Streptomyces flagstone HC-2-20, compound fertilizer and application of streptomyces flagstone HC-2-20

Abstract

The invention discloses streptomyces flagstone HC-2-20, a compound fertilizer and application of the streptomyces flagstone HC-2-20. The streptomyces flagstone HC-2-20 is preserved in the China General Microbiological Culture Collection Center (CGMCC), the preservation number is CGMCC No.36145, the preservation time is October 11, 2025, and the preservation address is Institute of Microbiology, Chinese Academy of Sciences, No.3, No.1 Yard, West Beichen Road, Chaoyang District, Beijing. By compounding the streptomyces flagstone HC-2-20 and the organic material, the efficient improvement of the saline-alkali soil is realized, the growth of crops is promoted, and a new technical approach is provided for the sustainable utilization of the saline-alkali soil.

Description

Technical Field

[0001] This invention belongs to the field of microbial technology, specifically relating to a Streptomyces slateii HC-2-20, compound fertilizer, and their applications. Background Technology

[0002] Global salinization is worsening, becoming a key challenge affecting food security, ecological stability, and sustainable land use. Current research focuses primarily on plant responses to salt stress, salt tolerance mechanisms, and remediation technologies targeting soil physicochemical properties.

[0003] Saline-alkali land remediation technologies are showing a diversified development trend, employing various methods including physical, chemical, and biological approaches. Physical remediation regulates water and salt dynamics by optimizing soil physical structure, primarily focusing on improving the topsoil configuration to reduce the ratio of evaporation to precipitation. Examples include drainage and irrigation, deep plowing to reconstruct the topsoil through mechanical disturbance, and using mulch to retain soil moisture. Physical control measures have clear mechanisms and operational feasibility, but their effectiveness is often limited by soil texture and local meteorological conditions. Chemical remediation often uses amendments such as gypsum, phosphogypsum, and acid salts to adjust soil pH. While effective quickly, it easily leads to secondary soil salinization, and long-term use may negatively impact soil microbial communities. Moreover, some chemical amendments are associated with heavy metal pollution, and long-term application may lead to environmental degradation. Bioremediation utilizes salt-tolerant plants, microorganisms, or biochar to reduce soil salinity through biotransformation and absorption, offering advantages in environmental friendliness and sustainability. However, its remediation cycle is relatively long, and its adaptability to extreme saline-alkali environments still needs further improvement.

[0004] Therefore, there is a need to develop an efficient, economical, and environmentally friendly solution for improving saline-alkali soil, in order to address the problems of limited effectiveness, high cost, or significant ecological risks associated with existing remediation methods.

[0005] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a *Streptomyces slate* HC-2-20, compound fertilizer, and their applications, which solves the problems of existing methods being limited by soil texture, and chemical methods easily causing secondary salinization and ecological risks. By combining *Streptomyces slate* HC-2-20 with organic materials, this invention achieves efficient improvement of saline-alkali soil, while promoting crop growth, and provides a new technical approach for the sustainable use of saline-alkali land.

[0007] To achieve the above objectives, the present invention provides a *Streptomyces slate* ( Streptomyces ardesiacus HC-2-20, this Streptomyces slateis HC-2-20 has been deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 36145, deposited on October 11, 2025, at Institute of Microbiology, Chinese Academy of Sciences, No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing.

[0008] A second objective of the present invention is to provide a compound fertilizer containing the aforementioned Streptomyces slate HC-2-20, the compound fertilizer comprising the following components by mass fraction: 30% cow manure and / or sheep manure, 20% soybean straw, 37-38% potato straw and 12-13% rapeseed straw, wherein the compound fertilizer contains a bacterial solution of the aforementioned Streptomyces slate HC-2-20.

[0009] Preferably, the compound fertilizer contains the following components by mass fraction: 30% cow and sheep manure, 20% soybean straw, 37-38% potato straw and 12-13% rapeseed straw, and the compound fertilizer contains the bacterial solution of Streptomyces slate HC-2-20.

