An organic soil amendment suitable for use in poor soils and a method of making the same

Abstract

The present application relates to the technical field of soil improvement, and particularly relates to an organic improver suitable for infertile soil and a preparation method thereof. The improver takes sodium humate as a basic raw material, constructs a water / ethanol suspension dispersion system through hydrochloric acid-ethanol, activates part of carboxyl groups of the sodium humate under the action of carbodiimide / N-hydroxysuccinimide, carries out grafting reaction with pre-hydrolyzed 3-aminopropyl triethoxysilane, and realizes condensation by adjusting the liquid through triethylamine and accurately controlling pH through ammonia water. The method can effectively inhibit silane self-polymerization and improve grafting efficiency, retains natural active sites of the sodium humate while enhancing the adhesion capacity of the sodium humate on the surface of soil particles. The obtained improver can significantly improve soil structure, improve water and fertilizer retention performance, and promote seed germination, and has excellent comprehensive improvement effect.

Description

Technical Field

[0001] This invention relates to the field of soil improvement technology, and in particular to an organic soil conditioner suitable for infertile soil and its preparation method. Background Technology

[0002] Humic acid, a widely available natural organic macromolecule rich in various active groups, has shown significant potential in improving soil structure, enhancing water and fertilizer retention capacity, and promoting plant growth, and is considered one of the ideal materials for improving infertile soils. However, untreated natural humic acid has a wide molecular weight distribution and high water solubility, making it easily leached from the soil and difficult to maintain a stable presence in the topsoil for a long period. Its improvement effect is usually short-term and unstable.

[0003] To enhance the retention of humic acid in soil, existing technologies attempt to modify it through chemical cross-linking, granulation, or compounding with inorganic minerals (such as diatomaceous earth and bentonite). Among these methods, chemical grafting modification of humic acid with aminosilanes (such as 3-aminopropyltriethoxysilane) is considered a promising technological direction, aiming to combine the bonding ability of organosilicon with the activity of humic acid to improve its adhesion and long-term effectiveness on soil particle surfaces. However, the humic acid-aminosilane composite system still faces a series of technical challenges in practical applications.

[0004] First, humic acid molecules contain numerous active sites such as carboxyl groups and phenolic hydroxyl groups. Grafting reactions with aminosilanes often occur in aqueous or water-alcohol mixtures, leading to competing side reactions. Aminosilanes readily undergo self-hydrolysis and condensation in aqueous environments, generating polysiloxane oligomers, significantly reducing the effective grafting rate with humic acid. This results in wasted silane raw materials and insufficient effective active ingredients in the modifier. Second, in pursuit of high grafting rates, existing methods often focus on highly activating the carboxyl groups of humic acid. However, this excessively depletes its original complexing and buffering bioactive sites, greatly diminishing its natural advantages. The modified product may only possess skeletal adhesion functions, while its fertilizer retention and growth-promoting abilities decrease. Furthermore, conventional one-pot reactions or simple stepwise mixing make it difficult to precisely control the "reaction window" and sequence of key reaction steps such as carboxyl activation, amino grafting, and silanol condensation. This leads to uncontrollable final product structure, large performance fluctuations, and an inability to achieve an ideal balance between "enhanced soil particle adhesion" and "preservation of bioactivity." These factors collectively limit the synergistic effect and long-lasting effect of modified humic acid organic amendments in improving the overall fertility of infertile soils (such as aggregate stability, cation exchange capacity, and nutrient slow-release properties). Summary of the Invention

[0005] In view of this, the purpose of this invention is to propose an organic soil conditioner suitable for infertile soil and its preparation method, so as to overcome the problems of low effective grafting rate and insufficient retention of natural activity caused by silane self-polymerization, excessive consumption of active sites and competition of multi-step reaction windows during the modification of humic acid with aminosilane. In this way, a long-lasting organic soil conditioner can be prepared that can firmly stay on the surface of soil particles and maximize the retention and synergistic effect of the inherent biological activity of humic acid.

[0006] To achieve the above objectives, this invention provides an organic soil conditioner suitable for infertile soils, prepared from the following raw materials in parts by mass, based on 100 parts by mass of sodium humate: 1000-1400 parts by mass of first deionized water, 32-40 parts by mass of hydrochloric acid with a mass fraction of 37%, 500-800 parts by mass of first anhydrous ethanol, 14-24 parts by mass of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, 9-16 parts by mass of N-hydroxysuccinimide, 11-18 parts by mass of 3-aminopropyltriethoxysilane, 130-200 parts by mass of second anhydrous ethanol, 18-30 parts by mass of second deionized water, 2.2-4.0 parts by mass of glacial acetic acid, 4.5-8.0 parts by mass of triethylamine, 15-30 parts by mass of third anhydrous ethanol, and 16-25 parts by mass of ammonia water with a mass fraction of 25%. In this process, the first deionized water, hydrochloric acid, and first anhydrous ethanol are used to construct a water / ethanol suspension dispersion system with a pH of 4.9-5.3, and the first anhydrous ethanol is used as a process solvent for confined dispersion; the 3-aminopropyltriethoxysilane, the second anhydrous ethanol, the second deionized water, and glacial acetic acid are used for the pre-hydrolysis of the 3-aminopropyltriethoxysilane, and the second anhydrous ethanol is used as a process solvent for pre-hydrolysis; the triethylamine and the third anhydrous ethanol are used to prepare a triethylamine conditioning solution, and the third anhydrous ethanol is used as a dilution solvent for the triethylamine conditioning solution. The first anhydrous ethanol, the second anhydrous ethanol, and the third anhydrous ethanol are used in processes such as dispersion, pre-hydrolysis, or conditioning solution preparation. After filtration, washing, and vacuum drying to constant weight in step (5), a powdered organic modifier is obtained.

