Method for improving nitrogen utilization rate of eucalyptus

Abstract

The invention discloses a method for improving the nitrogen utilization rate of eucalyptus in the field of forestry cultivation. The method comprises the following steps: deeply plowing a forest land before planting, measuring the nitrogen content of soil, preparing an activating agent containing citric acid, humic acid and ammonium molybdate, spraying, and shallow raking and uniformly mixing; ditching along planting rows, applying an MPCM material, earthing, and applying a microbial activator containing N-acyl homoserine lactone, trehalose and monopotassium phosphate through drip irrigation, so that a root system is in moderate contact with the material; the loss-control nitrogen fertilizer and the MPCM material are mixed in the planting period, the fast-growing period and before canopy closure, and then annular furrow application is carried out; by monitoring the nitrogen conditions of rhizosphere soil and leaves, a nutrient solution containing amino acid chelated nitrogen, urea and trace elements is sprayed on the leaf surfaces in good time. The MPCM material is prepared by performing pyrolysis on eucalyptus residues to prepare a charcoal substrate, performing metal doping and intelligent polymer grafting, loading nitrogen-fixing bacteria and ammonifying bacteria, and performing activation, so that accurate supply and efficient utilization of nitrogen are realized, and the growth benefits of eucalyptus are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of forestry cultivation technology, and specifically to a method for improving nitrogen utilization efficiency in eucalyptus trees. Background Technology

[0002] Eucalyptus, as an important fast-growing timber species, is widely planted in southern my country. Its short growth cycle and high economic benefits make it a vital pillar of the forestry industry. However, low nitrogen utilization efficiency has been a key issue hindering the sustainable development of eucalyptus plantations. Due to their rapid growth and high nitrogen demand, traditional fertilization methods often lead to significant nitrogen loss, resulting in resource waste and a series of ecological and environmental problems. The currently prevalent practice of applying large amounts of nitrogen in a single application makes it difficult for nitrogen to be fully absorbed and utilized by the soil. Some nitrogen enters the environment through volatilization and leaching, leading to diminishing fertilization benefits. Furthermore, long-term, single application of chemical nitrogen fertilizers can cause soil acidification and compaction, further affecting the growth and development of eucalyptus roots and their nutrient absorption capacity, creating a vicious cycle.

[0003] While existing nitrogen management techniques for eucalyptus have explored various improvement measures such as controlled-release fertilizers and microbial agents, the actual results remain unsatisfactory. Conventional controlled-release fertilizers, although able to delay nitrogen release, often fail to match the nutrient requirements of eucalyptus at different growth stages, making precise supply difficult. The application of microbial agents alone is easily constrained by soil conditions, making it difficult to guarantee the survival rate and colonization of the microbial community, resulting in poor stability. Furthermore, current technologies often focus on specific improvements, lacking a systematic solution encompassing soil conditioning, material innovation, and monitoring and control. Particularly in the application of materials science, there has been no successful application of composite materials that simultaneously possess multiple functions such as nutrient slow release, microbial loading, and intelligent response in eucalyptus cultivation.

[0004] To address the aforementioned technical bottlenecks, there is an urgent need to develop a comprehensive management method that can significantly improve nitrogen utilization efficiency in eucalyptus trees. An ideal solution should begin with improving initial soil conditions, achieving intelligent controlled release of nitrogen through innovative material design, and establishing a precision fertilization system based on real-time monitoring. Particularly in terms of functional materials, a novel carrier material needs to be developed that can effectively support functional microorganisms and possess environmentally responsive characteristics, enabling it to intelligently regulate nitrogen release and transformation according to the growth needs of eucalyptus trees and changes in the soil environment. Simultaneously, this method should organically integrate soil pretreatment, microbial activation, and root regulation to form a complete system for efficient nitrogen utilization in eucalyptus trees, thereby overcoming the current nitrogen management challenges in eucalyptus cultivation and achieving a dual improvement in economic and ecological benefits. Summary of the Invention

[0005] The purpose of this invention is to provide a method for improving nitrogen utilization in eucalyptus, which solves the technical problems of low nitrogen fertilizer utilization, easy loss, and environmental pollution in existing eucalyptus plantations.

[0006] The present invention achieves the above objectives through the following technical solutions:

[0007] A method for improving nitrogen use efficiency in eucalyptus trees includes the following steps:

[0008] S1. Before planting eucalyptus trees, the forest land is thoroughly tilled and soil samples are taken to determine the initial ammonium nitrogen, nitrate nitrogen, and soluble organic nitrogen content. Based on the test results, an activator solution containing citric acid, humic acid, and ammonium molybdate is prepared, sprayed evenly on the soil surface, and then lightly raked to mix.

[0009] S2. Dig application trenches along the predetermined planting rows of eucalyptus trees, mix MPCM material with soil and apply it to the bottom of the trench, then cover it with fine soil for isolation; subsequently, apply a microbial activator containing N-acyl homoserine lactone, trehalose and potassium dihydrogen phosphate through a drip irrigation system; when planting eucalyptus seedlings, ensure that the roots of the eucalyptus seedlings are in direct contact with the MPCM material layer, but do not completely cover the roots of the eucalyptus seedlings;

[0010] S3, during the planting period, rapid growth period and before canopy closure of eucalyptus trees, apply controlled-release nitrogen fertilizer; when fertilizing, pre-mix the controlled-release nitrogen fertilizer with MPCM material to obtain a nitrogen fertilizer mixture, and apply the nitrogen fertilizer mixture in a circular trench dug around the root zone of the eucalyptus trees;

[0011] S4. By burying a soil solution extractor, rhizosphere soil solution is collected regularly, and a portable nitrogen analyzer is used to detect changes in ammonium nitrogen and nitrate nitrogen concentrations. A rapid nitrogen content detector for eucalyptus leaves is used to monitor the nitrogen nutrition status of the leaves. When the monitored indicators are below the threshold, a supplementary nutrient solution composed of amino acid chelated nitrogen, urea and trace elements is sprayed on the leaves to achieve precise replenishment of nitrogen for eucalyptus.