[0010] More preferably, the mass ratio of cow dung to sheep dung is 1:1.

[0011] More preferably, the cow dung, sheep dung, soybean straw, potato straw, and rapeseed straw must all be composted.

[0012] More preferably, the composting process includes: air-drying and crushing the material to be composted, adding EM bacteria, and composting it at high temperature for more than 120 days to kill pathogens and insect eggs; after composting for 3 to 7 days, the temperature is rapidly raised to 60 to 70°C and maintained for 1 to 2 weeks; when the temperature begins to drop, the pile is turned over; when the temperature no longer rises rapidly, the material is loose and dark brown, with no odor, at which point the composting is complete, and the composted material is piled up and aged for 1 to 2 months.

[0013] A third objective of this invention is to provide the application of the aforementioned Streptomyces slate HC-2-20, or the aforementioned compound fertilizer, in promoting crop growth in saline-alkali soils.

[0014] Preferably, the soil pH is lowered.

[0015] Preferably, the crops include: tomatoes and soybeans.

[0016] More preferably, the plant height, spread, stem diameter, germination rate, and root length of the tomato plant are increased by one or more.

[0017] More preferably, the bacterial culture of *Streptomyces slate* HC-2-20 is OD. 600 It is obtained by diluting 0.5 by 10 to 1000 times.

[0018] More preferably, the fresh weight of 100 soybeans and / or the yield per plant are increased.

[0019] More preferably, the height, diameter, and number of effective branches of the soybean plant are increased by one or more.

[0020] More preferably, the number of seeds per soybean pod is increased, or / and the length, width, and thickness of one, two, and three pods of the soybean are increased by one or more.

[0021] The present invention relates to *Streptomyces slateii* HC-2-20, compound fertilizer, and their applications, which solves the problems of existing methods being limited by soil texture, and chemical methods easily causing secondary salinization and ecological risks. It has the following advantages: (1) This invention utilizes the characteristic that organic fertilizer can moderately reduce soil alkalinity. On this basis, rapeseed straw rich in sulfur compounds is added. Cow and sheep manure and soybean straw decompose quickly, providing readily available nutrients required from the seedling stage to the flowering stage. Potato and rapeseed straw decompose slowly, continuously releasing carbon sources and nutrients to support the high nutritional needs during the grain-filling stage. Streptomyces slate HC-2-20 accelerates the conversion of organic matter and improves the nutrient release efficiency, so that the nutrient supply matches the fertilizer requirements of most crops, which are "stable in the early stage, sufficient in the middle stage, and extended in the later stage". While ensuring the recycling of agricultural waste, it achieves zero fertilizer input throughout the entire growth cycle of crops, demonstrating the goal of green and sustainable cultivation.

[0022] (2) This invention utilizes the synergistic effect of Streptomyces slate HC-2-20 and a specific ratio of organic materials to not only effectively reduce the pH value of saline-alkali soil and improve its physical and chemical properties, but also significantly promote crop growth. For tomatoes, it can improve growth indicators such as plant height, spread, stem diameter, germination rate, and root length; for soybeans, it can increase the fresh weight of 100 seeds and the yield per plant, while also improving economic traits such as plant height, diameter, number of effective branches, number of seeds per pod, and the length, width, and thickness of the pods, providing an efficient and environmentally friendly solution for agricultural production in saline-alkali land. Attached Figure Description

[0023] Figure 1 This is the phylogenetic tree of Streptomyces slate HC-2-20 of the present invention.

[0024] Figure 2 This invention demonstrates how Streptomyces slateii HC-2-20 promotes tomato seed germination.

[0025] Figure 3 This invention demonstrates how Streptomyces slateii HC-2-20 promotes the growth of tomato seedlings. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] It should be noted that: Unless otherwise specified in the examples, conditions should be followed according to standard conditions or the manufacturer's recommendations. Instruments whose manufacturers are not specified are all commercially available products. Raw materials and reagents whose manufacturers are not specified are all commercially available goods or can be prepared using known methods.