[0007] Preferably, the organic modifier is prepared by grafting humic acid activated by the 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and the N-hydroxysuccinimide with the pre-hydrolyzed 3-aminopropyltriethoxysilane, followed by condensation under the action of the triethylamine adjusting solution and the ammonia water. During the addition of the pre-hydrolyzed 3-aminopropyltriethoxysilane, the pH of the main system is maintained at 6.0-6.4, allowing the carboxyl-activated humic acid to first undergo a grafting reaction with the pre-hydrolyzed 3-aminopropyltriethoxysilane. After the grafting reaction is completed, the ammonia water is added for condensation and ripening, with the system pH at 8.6-9.0 during condensation.

[0008] Preferably, the sodium humate is derived from weathered coal or lignite and has a dry basis humic acid content of not less than 70%, a fineness of 80-100 mesh, and a pH of 9-10.

[0009] Preferably, the organic modifier is a powder with a sieve particle size of 60-100 mesh.

[0010] Preferably, when preparing the organic modifier, the triethylamine conditioning solution is added when the pre-hydrolyzed 3-aminopropyltriethoxysilane has been added to one-quarter to one-half of the total amount.

[0011] Furthermore, the present invention also provides a method for preparing an organic amendment suitable for barren soil, comprising the following steps: (1) Sodium humate was dispersed in the first deionized water, hydrochloric acid with a mass fraction of 37% was added, and then anhydrous ethanol was added to obtain a suspension. (2) Add 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to the suspension obtained in step (1) to activate it and obtain an activated humic acid dispersion system. (3) Mix 3-aminopropyltriethoxysilane, second anhydrous ethanol, second deionized water and glacial acetic acid and pre-hydrolyze them, then add them dropwise to the activated humic acid dispersion system obtained in step (2), and simultaneously add triethylamine conditioning solution prepared by triethylamine and third anhydrous ethanol. (4) After the addition is completed in step (3) and stirring is continued, add 25% ammonia water by mass to the resulting system to carry out condensation and ripening; (5) Filter, wash, dry, crush and sieve the material obtained in step (4) to obtain an organic amendment suitable for barren soil.

[0012] Preferably, in step (1), after adding sodium humate to the first deionized water, the mixture is stirred at 350-500 rpm for 20-40 min at 22-30℃; the hydrochloric acid is added within 10-20 min, and the pH of the system is adjusted to 4.9-5.3 by real-time monitoring with a calibrated pH meter; the first anhydrous ethanol is added within 15-25 min, and the mixture is stirred at 350-500 rpm for 30-50 min.

[0013] Preferably, in step (2), the activation is carried out at 22-30°C with stirring at 350-500 rpm for 25-40 min, and the pH of the system is maintained at 4.9-5.3.

[0014] Preferably, in step (3), the pre-hydrolysis is carried out by stirring at 22-30°C for 12-25 min; the pre-hydrolyzed 3-aminopropyltriethoxysilane is added dropwise to the activated humic acid dispersion system obtained in step (2) within 40-55 min; the triethylamine conditioning solution is added dropwise within 25-40 min; after all the addition is completed, stirring is continued at 22-30°C at 350-500 rpm for 25-40 min.

[0015] Preferably, in step (4), the ammonia water is added dropwise over 8-15 minutes to raise the pH of the system to 8.6-9.0, and the system is heated to 33-38°C and maintained for 15-30 minutes, and then naturally cooled to 22-30°C and allowed to stand for 45-90 minutes to mature.

[0016] Preferably, in step (5), the filter cake is first washed with an ethanol aqueous solution, then washed with deionized water, and then vacuum dried at 40-50°C to constant weight.

[0017] Compared with existing technologies, the organic soil conditioner and its preparation method provided by this invention, suitable for infertile soils, have the following significant advantages: (1) The present invention constructs a locally confined dispersion system by hydrochloric acid-ethanol, which achieves moderate flocculation and physical fixation of humic acid, while effectively regulating the environment of subsequent carboxyl activation reaction, preventing excessive diffusion and self-polymerization of aminosilane in the aqueous phase, and creating a favorable microenvironment for subsequent efficient and directional grafting reaction.

[0018] (2) A partial carboxyl activation strategy is adopted, that is, the amount of carbodiimide / N-hydroxysuccinimide activator is strictly controlled, and only some of the humic acid carboxyl groups are activated, rather than pursuing complete modification. This allows the final product to retain sufficient natural carboxyl groups and phenolic hydroxyl groups and other active sites while successfully grafting organosilanes and obtaining excellent soil particle adhesion ability. Thus, it has both excellent soil structure improvement function and strong nutrient complexing, buffering and biostimulation ability.

[0019] (3) Through a three-step precision reaction process of pre-hydrolysis of silane, simultaneous dropwise addition and pH program control, and subsequent alkaline locking, the control of three key reaction windows—carboxyl activation, amino grafting, and silanol condensation—was achieved. This design ensures that the grafting reaction is mainly carried out under pH conditions of 6.0-6.4, and after the grafting reaction, it is locked by alkaline condensation and ripening at pH 8.6-9.0, thereby inhibiting the ineffective self-condensation of silane and the premature hydrolysis of active ester intermediates. This significantly improves the effective grafting utilization rate of aminosilane and promotes the formation of a stable network structure of grafted products on the surface of soil particles, thus achieving an organic combination of short-term improvement effect and long-term aftereffect.

