Strontium-rich soil conditioner with slow-release function and preparation method thereof

Abstract

This invention discloses a strontium-enriched soil conditioner with slow-release function and its preparation method. The conditioner comprises the following raw materials in parts by weight: 10-30 parts strontium slow-release agent, 5-10 parts sodium alginate, 0.5-3 parts citric acid, 2-8 parts Bacillus subtilis, and 1-5 parts adjuvants. The strontium slow-release agent is prepared by calcining and acid-modifying a porous carrier, followed by conventional impregnation with a strontium impregnation solution, then activation impregnation with a composite activator of ethylenediaminetetraacetic acid and polyacrylamide, and finally solid-liquid separation and drying. The conditioner prepared by this invention can achieve gradient slow-release of strontium, and through the synergistic chelation and acidification effects of sodium alginate and citric acid, effectively improves the bioavailability of strontium in the soil, promotes the absorption and translocation of strontium by crops, and improves the soil micro-ecological environment, making it suitable for the large-scale production of strontium-enriched agricultural products.

Description

Technical Field

[0001] This invention relates to the fields of soil improvement and agricultural technology, specifically to a strontium-enriched soil conditioner that can effectively increase the strontium content in crop fruits, its preparation method, and its application in strontium-enriched crop cultivation. Background Technology

[0002] Strontium is one of the 14 essential trace elements for the human body. The body's daily requirement for strontium comes from food, but most foods contain very little strontium. Meat, potatoes, fruits, and dairy products contain less than 1 mg / kg of strontium, while root vegetables and seafood contain slightly higher amounts, approximately 1-4 mg / kg. Therefore, developing strontium-enriched agricultural products is of great significance for meeting the human body's strontium nutritional needs.

[0003] Strontium in soil exists in various forms, including residual, exchangeable, carbonate-bound, iron-manganese oxide-bound, and organically bound forms. Studies have shown that strontium exhibits a similar distribution across different geological soil samples, with residual form being the dominant form, accounting for up to 79% of the total. This bound form of strontium is difficult for plants to directly absorb and utilize, resulting in low strontium content in crop fruits despite the presence of strontium in the soil.

[0004] Currently, the main method for producing strontium-enriched agricultural products is to directly add inorganic strontium and base fertilizer to the soil to promote strontium enrichment in crops. However, this method has significant limitations: First, the directly added strontium easily forms strontium salt precipitates with carbonate or sulfate ions in the soil, which not only fails to achieve the desired strontium enrichment effect on crops but may also cause heavy metal pollution to the soil due to excessive accumulation; second, a large amount of bound strontium in the soil cannot be effectively utilized, resulting in resource waste.

[0005] In recent years, some researchers have begun to focus on strontium activation technologies. For example, Chinese patent document CN118060325A utilizes the S2-8-1 bacterial agent to enhance the enrichment of strontium in soil by ryegrass. Through the metabolic activity of S2-8-1 bacteria, the soil becomes weakly acidic, converting solid or insoluble Sr in the soil into water-soluble strontium salts via hydration and hydrolysis. Additionally, Chinese patent document CN 116286003 B uses potassium humate as a strontium activator to convert bound strontium in the soil into an available form. Experimental results show that potassium humate can activate strontium in soil at an efficiency of 22.7%-28.0%.

[0006] However, existing technologies still have some shortcomings: First, most technologies are aimed at the remediation of strontium-contaminated soil, rather than strontium nutrient fortification in agricultural production; second, the activation effect is limited and it is difficult to meet the needs of large-scale agricultural production; third, the chemical reagents used in some technologies may cause secondary pollution to the environment; and fourth, existing technologies mostly adopt foliar spraying and other methods, which have problems such as high application costs and unstable effects.