[0028] In this invention, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are used only for simplicity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0029] The features mentioned in this invention can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification, provided that there is no contradiction in the combination of these features. Each feature disclosed in the specification can be replaced by any alternative feature that provides the same, equivalent, or similar purpose. Therefore, unless otherwise specified, the disclosed features are merely general examples of equivalent or similar features.

[0030] In the description of this invention, it should be noted that the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0031] Some of the materials used in the following embodiments are as follows: 1. Tomato variety: Zhongshu No. 4 (Qingxian Chunfeng Seed Industry Co., Ltd.); Soybean variety: Kaikeyuan No. 5; 2. Culture media: nitrogen-fixing medium, phosphorus-solubilizing (organic phosphorus, inorganic phosphorus) medium, carbon-fixing medium, LB medium.

[0032] Table 1. Culture medium composition table 3. The cow and sheep manure and straw used in the following examples must be fully decomposed, specifically as follows: Both cow and sheep manure and straw are harvested from the field, naturally air-dried, crushed, and then inoculated with EM (Effective Microorganisms) bacteria. They are then composted at high temperatures for over 120 days to kill pathogens and insect eggs. After composting, the temperature rapidly rises to 60-70℃ within 3-7 days and is maintained for 1-2 weeks. When the temperature begins to drop, the pile is turned (outer layers to the inside, and inside layers to the outside), three times, with each turn spaced three weeks apart. When the temperature no longer rises rapidly, the material becomes loose, dark brown, and odorless; at this point, composting is complete. The composted material is then piled up and aged for 1-2 months before use.

[0033] The mass ratio of cow dung to sheep dung is approximately 1:1, and their carbon-to-nitrogen ratios are similar.

[0034] Example 1: Isolation, Screening and Identification of Growth-Promoting Bacteria Soil samples were collected from different farmlands in Qinghai Province. Healthy, vigorous crops were selected for rhizosphere sampling. Wearing disposable gloves, the top 5 cm of soil was removed using a sterile shovel. Rhizosphere soil was collected using a small shovel and placed into sterile centrifuge tubes. The sampling time and location were clearly marked, and the samples were transported to the laboratory at low temperature and stored at -20°C for later use.

[0035] Take 10 g of soil sample and add 90 mL of sterile water. Incubate on a shaker for 2 h, then allow to stand for 30 min to allow the resulting soil suspension to separate into layers. Dilute the suspension to 1 × 10⁻⁶ with sterile water using a serial dilution method. -5 100 μL of soil suspension from each gradient was taken and sequentially added to functional (organic phosphorus, inorganic phosphorus, nitrogen fixation, carbon fixation) plates. The plates were then spread evenly with a sterile spreader until dry. Each treatment was repeated in triplicate. The plates were then inverted and incubated at 24°C for 7 days.

[0036] Observe the colony growth and screen out functional bacteria based on whether they grow and whether they have a clear zone. Pick up the screened single colonies and streak them onto solid LB medium. Based on the growth characteristics of the colonies, remove duplicate strains to obtain strain numbered HC-2-20.

[0037] Single colonies of strain HC-2-20 were inoculated into liquid LB medium and cultured at 28°C and 150 r / min for 3 days. Two μL of the culture was then inoculated onto a multifunctional (organic phosphorus, inorganic phosphorus, nitrogen fixation, carbon fixation) medium. The inoculated plates were then inverted and incubated at 28°C for 15 days. The diameters D (total diameter of colony + clear zone) and d (colony diameter) were measured, and the standardized ratio was calculated.

[0038] Table 1. Functional strength of growth-promoting bacteria Note: Carbon fixation and nitrogen fixation do not have a clear zone. D is the colony diameter. Being able to grow on the corresponding culture medium indicates that it has this ability. The larger the colony, the stronger the ability.