[0020] (4) Compared with comparative examples where several key steps were missing or process parameters were inappropriate, the soil conditioner obtained in this embodiment of the invention, when applied to infertile soil, can simultaneously and significantly improve soil pH, organic matter content, cation exchange capacity, field water holding capacity, water-stable macroaggregate content, and nitrogen, phosphorus, and potassium nutrient availability, and significantly improve seed germination rate. This verifies the synergistic enhancement effect of this technical solution in improving soil physical structure, chemical fertility, and biological activity, and the overall improvement effect is significantly better than conventional modification methods. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0022] Raw materials and sources: Sodium humate, JINGFENG HUMIC ACID, product code JFHA-NaHA-1, is derived from weathered coal or lignite, is 100% water-soluble, contains no less than 70% humic acid (dry basis), has a fineness of 80-100 mesh, and a pH of 9-10; 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride is Sigma-Aldrich's E7750 specification product; N-hydroxysuccinimide can be Sigma-Aldrich's 130672 specification product; 3-aminopropyltriethoxysilane can be Sigma-Aldrich's 440140 specification product; hydrochloric acid is 37% analytical grade hydrochloric acid, anhydrous ethanol is analytical grade anhydrous ethanol, glacial acetic acid is analytical grade glacial acetic acid, triethylamine is analytical grade triethylamine, 25% ammonia water is analytical grade ammonia water, and deionized water is laboratory-prepared deionized water.

[0023] Example 1: Step 1: Add 100g of sodium humate to 1200g of deionized water and stir at 400rpm for 30min at 25℃ to completely disperse it and form a homogeneous brown-black solution; then add 36g of 37% hydrochloric acid within 15min, and adjust the pH of the system to 5.1 by real-time monitoring with a calibrated pH meter; then add 600g of anhydrous ethanol within 20min and continue stirring at 400rpm for 40min to obtain a brown-black suspension. Step 2: Add 18g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 12g of N-hydroxysuccinimide to the suspension obtained in Step 1, stir at 400rpm for 30min at 25℃, and keep the pH of the system at 5.1 to obtain a partially carboxyl-activated humic acid dispersion system. Step 3: Take 14g of 3-aminopropyltriethoxysilane, 160g of anhydrous ethanol, 24g of deionized water, and 3g of glacial acetic acid, and stir at 25°C for 15min to prepare a pre-hydrolyzed 3-aminopropyltriethoxysilane solution; simultaneously, add 6g of triethylamine to 20g of anhydrous ethanol to prepare a triethylamine adjusting solution. Add the pre-hydrolyzed 3-aminopropyltriethoxysilane solution dropwise to the system obtained in Step 2 at a uniform rate over 45min; when the pre-hydrolyzed 3-aminopropyltriethoxysilane solution has been added to one-third of the total volume, begin adding the triethylamine adjusting solution dropwise simultaneously over 30min to maintain the pH of the main system at 6.2±0.2; after all additions are complete, continue stirring at 25°C at 400rpm for 30min. Step 4: In the system obtained in step 3, add 20g of 25% ammonia solution dropwise over 10min to raise the pH of the system to 8.8±0.2, then raise the temperature to 35℃ and maintain it for 20min, then allow it to cool naturally to 25℃ and let it stand for 60min to mature. Step 5: Filter the material after maturation in Step 4 under reduced pressure. Wash the filter cake twice with a 300g 70% ethanol aqueous solution prepared by 210g anhydrous ethanol and 90g deionized water each time, and then wash it once with 500g deionized water until the filtrate is close to neutral. Then, vacuum dry it at 45℃ to constant weight, crush it and pass it through an 80-mesh sieve to obtain a modified humic acid organic conditioner suitable for barren soil.

[0024] Example 2: Step 1: Add 100g of sodium humate to 1100g of deionized water and stir at 350rpm for 25min at 22℃ to completely disperse it and form a homogeneous brown-black solution; then add 32g of 37% hydrochloric acid within 12min, and adjust the pH of the system to 4.9 by real-time monitoring with a calibrated pH meter; then add 500g of anhydrous ethanol within 15min and continue stirring at 350rpm for 35min to obtain a brown-black suspension. Step 2: Add 14g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 9g of N-hydroxysuccinimide to the suspension obtained in Step 1, stir at 350rpm for 25min at 22℃, and keep the pH of the system at 4.9 to obtain a partially carboxyl-activated humic acid dispersion system. Step 3: Take 11g of 3-aminopropyltriethoxysilane, 130g of anhydrous ethanol, 18g of deionized water, and 2.2g of glacial acetic acid, and stir at 22℃ for 12min to prepare a pre-hydrolyzed 3-aminopropyltriethoxysilane solution; simultaneously, add 4.5g of triethylamine to 15g of anhydrous ethanol to prepare a triethylamine adjusting solution. Add the pre-hydrolyzed 3-aminopropyltriethoxysilane solution dropwise to the system obtained in Step 2 at a uniform rate over 40min; when the pre-hydrolyzed 3-aminopropyltriethoxysilane solution has been added to one-quarter of the total volume, begin adding the triethylamine adjusting solution dropwise simultaneously over 25min to maintain the pH of the main system at 6.0±0.2; after all additions are complete, continue stirring at 22℃ and 350rpm for 25min. Step 4: In the system obtained in step 3, add 16g of 25% ammonia solution dropwise over 8 minutes to raise the pH of the system to 8.6±0.2. Then, raise the temperature to 33℃ and maintain it for 15 minutes. After that, allow it to cool naturally to 22℃ and let it stand for 45 minutes to mature. Step 5: Filter the material after maturation in Step 4 under reduced pressure. Wash the filter cake twice with a 280g 70% ethanol aqueous solution prepared by 196g anhydrous ethanol and 84g deionized water each time, and then wash it once with 450g deionized water until the filtrate is close to neutral. Then, vacuum dry it at 40℃ to constant weight, crush it and pass it through a 100-mesh sieve to obtain a modified humic acid organic conditioner suitable for barren soil.

