A liquid microalgae fertilizer that can reduce cadmium content in rice.

Abstract

This invention discloses a liquid microalgae fertilizer that can reduce the cadmium content of rice. The liquid microalgae fertilizer for reducing cadmium content in rice is composed of the following components by mass percentage: 50%-75% concentrated algae solution, 5%-12% humic acid, 2%-8% potassium fulvate, 0.1%-0.5% xanthan gum, 0.1%-0.5% sodium alginate, and the remainder being water.

Description

Technical Field

[0001] This invention belongs to the field of agricultural waste resource utilization and soil remediation technology, specifically relating to a liquid microalgae fertilizer that can reduce the cadmium content of rice. Background Technology

[0002] Biogas slurry is one of the main wastes generated by the livestock and poultry farming industry, and it is also an important source of fertilizer for my country's traditional crop farming. However, with the development of large-scale modern livestock and poultry farming, the limitations of the integrated crop-livestock farming model in terms of waste disposal capacity are becoming increasingly apparent. Improper treatment and application can also lead to negative effects such as root and seedling burn and soil compaction.

[0003] The soils in southern my country are mainly red soils, generally characterized by high acidity, low organic matter content, and poor fertility. Some areas also suffer from high levels of heavy metals, leading to their accumulation in crops. A representative example is the problem of excessive cadmium levels in rice from parts of Jiangxi and Hunan provinces. The main improvement methods include applying lime to adjust pH, increasing the application of organic fertilizers to improve soil structure and buffer acidity, and planting nitrogen-fixing plants to enhance soil fertility. However, these methods all have limitations such as being unsustainable, requiring large investments, and having slow results.

[0004] Microalgae are a major source of primary productivity in the natural environment. They can not only assimilate and absorb nitrogen and phosphorus elements and adsorb and passivate heavy metals, but also construct stable biological communities through complex interactions with microorganisms, plankton, and plants and animals in their surrounding environment. Patent CN118459271A discloses a microalgae bio-fertilizer that can increase rice yield through the synergistic effect of composite microalgae, biochar, and nanomaterials. The microalgae-biochar composite system improves soil porosity and microbial abundance, while nitrogen-fixing algae fix nitrogen and promote photosynthesis. Nano-hydroxyapatite-modified biochar enhances ammonia adsorption capacity and reduces ammonia volatilization in paddy fields. However, it does not mention the effect of inhibiting heavy metal absorption by crops, only achieving increased crop yield. Patent CN112707509B discloses biochar-based microalgae particles and their preparation method for the efficient removal of heavy metals from water. The microalgae-biochar composite structure enhances adsorption capacity and stability, and a domestication strategy enhances microalgae tolerance and protein expression. The granular design facilitates recycling and reuse. This method is suitable for treating industrial, agricultural, and domestic wastewater, and also removes nitrogen and phosphorus, achieving deep water purification. However, after the material is applied, it requires periodic recycling to remove heavy metals, and cannot achieve long-term in-situ adsorption and passivation. Therefore, developing a low-cost liquid microalgae fertilizer that can link biogas slurry resource utilization with the need for cadmium reduction in farmland and achieve long-term in-situ remediation is of great significance. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of the prior art and provide a liquid microalgae fertilizer that can reduce the cadmium content of rice.

[0006] To achieve the above objectives, the technical solution provided by this invention is as follows: The liquid microalgae fertilizer that can reduce cadmium content in rice is composed of the following components by mass percentage: 50%-75% concentrated algae solution, 5%-12% humic acid, 2%-8% potassium fulvate, 0.1%-0.5% xanthan gum, 0.1%-0.5% sodium alginate, and the remainder is water.

[0007] Preferably, the algae species in the concentrated algal solution are benthic diatoms.

[0008] Preferably, the concentration of live algae cells in the concentrated algae solution is ≥5×10⁻⁶. 6 cells / mL.