[0012] In this invention, the reaction mechanism by which MPCM material synergistically enhances nitrogen use efficiency in the eucalyptus growth system is as follows: After being applied to the soil, MPCM material works synergistically with other steps in this invention, forming a dynamic, precise, and efficient nitrogen management system through a series of physical, chemical, and biological reactions. The reaction mechanism begins with the interaction between the material and the rhizosphere environment. When eucalyptus seedlings are planted, their roots come into contact with the material layer. The secretions released by the roots and the infiltration of irrigation water first activate the intelligent polymer shell of the MPCM material. This shell responds to chemical signals in the rhizosphere microdomain, beginning to regulate the release rate of the controlled-release nitrogen fertilizer encapsulated within it and the nitrogen adsorbed by the material itself, achieving a preliminary synchronization between nitrogen supply and the absorption needs of the eucalyptus roots—this is called the "physicochemical controlled-release mechanism." Simultaneously, the microbial activators applied through the drip irrigation system, containing signaling molecules such as N-acylhomoserine lactone, efficiently awaken and activate the nitrogen-fixing and ammonifying bacteria loaded within the MPCM material. These activated functional microorganisms, using the material's pores as a protective habitat and the adsorbed organic nutrients and root exudates as energy, begin vigorous metabolism. Nitrogen-fixing bacteria convert atmospheric nitrogen, which eucalyptus trees cannot directly utilize, into absorbable ammonium nitrogen, continuously "opening up new sources"; while ammonifying bacteria decompose soluble organic nitrogen and some organic matter inherent in the soil that eucalyptus trees cannot absorb, converting them into ammonium nitrogen, thus "activating" the soil's original nitrogen pool—this is known as the "microbial transformation enhancement mechanism." Furthermore, the transition metals and their oxides doped into the material continuously catalyze the conversion of ammonium nitrogen to nitrate nitrogen, ensuring the diversity of nitrogen forms to meet the different nitrogen form preferences of eucalyptus trees at different growth stages. More importantly, the soil activator (containing citric acid, humic acid, etc.) applied before planting pre-optimizes the rhizosphere soil environment, not only activating potential soil nutrients, but also containing molybdenum, a key component of nitrogenase, thus externally enhancing the biological nitrogen fixation process. Finally, the entire system operates in a closed-loop feedback loop through buried soil solution extractors and leaf nutrient monitoring instruments. When the monitoring system detects that the effective nitrogen concentration in the rhizosphere or the nitrogen content in the leaves is below the threshold for maintaining optimal growth, it triggers the application of foliar nutrient solution. This nutrient solution, composed of amino acid chelated nitrogen and urea, can be rapidly absorbed through the stomata and cuticle of the leaves, directly participating in the metabolism within the eucalyptus tree and compensating for the temporary deficiency in root absorption; this is known as the "precise replenishment mechanism based on monitoring feedback." In summary, this invention, through the MPCM material as a core hub, organically couples four mechanisms—soil pretreatment, physicochemical controlled release, microbial-driven transformation, and real-time monitoring and replenishment—into a complete system. It works synergistically from four dimensions—"controlled loss-enhanced efficiency-transformation-replenishment"—to comprehensively block nitrogen loss pathways and significantly improve the efficiency of nitrogen transformation and utilization from the soil to the eucalyptus plant.

[0013] According to a preferred embodiment of the present invention, the preparation steps of the activator solution include: accurately weighing 50g of citric acid, 80g of humic acid, and 5g of ammonium molybdate, dissolving the above substances sequentially in 1000L of purified water, and stirring with a mechanical stirrer at 300r / min for 30min until all components are completely dissolved to form a homogeneous solution. In this activator, citric acid, as a low-molecular-weight organic acid, can activate phosphates and trace elements fixed in the soil; humic acid improves soil aggregate structure by complexing metal ions with its functional groups; and ammonium molybdate provides essential molybdenum for soil microorganisms, participating in the biological nitrogen fixation process as a key component of nitrogenase. When using, based on soil testing results, spray 3-5m³ of the prepared activator solution per hectare, and then lightly harrow to mix.

[0014] According to a preferred embodiment of the present invention, the preparation steps of the microbial activator include: accurately weighing 0.5g of N-acylhomoserine lactone, 120g of trehalose, and 200g of potassium dihydrogen phosphate, dissolving these components together in 1000L of irrigation water, and treating with an ultrasonic disperser for 20 minutes to ensure complete dissolution. N-acylhomoserine lactone, as a quorum sensing signaling molecule, can promote the formation of rhizosphere beneficial microbial communities; trehalose provides microorganisms with an efficient carbon source and enhances their stress resistance; and potassium dihydrogen phosphate provides phosphorus and potassium nutrition and adjusts the pH of the solution to a slightly acidic-neutral environment. This microbial activator is applied through a drip irrigation system, with 5-8L applied per eucalyptus seedling.

[0015] According to a preferred embodiment of the present invention, the preparation steps of the controlled-release nitrogen fertilizer include: using ordinary urea as a base material, and modifying it using fluidized bed coating technology. Specifically, the coating material composition includes 40g of polyurethane resin, 15g of bentonite, and 10g of diatomaceous earth. These coating materials are uniformly coated onto the surface of 1000g of urea granules to form a controlled-release layer with a thickness of 50-80μm. This controlled-release nitrogen fertilizer utilizes the microporous structure and hydrophilic-hydrophobic balance of the coating material to achieve slow nitrogen release, matching the nitrogen release cycle with the eucalyptus tree growth cycle, effectively reducing nitrogen volatilization and leaching losses.

[0016] According to a preferred embodiment of the present invention, the preparation steps of the supplementary nutrient solution include: accurately weighing 30g of amino acid chelated nitrogen and 50g of urea, and adding 5g of a trace element combination, wherein the trace elements include 2g of ferrous sulfate, 1g of zinc sulfate, 1g of boric acid, and 1g of manganese sulfate. The above components are dissolved sequentially in 100L of deionized water, heated to 40°C using a magnetic stirrer, and stirred for 40 minutes until a clear and transparent homogeneous solution is formed. This supplementary nutrient solution is applied by foliar spraying, wherein the amino acid chelated nitrogen can be directly absorbed and utilized by the leaves, urea provides a rapid nitrogen source, and the trace elements synergistically promote the metabolic transformation of nitrogen within the eucalyptus tree.

[0017] According to a preferred embodiment of the present invention, in step S1, the depth of the full deep turning is 30-40cm; the depth of the shallow rake is 10-15cm.

[0018] According to a preferred embodiment of the present invention, in step S2, the depth of the application trench is 25-30 cm.

[0019] According to a preferred embodiment of the present invention, in step S3, the radius of the annular groove is 20-25 cm and the depth of the annular groove is 15-20 cm.

[0020] According to a preferred embodiment of the present invention, in step S4, the supplementary nutrient solution is composed of amino acid chelated nitrogen, urea and trace elements.

[0021] According to a preferred embodiment of the present invention, the preparation steps of the MPCM material include:

[0022] A1. Eucalyptus bark and branches are crushed and placed in a tube furnace for programmed temperature pyrolysis under anaerobic conditions: the temperature is raised from room temperature to 340-360℃ and held; then raised to 640-660℃ and held; subsequently, nitrogen and oxygen-containing nitrogen mixtures are alternately introduced into the reaction system for a total of 4-6 cycles; after pyrolysis is completed, biochar is impregnated in potassium hydroxide solution, activated at 64-66℃, then washed with deionized water until neutral, and dried at 104-106℃ to obtain a biochar substrate;

[0023] A2. The biochar substrate was placed in a reactor, and a mixed iron-manganese-zinc metal salt solution was added. The mixture was impregnated under ultrasonic assistance to obtain a mixture. Subsequently, the mixture was transferred to a high-pressure reactor and hydrothermally reacted at 115-125℃. After the reaction was completed, the solid material was collected by filtration, washed with deionized water, and then calcined in a mixed gas of hydrogen and nitrogen at 440-460℃ to obtain biochar material doped with transition metals.