[0007] Therefore, developing a strontium-enriched soil conditioner with slow-release function to convert strontium into easily absorbed effective strontium is of great practical significance and application value for increasing the strontium content of crops and producing strontium-enriched agricultural products. Summary of the Invention

[0008] The purpose of this invention is to provide a strontium-enriched soil conditioner with slow-release function and its preparation method, in order to solve the problems of low strontium absorption efficiency by crops and poor strontium bioavailability in soil in the prior art. This method promotes efficient loading of strontium in a porous carrier by selecting specific activators and achieves gradient slow release of strontium, which is beneficial for long-term absorption by plants.

[0009] In a first aspect, the present invention provides a strontium-rich soil conditioner with slow-release function, comprising the following raw materials in parts by weight: 10-30 parts of strontium slow-release agent, 5-10 parts of sodium alginate, 0.5-3 parts of citric acid, 2-8 parts of Bacillus subtilis, and 1-5 parts of binder.

[0010] Preferably, the preparation method of the strontium sustained-release agent includes the following steps:

[0011] (1) The porous carrier is crushed through a 40-120 mesh sieve, calcined, modified with dilute acid, washed and dried to obtain an activated carrier; (2) A strontium impregnation solution is prepared, and the activated carrier and the strontium impregnation solution are mixed at a solid-liquid ratio of 1:8-1:18, stirred and impregnated for 3-10 hours, and then an activator is added for impregnation for 1-5 hours. The solid and liquid are separated and dried at low temperature to obtain a strontium slow-release agent.

[0012] The purpose of calcining the porous support is to remove organic impurities, increase the specific surface area and pore structure, and improve the adsorption capacity for strontium ions. Dilute acid modification can further activate the functional groups on the support surface and increase the number of active adsorption sites. Preferably, the calcination temperature in step (1) is 450-750℃ and the time is 3-5h.

[0013] Furthermore, the type of porous material in step (1) is not specifically required. Any porous material capable of loading strontium ions can be selected, preferably one or more of zeolite, diatomite, perlite, vermiculite, sepiolite or biochar, with zeolite or sepiolite being preferred.

[0014] Preferably, the dilute acid modification in step (1) is to soak the sample in 0.1-0.5 mol / L hydrochloric acid or nitric acid for 1-3 hours.

[0015] Preferably, in step (2), the activator is selected from ethylenediaminetetraacetic acid and polyacrylamide in a mass ratio of 1-3:0.1-0.5, and the amount added is 0.5% to 3% of the mass of the strontium impregnation solution.

[0016] Preferably, the strontium impregnation solution is a soluble strontium salt solution with a concentration of 0.2-0.8 mol / L, preferably strontium chloride or strontium nitrate.

[0017] Preferably, in step (2), the immersion temperature is 35-55℃ and the stirring speed is 180-300 r / min.

[0018] Furthermore, based on the impregnation effect, it is preferable that step (2) can be assisted by ultrasonic treatment during the impregnation process, with an ultrasonic power of 100-300W and an ultrasonic time of 30-60 minutes, in order to accelerate the diffusion of strontium ions.

[0019] Preferably, the low-temperature drying temperature is 80-100℃, and the product is dried to a constant weight.

[0020] Preferably, the Bacillus is at least one of Bacillus subtilis, Bacillus mucilaginosus, Bacillus amyloliquefaciens, and Bacillus megaterium. Bacillus can activate insoluble strontium in the soil by secreting organic acids, extracellular polysaccharides, and functional enzymes, thereby enhancing the bioavailability of strontium. Simultaneously, it optimizes soil aggregate structure and pore distribution, improves soil aeration and water retention, and constructs a suitable rhizosphere microenvironment. Together with sodium alginate and citric acid, it promotes the absorption and translocation of strontium by plants, achieving integrated regulation of soil structure improvement and strontium activation and utilization.

[0021] Preferably, the binder is at least one selected from sodium carboxymethyl cellulose, hydroxypropyl methyl cellulose, starch, guar gum, and polyvinyl alcohol. The binder facilitates the bonding of the various raw material components into a granular modifier, while simultaneously controlling the particle strength.

