Nut lignin-based rhizosphere micro-ecological conditioning fertilizer and preparation method thereof

Abstract

The present application relates to the technical field of fertilizer, in particular to a nut lignin-based rhizosphere micro-ecological conditioner and a preparation method thereof, which is made of modified lignin carrier, urea, potassium sulfate, calcium magnesium phosphate fertilizer, potassium humate and bentonite, wherein the modified lignin carrier is a grafting cross-linking product of epoxidized alkali lignin with (2S)-2,6-bis[(aminocarbonyl)amino]hexanoic acid, (2S)-2-[(aminocarbonyl)amino]-3-{[dihydroxy(oxido)-lambda 5 phosphorusyl]oxy}propanoic acid and N-(aminocarbonyl)-N-(carboxymethyl)glycine, with the ring-opening of the epoxy group by the carboxyl group to form a beta-hydroxy ester bond, and the preparation method comprises six processes such as lignin pretreatment and epoxidation, the release of nitrogen and phosphorus is triggered by the esterase, N-carbamoyl hydrolase and cluster root acid phosphatase in the rhizosphere of nuts, and the negative effect of phenolic acid and iron-aluminum complexation is eliminated by the closure of phenolic hydroxyl.

Description

Technical Field

[0001] This invention relates to the field of fertilizer technology, specifically to a nut lignin-based rhizosphere microecological conditioning fertilizer and its preparation method, which is suitable for rhizosphere fertilization of macadamia nuts and other woody nuts in southern producing areas such as Yunnan and Guangxi. Background Technology

[0002] Macadamia nuts and other southern woody nut crops are perennial plants belonging to the Proteaceae family. Their root systems exhibit the typical cluster root structure of Proteaceae plants. Cluster roots form abundantly under low phosphorus induction, secreting carboxylic acids such as citric acid and malic acid, as well as acid phosphatase. They autonomously extract phosphorus by dissolving and hydrolyzing fixed phosphorus and organic phosphorus in the rhizosphere soil. However, when the concentration of water-soluble phosphorus in the soil solution increases, cluster root formation is strongly inhibited. Excessive phosphorus supply can also lead to decreased plant biomass and phosphorus toxicity symptoms such as brownish-gray necrosis of young leaves. Southern nut orchards are mostly distributed in acidic red soil areas with a soil pH of 4.5–5.5 and high iron and aluminum oxide content. Water-soluble phosphorus is rapidly fixed by iron and aluminum after application, while nitrogen is easily leached away by heavy rainfall. Therefore, the health of the rhizosphere soil microecology and the continuous supply of nutrients have a decisive impact on the green and high yield of nuts. However, traditional nut fertilizers are mainly fast-acting chemical fertilizers, which have very limited ability to regulate the rhizosphere soil microecology of woody nuts and support the long-term continuous supply of nutrients.

[0003] Using industrial lignin as a slow-release carrier to prepare slow-release fertilizers has become a research hotspot in recent years. In existing technologies, the slow-release mechanisms of lignin-based slow-release fertilizers can be summarized into three categories: chemical modification (ammonia oxidation, Mannich reaction), coating, and chelation. For example, Chinese patent CN106478295A discloses a method for preparing a phosphorylated lignin-based slow-release fertilizer with chelated trace elements. This method involves reacting lignin sequentially with formaldehyde and an amination reagent via a Mannich reaction to obtain amination lignin, then reacting it with chlorohydroxyphosphate prepared by reacting a phosphorylation reagent with epichlorohydrin to obtain phosphorylated lignin. Finally, nitrogen, phosphorus, potassium, and trace elements are chelated and fixed onto this phosphorylated lignin at 60–90 °C. The slow-release mechanism of this method relies on the release of amino and imine groups that are released with the degradation of lignin itself, as well as the steric hindrance effect of the lignin three-dimensional network. In the examples, the release rates of nitrogen, phosphorus, and potassium reached 53% to 75% within 120 h. The timescale of nutrient release is determined by the swelling and degradation of the lignin network and is independent of the nutrient demand rhythm of the crop rhizosphere. At the same time, the Mannich reaction occurs at the ortho position of the phenolic hydroxyl group, and all the free phenolic hydroxyl groups of lignin are retained. These phenolic hydroxyl groups complex with iron and aluminum ions in acidic red soil and form precipitates on the carrier surface, fixing phosphorus to the carrier surface. The phenolic acids produced by lignin degradation have an inhibitory effect on roots and rhizosphere bacteria.

[0004] Chinese patent CN117263749A discloses a method for preparing a modified lignin-based sprayable slow-release urea fertilizer. This method involves forming a complex with maleic anhydride-modified lignin sulfonate, pre-oxidized kitchen waste, and urea, followed by encapsulation of the complex within a polyacrylate network via acrylate monomer emulsion polymerization. This method achieves slow release by physically encapsulating urea within a double-layer polymer network. In the examples, the cumulative release rate of urea in water after 96 hours was still 56.62%–81.37%. However, it introduces polyacrylate, which is difficult to degrade in soil, and does not contain phosphorus or potassium nutrients, nor does it possess conditioning functions for rhizosphere microorganisms. Furthermore, techniques such as introducing nitrogen-containing groups into lignin via ammonia oxidation to prepare lignin nitrogen fertilizer and chelating trace elements with lignin sulfonate have also been reported. However, these methods do not change the fundamental mode of relying on lignin skeleton degradation or network swelling as the driving force for release.

[0005] Regarding fertilizers specifically for macadamia nuts, Chinese patent CN102807410A discloses a compound fertilizer for promoting the vigorous growth of macadamia seedlings. It is formulated from borax, monoammonium phosphate, copper sulfate, zinc phosphate, and potassium sulfate in a specific ratio. All components are readily available inorganic salts, with phosphorus provided in the form of water-soluble monoammonium phosphate. Upon application to acidic red soil, this phosphorus is rapidly fixed by iron and aluminum, and the sudden increase in water-soluble phosphorus inhibits the formation of clustered roots. It lacks slow-release and rhizosphere microecological conditioning functions. Chinese patent CN109804765B discloses a method for applying a bio-fertilizer to macadamia nuts. This method involves applying organic fertilizer containing Bacillus licheniformis and Bacillus megaterium, along with a high-nitrogen, low-phosphorus compound fertilizer or slow-release fertilizer. While this method acknowledges the sensitivity of macadamia nuts to phosphorus, the exogenously inoculated Bacillus lacks a continuous carbon source in acidic red soil, making colonization difficult. Furthermore, there is no material or temporal coupling between the inoculants and the slow-release fertilizer, making sustained improvement in the rhizosphere microecology challenging.

[0006] In summary, existing lignin-based slow-release fertilizers generally use the degradation or network swelling of the lignin skeleton as the clock for nutrient release, decoupling nutrient release from rhizosphere biological activity. Free phenolic hydroxyl groups of lignin are retained as beneficial chelating sites, ignoring their negative effects of complexing iron and aluminum and releasing phenolic acids in acidic red soil. Different nut plantation soil conditions have significantly different requirements for rhizosphere microecological conditioning fertilizers, and there is a lack of differentiated preparation processes that can adjust release behavior according to soil conditions. Furthermore, there is a lack of fertilizer preparation processes that deeply integrate lignin-based slow-release carriers with rhizosphere microecological conditioning functions at the molecular level. Therefore, how to make the release rhythm of nitrogen and phosphorus in lignin-based conditioning fertilizers determined by the biological activity of nut rhizosphere, while eliminating the negative effects of free phenolic hydroxyl groups of lignin on the rhizosphere and ensuring that the carrier remains insoluble in the soil with controllable network density, is a technical problem urgently needing to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a nut lignin-based rhizosphere microecological conditioning fertilizer and its preparation method, so that the release of nitrogen and phosphorus in the conditioning fertilizer is triggered by the biological activities of acid phosphatase, esterase and N-carbamoyl hydrolase in the nut rhizosphere, rather than determined by the degradation rate of the lignin skeleton; at the same time, by epoxy etherification, the free phenolic hydroxyl groups of lignin are blocked and transformed into nutrient anchoring sites, eliminating the negative effects of phenolic hydroxyl groups complexing iron and aluminum and releasing phenolic acids in acidic red soil, and by using a dicarboxylic acid crosslinking agent, the carrier is kept insoluble in the soil and the network density is controllable, thereby realizing the resource utilization of industrial lignin.

[0008] To achieve the above objectives, the present invention adopts the following technical solution. A nut-based lignin-based rhizosphere microecological conditioning fertilizer is prepared from a modified lignin carrier, urea, potassium sulfate, calcium magnesium phosphate fertilizer, potassium humate, and bentonite in specific mass proportions. The modified lignin carrier is a graft crosslinking product of epoxidized alkali lignin and three carbamylated precursor compounds: Compound 1 is (2S)-2,6-bis[(aminocarbonyl)amino]hexanoic acid, whose two urea groups carry nitrogen, and the α-carboxyl group is used for anchoring; Compound 2 is (2S)-2-[(aminocarbonyl)amino]-3-{[dihydroxy(oxydimethyl)-λ 5 [-methylphosphono]oxy}propionic acid, in which phosphorus exists in the form of a phosphate monoester, the urea group blocks the amino group and carries nitrogen, and the carboxyl group is used for anchoring; compound 3 is N-(aminocarbonyl)-N-(carboxymethyl)glycine, in which the two carboxyl groups esterify with the two epoxy groups respectively to become cross-linking points. Epoxidized alkali lignin is generated by the etherification of the phenolic hydroxyl groups of alkali lignin with epichlorohydrin, and the epoxy value is 0.8~1.6 mmol / g; the carboxyl groups of compounds 1 and 2 and the two carboxyl groups of compound 3 each ring-open with an epoxy group to form a β-hydroxy ester bond, and the carboxyl group of potassium humate ring-opens with the residual epoxy group of the carrier during ripening to form an ester. The molar ratio of the total amount of carboxyl groups to the amount of epoxy groups in the three compounds is (0.6~0.9):1, and the molar ratio of compounds 1, 2 and 3 is (2~5):(0.5~2):1.

[0009] In the above raw materials, urea serves as a readily available nitrogen source embedded in the continuous phase of the carrier, and its dissolution is controlled by the carrier network density; potassium sulfate provides potassium and sulfur; calcium magnesium phosphate provides citrate-soluble phosphorus and simultaneously supplements calcium, magnesium, and silicon, and its alkaline components buffer the rhizosphere pH when in contact with acidic red soil inside the granules; potassium humate is incorporated into the carrier network through esterification of carboxyl groups and residual epoxy groups in step five of the curing process, and also serves as a granulation binder and an auxiliary carbon source for rhizosphere microorganisms, and its dosage does not constitute a complexation site for phosphorus fixation on the solid phase surface; bentonite provides the plasticity required for granule forming and regulates the water absorption rate of the granules.

