Preparation method and application of active microalgae and biochar compound fertilizer for increasing phosphorus in saline-alkali soil
Through modification and co-cultivation techniques, the microalgae-biochar composite system stably attaches to and activates phosphorus in saline-alkali land, solving the problems of microalgae colonization and insufficient utilization of biochar pores, and achieving the effects of enhancing phosphorus efficiency and improving soil quality in saline-alkali land.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JIANGSU UNIV
- Filing Date
- 2026-04-10
- Publication Date
- 2026-06-26
Smart Images
Figure CN122277338A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of agricultural resource utilization, specifically relating to a method for preparing and applying an active microalgae and biochar compound fertilizer for enhancing phosphorus efficiency in saline-alkali land. Background Technology
[0002] High concentrations of calcium and magnesium ions in saline-alkali soils readily combine with phosphorus to form insoluble phosphates, leading to phosphorus fixation and a significant reduction in bioavailability, thus becoming a major factor limiting crop growth. Biochar, as a porous carbon material, possesses certain adsorption and ion exchange capabilities, improving soil structure and nutrient retention, and is therefore widely used in soil improvement. However, single biochar materials have limited activation capacity for insoluble phosphorus, making it difficult to significantly increase the available phosphorus content in the soil.
[0003] Filamentous microalgae can activate phosphorus fixed in the soil by secreting metabolites such as organic acids and extracellular polymers, demonstrating good phosphorus solubilization potential. However, in high-adversity environments such as saline-alkali land, direct application of microalgae leads to difficulties in colonization and maintenance of activity, limiting their functional performance and restricting their effectiveness in practical applications.
[0004] In existing technologies, the simple physical mixing of biochar and microalgae can combine the functions of the two to some extent, but it has the following obvious drawbacks: microalgae cannot be stably attached to the surface of biochar and are easily washed away or deactivated; the porous structure of biochar is not fully utilized and it is difficult to play a protective role; there is a lack of effective functional synergy between the two, and the phosphorus activation effect is unstable, making it difficult to meet the actual needs of saline-alkali land improvement. Summary of the Invention
[0005] To address the problems of existing technologies, this invention provides an application for optimizing phosphorus in saline-alkali soils based on a compound fertilizer of activated microalgae and biochar. By optimizing the preparation process and ratio, a filamentous microalgae-biochar composite system is constructed. The core technology lies in: firstly, modifying the biochar with citric acid and other substances to optimize its pore structure and surface functional groups, thereby increasing the attachment sites for microalgae; secondly, using ultrasound-assisted cleaning of the biochar pores to promote the entry of microalgae cells into the pores; and finally, through a co-cultivation process, enabling the microalgae to actively colonize and grow within the porous structure of the biochar, achieving the integrated construction of the carrier and functional component. This compounding method overcomes the shortcomings of traditional mixing methods, such as the difficulty in microalgae colonization and the lack of sustained function. It fully leverages the protective effect of biochar on microalgae and the bio-activation function of microalgae on phosphorus, effectively increasing the available phosphorus content in saline-alkali soils, promoting crop growth, and improving soil physicochemical properties. This provides a stable and efficient technical path for enhancing phosphorus efficiency in saline-alkali soils.
[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A method for preparing an active microalgae and biochar compound fertilizer for enhancing phosphorus efficiency in saline-alkali land, comprising the following steps: (1) Acid modification treatment of biochar: Biochar obtained from biomass pyrolysis is modified by soaking in an organic acid solution to obtain modified biochar. (2) Microalgae-biochar co-culture loading: The modified biochar obtained in step (1) is first added to BG11 medium, dispersed by ultrasonication, and then inoculated with microalgae seed liquid for co-culture, so that microalgae cells attach to and grow on the porous structure of biochar to form an active microalgae-biochar complex. (3) Drying and granulation: The microalgae-biochar composite obtained in step (2) is dried and granulated to obtain granular compound fertilizer, which is active microalgae and biochar compound fertilizer.
[0007] Preferably, in step (1), the biomass includes corn stalks; the organic acid is citric acid or phosphoric acid, the mass concentration of the citric acid solution or phosphoric acid solution is 5%-8%, the soaking time is 2-3 hours, and the liquid-solid ratio is 5:1 mL / g.
[0008] Preferably, in step (1), the preparation method of the biochar is as follows: the biomass is naturally air-dried to a moisture content of <10%, and pulverized to a particle size of <2 mm; placed in a tube furnace, and heated to 500°C at a heating rate of 10°C / min under nitrogen protection, and pyrolyzed at a constant temperature for 60 min; after natural cooling, it is pulverized and sieved to obtain the biochar; the mesh size of the sieve is 20-40 mesh.
