A soil conditioner and a method of making the same

Abstract

The application belongs to the technical field of soil improvement, and particularly relates to a soil conditioner and a preparation method thereof. The soil conditioner is composed of an inner core layer, an intermediate regulation layer and an outer quick-acting layer. The inner core layer comprises the following raw materials: calcium-magnesium-humic acid loaded biochar, dolomite powder, gypsum powder, zeolite, sodium alginate, carboxymethyl cellulose and pre-gelatinized modified starch. The intermediate regulation layer comprises the following raw materials: a film-forming base material, bentonite and a structure stabilizing component. The outer quick-acting layer comprises the following raw materials: calcium carbonate, fulvic acid, an outer film-forming base material and glycerol. The outer quick-acting layer is used to start a surface layer slow acid process after being applied, to preferentially reduce the harm of surface layer active acid, and to quickly supplement part of Ca / Mg. The intermediate regulation layer is used to control the diffusion path of water and ions, and to delay the release speed of the conditioning components of the inner core layer. The inner core layer is used to continuously release slow acid and calcium-magnesium components, and to build a water and fertilizer retaining and microhabitat skeleton, so as to facilitate the continuous improvement of the subsurface layer.

Description

Technical Field

[0001] This invention belongs to the field of soil improvement technology, specifically relating to a soil conditioner and its preparation method. Background Technology

[0002] With the continuous advancement of intensive agricultural production, the long-term excessive application of chemical fertilizers, and the impact of atmospheric acid deposition, soil acidification has become an increasingly prominent problem, posing a significant challenge to the sustainable development of modern agriculture. Soil acidification not only directly leads to poor root development and reduced nutrient absorption efficiency in crops, but also induces increased activity of exchangeable heavy metal ions such as aluminum and manganese, resulting in significant physiological toxicity. Currently, remediation solutions for acidified soils mainly rely on the application of alkaline conditioning materials such as lime, dolomite powder, and alkaline industrial byproducts. However, existing technologies still face many limitations in practical applications. On the one hand, traditional alkaline conditioners are mostly applied directly in powder form, which easily generates dust during transportation and application, causing environmental pollution and material loss. Furthermore, the fine powder is easily leached away by runoff or rapidly adsorbed and passivated by soil particles after entering the soil, resulting in poor sustainability of its improvement effect. On the other hand, the improvement of acidified soil often exhibits obvious hierarchical characteristics. The surface layer has high and variable active acidity, while the subsurface and deep soils also suffer from severe acidification and calcium and magnesium nutrient deficiency due to long-term leaching. Simple powder mixing and application often fails to meet the dual needs of rapid neutralization of the surface layer and continuous improvement of the deep layer.

[0003] Furthermore, the remediation of acidified soils involves not only the physicochemical neutralization of pH but also the reconstruction of soil microhabitats. Existing soil amendments often have limited functions, focusing only on acid neutralization while neglecting the systematic improvement of soil water and fertilizer retention capacity, particle pore structure, and microbial colonization environment. Although biochar has shown potential in carbon sequestration, emission reduction, and soil structure improvement, the alkalinity release rate of unmodified biochar is difficult to control, and its pore structure is easily clogged by fine soil particles, preventing it from fully functioning as a nutrient carrier. In the field of coated controlled-release materials, existing coating processes mostly use synthetic polymers or single inorganic film-forming matrices. The former suffers from poor biodegradability and is prone to secondary pollution, while the latter generally suffers from high membrane brittleness, poor impact resistance, and a single release pathway. Under complex soil moisture transport conditions, how to achieve gradient release of conditioning components through reasonable structural design, that is, to quickly alleviate the damage of surface active acids in the early stage of application, and then maintain the long-term stability of the subsurface and rhizosphere environment through controlled diffusion pathways, while simultaneously constructing a water and fertilizer retention framework that is conducive to crop growth, is a key technical challenge currently facing the field of soil conditioner research and development. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a soil conditioner and its preparation method. The conditioner employs a multi-layered core-shell structure consisting of a core layer, an intermediate regulating layer, and an outer fast-acting layer. The outer fast-acting layer is used to quickly initiate the surface acid-slowing process after application, preferentially reducing the harmful effects of active acids in the surface soil and rapidly replenishing some Ca / Mg. The intermediate regulating layer controls water and ion diffusion pathways, slowing the release rate of the conditioning components in the core layer. The core layer continuously releases acid-slowing and calcium- and magnesium-supplying components, and constructs a water-retaining, fertilizer-retaining, and micro-habitat framework to facilitate continuous improvement of the subsurface layer.

[0005] The technical effects described in this invention are achieved through the following technical solution: a soil conditioner, which consists of a core layer, an intermediate regulating layer and an outer fast-acting layer; Furthermore, the core layer comprises, by weight, the following raw materials: 18-32 parts calcium-magnesium-humic acid-supported biochar, 8-18 parts dolomite powder, 2-6 parts gypsum powder, 6-12 parts zeolite, 1-3 parts sodium alginate, 1-4 parts carboxymethyl cellulose, and 1-4 parts pregelatinized modified starch.

