Method for improving saline-alkali soil by shallowly burying straw and applying composite microbial inoculum in combination with salt-resistant layer

Abstract

This invention discloses a method for improving saline-alkali land by shallowly burying straw to form a salt-barrier layer and applying a compound microbial agent. In autumn, straw is crushed and evenly spread across the entire surface. A diluted microbial agent composed of Bacillus subtilis, Bacillus licheniformis, Trichoderma harzianum, Bacillus mucilaginosa, Azotobacter chrysophagus, and Bacillus megaterium is then sprayed onto the soil. The straw is then turned over and buried 15-18 cm below the surface to form a 2-5 cm salt-barrier layer. The soil above the salt-barrier layer is then loosened. The following spring, shallow sowing is carried out on raised beds, and the land can be planted and harvested in the same year. This invention uses a shallowly buried, continuous salt-barrier layer to cut off soil capillaries and prevent salt from ascending into the topsoil. Simultaneously, salt-tolerant microorganisms accelerate straw decomposition, secrete organic acids to neutralize alkalinity, and fix nitrogen, solubilize phosphorus, and solubilize potassium to supplement nutrients, overcoming the drawback of competition for nitrogen during shallow-buried straw decomposition. After one year of improvement, the salinity, pH and alkalinity of the 0-20 cm soil layer were significantly reduced, the straw decomposition rate reached 70.1-76.2%, and the corn yield increased from 3150 kg / ha to 7593-8443 kg / ha, an increase of 141.0-168.0%.

Description

Technical Field

[0001] This invention belongs to the field of saline-alkali land improvement and agricultural microbial application technology, specifically involving a method for improving saline-alkali land by shallowly burying crop straw below the topsoil to construct a continuous salt-blocking layer and applying salt-alkali tolerant compound microbial agents. Background Technology

[0002] Saline-alkali soils are characterized by high salt content, high alkalinity, dispersed structure, and lack of organic matter, making it difficult for crops to establish themselves and resulting in low and unstable yields. In irrigated areas with shallow groundwater levels and strong evaporation, soluble salts in deep soil and groundwater rise continuously with capillary water and accumulate in the topsoil, forming a surface accumulation process where "salt comes with water and water disperses while salt remains." This is the fundamental reason why saline-alkali farmland repeatedly re-salinates and the improvement effect is difficult to consolidate.

[0003] Improving saline-alkali land using crop straw has become a research hotspot in recent years. Returning straw to the field can increase soil organic matter, improve pore structure, and provide nitrogen, phosphorus, potassium, and trace elements. Concentrated straw layering in the soil profile can also directly sever soil capillary action and block the upward movement of salts. However, practice shows that existing straw-returning methods still have significant drawbacks: First, when straw is mixed with topsoil, the decomposition process competes with crops for nitrogen and water, producing intermediate products such as organic acids, leading to seedling burn, yellowing, and decreased emergence rates. Second, straw scattered in the topsoil cannot form a continuous structural layer, limiting its effectiveness in blocking capillary water. Third, high salinity inhibits the activity of native microorganisms, resulting in slow natural decomposition of straw, a high carbon-to-nitrogen ratio, and delayed fertilizer release.