[0022] Secondly, the present invention provides a method for preparing a strontium-rich soil conditioner with a slow-release function, comprising the following steps: mixing 10-30 parts of strontium slow-release agent, 5-10 parts of sodium alginate, 0.5-3 parts of citric acid, 2-8 parts of Bacillus subtilis, and 1-5 parts of binder to obtain a strontium-rich soil conditioner.

[0023] Thirdly, the present invention also provides an application of the above-mentioned strontium-rich soil conditioner in crop planting, wherein the strontium-rich soil conditioner is applied to the soil as a base fertilizer or top dressing, with an application rate of 20-200 kg / mu.

[0024] After soil conditioner is applied to the soil, because the soil contains a large amount of soluble sulfates and carbonates, the strontium released from the carrier readily reacts with SO4. 2- CO3 2- Strontium forms insoluble SrSO4 and SrCO3, which are difficult for plants to absorb and utilize. Therefore, this invention achieves synergistic activation of strontium by further adding sodium alginate and citric acid. Sodium alginate contains a large number of carboxyl and hydroxyl groups, which can chelate with strontium ions, converting fixed strontium into ionic chelates. Citric acid, as an acidic chelating agent, not only chelates strontium ions but also converts insoluble SrSO4 and SrCO3 into water-soluble strontium-citric acid complexes through acidification and complexation. The synergistic effect of sodium alginate and citric acid effectively prevents strontium from being fixed in the soil, improves the migration ability of strontium in the soil-crop system, and facilitates its absorption and utilization by plants.

[0025] This invention employs a combination of conventional impregnation and activated impregnation in the preparation of strontium sustained-release agents. In conventional impregnation, strontium ions are initially loaded onto the carrier surface and pores primarily through physical adsorption and ion exchange. This invention uses a complex of ethylenediaminetetraacetic acid (EDTA) and polyacrylamide as the impregnation activator. The carboxyl groups in EDTA can chelate with strontium ions, promoting strontium loading on the carrier surface. Polyacrylamide, with its three-dimensional network structure, can form a physical barrier, delaying strontium release. The combined effect of these two agents allows for the formation of a more stable complex with the adsorbed strontium ions, thereby achieving a gradient sustained release.

[0026] The advantages or beneficial effects of the strontium-rich soil conditioner with slow-release function of the present invention include at least the following:

[0027] 1. By employing a composite activator of ethylenediaminetetraacetic acid (EDTA) and polyacrylamide, EDTA chelates with strontium ions through its carboxyl groups, enhancing the loading stability of strontium on the carrier surface; polyacrylamide forms a three-dimensional network physical barrier, slowing down the release rate of strontium. Together, these two agents enable strontium to exhibit a gradient slow-release characteristic. The strontium slow-release agent prepared in Example 1 showed cumulative release rates of 15.2%, 38.6%, and 72.3% on days 1, 7, and 30, respectively, extending the nutrient supply cycle.

[0028] 2. By synergistically chelating and acidifying sodium alginate and citric acid, the bioavailability of strontium in the soil and the strontium enrichment effect in crops are significantly improved. Sodium alginate is rich in carboxyl and hydroxyl groups, which can form chelates with strontium ions; citric acid has both acidifying and complexing effects, which can convert insoluble SrSO4 and SrCO3 in the soil into water-soluble strontium-citric acid complexes, effectively preventing strontium from being released from the carrier and fixed by the soil, while promoting the migration of strontium from the roots to the aboveground parts and grains. The results of rice and pepper planting trials showed that after applying the amendment in the example, the available strontium in the soil and the strontium content in crops were significantly increased, indicating that it can efficiently promote the migration and accumulation of strontium from the soil to the edible parts of crops, promote the absorption and translocation of strontium by crops, and is suitable for the large-scale production of strontium-enriched agricultural products. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to specific embodiments. However, it should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0030] Unless otherwise specified, the materials and reagents used in the following examples and comparative examples are commercially available. Unless otherwise specified, the amount of each component in the following examples is 1 g per part by weight.

[0031] Raw materials used in the following embodiments

[0032] Strontium chloride (SrCl2·6H2O): analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0033] Strontium nitrate (Sr(NO3)2): analytical grade, purchased from Tianjin Damao Chemical Reagent Factory.