[0010] The preparation method of this invention includes six steps: Step 1 involves acid precipitation, washing, drying, and pulverizing of black liquor from papermaking to obtain alkali lignin; Step 2 involves the preparation of the lignin-based slow-release carrier framework, where alkali lignin undergoes a two-stage temperature etherification reaction with epichlorohydrin in an aqueous sodium hydroxide solution to obtain epoxidized alkali lignin with an epoxy value of 0.8~1.6 mmol / g; Step 3 involves the loading of nutrients and microbial carbon and nitrogen source precursors, where the mixture is refluxed in a mixed solvent of water and ethanol at pH 6.0~6.5 under the catalysis of tetrabutylammonium bromide, causing the carboxyl groups of compounds 1, 2, and 3 to open the ring-oxygen groups, forming a grafted and cross-linked modified lignin carrier containing residual epoxy groups; Step 4 involves mixing the modified lignin carrier with urea, potassium sulfate, calcium magnesium phosphate fertilizer, potassium humate, and bentonite, and granulating the mixture in a disc granulator; Step 5 involves the final regulation of the release behavior, where the wet granules are sealed and matured until the residual epoxy group content is ≤0.03%. In this process, the residual epoxy groups and the carboxyl groups of potassium humate undergo ring-opening esterification, causing potassium humate to be incorporated into the carrier network. The remaining epoxy groups are hydrolyzed into vicinal diols, followed by drying. Step six involves testing the total nutrient content, residual epoxy group content, particle size, moisture content, and particle crushing resistance, followed by packaging.

[0011] The technical solution of this invention is based on the following understanding. It is generally believed in the art that the slow-release and carbon-supplying capacity of lignin-based slow-release fertilizers comes from the degradation of the lignin skeleton in the soil, and that the phenolic hydroxyl groups of lignin are beneficial chelation sites. However, in reality, the mineralization of the industrial alkali lignin skeleton in the soil takes years and mainly depends on the extracellular peroxidase and laccase of white-rot fungi; rhizosphere bacteria can hardly directly use the lignin skeleton as a carbon source; the free phenolic hydroxyl groups on solid lignin react with Fe in acidic red soil. 3+ Al 3+ Complexation and precipitation on the carrier surface fix phosphorus to the carrier surface. The phenolic acids released by lignin oxidation and degradation, such as ferulic acid, p-coumaric acid, and vanillic acid, inhibit root elongation and rhizosphere bacterial proliferation. Using lignin skeleton degradation as the nutrient release clock inevitably leads to a mismatch with the weekly nutrient demand rhythm of nut trees, resulting in a net negative effect on the rhizosphere microecology. This invention shifts the nutrient release clock from lignin skeleton degradation to rhizosphere bioactivity itself: nitrogen and phosphorus are prepared as precursor compounds that can only be cleaved by rhizosphere enzymes, anchored to the lignin skeleton by β-hydroxy ester bonds. The lignin skeleton serves only as an insoluble anchor and a long-term source of organic matter; phenolic hydroxyl groups are sealed by epoxy etherification and transformed into anchoring sites.

[0012] In the above scheme, each of the three compounds undertakes an independent yet coupled release channel. Compound 1 constitutes a nitrogen channel: its α-carboxyl group is anchored by a β-hydroxy ester bond. After the ester bond is hydrolyzed by esterases secreted by rhizosphere bacteria, (2S)-2,6-bis[(aminocarbonyl)amino]hexanoic acid is released. The two urea groups of this molecule are then gradually hydrolyzed by N-carbamoyl-L-amino acid hydrolases (EC 3.5.1.87) and amide hydrolases of rhizosphere microorganisms into ammonia, carbon dioxide, and L-lysine. L-lysine is both a nitrogen source and a carbon source and chemotactic agent for rhizosphere Bacillus and Pseudomonas. This forms a positive feedback loop of enzyme release—microbial proliferation—increased enzyme activity—accelerated release. The nitrogen release rate is synchronized with the activity of rhizosphere microorganisms. Compound 2 constitutes a phosphorus channel: its phosphorus exists in the form of phosphate monoesters rather than water-soluble orthophosphate, and is mainly hydrolyzed in situ to orthophosphate by acid phosphatase secreted by the clustered roots. The formation of the clustered roots is itself induced by low phosphorus and automatically regresses when phosphorus is sufficient. Therefore, the release of phosphorus is consistent with the appearance of clustered roots at the organ level. The citrate-soluble phosphorus in calcium magnesium phosphate fertilizer is also dissolved by citric acid secreted by the clustered roots. Water-soluble orthophosphate was not detected in the conditioning fertilizer. Compound 3 constitutes a network channel: its two carboxyl groups form esters with two epoxy groups to become cross-linking points. The cross-linking density is determined by the molar fraction of compound 3 and the carboxyl / epoxy ratio, which keeps the carrier insoluble in the soil and controls the diffusion of urea and potassium sulfate in the continuous phase of the carrier. After the ester bonds are gradually hydrolyzed by esterases, the network gradually relaxes. The released N-(aminocarbonyl)-N-(carboxymethyl)glycine is converted into iminodiacetic acid by N-carbamoyl hydrolases. The latter acts as a soluble small molecule ligand to transiently complex Fe in the rhizosphere. 3+ Al 3+ This keeps it soluble, reduces the refixation of orthophosphate released from compound 2 on the solid surface, and ultimately allows it to be mineralized by microorganisms as a carbon and nitrogen source; this is related to the phenolic hydroxyl complexation of Fe in the lignin solid phase. 3+ Al 3+ The opposite direction of phosphorus fixation occurs when phosphorus is precipitated on the carrier surface.

[0013] In terms of the mass fraction of each raw material, when the modified lignin carrier is less than 55 parts, the slow-release continuous phase is insufficient to completely encapsulate urea and potassium sulfate; when it is more than 65 parts, the total nutrients are less than 15%. When the urea is less than 12 parts, the total nitrogen is insufficient; when it is more than 18 parts, the initial nitrogen release rate exceeds 10%. The potassium sulfate is 12-16 parts and the calcium magnesium phosphate fertilizer is 5-8 parts, determined according to the fertilizer ratio required by nut trees for high potassium and low phosphorus. When the potassium humate is less than 3 parts, it is difficult to form granules; when it is more than 6 parts, the residual epoxy groups during ripening are insufficient to incorporate them all into the network and allow them to dissolve with water. When the bentonite is less than 1 part, the granule strength is insufficient; when it is more than 3 parts, it dilutes the nutrients.

[0014] Furthermore, the alkali lignin is alkali lignin precipitated from papermaking black liquor, with a phenolic hydroxyl content of 2.0~3.5 mmol / g, a weight-average molecular weight of 3000~8000, and an ash content of ≤3%. When the phenolic hydroxyl content is below 2.0 mmol / g, there are insufficient anchoring sites for etherification; when the lignin content is above 3.5 mmol / g, it is mostly low molecular weight components with excessive water solubility. When the weight-average molecular weight is below 3000, the carrier is easily lost with water; when it is above 8000, dissolution and epoxidation are difficult. The residual phenolic hydroxyl content of epoxidized alkali lignin is ≤0.8 mmol / g; when it is above this value, the phenolic acid content in the soil solution increases significantly. Furthermore, the equilibrium swelling rate of the modified lignin carrier before granulation is 120%~220%, and the gel fraction is ≥85%. When the swelling rate is below 120%, the release of urea and potassium sulfate is too slow; when it is above 220% or the gel fraction is below 85%, the carrier fragments dissolve with water. The mass fraction of nitrogen in the carrier is 1.8%~3.5%, and the mass fraction of phosphorus is 0.2%~1.1%, determined by the amount of the three compounds used. Furthermore, the mass fraction of phosphorus monophosphate in the modified lignin carrier before granulation is ≥95% of the total phosphorus. The water-soluble phosphorus in the finished product, as determined by GB / T 8573, is ≤0.1% as P2O5, and the residual epoxy content of the finished product is ≤0.03 mmol / g. Furthermore, the finished product is granules with a particle size of 2~4 mm, a moisture content of ≤5%, and a crushing force of ≥15 N. When the particle size is less than 2 mm, the specific surface area of ​​the particles is too large, causing the release to be delayed; when the particle size is greater than 4 mm, it is inconvenient for mechanical application.

[0015] Further, compound 1 is prepared by reacting L-lysine or L-lysine hydrochloride with potassium cyanate in water at pH 8.5-9.5 and 45-60 °C for 4-8 h, with the amount of potassium cyanate being (2.1-2.5) times the amount of substance; compound 2 is prepared by reacting O-phospho-L-serine with potassium cyanate at pH 8.5-9.5 and 40-50 °C for 4-6 h, with the amount of potassium cyanate being (1.1-1.3) times the amount of substance; compound 3 is prepared by reacting iminodiacetic acid with potassium cyanate at pH 9.0-9.5 and 55-65 °C for 6-10 h, with the amount of potassium cyanate being (1.2-1.5) times the amount of substance. When the pH is below 8.5, the hydrolysis of isocyanate and the cyclization side reactions of urea acid intensify; when it is above 9.5, the protonation ratio of cyanate ions is too low, resulting in a decrease in the reaction rate. Iminodiacetic acid is a secondary amine, so a higher temperature, a longer time, and more potassium cyanate are used. After the reaction, the solution is acidified at 0-5 °C to pH 1.5-2.5 to prevent urea acid from cyclizing to hydantoin under acid-heat conditions. Further, in step two, the mass concentration of the sodium hydroxide aqueous solution is 2%-4%, and the mass ratio of alkali lignin to sodium hydroxide aqueous solution is 1:(4-6) to ensure complete dissolution of lignin and that the phenolic hydroxyl group participates in etherification in the form of phenoxy anions. The reaction is first carried out at 55-65 °C for 2-4 h to allow the phenoxy anions to open the epoxy group of epichlorohydrin to generate chlorool, and then the reaction is carried out at 70-80 °C for 1-3 h to allow the chlorool to dehydrochlorinate and close the ring to glycidyl ether under alkaline conditions. Further, in step three, the volume ratio of water to ethanol is (1.5~2.5):1, the ratio of epoxide lignin to mixed solvent is 1 g:(5~8) mL, and the amount of tetrabutylammonium bromide is 0.5%~2% of the amount of epoxy group. Ethanol fully swells the epoxide lignin, and tetrabutylammonium bromide acts as a phase transfer catalyst to carry carboxylate anions into the lignin phase. The filtrate from step three is concentrated under reduced pressure and returned to the next batch for use. Further, in step four, the water used for granulation is 8%~12% of the total mass of the material, the disc granulator has an inclination angle of 45°~55° and a rotation speed of 15~25 r / min; in step five, the curing temperature is 75~85 °C, the time is 2.5~3.5 h, and the drying temperature is 55~65 °C.

[0016] Compared with existing technologies, the beneficial effects of this invention are as follows: the release of nitrogen and phosphorus in the conditioning fertilizer is triggered by rhizosphere acid phosphatase, esterase, and N-carbamoyl hydrolase. Under sterile conditions, release is almost nonexistent, but under rhizosphere conditions, release is accelerated, and the nutrient release rhythm is synchronized with the biological activity of the nut tree; after the phenolic hydroxyl groups of lignin are blocked, the phenolic acid content in the rhizosphere soil solution is significantly reduced, and the number of culturable bacteria and the abundance of Bacillus in the rhizosphere are greatly increased; the conditioning fertilizer does not contain water-soluble orthophosphate, and the number of nut cluster roots increases rather than decreases under fertilization conditions, while the phosphorus content in the leaves remains within an appropriate range; the carrier remains insoluble in the soil, and the lignin skeleton is transformed into soil organic matter over a long period, resulting in increased soil organic matter content in two years of field trials; alkali lignin, a byproduct of papermaking, is utilized as a resource. There is a non-additive interdependence between nitrogen channels, phosphorus channels, and network channels; the sum of the seedling dry matter loss from removing any one channel and the abundance of Bacillus in the rhizosphere is far greater than the total increase brought by all three channels. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the preparation method of the nut lignin-based rhizosphere microecological conditioning fertilizer of the present invention.

