An irrigation and fertilization control method for balancing soil nitrogen leaching and salt leaching

Abstract

An irrigation and fertilization control method for balancing soil nitrogen leaching and salt leaching belongs to the field of irrigation. The method includes: obtaining soil hydraulic parameters, soil solute transport parameters, and irrigation system parameters; based on the above parameters, constructing a simulation model for soil water, nitrogen, and salt transport, and calibrating and validating the constructed model; setting different combinations of irrigation water volume, nitrogen application rate, and irrigation water quality scenarios, inputting the calibrated parameters into the simulation model, and calculating the soil nitrogen leaching rate under different scenarios; calculating the characterization quantity of salt leaching degree according to the salt tolerance of crops at different growth stages and the change of soil salt content; obtaining the nitrogen leaching and salt leaching balance index of each group of scenarios according to the nitrogen leaching rate and the characterization quantity of salt leaching degree; selecting the group with the lowest balance index as the optimal irrigation and fertilization mode; the present invention solves the problem that the salt leaching amount and nitrogen leaching amount cannot reach the optimal simultaneously in the existing irrigation process.

Description

Technical Field

[0001] The present invention relates to the field of irrigation, and particularly to an irrigation and fertilization control method for balancing soil nitrogen leaching and salt leaching. Background Art

[0002] The problem of soil salinization is a key factor restricting the sustainable development of agriculture. Globally, soil salinization shows characteristics such as coexistence of local mitigation and global aggravation, coexistence of primary and secondary salinization, coexistence of natural succession and extreme meteorological disturbances, etc. At the same time, in future scenarios such as climate change, the salinization evolution process accelerates and becomes more sensitive. In recent years, especially in arid areas, the problem of secondary salinization caused by improper utilization of water resources has attracted the attention of the majority of scientific and technological workers and society. At present, irrigation leaching measures are still the most effective method for treating soil salinization. However, in the actual irrigation and fertilization management of farmland, since nitrogen in fertilizers is extremely difficult to be fixed by the soil, nitrogen leaching is bound to occur during salt leaching. In particular, a large leaching quota is extremely likely to result in a low nitrogen fertilizer utilization efficiency and increase the pollution risk of nitrate nitrogen in groundwater. Previous studies have shown that on the premise of considering the requirements of soil salt leaching, measures such as increasing the irrigation quota and adjusting the irrigation frequency can effectively increase the amount of salt leaching, but the salt tolerance threshold of crops is not considered, resulting in a lack of quantitative indicators in the salt regulation process. At the same time, reducing the amount of nitrogen leaching requires reducing the application amounts of water and nitrogen without reducing the yield. However, in a salinized soil environment, the inhibitory effect of salt accumulation on crops needs to be considered in the measures to reduce nitrogen leaching, but relevant research reports are rare. On the other hand, the amount of salt leaching and the amount of nitrogen leaching are respectively "the larger the better" and "the smaller the better" type indicators for crop growth and the soil environment, and it is difficult to simultaneously meet the optimal requirements of both indicators in the actual regulation process. Summary of the Invention

[0003] Aiming at the deficiencies in the above-mentioned prior art, the irrigation and fertilization control method for balancing soil nitrogen leaching and salt leaching provided by the present invention solves the problem that the amount of salt leaching and the amount of nitrogen leaching cannot reach the optimal simultaneously in the existing irrigation process.

[0004] In order to achieve the above-mentioned invention purpose, the technical solution adopted by the present invention is: an irrigation and fertilization control method for balancing soil nitrogen leaching and salt leaching, comprising the following steps:

[0005] S1. Obtain soil hydraulic parameters, soil solute transport parameters, and irrigation system parameters;

[0006] S2. Construct a simulation model for the transport of soil moisture, nitrogen, and salt;

[0007] S3. Calibrate and verify the soil hydraulic parameters, soil solute transport parameters, and irrigation system parameters using a simulation model to obtain the calibrated and verified soil hydraulic parameters, soil solute transport parameters, and irrigation system parameters.

[0008] S4. Input the calibrated and verified soil hydraulic parameters, soil solute transport parameters, and irrigation system parameters into the simulation model, set different combinations of irrigation water volume, nitrogen application rate, and irrigation water quality scenarios, calculate the change process of soil salt content and nitrogen leaching loss under each scenario, and calculate the soil nitrogen leaching rate.

[0009] S5. Calculate the characterization quantity of salt leaching degree according to the salt tolerance of the crop at different growth stages and the change of soil salt content.