[0025] Example 3: Step 1: Add 100g of sodium humate to 1300g of deionized water and stir at 450rpm for 35min at 28℃ to completely disperse it and form a homogeneous brown-black solution; then add 38g of 37% hydrochloric acid within 18min, and adjust the pH of the system to 5.2 by real-time monitoring with a calibrated pH meter; then add 700g of anhydrous ethanol within 25min and continue stirring at 450rpm for 45min to obtain a brown-black suspension. Step 2: Add 20g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 14g of N-hydroxysuccinimide to the suspension obtained in Step 1, stir at 450rpm for 35min at 28℃, and keep the pH of the system at 5.2 to obtain a partially carboxyl-activated humic acid dispersion system. Step 3: Take 16g of 3-aminopropyltriethoxysilane, 180g of anhydrous ethanol, 28g of deionized water, and 3.5g of glacial acetic acid, and stir at 28℃ for 20min to prepare a pre-hydrolyzed 3-aminopropyltriethoxysilane solution; simultaneously, add 7g of triethylamine to 25g of anhydrous ethanol to prepare a triethylamine adjusting solution. Add the pre-hydrolyzed 3-aminopropyltriethoxysilane solution dropwise to the system obtained in Step 2 at a uniform rate over 50min; when the pre-hydrolyzed 3-aminopropyltriethoxysilane solution has been added to one-third of the total volume, begin adding the triethylamine adjusting solution dropwise simultaneously over 35min to maintain the pH of the main system at 6.3±0.2; after all additions are complete, continue stirring at 28℃ and 450rpm for 35min. Step 4: In the system obtained in Step 3, add 22g of 25% ammonia solution dropwise over 12 minutes to raise the pH of the system to 8.9±0.2. Then raise the temperature to 36℃ and maintain it for 25 minutes. After that, let it cool naturally to 28℃ and let it stand for 75 minutes to mature. Step 5: Filter the material after maturation in Step 4 under reduced pressure. Wash the filter cake twice with a 320g 70% ethanol aqueous solution prepared by 224g anhydrous ethanol and 96g deionized water each time, and then wash it once with 550g deionized water until the filtrate is close to neutral. Then, vacuum dry it at 48℃ to constant weight, crush it and pass it through an 80-mesh sieve to obtain a modified humic acid organic conditioner suitable for barren soil.

[0026] Example 4: Step 1: Add 100g of sodium humate to 1000g of deionized water and stir at 380rpm for 20min at 24℃ to completely disperse it and form a homogeneous brown-black solution; then add 34g of 37% hydrochloric acid within 10min, and adjust the pH of the system to 5.0 by real-time monitoring with a calibrated pH meter; then add 800g of anhydrous ethanol within 20min and continue stirring at 380rpm for 50min to obtain a brown-black suspension. Step 2: Add 16g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 10g of N-hydroxysuccinimide to the suspension obtained in Step 1, stir at 380rpm for 30min at 24℃, and keep the pH of the system at 5.0 to obtain a partially carboxyl-activated humic acid dispersion system. Step 3: Take 13g of 3-aminopropyltriethoxysilane, 200g of anhydrous ethanol, 22g of deionized water, and 2.8g of glacial acetic acid, and stir at 24℃ for 18min to prepare a pre-hydrolyzed 3-aminopropyltriethoxysilane solution; simultaneously, add 5g of triethylamine to 20g of anhydrous ethanol to prepare a triethylamine adjusting solution. Add the pre-hydrolyzed 3-aminopropyltriethoxysilane solution dropwise to the system obtained in Step 2 at a uniform rate over 45min; when the pre-hydrolyzed 3-aminopropyltriethoxysilane solution has been added to two-fifths of the total volume, begin adding the triethylamine adjusting solution dropwise simultaneously over 30min to maintain the pH of the main system at 6.1±0.2; after all additions are complete, continue stirring at 24℃ at 380rpm for 30min. Step 4: In the system obtained in Step 3, add 18g of 25% ammonia solution dropwise over 10 minutes to raise the pH of the system to 8.7±0.2. Then, raise the temperature to 34℃ and maintain it for 20 minutes. After that, allow it to cool naturally to 24℃ and let it stand for 60 minutes to mature. Step 5: Filter the material after maturation in Step 4 under reduced pressure. Wash the filter cake twice with a 300g 70% ethanol aqueous solution prepared by 210g anhydrous ethanol and 90g deionized water each time, and then wash it once with 500g deionized water until the filtrate is close to neutral. Then, vacuum dry it at 42℃ to constant weight, crush it and pass it through an 80-mesh sieve to obtain a modified humic acid organic conditioner suitable for barren soil.