[0018] Figure 2 Here are the chemical structural formulas of compounds 1, 2, and 3.

[0019] Figure 3 The cumulative release curves of mineral nitrogen in Example 1, Comparative Example 1, and Comparative Example 3 after 90 days of cultivation in acidic red soil are shown.

[0020] Figure 4 Bar graph showing the number of clustered roots and the abundance of rhizosphere Bacillus in macadamia seedlings under each treatment in a pot experiment. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to the following embodiments. Operations in the embodiments without specific conditions are performed under conventional conditions, and the raw materials and reagents used are commercially available products unless otherwise specified.

[0022] The alkali lignin used in this example was obtained from black liquor from a eucalyptus sulfate pulping plant in Guangxi, with a solid content of 15.2%. The black liquor was adjusted to pH 2.5 at 60 °C with 20% sulfuric acid, kept at this temperature for 30 min, and then filtered. The filter cake was first washed twice with 0.01 mol / L sulfuric acid, then washed with deionized water until the conductivity of the filtrate was ≤200 μS / cm. It was then dried at 60 °C until the moisture content was ≤5%, pulverized, and passed through a 100-mesh sieve (particle size ≤0.15 mm), which is the alkali lignin obtained from the industrial lignin pretreatment described in step one. 31P-NMR (2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxophosphazenecyclopentane derivatization) analysis revealed that the alkali lignin contained 2.60 mmol / g of phenolic hydroxyl groups, 1.92 mmol / g of aliphatic hydroxyl groups, and 0.41 mmol / g of carboxyl groups. Gel permeation chromatography showed a weight-average molecular weight of 5200, a polydispersity index of 2.4, and an ash content of 1.8%. The structural formulas of compounds 1, 2, and 3 are as follows: Figure 2 As shown.

[0023] In the examples, the epoxy value was determined according to the hydrochloric acid-acetone method specified in GB / T 1677; the phenolic hydroxyl content was determined according to the above. 31 The mass fraction of phosphate monoester phosphorus in the modified lignin carrier was determined by nuclear magnetic resonance (NMR) method from the solid. 31 The peak area of ​​phosphate monoester with a chemical shift of 3.0–5.5 ppm in the P-magic angle rotating NMR spectrum (rotation speed 12 kHz) was obtained as the ratio of the peak area of ​​all phosphorus peaks; the equilibrium swelling rate was the ratio of the difference between the swollen mass and the dry mass of the modified lignin carrier after soaking in deionized water at 25 °C for 24 h to the dry mass; the gel fraction was the ratio of the residual mass of the modified lignin carrier after soaking in phosphate buffer (0.05 mol / L) at 25 °C for 48 h to the initial dry mass; nitrogen and phosphorus in the carrier were determined according to GB / T 8572 and GB / T 8573, respectively. The total nitrogen of the conditioning fertilizer was determined according to GB / T 8572, the total phosphorus was determined according to GB / T 8573 after the sample was digested with sulfuric acid and nitric acid, and the potassium was determined according to GB / T 8574. Water-soluble phosphorus refers to orthophosphate phosphorus obtained after water extraction as specified in GB / T 8573. The initial nutrient release rate (24 h) and the cumulative nutrient release rate over 28 days were determined according to the 25 °C static water extraction method specified in GB / T 23348. The phosphorus in the extract was calculated as total phosphorus after digestion. The particle size was determined according to GB / T 24891, the moisture content was determined according to GB / T 8576, the residual epoxy content of the finished product was determined according to the hydrochloric acid-acetone method and the blank of the same formula without modified lignin carrier was subtracted. The crushing force of the particles was determined by a particle strength tester. Twenty particles with a particle size of 2.8~3.2 mm were loaded radially one by one until they were crushed, and the average crushing force was taken. The data for each experiment below are the average values ​​of repeated measurements. Differences between treatments were tested using Duncan's new multiple range test. The differences between the examples and each control and comparative example in the listed indicators all reached the significance level of P<0.05, and the coefficients of variation of each indicator were all less than 8%.

[0024] In the preparation method of this invention, the epoxy value in step two is 0.8~1.6 mmol / g. When the epoxy value is below 0.8 mmol / g, the phenolic hydroxyl groups are not sufficiently blocked and the anchoring sites are insufficient. When it is above 1.6 mmol / g, a large excess of epichlorohydrin is required, and the aliphatic hydroxyl groups are also etherified, making the support excessively hydrophobic. The pH in step three is 6.0~6.5. At this pH, the carboxyl groups of the three compounds have been completely ionized into carboxylate anions and enter the lignin relative to the epoxy group for ring opening under the phase transfer of tetrabutylammonium bromide. When the pH is below 6.0, the acid-catalyzed hydrolysis of the epoxy group and the cyclization of the urea acid are intensified. When the pH is above 6.5, the ring opening of the epoxy group by hydroxide ions and the saponification of the β-hydroxy ester bond are intensified. Although the phosphate monoester group is mainly a divalent anion at this pH, its nucleophilicity to the epoxy group is much lower than that of the carboxylate ion, and it basically does not participate in the ring opening. The reaction temperature is 80~90 °C and refluxed. When the temperature is below 80 °C, the ring opening reaction is at 80 °C. The process cannot be completed within h. At temperatures above 90 °C, the hydrolysis of β-hydroxy ester bonds and the cyclization of urea amino acids intensify. The aging temperature in step five is 70-90 °C and the time is 2-4 h. If the temperature is too low or the time is too short, the residual epoxy groups cannot be completely eliminated. If the temperature is too high or the time is too long, the urea reacts with the moisture in the particles, causing the particles to stick together. The molar ratio of compound 1, compound 2 and compound 3 is (2~5):(0.5~2):1, where the ratio of compound 1 to compound 3 determines the crosslinking density. When the ratio is higher than 5:1, there are insufficient crosslinking points and the gel fraction is lower than 85%. When the ratio is lower than 2:1, the carrier swelling rate is too low, resulting in slow release of urea and potassium sulfate. The ratio of compound 2 to compound 3 is adjusted between 0.5:1 and 2:1 according to the available phosphorus (Bray-1) status of the nut orchard soil. When the available phosphorus in the soil is lower than 3 mg / kg, the ratio is 2:1; when it is 3~8 mg / kg, the ratio is 1.5:1; and when it is higher than 8 mg / kg, the ratio is 0.5:1. This allows for differentiated preparation for different soil conditions in nut orchards.

[0025] Preparation Example 1: Preparation of Compound 1.

[0026] 18.27 g (0.100 mol) of L-lysine hydrochloride was dissolved in 200 mL of deionized water, and the pH was adjusted to 9.0 with 20% potassium hydroxide solution. 18.65 g (0.230 mol) of potassium cyanate was added, and the mixture was stirred at 50 °C for 6 h, maintaining the pH at 8.8–9.2 with potassium hydroxide solution until the ninhydrin color reaction was negative. The reaction solution was cooled to 0–5 °C, and at this temperature, it was slowly acidified to pH 2.0 with 6 mol / L hydrochloric acid. Stirring was continued for 2 h, resulting in the precipitation of white crystals. The crystals were filtered, washed with cold water, recrystallized once with deionized water, and dried under vacuum at 50 °C to obtain compound 1, (2S)-2,6-bis[(aminocarbonyl)amino]hexanoic acid, in 19.3 g (83% yield). The product was a white crystalline powder, and the electrospray ionization mass spectrometry (ESI-MS) showed a m / z of 231.1 [M−H]. − Elemental analysis showed the following measured values: C 41.32%, H 6.98%, N 24.09%, according to C8H... 16 The theoretical values ​​for N4O4 are calculated to be 41.37% C, 6.94% H, and 24.13% N. 1 H NMR (D2O) δ 4.06 (dd, 1H, α-CH), 3.09 (t, 2H, ε-CH2), 1.82~1.32 (m, 6H); 13 C NMR (D₂O) δ 178.8, 161.7, 161.1, 54.7, 40.2, 31.6, 29.2, 22.8. Acidification was carried out at low temperature to avoid cyclization of urea amino acids under acidic thermal conditions to form 5-(4-ureobutyl)hydantoin.

[0027] Preparation Example 2: Preparation of Compound 2

[0028] 18.51 g (0.100 mol) of O-phospho-L-serine was dissolved in 150 mL of deionized water, and the pH was adjusted to 9.0 with 20% potassium hydroxide solution. 9.73 g (0.120 mol) of potassium cyanate was added, and the mixture was stirred at 45 °C for 5 h, maintaining the pH between 8.8 and 9.2 until the ninhydrin color reaction was negative. The reaction solution was cooled to 0–5 °C and acidified to pH 2.0 with 6 mol / L hydrochloric acid. The solution was then passed through a strongly acidic cation exchange resin (H2O). + The potassium ions were removed using a column (type 1). The eluent was concentrated under reduced pressure at ≤40 °C to a syrupy consistency. Three volumes of anhydrous ethanol were added, and the mixture was allowed to stand at 0–5 °C for 12 h. A white solid precipitated. The solid was filtered, washed with cold ethanol, and dried under vacuum at 40 °C to obtain compound 2, namely (2S)-2-[(aminocarbonyl)amino]-3-{[dihydroxy(oxymethylene)-λ 518.9 g of [-methphosphono]oxy}propionic acid, yield 83%. Electrospray ionization mass spectrometry m / z 227.0 [M−H] − ; 31 P NMR (D2O) δ4.3 (single peak, phosphate monoester); elemental analysis results: C 21.02%, H 4.03%, N 12.24%; theoretical values ​​calculated using C4H9N2O7P: C 21.06%, H 3.98%, N 12.28%. In industrial production, the eluent after potassium removal is neutralized to pH 6.0 with potassium hydroxide and can be directly quantified according to the content of compound 2 for step three without further separation.

[0029] Preparation Example 3: Preparation of Compound 3

[0030] 13.31 g (0.100 mol) iminodiacetic acid was suspended in 150 mL of deionized water and dissolved by adjusting the pH to 9.3 with 20% potassium hydroxide solution. 11.36 g (0.140 mol) potassium cyanate was added, and the mixture was stirred at 60 °C for 8 h, maintaining the pH at 9.0–9.5 during the reaction. The reaction solution was cooled to 0–5 °C and acidified to pH 1.8 with 6 mol / L hydrochloric acid. Stirring was continued for 3 h, resulting in the precipitation of white crystals. These crystals were filtered, washed with cold water, recrystallized once with deionized water, and dried under vacuum at 50 °C to obtain 13.6 g of compound 3, N-(aminocarbonyl)-N-(carboxymethyl)glycine, with a yield of 77%. Electrospray ionization mass spectrometry (ESI-MS) showed a concentration of 175.0 [M−H]. − Elemental analysis showed that the measured values ​​were C 34.06%, H 4.61%, and N 15.88%, while the theoretical values ​​calculated based on C5H8N2O5 were C 34.10%, H 4.58%, and N 15.91%. 1 H NMR (D2O) δ 4.05 (s, 4H); 13 C NMR (D2O) δ 174.9, 160.5, 50.8. Iminodiacetic acid is a secondary amine, and its carbamylation rate is lower than that of primary amines, so a higher temperature and potassium cyanate dosage are used; low-temperature acidification can prevent the product from cyclizing to 2-(2,4-dioxoimidazolidine-1-yl)acetic acid.