[0034] Sodium alginate: Industrial grade, purchased from Qingdao Mingyue Seaweed Group Co., Ltd.

[0035] Citric acid: Industrial grade, purity ≥99.5%, purchased from Shandong Weifang Yingxuan Industrial Co., Ltd.

[0036] Bacillus subtilis: effective viable count ≥10 billion / g, purchased from Shandong Lvlong Biotechnology Co., Ltd.

[0037] Gelatinous Bacillus: effective viable count ≥10 billion / g, purchased from Shandong Linghang Biotechnology Co., Ltd.

[0038] Bacillus megaterium: effective viable count ≥10 billion / g, purchased from Shandong Sukehan Bioengineering Co., Ltd.

[0039] Sodium carboxymethyl cellulose: Industrial grade, purchased from Shanghai Shenguang Edible Chemicals Co., Ltd.

[0040] Polyvinyl alcohol: Industrial grade, degree of alcoholysis 88%, purchased from the organic chemical plant of Beijing Dongfang Petrochemical Co., Ltd.

[0041] Ethylenediaminetetraacetic acid (EDTA): Industrial grade, purity ≥99%, purchased from Hebei Chengxin Group Co., Ltd.

[0042] Polyacrylamide (PAM): anionic, molecular weight 7 million, purchased from Beijing Hengju Chemical Group Co., Ltd.

[0043] Hydrochloric acid, nitric acid, zeolite, sepiolite, perlite, and diatomaceous earth are all commercially available.

[0044] I. Experimental examples and comparative examples of methods for preparing strontium-rich soil conditioners with slow-release function.

[0045] Example 1

[0046] A strontium-rich soil conditioner with slow-release function is composed of the following raw materials in parts by weight: 20 parts strontium slow-release agent, 8 parts sodium alginate, 1.5 parts citric acid, 3 parts Bacillus subtilis, and 3 parts carboxymethyl cellulose.

[0047] The preparation method of the strontium sustained-release agent is as follows:

[0048] (1) The zeolite was crushed and passed through an 80-mesh sieve, calcined at 600℃ for 4 hours, then soaked in 0.3mol / L hydrochloric acid for 2 hours, washed until neutral, and dried to obtain the activated carrier.

[0049] (2) Prepare a 0.5 mol / L strontium chloride solution as the strontium impregnation solution. Mix the activated carrier with the strontium impregnation solution at a solid-liquid ratio of 1:12 and impregnate for 6 h at 45 °C and 240 r / min stirring. Then add the activator, which is a mixture of ethylenediaminetetraacetic acid and polyacrylamide at a mass ratio of 2:0.3, at a mass of 1.5% of the strontium impregnation solution. Continue impregnation for 2 h, and after solid-liquid separation, dry at 90 °C to constant weight to obtain the strontium sustained-release agent.

[0050] Mix the above-mentioned strontium slow-release agent, sodium alginate, citric acid, Bacillus subtilis, and binder evenly according to the specified ratio to obtain a strontium-rich soil conditioner.

[0051] Example 2

[0052] A strontium-rich soil conditioner with slow-release function is composed of the following raw materials in parts by weight: 15 parts strontium slow-release agent, 6 parts sodium alginate, 1.0 part citric acid, 5 parts gelatinous Bacillus subtilis, and 2 parts polyvinyl alcohol.

[0053] The preparation method of the strontium sustained-release agent is as follows:

[0054] (1) The sepiolite was crushed and passed through a 100-mesh sieve, calcined at 550℃ for 3.5h, then soaked in 0.2mol / L nitric acid for 2.5h, washed until neutral, and dried to obtain the activated carrier.

[0055] (2) Prepare a 0.4 mol / L strontium nitrate solution as the strontium impregnation solution. Mix the activated carrier with the strontium impregnation solution at a solid-liquid ratio of 1:10 and impregnate for 8 h at 40 °C and 200 r / min stirring. Then add the activator, which is a mixture of ethylenediaminetetraacetic acid and polyacrylamide at a mass ratio of 1.5:0.2, at a mass of 2.0% of the strontium impregnation solution. Continue impregnation for 3 h. After solid-liquid separation, dry at 85 °C to constant weight to obtain the strontium sustained-release agent.