[0024] A3. Transition metal-doped biochar material was dispersed in an anhydrous ethanol solution containing γ-aminopropyltriethoxysilane. Under nitrogen protection, the mixture was refluxed and stirred at 74-76°C. Then, pyrrole monomer and acrylic monomer were added, and ammonium persulfate was added dropwise. The polymerization reaction was carried out in an ice-water bath at 0-5°C. After the reaction was completed, the product was collected by centrifugation, washed alternately with ethanol and deionized water, and finally dried in a vacuum drying oven at 58-62°C to obtain a composite material with smart responsive polymer grafted on its surface.

[0025] A4, the composite material with smart responsive polymer grafted on its surface is placed in an activation solution and cultured in a constant temperature shaker at 34-36℃; finally, the microbial activity is preserved by vacuum freeze-drying technology; the activation solution contains: monosodium glutamate, asparagine, chitosan oligosaccharide, and nitrogen-fixing bacteria and ammonifying bacteria extracted from eucalyptus rhizosphere soil.

[0026] In this invention, the preparation mechanism of the MPCM material is rooted in its meticulously designed multi-level structure and functional integration. The material uses eucalyptus bark and branches as raw materials, transforming them into a biochar matrix through a programmed controlled pyrolysis process. This process not only realizes the resource utilization of forestry waste but, more importantly, constructs a highly porous and stable carbon skeleton with a large specific surface area. This carbon skeleton serves as the basis for subsequent functionalization; its surface is treated with alternating atmospheres to introduce abundant oxygen-containing functional groups. These functional groups act as "anchors," providing reaction sites for subsequent modifications. Subsequently, through impregnation and controlled calcination, transition metal elements such as iron, manganese, and zinc are precisely doped into the biochar matrix and pores. These metal species play multiple roles: they are "microreactors" catalyzing nitrogen conversion, promoting key processes such as the conversion of ammonium nitrogen to nitrate nitrogen; their variable valence states also help regulate the micro-oxygen environment of the rhizosphere. Simultaneously, they act as physical barriers, fixing nitrogen molecules through coordination bonds and electrostatic adsorption, effectively slowing their loss. The third layer of functionality comes from surface-grafted smart responsive polymers. This polymer, based on pyrrole and acrylic acid, forms an environmentally sensitive gel network on the surface of biochar. When eucalyptus roots secrete organic acids or rhizosphere microbial activity causes slight fluctuations in soil pH, the polymer chains intelligently swell or contract, acting like a "smart valve" to regulate the opening and closing of the pores, enabling the on-demand, rate-controlled release of loaded nitrogen or adsorbed nutrients. Finally, this physically modified, chemically doped, and polymer-grafted composite material is cultured in an activation solution rich in specific nutrients and functional microorganisms. Chitosan oligosaccharides and other components, acting as prebiotics for microorganisms, promote the colonization and enrichment of nitrogen-fixing and ammonifying bacteria screened from eucalyptus rhizosphere soil within the porous structure of the material. Vacuum freeze-drying technology induces their dormancy, allowing for long-term preservation. Thus, the MPCM material becomes a multifunctional platform integrating physical adsorption space, chemical catalysis center, intelligent controlled-release system, and microbial habitat, laying the material foundation for fundamentally altering soil nitrogen behavior.

[0027] In this invention, MPCM material is a smart composite material designed to improve nitrogen utilization in eucalyptus trees. Its name originates from the first letters of four key characteristics: M represents multifunctionality, reflecting its comprehensive capabilities integrating physical adsorption, chemical catalysis, and biotransformation; P represents phase change characteristics, indicating that the grafted polypyrrole-acrylic acid copolymer can intelligently regulate nutrient release in response to changes in the rhizosphere environment; C represents composite material, indicating that it consists of multiple components including a biochar substrate, transition metal active sites, smart polymers, and functional microorganisms; and M represents the material's essence. This material uses porous biochar formed from the segmented pyrolysis of eucalyptus bark as a substrate. It promotes nitrogen speciation by loading iron-manganese-zinc transition metals to construct catalytic sites. The grafted smart polymers can achieve controlled nutrient release in response to the rhizosphere environment. Finally, functional microorganisms such as Azotobacter chrysophagus and Bacillus megaterium are immobilized to continuously activate soil nitrogen. As the core of the technology system, this material works in conjunction with measures such as deep soil tillage activation, drip irrigation with microbial activators, and controlled-release nitrogen fertilizer furrow application. Through a four-fold mechanism of "physical adsorption and fixation, chemical catalytic transformation, intelligent controlled-release, and biological nitrogen fixation activation," it constructs a full-chain management solution from soil conditioning and intelligent nutrient supply to microbial-driven transformation and precise leaf nutrition supplementation. This achieves precise regulation of the entire process of nitrogen "controlled release-efficiency enhancement-conversion-replenishment," thereby significantly improving the nitrogen fertilizer utilization efficiency and growth benefits of eucalyptus trees.

[0028] According to a preferred embodiment of the present invention, the preparation steps of the iron-manganese-zinc mixed metal salt solution include: weighing 100g of ferrous sulfate heptahydrate, 60g of manganese sulfate tetrahydrate, and 40g of zinc sulfate heptahydrate, dissolving these salts sequentially in 1000L of deionized water, and stirring at 250r / min for 1h at 25°C using a constant temperature stirrer until a homogeneous mixed solution is formed. The molar ratio of iron, manganese, and zinc in this mixed metal salt solution is 3:2:1. After hydrothermal reaction, uniformly distributed metal oxide active sites can be formed on the surface of biochar. These active sites can catalyze the conversion of ammonium nitrogen to nitrate nitrogen.

[0029] According to a preferred embodiment of the present invention, the preparation steps of the activation solution include: adding 500g of sodium glutamate, 300g of asparagine, and 200g of chitosan oligosaccharide sequentially to 200L of sterile deionized water, and sterilizing in a steam sterilizer at 121°C for 20min. After the solution cools to room temperature, 10L of a mixed inoculum of nitrogen-fixing bacteria and ammonifying bacteria isolated and screened from the rhizosphere soil of healthy eucalyptus trees is added, wherein the nitrogen-fixing bacteria are *Azotobacter chrysophagus*, and the ammonifying bacteria are *Bacillus megaterium*, with the concentration of both bacteria reaching 1×10⁻⁶. 8 CFU / mL. The inoculated activation solution was placed in a constant temperature shaker and cultured at 35℃ and 150r / min for 48h to allow the functional microorganisms to fully proliferate and adapt to the culture medium environment.

