embolism, and the system generates an early warning signal.

[0026] Step 4, Early Warning Response and Closed-Loop Water Control: Upon triggering an early warning, the pre-installed underground infiltration irrigation system is immediately and automatically activated for targeted water replenishment; the liquid flow data is continuously monitored, and the system will continue to monitor the flow rate until the monitored real-time average flow rate drops to ≤0.17 L•h. -1 If the water level remains stable (fluctuation range ≤10%) for more than 2 hours, it is determined that the plant has exited the high-load hydraulic stress state, and the system automatically closes the irrigation valve to complete closed-loop irrigation.

[0027] The following examples illustrate... Figure 1 The technical solution of the present invention will be further described below.

[0028] A precision irrigation method for crops in karst regions based on early warning of tree trunk sap flow, taking the Dingtan pepper planted in a typical karst dry-hot valley area as an example:

[0029] Step 1: Pre-installation: In plots with gentle slopes and soil thickness ≥45 cm, drip irrigation pipes are horizontally buried in the soil layer at a depth of 15-45 cm, and moss plants are artificially inoculated in the topsoil layer at a depth of 0-15 cm to construct a synergistic system of precise underground water replenishment and surface water retention.

[0030] Step 2: Install the equipment: Select healthy plants from the east, south, west, and north directions, peel off a small amount of phloem, drill a hole on the north side (shaded side) of the trunk and insert a thermal pulse flow sensor (model: SFM-5), seal the hole with silicone and wrap it with aluminum foil reflective film to prevent rain and radiation interference, and finally connect it to the data acquisition unit.

[0031] Step 3, Monitoring and Early Warning: The data acquisition device is set to record sap flow data every 30 minutes. The system compares the data in real time. When it detects that the plant sap flow has not decreased (normally not exceeding 0.17 L·h⁻¹) and has been operating at a high load in the range of 0.17 L·h⁻¹ to 0.63 L·h⁻¹ for a long time, it is determined that the xylem is at serious risk of embolism, triggering an early warning signal.

[0032] Step 4: Irrigation and Automatic Shutdown: After the warning is triggered, the system automatically activates the underground drip irrigation system at a depth of 15-45 cm for targeted water supply. During the water supply period, the data acquisition unit continues to work. When the sap flow curve returns to a stable and conservative low flow state, it is determined that the plant water deficit has been resolved, and the system automatically shuts down the underground drip irrigation system, achieving water-saving and efficient automatic irrigation.

Claims

1. A method for precision irrigation of crops in karst areas based on early warning of tree trunk sap flow, characterized in that: The method includes: Step 1: Lay out the underground infiltration irrigation system drip irrigation pipes and surface water-retaining layer; Step 2: Install a thermal pulse flow sensor on the trunk of a healthy beaded tree; Step 3: Generate an early warning signal based on the dry flow rate of the thermal pulse flow sensor, which serves as the start signal for the drip irrigation system; Step 4: After starting the seepage irrigation system, start the pre-drip irrigation system for targeted water replenishment. When the monitored real-time average liquid flow rate drops back to the normal level, close the irrigation valve to complete closed-loop irrigation.

2. The method for precision irrigation of crops in karst areas based on early warning of tree trunk sap flow according to claim 1, characterized in that: Drip irrigation pipes were laid horizontally at soil depths of 15 cm, 30 cm, and 45 cm.

3. The method for precision irrigation of crops in karst areas based on early warning of tree trunk sap flow according to claim 1, characterized in that: Inoculate 0-15 cm of *Moss sphaeroides* to construct a bio-soil crust as a surface water-retaining layer.

4. A method for precision irrigation of crops in karst areas based on early warning of tree trunk sap flow, as described in claim 1, is characterized in that: The method for installing the thermal pulse flow sensor is as follows: Select a healthy plant and peel off the surface phloem to expose the xylem; Using a drill bit, drill holes on the north side of the trunk according to the positioning template, and insert the thermal pulse flow sensor probe into the middle layer of sapwood to the required depth; seal the pores with medical silicone; and wrap the outside with a heat insulation film for heat insulation and radiation protection.

5. A method for precision irrigation of crops in karst areas based on early warning of tree trunk sap flow, as described in claim 1, characterized in that: The method for generating early warning signals includes: during drought, if the plant sap flow fails to decrease normally (i.e., the plant sap flow is greater than or equal to 0.17 L·h⁻¹ and the value remains between 0.17 L·h⁻¹ and 0.63 L·h⁻¹), an early warning signal is generated.

6. A method for precision irrigation of crops in karst areas based on early warning of tree trunk sap flow, as described in claim 1, characterized in that: The criterion for closing the irrigation valve is: when the monitored real-time average liquid flow rate drops to ≤0.17 L•h -1 And maintain a fluctuation range of ≤10% for more than 2 hours.

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