[0010] S6. Obtain the nitrogen leaching and salt leaching balance indexes for each scenario according to the nitrogen leaching rate and the characterization quantity of salt leaching degree.

[0011] S7. Select the scenario with the lowest balance index as the optimal irrigation and fertilization mode for irrigation.

[0012] Further, in step S1, obtaining the soil hydraulic parameters includes the saturated water content θ s of the soil, the residual water content θ r and the saturated hydraulic conductivity K s of the soil; obtaining the soil solute transport parameters includes the longitudinal dispersion coefficient D L of the soil, the transverse dispersion coefficient D T of the soil, the molecular diffusion coefficient D w in free water, and the maximum concentration c max of the solute that the root system allows to absorb; the irrigation system parameters include the irrigation water volume and the boundary conditions of the irrigation area.

[0013] Further, in step S2, constructing the simulation model for soil water, nitrogen, and salt transport includes obtaining the water transport characteristic equation based on the soil hydraulic parameters and the solute transport parameters, as well as the nitrogen and salt transport characteristic equations, and constructing the simulation model for water, nitrogen, and salt transport during irrigation and fertilization based on the water transport characteristic equation, the nitrogen and salt transport characteristic equations, the irrigation water volume, and the boundary conditions of the irrigation area.

[0014] Further, in step S3, calibrating and verifying the constructed model includes selecting the treatment with relatively complete data monitoring for model calibration, and selecting the treatment covering all gradients of water, fertilizer, and salt settings to verify the calibrated soil water, nitrogen, and salt transport and transformation parameters.

[0015] Further, in step S4, the calibrated parameters are input into the simulation model. Considering the effects of fertilization frequency, irrigation water volume, and irrigation water quality factors, multiple scenarios are set, including setting different fertilization frequencies, different irrigation water volumes, and irrigation water quality combinations for crop irrigation during different growth periods.

[0016] Further, the formula for calculating the soil nitrogen leaching rate in step S4 is as follows:

[0017]

[0018] where NLF is the soil nitrogen leaching rate after irrigation, N leached is the amount of soil inorganic nitrogen leaching, and N added is the nitrogen application rate.

[0019] Further, the formula for calculating the characterization quantity of salt leaching degree in step S5 is as follows:

[0020] ΔSSC = SSC - SSC t

[0021] where ΔSSC is the characterization quantity of salt leaching degree, SSC is the soil salt content in the crop root zone after irrigation leaching, and SSC t is the salt tolerance threshold of the crop at different growth stages.

[0022] Further, the formula for calculating the nitrogen leaching and salt leaching balance index in step S6 is as follows:

[0023] LBI = NLF·|ΔSSC|

[0024] where LBI is the nitrogen leaching and salt leaching balance index, NLF is the soil nitrogen leaching rate of the soil to be irrigated, and ΔSSC is the characterization quantity of salt leaching degree.

[0025] Further, step S7 is specifically as follows:

[0026] S71. Calculate the values of the soil nitrogen leaching rate NLF and the characterization quantity of salt leaching degree ΔSSC of the soil after irrigation for each scenario;

[0027] S72. Calculate and obtain the nitrogen leaching and salt leaching balance index LBI according to the values of the soil nitrogen leaching rate NLF and the characterization quantity of salt leaching degree ΔSSC of the soil after irrigation for each scenario in step S71;

[0028] S73. Select the minimum nitrogen leaching and salt leaching balance index LBI as the optimal nitrogen leaching and salt leaching balance parameter, and the corresponding scenario is set as the optimal irrigation and fertilization mode.

[0029] In summary, the beneficial effects of the present invention are as follows: When calculating the characterization quantity of salt leaching degree, the present invention takes into account the salt tolerance threshold of crops, which is used as a soil salt regulation parameter. By comprehensively considering the characterization quantity of salt leaching degree and the nitrogen leaching rate, the nitrogen leaching and salt leaching balance index is proposed. When the nitrogen leaching and salt leaching balance value LBI is the smallest, the salt leaching amount and the nitrogen leaching amount reach the optimal values simultaneously, facilitating the balance between the salt leaching amount and the nitrogen leaching amount during the irrigation and fertilization process. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a flowchart of an irrigation and fertilization control method for balancing soil nitrogen leaching and salt leaching. DETAILED DESCRIPTION OF THE INVENTION

[0031] The following is a description of the specific embodiments of the present invention to facilitate those skilled in the art to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions made using the concept of the present invention are within the scope of protection.