[0030] According to a preferred embodiment of the present invention, the vacuum freeze-drying technology includes the following steps: MPCM material loaded with microorganisms is evenly spread in a freeze-drying tray, with a thickness not exceeding 3 cm. First, the material is pre-frozen in an ultra-low temperature freezer at -40°C for 4 hours to completely solidify the internal moisture. Then, it is transferred to a vacuum freeze dryer for primary drying under a vacuum of less than 10 Pa, maintaining the partition temperature at -20°C for 20 hours. Next, secondary drying is performed, gradually increasing the partition temperature to 25°C and maintaining vacuum conditions for another 10 hours. Finally, MPCM finished material with a moisture content of less than 5% is obtained, wherein the survival rate of functional microorganisms remains above 90%.

[0031] According to a preferred embodiment of the present invention, in step A1, the temperature is raised to 340-360°C and held for 30-40 minutes; the temperature is raised to 640-660°C and held for 45-50 minutes; and the activation time at 64-66°C is 6-8 hours.

[0032] According to a preferred embodiment of the present invention, in step A2, the calcination time is 2-4 hours; the hydrogen gas fraction in the hydrogen and nitrogen mixture is 5-10%.

[0033] According to a preferred embodiment of the present invention, in step A3, the reflux stirring time at 74-76°C is 8-10 hours; the polymerization reaction time in the ice-water bath at 0-5°C is 12-14 hours.

[0034] According to a preferred embodiment of the present invention, in step A4, the shaking culture time in a constant temperature shaker at 34-36℃ is 48-50h.

[0035] The beneficial effects of this invention are as follows:

[0036] The method for improving nitrogen utilization in eucalyptus provided by this invention has significant technical effects, mainly reflected in the construction of a complete nitrogen-efficient utilization system. This method, through deep soil tillage and activator treatment before planting, effectively improves the soil's physical structure and enhances its water and fertilizer retention capacity, creating favorable conditions for subsequent efficient nitrogen utilization. The activator, formulated based on soil nitrogen content measurements, can specifically activate insoluble nitrogen in the soil, improving the effectiveness of the soil's existing nitrogen pool. By excavating application trenches and applying specially formulated functional materials, combined with drip irrigation using microbial activators, a rhizosphere microenvironment conducive to root growth and nutrient absorption is constructed. Controlled-release nitrogen fertilizer is applied at different critical growth stages of eucalyptus, mixed with the functional materials, achieving synchronous matching between nitrogen release and eucalyptus nutrient requirements. The established soil-plant joint monitoring system can promptly grasp the nitrogen nutrition status of eucalyptus, ensuring a continuous and stable nitrogen supply through precise foliar application.

[0037] The core innovation of this method lies in the development of a multifunctional composite material. This material, based on biochar prepared from eucalyptus tree residues, achieves the resource utilization of forestry waste. Through precisely controlled pyrolysis and surface modification, the material possesses a rich porous structure and numerous surface active sites. Doping with transition metal elements further enhances the material's catalytic performance and adsorption capacity, providing a favorable reaction interface for nitrogen conversion. The surface-grafted smart responsive polymer can adjust the material's properties according to changes in environmental conditions, achieving intelligent regulation of the nitrogen release rate. Of particular note is the construction of a stable microbial community by loading functional microorganisms such as nitrogen-fixing bacteria and ammonifying bacteria, continuously promoting nitrogen conversion and fixation in the soil and forming a long-term nitrogen supply mechanism.

[0038] This method demonstrates several significant advantages in practical applications. First, by systematically combining soil improvement, materials science, and microbial technology, it solves the problem of severe nitrogen loss in traditional fertilization methods. Second, it innovatively establishes a comprehensive monitoring and control system from soil to plant, achieving precise management of nitrogen nutrients and significantly improving nitrogen fertilizer utilization. Third, utilizing eucalyptus residues to prepare functional materials reduces production costs and realizes internal material cycling within the forestry production system, aligning with the concept of green and sustainable development. Finally, this method is simple to operate, easy to promote, and can effectively improve the production efficiency of eucalyptus plantations while reducing nitrogen loss and environmental pollution, possessing significant ecological and economic value. Long-term practical verification shows that this method can significantly improve nitrogen utilization and substantially increase eucalyptus growth, providing reliable technical support for the sustainable development of eucalyptus plantations. Detailed Implementation

[0039] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content.

[0040] The following is information on domestic suppliers of the relevant equipment and materials:

[0041] The γ-aminopropyltriethoxysilane was purchased from Nanjing Chenggong Organosilicon Materials Co., Ltd.

[0042] The pyrrole monomer was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0043] The acrylic acid monomer was purchased from Wanhua Chemical Group Co., Ltd.

[0044] The ammonium persulfate was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0045] Preparation Example 1

[0046] A method for preparing an activator solution is provided. Accurately weigh 50g of citric acid, 80g of humic acid, and 5g of ammonium molybdate. Dissolve these substances sequentially in 1000L of purified water. Stir using a mechanical stirrer at 300 rpm for 30 minutes until all components are completely dissolved to form a homogeneous solution. In this activator, citric acid, as a low-molecular-weight organic acid, can activate fixed phosphates and trace elements in the soil. Humic acid improves soil aggregate structure by complexing metal ions with its functional groups. Ammonium molybdate provides essential molybdenum for soil microorganisms and participates in biological nitrogen fixation as a key component of nitrogenase. When using, spray 3-5m³ of the prepared activator solution per hectare based on soil testing results, and then lightly harrow to mix.

[0047] Preparation Example 2

[0048] A method for preparing a microbial activator is provided. 0.5g of N-acylhomoserine lactone, 120g of trehalose, and 200g of potassium dihydrogen phosphate are accurately weighed and dissolved together in 1000L of irrigation water. The solution is then treated with an ultrasonic disperser for 20 minutes to ensure complete dissolution. N-acylhomoserine lactone acts as a quorum sensing signaling molecule, promoting the formation of beneficial rhizosphere microbial communities. Trehalose provides an efficient carbon source for microorganisms and enhances their stress resistance. Potassium dihydrogen phosphate provides phosphorus and potassium nutrients and adjusts the solution pH to a slightly acidic-neutral environment. This microbial activator is applied via a drip irrigation system, with 5-8L applied per eucalyptus seedling.

[0049] Preparation Example 3

[0050] A method for preparing controlled-release nitrogen fertilizer is provided, using ordinary urea as the base raw material and modifying it using fluidized bed coating technology. The specific coating material composition includes 40g of polyurethane resin, 15g of bentonite, and 10g of diatomaceous earth. These coating materials are uniformly coated onto the surface of 1000g of urea granules, forming a controlled-release layer with a thickness of 50-80μm. This controlled-release nitrogen fertilizer utilizes the microporous structure and hydrophilic-hydrophobic balance of the coating material to achieve slow nitrogen release, matching the nitrogen release cycle with the eucalyptus tree growth cycle, effectively reducing nitrogen volatilization and leaching losses.