[0056] The above-mentioned strontium slow-release agent, sodium alginate, citric acid, gelatinous Bacillus subtilis, and polyvinyl alcohol are mixed evenly according to the specified ratio to obtain a strontium-rich soil conditioner.

[0057] Example 3

[0058] A strontium-rich soil conditioner with slow-release function is composed of the following raw materials in parts by weight: 25 parts strontium slow-release agent, 9 parts sodium alginate, 2.5 parts citric acid, 6 parts Bacillus megaterium, and 4 parts carboxymethyl cellulose.

[0059] The preparation method of the strontium sustained-release agent is as follows:

[0060] (1) The perlite was crushed and passed through a 60-mesh sieve, calcined at 700℃ for 4.5h, then soaked in 0.4mol / L hydrochloric acid for 1.5h, washed until neutral, and dried to obtain the activated carrier.

[0061] (2) Prepare a 0.7 mol / L strontium chloride solution as the strontium impregnation solution. Mix the activated carrier with the strontium impregnation solution at a solid-liquid ratio of 1:15 and impregnate for 4 h at 50 °C and 280 r / min stirring. Then add the activator, which is a mixture of ethylenediaminetetraacetic acid and polyacrylamide at a mass ratio of 2.5:0.4, at a mass of 1.0% of the strontium impregnation solution. Continue impregnation for 4 h. After solid-liquid separation, dry at 95 °C to constant weight to obtain the strontium sustained-release agent.

[0062] The above-mentioned strontium slow-release agent, sodium alginate, citric acid, Bacillus megaterium, and carboxymethyl cellulose are mixed evenly according to the specified ratio to obtain a strontium-rich soil conditioner.

[0063] Example 4

[0064] A strontium-rich soil conditioner with slow-release function is composed of the following raw materials in parts by weight: 12 parts strontium slow-release agent, 7 parts sodium alginate, 2.0 parts citric acid, 5 parts Bacillus subtilis, and 5 parts carboxymethyl cellulose.

[0065] The preparation method of the strontium sustained-release agent is as follows:

[0066] (1) The diatomaceous earth was crushed and passed through a 120-mesh sieve, calcined at 500℃ for 5h, then soaked in 0.5mol / L nitric acid for 3h, washed until neutral, and dried to obtain the activated carrier.

[0067] (2) Prepare a 0.6 mol / L strontium nitrate solution as the strontium impregnation solution. Mix the activated carrier with the strontium impregnation solution at a solid-liquid ratio of 1:14 and impregnate for 10 h at 55 °C and 260 r / min stirring. Then add the activator, which is a mixture of ethylenediaminetetraacetic acid and polyacrylamide at a mass ratio of 3:0.5, at a mass of 2.5% of the strontium impregnation solution. Continue impregnation for 5 h. After solid-liquid separation, dry at 100 °C to constant weight to obtain the strontium sustained-release agent.

[0068] The above-mentioned strontium slow-release agent, sodium alginate, citric acid, Bacillus subtilis, and carboxymethyl cellulose are mixed evenly according to the specified ratio to obtain a strontium-rich soil conditioner.

[0069] Comparative Example 1

[0070] The difference from Example 1 is that the preparation method of the strontium sustained-release agent is different, while the other steps are the same as in Example 1.

[0071] The preparation method of the strontium sustained-release agent is as follows:

[0072] (1) The zeolite was crushed and passed through an 80-mesh sieve, calcined at 600℃ for 4 hours, then soaked in 0.3mol / L hydrochloric acid for 2 hours, washed until neutral, and dried to obtain the activated carrier.