[0027] Example 5: Step 1: Add 100g of sodium humate to 1400g of deionized water and stir at 500rpm for 40min at 30℃ to completely disperse it and form a homogeneous brown-black solution; then add 40g of 37% hydrochloric acid within 20min, and adjust the pH of the system to 5.3 by real-time monitoring with a calibrated pH meter; then add 550g of anhydrous ethanol within 18min and continue stirring at 500rpm for 30min to obtain a brown-black suspension. Step 2: Add 24g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 16g of N-hydroxysuccinimide to the suspension obtained in Step 1, stir at 500rpm for 40min at 30℃, and keep the pH of the system at 5.3 to obtain a partially carboxyl-activated humic acid dispersion system. Step 3: Take 18g of 3-aminopropyltriethoxysilane, 150g of anhydrous ethanol, 30g of deionized water, and 4.0g of glacial acetic acid. Stir at 30°C for 25min to prepare a pre-hydrolyzed 3-aminopropyltriethoxysilane solution. Simultaneously, add 8.0g of triethylamine to 30g of anhydrous ethanol to prepare a triethylamine adjusting solution. Add the pre-hydrolyzed 3-aminopropyltriethoxysilane solution dropwise to the system obtained in Step 2 at a uniform rate over 55min. When the pre-hydrolyzed 3-aminopropyltriethoxysilane solution has been added to half of the total volume, start adding the triethylamine adjusting solution dropwise simultaneously over 40min to maintain the pH of the main system at 6.4±0.2. After all the addition is complete, continue stirring at 500rpm at 30°C for 40min. Step 4: In the system obtained in Step 3, add 25g of 25% ammonia solution dropwise over 15min to raise the pH of the system to 9.0±0.2, then raise the temperature to 38℃ and maintain it for 30min, then allow it to cool naturally to 30℃ and let it stand for 90min to mature. Step 5: Filter the material after maturation in Step 4 under reduced pressure. Wash the filter cake twice with a 350g 70% ethanol aqueous solution prepared by 245g anhydrous ethanol and 105g deionized water each time, and then wash it once with 600g deionized water until the filtrate is close to neutral. Then, vacuum dry it at 50℃ to constant weight, crush it and pass it through a 60-mesh sieve to obtain a modified humic acid organic conditioner suitable for barren soil.

[0028] Example 6: Step 1: Add 100g of sodium humate to 1150g of deionized water and stir at 420rpm for 28min at 26℃ to completely disperse it and form a homogeneous brown-black solution; then add 35g of 37% hydrochloric acid within 14min, and adjust the pH of the system to 5.1 by real-time monitoring with a calibrated pH meter; then add 650g of anhydrous ethanol within 22min and continue stirring at 420rpm for 42min to obtain a brown-black suspension. Step 2: Add 17g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 11g of N-hydroxysuccinimide to the suspension obtained in Step 1, stir at 420rpm for 28min at 26℃, and keep the pH of the system at 5.1 to obtain a partially carboxyl-activated humic acid dispersion system. Step 3: Take 15g of 3-aminopropyltriethoxysilane, 170g of anhydrous ethanol, 26g of deionized water, and 3.2g of glacial acetic acid, and stir at 26℃ for 15min to prepare a pre-hydrolyzed 3-aminopropyltriethoxysilane solution; simultaneously, add 6.5g of triethylamine to 22g of anhydrous ethanol to prepare a triethylamine adjusting solution. Add the pre-hydrolyzed 3-aminopropyltriethoxysilane solution dropwise to the system obtained in Step 2 at a uniform rate over 48min; when the pre-hydrolyzed 3-aminopropyltriethoxysilane solution has been added to one-third of the total volume, begin adding the triethylamine adjusting solution dropwise simultaneously over 30min to maintain the pH of the main system at 6.2±0.2; after all additions are complete, continue stirring at 26℃ and 420rpm for 32min. Step 4: In the system obtained in Step 3, add 21g of 25% ammonia solution dropwise over 10min to raise the pH of the system to 8.8±0.2, then raise the temperature to 35℃ and maintain it for 20min, then allow it to cool naturally to 26℃ and let it stand for 60min to mature. Step 5: Filter the material after maturation in Step 4 under reduced pressure. Wash the filter cake twice with a 310g 70% ethanol aqueous solution prepared by 217g anhydrous ethanol and 93g deionized water each time, and then wash it once with 520g deionized water until the filtrate is close to neutral. Then, vacuum dry it at 45℃ to constant weight, crush it and pass it through an 80-mesh sieve to obtain a modified humic acid organic conditioner suitable for barren soil.

[0029] Comparative Example 1: The difference from Example 1 is that 600g of anhydrous ethanol is not added in step 1; in order to keep the total amount of liquid added in step 1 consistent, 600g of deionized water is used instead of anhydrous ethanol, and the other conditions are the same as in Example 1.

[0030] Comparative Example 2: The difference from Example 1 is that 18g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 12g of N-hydroxysuccinimide are not added in step 2; in order to keep the total amount of materials added in step 2 consistent, 30g of deionized water is used to replace the 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide, and the other conditions are the same as in Example 1.

[0031] Comparative Example 3: The difference from Example 1 is that the amounts of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide added in step 2 were adjusted to 36g and 24g, respectively, while the other conditions were the same as in Example 1.