[0009] Preferably, in step (1), the modified biochar has the following physicochemical properties: pore volume 0.28~0.35 cm³. 3 / g, with an average pore size of 5.8~8.5 nm and a specific surface area (BET) of 160~195 m². 2 / g.
[0010] Preferably, in step (2), the filamentous microalgae are nitrogen-fixing or non-nitrogen-fixing active filamentous microalgae, including microsheath algae ( Microcoleus ), Common filamentous algae ( Tychonema Monofibrillaria ( Tolypothrix ).
[0011] Preferably, in step (2), the amount of modified biochar added is 5%-10% of the mass of BG11 culture medium, the initial chlorophyll a concentration of the microalgae seed solution is 5-15 μg / mL, and the ultrasonic dispersion conditions are: ultrasonic frequency 40-80 kHz, dispersion for 10-15 minutes; when co-culturing, the microalgae culture conditions are: light intensity 3000 lux, temperature 25 ± 2℃, light-dark cycle 16 h: 8 h, culture for 8-10 days. During the culture process, a magnetic stirrer is used to stir for 10-15 minutes at 30 rpm every 24 hours to promote uniform attachment of microalgae.
[0012] Preferably, in step (2), the liquid-solid ratio of microalgae seed liquid to modified biochar is 50:1 to 20:1 (mL:g).
[0013] Preferably, in step (3), a temperature-controlled blowing method is used for drying, with a drying temperature of 30-40℃, in order to avoid the damage of high temperature to the activity of microalgae cells; the drying process is kept with uniform ventilation until the moisture content drops to ≤ 8%, to ensure that the microalgae cells are in a metabolic dormant state and retain their activity.
[0014] Preferably, in step (3), the granulation after drying adopts a physical extrusion granulation process, and the granulation is carried out under normal temperature conditions to avoid the use of high temperature adhesives or chemical additives. The granulation pressure is controlled at 10-20 N, the particle diameter is controlled at 3-5 mm, and the compressive strength is >15 N.
[0015] This invention provides the use of the above-mentioned compound fertilizer for enhancing phosphorus efficiency in saline-alkali soil. Specifically, the application method is as follows: the active microalgae and biochar compound fertilizer is applied as a base fertilizer to saline-alkali soil at a rate of 1.5-4 t / hm². 2 .
[0016] The beneficial effects of this invention are: (1) This invention addresses the technical challenge of phosphorus in soil being easily fixed and having low effective utilization rate, demonstrating extremely strong phosphorus solubilization and dissolution capabilities. Its mechanism of action is as follows: the pore structure and surface functional groups of biochar are optimized through acid modification treatment, significantly improving its adsorption capacity and protective effect on microalgae; during co-culture loading, microalgae cells actively colonize the porous structure of biochar and form a biofilm on its surface, continuously secreting organic acids such as citric acid and oxalic acid, as well as extracellular polymers. These metabolites, on the one hand, reduce the fixation of phosphorus by calcium and magnesium ions in the soil through chelation, and on the other hand, convert insoluble phosphates (such as calcium phosphate and magnesium phosphate) into available phosphorus that can be directly absorbed and utilized by crop roots through acid dissolution; at the same time, the oxygen-containing functional groups such as carboxyl groups and phenolic hydroxyl groups on the surface of modified biochar can also complex with calcium and magnesium ions, further promoting the release of phosphorus. Through the synergistic effect of microalgae and biochar, insoluble phosphorus that has accumulated in the soil over a long period of time is converted into available phosphorus, which significantly improves the bioavailability of the original phosphorus in the soil, reduces the amount of chemical phosphate fertilizer applied, and effectively reduces the risk of agricultural non-point source pollution caused by phosphorus enrichment.
[0017] (2) Through the synergistic effect of scientific components, this invention can increase the content of available nitrogen and available potassium in the soil, effectively slowing down nutrient loss. At the same time, it can increase the accumulation of soil organic matter, promote the formation of soil aggregates, and improve soil aeration and permeability. In terms of pH regulation, this invention can adjust the soil to the neutral range most suitable for crop growth, improve soil physicochemical properties, and build a healthy and long-lasting soil micro-ecosystem. Attached Figure Description
[0018] Figure 1 To illustrate the effects of different treatments in Example 1 on soil phosphorus composition; Figure 2 To illustrate the effects of different treatments in Example 1 on soil pH; Figure 3 The effects of different treatments in Example 1 on rice stem diameter (a) and plant height (b); Figure 4 To illustrate the effects of different treatments in Example 1 on the root system of mature rice; Detailed Implementation
[0019] The present invention will be further described below with reference to specific embodiments. However, the scope of protection of the present invention is not limited to the scope described in the embodiments. Anyone can derive other various forms of products under the guidance of the present invention. However, regardless of any changes in their shape or composition ratio, any technical solution that is the same as or similar to that of this application falls within the protection scope of the present invention. The filamentous microalgae used in the present invention is *Monifocybe pyrenoidosa* (…). Tolypothrix tenuis ) and Microcoleopteranus ( Microcoleus vaginatusThe samples were obtained from the Freshwater Algae Culture Bank of the Chinese Academy of Sciences; other materials and devices, unless otherwise specified, are commercially available.