[0006] Furthermore, the preparation steps of the calcium-magnesium-humic acid-supported biochar are as follows: Soluble humic substances are added to water to prepare a humic substance loading solution of 3-6 wt%. Dolomite powder and gypsum powder are added to the humic substance loading solution to prepare a calcium-magnesium loading slurry. Alkaline biochar is then added to allow the loading slurry to fully enter the pores of the biochar and adhere to its surface. The mixture is allowed to stand for 2-4 hours to mature. It is then dried at 60-80℃ until the water content is ≤10 wt% to obtain calcium-magnesium-humic substance-loaded biochar.

[0007] Furthermore, the soluble humic substance is selected from either fulvic acid or potassium humate; Furthermore, the pH of the aqueous extract of the alkaline biochar is 8.5–10.5; Furthermore, the mass ratio of the biochar, dolomite powder, gypsum powder, and humic load liquid is 1:0.3-0.8:0.1-0.3:2-4.

[0008] By preloading soluble humic substances, dolomite powder, and gypsum powder onto the pores and surface of biochar, the calcium and magnesium conditioning components can be transformed from a dispersed powder state to a carrier-loaded state, which helps to improve their distribution uniformity and retention in the core layer and provides a basis for subsequent continuous release.

[0009] Among them, the calcium-magnesium-humic matter-loaded biochar serves as the core functional carrier of the core layer. On the one hand, the porous structure of biochar carries calcium-magnesium conditioning components and humic components to reduce the initial loss of conditioning components and prolong their action time. On the other hand, it is conducive to the formation of a composite skeleton inside the particles that has the functions of water retention, buffering and microenvironment maintenance, thereby facilitating the continuous conditioning of acidified soil and the improvement of the rhizosphere environment.

[0010] Dolomite powder is used to further provide a slow-release source of calcium and magnesium to continuously neutralize soil acidity and replenish Ca and Mg; gypsum powder is used to supplement a more mobile source of calcium to facilitate the continuous improvement of the subsurface acidification environment and the hazards of exchangeable aluminum.

[0011] Furthermore, the intermediate control layer comprises, by weight, the following raw materials: 2-6 parts of film-forming substrate, 5-10 parts of bentonite, and 1-4 parts of structural stabilizing component; Furthermore, the film-forming substrate is selected from one or both of sodium alginate and pectin; Furthermore, the structurally stabilizing component is selected from one or both of lignin and calcium lignin sulfonate; Furthermore, the outer fast-acting layer comprises, by weight, the following raw materials: 3-8 parts calcium carbonate, 0.5-2 parts fulvic acid, 1-3 parts outer film-forming substrate, and 0.2-0.8 parts glycerol; Furthermore, the outer film-forming substrate is selected from one or both of pectin and pregelatinized modified starch.

[0012] A second aspect of the present invention is to provide a method for preparing a soil conditioner, specifically comprising the following steps: S101: Sodium alginate, carboxymethyl cellulose and pregelatinized modified starch are added to water to prepare a core bonding matrix solution; S102: Mix calcium-magnesium-humic material-loaded biochar, dolomite powder, gypsum powder and zeolite, then add the core bonding matrix solution obtained in step S101 to make a wet material; then granulate to make wet core particles, and contact the wet core particles with a 3-5 wt% calcium chloride solution for curing for 10-20 min; then dry at 50-60℃ until the particle moisture content is ≤15 wt% to obtain core particles; S103: Add film-forming substrate, bentonite and structural stabilizing components to water to prepare intermediate control layer coating slurry; coat the core particles obtained in step S102 so that the weight gain of the intermediate control layer coating accounts for 10-18 wt% of the core particle mass on a dry basis; after coating, perform secondary curing with 1-3 wt% calcium chloride solution for 10-30 min, and then dry at 45-55℃ until the particle moisture content is ≤12 wt% to obtain intermediate coated particles; S104: Add calcium carbonate, humic acid, outer film-forming substrate and glycerin to water to prepare an outer fast-acting coating slurry; coat the intermediate coating particles obtained in step S103 so that the weight gain of the outer fast-acting coating layer accounts for 8-14 wt% of the mass of the intermediate coating particles on a dry basis; dry at 40-50℃ after coating until the moisture content of the finished product is ≤10 wt% to obtain the soil conditioner finished product.