[0039] The results are shown in Table 1. The D / d value of strain HC-2-20 was 1.60 on inorganic phosphorus medium, 8.00 mm on nitrogen-fixing medium, and 4.27 mm on carbon-fixing medium. However, no clear zone was observed around the strain on organic phosphorus medium, indicating that it does not possess the ability to solubilize organic phosphorus. In summary, the HC-2-20 strain of this invention possesses combined growth-promoting characteristics of inorganic phosphorus solubilization, nitrogen fixation, and carbon fixation, laying the foundation for further research into its application potential in agricultural production.

[0040] Morphological observation, physiological and biochemical characterization, and 16S rRNA gene sequence analysis were performed on the above-mentioned HC-2-20 strain, and a phylogenetic tree was constructed (see [link to phylogenetic tree]). Figure 1 Analyzing its phylogenetic position, the strain was ultimately identified as *Streptomyces slate*. Streptomyces ardesiacus The HC-2-20 strain has been deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 36145, on October 11, 2025. The deposit address is Institute of Microbiology, Chinese Academy of Sciences, No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing.

[0041] Example 2: Study on the growth-promoting effect of strain HC-2-20 on tomatoes 1. Seed germination Select plump tomato seeds of uniform size, disinfect them by soaking them in a 1% sodium hypochlorite solution, rinse them with sterile water until there is no odor, and then soak them in warm water.

[0042] The tested bacterial strain (HC-2-20) was cultured at 28℃ for 2 days, centrifuged at 8000 r / min for 10 min, and the precipitate was collected. The bacterial culture was prepared using sterile water to an OD value of [missing value]. 600 The concentration is 0.5, then diluted with sterile water 10, 100, and 1000 times.

[0043] Sterilized filter paper was placed in a sterile petri dish. Ten plump, swollen tomato seeds were randomly placed on the filter paper, and 1.5 mL of bacterial solution with a pH of 8.0 was added. Each group had three replicates. The control group (CK) received sterile water with a pH adjusted to 8.0 (using sodium hydroxide). The treated seeds were placed in a light incubator. Germination rate was calculated after 4 days, and root length was measured after 8 days. Results are shown below. Figure 2 And Table 2.

[0044] 2. Pot experiment After germination, tomato seedlings were transplanted into plastic pots and allowed to acclimate for one week in a light-controlled incubator, followed by another week in a greenhouse. When the seedlings reached the four-leaf stage, they were sprayed with a bacterial solution (treatment similar to that used for seed germination). Simultaneously, sterile water at pH 8.0 was used as a control. 20 mL of the solution was sprayed on the leaves and 30 mL was applied to the roots per plant. After 15 days, plant height, stem diameter, and stem spread were measured. Results are shown in [link to relevant documentation]. Figure 3 And Table 2.

[0045] Table 2. Growth-promoting effects of strain HC-2-20 on tomatoes. The results are shown in Table 2. Compared with the control group, the plant height, spread, stem diameter, germination rate, and root length of tomatoes were significantly improved under each concentration of bacterial solution treatment. Specifically, the plant height treated with a 100-fold dilution of bacterial solution reached 25.00 cm, significantly higher than the 7.33 cm in the control group. The spread was highest in the 100-fold dilution treatment at 29.50 cm, an increase of 110.71% compared to the 14.00 cm in the control group. Regarding stem diameter, the 4.77 cm in the 100-fold dilution treatment was significantly better than other treatments and the control group. The germination rate reached 46.70% in the 1000-fold dilution treatment and 46.67% in the 100-fold dilution treatment, both significantly higher than the 23.30% in the control group. The root length was highest in the 1000-fold dilution treatment at 97.92 cm, an increase of 35.59% compared to the 72.22 cm in the control group. In summary, the 100-fold and 1000-fold dilutions of the bacterial solution showed outstanding performance in promoting different indicators of tomato growth, indicating that the HC-2-20 strain has a significant growth-promoting effect on tomatoes and exhibits a good dose-response effect within a certain concentration range.