[0031] Example 1

[0032] The nut lignin-based rhizosphere microecological conditioning fertilizer of this embodiment is prepared according to the following six processes, the process flow of which is as follows: Figure 1As shown. Step 1, Industrial lignin pretreatment: Alkali lignin was prepared from eucalyptus sulfate black liquor using the aforementioned method, with a phenolic hydroxyl content of 2.60 mmol / g. Step 2, Preparation of epoxidized alkali lignin, i.e., preparation of the lignin-based slow-release carrier framework: 100 g of alkali lignin was added to 500 g of a 2.4% sodium hydroxide aqueous solution and stirred at 40 °C for 30 min until completely dissolved. 48.0 g (0.519 mol) of epichlorohydrin was added, with a molar ratio of epichlorohydrin to alkali lignin phenolic hydroxyl groups (0.260 mol) of 2.0:1. The mixture was stirred at 60 °C for 3 h, then heated to 75 °C for 2 h. After cooling to room temperature, the mixture was acidified with 10% hydrochloric acid to pH 3.0, filtered, and the filter cake was washed with deionized water until neutral. It was then dried at 55 °C to obtain 106 g of epoxidized alkali lignin. The epoxy value was determined to be 1.25 mmol / g, and the residual phenolic hydroxyl content was 0.55 mmol / g. Based on the mass conversion of the product before and after etherification, 77% of the phenolic hydroxyl groups were blocked by etherification. The infrared spectrum at 1250 cm⁻¹ showed... −1 and 910 cm −1 Characteristic absorption of epoxy groups appears at the location.

[0033] Step 3, compound grafting and cross-linking, i.e., loading of nutrients and microbial carbon and nitrogen source precursors: 100 g of epoxidized alkali lignin (0.125 mol of epoxy groups) was dispersed in a mixed solvent consisting of 400 mL of deionized water and 200 mL of ethanol. 10.72 g (0.0462 mol) of compound 1, 5.27 g (0.0231 mol) of compound 2 and 2.71 g (0.0154 mol) of compound 3 were added, with a molar ratio of 3:1.5:1. The total amount of carboxyl groups was 0.100 mol, and the molar ratio of carboxyl groups to epoxy groups was 0.8:1. The pH was adjusted to 6.2 with a 20% potassium hydroxide solution, and 0.40 g (1.24 mmol, which is 1.0% of the molar amount of epoxy groups) of tetrabutylammonium bromide was added. The mixture was refluxed and stirred at 85 °C for 6 h. Under these conditions, the carboxylate anion undergoes nucleophilic ring-opening of the methylene carbon of the epoxy group via phase transfer in tetrabutylammonium bromide. The resulting alkoxy anion is protonated by the solvent water to form a β-hydroxy ester bond, while the urea and phosphate monoester groups do not participate in ring-opening at this pH and temperature. After the reaction, the mixture is filtered, and the filter cake is washed three times with 50% ethanol (v / v) and dried at 55 °C to obtain 116 g of modified lignin carrier. High-performance liquid chromatography (HPLC) analysis of the filtrate showed that the unreacted amounts of compounds 1, 2, and 3 were 15%, 13%, and 10% of the feed amount, respectively. The filtrate was concentrated under reduced pressure and reused in the next batch in step three. The modified lignin carrier was found to have a nitrogen mass fraction of 2.70%, a phosphorus mass fraction of 0.53%, a residual epoxy group content of 0.33 mmol / g, an equilibrium swelling ratio of 165%, and a gel fraction of 91%. 31 The phosphate monoester peak at a chemical shift of 4.1 ppm in the P magic angle rotation NMR spectrum accounts for 97% of the total phosphorus peak area, indicating that the phosphate monoester of compound 2 was retained during the grafting process. According to the conversion rate of the three compounds in the filtrate, the consumption of epoxy groups was 0.087 mol, which is consistent with the measured residual epoxy group content, indicating that both carboxyl groups of compound 3 have been esterified.

[0034] Step 4, Granulation: Mix 60 kg of modified lignin carrier, 15 kg of urea, 13 kg of potassium sulfate (K2O content 52%), 6 kg of calcium magnesium phosphate fertilizer (P2O5 content 16%), 4 kg of potassium humate, and 2 kg of bentonite in a mixer for 15 min. Transfer the mixture to a disc granulator with an inclination angle of 50° and a rotation speed of 20 r / min. While the disc granulator is rotating, spray in 10% of the total mass of deionized water to obtain wet granules with a particle size of 2-4 mm. Step 5, Sealed Curing, i.e., the final control of release behavior: Transfer the wet granules to a sealed curing chamber and cure at 80 °C for 3 h. With the participation of the granules' own moisture, the residual epoxy groups in the modified lignin carrier ring-open with the carboxyl groups of potassium humate to form esters, and the remaining epoxy groups hydrolyze to vicinal diols. Then dry at 60 °C until the moisture content is ≤5%, and sieve to obtain finished granules with a particle size of 2-4 mm. The granules before and after aging were washed with water to remove urea and potassium sulfate, respectively. The grafted nitrogen and grafted phosphorus of the carrier were then measured. The changes in both were less than 3%, indicating that the β-hydroxy ester bonds and phosphate monoester bonds remained stable under aging conditions. Step Six, Testing and Packaging: The finished product was tested and found to contain 8.6% total nitrogen, 1.7% total phosphorus (as P2O5), 7.4% potassium (as K2O), 17.7% total nutrients, 56% organic matter, no detectable water-soluble phosphorus, 0.02 mmol / g residual epoxy group content, 3.8% moisture content, 24 N crushing resistance, and a pH (1:10 water extraction) of 6.3. After testing, the granules were packaged in 25 kg bags.

[0035] Example 2

[0036] The difference between this embodiment and Example 1 is as follows: In step two, the amount of epichlorohydrin used is 38.5 g (0.416 mol), and the molar ratio of epichlorohydrin to phenolic hydroxyl groups is 1.6:1. The reaction is carried out at 58 °C for 3.5 h, then heated to 72 °C for another 2.5 h, yielding 105 g of epoxidized alkali lignin with an epoxy value of 1.05 mmol / g, a residual phenolic hydroxyl content of 0.72 mmol / g, and a phenolic hydroxyl group blocking rate of 71%. In step three, based on 100 g of epoxidized alkali lignin (epoxy groups 0.105 mol), 7.59 g (0.0327 mol) of compound 1, 1.86 g (0.0082 mol) of compound 2, and 2.88 g (0.0163 mol) of compound 2 are added. Compound 3 (mol) was prepared with a molar ratio of 4:1:2 for the three components, a molar ratio of total carboxyl groups to epoxy groups of 0.7:1, pH adjusted to 6.0, and tetrabutylammonium bromide used at 1.5% of the molar amount of epoxy groups. The mixture was refluxed at 82 °C for 7 h. The resulting modified lignin carrier had a nitrogen mass fraction of 1.95%, a phosphorus mass fraction of 0.20%, a residual epoxy group content of 0.37 mmol / g, an equilibrium swelling rate of 140%, a gel fraction of 93%, and phosphate monoester phosphorus accounting for 96% of the total phosphorus mass fraction. In step four, the raw materials were: 62 parts modified lignin carrier, 14 parts urea, 13 parts potassium sulfate, 5 parts calcium magnesium phosphate fertilizer, 4 parts potassium humate, and 2 parts bentonite. In step five, the curing temperature was 85 °C, and the curing time was 2.5 h. The rest was the same as in Example 1. The finished product contains 7.7% total nitrogen, 1.1% total phosphorus, 7.3% potassium, 16.1% total nutrients, no water-soluble phosphorus detected, 0.02 mmol / g residual epoxy group content, 4.1% moisture content, and 27 N crushing resistance of the particles.

[0037] Example 3

[0038] The difference between this embodiment and Example 1 is as follows: In step two, the amount of epichlorohydrin used is 62.5 g (0.676 mol), and the molar ratio of epichlorohydrin to phenolic hydroxyl groups is 2.6:1. After reacting at 62 °C for 2.5 h, the temperature is raised to 78 °C for 3 h, resulting in 108 g of epoxidized alkali lignin with an epoxy value of 1.55 mmol / g, a residual phenolic hydroxyl content of 0.42 mmol / g, and a phenolic hydroxyl group blocking rate of 83%. In step three, based on 100 g of epoxidized alkali lignin (epoxy groups 0.155 mol), 10.80 g (0.0465 mol) of compound 1, 10.61 g (0.0465 mol) of compound 2, and 4.10 g (0.0233 mol) of compound 2 are added. Compound 3 (mol) was prepared with a molar ratio of 2:2:1 for the three components, a molar ratio of total carboxyl groups to epoxy groups of 0.9:1, pH adjusted to 6.5, and tetrabutylammonium bromide used at 0.8% of the molar amount of epoxy groups. The mixture was refluxed at 88 °C for 5 h. The resulting modified lignin carrier had a nitrogen mass fraction of 3.21%, a phosphorus mass fraction of 1.02%, a residual epoxy group content of 0.27 mmol / g, an equilibrium swelling rate of 205%, a gel fraction of 86%, and phosphate monoester phosphorus accounting for 95% of the total phosphorus mass fraction. In step four, the mass fractions of each raw material were 55 parts modified lignin carrier, 18 parts urea, 15 parts potassium sulfate, 8 parts calcium magnesium phosphate fertilizer, 3 parts potassium humate, and 1 part bentonite. In step five, the curing temperature was 75 °C and the curing time was 3.5 h. The rest was the same as in Example 1. The finished product contains 10.1% total nitrogen, 2.6% total phosphorus, 8.5% potassium, 21.2% total nutrients, no water-soluble phosphorus detected, 0.03 mmol / g residual epoxy group content, 4.4% moisture content, and 19 N crushing resistance of the particles.

[0039] When applying the conditioning fertilizer of this invention, apply 1.0-1.5 kg per tree per year to young trees and 2.5-3.5 kg per tree per year to mature fruit-bearing trees. Apply the fertilizer twice, once before the spring shoots sprout and once during the fruit enlargement period, in a circular trench 15-20 cm deep along the inner side of the tree canopy drip line and cover with soil. No further inoculation with microbial agents is required after application. For orchards with soil available phosphorus (Bray-1) below 3 mg / kg, use the formulation with a higher proportion of compound 2 as described in Example 3; for orchards with 3-8 mg / kg, use the formulation as described in Example 1; and for orchards with more than 8 mg / kg, use the formulation as described in Example 2.