[0004] Reported methods for shallowly tilling straw into the field to prevent salinity and improve arable soil involve spreading straw pulverized to 4-5 cm in size evenly at a rate of 5 t / ha on the soil surface, then using a plow to bury it 15-18 cm below the surface to create a 2-4 cm salt-blocking layer. A rotary tiller is then used to loosen the soil above the salt-blocking layer before ridging and planting. This method uses a small amount of straw to disrupt the capillary connection between the topsoil and deeper soil layers, without requiring deep tilling or disturbing deep saline-alkali soil, and is simple to operate. However, it still has three shortcomings: (1) The salt barrier layer is located in the root-dense layer, and the contradiction between straw decomposition and crop competition for water and nitrogen is prominent. When functional microorganisms are not inoculated, decomposition is slow, seedling emergence and seedling growth are suppressed, and the yield increase is very small; (2) Straw is not enhanced by microorganisms, the decomposition rate is low, the structure of the salt barrier layer is easy to lose continuity after decomposition and collapse, and the salt-suppressing effect decays rapidly from year to year; (3) Relying solely on the nutrient return of the straw itself, the soil improvement and fertilization capacity is limited, and the soil alkalinity decreases not significantly. In addition, although engineering barriers such as sand, slag, and geomembrane can block capillary action, they are costly, non-degradable, and destroy the continuity of the soil profile. Therefore, there is an urgent need for a method for improving saline-alkali land that allows for crop planting in the same year, provides long-lasting salt suppression, combines soil improvement and fertilization, and is inexpensive. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problems of slow decomposition of straw in existing shallow straw-incorporated salt-barrier layers, low seedling emergence rate and limited yield increase due to competition for water and nitrogen with crops, as well as discontinuous salt-barrier layer structure, weak soil improvement and fertilization effect, and rapid interannual decay of salt-suppressing effect. The invention provides a salt-alkali tolerant straw decomposition compound microbial agent and a method for improving saline-alkali land by applying the compound microbial agent in combination with shallow straw burial salt-barrier layer.

[0006] To achieve its purpose, the present invention adopts the following technical solution: As a first aspect of the technical solution of this invention, this invention provides a compound microbial agent for the decomposition of salt-alkali resistant straw. The compound microbial agent is composed of *Bacillus subtilis*, *Bacillus licheniformis*, *Trichoderma harzianum*, *Bacillus mucilaginosa*, *Azotobacter chrysophyllariae*, and *Bacillus megaterium* in a volume ratio of (25-35):(15-25):(15-20):(10-15):(10-15):(10-15), and the effective viable count of the compound microbial agent is not less than 5.0 × 10⁻⁶. 9 The straw cellulose degradation rate is no less than 45% after 30 days of cultivation in saline-alkali soil with a salt content of 8 g / kg and a pH of 9.5, at a concentration of CFU / mL and a pH of 6.5-7.5. As a second aspect of the technical solution of the present invention, the present invention provides a method for improving saline-alkali land by applying compound microbial agents in combination with shallow burial of straw in a salt-inhibiting layer, the method comprising the following steps: Step 1: Collect straw after the autumn crop harvest, shred it to a length of 4 cm to 6 cm, and set it aside; Step 2: Determine the salt content of the 0 cm to 20 cm soil layer of the saline-alkali land to be improved, and determine the top burial depth of the straw salt-blocking layer according to the salt content: when the salt content is 3 g / kg to 5 g / kg, the burial depth is 12 cm to 15 cm; when the salt content is 5 g / kg to 8 g / kg, the burial depth is 15 cm to 18 cm; when the salt content is > 8 g / kg, the burial depth is 18 cm to 22 cm. Step 3: Spread the straw obtained in Step 1 evenly on the ground surface, with a spreading amount of 5 t / ha to 15 t / ha on a dry basis; then spray the straw surface evenly with a diluted compound microbial agent, and let it stand for 2 h to 6 h to allow the microbial solution to penetrate into the straw, thus obtaining inoculated straw. Step 4: Plow the inoculated straw obtained in Step 3 to the depth determined in Step 2 to construct a continuous straw salt barrier layer with a thickness of 2 cm to 5 cm in the soil layer; immediately after plowing, rotary tillage is carried out to loosen the soil above the top surface of the salt barrier layer to the ground surface, with a loosening depth of not less than 10 cm, and a loose soil layer with a thickness of not less than 8 cm is retained above the salt barrier layer. Step 5: In the following spring, ridging is carried out, and base fertilizer is applied and sown in one go. The sowing depth is 4 cm to 5 cm. After that, routine field management is carried out.

[0007] Preferably, in step one, the straw is one or a mixture of several of the following: corn straw, sunflower straw, sweet sorghum straw, wheat straw, or rice straw.

[0008] Preferably, in step three, the dosage of the compound microbial agent is 15 L / ha to 45 L / ha, and it is diluted with water 80 to 120 times before spraying to obtain the diluted compound microbial agent solution.