[0020] Example 1: (1) Microalgae culture: Filamentous microalgae were inoculated into a microalgae culture medium, wherein the cyanobacterium was *Monifocobalamins microcarpa* (…). Tolypothrix tenuis The cultivation conditions were: light intensity 3000 lux, temperature 25 ± 2 ℃, light-dark cycle 16 h : 8 h; after cultivation to the logarithmic growth stationary phase, the algal solution was collected by centrifugation, and the algal solution concentration was adjusted. The initial chlorophyll a concentration was 10 μg / mL for later use.
[0021] (2) Preparation of biochar: Corn stalks were air-dried naturally until the moisture content was <10%, and then crushed to a particle size of <2 mm. They were then placed in a tube furnace and pyrolyzed under nitrogen protection at a nitrogen flow rate of 100 mL / min. The temperature was increased to 500 °C at a rate of 10 °C / min, and pyrolyzed under constant temperature and limited oxygen for 60 min. After natural cooling, the stalks were crushed and passed through a 20-mesh sieve to obtain pyrolyzed biochar.
[0022] Acid modification: The pyrolyzed biochar was soaked in 5% citric acid for 2 hours (liquid-solid ratio 5:1 mL:g), shaken at 25℃ (150 rpm), filtered, rinsed with deionized water until neutral, and dried at 60℃ until the moisture content was <10% to obtain the modified biochar.
[0023] (3) Preparation of compound fertilizer: The modified biochar was added to BG11 medium at a mass ratio of 5%, and ultrasonically dispersed for 10 minutes. Then, it was inoculated with *Monopsidae* seed culture (initial chlorophyll a concentration of 10 μg / mL), with the ratio of *Monopsidae* seed culture to modified biochar being 20:1 (mL:g). The culture was carried out under a light intensity of 3000 lux, a temperature of 25±2℃, and a light-dark cycle of 16h:8h for 10 days. During the culture, a magnetic stirrer was used to stir for 10 minutes every 24 hours at a speed of 30 rpm to promote uniform attachment of microalgae.
[0024] (4) Drying and granulation: After cultivation, the algae and biochar are dried at 40℃ with forced air until the moisture content is 8%, producing 3-5 mm biochar granules, which are microalgae and biochar compound fertilizers.
[0025] Calculations using a fully automated specific surface area and pore size analyzer revealed the following physicochemical properties of the acid-modified biochar: pore volume 0.30~0.35 cm³. 3 / g, average pore size 7.50~8.50 nm, specific surface area (BET) 165~185 m² 2 / g. Example 2:
[0026] (1) Microalgae culture: Filamentous microalgae were inoculated into a microalgae culture medium, wherein the cyanobacteria were *Microcoleis sheathed* (a type of microalga). Microcoleus vaginatus The cultivation conditions were: light intensity 3000 lux, temperature 25 ± 2 ℃, light-dark cycle 16 h : 8 h; after cultivation to the logarithmic growth stationary phase, the algal solution was collected by centrifugation, and the algal solution concentration was adjusted. The initial chlorophyll a concentration was 10 μg / mL for later use.
[0027] (2) Preparation of biochar: Corn stalks were air-dried naturally until the moisture content was <10%, and then crushed to a particle size of <2 mm. They were then placed in a tube furnace and pyrolyzed under nitrogen protection at a nitrogen flow rate of 100 mL / min. The temperature was increased to 500 ℃ at a rate of 10 ℃ / min, and pyrolyzed under constant temperature and limited oxygen for 60 min. After natural cooling, the stalks were crushed and passed through a 20-mesh sieve to obtain pyrolyzed biochar.
[0028] The pyrolyzed biochar was soaked in 7% phosphoric acid solution for 2 hours (liquid-solid ratio 5:1 mL:g), shaken at 25℃ (150 rpm), filtered, rinsed with deionized water until neutral, and dried at 60℃ until the moisture content was <10% to obtain the modified biochar.