[0046] Example 3: Study on the effects of straw monoculture on soybean pot cultivation in saline-alkali soil 1. The influence of straw univariate combination The effect of straw-based monoculture was studied using a pot experiment on soybeans. The soybean variety used was Kaikeyuan No. 5, and plump, disease-free seeds were selected. The potting mix consisted of 40% fertilizer and 60% saline-alkali soil. Soil samples (0-20cm topsoil) were collected from Heerjia Village, Hexi Town, Guide County, Hainan Prefecture, Qinghai Province. Impurities were removed by sieving through a 2 mm sieve, and the initial pH was determined to be 8.47. Specific fertilizer combinations are shown in Table 3. The bacterial strain used was a 100-fold dilution from Example 2.

[0047] Table 3. Component ratio of straw univariate combination The specific experimental procedure is as follows: Mix the sifted and impurity-free soil and fertilizer evenly at a mass ratio of 6:4 and set aside. Select plastic pots with a diameter of 20cm and a height of 25cm, and fill each pot with 5kg of dry mixed substrate. Disinfect the seeds by soaking them in 1% sodium hypochlorite solution for 10 minutes, rinse them three times with distilled water, and germinate them in a constant temperature incubator at 25℃ for 24 hours. Sow 3-5 seeds with white sprouts in each pot, cover with 2-3cm of soil, and water thoroughly with distilled water. Seedlings will emerge 5-7 days after sowing. Thin the seedlings to leave 2 strong seedlings per pot. Control the greenhouse temperature at 25-30℃ during the day and 15-20℃ at night, with natural light (more than 12 hours per day). Maintain the substrate moisture content at 60%-80% during the seedling stage, increase it to 70%-80% during the flowering stage, and reduce it to 50%-60% during the grain-filling stage.

[0048] Determination of 100-seed fresh weight and yield per plant: During the R6-R6.5 stage after the pod-filling stage, the 100-seed fresh weight and yield of fresh pods per plant were measured for different treatments. After harvesting the fresh pods, substrate samples from 0 to 20 cm depth were collected, and the pH was measured. The results are shown in Table 4.

[0049] Table 4. Results of the effects of straw-based single-element fertilizer on soybean pot plants The results are shown in Table 4. After adding HC-2-20 strain, all combinations significantly reduced pH and increased 100-seed fresh weight and single-plant yield compared with CK-1. After adding rapeseed straw, the yield was lower than that of other combinations and it affected the colonization efficiency of HC-2-20 strain. Therefore, the amount of rapeseed straw should be reduced.

[0050] 2. The effect of rapeseed straw content The experiment was basically the same as the one on the effects of straw composition, except that the content of rapeseed straw was changed. For the specific fertilizer composition, please refer to Table 5. In addition to measuring the fresh weight of 100 seeds, the yield of fresh pods per plant and the pH of the substrate, the incidence of root rot was also counted. The results are shown in Table 6.

[0051] Table 5. Combination ratio of different rapeseed straw contents using single-component straw blends. Table 6. Effects of different rapeseed straw content combinations on soybean pot cultivation. The results are shown in Table 6. With increasing rapeseed straw content, the substrate pH gradually decreased. The lowest pH was observed in combination 3-1-3 (10% rapeseed straw), at 7.89, significantly lower than CK-2 (8.05) and combination 3-1-1 (8.10). However, the 100-seed fresh weight and yield per plant decreased with increasing rapeseed straw content. This indicates that when low proportions (2%, 5%) of rapeseed straw are applied in combination with cow / sheep manure and bacterial strains, their effect on substrate pH regulation and soybean growth promotion is similar to CK-2. However, a high proportion (10%) of rapeseed straw significantly inhibits soybean 100-seed fresh weight and yield per plant. Rapeseed straw is indeed less effective than cow / sheep manure in improving fertility; its advantage lies in its ability to lower pH more effectively, and the sulfur-containing compounds can significantly reduce the incidence of root rot. Therefore, combination 3-1-2 was determined to have a rapeseed straw addition of 5%, yield ≥95% of CK-2, colonization efficiency of HC-2-20 strain ≥80% of CK-2, and root rot incidence rate reduced by ≥30%.