[0013] Further, in step S101, the total solid content of the core bonding matrix solution is controlled to be 5-10 wt%; Further, in step S102, the moisture content of the wet material is 25-40 wt%; Further, in step S103, the total solids content of the intermediate regulating layer coating slurry is controlled to be 10-18 wt%. In step S103, an intermediate control layer is set up. On the one hand, it is used to control the diffusion path and release rate of the active components in the core layer. On the other hand, it is used to improve the interlayer stability of the particles during subsequent drying, storage and application, so as to facilitate the division of labor and cooperation between the rapid effect of the outer layer and the slow release of the core. Further, in step S104, the total solids content of the outer fast-acting coating slurry is controlled to be 20-35 wt%; Furthermore, in step S104, the particle size of the finished soil conditioner is screened to be 2-5 mm; In step S104, an outer fast-acting layer is set up. By utilizing the weak interaction between fulvic acid and calcium carbonate, the outer film-forming substrate is synergistically improved to enhance the loose and porous structure of the outer layer, thus facilitating rapid disintegration after being applied to the soil. This allows the particles to release the fast-acting slow-acting acid components in the outer layer first after being applied to the soil, thereby preferentially improving the surface acidification environment. At the same time, the outer coating can also reduce the direct exposure of the core layer in the finished particle stage, which is conducive to maintaining the subsequent continuous conditioning effect of the core layer.

[0014] The beneficial effects of this invention are as follows: The soil conditioner for acidified soil provided by this invention adopts a single-particle, multi-layer structure consisting of a core layer, an intermediate regulating layer, and an outer fast-acting layer. This integrates fast-acting acid mitigation, diffusion regulation, continuous supply, and water retention stability within a single particle. Compared to directly mixing dolomite, gypsum, biochar, humic substances, and water-retaining components, this method is more conducive to forming a synergistic conditioning process with spatial division of labor and temporal gradient. The outer fast-acting layer contains calcium carbonate, fulvic acid, and a film-forming substrate. After the particles are applied to acidified soil, they can first contact the surface acidic medium, preferentially initiating the surface acid mitigation process. This rapidly improves the initial acidification environment of the topsoil, reduces the adverse effects of surface acid damage on root germination and early growth, and provides more suitable external conditions for the subsequent continuous action of the core layer.

[0015] The intermediate regulation layer is located between the outer layer and the core. It forms a diffusion-blocking interface through the film-forming substrate, bentonite and structural stabilizing components. It can delay the rapid exchange of water and ions between the inside and outside of the particles to a certain extent, reduce the initial concentrated release of calcium and magnesium conditioning components and humic components in the core, and help maintain the integrity of the particle structure and prolong the duration of the improvement effect.

[0016] The calcium-magnesium-humic acid-loaded biochar in the core layer serves two purposes. First, the biochar's porous structure and surface loading capacity support dolomite, gypsum, and soluble humic substances, transforming the source of calcium and magnesium from a dispersed powder state to a carrier-loaded state. This improves the uniformity of component distribution within the particles and enhances their retention. Second, the loaded biochar, together with dolomite, gypsum, zeolite, and the binding and water-retaining matrix, forms a carbon-mineral-humic composite framework. This facilitates the continuous replenishment of Ca and Mg, mitigates soil acidity, reduces the harmful effects of exchangeable aluminum, and improves the subsurface environment. Simultaneously, the composite framework also possesses water-holding, buffering, and adsorption properties, reducing water evaporation and nutrient leaching, improving the rhizosphere microenvironment, promoting the activity of indigenous microorganisms and the maintenance of related enzyme activity, and contributing to the formation and stability of soil aggregates.

[0017] In summary, this invention achieves a balance between rapid acidification in the outer layer, the intermediate regulating layer, and the core layer through a layered synergistic effect, avoiding the one-time neutralization effect of a single component. This balances the rapid acidification in the surface layer with the continuous conditioning in the subsurface layer, thus providing a more comprehensive improvement to the physicochemical properties and rhizosphere ecological environment of acidified soil. Attached Figure Description

[0018] Figure 1 Soil conditioner sample particles Ca for examples and comparative examples 2+ Cumulative release curve; Figure 2 Soil conditioner sample particles Mg for examples and comparative examples 2+ Cumulative release curve; Figure 3 The effect of soil conditioner sample particles on pH in the 0-20cm soil layer is shown in the example and comparative examples. Figure 4 The graph shows the effect of soil conditioner sample particles on the pH of the 20-40cm soil layer in the examples and comparative examples. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Unless otherwise specified, the raw materials involved in the present invention are all purchased through conventional commercial channels. Experimental methods without specific conditions are conventional methods and conditions well known in the art, or according to the conditions recommended by the instrument manufacturer.