[0009] Preferably, the concentrated algal solution is prepared according to the following steps: (1) Inoculate benthic diatoms into BG11 medium supplemented with Na2SiO4, and activate and proliferate them for 3-5 days at 20-25℃, 2000-4000 lx, and a light-dark ratio of 12:12 to obtain microalgae seed liquid; the concentration of Na2SiO4 in BG11 medium is 50-100 mg / L; (2) After aeration and sedimentation treatment of biogas slurry from livestock and poultry farming, dilute it, add supplementary nitrogen source, supplementary phosphorus source and supplementary silicon source, adjust the mass ratio of nitrogen source and phosphorus source to 5:1 to 15:1, adjust the pH of the culture medium to 7.0-8.0, and obtain microalgae culture medium; the concentration of the supplementary silicon source in the microalgae culture medium is 50-100 mg / L. (3) Inoculate the microalgae seed solution obtained in step (1) into the microalgae culture medium prepared in step (2) at an inoculation rate of 10-20%. In a tray-type simple photobioreactor, under natural temperature and light conditions, introduce 1% CO2 at an aeration rate of 0.5-1.0 vvm during the light period and culture for 3-5 days to obtain an algal cell density ≥5×10⁻⁶. 6 Algal solution with cells / mL; (4) Adjust the pH of the algal solution obtained in step (3) to 8.5-9.0, let it stand in the dark for 2-12 hours (to promote the secretion of EPS), pour the algal solution into a cylindrical bucket, let it settle naturally through self-flocculation, remove the supernatant to obtain concentrated algal solution.

[0010] Preferably, the dilution of the biogas slurry from livestock and poultry farming after aeration and sedimentation in step (2) is 10-30%, more preferably 20%.

[0011] Preferably, the supplementary nitrogen source in step (2) is NaNO3, the supplementary phosphorus source is a phosphate mixture of Na2HPO4 and KH2PO4 in a mass ratio of 1:1, and the supplementary silicon source is Na2SiO4.

[0012] Preferably, the liquid microalgae fertilizer is applied by spraying it onto the paddy field at a rate of 100-200 kg / ha after the rice seedlings are planted, and then applying top dressing at the same rate 3-5 days after each application of herbicide to the paddy field.

[0013] The present invention will be further described below: This invention uses pretreated livestock and poultry biogas slurry as a microalgae culture medium, and then concentrates it using its self-flocculation properties to formulate a liquid bio-fertilizer. This effectively links the resource utilization of biogas slurry with agricultural planting needs, providing a new technical route to solve the spatiotemporal asynchrony between biogas slurry discharge and crop fertilizer demand. This invention provides a method for cultivating benthic diatoms using pretreated livestock and poultry biogas slurry. Nitzschia (sp.), and through self-flocculation and concentration, compounded liquid microalgae fertilizer is applied to cadmium-contaminated paddy fields. Through biological interactions between rice and its root microbial community, and the adsorption capacity of organisms and their extracellular secretions, it passivates cadmium in the soil, reduces the cadmium content in rice, and promotes increased yield.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The liquid microalgae bio-fertilizer prepared in this invention, when applied to paddy fields, passivates cadmium in the soil and reduces the cadmium content in the rice through biological interactions with the rice and its root microbial community, and the adsorption capacity of the organisms and their extracellular secretions. The benthic diatom cultivation method, based on pretreated biogas slurry, realizes the resource utilization of biogas slurry.

[0015] 2. This invention utilizes a low-cost concentration method for the large-scale cultivation of benthic diatoms and self-flocculation sedimentation of biogas slurry from livestock and poultry farming to prepare liquid microalgae fertilizer. Compared with biogas slurry fertilizer, it reduces storage and transportation costs, improves ease of use and application effect, and effectively solves the problems of biogas slurry resource utilization and the spatial and temporal mobility of agricultural planting. Attached Figure Description

[0016] Figure 1 This is a picture of a simple tray-type photobioreactor. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. Example 1

[0018] The liquid microalgae fertilizer that can reduce cadmium content in rice is composed of the following components by mass percentage: The solution contains 50% concentrated algae extract, 5% humic acid, 5% potassium humate, 0.5% xanthan gum, 0.5% sodium alginate, and the remainder is water.