[0029] (3) Preparation of compound fertilizer: The modified biochar was added to BG11 medium at a mass ratio of 8%, and after ultrasonic dispersion for 10 minutes, it was inoculated with seed culture of *Micrococcus sheathingus* (initial chlorophyll a concentration of 10 μg / mL). The ratio of *Micrococcus sheathingus* seed culture to modified biochar was 20:1 (mL:g). The culture was carried out under a light intensity of 3000 lux, a temperature of 25±2℃, and a light-dark cycle of 16h:8h for 8 days. During the culture, a magnetic stirrer was used to stir for 10 minutes every 24 hours at a speed of 30 rpm to promote uniform attachment of microalgae.
[0030] (4) Drying and granulation: After cultivation, the algae and biochar are dried at 40℃ with forced air until the moisture content is 8%, producing 3-5 mm biochar granules, which are microalgae and biochar compound fertilizers.
[0031] Calculations using a fully automated specific surface area and pore size analyzer revealed the following physicochemical properties of the acid-modified biochar: pore volume 0.28–0.34 cm³. 3 / g, average pore size 5.80~6.80 nm, specific surface area (BET) 160~195m² 2 / g.
[0032] Comparative Example 1: (Modified Biochar Group): Acid-modified biochar was prepared according to step (2) of Example 1, without carrying out microalgae co-culture loading in step (3), and modified biochar particles were obtained directly according to the drying and granulation process in step (4) of Example 1.
[0033] The difference is that in step (3), microalgae liquid is not added, but replaced with an equal amount of sterile distilled water, and biochar particles are obtained by following the operation of step (4) in Example 1.
[0034] Comparative Example 2: (Blank Group) The blank group refers to the control group, which does not add any fertilizer materials and uses an equal amount of distilled water as a control.
[0035] Comparative Example 3: (Unmodified group: Ordinary biochar group) Similar to Example 1, the difference is that in step (3), the pyrolyzed biochar is used directly without modification, and unmodified biochar granules are obtained according to the drying and granulation process in step (4) of Example 1.
[0036] After calculation using a fully automated specific surface area and pore size analyzer, the pore volume is 0.25~0.29 cm³. 3 / g, average pore size 7.10~7.80 nm, specific surface area (BET) 110~135 m² 2 / g.
[0037] Analysis of specific surface area and pore size showed that the acid modification treatment in Examples 1-2 optimized the pore structure of biochar. After acid modification, the pore volume of biochar was more concentrated in 0.28-0.35 nm, and the specific surface area was increased by about 45%, which can provide more space for containment and adsorption sites, thereby significantly improving its adsorption capacity and protection effect on microalgae.
[0038] Application Example 1: The microalgae and biochar compound fertilizer prepared in this invention can be added to saline-alkali soil for rice cultivation, with an addition rate of 2 t / hm² per soil area. 2 .
[0039] The microalgae and biochar compound fertilizers prepared in Examples 1 and 2, as well as the biochar prepared in Comparative Examples 1 and 3, were selected for planting experiments on salt-tolerant rice variety Yanfeng 47. The experimental site was Zhenjiang, Jiangsu Province. Rice seedlings with uniform growth were randomly combined into 5 groups, with 12 replicates for each treatment. The seedlings were planted continuously for 160 days (until maturity). The experimental groupings and application schemes are shown in Table 1.
[0040] Table 1 Experimental Groups and Application Schemes
[0041] Table 2 shows the effects of different treatments in Application Example 1 on the root system of mature rice.
[0042] Combine Table 2 and Figures 2-4 As shown, the microalgae and biochar compound fertilizers prepared in Examples 1 and 2 were compared with modified biochar, ordinary biochar, and a blank control. The results showed that the modified biochar group, *Monopsidae* group, and *Microcoleus* group all exhibited significant differences in soil phosphorus content and rice growth performance compared to the blank control group and the ordinary biochar group. At the rice maturity stage, compared to the ordinary biochar group, the modified biochar group showed a 9.32% increase in plant height, an 8.87% increase in stem diameter, an 11.12% increase in active phosphorus, and a 5.67% increase in moderately active phosphorus, indicating that the addition of modified biochar significantly enhances soil phosphorus activation, providing more usable phosphorus for rice growth. Root growth also showed a clear difference; the total area and total volume of the modified biochar group were significantly better than those of the ordinary biochar group by 24.65% and 15.3%, respectively, indicating that the modified biochar group tends to promote fine root proliferation and increase root absorption area. During the rice ripening period, the soil pH from low to high was: Microsheath algae compound fertilizer group < Monofibrillaria < Modified biochar group < Ordinary biochar group < Blank group; indicating that the treatment group with modified biochar added has a greater advantage in reducing the pH of saline-alkali soil, decreasing by 0.67% compared with the ordinary biochar group.