[0020] Example 1: A soil conditioner, which consists of a core layer, an intermediate regulating layer and an outer fast-acting layer; The core layer, by weight, comprises the following raw materials: 25 parts calcium magnesium-humic material-supported biochar, 14 parts dolomite powder, 4 parts gypsum powder, 9 parts zeolite, 2 parts sodium alginate, 2 parts carboxymethyl cellulose, and 2.5 parts pregelatinized modified starch. The preparation steps of the calcium-magnesium-humic acid-supported biochar are as follows: Fulvic acid was added to water to prepare a 5wt% humic load solution; 5g of dolomite powder and 2g of gypsum powder were added to 30g of humic load solution to prepare a calcium-magnesium load slurry; then 10g of alkaline biochar was added to allow the load slurry to fully enter the pores of the biochar and adhere to its surface, and the mixture was allowed to stand and mature for 3 hours; the mixture was then dried at 70℃ until the water content was ≤10wt% to obtain calcium-magnesium-humic load biochar. The pH of the aqueous extract of the alkaline biochar is 9.5; The intermediate control layer, by weight, comprises the following raw materials: 4 parts sodium alginate, 8 parts bentonite, and 2.5 parts calcium lignosulfonate. The outer fast-acting layer, by weight, comprises the following raw materials: 6 parts calcium carbonate, 1.4 parts humic acid, 2 parts pregelatinized modified starch, and 0.5 parts glycerol; The preparation method of the soil conditioner specifically includes the following steps: S101: Sodium alginate, carboxymethyl cellulose and pregelatinized modified starch are added to water to prepare a core bonding matrix solution with a total solid content of 8 wt%. S102: Calcium-magnesium-humic material-loaded biochar, dolomite powder, gypsum powder and zeolite are mixed, and the core bonding matrix solution prepared in step S101 is added to make a wet material with a water content of 30wt%; then granulation is carried out to make wet core particles, and the wet core particles are solidified by contacting a 4wt% calcium chloride solution for 15min; then dried at 55℃ until the particle water content is ≤15wt% to obtain core particles; S103: Sodium alginate, bentonite, and calcium lignosulfonate are added to water to prepare an intermediate control layer coating slurry with a total solid content of 15wt%; the core particles obtained in step S102 are coated so that the weight gain of the intermediate control layer coating accounts for 15wt% of the core particle mass on a dry basis; after coating, a 2wt% calcium chloride solution is used for secondary curing for 20min, and then dried at 50℃ until the particle moisture content is ≤12wt% to obtain intermediate coated particles; S104: Add calcium carbonate, humic acid, pregelatinized modified starch and glycerol to water to prepare an outer fast-acting coating slurry with a total solid content of 30wt%; coat the intermediate coating particles obtained in step S103 so that the weight gain of the outer fast-acting coating layer accounts for 10wt% of the mass of the intermediate coating particles on a dry basis; after coating, dry at 45℃ until the moisture content of the finished product is ≤10wt% to obtain a soil conditioner finished product with a particle size of 4mm.

[0021] Example 2: A soil conditioner, which consists of a core layer, an intermediate regulating layer and an outer fast-acting layer; The core layer comprises, by weight, the following raw materials: 18 parts calcium magnesium-humic material-supported biochar, 8 parts dolomite powder, 2 parts gypsum powder, 6 parts zeolite, 1 part sodium alginate, 1 part carboxymethyl cellulose, and 1 part pregelatinized modified starch. The preparation steps of the calcium-magnesium-humic acid-supported biochar are as follows: Fulvic acid was added to water to prepare a 3wt% humic load solution; dolomite powder and gypsum powder were added to the humic load solution to prepare a calcium-magnesium load slurry; then alkaline biochar was added to allow the load slurry to fully enter the pores of the biochar and adhere to its surface, and the mixture was allowed to stand for 2 hours to mature; the mixture was then dried at 60℃ until the water content was ≤10wt% to obtain calcium-magnesium-humic load biochar. The pH of the aqueous extract of the alkaline biochar is 8.5; The intermediate control layer is composed of the following raw materials by weight: 2 parts pectin, 5 parts bentonite and 1 part calcium lignosulfonate. The outer fast-acting layer, by weight, comprises the following raw materials: 3 parts calcium carbonate, 0.5 parts fulvic acid, 1 part pectin, and 0.2 parts glycerin; The preparation method of the soil conditioner specifically includes the following steps: S101: Sodium alginate, carboxymethyl cellulose and pregelatinized modified starch are added to water to prepare a core bonding matrix solution with a total solid content of 5 wt%. S102: Calcium-magnesium-humic material-loaded biochar, dolomite powder, gypsum powder and zeolite are mixed, and then the core bonding matrix solution prepared in step S101 is added to make a wet material with a water content of 40wt%; then granulation is carried out to make wet core particles, and the wet core particles are contacted with a 3wt% calcium chloride solution for curing for 20min; then dried at 50℃ until the particle water content is ≤15wt% to obtain core particles; S103: Pectin, bentonite and calcium lignosulfonate are added to water to prepare an intermediate control layer coating slurry with a total solid content of 10wt%; the core particles obtained in step S102 are coated so that the weight gain of the intermediate control layer coating accounts for 10wt% of the mass of the core particles on a dry basis; after coating, a 1wt% calcium chloride solution is used for secondary curing for 30min, and then dried at 45℃ until the particle moisture content is ≤12wt% to obtain intermediate coated particles; S104: Add calcium carbonate, humic acid, pectin and glycerol to water to prepare an outer quick-acting coating slurry with a total solid content of 20wt%; coat the intermediate coating particles obtained in step S103 so that the weight gain of the outer quick-acting coating layer accounts for 8wt% of the mass of the intermediate coating particles on a dry basis; after coating, dry at 40℃ until the moisture content of the finished product is ≤10wt% to obtain a soil conditioner finished product with a particle size of 2mm.