[0032] In agricultural production practice, salt leaching will inevitably lead to nitrogen leaching. In existing research, for increasing salt leaching and reducing nitrogen leaching, the salt leaching amount and the nitrogen leaching amount used are "the larger the better" and "the smaller the better" type indicators respectively. In actual production practice, these two indicators are often difficult to balance, and the contradiction between salt and nitrogen leaching cannot be solved. To address this problem, the present invention introduces the salt tolerance threshold of crops, and uses the difference between the soil salt content in the crop root zone after irrigation leaching and the salt tolerance threshold of the crops as the characterization quantity of salt leaching degree, which is used as a soil salt regulation parameter to guide the salt leaching irrigation practice. At the same time, taking into account both salt leaching and nitrogen leaching, the two contradictory indicators are successfully transformed into a "the smaller the better" type comprehensive indicator. The specific scheme is as follows:

[0033] Example 1:

[0034] As Figure 1 shown, an irrigation and fertilization control method for balancing soil nitrogen leaching and salt leaching includes the following steps:

[0035] S1. Obtain soil hydraulic parameters, soil solute transport parameters, and irrigation system parameters;

[0036] In step S1, the obtained soil hydraulic parameters include soil saturated water content θ s , residual water content θ r , and saturated hydraulic conductivity K s ; the obtained soil solute transport parameters include longitudinal dispersion coefficient D L , transverse dispersion coefficient DT 1. The molecular diffusion coefficient D of free water w and the maximum concentration c of solutes that the root system allows to absorb max ; The irrigation system parameters include the irrigation amount and the boundary conditions of the irrigation area.

[0037] S2. Construct a simulation model for soil water, nitrogen, and salt transport;

[0038] In step S2, constructing a simulation model for soil water, nitrogen, and salt transport includes obtaining the water transport characteristic equation, as well as the nitrogen and salt transport characteristic equations based on the soil hydraulic parameters and the solute transport parameters, and constructing a simulation model for water, nitrogen, and salt transport during irrigation and fertilization based on the water transport characteristic equation, the nitrogen and salt transport characteristic equations, the irrigation amount, and the boundary conditions of the irrigation area.

[0039] S3. Calibrate and verify the soil hydraulic parameters, soil solute transport parameters, and irrigation system parameters using the simulation model to obtain the calibrated and verified soil hydraulic parameters, soil solute transport parameters, and irrigation system parameters;

[0040] S4. Input the calibrated and verified soil hydraulic parameters, soil solute transport parameters, and irrigation system parameters into the simulation model, set different combinations of irrigation amounts, nitrogen application rates, and irrigation water qualities, calculate the change process of soil salt content and nitrogen leaching loss under each group of scenarios, and calculate the soil nitrogen leaching rate;

[0041] In step S4, input the calibrated parameters into the simulation model, consider the effects of fertilization frequency, irrigation amount, and irrigation water quality factors, and set multiple groups of scenarios including setting different fertilization frequencies, irrigation amounts, and irrigation water quality combinations for crop irrigation during different growth stages.

[0042] S5. Calculate the characterization quantity of salt leaching degree according to the salt tolerance of the crop at different growth stages and the change of soil salt content;

[0043] S6. Obtain the nitrogen leaching and salt leaching balance indices for each group of scenarios according to the nitrogen leaching rate and the characterization quantity of salt leaching degree;

[0044] S7. Select the group with the lowest balance index as the optimal irrigation and fertilization mode for irrigation.

[0045] The first embodiment of the present invention has at least the following technical effects: When calculating the characterization quantity of salt leaching degree, the present invention takes into account the salt tolerance threshold of crops, which is used as a soil salt regulation parameter. By integrating the characterization quantity of salt leaching degree and the nitrogen leaching rate, a balance model of nitrogen leaching and salt leaching is constructed. When the balance value LBI of nitrogen leaching and salt leaching is the smallest, the salt leaching amount and the nitrogen leaching amount reach the optimum simultaneously, which is convenient for achieving the balance between the salt leaching amount and the nitrogen leaching amount during the drip irrigation under plastic film process.

[0046] The following further describes the irrigation and fertilization control method for balancing soil nitrogen leaching and salt leaching provided in the first embodiment of the present invention, and further explains the technical content of steps S4 to S5:

[0047] One implementation manner for calculating the nitrogen leaching rate of the soil after irrigation in Embodiment 1 is:

[0048]

[0049] where NLF is the nitrogen leaching rate of the soil after irrigation, N leached is the amount of soil inorganic nitrogen leaching, and N added is the nitrogen application rate.