[0040] Comparative Example 1

[0041] This comparative example was used to verify the role of the feature of anchoring compounds 1, 2, and 3 to the lignin framework via β-hydroxy ester bonds. The epoxidation in step two and the grafting reaction in step three were omitted. 100 g of unmodified alkali lignin was directly mixed with 10.72 g of compound 1, 5.26 g of compound 2, and 2.71 g of compound 3 in water at 60 °C for 2 h, and then dried to obtain a carrier in which the three compounds existed only in a physically adsorbed form. The remaining raw material ratios, granulation, curing, and detection were the same as in Example 1. The phenolic hydroxyl content of this carrier remained at 2.60 mmol / g, and the gel fraction was 71% after soaking in pH 7.0 buffer for 48 h. 94% of the three compounds dissolved within 24 h.

[0042] Comparative Example 2

[0043] This comparative example was used to verify the role of the carbamoyl group in compounds 1, 2, and 3. In step three, compounds 1, 2, and 3 were replaced with equal amounts of L-lysine, O-phospho-L-serine, and iminodiacetic acid, respectively, with the remaining conditions the same as in Example 1. Although the α-amino and ε-amino groups of L-lysine and the secondary amino group of iminodiacetic acid are predominantly ammonium ions at this pH, the nucleophilicity of their small amount of free amines to the epoxy group is much higher than that of the carboxyl group, and the reaction is irreversible. The three substances are mainly anchored by carbon-nitrogen bonds through ring opening of the epoxy group by the amino group. The two amino groups of L-lysine react simultaneously to form non-hydrolyzable crosslinking points. The equilibrium swelling ratio of the resulting carrier is only 95%, the gel fraction is 96%, the nitrogen mass fraction of the carrier is 1.55%, and the phosphorus mass fraction is 0.60%. There is no urea nitrogen that can be released by N-carbamoyl hydrolases, and the nitrogen anchored by carbon-nitrogen bonds cannot be released by esterases.

[0044] Comparative Example 3

[0045] This comparative example was used to verify the role of epoxy value. In step two, the amount of epichlorohydrin used was 14.4 g (0.156 mol), with a molar ratio of 0.6:1 to phenolic hydroxyl groups. The reaction was carried out at 50 °C for 2 h without further heating. The resulting epoxy value of the epoxidized alkali lignin was 0.45 mmol / g, and the residual phenolic hydroxyl content was 1.90 mmol / g. In step three, the molar ratio of total carboxyl groups to epoxy groups remained at 0.8:1, i.e., the amounts of compounds 1, 2, and 3 were 3.86 g, 1.89 g, and 0.98 g, respectively. The remaining conditions were the same as in Example 1. The resulting carrier had a nitrogen mass fraction of 1.07%, a phosphorus mass fraction of 0.21%, an equilibrium swelling rate of 260%, and a gel fraction of 78%.

[0046] Comparative Example 4

[0047] This comparative example follows the approach described in patent CN106478295A, using the Mannich reaction to prepare aminated lignin while retaining phenolic hydroxyl groups. 100 g of alkali lignin was dissolved in 500 g of a 2.4% sodium hydroxide aqueous solution, followed by the addition of 16.2 g of a 37% formaldehyde solution and 21.0 g of diethanolamine. The reaction was carried out at 80 °C for 4 h. After acid precipitation, washing, and drying, 121 g of aminated lignin was obtained, with a phenolic hydroxyl content of 2.15 mmol / g and a nitrogen mass fraction of 2.05%. Then, 100 g of the aminated lignin was mixed with 10.72 g of compound 1, 5.26 g of compound 2, and 2.71 g of compound 3 in water at 60 °C for 2 h, followed by drying. This allowed the three compounds to be electrostatically adsorbed onto the aminated lignin. The remaining raw material ratios, granulation, curing, and testing were the same as in Example 1.

[0048] Comparative Example 5

[0049] This comparative example was used to verify the effect of compound 3. In step three, compound 3 was not added, and the amounts of compound 1 and compound 2 were increased to 15.48 g (0.0667 mol) and 7.60 g (0.0333 mol), respectively, so that the molar ratio of total carboxyl groups to epoxy groups remained at 0.8:1. All other conditions were the same as in Example 1. The resulting support had a nitrogen mass fraction of 3.31% and a phosphorus mass fraction of 0.75%. Because there were no dicarboxyl crosslinking points, the gel fraction of the support was only 62% after soaking in pH 7.0 buffer for 48 h, with an equilibrium swelling rate of 310%. Furthermore, dissolved grafted lignin fragments were detected in the soaking solution.

[0050] Comparative Example 6

[0051] This comparative example was used to verify the role of phosphorus existing in the form of monophosphate monoesters. In step three, compound 2 was not added, the amounts of compounds 1 and 3 remained unchanged, and the molar ratio of total carboxyl groups to epoxy groups was 0.62:1. In step four, monoammonium phosphate (0.32 kg as P, equivalent to 1.19 kg of monoammonium phosphate) was added in an amount equal to that of compound 2 in Example 1, and the amount of urea was adjusted to 15.2 kg to maintain the same total nitrogen content. All other conditions were the same as in Example 1. The resulting conditioning fertilizer had a water-soluble phosphorus content of 0.71% (calculated as P2O5).

[0052] Parameter out-of-range test

[0053] To further define the basis for the molar ratio of carboxyl groups to epoxy groups, the ratio was adjusted to 0.5:1 and 1.2:1 respectively, based on Example 1, while other conditions remained unchanged. When the ratio was 0.5:1, the nitrogen mass fraction of the carrier decreased to 1.72%, the phosphorus mass fraction decreased to 0.34%, and the residual epoxy groups still reached 0.08 mmol / g after aging in step five. During the aging process, excessive cross-linking with potassium humate led to an increase in the crushing resistance of the particles to 41 N, while the cumulative potassium release rate after 28 days decreased to 36%. When the ratio was 1.2:1, the total amount of the three unreacted compounds in the filtrate reached 28% of the feed amount, and the initial nitrogen release rate of the finished product in still water at 25 °C for 24 hours increased to 15.6%, indicating that the excess compounds failed to anchor and dissolved in water in a free form. Therefore, the ratio was set between 0.6:1 and 0.9:1.

[0054] Test methods

[0055] The static water release test was conducted according to GB / T 23348. 10.0 g of the finished product was placed in 200 mL of deionized water at 25 °C and allowed to stand. The percentages of dissolved nitrogen, phosphorus, and potassium relative to the total nutrient content of the finished product were measured at 24 h and 28 d. For the enzyme-triggered phosphorus release test, 0.500 g of the modified lignin carrier was placed in 50 mL of pH 5.0 acetate buffer (0.1 mol / L). The mixture was shaken at 30 °C for 7 days with and without enzyme, and with the addition of 2 U / mL wheat germ acid phosphatase (EC 3.1.3.2). The released orthophosphate was determined using the molybdenum antimony colorimetric method, and the release rate was calculated based on the grafted phosphorus in the carrier. In the bio-triggered release test of carrier nitrogen, 1.00 g of carrier was mixed with 100 g of test red soil. Sterilized soil (sterilized at 121 °C for 30 min with 0.5% chloroform added for sterilization), unsterilized soil, and rhizosphere soil collected 120 days after planting macadamia seedlings in the same red soil were used. The mixture was cultured at 25 °C and 60% field capacity for 60 days. The extract was then extracted with 2 mol / L potassium chloride. After digestion with potassium sulfate, the total nitrogen in the extract was measured using a flow analyzer. After deducting the soil background, the leaching release rate was calculated based on the grafted nitrogen in the carrier.

[0056] The soil incubation experiment used acidic red soil (0-20 cm depth) from a macadamia nut orchard in Lincang, Yunnan Province, with a pH of 4.9, organic matter content of 18.2 g / kg, and available phosphorus (Bray-1) content of 3.2 mg / kg. 2.0 g of the finished product was applied per kilogram of air-dried soil. A control of urea with equal nitrogen content and a control of 15-15-15 compound fertilizer were also included. The soil was incubated at 25 °C and 60% field capacity for 90 days. Mineral nitrogen was measured at 14, 28, 56, and 90 days. Available phosphorus (Bray-1) was measured at 90 days. At 28 days, soil solution was extracted by shaking at a water-to-soil ratio of 5:1, and ferulic acid, p-coumaric acid, and vanillic acid were determined by high-performance liquid chromatography. Ammonia volatilization loss within 30 days was measured using a closed-chamber ventilation method. The pot experiment used one-year-old grafted seedlings of the 'O.C' variety as material. Each pot contained 8 kg of the above-mentioned red soil and 16 g of the finished product. There were no fertilized control and a control with the same nitrogen content of 15-15-15 compound fertilizer. There were 6 pots for each treatment. After culturing in a greenhouse for 180 days, the number of clustered roots, seedling dry matter and leaf phosphorus content of each plant were measured. Rhizosphere soil was collected and the number of culturable bacteria was determined by dilution plate method. Bacillus abundance was determined by real-time quantitative PCR using Bacillus-specific 16S rRNA gene primers. Acid phosphatase activity was determined by disodium p-nitrophenyl phosphate method. Soil esterase activity was determined by fluorescein diacetate (FDA) hydrolysis method and recorded as FDA hydrolase activity. Field trials were conducted in two macadamia orchards in Lincang, Yunnan and Chongzuo, Guangxi. The test trees were 8-year-old 'O.C' varieties, with 30 trees per treatment. For Example 1 and Comparative Examples 1, 4, and 6, 3.0 kg of fertilizer was applied per tree per year in March and September, respectively, through a circular trench inside the drip line of the canopy. The conventional fertilization control was applied with 15-15-15 compound fertilizer and urea of ​​equal nitrogen content according to local practice. The trials were conducted for two consecutive years, and the yield of shelled macadamia nuts per tree, kernel yield, leaf nitrogen content, organic matter and pH in the 0-20 cm soil layer, and abundance of rhizosphere Bacillus were measured.

[0057] Carrier structural parameters

[0058] Table 1. Carrier structural parameters and nutrient indexes of finished products for each embodiment and comparative example.

[0059] deal with Epoxy value (mmol / g) Residual phenolic hydroxyl groups / (mmol / g) Carrier nitrogen / % Carrier phosphorus / % Equilibrium swelling rate / % Gel fraction / % Phosphate monoester phosphorus content / % Total nutrients in finished product / % <![CDATA[Water-soluble phosphorus in finished product (as P2O5) / %]]> Example 1 1.25 0.55 2.70 0.53 165 91 97 17.7 Not detected Example 2 1.05 0.72 1.95 0.20 140 93 96 16.1 Not detected Example 3 1.55 0.42 3.21 1.02 205 86 95 21.2 Not detected Comparative Example 1 0 2.60 3.09 0.60 230 71 97 18.0 Not detected Comparative Example 2 1.25 0.55 1.55 0.60 95 96 94 17.1 Not detected Comparative Example 3 0.45 1.90 1.07 0.21 260 78 96 16.1 Not detected Comparative Example 4 0 2.15 4.81 0.60 240 74 97 19.1 Not detected Comparative Example 5 1.25 0.55 3.31 0.75 310 62 96 18.4 Not detected Comparative Example 6 1.25 0.55 2.30 0 170 90 — 17.7 0.71

[0060] Note: The nitrogen and phosphorus contents of the carriers in Comparative Examples 1 and 4 include compounds that are physically adsorbed; the gel fractions of Comparative Examples 1 and 4 are the insoluble residues of uncrosslinked lignin in the buffer solution; the carrier of Comparative Example 6 does not contain grafted phosphorus; water-soluble phosphorus refers to orthophosphate phosphorus measured after water extraction; the phosphate monoester phosphorus of adsorbed compound 2 in Comparative Examples 1 and 4 is not water-soluble orthophosphate.