[0022] Example 3: A soil conditioner, which consists of a core layer, an intermediate regulating layer and an outer fast-acting layer; The core layer comprises, by weight, the following raw materials: 32 parts calcium magnesium-humic material-supported biochar, 18 parts dolomite powder, 6 parts gypsum powder, 12 parts zeolite, 3 parts sodium alginate, 4 parts carboxymethyl cellulose, and 4 parts pregelatinized modified starch. The preparation steps of the calcium-magnesium-humic acid-supported biochar are as follows: Potassium humate was added to water to prepare a 6 wt% humic loading solution; dolomite powder and gypsum powder were added to the humic loading solution to prepare a calcium-magnesium loading slurry; then alkaline biochar was added to allow the loading slurry to fully enter the pores of the biochar and adhere to its surface, and the mixture was allowed to stand and mature for 4 hours; it was then dried at 80℃ until the water content was ≤10 wt% to obtain calcium-magnesium-humic loading biochar. The pH of the aqueous extract of the alkaline biochar is 10.5; The intermediate control layer is composed of the following raw materials by weight: 6 parts sodium alginate, 10 parts bentonite and 4 parts lignin. The outer fast-acting layer, by weight, comprises the following raw materials: 8 parts calcium carbonate, 2 parts humic acid, 3 parts pregelatinized modified starch, and 0.8 parts glycerol; The preparation method of the soil conditioner specifically includes the following steps: S101: Sodium alginate, carboxymethyl cellulose and pregelatinized modified starch are added to water to prepare a core bonding matrix solution with a total solid content of 10 wt%. S102: Calcium-magnesium-humic material-loaded biochar, dolomite powder, gypsum powder and zeolite are mixed, and then the core bonding matrix solution prepared in step S101 is added to make a wet material with a water content of 25wt%; then granulation is carried out to make wet core particles, and the wet core particles are contacted with 5wt% calcium chloride solution for curing for 10min; then dried at 60℃ until the particle water content is ≤15wt% to obtain core particles; S103: Sodium alginate, bentonite, and lignin are added to water to prepare an intermediate control layer coating slurry with a total solid content of 18wt%; the core particles obtained in step S102 are coated so that the weight gain of the intermediate control layer coating accounts for 18wt% of the core particle mass on a dry basis; after coating, a 3wt% calcium chloride solution is used for secondary curing for 10min, and then dried at 55℃ until the particle moisture content is ≤12wt% to obtain intermediate coated particles; S104: Add calcium carbonate, humic acid, pregelatinized modified starch and glycerol to water to prepare an outer fast-acting coating slurry with a total solid content of 35wt%; coat the intermediate coating particles obtained in step S103 so that the weight gain of the outer fast-acting coating layer accounts for 14wt% of the mass of the intermediate coating particles on a dry basis; after coating, dry at 50℃ until the moisture content of the finished product is ≤10wt% to obtain a soil conditioner finished product with a particle size of 5mm.

[0023] Comparative Example 1: The calcium-magnesium-humic matter-loaded biochar was replaced with a direct mixture of unloaded alkaline biochar, equal amounts of dolomite powder, equal amounts of gypsum powder, and equal amounts of soluble humic matter. The composition of the core layer, the intermediate regulating layer, and the outer fast-acting layer remained unchanged. The composition of the remaining raw materials and the steps were consistent with those in Example 1. The comparative example was used to verify whether the pre-loading modification in step S1 could improve the uniformity, retention, and continuous release capacity of the calcium-magnesium conditioning components and humic matter in the core, rather than simply a blending of raw materials.

[0024] Comparative Example 2: Step S103 is omitted, and no intermediate control layer is set. The core particles obtained in step S102 directly enter step S104 for outer fast-acting layer coating; the remaining raw material composition and steps are consistent with Example 1. The comparative example is used to verify whether the intermediate control layer plays a key role in delaying the outward expansion of core components, maintaining the stability of interlayer structure, and realizing the temporal division of labor between outer fast start-up and core continuous operation.

[0025] Comparative Example 3: In step S104, the outer film-forming substrate and glycerol are retained, but calcium carbonate and fulvic acid are not added. The deleted portion is made up with an equal amount of inert filler quartz sand; the remaining raw material composition and steps are consistent with Example 1. The comparative example is used to verify whether the effect of the outer fast-acting layer mainly comes from the fast-acting acid-slowing active component itself, rather than simply from the physical covering behavior of the outer coating.

[0026] Comparative Example 4: All dolomite powder, including the dolomite powder used in step S1 and the dolomite powder in the core layer, was replaced with an equal amount of calcium carbonate; the remaining raw material composition and steps were consistent with Example 1. This comparative example was used to verify whether dolomite providing a dual source of Ca / Mg and its relatively mild and sustained acid-mitigating effect is superior to a single calcium carbonate system that only provides Ca.

[0027] Comparative Example 5: All gypsum powder, including the gypsum powder used for loading in step S1 and the gypsum powder in the core layer, was removed and replaced with an equal amount of inert filler quartz sand; the remaining raw material composition and steps were consistent with Example 1. This comparative example was used to verify whether gypsum has an irreplaceable synergistic effect in supplementing relatively easily migratable calcium sources, mitigating the hazards of exchangeable aluminum in the subsurface layer, and improving the subsurface layer environment.