[0032] Comparative Example 4: The difference from Example 1 is that in step 3, 14g of 3-aminopropyltriethoxysilane, 160g of anhydrous ethanol, 24g of deionized water and 3g of glacial acetic acid are mixed and immediately added dropwise to the system obtained in step 2, without pre-hydrolysis by stirring at 25°C for 15min. The other conditions are the same as in Example 1.

[0033] Comparative Example 5: The difference from Example 1 is that: after all the 3-aminopropyltriethoxysilane solution to be pre-hydrolyzed was added in step 3, the triethylamine conditioning solution prepared by 6g of triethylamine and 20g of anhydrous ethanol was added to the main system within 30 minutes. During the addition of the pre-hydrolyzed 3-aminopropyltriethoxysilane solution, the pH of the main system was not maintained at 6.2±0.2. The other conditions were the same as in Example 1.

[0034] Comparative Example 6: The difference from Example 1 is that 20g of 25% ammonia water is not added in step 4; in order to keep the total amount of liquid added in step 4 consistent, 20g of deionized water is used instead of 25% ammonia water, and the pH of the system is not raised to 8.8±0.2. The other conditions are the same as in Example 1.

[0035] Preparation and source of test samples: The test samples included the modified humic acid organic conditioner obtained in Examples 1-6, the samples obtained in Comparative Examples 1-6, and the blank control soil sample. All samples from the examples and comparative examples were prepared according to the methods described above and stored in sealed containers. The infertile soil used in the pot experiments was taken from the top 0-20cm layer of degraded sandy loam, naturally air-dried, and after removing plant debris and gravel, it was sieved through a 2mm sieve for later use. The basic properties of the test soil were: pH 5.2, organic matter 8.6 g / kg, total nitrogen 0.42 g / kg, available phosphorus 6.8 mg / kg, available potassium 51 mg / kg, cation exchange capacity 6.4 cmol(+) / kg, and field capacity 19.5%. Each treatment consisted of 2.50 kg of air-dried soil per pot, with 0.30% of the soil mass (7.50 g of soil conditioner) added per pot. The soil was dry-mixed for 5 minutes, then deionized water was added to adjust the soil to 60% field capacity. Sowing was carried out 7 days after equilibration. The control soil samples were prepared using the same procedure except for the absence of soil conditioner. The tested maize seeds were from the same batch of Zhengdan 958, selected for their plumpness and uniformity. Before sowing, the seeds were rinsed with deionized water and air-dried at room temperature. Ten seeds were sown per pot, and seedlings were thinned to 6 plants per pot after emergence. Greenhouse conditions were controlled at 25±2℃ during the day and 20±2℃ at night, with a relative humidity of 60%±10%. Watering was performed by weighing during the experiment to maintain each treatment at 55%-65% field capacity. No additional fertilizer was applied. Each potted treatment had three replicates.

[0036] Performance testing: Determination of basic physicochemical properties of soil conditioner: Samples obtained in Examples 1-6 and Comparative Examples 1-6 were pulverized, mixed thoroughly, and then sampled. Basic properties of the product can be determined by referring to both the general requirements for soil conditioners and relevant standards for humic acid soil conditioners. Total humic acid content was determined according to GB / T 34766-2017, and soluble humic acid content was determined according to GB / T 35107-2017. Each sample was measured in triplicate, and the average value was taken.

[0037] Soil pH, organic matter, and cation exchange capacity were determined after application: Samples were taken from the 0-15cm layer of each pot 30 days after sowing, mixed thoroughly, air-dried, and sieved through a 2mm sieve. Soil pH was determined according to NY / T 1121.2-2006. 10.00g of air-dried soil sample was weighed, and 25mL of deionized water was added at a soil-to-water ratio of 1:2.5. The mixture was shaken for 1 min and allowed to stand for 30 min. The pH was measured using a pH meter calibrated with standard buffer solutions of pH 4.01, pH 6.86, and pH 9.18. Soil organic matter was determined according to the external heating potassium dichromate oxidation method of NY / T 1121.6-2006. The air-dried soil sample was finely ground, sieved through a 0.149mm sieve, and then sampled. Oxidation, titration, and conversion of organic matter content were performed according to standard methods. Cation exchange capacity was determined according to the hexaamminecobalt trichloride extraction-spectrophotometric method of HJ 889-2017. Each treatment was performed in triplicate.

[0038] Soil bulk density and field water holding capacity were measured after application: 30 days after sowing, water was collected from the center of each pot using a 100cm water sample. 3 Uncirculated soil samples were collected using a ring sampler, with three ring samples taken for each treatment. Soil bulk density was determined according to NY / T 1121.4-2006. After drying the ring sample at 105℃ to constant weight, the bulk density was calculated as the ratio of dry soil mass to ring sample volume. Soil field capacity was determined according to the ring sampler method in NY / T1121.22-2010. The ring sample was slowly saturated with water from bottom to top and kept saturated for 24 hours. It was then placed on a specified device for free drainage until the mass stabilized, weighed, dried, and the field capacity was calculated. Each treatment was performed in triplicate.

[0039] Determination of water-stable macroaggregate content in soil after application: The determination was performed according to the wet sieving method of NY / T 1121.19-2008. 30 days after sowing, air-dried soil samples were collected from each treatment. 50.00 g of aggregates with a particle size of 2-5 mm were sieved and pre-wetted on a 0.25 mm sieve for 10 min using capillary wetting, followed by wet sieving for 5 min at a sieving frequency of 30 times / min. The residue retained on the sieve was collected, dried at 105℃ to constant weight, and weighed. The content of water-stable macroaggregates with a particle size greater than 0.25 mm was calculated. Each treatment was repeated in triplicate.