[0019] The concentrated algal solution is prepared according to the following steps: (1) Take a small amount of the microalgae culture preserved on the slant and inoculate it into BG11 medium. Add Na2SiO4 as a supplementary silicon source. The concentration of Na2SiO4 in BG11 medium is 50 mg / L. Culture for 5 days at 25℃, 2000 lx, light-dark ratio = 12:12 to obtain microalgae seed liquid. (2) The aeration and sedimentation biogas slurry taken from a pig farm was diluted with tap water to a concentration of 20%, and seed liquid was inoculated at a ratio of 20%. NaNO3 was used as a supplementary nitrogen source, and a mixed phosphate of Na2HPO4:KH2PO4=1:1 was used as a supplementary phosphorus source. The N / P ratio was adjusted to 5:1, and Na2SiO4 was added as a supplementary silicon source. The pH of the culture medium was adjusted to 7.5 to obtain microalgae culture medium. The concentration of the supplementary silicon source in the culture medium was 100 mg / L. (3) Dispense the inoculated culture medium into a tray-type simple photobioreactor ( Figure 1 The cells were cultured at a ventilation rate of 1.0 vvm during the light period with 1% CO2, and cultured for 5 days under ambient temperature and light conditions to obtain a cell density ≥5×10⁻⁶. 6 Algal solution with cells / mL; (4) Collect the obtained algal solution into a cylindrical plastic bucket, adjust the pH of the algal solution to 8.5-9.0, let it stand in the dark for 2-12 hours to promote the secretion of EPS, pour the algal solution into the cylindrical bucket, let it settle naturally through self-flocculation, remove the supernatant to obtain concentrated algal solution. (5) Dissolve humic acid, potassium humate, xanthan gum and sodium alginate in water to prepare a high-concentration mother liquor. Then add it to the concentrated algae liquid so that the volume ratio of the concentrated algae liquid is 50%. The concentrations of other substances are 5% for humic acid, 5% for potassium humate, 0.5% for xanthan gum and 0.5% for sodium alginate. Mix them using a low-shear mixing device and then fill and store them to obtain the liquid microalgae fertilizer product.

[0020] The method of using liquid microalgae fertilizer is as follows: After the rice seedlings are planted in the paddy field, they are sprayed on the paddy field using a drone at a rate of 100 kg / ha. During the planting process, topdressing is applied 5 days after each application of herbicide to the paddy field at the same rate. Example 2

[0021] The liquid microalgae fertilizer that can reduce cadmium content in rice is composed of the following components by mass percentage: The solution contains 75% concentrated algae extract, 5% humic acid, 5% potassium humate, 0.5% xanthan gum, 0.5% sodium alginate, and the remainder is water.