[0073] (2) Prepare a 0.5 mol / L strontium chloride solution as the strontium impregnation solution. Mix the activated carrier with the strontium impregnation solution at a solid-liquid ratio of 1:12 and impregnate for 8 h at 45 °C and 240 r / min stirring. Then, after solid-liquid separation, dry at 90 °C to constant weight to obtain the strontium sustained-release agent.

[0074] Comparative Example 2

[0075] The difference from Example 1 is that an equal amount of ethylenediaminetetraacetic acid is used instead of polyacrylamide, while the remaining steps are the same as in Example 1.

[0076] Comparative Example 3

[0077] The difference from Example 1 is that an equal amount of polyacrylamide is used instead of ethylenediaminetetraacetic acid, while the remaining steps are the same as in Example 1.

[0078] Comparative Example 4

[0079] The difference from Example 1 is that the strontium-rich soil conditioner does not contain sodium alginate and citric acid, while the remaining steps are the same as in Example 1.

[0080] Comparative Example 5

[0081] The difference from Example 1 is that an equal amount of sodium alginate is used instead of citric acid, while the rest of the steps are the same as in Example 1.

[0082] Comparative Example 6

[0083] The difference from Example 1 is that an equal amount of citric acid is used instead of sodium alginate, while the rest of the steps are the same as in Example 1.

[0084] II. Performance Testing and Result Analysis

[0085] To verify the technical effects of the present invention, a systematic performance test was conducted on the strontium-rich soil conditioners prepared in Examples 1-4 and Comparative Examples 1-6.

[0086] 1. Strontium sustained-release agent sustained-release performance test

[0087] Test method: 10g of the strontium sustained-release agents prepared in Examples 1-4 and Comparative Examples 1-3 were weighed and placed in 100mL of deionized water, and allowed to stand at 25℃. The supernatant was collected on day 1, day 7, and day 30, and the strontium ion concentration was measured to calculate the cumulative release rate.

[0088] Table 1 shows the sustained-release performance of the examples and comparative examples as follows.

[0089]

[0090] As shown in Table 1, the cumulative release rates of the strontium sustained-release agents prepared in Examples 1-4 were significantly lower than those in Comparative Examples 1-3 at 1 day, 7 days, and 30 days, exhibiting a gradient sustained-release characteristic. No activator was added during the preparation of the strontium sustained-release agent in Comparative Example 1. Strontium ions were loaded onto the carrier surface and pores solely through physical adsorption and ion exchange, lacking the chelating stabilizing effect of EDTA and the three-dimensional network barrier effect of PAM. This resulted in rapid release of strontium in the early stages of leaching, with a release rate on day 1 (28.5%) significantly higher than that in Example 1 (15.2%), and a release rate approaching 90% within 30 days, indicating a significant deterioration in the sustained-release effect.

[0091] Comparative Example 2, using only EDTA, while enhancing the loading stability of strontium on the carrier surface through chelation, lacked the physical barrier formed by PAM, resulting in a still relatively high release rate. Comparative Example 3, using only PAM, while providing some barrier effect, lacked the chelating stability of EDTA, leading to insufficient binding strength of strontium on the carrier and a higher release rate than the examples.

[0092] 2. Application in chili pepper cultivation

[0093] The tested soil was yellow-brown soil, with the following basic physicochemical properties: pH = 6.8, organic matter 18.5 g / kg, total strontium content 185.2 mg / kg, and available strontium content (DTPA extraction) 8.3 mg / kg.

[0094] Pot experiment: Plastic pots with a diameter of 25cm and a height of 20cm were used, and each pot contained 5kg of soil. 7.5g of soil conditioner was applied to each pot and mixed with the soil. After equilibration for 7 days, two uniformly growing "Su Jiao No. 5" pepper seedlings were transplanted into each pot. Conventional water and fertilizer management was applied. After 90 days of growth, the fruits were harvested, and the available strontium content in the soil and the strontium content in the pepper fruits were measured.

[0095] Available strontium content in soil: After fruit harvest, soil from the pots was taken, air-dried, sieved, and determined by DTPA (diethylenetriaminepentaacetic acid) extraction-atomic absorption spectrophotometry.