[0051] Preparation Example 4

[0052] A method for preparing a nutrient supplement solution is provided. 30g of amino acid chelated nitrogen and 50g of urea are accurately weighed, and 5g of a trace element combination is added, including 2g of ferrous sulfate, 1g of zinc sulfate, 1g of boric acid, and 1g of manganese sulfate. The above components are dissolved sequentially in 100L of deionized water, heated to 40℃ using a magnetic stirrer, and stirred for 40 minutes until a clear, transparent, homogeneous solution is formed. This nutrient supplement solution is applied via foliar spraying. The amino acid chelated nitrogen can be directly absorbed and utilized by the leaves, urea provides a rapid nitrogen source, and the trace elements synergistically promote the metabolic transformation of nitrogen within the eucalyptus tree.

[0053] Preparation Example 5

[0054] A method for preparing an iron-manganese-zinc mixed metal salt solution is provided. 100g of ferrous sulfate heptahydrate, 60g of manganese sulfate tetrahydrate, and 40g of zinc sulfate heptahydrate are weighed and dissolved sequentially in 1000L of deionized water. The solution is stirred at 250 rpm for 1 hour at 25°C using a constant-temperature stirrer until a homogeneous mixed solution is formed. The molar ratio of iron, manganese, and zinc in this mixed metal salt solution is 3:2:1. After hydrothermal reaction, uniformly distributed metal oxide active sites can be formed on the surface of biochar. These active sites can catalyze the conversion of ammonium nitrogen to nitrate nitrogen.

[0055] Preparation Example 6

[0056] A method for preparing an activation solution is provided. 500g of sodium glutamate, 300g of asparagine, and 200g of chitosan oligosaccharide are added sequentially to 200L of sterile deionized water, and the solution is sterilized in a steam sterilizer at 121℃ for 20min. After the solution cools to room temperature, 10L of a mixed inoculum of nitrogen-fixing bacteria and ammonifying bacteria isolated and screened from the rhizosphere soil of healthy eucalyptus trees is inoculated. The nitrogen-fixing bacteria are *Azotobacter chrysophagus*, and the ammonifying bacteria are *Bacillus megaterium*, with both bacteria reaching a concentration of 1×10⁻⁶. 8 CFU / mL. The inoculated activation solution was placed in a constant temperature shaker and cultured at 35℃ and 150r / min for 48h to allow the functional microorganisms to fully proliferate and adapt to the culture medium environment.

[0057] Example 1

[0058] Before planting eucalyptus trees, the forest land was thoroughly tilled to a depth of 35 cm per square meter. Soil samples were taken to determine the initial ammonium nitrogen, nitrate nitrogen, and soluble organic nitrogen content. An activator solution was then prepared: 3 L of a solution containing 50 g citric acid, 80 g humic acid, and 5 g ammonium molybdate was sprayed per square meter, followed by shallow raking to a depth of 12 cm. Application trenches were dug 28 cm deep along the planned planting rows of eucalyptus trees. MPCM material was mixed with soil at a mass ratio of 1:5 and applied to the bottom of the trenches, using 200 g of MPCM material per square meter. The mixture was then covered with fine soil for isolation. 5 L of a microbial activator containing 0.5 g N-acylhomoserine lactone, 120 g trehalose, and 200 g potassium dihydrogen phosphate was applied per square meter via a drip irrigation system. When planting eucalyptus seedlings, it was ensured that the seedling roots had direct contact with the MPCM material layer but were not completely enveloped by it. Controlled-release nitrogen fertilizer was applied to eucalyptus trees at the planting, rapid growth, and pre-canopy closure stages, with 150g applied per tree each time. During fertilization, the controlled-release nitrogen fertilizer was pre-mixed with MPCM material at a mass ratio of 3:2, and the mixture was applied to a circular trench with a radius of 22cm and a depth of 18cm dug around the eucalyptus roots. Soil solutions from the rhizosphere were collected periodically using buried soil solution extractors, and changes in ammonium and nitrate nitrogen concentrations were detected using a portable nitrogen analyzer. Leaf nitrogen nutrition status was monitored using a rapid nitrogen content detector for eucalyptus leaves. When the monitored indicators fell below the threshold, a supplementary nutrient solution consisting of 30g amino acid chelated nitrogen, 50g urea, and 5g trace elements was sprayed on the leaves at a rate of 2L per square meter. The preparation steps of the MPCM material include: Step A1: 500g of eucalyptus bark and branches are crushed and placed in a tube furnace for programmed temperature pyrolysis under anaerobic conditions: the temperature is raised from room temperature to 350℃ and held for 35min, then raised to 650℃ and held for 48min; subsequently, nitrogen and a nitrogen-oxygen mixture are alternately introduced into the reaction system for a total of 5 cycles; after pyrolysis is completed, biochar is impregnated in 1L of 0.1mol / L potassium hydroxide solution, activated at 65℃ for 7h, then washed with deionized water until neutral, and dried at 105℃ to obtain the biochar substrate. In step A2, the biochar substrate was placed in a reactor, and 1 L of a mixed iron-manganese-zinc metal salt solution containing 100 g of ferrous sulfate heptahydrate, 60 g of manganese sulfate tetrahydrate, and 40 g of zinc sulfate heptahydrate was added. The mixture was then impregnated under ultrasonic assistance. Subsequently, the mixture was transferred to a high-pressure reactor and hydrothermally reacted at 120 °C for 3 h. After the reaction, the solid material was collected by filtration, washed with deionized water, and then calcined at 450 °C for 3 h in a mixed gas of hydrogen and nitrogen with a hydrogen integral of 8% to obtain the transition metal-doped biochar material.In step A3, the transition metal-doped biochar material was dispersed in 1 L of anhydrous ethanol solution containing 50 g of γ-aminopropyltriethoxysilane and stirred under nitrogen protection at 75 °C for 9 h under reflux. Then, 30 g of pyrrole monomer and 20 g of acrylic acid monomer were added, followed by dropwise addition of 40 g of ammonium persulfate. The polymerization reaction was carried out in an ice-water bath at 2 °C for 13 h. After the reaction was completed, the product was collected by centrifugation, washed alternately with ethanol and deionized water, and finally dried in a vacuum drying oven at 60 °C to obtain a composite material with a surface grafted with a smart responsive polymer. In step A4, the composite material with the surface grafted with the smart responsive polymer was placed in 2 L of activation solution containing 500 g of monosodium glutamate, 300 g of asparagine, and 200 g of chitosan oligosaccharide, and 1 × 10⁻⁶ nitrogen-fixing bacteria and ammonifying bacteria extracted from eucalyptus rhizosphere soil were added. 8 The microbial activity was preserved by vacuum freeze-drying technology. The activator solution, microbial activator, controlled-release nitrogen fertilizer supplementary nutrient solution, iron-manganese-zinc mixed metal salt solution and activation solution in this embodiment were prepared using the substances obtained in Preparation Examples 1-6.