[0052] 3. The effect of potato straw content The experiment was basically the same as the one on the "effect of straw mono-combination" above, except that the content of potato straw was changed. For the specific fertilizer combination, please refer to Table 7, and for the results, please refer to Table 8.

[0053] Table 7. Straw composition ratios with different potato straw contents Table 8. Effects of different potato straw contents on soybean pot cultivation. The results are shown in Table 8. Compared with the control CK-2, the substrate pH, 100-seed fresh weight, and yield per plant all showed certain variation patterns in the potato straw ratio combinations. As the potato straw content increased from 10% to 20%, the substrate pH generally increased, with combination 2-1-3 (20% potato straw) showing the highest pH at 8.19, significantly higher than CK-2 (8.05) and combination 2-1-1 (8.10). The 100-seed fresh weight initially increased and then slightly decreased with increasing potato straw content. The yield per plant was significantly higher in combination 2-1-2 (1.09 kg / plant) than in other treatments. This indicates that in the single-component potato straw combinations, 15% potato straw addition is more effective in promoting soybean growth and increasing 100-seed fresh weight and yield per plant. Therefore, it was determined that all combinations with added potato straw had higher yields than CK, with combination 2-1-2 showing the best yield increase, and the optimal addition ratio of potato straw was determined to be 15%.

[0054] 4. The effect of soybean straw content The experiment was basically the same as the one on the "effect of straw mono-combination" mentioned above, except that the content of soybean straw was changed. For the specific fertilizer combination, please refer to Table 9, and for the results, please refer to Table 10.

[0055] Table 9. Combination ratio of different soybean straw contents using single-component straw blends. Table 10. Effects of different soybean straw content univariate combinations on soybean pot cultivation. The results are shown in Table 10. Compared with the control CK-2, the substrate pH, 100-seed fresh weight, and yield per plant of each soybean straw ratio combination showed certain trends. As the soybean straw content increased from 5% to 10%, the substrate pH generally increased, with combination 1-1-3 (10% soybean straw) having the highest pH at 8.29, significantly higher than CK-2 (8.05), combination 1-1-1 (8.17), and combination 1-1-2 (8.18). The 100-seed fresh weight decreased slightly with increasing soybean straw content, with combination 1-1-3 having the lowest at 84.31 g. Yield per plant also decreased with increasing soybean straw content. This indicates that in mono-component soybean straw combinations, lower proportions (5%, 8%) of soybean straw addition had a similar promoting effect on potted soybeans as CK-2. Therefore, considering all indicators, the optimal addition ratio of soybean straw in mono-component combinations is 8%.

[0056] Example 4: Study on the effects of straw binary and ternary combinations on soybean pot cultivation in saline-alkali soil. The experiment was basically the same as the "effect of straw mono-combination" in Example 3 above, except that binary and ternary straw combinations were used. In the binary and ternary combinations, the amount of potato straw was increased to 15%, and the amount of rapeseed straw was reduced to 5%. For specific fertilizer combinations, please refer to Table 11, and for the results, please refer to Table 12.

[0057] Table 11 Different Binary and Ternary Combinations of Straw Table 12 Results of the effects of different binary and ternary straw combinations on soybean pot cultivation. The results are shown in Table 12. Compared with the control CK-2, the binary and ternary combinations showed different trends in substrate pH, 100-seed fresh weight, and yield per plant. Among the binary combinations, combination 2+3 performed the best, with a substrate pH (8.02) slightly lower than CK-2, and significantly higher 100-seed fresh weight (86.85 g) and yield per plant (1.09 kg / plant). Among the ternary combinations, combination 1+2+3-1 with added strains showed the best overall effect, with a substrate pH (8.02) similar to combination 2+3, and the highest 100-seed fresh weight (86.92 g) and yield per plant (1.11 kg / plant) among all treatments. Overall, the ternary combination 1+2+3-1 showed better promoting effects than the binary combination. Among the binary combinations, combination 2+3 was better than combinations 1+2 and 1+3. This may be because the multi-element straw combination optimized the physical and chemical properties of the substrate through synergistic effects, promoted the absorption and utilization of nutrients by soybean roots, and thus increased the fresh weight of 100 seeds and the yield per plant.