[0009] Preferably, in step five, the base fertilizer is compound fertilizer 15-15-15, and the dosage is 450 kg / ha to 600 kg / ha.

[0010] Preferably, the crop sown is corn, sunflower, or sweet sorghum.

[0011] Preferably, in step five, the row spacing for crop sowing is 60 cm to 65 cm, the plant spacing is 25 cm to 30 cm, and the planting density is 55,000 plants / hectare to 65,000 plants / hectare.

[0012] Preferably, in step four, the continuous straw salt-blocking layer is replenished every 2 to 3 years.

[0013] The technical principles of this invention are as follows: First, the salt-barrier layer is a continuous, layered structure that covers the entire plot, rather than the existing strip-like laying method. Its large pores interrupt the soil capillary action, physically cutting off the upward flow channels of the lower salt-containing capillaries. This prevents salt from evaporating into the topsoil and surface, thus inhibiting salt return at the source. The burial depth of the salt-barrier layer is set according to the salt content of the topsoil, with higher salt content requiring greater depth, ensuring that the salt-barrier layer is always below the main salt accumulation layer. Second, the compound microbial agent contains Azotobacter chrysophagus (a nitrogen-fixing bacterium), Bacillus megaterium, and Bacillus mucilaginosus (a type of Bacillus mucilaginosus) that solubilize phosphorus and potassium, continuously replenishing nitrogen, phosphorus, and potassium to the salt-barrier layer and the topsoil, offsetting the competition for soil nitrogen from straw decomposition. This is the key to achieving planting in the same year without yield reduction with shallow burial of the salt-barrier layer. At the same time, the extracellular polysaccharides secreted by microorganisms and the hyphal entanglement promote the formation of water-stable aggregates. In addition, the rotary tillage machine loosens the soil layer above the salt-barrier layer, significantly improving the permeability of the topsoil and the conditions of the seedbed. Third, a loose soil layer of no less than 8 cm is retained above the salt barrier layer to physically isolate the seeds from the straw layer and further avoid the adverse effects of decomposition products on germination.

[0014] Based on the above technical principles, the beneficial effects of the present invention are as follows: (1) Significant and lasting salt suppression. One year after improvement, the salt content of the 0 cm to 20 cm soil layer decreased from 5.62 g / kg in the control to 2.08 g / kg to 2.42 g / kg (a decrease of 56.9% to 63.0%), the pH decreased from 9.35 to 8.25 to 8.46, and the alkalinity decreased from 33.1% to 15.6% to 18.2%. The average annual salt return rate observed for two consecutive years was about 0.14 g / kg, which was only 27% of that of the uninoculated shallow tillage treatment (0.52 g / kg / year).

[0015] (2) The straw decomposes quickly and has a good fertilization effect. After inoculation with compound microbial agent, the decomposition rate of salt barrier straw reached 70.1%~76.2% in one year, which is 28.8~34.9 percentage points higher than that of uninoculated shallow tillage treatment (41.3%); the organic matter in the 0 cm~20 cm soil layer increased from 7.3 g / kg to 9.1 g / kg~10.2 g / kg, and the water-stable aggregates larger than 0.25 mm increased from 28.6% to 49.6%~54.1%.

[0016] (3) Significant increase in yield in the same year. The nitrogen fixation and phosphorus solubilization of the microbial agent and the physical isolation of the salt barrier layer jointly overcome the disadvantage of straw decomposition competing for nitrogen. The corn emergence rate increased from 53.6% to 86.5%~90.8%, and the yield increased from 3150 kg / ha to 7593 kg / ha~8443 kg / ha, an increase of 141.0%~168.0% compared with the control, and an increase of 58.2%~75.9% compared with the shallow tillage treatment without inoculation (4799 kg / ha).

[0017] (4) Low cost and easy to promote. The amount of straw used is only 5 t / ha to 15 t / ha, with an input of RMB162 to RMB242 per mu. The cost can be recovered with an increase in production of about RMB711 per mu in the same year, and the net increase is RMB469 to RMB549 per mu. The machinery used is a combination of conventional plowing machine, rotary tiller and spraying device, without the need for special equipment, which is suitable for large-scale promotion.