[0059] Example 2

[0060] The specific implementation method is the same as in Example 1, except that before planting eucalyptus trees, the forest land is thoroughly tilled to a depth of 32cm per square meter. Soil samples are taken to determine the initial ammonium nitrogen, nitrate nitrogen, and soluble organic nitrogen content. An activator solution is then prepared: 2.5L of a solution containing 45g citric acid, 75g humic acid, and 4g ammonium molybdate is sprayed per square meter, followed by shallow raking to a depth of 11cm. Application trenches are dug to a depth of 26cm along the planned planting rows of eucalyptus trees. MPCM material is mixed with soil at a mass ratio of 1:5 and applied to the bottom of the trench, using 180g of MPCM material per square meter. This is then covered with fine soil for isolation. 4L of a microbial activator containing 0.4g N-acylhomoserine lactone, 110g trehalose, and 180g potassium dihydrogen phosphate is applied per square meter via a drip irrigation system. When planting eucalyptus seedlings, it is ensured that the seedling roots have direct contact with the MPCM material layer but are not completely enveloped by it. Controlled-release nitrogen fertilizer was applied to each eucalyptus tree at the planting, rapid growth, and pre-canopy closure stages, at a rate of 130g per tree per application. During fertilization, the controlled-release nitrogen fertilizer was pre-mixed with MPCM material at a mass ratio of 3:2, and the mixture was then applied to a circular trench with a radius of 21cm and a depth of 17cm dug around the eucalyptus roots. Soil solutions from the rhizosphere were collected periodically using buried soil solution extractors, and changes in ammonium and nitrate nitrogen concentrations were detected using a portable nitrogen analyzer. Leaf nitrogen nutrition status was monitored using a rapid nitrogen content detector for eucalyptus leaves. When the monitored indicators fell below the threshold, a supplementary nutrient solution consisting of 25g amino acid chelated nitrogen, 45g urea, and 4g trace elements was sprayed on the leaves at a rate of 1.5L per square meter. The preparation steps of the MPCM material include: Step A1: 450g of eucalyptus bark and branches are crushed and placed in a tube furnace for programmed temperature pyrolysis under anaerobic conditions: the temperature is raised from room temperature to 340℃ and held for 38 min, then raised to 640℃ and held for 46 min; subsequently, nitrogen and a nitrogen-oxygen mixture are alternately introduced into the reaction system for a total of 4 cycles; after pyrolysis is completed, biochar is impregnated in 1L of 0.1mol / L potassium hydroxide solution, activated at 64℃ for 6.5h, then washed with deionized water until neutral, and dried at 104℃ to obtain the biochar substrate. In step A2, the biochar substrate was placed in a reactor, and 1 L of a mixed iron-manganese-zinc metal salt solution containing 90 g of ferrous sulfate heptahydrate, 55 g of manganese sulfate tetrahydrate, and 35 g of zinc sulfate heptahydrate was added. The mixture was then impregnated under ultrasonic assistance. Subsequently, the mixture was transferred to a high-pressure reactor and hydrothermally reacted at 115 °C for 2.5 h. After the reaction, the solid material was collected by filtration, washed with deionized water, and then calcined at 440 °C for 2 h in a mixed gas of hydrogen and nitrogen with a hydrogen integral of 5% to obtain the transition metal-doped biochar material.In step A3, the transition metal-doped biochar material was dispersed in 1 L of anhydrous ethanol solution containing 45 g of γ-aminopropyltriethoxysilane and refluxed at 74 °C for 8.5 h under nitrogen protection. Then, 25 g of pyrrole monomer and 15 g of acrylic acid monomer were added, followed by dropwise addition of 35 g of ammonium persulfate. The polymerization reaction was carried out in an ice-water bath at 0 °C for 12.5 h. After the reaction was completed, the product was collected by centrifugation, washed alternately with ethanol and deionized water, and finally dried in a vacuum drying oven at 58 °C to obtain a composite material with a surface grafted with a smart responsive polymer. In step A4, the composite material with the surface grafted with the smart responsive polymer was placed in 2 L of activation solution containing 450 g of monosodium glutamate, 280 g of asparagine, and 180 g of chitosan oligosaccharide, and 1 × 10⁻⁶ nitrogen-fixing bacteria and ammonifying bacteria extracted from eucalyptus rhizosphere soil were added. 8 The microbial activity was preserved by vacuum freeze-drying technology. The activator solution, microbial activator, controlled-release nitrogen fertilizer supplementary nutrient solution, iron-manganese-zinc mixed metal salt solution and activation solution in this embodiment were prepared using the substances obtained in Preparation Examples 1-6.