[0050] One implementation manner for calculating the characterization quantity of salt leaching degree in Embodiment 1 is:

[0051] ΔSSC = SSC - SSC t (2)

[0052] where ΔSSC is the characterization quantity of salt leaching degree, SSC is the soil salt content in the crop root zone after irrigation leaching, and SSC t is the salt tolerance threshold at different growth stages of the crop.

[0053] In this embodiment, the nitrogen leaching rate and the characterization quantity of salt leaching degree in steps S4 and S5 can be obtained through the following methods:

[0054] A1. Establish a soil water and solute transport model, which is used to simulate the transport of soil water, nitrogen, and salt;

[0055] A2. Use the field measured data of soil moisture, salt, ammonium nitrogen, and nitrate nitrogen under different irrigation water qualities, irrigation amounts, and nitrogen application rates to calibrate and verify the constructed soil water and solute transport model;

[0056] A3. Set multiple scenarios, and use the verified soil water and solute transport model to simulate the spatio-temporal dynamic changes of soil moisture, salt, ammonium nitrogen, and nitrate nitrogen during the irrigation cycle under different scenarios, and calculate the soil nitrogen leaching amount and the characterization quantity of salt leaching degree under different fertilization frequencies, irrigation amounts, and irrigation water quality combinations based on formulas (1) and (2).

[0057] One implementation method for calculating the nitrogen leaching and salt leaching balance index in Example 1 is as follows:

[0058] LBI = NLF·|ΔSSC| (3)

[0059] Wherein, LBI is the nitrogen leaching and salt leaching balance value, NLF is the nitrogen leaching rate of the soil after irrigation, and ΔSSC is the characterization quantity of the salt leaching degree.

[0060] This embodiment provides a specific processing procedure for step S7:

[0061] S71. Calculate the values of the nitrogen leaching rate NLF and the salt leaching degree characterization quantity ΔSSC of the soil after irrigation for each group of scenarios;

[0062] S72. Calculate and obtain the nitrogen leaching and salt leaching balance index LBI according to the values of the nitrogen leaching rate NLF and the salt leaching degree characterization quantity ΔSSC of the soil after irrigation for each group of scenarios in step S71;

[0063] S73. Select the minimum nitrogen leaching and salt leaching balance index LBI as the optimal nitrogen leaching and salt leaching balance parameter, and the corresponding scenario is set as the optimal irrigation and fertilization mode.

[0064] The present invention fully considers the response relationship between crops and soil salinity, realizes the quantitative regulation of salinity based on crop growth, and effectively avoids the loss of root zone nutrients during the soil salt leaching process. The method of the present invention is simple, highly operable, and has broad application prospects.

[0065] The first embodiment of the present invention further includes at least the following technical effects: After calculating the optimal nitrogen leaching and salt leaching balance parameters, the present invention can achieve the optimal allocation of irrigation water and fertilization during irrigation, and can provide a suitable soil environment for crops, including a lower soil salt content and a suitable soil inorganic nitrogen content. At the same time, it improves the microbial activity in the root zone soil, which is conducive to the absorption and utilization of crop water, nutrients, etc., promotes crop growth, and increases crop yield. On the other hand, from an environmental perspective, applying the nitrogen leaching and salt leaching balance value LBI to environmental governance practices helps to save farmland irrigation water, reduce the risk of soil salinization, improve soil ecology, reduce the amount of chemical fertilizers applied, reduce the risk of groundwater pollution, slow down greenhouse gas emissions, provide technical support for the sustainable development of green agriculture, and serve the country's "dual carbon" goal.

[0066] The salt and nitrogen distribution in the soil and groundwater after using traditional irrigation to leach salts and after using the method of the present invention. With traditional irrigation, the leaching amount is large, the salt and nitrogen content in the soil root zone decreases, the salt and nitrogen content in the groundwater increases, the soil salt content is less than the threshold, and the soil nitrogen is less than the nitrogen requirement of the crop. After using the method of the present invention, the leaching amount decreases, the salt and nitrogen content in the soil root zone increases, the soil salt content is closer to the threshold, and the soil nitrogen can meet the nitrogen requirement of the crop.