[0028] Comparative Example 6: The zeolite in the core layer was removed and replaced with an equal amount of inert filler quartz sand; the remaining raw material composition and steps were consistent with Example 1. This comparative example was used to verify whether zeolite substantially contributes to the synergistic effect of the present invention in improving cation exchange and adsorption buffering capacity, reducing nutrient and water leaching, and improving the rhizosphere microenvironment.

[0029] Performance Testing: To verify the improvement effects of the soil conditioner of this invention on rapid acidification slowing in the surface layer, continuous aluminum reduction and calcium and magnesium supplementation in the subsurface layer, as well as water retention, stable aggregation, and promotion of soil biological activity, the soil conditioners obtained in Examples 1-3 and Comparative Examples 1-6 were subjected to indoor incubation and particle release tests. The test soils were selected from the topsoil of acidified cultivated land of the same source, and were mixed after removing stones and plant residues; physicochemical and structural indicators were obtained from air-dried 2mm soil samples, while enzyme activity and basal respiration tests were performed using fresh soil samples. Unless otherwise specified, each treatment was set at an application rate of 1.0% of the dry weight of the soil conditioner, with three parallel replicates.

[0030] To evaluate the rapid acidification control capacity of the surface layer and the sustained conditioning capacity of the subsurface layer, a PVC soil column culture method was used. The soil column had an inner diameter of 10 cm and a height of 40 cm, divided into two layers: 0–20 cm and 20–40 cm. Soil conditioner was only mixed with the 0–20 cm soil layer and applied; no conditioner was added directly to the 20–40 cm soil layer to simulate actual surface application conditions (the blank control did not add any conditioner or related reagents). The culture temperature was controlled at 25 ± 2℃, and the soil moisture content was maintained at 60–65% of field capacity. Following HJ962-2018, the pH values ​​of the two soil layers in Example 1 and its corresponding Comparative Examples 2, 3, and 5 were determined using the potentiometry method at 7, 14, 28, and 60 days of culture to investigate the effects of the intermediate conditioning layer, the outer quick-acting layer, and the gypsum component on the rapid onset of surface acidity and the sustained conditioning capacity of the subsurface layer. Additionally, after 60 days of cultivation, the exchangeable aluminum, exchangeable calcium, and exchangeable magnesium were determined in soil samples from 0–20 cm and 20–40 cm depths of Examples 1–3 and Comparative Examples 1–6, respectively. The exchangeable aluminum was determined by titration after extraction with 1 mol / L KCl, while the exchangeable calcium and magnesium were determined by EDTA titration after extraction with 1 mol / L ammonium acetate. These methods were used to evaluate the combined effects of loading modification, multilayer coating, and dolomite and gypsum components on reducing aluminum, supplementing calcium and magnesium, and improving the subsurface environment.

[0031] In vitro release tests were conducted on Example 1, Comparative Examples 1, 2, and 3. 2 g of each treated particle was weighed and added to 200 mL of acetic acid-citric acid buffer (pH 4.5). The mixture was incubated at 25°C. Samples were taken from the supernatant at 1, 3, 7, 14, and 28 days to determine the Ca content. 2+ and Mg 2+ The concentration was determined and replenished with an equal volume of fresh buffer solution to plot the cumulative release curve. Since Comparative Examples 4–6 mainly correspond to changes in the composition of raw materials such as dolomite, gypsum, and zeolite, their correlation with the particle stratification release sequence is relatively weak, and therefore they are not considered in this test.

[0032] Combined water-holding-evaporation-aggregate tests were conducted on Examples 1-3, Comparative Examples 1, 2, and 6. Specifically, each treatment was mixed with air-dried soil at the same application rate and placed in culture cups. After saturation water absorption for 24 hours, the soil was allowed to drain freely for 12 hours, and the maximum water holding capacity was measured. Soil samples from the same batch were adjusted to the same initial moisture content and cultured continuously at 25°C for 10 days, weighed every 24 hours, and the cumulative evaporation loss rate was calculated. After 60 days of culture, samples were taken, and the content and average weight diameter of water-stable aggregates >0.25 mm were determined using the wet sieving method. This was used to investigate the synergistic effects of load modification, the intermediate control layer, and zeolite components on particle water retention, reduction of water loss, and improvement of soil aggregate structure. Since Comparative Examples 3 and 5 mainly correspond to the outer layer's fast-acting acid-slowing behavior and the role of gypsum in calcium supply to the subsurface migration, their correlation with water holding capacity and aggregate improvement is relatively weak, and therefore they were not considered in this test.