[0040] Determination of total nitrogen, available phosphorus, and available potassium in the soil after application: Air-dried soil samples from each treatment were collected 30 days after sowing and passed through a 2mm sieve. Total nitrogen was determined using the automatic nitrogen analyzer method according to NY / T 1121.24-2012. The total nitrogen content was calculated after high-temperature digestion, distillation, and titration. Available phosphorus was determined according to NY / T 1121.7-2014. Given that the pH of the tested soil was 5.2, the ammonium fluoride-hydrochloric acid extraction-molybdenum antimony colorimetric method suitable for acidic soils was used. 5.00g of air-dried soil sample was weighed, 25mL of extract was added, shaken under specified conditions, filtered, and the absorbance was measured to calculate the available phosphorus content. Available potassium was determined according to NY / T 889-2004 using the 1mol / L neutral ammonium acetate extraction-flame photometric method. 5.00g of air-dried soil sample was weighed, 50mL of extract was added, shaken for 30min, filtered, and the result was measured. Each treatment was tested in triplicate.

[0041] Germination rate determination of maize seeds: The germination test and normal seedling determination principles were followed according to GB / T 3543.4-2025. Soil samples from each treatment after 7 days of equilibration were placed in germination boxes with a thickness of 4 cm and a sowing depth of 1 cm. Four replicates were set up for each treatment, with 50 maize seeds sown in each replicate. The samples were incubated in a 25℃ germination chamber, maintaining a substrate moisture content of 60% ± 5% of field capacity during the incubation period. Germination rate was calculated on day 7 according to the criteria for normal seedling determination.

[0042] The test results are shown in Table 1.

[0043] Table 1 Performance Test Results

[0044] As shown in Table 1, the blank control soil sample was highly acidic, nutrient-poor, and loosely structured. 30 days after sowing, the soil pH was only 5.2, the organic matter content was 8.6 g / kg, the cation exchange capacity was 6.4 cmol(+) / kg, and the bulk density was 1.51 g / cm³. 3 The field water holding capacity and water-stable macroaggregates were only 19.5% and 31.5%, respectively, and the corn germination rate was only 84.0%. Compared with the blank control, the modified humic acid organic amendments obtained in Examples 1-6 could all increase soil pH, organic matter, cation exchange capacity, and the contents of total nitrogen, available phosphorus, and available potassium to varying degrees, while simultaneously reducing bulk density, increasing field water holding capacity, water-stable macroaggregate content, and seed germination rate, indicating that the amendments obtained in this application have a comprehensive effect of structural improvement, water and fertilizer retention, and germination promotion. Among them, Example 3 had the best comprehensive effect, with total humic acid and soluble humic acid of 63.4% and 46.0%, respectively. After application, the soil pH increased to 5.8, organic matter increased to 10.5 g / kg, cation exchange capacity increased to 8.1 cmol(+) / kg, and bulk density decreased to 1.37 g / cm³. 3The field water holding capacity and water-stable macroaggregates increased to 24.1% and 46.7%, respectively, while the total nitrogen, available phosphorus, and available potassium reached 0.46 g / kg, 9.2 mg / kg, and 59.6 mg / kg, respectively. The germination rate of maize increased to 94.0%. This indicates that when the ethanol confined dispersion in step 1, the partial carboxyl activation in step 2, the simultaneous pH control during the APTES pre-hydrolysis and dripping process in step 3, and the alkaline locking condensation in step 4 are synchronized, the organosilicon grafting efficiency and soil particle surface retention capacity can be improved while retaining the humic acid active sites, thereby achieving a synergistic enhancement of aggregate construction, water and fertilizer retention, and germination promotion.

[0045] It is worth noting that the soluble humic acid content in Example 3 was not the highest, but the overall soil improvement effect was the best. This indicates that the technical advantage of the present invention does not lie in simply pursuing a high dissolution ratio, but in the balance between humic acid activity retention, effective silane grafting, and subsequent condensation locking. Comparative Example 1, lacking ethanol-confined dispersion; Comparative Example 4, lacking APTES pre-hydrolysis; and Comparative Example 5, lacking pH window control during the dripping process, all showed significantly limited improvements in field water holding capacity, water-stable large aggregates, and cation exchange capacity. Although Comparative Example 2 still achieved 48.3% soluble humic acid, the lack of EDC / NHS activation made it difficult for humic acid and silane to form a stable and effective graft, resulting in significantly lower soil improvement indicators than the examples after application. Comparative Example 3, due to excessive activator dosage, caused excessive consumption of active sites and induced side reactions, resulting in an overall effect inferior to the examples. Comparative Example 6, without alkaline locking condensation, retained a high level of soluble humic acid, but its structural stability was insufficient, leading to weaker subsequent soil particle adhesion and structural reinforcement. Example 5 further illustrates that the amount of each raw material and the reaction intensity are not necessarily better the higher they are. Excessive activation and condensation will cause the soluble humic acid to drop to 40.6%, and its overall synergistic effect will be lower than that of Example 3.

[0046] In summary, this application achieves a simultaneous improvement in the retention of humic acid activity, silane utilization efficiency, and soil amendment stability through the overall synergistic design of each reaction window.