[0022] The concentrated algal solution is prepared according to the following steps: (1) Take a small amount of the microalgae culture preserved on the slant and inoculate it into BG11 medium. Add Na2SiO4 as a supplementary silicon source. The concentration of Na2SiO4 in BG11 medium is 50 mg / L. Culture for 5 days at 25℃, 2000 lx, light-dark ratio = 12:12 to obtain microalgae seed liquid. (2) The aeration and sedimentation biogas slurry taken from a pig farm was diluted with tap water to a concentration of 20%, and seed liquid was inoculated at a ratio of 20%. NaNO3 was used as a supplementary nitrogen source, and a mixed phosphate of Na2HPO4:KH2PO4=1:1 was used as a supplementary phosphorus source. The N / P ratio was adjusted to 10:1, and Na2SiO4 was added as a supplementary silicon source. The pH of the culture medium was adjusted to 7.5 to obtain microalgae culture medium. The concentration of the supplementary silicon source in the culture medium was 100 mg / L. (3) Dispense the inoculated culture medium into a tray-type simple photobioreactor ( Figure 1 The cells were cultured at a ventilation rate of 1.0 vvm during the light period with 1% CO2, and cultured for 5 days under ambient temperature and light conditions to obtain a cell density ≥5×10⁻⁶. 6 Algal solution with cells / mL; (4) Collect the obtained algal solution into a cylindrical plastic bucket, adjust the pH of the algal solution to 8.5-9.0, let it stand in the dark for 2-12 hours to promote the secretion of EPS, pour the algal solution into the cylindrical bucket, let it settle naturally through self-flocculation, remove the supernatant to obtain concentrated algal solution. (5) Dissolve humic acid, potassium fulvate, xanthan gum and sodium alginate in water to prepare a high-concentration mother liquor. Then add it to the concentrated algae liquid so that the volume ratio of the concentrated algae liquid is 75%. The concentrations of other substances are 5% for humic acid, 5% for potassium fulvate, 0.5% for xanthan gum and 0.5% for sodium alginate. Mix them using a low-shear mixing device and then fill and store them to obtain the liquid microalgae fertilizer product.

[0023] The method of using liquid microalgae fertilizer is as follows: After rice seedlings are planted in paddy fields, they are sprayed on the paddy fields using drones at a rate of 150 kg / ha. During the planting process, topdressing is applied 5 days after each application of herbicide to the paddy fields at the same rate. Example 3

[0024] The liquid microalgae fertilizer that can reduce cadmium content in rice is composed of the following components by mass percentage: The solution contains 50% concentrated algae extract, 5% humic acid, 5% potassium humate, 0.5% xanthan gum, 0.5% sodium alginate, and the remainder is water.

[0025] The concentrated algal solution is prepared according to the following steps: (1) Take a small amount of the microalgae culture preserved on the slant and inoculate it into BG11 medium. Add Na2SiO4 as a supplementary silicon source. The concentration of Na2SiO4 in BG11 medium is 100 mg / L. Culture for 5 days at 25℃, 2000 lx, light-dark ratio = 12:12 to obtain microalgae seed liquid. (2) The aeration and sedimentation biogas slurry taken from a pig farm was diluted with tap water to a concentration of 20%, and seed liquid was inoculated at a ratio of 20%. NaNO3 was used as a supplementary nitrogen source, and a mixed phosphate of Na2HPO4:KH2PO4=1:1 was used as a supplementary phosphorus source. The N / P ratio was adjusted to 15:1, and Na2SiO4 was added as a supplementary silicon source. The pH of the culture medium was adjusted to 7.5 to obtain microalgae culture medium. The concentration of the supplementary silicon source in the culture medium was 100 mg / L. (3) Dispense the inoculated culture medium into a tray-type simple photobioreactor ( Figure 1 The cells were cultured at a ventilation rate of 1.0 vvm during the light period with 1% CO2, and cultured for 5 days under ambient temperature and light conditions to obtain a cell density ≥5×10⁻⁶. 6 Algal solution with cells / mL; (4) Collect the obtained algal solution into a cylindrical plastic bucket, adjust the pH of the algal solution to 8.5-9.0, let it stand in the dark for 2-12 hours to promote the secretion of EPS, pour the algal solution into the cylindrical bucket, let it settle naturally through self-flocculation, remove the supernatant to obtain concentrated algal solution. (5) Dissolve humic acid, potassium fulvate, xanthan gum and sodium alginate in water to prepare a high-concentration mother liquor. Then add it to the concentrated algae liquid so that the volume ratio of the concentrated algae liquid is 50%. The concentrations of other substances are 5% for humic acid, 5% for potassium fulvate, 0.5% for xanthan gum and 0.5% for sodium alginate. Mix them using a low-shear mixing device and then fill and store them to obtain the liquid microalgae fertilizer product.