[0043] In summary, this invention, through the synergistic effect of its scientifically formulated components, produces a fertilizer that increases the content of available nitrogen and potassium in the soil, effectively slowing nutrient loss. Simultaneously, it increases soil organic matter accumulation, promotes soil aggregate formation, and improves soil aeration and permeability. Regarding pH regulation, it can adjust the soil to the neutral range optimal for crop growth, improve soil physicochemical properties, and construct a healthy and long-lasting soil micro-ecosystem. The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Therefore, although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.
Claims
1. A method for preparing an active microalgae and biochar compound fertilizer for enhancing phosphorus efficiency in saline-alkali land, characterized in that, Includes the following steps: (1) Acid modification treatment of biochar: Biochar obtained from biomass pyrolysis is modified by soaking in an organic acid solution to obtain modified biochar. (2) Microalgae-biochar co-culture loading: The modified biochar obtained in step (1) is first added to BG11 medium, dispersed by ultrasonication, and then inoculated with microalgae seed liquid for co-culture, so that microalgae cells attach to and grow on the porous structure of biochar to form an active microalgae-biochar complex. (3) Drying and granulation: The microalgae-biochar composite obtained in step (2) is dried and granulated to obtain granular compound fertilizer, which is active microalgae and biochar compound fertilizer.
2. The method for preparing an active microalgae and biochar compound fertilizer for enhancing phosphorus efficiency in saline-alkali land according to claim 1, characterized in that, In step (1), the biomass includes corn stalks; the organic acid is citric acid or phosphoric acid, the mass concentration of the citric acid solution or phosphoric acid solution is 5%-8%, the soaking time is 2-3 hours, and the liquid-solid ratio is 5:1 mL / g.
3. A method for preparing an activated microalgae and biochar compound fertilizer for enhancing phosphorus efficiency in saline-alkali land according to claim 1, characterized in that, In step (1), the preparation method of the biochar is as follows: the biomass is naturally air-dried to a moisture content of <10%, and crushed to a particle size of <2 mm; placed in a tube furnace, and heated to 500℃ at a heating rate of 10℃ / min under nitrogen protection, and pyrolyzed at a constant temperature for 60 min; after natural cooling, it is crushed and sieved to obtain the biochar; the mesh size of the sieve is 20-40 mesh.
4. A method for preparing an activated microalgae and biochar compound fertilizer for enhancing phosphorus efficiency in saline-alkali land according to claim 1, characterized in that, In step (1), the physicochemical properties of the modified biochar are as follows: pore volume 0.28~0.35 cm³. 3 / g, with an average pore size of 5.8~8.5 nm and a specific surface area of 160~195 m². 2 / g.
5. The method for preparing an active microalgae and biochar compound fertilizer for enhancing phosphorus efficiency in saline-alkali land according to claim 1, characterized in that, In step (2), the filamentous microalgae are nitrogen-fixing or non-nitrogen-fixing active filamentous microalgae, including microsheath algae, common filamentous algae, and monofibrillary algae.
6. A method for preparing an activated microalgae and biochar compound fertilizer for enhancing phosphorus efficiency in saline-alkali land according to claim 1, characterized in that, In step (2), the amount of modified biochar added is 5%-10% of the mass of BG11 medium, the initial chlorophyll a concentration of microalgae seed liquid is 5-15 μg / mL, and the ultrasonic dispersion conditions are: ultrasonic frequency 40-80 kHz, dispersion for 10-15 minutes; when co-culturing, the microalgae culture conditions are: light intensity 3000 lux, temperature 25 ± 2℃, light-dark cycle 16 h : 8 h, culture for 8-10 days.
7. A method for preparing an activated microalgae and biochar compound fertilizer for enhancing phosphorus efficiency in saline-alkali land according to claim 6, characterized in that, During the cultivation process, use a magnetic stirrer to stir for 10-15 minutes at 30 rpm every 24 hours.
8. The use of the activated microalgae and biochar compound fertilizer prepared according to any one of claims 1-7 for enhancing phosphorus efficiency in saline-alkali land.
9. The use according to claim 8, characterized in that, The specific steps are as follows: Apply the activated microalgae and biochar compound fertilizer as base fertilizer to the saline-alkali soil, with an application rate of 1.5-4 t / hm². 2 .