[0096] Strontium content in chili pepper fruits: The harvested chili pepper fruits were dried, ground, and then digested using HNO3-H2O2 microwave method, followed by atomic absorption spectrophotometry.

[0097] Table 2. Effects of different treatments on available strontium in soil and strontium content in pepper fruits.

[0098]

[0099] As shown in Table 2, the available strontium content in the soil treated in Examples 1-4 was 16.5–19.1 mg / kg, and the strontium content in the pepper fruits was 2.2–2.9 mg / kg, both significantly higher than those in Comparative Examples 1-6.

[0100] In Comparative Examples 1-3, due to the poor slow-release performance of the strontium slow-release agent, the strontium was easily fixed or lost by the soil after being released in large quantities in the early stage, resulting in the effective strontium content in the soil being only 12.3, 14.8, and 15.1 mg / kg, respectively, which was far lower than that in Example 1, thus affecting the absorption of strontium by chili peppers.

[0101] Comparative Example 4, lacking the dual protection of chelation and acidification complexation without the addition of sodium alginate and citric acid, allowed strontium released from the carrier to readily react with SO4 in the soil. 2- CO3 2- Insoluble salts were formed, and the available strontium content in the soil was only 9.6 mg / kg, while the strontium content in the chili pepper fruit was only 1.5 mg / kg, which was significantly lower than in Example 1.

[0102] Comparative Example 5 used sodium alginate instead of citric acid. Although strontium ions could be chelated by carboxyl and hydroxyl groups, it lacked the acidification and complexation effect of citric acid, making it difficult to effectively convert the already formed SrSO4 and SrCO3. The available strontium in the soil was 13.5 mg / kg and the strontium content in the capsicum was 1.8 mg / kg, both of which were lower than those in Example 1.

[0103] Comparative Example 6, which replaced sodium alginate with citric acid, could convert some of the insoluble strontium salts through acidification and complexation, but lacked the sustained chelating and protective effects of sodium alginate, and its effect was not as good as the synergistic effect of the two.

[0104] Therefore, in Examples 1-4, sodium alginate and citric acid were added simultaneously. Through the dual effects of chelation and acidification complexation, the two effectively inhibited the fixation of strontium in the soil and significantly improved the available strontium content in the soil and the crop absorption efficiency.

[0105] 3. Application in rice cultivation

[0106] The tested soil was paddy soil with the following basic physicochemical properties: pH = 6.5, organic matter 22.3 g / kg, total strontium content 178.5 mg / kg, and available strontium content (DTPA extraction) 7.1 mg / kg.

[0107] Pot experiment: Plastic pots (50cm in diameter, 25cm in height) were used, with 8kg of soil in each pot. 15g of soil conditioner was applied to each pot and mixed thoroughly with the soil. After equilibration for 7 days, the pots were watered and 3 uniformly growing "Xiangliangyou 900" rice seedlings were transplanted into each pot. Conventional water and fertilizer management was implemented, maintaining the soil submerged until the late grain-filling stage. The plants were harvested after 120 days of growth, and relevant indicators were measured. The results are shown in Table 3.

[0108] Table 3 Effects of different treatments on strontium content in different parts of rice

[0109]

[0110] As shown in Table 3, the available strontium content in the soil, roots, stems and leaves, and brown rice of the treatments in Examples 1-4 were significantly higher than those in the comparative examples. Rice has a long growth period, requiring higher levels of slow-release performance. In Comparative Examples 1-3, the slow-release agent was released too quickly in the early stages, resulting in insufficient supply in the later stages, which limited strontium absorption by the roots. The strontium content in brown rice was only 1.1–1.6 mg / kg, significantly lower than the 2.3 mg / kg in Example 1. The activator treatment in these examples improved the loading stability and slow-release performance of strontium on the carrier, enabling strontium to be continuously and stably absorbed by the rice roots.