[0026] The method of using liquid microalgae fertilizer is as follows: After the rice seedlings are planted in the paddy field, they are sprayed with herbicide at a rate of 200 kg / ha using a drone. During the planting process, topdressing is applied 5 days after each application of herbicide to the paddy field, at the same rate. Example 4

[0027] The liquid microalgae fertilizer that can reduce cadmium content in rice is composed of the following components by mass percentage: The solution contains 75% concentrated algae extract, 5% humic acid, 5% potassium humate, 0.5% xanthan gum, 0.5% sodium alginate, and the remainder is water.

[0028] A method for preparing a low-calcium liquid microalgae fertilizer that can reduce the cadmium content of rice includes the following steps: The concentrated algal solution is prepared according to the following steps: (1) Take a small amount of the microalgae culture preserved on the slant and inoculate it into BG11 medium. Add Na2SiO4 as a supplementary silicon source. The concentration of Na2SiO4 in BG11 medium is 50 mg / L. Culture for 5 days at 25℃, 2000 lx, light-dark ratio = 12:12 to obtain microalgae seed liquid. (2) The aeration and sedimentation biogas slurry taken from a pig farm was diluted with tap water to a concentration of 20%, and seed liquid was inoculated at a ratio of 20%. NaNO3 was used as a supplementary nitrogen source, and a mixed phosphate of Na2HPO4:KH2PO4=1:1 was used as a supplementary phosphorus source. The N / P ratio was adjusted to 15:1, and Na2SiO4 was added as a supplementary silicon source. The pH of the culture medium was adjusted to 7.5 to obtain microalgae culture medium. The concentration of the supplementary silicon source in the culture medium was 50 mg / L. (3) Dispense the inoculated culture medium into a tray-type simple photobioreactor ( Figure 1 The cells were cultured at a ventilation rate of 1.0 vvm during the light period with 1% CO2, and cultured for 5 days under ambient temperature and light conditions to obtain a cell density ≥5×10⁻⁶. 6 Algal solution with cells / mL; (4) Collect the obtained algal solution into a cylindrical plastic bucket, adjust the pH of the algal solution to 8.5-9.0, let it stand in the dark for 2-12 hours to promote the secretion of EPS, pour the algal solution into the cylindrical bucket, let it settle naturally through self-flocculation, remove the supernatant to obtain concentrated algal solution. (5) Dissolve humic acid, potassium fulvate, xanthan gum and sodium alginate in water to prepare a high-concentration mother liquor. Then add it to the concentrated algae liquid so that the volume ratio of the concentrated algae liquid is 75%. The concentrations of other substances are 5% for humic acid, 5% for potassium fulvate, 0.5% for xanthan gum and 0.5% for sodium alginate. Mix them using a low-shear mixing device and then fill and store them to obtain the liquid microalgae fertilizer product.

[0029] The method of using liquid microalgae fertilizer is as follows: After rice seedlings are planted in paddy fields, they are sprayed on the paddy fields using drones at a rate of 150 kg / ha. During the planting process, topdressing is applied 5 days after each application of herbicide to the paddy fields at the same rate.

[0030] Comparative Example 1

[0031] This is the pretreated aquaculture slurry culture medium used in Examples 1-3. The application method is the same as in Example 3. The liquid fertilizers obtained in Examples 1-3 and Comparative Example 1 were applied evenly according to the application method described therein. If the application rate was less than 200 kg / ha, it was supplemented with water to 200 kg / ha. A blank group was set up with an equal amount of water (ck). The rice variety used in the test was Huixiang Youyujing.

[0032] The experimental rice paddies are located in the rice experimental fields of Changsha City, Hunan Province. Each field has been fertilized with 96 kg / ha of nitrogen fertilizer (urea), 96 kg / ha of phosphorus fertilizer (superphosphate), and 192 kg / ha of potassium fertilizer (potassium chloride). Nitrogen fertilizer was applied at the tillering stage of rice and 48 kg / ha of nitrogen fertilizer was applied after the panicles formed.

[0033] The effective tiller number, grains per panicle, thousand-grain weight, yield per mu, and cadmium content of rice grains in Examples 1-3 and Comparative Example 1 were tested (average values ​​were taken), and the results are shown in Table 1.