[0061] Example 3

[0062] The specific implementation method is the same as in Example 1, except that before planting eucalyptus trees, the forest land is thoroughly tilled to a depth of 38cm per square meter. Soil samples are taken to determine the initial ammonium nitrogen, nitrate nitrogen, and soluble organic nitrogen content. An activator solution is then prepared: 3.5L of a solution containing 55g citric acid, 85g humic acid, and 6g ammonium molybdate is sprayed per square meter, followed by shallow raking to a depth of 13cm. Application trenches are dug to a depth of 30cm along the planned planting rows of eucalyptus trees. MPCM material is mixed with soil at a mass ratio of 1:5 and applied to the bottom of the trench, using 220g of MPCM material per square meter. This is then covered with fine soil for isolation. 6L of a microbial activator containing 0.6g N-acylhomoserine lactone, 130g trehalose, and 220g potassium dihydrogen phosphate is applied per square meter via a drip irrigation system. When planting eucalyptus seedlings, it is ensured that the seedling roots have direct contact with the MPCM material layer but are not completely enveloped by it. Controlled-release nitrogen fertilizer was applied to eucalyptus trees at the planting, rapid growth, and pre-canopy closure stages, with 170g applied per tree each time. During fertilization, the controlled-release nitrogen fertilizer was pre-mixed with MPCM material at a mass ratio of 3:2, and the mixture was applied to a circular trench with a radius of 25cm and a depth of 20cm dug around the eucalyptus roots. Soil solutions from the rhizosphere were collected periodically using buried soil solution extractors, and changes in ammonium and nitrate nitrogen concentrations were detected using a portable nitrogen analyzer. Leaf nitrogen nutrition status was monitored using a rapid nitrogen content detector for eucalyptus leaves. When the monitored indicators fell below the threshold, a supplementary nutrient solution consisting of 35g amino acid chelated nitrogen, 55g urea, and 6g trace elements was sprayed on the leaves at a rate of 2.5L per square meter. The preparation steps of the MPCM material include: Step A1: 550g of eucalyptus bark and branches are crushed and placed in a tube furnace for programmed temperature pyrolysis under anaerobic conditions: the temperature is raised from room temperature to 360℃ and held for 40min, then raised to 660℃ and held for 50min; subsequently, nitrogen and a nitrogen-oxygen mixture are alternately introduced into the reaction system for a total of 6 cycles; after pyrolysis is completed, biochar is impregnated in 1L of 0.1mol / L potassium hydroxide solution, activated at 66℃ for 8h, then washed with deionized water until neutral, and dried at 106℃ to obtain the biochar substrate. In step A2, the biochar substrate was placed in a reactor, and 1 L of a mixed iron-manganese-zinc metal salt solution containing 110 g of ferrous sulfate heptahydrate, 65 g of manganese sulfate tetrahydrate, and 45 g of zinc sulfate heptahydrate was added. The mixture was then impregnated under ultrasonic assistance. Subsequently, the mixture was transferred to a high-pressure reactor and hydrothermally reacted at 125 °C for 4 h. After the reaction was completed, the solid material was collected by filtration, washed with deionized water, and then calcined at 460 °C for 4 h in a mixed gas of hydrogen and nitrogen with a hydrogen integral of 10% to obtain the transition metal-doped biochar material.In step A3, the transition metal-doped biochar material was dispersed in 1 L of anhydrous ethanol solution containing 55 g of γ-aminopropyltriethoxysilane and stirred under nitrogen protection at 76 °C for 10 h under reflux. Then, 35 g of pyrrole monomer and 25 g of acrylic monomer were added, and 45 g of ammonium persulfate was added dropwise. The polymerization reaction was carried out in an ice-water bath at 5 °C for 14 h. After the reaction was completed, the product was collected by centrifugation, washed alternately with ethanol and deionized water, and finally dried in a vacuum drying oven at 62 °C to obtain a composite material with smart responsive polymer grafted on its surface. In step A4, the composite material grafted with the smart responsive polymer was placed in 2L of activation solution containing 550g of sodium glutamate, 320g of asparagine, and 220g of chitosan oligosaccharide. 1×10^8 CFU / mL of nitrogen-fixing bacteria and ammonifying bacteria extracted from eucalyptus rhizosphere soil were added, and the mixture was cultured in a shaker at 36℃ for 50h. Finally, the microbial activity was preserved using vacuum freeze-drying technology. The activator solution, microbial activator, controlled-release nitrogen fertilizer supplemental nutrient solution, iron-manganese-zinc mixed metal salt solution, and activation solution in this embodiment were prepared using the substances obtained in Preparation Examples 1-6.

[0063] Comparative Example 1

[0064] The specific implementation method is the same as in Example 1, except that the transition metal doping step is omitted in the preparation of MPCM materials, and the biochar substrate is not impregnated with iron-manganese-zinc solution and subjected to hydrothermal reaction, but directly subjected to polymer grafting and microbial loading. Specifically, after obtaining the biochar substrate in step A1, polymer grafting in step A3 is performed directly, followed by microbial loading in step A4; the activator solution, microbial activator, controlled-release nitrogen fertilizer supplemental nutrient solution, iron-manganese-zinc mixed metal salt solution, and activation solution in this comparative example are the substances obtained in Preparation Examples 1-6.

[0065] Comparative Example 2

[0066] The specific implementation method is the same as in Example 1, except that the smart polymer grafting step is omitted in the preparation of MPCM materials, and the transition metal-doped biochar material is directly loaded with microorganisms without undergoing silane treatment and pyrrole acrylic acid polymerization. Specifically, after obtaining the transition metal-doped biochar material in step A2, the microbial loading in step A4 is carried out directly; the activator solution, microbial activator, controlled-release nitrogen fertilizer supplementary nutrient solution, iron-manganese-zinc mixed metal salt solution, and activation solution in this comparative example are the substances obtained in Preparation Examples 1-6.

[0067] Comparative Example 3

[0068] The specific implementation method is the same as in Example 1, except that the functional microbial loading step is omitted in the preparation of MPCM materials, and the composite material after surface grafting of polymer is not subjected to activation solution culture and vacuum freeze-drying. Specifically, after obtaining the composite material with surface grafting polymer in step A3, step A4 is not performed, and it is used directly as MPCM material; the activator solution, microbial activator, controlled-release nitrogen fertilizer supplementary nutrient solution, iron-manganese-zinc mixed metal salt solution and activation solution in this comparative example are the substances obtained in Preparation Examples 1-6.

[0069] Performance testing

[0070] The above Examples 1-3 and Comparative Examples 1-3, based on the method for improving nitrogen use efficiency in eucalyptus trees, were subjected to performance tests according to the following method, which included the following steps:

[0071] To evaluate the practical effectiveness of the method of this invention, experimental forest plots were set up under the same site conditions, and eucalyptus cultivation and management were carried out according to the technical schemes of Examples 1-3 and Comparative Examples 1-3, respectively. Each treatment had 3 replicate plots, each with an area of ​​100 square meters and 50 eucalyptus seedlings planted. Systematic monitoring was carried out during the eucalyptus growth cycle (12 months): rhizosphere soil solution was collected every 15 days using a soil solution sampler, and the concentrations of ammonium nitrogen and nitrate nitrogen were measured using a HACH DR3900 portable nitrogen analyzer; the total nitrogen content of leaves was measured monthly using a YLS-N1 eucalyptus leaf nitrogen content rapid detector; soil samples from the 0-20 cm soil layer were collected at 6 months and 12 months after planting, and the total nitrogen content of the soil was determined by the Kjeldahl method, and the alkaline nitrogen content of the soil was determined by the alkaline diffusion method; at 12 months after planting, the height, diameter at breast height (DBH), and biomass of eucalyptus trees were measured, and nitrogen fertilizer utilization rate was calculated. The nitrogen fertilizer utilization rate was calculated using the formula: (nitrogen uptake by plants in the nitrogen-applied area - nitrogen uptake by plants in the non-nitrogen-applied area) / nitrogen application rate × 100%. All test data were analyzed using SPSS 23.0 software for variance analysis, and multiple comparisons were performed using Duncan's method (p < 0.05).

[0072] Test results:

[0073] Table 1: Test results of each embodiment and comparative example

[0074]

[0075] Note: The data in the table are the average of three replicates. Different letters after the data in the same row indicate significant differences (p<0.05).