[0061] As shown in Table 1, the epoxy value of the epoxidized alkali lignin in Examples 1 to 3 was 1.05~1.55 mmol / g, and the residual phenolic hydroxyl content was 0.42~0.72 mmol / g, meaning that 71%~83% of the phenolic hydroxyl groups had been etherified and blocked. The nitrogen mass fraction of the modified lignin carrier was 1.95%~3.21%, the phosphorus mass fraction was 0.20%~1.02%, and the phosphorus monophosphate accounted for 95%~97% of the total phosphorus mass fraction, indicating that the phosphorus monophosphate of compound 2 did not undergo any side reaction with the epoxy groups under the grafting conditions of pH 6.0~6.5 and 80~90 °C. The equilibrium swelling rate was 140%~205%, and the gel fraction was 86%~93%, indicating that the dicarboxyl crosslinking of compound 3 enabled the carrier to form a water-insoluble network. Comparative Example 3 had an epoxy value of only 0.45 mmol / g and a residual phenolic hydroxyl group of up to 1.90 mmol / g, resulting in insufficient grafting amount and cross-linking density. Comparative Example 5 did not contain compound 3, had a gel fraction of only 62%, and an equilibrium swelling rate as high as 310%. Comparative Example 2 was grafted with uncarbamylated amino acids, which formed non-hydrolyzable carbon-nitrogen bonds with the amino and epoxy groups, causing excessive cross-linking, resulting in an equilibrium swelling rate of only 95%.

[0062] Table 2 Nutrient release characteristics (static water method, enzyme-triggered method, and soil method)

[0063] deal with 24 h nitrogen / % 24 h phosphorus / % 24 h potassium / % 28-day nitrogen / % 28 d phosphorus / % 28-day potassium / % Carrier phosphorus 7 d enzyme-free / % Carrier phosphorus 7 days plus acid phosphatase / % Carrier nitrogen 60 d sterilized soil / % Carrier nitrogen 60 d non-sterile soil / % Carrier nitrogen in rhizosphere soil (60 days) / % Example 1 6.8 1.9 12.5 38 6 55 3.6 63.4 5.8 47.2 68.1 Example 2 5.9 1.6 11.8 34 5 52 3.1 60.8 5.1 44.6 65.0 Example 3 8.2 2.4 13.9 43 7 59 4.4 66.9 6.7 50.3 70.9 Comparative Example 1 41.3 40.5 47.6 92 47 95 95.2 97.0 90.4 93.1 94.0 Comparative Example 2 8.9 3.1 10.9 33 8 49 2.9 55.7 4.1 9.5 12.3 Comparative Example 3 12.8 6.5 18.3 61 22 74 12.1 70.5 14.6 58.2 71.4 Comparative Example 4 24.1 28.4 30.4 78 45 90 80.3 92.5 74.5 81.0 83.2 Comparative Example 5 10.5 4.2 16.1 57 18 71 8.9 68.0 16.3 52.7 69.5 Comparative Example 6 8.1 41.8 13.2 40 45 56 — — 5.5 45.8 66.3

[0064] Note: The 24-hour and 28-day release rates were determined based on the finished product according to GB / T 23348. The phosphorus in the extract was calculated as total phosphorus after digestion. The phosphorus in calcium magnesium phosphate fertilizer is basically insoluble in still water. The phosphorus release from the carrier was based on the grafted phosphorus in the carrier (comparative examples 1 and 4 were adsorbed phosphorus). The nitrogen release from the carrier was the total dissolved nitrogen measured after digestion of the potassium chloride extract, based on the grafted nitrogen in the carrier (comparative examples 1 and 4 were adsorbed nitrogen).

[0065] As shown in Table 2, the initial nitrogen release rate of Examples 1 to 3 in still water at 25 °C for 24 h was 5.9%–8.2%, and the phosphorus release rate was 1.6%–2.4%. The cumulative nitrogen release rate after 28 days was 34%–43%. Both the initial release rate and the cumulative release rate after 28 days met the requirements of GB / T 23348 for slow-release fertilizers. The nitrogen released in still water mainly came from urea embedded in the continuous phase of the carrier, and the small amount of phosphorus released came from the water-soluble part of calcium magnesium phosphate fertilizer and a small amount of dissolved grafting material. Grafted nitrogen was hardly released in still water. In the enzyme-triggered test, the carrier of Example 1 released only 3.6% of the grafted phosphorus in the buffer solution without enzyme after 7 days, while 63.4% was released after the addition of acid phosphatase, indicating that the monophosphate ester of compound 2 was mainly hydrolyzed into orthophosphate under the action of phosphatase. The phosphorus in Comparative Example 6 existed in the form of monoammonium phosphate, and 41.8% was dissolved in 24 h, which was equivalent to all the phosphorus contained in monoammonium phosphate. In the biotriggered experiment, the grafted nitrogen of the carrier in Example 1 released only 5.8% in sterilized soil after 60 days, 47.2% in non-sterilized soil, and 68.1% in macadamia rhizosphere soil. The release rate increased with the increase of soil biological activity. Comparative Example 2, which is anchored by carbon-nitrogen bonds and does not contain urea nitrogen, released only 12.3% in rhizosphere soil after 60 days, proving that carbamoyl and β-hydroxy ester bonds together constitute the release channel that rhizosphere enzymes can cleave. The three compounds in Comparative Examples 1 and 4 exist in the form of physical adsorption and are almost completely dissolved in a short period of time, regardless of whether they are sterilized or not. The dissolved urea compounds cannot be mineralized in sterilized soil, but are rapidly mineralized in non-sterilized soil.

[0066] Table 3 Results of the acid red soil incubation experiment (25 °C, 90 d)

[0067] deal with Mineral nitrogen 14d / % Mineral nitrogen 28d / % Mineral nitrogen 56d / % Mineral nitrogen 90d / % Available phosphorus in soil over 90 days (mg / kg) Phosphate utilization rate / % 28-day soil solution phenolic acid (mg / kg) 30-day ammonia volatilization loss / % Example 1 22 35 58 76 14.2 74.6 0.8 3.1 Example 2 20 32 54 72 10.2 74.3 1.0 2.8 Example 3 25 39 62 79 16.8 60.6 0.7 3.5 Comparative Example 1 68 85 91 93 6.5 21.2 3.8 12.4 Comparative Example 2 20 32 52 68 12.6 60.5 0.9 3.3 Comparative Example 3 41 60 79 88 9.1 54.1 2.9 6.9 Comparative Example 4 55 74 86 91 5.9 17.4 3.5 9.8 Comparative Example 5 38 57 76 87 12.0 50.7 0.9 6.2 Comparative Example 6 23 36 59 77 9.8 44.7 0.8 3.2 Urea control 88 94 95 95 3.0 — 0.5 21.3 Compound fertilizer comparison 85 92 94 94 17.6 19.3 0.5 7.6

[0068] Note: The cumulative release rate of mineral nitrogen is calculated based on the total nitrogen applied; the urea control and compound fertilizer control are urea with the same nitrogen content and 15-15-15 compound fertilizer, respectively; the available phosphorus in the soil is the value determined by the Bray-1 method, and the initial available phosphorus in the tested soil is 3.2 mg / kg; the phosphorus availability rate is the percentage of phosphorus amount converted from the increase in available phosphorus to the actual amount of phosphorus applied in each treatment; phenolic acid is the sum of ferulic acid, p-coumaric acid and vanillic acid.

[0069] The cumulative release curves of mineral nitrogen in soil incubation experiments for Example 1, Comparative Example 1, and Comparative Example 3 are shown below. Figure 4As shown, the mineral nitrogen in Example 1 was 22%, 35%, 58%, and 76% at 14, 28, 56, and 90 days, respectively, showing a near-linear and continuous release. Comparative Example 1 reached 68% at 14 days, and Comparative Example 4 reached 55% at 14 days, both exhibiting a rapid release in the early stages. Comparative Examples 3 and 5 also showed a significantly earlier release due to insufficient phenolic hydroxyl group blocking or lack of cross-linking. The ammonia volatilization loss in Example 1 at 30 days was only 3.1%, far lower than the 21.3% of the urea control and the 7.6% of the compound fertilizer control. Regarding available phosphorus over 90 days, in Example 1, the phosphorus availability was increased from the initial 3.2 mg / kg to 14.2 mg / kg, with a phosphorus availability rate of 74.6%. In contrast, in Comparative Example 6, which used monoammonium phosphate to supply phosphorus, although the amount of phosphorus applied was the same, the available phosphorus in the soil was only 9.8 mg / kg, with a phosphorus availability rate of 44.7%, as the remaining phosphorus was fixed by iron and aluminum in the red soil. The compound fertilizer control had 5.1 times the amount of phosphorus applied in Example 1, with a phosphorus availability rate of only 19.3%. The phenolic acid content in the soil solution after 28 days showed a significant positive correlation with the residual phenolic hydroxyl content of the carrier: the residual phenolic hydroxyl content in Examples 3, 1, and 2, which were 0.42 mmol / g, 0.55 mmol / g, and 0.72 mmol / g, were 0.7 mg / kg, 0.8 mg / kg, and 1.0 mg / kg, respectively, while the residual phenolic hydroxyl content in Comparative Examples 3, 4, and 1, which were 1.90 mmol / g, 2.15 mmol / g, and 2.60 mmol / g, increased to 2.9 mg / kg, 3.5 mg / kg, and 3.8 mg / kg, respectively. This confirms that epoxy etherification effectively inhibits the release of phenolic acid from lignin into the soil solution by blocking phenolic hydroxyl groups.

[0070] Table 4. Results of pot experiment on macadamia seedlings (180 days)

[0071] deal with Number of clustered roots / (units / plant) Seedling dry weight (g / plant) Leaf phosphorus / % <![CDATA[Culturable rhizosphere bacteria / (×10 7 CFU / g)]]> <![CDATA[Rhizosphere Bacillus / (×10 6 copies / g)]]> Acid phosphatase / (μmol / (g·h)) FDA hydrolase activity (μg fluorescein / (g·h)) No fertilizer control 18 21.3 0.062 2.1 0.9 1.9 28 Compound fertilizer comparison 6 29.6 0.135 2.8 1.1 1.1 33 Example 1 27 41.8 0.104 9.6 6.8 3.4 76 Example 2 24 38.9 0.098 8.7 6.0 3.1 70 Example 3 25 39.7 0.108 9.1 6.3 3.3 73 Comparative Example 1 12 30.2 0.091 4.2 2.0 1.8 45 Comparative Example 2 16 31.5 0.099 4.9 2.4 2.5 44 Comparative Example 3 15 32.4 0.093 5.3 2.9 2.2 49 Comparative Example 4 11 28.8 0.088 3.1 1.4 1.6 36 Comparative Example 5 14 32.9 0.095 6.0 3.6 2.4 55 Comparative Example 6 7 30.1 0.142 5.8 3.3 1.2 48

[0072] Note: Each treatment consists of 6 pots, and the data are averages; the compound fertilizer control is a 15-15-15 compound fertilizer with equal nitrogen content; acid phosphatase is measured by the amount of p-nitrophenol produced.