[0034] Table 1

[0035] As can be seen from Table 1, the yield of rice per mu in Example 1 was higher than that in other groups, and the cadmium content was also significantly reduced. This indicates that the microalgae bio-fertilizer prepared by the present invention can effectively increase rice yield while inhibiting the accumulation of cadmium in rice.

[0036] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A liquid microalgae fertilizer that can reduce cadmium content in rice, characterized in that, The liquid microalgae fertilizer that can reduce cadmium content in rice is composed of the following components by mass percentage: 50%-75% concentrated algae solution, 5%-12% humic acid, 2%-8% potassium fulvate, 0.1%-0.5% xanthan gum, 0.1%-0.5% sodium alginate, and the remainder is water.

2. The liquid microalgae fertilizer for reducing cadmium content in rice as described in claim 1, characterized in that, The algae species in the concentrated algal solution are benthic diatoms.

3. The liquid microalgae fertilizer for reducing cadmium content in rice as described in claim 1, characterized in that, The concentrated algal solution contains ≥5×10⁻⁵ live algal cells. 6 cells / mL.

4. The liquid microalgae fertilizer for reducing cadmium content in rice as described in any one of claims 1 to 3, characterized in that, The concentrated algal solution is prepared according to the following steps: (1) Inoculate benthic diatoms into BG11 medium supplemented with Na2SiO4, and activate and proliferate them for 3-5 days at 20-25℃, 2000-4000 lx, and a light-dark ratio of 12:12 to obtain microalgae seed liquid; the concentration of Na2SiO4 in BG11 medium is 50-100 mg / L; (2) After aeration and sedimentation treatment of biogas slurry from livestock and poultry farming, dilute it, add supplementary nitrogen source, supplementary phosphorus source and supplementary silicon source, adjust the mass ratio of nitrogen source and phosphorus source to 5:1 to 15:1, adjust the pH of the culture medium to 7.0-8.0, and obtain microalgae culture medium; the concentration of the supplementary silicon source in the microalgae culture medium is 50-100 mg / L. (3) Inoculate the microalgae seed solution obtained in step (1) into the microalgae culture medium prepared in step (2) at an inoculation rate of 10-20%. In a tray-type simple photobioreactor, under natural temperature and light conditions, introduce 1% CO2 at an aeration rate of 0.5-1.0 vvm during the light period and culture for 3-5 days to obtain an algal cell density ≥5×10⁻⁶. 6 Algal solution with cells / mL; (4) Adjust the pH of the algal solution obtained in step (3) to 8.5-9.0, let it stand in the dark for 2-12 hours, and obtain concentrated algal solution by natural sedimentation through self-flocculation and removal of the supernatant.

5. The liquid microalgae fertilizer for reducing cadmium content in rice as described in claim 4, characterized in that, The dilution of the biogas slurry from livestock and poultry farming after aeration and sedimentation in step (2) is 10-30%.

6. The liquid microalgae fertilizer for reducing cadmium content in rice as described in claim 5, characterized in that, The dilution of the biogas slurry from livestock and poultry farming after aeration and sedimentation in step (2) is 20%.

7. The liquid microalgae fertilizer for reducing cadmium content in rice as described in claim 4, characterized in that, The supplementary nitrogen source in step (2) is NaNO3, the supplementary phosphorus source is a phosphate mixture of Na2HPO4 and KH2PO4 in a mass ratio of 1:1, and the supplementary silicon source is Na2SiO4.

8. The liquid microalgae fertilizer for reducing cadmium content in rice as described in claim 4, characterized in that, The method of applying the liquid microalgae fertilizer is as follows: after rice seedlings are planted in the paddy field, the liquid microalgae fertilizer is sprayed onto the paddy field at a dosage of 100-200 kg / ha, and topdressing is carried out 3-5 days after each application of herbicide to the paddy field at the same dosage.

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