[0047] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. An organic soil conditioner suitable for infertile soils, characterized in that, Based on 100 parts by mass of sodium humate, the following raw materials were prepared in the following proportions by mass: 1000-1400 parts by mass of first deionized water, 32-40 parts by mass of hydrochloric acid with a mass fraction of 37%, 500-800 parts by mass of first anhydrous ethanol, 14-24 parts by mass of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, 9-16 parts by mass of N-hydroxysuccinimide, 11-18 parts by mass of 3-aminopropyltriethoxysilane, 130-200 parts by mass of second anhydrous ethanol, 18-30 parts by mass of second deionized water, 2.2-4.0 parts by mass of glacial acetic acid, 4.5-8.0 parts by mass of triethylamine, 15-30 parts by mass of third anhydrous ethanol, and 16-25 parts by mass of ammonia water with a mass fraction of 25%. The first deionized water, hydrochloric acid, and first anhydrous ethanol are used to construct a water / ethanol suspension dispersion system with a pH of 4.9-5.3, and the first anhydrous ethanol is used as a process solvent for confined dispersion; the 3-aminopropyltriethoxysilane, second anhydrous ethanol, second deionized water, and glacial acetic acid are used for the pre-hydrolysis of the 3-aminopropyltriethoxysilane, and the second anhydrous ethanol is used as a process solvent for pre-hydrolysis; the triethylamine and third anhydrous ethanol are used to prepare a triethylamine conditioning solution, and the third anhydrous ethanol is used as a dilution solvent for the triethylamine conditioning solution; The organic modifier is prepared by grafting humic acid activated by the 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and the N-hydroxysuccinimide with the pre-hydrolyzed 3-aminopropyltriethoxysilane, followed by condensation under the action of the triethylamine adjusting solution and the ammonia water. During the addition of the pre-hydrolyzed 3-aminopropyltriethoxysilane, the pH of the main system is maintained at 6.0-6.4, allowing the carboxyl-activated humic acid and the pre-hydrolyzed 3-aminopropyltriethoxysilane to undergo a grafting reaction first. After the grafting reaction is completed, the ammonia water is added for condensation and ripening, with the system pH at 8.6-9.0 during condensation. When preparing the organic modifier, the triethylamine conditioning solution is added when the pre-hydrolyzed 3-aminopropyltriethoxysilane is added to one-quarter to one-half of the total amount.

2. The organic soil conditioner suitable for infertile soil according to claim 1, characterized in that, The sodium humate is derived from weathered coal or lignite and has a dry basis humic acid content of not less than 70%, a fineness of 80-100 mesh, and a pH of 9-10.

3. The organic soil conditioner suitable for infertile soil according to claim 1, characterized in that, The organic modifier is in powder form, and the particle size is 60-100 mesh.

4. A method for preparing an organic soil conditioner suitable for infertile soil according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Sodium humate was dispersed in the first deionized water, hydrochloric acid with a mass fraction of 37% was added, and then anhydrous ethanol was added to obtain a suspension. (2) Add 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to the suspension obtained in step (1) to activate it and obtain an activated humic acid dispersion system. (3) Mix 3-aminopropyltriethoxysilane, second anhydrous ethanol, second deionized water and glacial acetic acid and pre-hydrolyze them, then add them dropwise to the activated humic acid dispersion system obtained in step (2), and simultaneously add triethylamine conditioning solution prepared by triethylamine and third anhydrous ethanol. (4) After the addition is completed in step (3) and stirring is continued, add 25% ammonia water by mass to the resulting system to carry out condensation and ripening; (5) Filter, wash, dry, crush and sieve the material obtained in step (4) to obtain an organic amendment suitable for barren soil.

5. The method for preparing the organic amendment suitable for barren soil according to claim 4, characterized in that, In step (1), sodium humate is added to the first deionized water and stirred at 350-500 rpm for 20-40 min at 22-30℃; hydrochloric acid is added within 10-20 min and the pH of the system is adjusted to 4.9-5.3 by real-time monitoring with a calibrated pH meter; the first anhydrous ethanol is added within 15-25 min and stirring is continued at 350-500 rpm for 30-50 min.

6. The method for preparing the organic amendment suitable for barren soil according to claim 4, characterized in that, In step (2), the activation is carried out at 22-30°C with stirring at 350-500 rpm for 25-40 min, and the pH of the system is maintained at 4.9-5.

3.

7. The method for preparing the organic amendment suitable for barren soil according to claim 4, characterized in that, In step (3), the pre-hydrolysis is carried out by stirring at 22-30℃ for 12-25 min; the pre-hydrolyzed 3-aminopropyltriethoxysilane is added dropwise to the activated humic acid dispersion system obtained in step (2) within 40-55 min; the triethylamine conditioning solution is added dropwise within 25-40 min; after all the addition is completed, stirring is continued at 22-30℃ at 350-500 rpm for 25-40 min.

8. The method for preparing the organic amendment suitable for barren soil according to claim 4, characterized in that, In step (4), the ammonia water is added dropwise over 8-15 minutes to raise the pH of the system to 8.6-9.0, and the system is heated to 33-38°C and maintained for 15-30 minutes. Then, it is naturally cooled to 22-30°C and allowed to stand for 45-90 minutes to mature.

9. The method for preparing the organic amendment suitable for barren soil according to claim 4, characterized in that, In step (5), the filter cake is first washed with an ethanol aqueous solution, then washed with deionized water, and then vacuum dried at 40-50°C to constant weight.

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