[0058] Example 5: Effects of Organic Compound Fertilizer on Soil and Soybean Cultivation in Fields The experimental site was located in Heerjia Village, Hexi Town, Guide County, Hainan Prefecture, Qinghai Province. The soil was chestnut calcareous soil with a pH of 8.47, an organic matter content of 8.19 g / kg, a total nitrogen content of 1.01 g / kg, an available phosphorus content of 1.55 g / kg, and a available potassium content of 53.21 g / kg. The previous crop was winter wheat.

[0059] The experiment consisted of four treatments and two controls (Table 13), with each control and treatment plot measuring 4 m². 2 Each plot was treated with a fertilizer containing bacteria (18 kg of organic compound fertilizer and 1000 mL of a 100-fold diluted HC-2-20 bacterial solution) as base fertilizer. Control CK-1 received no fertilizer, while control CK-0 received only 1000 mL of a 100-fold diluted HC-2-20 bacterial solution. See Table 13 for details. Soil samples from 0 to 40 cm depth were collected during the fresh pod harvest period for soil physicochemical property testing.

[0060] Table 13 Fertilizer Ratio Note: The strain is a 100-fold dilution of HC-2-20 in 1000 mL; -- indicates that it is not present.

[0061] The soybean variety used is Kaikeyuan No. 5. Double-row cultivation with raised beds covered with black plastic film is employed. The raised beds are 0.8 m wide, with furrows of 0.3 m in length and 0.3 m in height. The plant spacing is 0.25 m × 0.3 m. 3-4 seeds are sown per hole at a depth of 5 cm, leaving 2-3 seedlings per hole. Sowing date is April 26th. Throughout the growing season, watering should be done as needed, depending on soil moisture.

[0062] 105 days after sowing, Kaikeyuan No. 5 reached the standard for fresh pod harvesting. The pH, organic matter, total nitrogen, available phosphorus and available potassium content of the soil in each treatment at the fresh pod harvesting period were investigated, as well as the agronomic traits and fresh pod characteristics of the soybeans in different treatments.

[0063] The results are shown in Table 14. All different fertilizer combinations reduced soil pH. Combination 1 (30% cow / sheep manure, 20% soybean straw, 37.5% potato straw, 12.5% ​​rapeseed straw, and *Streptomyces slate* strain) lowered the pH to 8.03, significantly lower than other treatments. The CK-0 treatment, containing only *Streptomyces slate* strain, lowered the pH to 8.27. Furthermore, fertilizers containing diluted HC-2-20 strain (combinations 1 and CK-2) showed a more significant increase in soil organic matter content. Combination 1 achieved an organic matter content of 15.80 g / kg, a 10.49% increase compared to Combination 2's 14.30 g / kg. Available phosphorus and potassium contents showed similar trends, both significantly higher than the corresponding treatments without the strain. This indicates that the synergistic effect of organic compound fertilizer and HC-2-20 strain can more effectively improve soil physicochemical properties, enhance soil fertility, and provide a more suitable nutrient environment for crop growth.

[0064] Table 14 Effects of different fertilizer ratios on soil The results are shown in Table 15. Compared with the four treatment groups (Table 5), the plant height of the control group was 53.12 cm, and the stem diameter and number of effective branches were also significantly lower than those of the treatment groups. P <0.05); the stem diameter of combination 1 reached 10.20 mm, significantly higher than the other treatments ( P <0.05), with an average of 6.08 effective branches; meanwhile, combination 1 had a combined proportion of 81.68% two- and three-pod plants, with three-pod plants accounting for 31.29%, and a plot yield of 7.81 kg, which was also significantly better than other treatments ( P <0.05).