Claims

1. A method for controlling irrigation and fertilization to balance soil nitrogen leaching and salt leaching, characterized in that, It includes the following steps: S1. Obtain soil hydraulic parameters, soil solute transport parameters, and irrigation system parameters; S2. Construct a simulation model for soil water, nitrogen, and salt transport; S3. Calibrate and verify the soil hydraulic parameters, soil solute transport parameters, and irrigation system parameters using the simulation model to obtain the calibrated and verified soil hydraulic parameters, soil solute transport parameters, and irrigation system parameters; S4. Input the calibrated and verified soil hydraulic parameters, soil solute transport parameters, and irrigation system parameters into the simulation model, set different combinations of irrigation water volume, nitrogen application rate, and irrigation water quality scenarios, calculate the change process of soil salt content and nitrogen leaching loss under each scenario, and calculate the soil nitrogen leaching rate; S5. Calculate the characterization quantity of salt leaching degree according to the salt tolerance of the crop at different growth stages and the change of soil salt content; S6. Obtain the nitrogen leaching and salt leaching balance index for each scenario according to the nitrogen leaching rate and the characterization quantity of salt leaching degree; S7. Select the scenario with the lowest balance index as the optimal irrigation and fertilization mode for irrigation; The formula for calculating the soil nitrogen leaching rate under each scenario in step S4 is: Among them, NLF is the nitrogen leaching rate of the soil after irrigation, N leached is the amount of inorganic nitrogen leached from the soil, N added is the nitrogen application rate; The formula for calculating the characterization quantity of salt leaching degree in step S5 is: ΔSSC = SSC - SSC th Among them, ΔSSC is the characterization quantity of salt leaching degree, SSC is the soil salt content in the crop root zone after irrigation leaching obtained by model simulation calculation, and SSC th is the salt tolerance threshold at different growth stages of the crop; The formula for calculating the nitrogen leaching and salt leaching balance index in step S6 is: LBI = NLF·|ΔSSC| Where, LBI is the nitrogen leaching and salt leaching balance index, NLF is the nitrogen leaching rate of the soil after irrigation, and ΔSSC is the characterization quantity of salt leaching degree.

2. The method for controlling irrigation and fertilization to balance soil nitrogen leaching and salt leaching according to claim 1, characterized in that, In the step S1, the soil hydraulic parameters are obtained, including the saturated soil water content θ s , the residual water content θ r and the saturated hydraulic conductivity K s ; the soil solute transport parameters are obtained, including the longitudinal dispersion coefficient D L , the transverse dispersion coefficient D T , the molecular diffusion coefficient D w in free water, and the maximum concentration c max of solute allowed to be absorbed by roots; the irrigation system parameters include the irrigation water volume and the boundary conditions of the irrigation area.

3. The method for controlling irrigation and fertilization to balance soil nitrogen leaching and salt leaching according to claim 2, characterized in that, The construction of the simulation model for soil water, nitrogen, and salt transport in step S2 includes obtaining the water transport characteristic equation, as well as the nitrogen and salt transport characteristic equations based on the soil hydraulic parameters and the solute transport parameters, and constructing a simulation model for water, nitrogen, and salt transport during irrigation and fertilization based on the water transport characteristic equation, the nitrogen and salt transport characteristic equations, the irrigation water volume, and the irrigation area boundary conditions.

4. The method for controlling irrigation and fertilization to balance soil nitrogen leaching and salt leaching according to claim 1, characterized in that, In step S4, the calibrated parameters are input into the simulation model, considering the effects of fertilization frequency, irrigation water volume, and irrigation water quality factors, and multiple scenarios are set, including setting different fertilization frequencies, different irrigation water volumes for crops at different growth stages, and combinations of irrigation water quality.

5. The method for controlling irrigation and fertilization to balance soil nitrogen leaching and salt leaching according to claim 1, characterized in that, Step S7 is specifically: S71. Calculate the values of the nitrogen leaching rate NLF and the characterization quantity of salt leaching degree ΔSSC of the soil after irrigation for each scenario; S72. Calculate and obtain the nitrogen leaching and salt leaching balance index LBI according to the values of the nitrogen leaching rate NLF and the characterization quantity of salt leaching degree ΔSSC of the soil after irrigation for each scenario in step S71; S73. Select the smallest nitrogen leaching and salt leaching balance index LBI as the optimal nitrogen leaching and salt leaching balance parameter, and the corresponding scenario is set as the optimal irrigation and fertilization mode.

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