[0111] Comparative Examples 4-6 showed a significant decrease in available strontium content in the soil due to the lack of synergistic protection from sodium alginate and citric acid, and a weakened ability of strontium to migrate within the soil-crop system. In particular, Comparative Example 4 showed a brown rice strontium content of only 0.7 mg / kg, indicating that even if some strontium is absorbed by the roots, the lack of the auxiliary effect of sodium alginate and citric acid still inhibits the translocation efficiency of strontium to the aboveground parts and grains. Examples 1-4, through the synergistic effect of these two agents, not only increased the available strontium content in the soil but also promoted the migration of strontium from the roots to the stems, leaves, and grains.

[0112] It should be clarified that the above embodiments are merely illustrative of specific implementations of the present invention and do not constitute a limitation on the scope of protection of the present invention. Based on the technical content disclosed in this invention, those skilled in the art can make various modifications, adjustments, or equivalent substitutions within its basic principles and design concepts. These modifications and improvements need not be listed exhaustively, but should all be considered to fall within the scope of protection of this invention.

Claims

1. A strontium-rich soil conditioner with slow-release function, characterized in that, It is composed of the following raw materials in parts by weight: 10-30 parts of strontium slow-release agent, 5-10 parts of sodium alginate, 0.5-3 parts of citric acid, 2-8 parts of Bacillus subtilis, and 2-5 parts of binder; The preparation method of the strontium sustained-release agent includes the following steps: (1) The porous carrier is crushed through a 40-120 mesh sieve, calcined, modified with dilute acid, washed, and dried to obtain an activated carrier; (2) A strontium impregnation solution is prepared, and the activated carrier and the strontium impregnation solution are mixed at a solid-liquid ratio of 1:8-1:18, stirred and impregnated for 3-10 hours, and then an activator is added for impregnation for 1-5 hours. The solid and liquid are separated and dried to obtain a strontium slow-release agent; the activator is selected from a combination of ethylenediaminetetraacetic acid and polyacrylamide with a mass ratio of 1-3:0.1-0.5, and the amount added is 0.5%~3% of the mass of the strontium impregnation solution; the strontium impregnation solution is a soluble strontium salt solution; The porous carrier in step (1) is one or more of zeolite, diatomite, perlite, vermiculite, sepiolite, or biochar. The Bacillus species is at least one of Bacillus subtilis, Bacillus jellyoidis, Bacillus amyloliquefaciens, and Bacillus megaterium.

2. The strontium-rich soil conditioner with slow-release function as described in claim 1, characterized in that, In step (1), the calcination temperature is 450-750℃ and the time is 3-5h; in step (1), the dilute acid modification is to soak in 0.1-0.5mol / L hydrochloric acid or nitric acid for 1-3h.

3. The strontium-rich soil conditioner with slow-release function as described in claim 1, characterized in that, The concentration of the soluble strontium salt solution is 0.2-0.8 mol / L.

4. The strontium-rich soil conditioner with slow-release function as described in any one of claims 1-3, characterized in that, The strontium salt is at least one of strontium chloride or strontium nitrate.

5. The strontium-rich soil conditioner with slow-release function as described in any one of claims 1-3, characterized in that, The immersion temperature in step (2) is 35-55℃, and the stirring speed is 180-300r / min; the drying temperature is 80-100℃.

6. The strontium-rich soil conditioner with slow-release function as described in any one of claims 1-3, characterized in that, The binder is selected from at least one of sodium carboxymethyl cellulose, hydroxypropyl methyl cellulose, starch, guar gum, and polyvinyl alcohol.

7. A method for preparing a strontium-rich soil conditioner with slow-release function as described in any one of claims 1-6, characterized in that, Includes the following steps: Mix 10-30 parts of strontium slow-release agent, 5-10 parts of sodium alginate, 0.5-3 parts of citric acid, 2-8 parts of Bacillus subtilis, and 2-5 parts of binder to obtain a strontium-rich soil conditioner.

8. The application of a strontium-rich soil conditioner with slow-release function as described in any one of claims 1-6 in crop cultivation, wherein the strontium-rich soil conditioner is applied to the soil as a base fertilizer or top dressing at a rate of 20-200 kg / mu.

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