[0076] As shown in Table 1, Examples 1-3 were significantly superior to Comparative Examples 1-3 in terms of nitrogen fertilizer utilization rate, soil nitrogen content, leaf nitrogen nutrition status, and eucalyptus growth indicators. Example 1 achieved the highest nitrogen fertilizer utilization rate of 68.5%, which was 23.2%, 25.8%, and 29.6% higher than Comparative Examples 1-3, respectively; the total soil nitrogen content reached 1.85 g / kg, significantly higher than the 1.35 g / kg, 1.28 g / kg, and 1.21 g / kg of Comparative Examples 1-3; at the same time, eucalyptus tree height, diameter at breast height, and biomass also showed significant advantages. This significant difference proves that the present invention effectively solves the problems existing in the prior art through the synergistic effect of the triple functions of MPCM materials: Comparative Example 1 lacked nitrogen form conversion ability due to the lack of transition metal doping; Comparative Example 2 lost nutrient controlled release function due to the lack of intelligent polymer grafting; and Comparative Example 3 weakened biological nitrogen fixation ability due to the lack of functional microorganisms. Examples 1-3, through complete material design and system management schemes, achieved synergistic effects of intelligent controlled release, catalytic conversion, and biological activation of nitrogen, increasing nitrogen fertilizer utilization rate from less than 40% in traditional technologies to over 65%. At the same time, it significantly improved soil nitrogen pool capacity and eucalyptus nitrogen absorption efficiency, fundamentally solving the technical problems of low nitrogen fertilizer utilization, easy loss, and environmental pollution in eucalyptus plantations.

[0077] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method of increasing nitrogen use efficiency in Eucalyptus, characterised by, The method comprises the following steps: S1, before eucalyptus planting, the forest land is fully deep ploughed, and soil samples are taken to determine the initial ammonium nitrogen, nitrate nitrogen and soluble organic nitrogen content; according to the determination results, an activator solution containing citric acid, humic acid and ammonium molybdate is prepared and uniformly sprayed on the soil surface, and then shallowly raked to mix evenly; S2, a MPCM material is mixed with soil and applied to the bottom of the trench, and then covered with fine soil to isolate; subsequently, a microbial activator containing N-acyl homoserine lactone, trehalose and potassium dihydrogen phosphate is applied through a drip irrigation system; when the eucalyptus seedling is planted, the eucalyptus seedling root system is ensured to have direct contact with the MPCM material layer, but not completely wrapped around the eucalyptus seedling root system; S3, during the eucalyptus planting period, fast-growing period and pre-closing period, controlled-release nitrogen fertilizer is applied; when the fertilizer is applied, the controlled-release nitrogen fertilizer is mixed with the MPCM material in advance to obtain a nitrogen fertilizer mixture, and the nitrogen fertilizer mixture is applied to the eucalyptus rhizosphere by digging a ring-shaped trench; S4, by burying soil solution extractors, rhizosphere soil solution is collected regularly, and a portable nitrogen analyzer is used to detect the concentration changes of ammonium nitrogen and nitrate nitrogen; a eucalyptus leaf nitrogen content rapid detection instrument is used to monitor the leaf nitrogen nutrition status; when the monitoring index is lower than the threshold value, a supplementary nutrient solution composed of amino acid chelated nitrogen, urea and trace elements is sprayed on the leaves to realize precise supply of nitrogen to the eucalyptus.

2. The method of increasing nitrogen use efficiency in eucalyptus of claim 1, wherein, In step S1, the depth of the full deep ploughing is 30-40 cm; the depth of the shallow raking is 10-15 cm.

3. The method of increasing nitrogen use efficiency in eucalyptus of claim 1, wherein, In step S2, the depth of the trench is 25-30 cm.

4. The method of increasing nitrogen use efficiency in eucalyptus of claim 1, wherein, In step S3, the radius of the ring-shaped trench is 20-25 cm, and the depth of the ring-shaped trench is 15-20 cm.

5. The method of increasing nitrogen use efficiency in eucalyptus of claim 1, wherein, In step S4, the supplementary nutrient solution is composed of amino acid chelated nitrogen, urea and trace elements.

6. The method of increasing nitrogen use efficiency in eucalyptus of any one of claims 1-5, wherein, The preparation steps of the MPCM material comprise: A1, eucalyptus bark and branches are crushed and placed in a tube furnace, and pyrolysis is carried out under anaerobic conditions through programmed temperature rising: from room temperature to 340-360 DEG C and kept; then raised to 640-660 DEG C and kept; subsequently, nitrogen gas and oxygen-containing nitrogen gas mixture gas are alternately introduced into the reaction system, and a total of 4-6 cycles are carried out; after pyrolysis is completed, the biochar is immersed in a potassium hydroxide solution, activated at 64-66 DEG C, then washed to neutral with deionized water, and dried at 104-106 DEG C to obtain a biochar base; A2, the biochar base is placed in a reactor, and an iron-manganese-zinc mixed metal salt solution is added and immersed under ultrasonic assistance to obtain a mixture; subsequently, the mixture is transferred to a high-pressure reaction kettle and subjected to hydrothermal reaction at 115-125 DEG C; after the reaction is completed, the solid material is collected by filtration, washed with deionized water, and then calcined in a hydrogen and nitrogen gas mixture to 440-460 DEG C to obtain a transition metal-doped biochar material; A3, the transition metal doped biochar material is dispersed in anhydrous ethanol solution containing γ-aminopropyl triethoxysilane, under nitrogen protection, reflux stirring at 74-76℃, then adding pyrrole monomer and acrylic acid monomer, and dropping ammonium persulfate, polymerization reaction in 0-5℃ ice water bath; after the reaction is completed, the product is collected by centrifugation, washed with ethanol and deionized water alternately, and finally dried in a vacuum drying oven at 58-62℃ to obtain a composite material grafted with intelligent responsive polymer on the surface; A4, the composite material grafted with intelligent responsive polymer on the surface is placed in an activation solution, and cultured in a constant temperature shaking bed at 34-36℃; finally, the microbial activity is preserved by vacuum freeze-drying technology; the activation solution contains sodium glutamate, asparagine, chitooligosaccharide, and nitrogen-fixing bacteria and ammonifying bacteria extracted from eucalyptus rhizosphere soil.

7. The method of increasing nitrogen use efficiency in eucalyptus of claim 6, wherein, In step A1, the temperature is raised to 340-360℃ and maintained for 30-40min; the temperature is raised to 640-660℃ and maintained for 45-50min; and the activation time at 64-66℃ is 6-8h.

8. The method of increasing nitrogen use efficiency in eucalyptus of claim 6, wherein, In step A2, the calcination time is 2-4h; and the hydrogen volume fraction in the hydrogen and nitrogen mixed gas is 5-10%.

9. The method of increasing nitrogen use efficiency in eucalyptus of claim 6, wherein, In step A3, the reflux stirring time at 74-76℃ is 8-10h; and the polymerization reaction time in 0-5℃ ice water bath is 12-14h.

10. The method of increasing nitrogen use efficiency in eucalyptus of claim 6, wherein, In step A4, the oscillation culture time in a constant temperature shaking bed at 34-36℃ is 48-50h.

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