[0073] The number of clustered roots and the abundance of rhizosphere Bacillus in each treatment during the pot experiment are as follows: Figure 4As shown. The unfertilized control formed 18 root clusters due to phosphorus deficiency, but the dry matter weight was only 21.3 g. The compound fertilizer control with equal nitrogen content had a sudden increase in water-soluble phosphorus, resulting in a decrease in the number of root clusters to 6, while the phosphorus content in the leaves increased to 0.135%. The number of root clusters in Examples 1 to 3 was 24-27, which not only did not decrease due to fertilization, but was actually higher than that in the unfertilized control. This is because the overall growth of the plants in the unfertilized control was limited, and the total root system was small, so the absolute number of root clusters was limited by the total root system. In contrast, the total root system increased under the treatment of Examples 1 and 3, and there was no sudden increase in water-soluble orthophosphate in the rhizosphere. The phosphorus concentration in the rhizosphere remained within the range that induces root clusters. The phosphorus content in the leaves of the examples was maintained in the suitable range of 0.098% to 0.108%, and the dry matter weight of the seedlings reached 38.9-41.8 g, which was 31%-41% higher than that of the compound fertilizer control. Although Comparative Example 6 also possessed nitrogen channels and network channels, because phosphorus was provided in the form of monoammonium phosphate, the number of clustered roots decreased to 7, the phosphorus content in the leaves increased to 0.142%, and the dry matter weight was only 30.1 g. This demonstrates that the presence of phosphorus in the form of monophosphate is a necessary condition for the clustered roots to retain their autonomous phosphorus uptake function. Regarding the rhizosphere microecology, the number of culturable bacteria in the rhizosphere of Example 1 was 9.6 × 10⁶. 7 CFU / g, Bacillus abundance was 6.8 × 10⁻⁶. 6 The copies / g were 3.4 times and 6.2 times that of the compound fertilizer control, respectively. The acid phosphatase activity and FDA hydrolase activity were also 3.1 times and 2.3 times that of the compound fertilizer control, respectively. Comparative Example 4 retained all phenolic hydroxyl groups and loaded the compound in an adsorbed form. The number of rhizosphere bacteria and the abundance of Bacillus were close to the control, indicating that the blocking of phenolic hydroxyl groups and enzyme-triggered release jointly determined the improvement of the rhizosphere microecology.

[0074] Table 5 Results of two-year field trials (8-year-old macadamia nuts in Lincang, Yunnan and Chongzuo, Guangxi)

[0075] test point deal with Yield per plant (kg / plant) Kernel yield / % Leaf nitrogen / % Soil organic matter (g / kg) Soil pH <![CDATA[Rhizosphere Bacillus / (×10 6 copies / g)]]> Lincang Conventional fertilization control 11.6 33.1 1.52 18.0 4.7 1.3 Lincang Example 1 14.9 36.4 1.61 21.9 5.3 6.1 Lincang Comparative Example 1 12.1 33.6 1.50 20.6 4.9 2.2 Lincang Comparative Example 4 11.9 33.4 1.55 20.1 4.8 1.5 Lincang Comparative Example 6 12.8 34.0 1.58 21.5 5.1 3.0 Chongzuo Conventional fertilization control 10.2 32.5 1.49 15.3 4.5 1.1 Chongzuo Example 1 13.4 35.8 1.60 19.0 5.1 5.6 Chongzuo Comparative Example 1 10.9 32.9 1.48 17.8 4.7 1.9 Chongzuo Comparative Example 4 10.5 32.7 1.53 17.4 4.6 1.3 Chongzuo Comparative Example 6 11.3 33.3 1.57 18.7 4.9 2.7

[0076] Note: The yield is the two-year average of the yield of fruit with shells (10% moisture content); the initial organic matter content of the soil at the Lincang test site was 18.2 g / kg and the pH was 4.9, while the initial organic matter content of the soil at the Chongzuo test site was 15.6 g / kg and the pH was 4.7; the soil indicators are the values ​​measured in the 0-20 cm soil layer at the end of the experiment.

[0077] As shown in Table 5, at the two experimental sites in Lincang and Chongzuo, the average yield per plant in Example 1 over two years was 14.9 kg and 13.4 kg, respectively, which was 28.4% and 31.4% higher than that of the conventional fertilization control. The kernel yield increased by 3.3 percentage points, and the nitrogen content in the leaves increased to 1.60%~1.61%. At the end of the experiment, the organic matter in the 0~20 cm soil layer increased from 18.2 g / kg and 15.6 g / kg to 21.9 g / kg and 19.0 g / kg, respectively. The soil pH rose from 4.9 and 4.7 to 5.3 and 5.1, respectively. The abundance of rhizosphere Bacillus was 4.7~5.1 times that of the conventional fertilization control. Although Comparative Example 1 also incorporated alkali lignin and increased organic matter, the yield increase was only 4.3% to 6.9% due to the rapid release of nutrients in the early stage and the inhibition of phenolic acids; Comparative Example 4 saw a yield increase of only 2.6% to 2.9%; and Comparative Example 6, due to the inhibition of clustered roots by water-soluble phosphorus and its fixation by the soil, achieved a yield increase of 10.3% to 10.8%, which was significantly lower than that of Example 1.

[0078] The above results indicate that the technical effect of the present invention stems from the mutual coupling between the three release channels and the phenolic hydroxyl group blockade: the β-hydroxy ester linker arms on the lignin skeleton are respectively attached to the grafting units of compound 1 and compound 2, the crosslinking unit of compound 3 connects to the adjacent lignin skeleton, potassium humate is incorporated into the network after ripening, the acid phosphatase secreted by the clustered roots and the esterase and N-carbamoyl hydrolase secreted by rhizosphere bacteria respectively trigger the release of the corresponding channels, and the proliferation of rhizosphere bacteria in turn increases the secretion of enzymes. In the nitrogen channel, compound 1 is anchored to the lignin skeleton via a β-hydroxy ester bond. The ester bond is hydrolyzed by esterases secreted by rhizosphere bacteria, releasing (2S)-2,6-bis[(aminocarbonyl)amino]hexanoic acid, which is then gradually hydrolyzed by N-carbamoyl hydrolases and amide hydrolases into ammonia, carbon dioxide, and L-lysine. L-lysine acts as a carbon and nitrogen source and a chemotactic agent, promoting the proliferation of Bacillus and Pseudomonas in the rhizosphere. The proliferated bacteria secrete more esterases and N-carbamoyl hydrolases, thus creating a positive feedback loop between the nitrogen release rate and rhizosphere biological activity. This is confirmed by the increasing carrier nitrogen release rate in sterilized soil, non-sterile soil, and rhizosphere soil in Table 2, and the synchronous increase in FDA hydrolase activity in Table 4. In the phosphorus channel, the phosphate monoester of compound 2 is mainly hydrolyzed by acid phosphatase. The acid phosphatase activity secreted by macadamia nut cluster roots is 3 to 5 times that of ordinary root tips. Cluster roots are induced to form under low phosphorus conditions and automatically disappear when phosphorus is sufficient. Therefore, the release of phosphorus is consistent with the phosphorus uptake behavior of nuts at the organ level. The conditioning fertilizer does not contain water-soluble orthophosphate, so the cluster roots are not inhibited. The citrate-soluble phosphorus of calcium magnesium phosphate fertilizer is dissolved by citric acid secreted by the cluster roots. The fact that the number of cluster roots in the example in Table 4 is higher than that in the unfertilized control while the phosphorus in the leaves is still within the appropriate range is direct evidence of this match. In the network channel, the dicarboxyl crosslinking of compound 3 determines the gel fraction and equilibrium swelling rate of the carrier, thereby controlling the diffusion rate of urea and potassium sulfate in the continuous phase. As the ester bonds are gradually hydrolyzed, the network relaxes step by step, and the released N-(aminocarbonyl)-N-(carboxymethyl)glycine is converted into iminodiacetic acid by N-carbamoyl hydrolases. The latter acts as a soluble small molecule ligand to instantaneously complex iron and aluminum ions in the rhizosphere and keep them soluble, reducing the re-fixation of orthophosphate released by compound 2 on the solid phase surface. The phosphoric acid utilization rate of Example 1 in Table 3 is much higher than that of Comparative Example 6, which reflects this.

[0079] Phenolic hydroxyl group blockade is a prerequisite for the three pathways mentioned above to function. Epoxy etherification converts 71%–83% of the phenolic hydroxyl groups into glycidyl ethers, providing anchoring sites for the three compounds and interrupting the pathway of phosphorus fixation through complexation of solid-phase phenolic hydroxyl groups with iron and aluminum ions, while also reducing the tendency of lignin oxidation and degradation to release phenolic acids. The positive correlation between phenolic acid content and residual phenolic hydroxyl content in soil solution shown in Table 3, and the significant reduction in rhizosphere bacteria count in Comparative Examples 3 and 4 shown in Table 4, both confirm this. The lignin skeleton itself mineralizes slowly in the soil; its role is to act as an insoluble anchor, fixing the three compounds in the rhizosphere and converting them into soil organic matter on a biennial scale. The increase in soil organic matter shown in Table 5 originates from this process.

[0080] All small molecular fragments released into the rhizosphere by this invention are natural metabolites or substances that can be mineralized by soil microorganisms: Compound 1 is ultimately converted into L-lysine, ammonia, and carbon dioxide; Compound 2 is converted into orthophosphate, L-serine, ammonia, and carbon dioxide; Compound 3 is converted into iminodiacetic acid and further mineralized into glycine and carbon dioxide. The 3-aryloxy-1,2-propanediol unit remaining on the lignin skeleton after ester bond hydrolysis is hydrophilic and non-toxic; the carrier does not contain recalcitrant synthetic polymers such as polyacrylates, and the lignin skeleton is converted into soil humus on a multi-year scale. The residual epoxy content of the finished product after step five curing is ≤0.03 mmol / g, close to the detection limit of the hydrochloric acid-acetone method.

[0081] Step five, curing, structurally completes the final construction of the carrier network. At the end of step three, the carrier still retains 0.27–0.37 mmol / g of residual epoxy groups. These epoxy groups esterify with the carboxyl groups of potassium humate during the closed curing process after granulation, causing humic acid to be incorporated into the carrier network and become part of the continuous phase. The remainder is hydrolyzed into hydrophilic vicinal diols, reducing the residual epoxy group in the finished product to below 0.03 mmol / g. In the parameter over-limit test, when the ratio of carboxyl groups to epoxy groups was 0.5:1, there were too many residual epoxy groups. During curing, the particles were over-crosslinked and the potassium release was too slow, indicating that curing is the final step in the network channel construction rather than simple drying.