[0033] Biological parameters were determined using fresh soil samples from Examples 1-3, Comparative Examples 1, 4, and 6 after 60 days of culture. For the urease activity test, 5g of fresh soil sample was weighed, and 10% urea solution and citrate buffer were added. After incubation at 37℃ for 24 hours, the generated NH4+ was measured. 4+ -N content; for acid phosphatase activity testing, 1g of fresh soil sample was weighed, added to acetate buffer and p-nitrophenyl phosphate substrate, reacted at 37℃ for 1h, and the amount of p-nitrophenol generated was measured at 400nm; for soil basal respiration rate testing, 20g of fresh soil sample was incubated in a sealed culture bottle at 25℃ for 24h, and the CO2 release was determined by alkaline absorption-back titration method. This test is mainly used to investigate the effects of loading modification, dolomite magnesium supplementation, and zeolite adsorption buffering on the rhizosphere microenvironment and the activation of indigenous microorganisms. Comparative Examples 2 and 3 mainly reflect the granular layered release behavior and are relatively less specific to this type of biological indicator, so they are not the focus of this test group.

[0034] The test results are shown in Tables 1-3 and 3 respectively. Figures 1-4 ,in, Figure 1 and Figure 2 For different treatment particles Ca 2+ / Mg 2+ Cumulative release curves are used to characterize the effects of particle layering structure and loading modification on release timing; Figure 3 and Figure 4 Table 1 shows the pH-incubation time curves for Example 1 and the comparative example in soil layers of 0–20 cm and 20–40 cm, used to characterize the temporal differences between rapid acidification in the surface layer and continuous conditioning in the subsurface layer. Table 1 shows the test results of exchangeable aluminum, exchangeable calcium, and exchangeable magnesium in soil columns under different treatments after 60 days of incubation, used to evaluate the effects of aluminum reduction, calcium and magnesium supplementation, and improvement of the subsurface environment. Table 2 shows the test results of maximum water holding capacity, cumulative evaporation loss rate over 10 days, and water-stable aggregates for different treatments, used to evaluate the effects of water retention reduction and structural improvement. Table 3 shows the test results of urease activity, acid phosphatase activity, and basal respiration rate for different treatments, used to evaluate the effects of improving the activity of indigenous microorganisms and key enzyme activities.

[0035] Table 1. Results of stratified exchangeable aluminum, exchangeable calcium, and exchangeable magnesium in soil columns under different treatments after 60 days of incubation.

[0036] Table 2. Maximum water holding capacity, cumulative evaporation loss rate over 10 days, and water-stable aggregate test results for different treatments.

[0037] Table 3. Results of urease activity, acid phosphatase activity, and basal respiratory rate tests under different treatments.

[0038] Depend on Figures 1-4 As can be seen from Tables 1-3, the mechanism of action of this invention is not the direct neutralization of acidity by a single alkaline component, but rather relies on the synergistic effect of pre-loading modification, multi-layered structural division of labor, and soil microenvironment reconstruction. The calcium-magnesium-humic acid-loaded biochar formed in step S1 transforms the dolomite, gypsum, and humic acid components from a simple blended state to a carrier-loaded state, improving the uniformity and retention of the calcium-magnesium conditioning components in the core. Therefore, Example 1 exhibits a smoother and more sustained Ca... 2+ / Mg 2+ Release characteristics. Correspondingly, soil column culture results show that the surface layer can quickly initiate the acid-slowing process, while the subsurface layer can maintain a good and continuous improvement effect, indicating that the system can take into account both early initiation and later maintenance. Conversely, after removing the pre-loading modification, the components are more likely to be released in the early stage, and the subsequent maintenance ability is weakened; after omitting the intermediate regulation layer, although the early effect is faster, the sustainability decreases, indicating that the intermediate layer plays a key role in delaying the expansion of the core, maintaining the stability of the interlayer structure, and realizing the temporal division of labor of "rapid initiation of the outer layer and continuous action of the core". After removing the active components from the outer fast-acting layer, the surface layer's effect is significantly delayed, which further illustrates that the core function of the outer layer lies in the fast-acting acid-slowing activity, rather than simple physical coating.

[0039] Dolomite, gypsum, and zeolite play different but complementary roles in the system. Dolomite provides a dual source of Ca / Mg, which helps to continuously mitigate acidity and improve Mg supply. Therefore, although replacing dolomite with calcium carbonate still provides some Ca source, Mg replenishment, buffering sustainability, and the rhizosphere biological environment are significantly weakened. Gypsum focuses more on providing a relatively easily migratable calcium source, and is more important for mitigating exchangeable aluminum in the subsurface and improving the deep environment. Therefore, removing gypsum has the most limited effect on deep acid mitigation and aluminum reduction. Zeolite mainly participates in synergistic effects through cation exchange, adsorption buffering, and water retention. Its absence not only weakens ion retention but also simultaneously reduces water retention, agglomeration stabilization, and microbial activation, indicating that zeolite makes a significant contribution to maintaining the microenvironment of the entire system.