[0065] Table 15 Agronomic traits of fresh soybean pods under different treatments Based on the effects of different treatments on the characteristics of soybean fresh pods shown in Table 6, it can be seen that each treatment promoted the length, width, and thickness of one-pod, two-pod, and three-pod soybeans to varying degrees, with combination 1 showing the best overall effect. Compared with the control (CK), each combination treatment improved the size indicators of all types of pods. In one-pod soybeans, the length (46.85 mm), width (14.80 mm), and thickness (11.36 mm) of combination 1 were all higher than those of CK and other treatments, with the thickness showing the most significant increase, increasing by approximately 4.7% compared to CK-1 (10.85 mm). A similar trend was observed in two-pod and three-pod soybeans, with combination 1 achieving maximum lengths (59.21 mm), widths (15.01 mm), and thicknesses (11.62 mm) for two-pod soybeans and (69.14 mm), widths (15.42 mm), and thicknesses (11.68 mm) for three-pod soybeans, significantly better than the control.

[0066] Table 6 Characteristics of fresh soybean pods under different treatments Overall, all fertilization or management combinations helped improve the morphological traits of soybean fresh pods. Combination 1 showed the best overall performance, possibly due to its robust root system, strong absorption capacity, sufficient nutrients, stable nutrient supply during the pod-filling stage, high seed fullness, and thus increased fresh weight per 100 seeds. It also increased pod volume and seed-accommodating space, laying the foundation for increased yield.

[0067] This invention addresses the issue that the long-term, large-scale application of insufficiently decomposed cow and sheep manure (especially manure from penned livestock) in existing technologies can exacerbate secondary salinization due to its relatively high salt content. Straw, on the other hand, has extremely low salt content, and its use after decomposition does not impose a salt load, making it more suitable for the already saline soils of Northwest China. The compound fertilizer of this invention achieves the same yield-increasing effect as using only livestock manure without causing secondary soil salinization, thus promoting long-term soil health.

[0068] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A type of *Streptomyces slate* ( Streptomyces ardesiacus HC-2-20, characterized in that, The Streptomyces slateiformis HC-2-20 has been deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 36145, on October 11, 2025. The deposit address is Institute of Microbiology, Chinese Academy of Sciences, No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing.

2. A compound fertilizer containing *Streptomyces slate* HC-2-20 as described in claim 1, characterized in that, The compound fertilizer contains the following components by mass fraction: 30% cow manure and / or sheep manure, 20% soybean straw, 37-38% potato straw and 12-13% rapeseed straw, and the compound fertilizer contains the bacterial solution of Streptomyces slate HC-2-20.

3. The application of Streptomyces slate HC-2-20 as described in claim 1, or the compound fertilizer as described in claim 2, to promote crop growth in saline-alkali land.

4. The application according to claim 3, characterized in that, Lower the soil pH.

5. The application according to claim 3, characterized in that, The crops mentioned include: tomatoes and soybeans.

6. The application according to claim 5, characterized in that, Increase any one or more of the following in the tomato plant: plant height, spread, stem diameter, germination rate, and root length.

7. The application according to claim 6, characterized in that, The bacterial culture of *Streptomyces slate* HC-2-20 was OD. 600 It is obtained by diluting 0.5 by 10 to 1000 times.

8. The application according to claim 5, characterized in that, Increase the 100-seed fresh weight and / or yield per plant of the soybean.

9. The application according to claim 5, characterized in that, Increase the plant height, diameter, and number of effective branches of the soybean by one or more.

10. The application according to claim 8 or 9, characterized in that, Increase the number of seeds per soybean pod, and / or increase the length, width, and thickness of one, two, or three pods of the soybean by any one or more.

Images