[0082] There is a clear non-additive interdependence among the three channels, which can be quantitatively described by removing channels one by one. Using seedling dry weight as an indicator, Comparative Example 1, where none of the three channels were present, yielded 30.2 g; Example 1, where all three channels were present, yielded 41.8 g, for a total increase of 11.6 g; Comparative Example 5, where network channels were removed, yielded 32.9 g, a loss of 8.9 g; Comparative Example 6, where monoammonium phosphate was used to replace compound 2 to remove phosphorus channels, yielded 30.1 g, a loss of 11.7 g; Comparative Example 2, where the nitrogen channels were disabled due to the compound not being carbamylated, yielded 31.5 g, a loss of 10.3 g; the sum of the losses from removing the three individual channels was 30.9 g, 2.7 times the total increase of 11.6 g. Using rhizosphere Bacillus abundance as an indicator, Comparative Example 1 yielded 2.0 × 10⁻⁶ g. 6 copies / g, Example 1: 6.8 × 10 6 copies / g, with a total increment of 4.8 × 10⁻⁶. 6 The loss of Comparative Examples 5, 6, and 2 compared to Example 1 was 3.2 × 10⁻⁶ copies / g, while the losses were 3.2 × 10⁻⁶ copies / g, respectively. 6 copies / g, 3.5×10 6 copies / g and 4.4×10 6 The total loss is 11.1 × 10 copies / g. 6 The copies / g is 2.3 times the total increment. If the effects of the three channels are independent and simply added together, the sum of the losses from removing each channel individually should equal the total increment. However, the measured sum of losses is 2.3 to 2.7 times the total increment, indicating that the effect of each channel depends on the presence of the other channels: the phosphorus channel preserves the clustered roots, and the acid phosphatase and carboxylic acid secreted by the clustered roots provide a microenvironment for the rhizosphere bacteria on which the nitrogen channel depends; the L-lysine released by the nitrogen channel drives bacterial proliferation and increases enzyme activity; the network channel confines this positive feedback to the rhizosphere microenvironment near the carrier to prevent a sudden release of nutrients. In Comparative Example 5, when compound 3 is missing, the carrier fragment dissolution, nitrogen release shifts forward, and the abundance of Bacillus is only 53% of that in Example 1, indicating that the network channel is the structural basis for the sustained positive feedback.

[0083] In summary, this invention blocks the phenolic hydroxyl groups of lignin through epoxy etherification and transforms them into anchoring sites. It constructs nitrogen channels, phosphorus channels, and network channels triggered by rhizosphere acid phosphatases, esterases, and N-carbamoyl hydrolases using three carbamylated precursor compounds. This allows the nutrient release rhythm of the conditioning fertilizer to be determined by the biological activity of the nut rhizosphere, thus possessing the dual functions of continuous nutrient supply and rhizosphere microecological regulation. Furthermore, it realizes the resource utilization of alkali lignin, a byproduct of papermaking, and can be widely applied in macadamia nut cultivation in Yunnan and Guangxi, as well as other southern woody nut cultivation scenarios.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A nut-based lignin-based rhizosphere microecological conditioning fertilizer, characterized in that, It is made from the following raw materials in parts by weight: 55-65 parts modified lignin carrier, 12-18 parts urea, 12-16 parts potassium sulfate, 5-8 parts calcium magnesium phosphate fertilizer, 3-6 parts potassium humate, and 1-3 parts bentonite; the modified lignin carrier is a graft crosslinking product of epoxidized alkali lignin with compounds 1, 2, and 3; compound 1 is (2S)-2,6-bis[(aminocarbonyl)amino]hexanoic acid, and compound 2 is (2S)-2-[(aminocarbonyl)amino]-3-{[dihydroxy(oxymethylene)-λ 5 [-methoxy]propionic acid, wherein compound 3 is N-(aminocarbonyl)-N-(carboxymethyl)glycine; wherein the epoxidized alkali lignin is glycidyl ether formed by etherification of the phenolic hydroxyl group of alkali lignin with epichlorohydrin, and its epoxy value is 0.8~1.6 mmol / g; the α-carboxyl group of compound 1 and the carboxyl group of compound 2 respectively ring-open with the epoxy group of the epoxidized alkali lignin to form β-hydroxy ester bonds, and the two carboxyl groups of compound 3 each ring-open with one epoxy group to form β-hydroxy ester bonds to form cross-linking points; the carboxyl group of potassium humate ring-opens with the residual epoxy group in the modified lignin carrier to form β-hydroxy ester bonds; the ratio of the total amount of carboxyl groups of compounds 1, 2 and 3 to the amount of epoxy groups of the epoxidized alkali lignin is (0.6~0.9):1, and the ratio of the amount of compounds 1, 2 and 3 to the amount of epoxy groups is (2~5):(0.5~2):

1.

2. The nut lignin-based rhizosphere microecological conditioning fertilizer according to claim 1, characterized in that, The alkali lignin is alkali lignin precipitated from papermaking black liquor, with a phenolic hydroxyl content of 2.0~3.5 mmol / g, a weight-average molecular weight of 3000~8000, and an ash content of ≤3%; the residual phenolic hydroxyl content of the epoxidized alkali lignin is ≤0.8 mmol / g.

3. The nut lignin-based rhizosphere microecological conditioning fertilizer according to claim 1, characterized in that, The equilibrium swelling rate of the modified lignin carrier before granulation is 120%~220%, and the gel fraction is ≥85%; The equilibrium swelling rate is the ratio of the difference between the swelling mass and the dry mass of the modified lignin carrier after soaking in water at 25 °C for 24 h to the dry mass. The gel fraction is the ratio of the dried residual mass of the modified lignin carrier after soaking in phosphate buffer at 25 °C and pH 7.0 for 48 h to the initial dry mass. The modified lignin carrier contains 1.8% to 3.5% nitrogen and 0.2% to 1.1% phosphorus by mass.

4. The nut lignin-based rhizosphere microecological conditioning fertilizer according to claim 1, characterized in that, Before granulation, the modified lignin carrier contains phosphate monoester phosphorus accounting for ≥95% of the total phosphorus by mass; the nut lignin-based rhizosphere microecological conditioning fertilizer contains ≤0.1% water-soluble phosphorus (calculated as P2O5) as determined by GB / T 8573, and the residual epoxy content is ≤0.03 mmol / g.

5. The nut lignin-based rhizosphere microecological conditioning fertilizer according to claim 1, characterized in that, The nut lignin-based rhizosphere microecological conditioning fertilizer consists of particles with a diameter of 2-4 mm, a moisture content of ≤5%, and a crushing resistance of ≥15 N. The urea, potassium sulfate, and calcium magnesium phosphate fertilizer are dispersed and embedded in a continuous phase composed of the modified lignin carrier, potassium humate, and bentonite.

6. The method for preparing the nut lignin-based rhizosphere microecological conditioning fertilizer according to any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1, Industrial lignin pretreatment: The black liquor from papermaking is acidified with sulfuric acid to pH 2.0~3.0, filtered, washed until the conductivity of the filtrate is ≤200 μS / cm, dried and pulverized to a particle size ≤0.15 mm to obtain alkali lignin; Step 2, Preparation of Epoxidized Alkali Lignin: Alkali lignin is dissolved in an aqueous sodium hydroxide solution, epichlorohydrin is added, and the molar ratio of epichlorohydrin to the phenolic hydroxyl groups of alkali lignin is (1.5~2.6):

1. The reaction is carried out at 55~65 °C for 2~4 h, and then at 70~80 °C for 1~3 h. After acid precipitation, washing, and drying, epoxidized alkali lignin with an epoxy value of 0.8~1.6 mmol / g is obtained. Step 3, Compound grafting and crosslinking: Epoxidized alkali lignin is dispersed in a mixed solvent of water and ethanol, compound 1, compound 2 and compound 3 are added, the pH is adjusted to 6.0~6.5 with potassium hydroxide, tetrabutylammonium bromide is added, and the mixture is refluxed at 80~90 °C for 4~8 h. After filtration and washing, the mixture is dried at ≤60 °C to obtain a modified lignin carrier containing residual epoxy groups. Step 4: Granulation and molding: The modified lignin carrier, urea, potassium sulfate, calcium magnesium phosphate fertilizer, potassium humate and bentonite are mixed according to the mass fractions mentioned above, and water is added in a disc granulator to granulate wet granules with a particle size of 2~4 mm. Step 5, Sealed Curing: The wet granules obtained in Step 4 are sealed and cured at 70~90 °C for 2~4 h until the residual epoxy group content is ≤0.03 mmol / g, and then dried until the moisture content is ≤5%; Step 6, Testing and Packaging: Test total nutrient content, residual epoxy content, particle size, moisture content and particle crushing resistance, and then package the particles.

7. The preparation method according to claim 6, characterized in that, Compound 1 is prepared by reacting L-lysine or L-lysine hydrochloride with potassium cyanate in water at pH 8.5–9.5 and 45–60 °C for 4–8 h, with a molar ratio of potassium cyanate to L-lysine or L-lysine hydrochloride of (2.1–2.5):1; Compound 2 is prepared by reacting O-phospho-L-serine with potassium cyanate in water at pH 8.5–9.5 and 40–50 °C for 4–6 h, with a molar ratio of potassium cyanate to O-phospho-L-serine of (1.1–1.3):1; Compound 3 is prepared by reacting iminodiacetic acid with potassium cyanate in water at pH 9.0–9.5 and 55–65 °C for 6–10 h, with a molar ratio of potassium cyanate to iminodiacetic acid of (1.2–1.5):1; after the reaction, each compound is acidified with hydrochloric acid at 0–5 °C to the pH value. 1.5~2.5, crystallize or precipitate with alcohol, filter and dry.

8. The preparation method according to claim 6, characterized in that, In step two, the mass concentration of the sodium hydroxide aqueous solution is 2%~4%, and the mass ratio of alkali lignin to sodium hydroxide aqueous solution is 1:(4~6); in step three, the volume ratio of water to ethanol is (1.5~2.5):1, the volume ratio of epoxidized alkali lignin to mixed solvent is 1 g:(5~8) mL, and the amount of tetrabutylammonium bromide is 0.5%~2% of the amount of epoxy group.

9. The preparation method according to claim 6, characterized in that, After the reaction in step three is completed, the filtrate is concentrated under reduced pressure and then returned to the next batch for use in step three. In step four, the amount of water added for granulation is 8% to 12% of the total mass of the material, the disc granulator is tilted at an angle of 45° to 55° and rotated at a speed of 15 to 25 r / min. In step five, the maturation temperature is 75 to 85 °C, the maturation time is 2.5 to 3.5 h, and the drying temperature is 55 to 65 °C.

10. The preparation method according to claim 6, characterized in that, The mass fraction of phosphate monoester phosphorus in the modified lignin carrier obtained in step three was determined by the solid content of the total phosphorus. 31 P-magic angle rotation NMR spectroscopy determination; in step six, total nitrogen was determined according to GB / T 8572, total phosphorus was determined according to GB / T 8573 after the sample was digested with sulfuric acid-nitric acid, potassium was determined according to GB / T 8574, residual epoxy content was determined by hydrochloric acid-acetone method and the blank of the same formula without modified lignin carrier was subtracted, particle size was determined according to GB / T 24891, moisture content was determined according to GB / T 8576, and particle crushing resistance was the average value of the crushing force when 20 particles with a particle size of 2.8~3.2 mm were loaded radially until crushing.

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