[0040] The results in Tables 2 and 3 further illustrate that this invention does not merely improve pH, but rather reconstructs a more favorable soil microenvironment while regulating acidity. The calcium-magnesium-humic acid-loaded biochar, zeolite, and the core water-retaining matrix together form a carbon-mineral-gel composite framework, which is beneficial for improving water retention capacity, reducing evaporation loss, and promoting aggregate stability. Furthermore, the lower aluminum toxicity level, higher Ca / Mg retention, better moisture conditions, and aggregate structure provide a more suitable environment for indigenous microbial activity and the activity of key enzymes such as urease and acid phosphatase. Therefore, water retention, aggregate stabilization, and promotion of biological activity are not incidental phenomena, but rather constitute a synergistic process that mutually promotes each other, together with aluminum reduction, calcium and magnesium supplementation, and acid stabilization.

[0041] Example 1 showed the best overall performance because its proportions were relatively balanced, achieving a more reasonable match between rapid outer layer release, mid-layer regulation, and sustained core release. Example 2 was generally too low, exhibiting insufficient buffer capacity, sustained supply, and structural maintenance. Example 3 was generally too high; although it had strong reserves, its thicker coating and larger particles resulted in a slightly slower diffusion and release pace, and its overall coordination was not as good as Example 1. This demonstrates that the substantial advantage of this invention lies not in increasing the amount of a single component, but in unifying rapid outer layer activation, slow core release, deep migration, and microenvironment improvement within the same particle system through appropriate proportions, thereby achieving synergistic improvement of the surface and subsurface layers of acidified soil.

[0042] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A soil conditioner, characterized in that, It consists of a kernel layer, an intermediate control layer, and an outer fast-acting layer; The core layer comprises, by weight, the following raw materials: 18-32 parts calcium magnesium-humic material-supported biochar, 8-18 parts dolomite powder, 2-6 parts gypsum powder, 6-12 parts zeolite, 1-3 parts sodium alginate, 1-4 parts carboxymethyl cellulose, and 1-4 parts pregelatinized modified starch. The intermediate control layer comprises, by weight, the following raw materials: 2-6 parts of film-forming substrate, 5-10 parts of bentonite, and 1-4 parts of structural stabilizing component; The outer fast-acting layer, by weight, comprises the following raw materials: 3-8 parts calcium carbonate, 0.5-2 parts fulvic acid, 1-3 parts outer film-forming substrate, and 0.2-0.8 parts glycerol.

2. The soil conditioner according to claim 1, characterized in that, The film-forming substrate is selected from one or both of sodium alginate and pectin.

3. The soil conditioner according to claim 1, characterized in that, The structural stabilizing component is selected from one or both of lignin and calcium lignin sulfonate.

4. A soil conditioner according to claim 1, characterized in that, The outer film-forming substrate is selected from one or both of pectin and pregelatinized modified starch.

5. A soil conditioner according to claim 1, characterized in that, The preparation steps of the calcium-magnesium-humic acid-supported biochar are as follows: Soluble humic substances were added to water to prepare a humic substance loading solution. Dolomite powder and gypsum powder were added to the humic substance loading solution to prepare a calcium-magnesium loading slurry. Alkaline biochar was then added to allow the loading slurry to fully enter the pores of the biochar and adhere to its surface. The mixture was allowed to stand and mature. After drying, calcium-magnesium-humic substance-loaded biochar was obtained.

6. A soil conditioner according to claim 5, characterized in that, The soluble humic substance is selected from either fulvic acid or potassium humate; the pH of the aqueous extract of the alkaline biochar is 8.5–10.5; the mass ratio of the biochar, dolomite powder, gypsum powder and humic substance loading solution is 1:0.3–0.8:0.1–0.3:2–4.

7. A method for preparing a soil conditioner according to any one of claims 1-6, characterized in that, Includes the following steps: S101: Sodium alginate, carboxymethyl cellulose and pregelatinized modified starch are added to water to prepare a core bonding matrix solution; S102: Mix calcium-magnesium-humic material-loaded biochar, dolomite powder, gypsum powder and zeolite, then add the core bonding matrix solution prepared in step S101 to make a wet material; then granulate to make wet core particles, and solidify the wet core particles by contacting calcium chloride solution; dry to obtain core particles. S103: Add film-forming substrate, bentonite and structural stabilizing components to water to prepare intermediate control layer coating slurry; coat the core particles obtained in step S102; after coating, use calcium chloride solution for secondary curing and drying to obtain intermediate coated particles; S104: Add calcium carbonate, humic acid, outer film-forming substrate and glycerin to water to prepare an outer fast-acting coating slurry; coat the intermediate coating particles obtained in step S103; dry after coating to obtain the finished soil conditioner.

8. A method for preparing a soil conditioner according to claim 7, characterized in that, In step S101, the total solid content of the core bonding matrix solution is controlled to be 5-10 wt%; in step S102, the moisture content of the wet material is 25-40 wt%.

9. A method for preparing a soil conditioner according to claim 7, characterized in that, In step S103, the total solids content of the intermediate control layer coating slurry is controlled to be 10-18 wt%.

10. A method for preparing a soil conditioner according to claim 7, characterized in that, In step S104, the total solids content of the outer quick-acting coating slurry is controlled to be 20-35 wt%; the particle size of the finished soil conditioner is screened to be 2-5 mm.

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