[0018] (5) Eco-friendly. The salt barrier layer is made of biodegradable biomass material, which decomposes into soil organic matter without producing secondary pollution, and at the same time realizes the resource utilization of straw. Detailed Implementation

[0019] This invention discloses a method for improving saline-alkali land by shallowly burying straw in a salt-blocking layer and applying a compound microbial agent, which is carried out according to steps one to five as described in the invention. The straw is crushed to a length of 4 cm to 6 cm, the burial depth of the top surface of the salt-blocking layer is determined according to the salt content of the soil layer from 0 cm to 20 cm, and is 12 cm to 22 cm. The amount of straw used is 5 t / ha to 15 t / ha on a dry basis, the straw moisture content is 55% to 65%, the thickness of the salt-blocking layer is 2 cm to 5 cm, and a loose soil layer of not less than 8 cm is retained above the salt-blocking layer. The salt-blocking layer is replenished every 2 to 3 years.

[0020] The straw mentioned in step one is one or a mixture of several of the following: corn straw, sunflower straw, sweet sorghum straw, wheat straw, and rice straw.

[0021] The compound microbial agent described in step three is prepared by mixing Bacillus subtilis, Bacillus licheniformis, Trichoderma harzianum, Bacillus mucilaginosus, Azotobacter chrysophagus, and Bacillus megaterium in a volume ratio of (25-35):(15-25):(15-20):(10-15):(10-15):(10-15), with an effective viable count of not less than 5.0 × 10⁻⁶. 9 CFU / mL.

[0022] In step five, the row spacing for planting corn is 60 cm to 65 cm, the plant spacing is 25 cm to 30 cm, and the planting density is 55,000 plants / hectare to 65,000 plants / hectare.

[0023] The beneficial effects of the present invention are verified below through specific embodiments and comparative examples: Example 1 This embodiment was conducted at the saline-alkali farmland improvement demonstration base in Beizheng Town, Songyuan City, Jilin Province. The tested soil was soda-type saline-alkali soil. The basic characteristics of the 0 cm to 20 cm soil layer before improvement are shown in Table 1.

[0024] Table 1. Basic properties of soil layers 0 cm to 20 cm in the tested soil samples. This embodiment was carried out according to the following steps: Corn stalks were collected after the corn harvest in early October 2023, shredded and crushed to a thickness of 4-6 cm, with an air-dried moisture content of 12.4%; the salt content of the soil layer from 0 cm to 20 cm was measured to be 5.85 g / kg, and the top surface of the salt-blocking layer was determined to be buried at a depth of 15 cm; the stalks were evenly spread on the ground at a rate of 8 t / ha (dry basis), and a diluted compound microbial agent solution (30 L / ha, effective viable bacteria count 6.2 × 10⁻⁶) was evenly sprayed onto the stalk surface using a vehicle-mounted sprayer. 9(CFU / mL, diluted 100 times), let stand for 2-6 hours; use a plow to turn over and bury the inoculated straw to 15 cm-19 cm below the surface, forming a continuous salt-barrier layer of about 4 cm thickness, and then use a rotary tiller to loosen the soil layer 0 cm-15 cm above the salt-barrier layer; in late April 2024, ridging was carried out, and a no-till planter was used to complete the application of base fertilizer (compound fertilizer 15-15-15, application rate 525 kg / ha) and sowing in one go, with a sowing depth of 5 cm. The crop sown was the maize variety Jinqing D1688, with a row spacing of 65 cm, a plant spacing of 25 cm, and a planting density of 60,000 plants / hectare. After that, field management such as fertilization and plant protection was carried out according to local standards, and harvesting was carried out in late September. The strain composition of the compound microbial agent is shown in Table 2.

[0025] Table 2. Composition and main functions of the compound microbial agent strains Example 2 The difference between this embodiment and Embodiment 1 is that: the straw usage is 12 t / ha (dry basis); the top surface of the salt barrier layer is buried at a depth of 16 cm and a thickness of approximately 5 cm; and the compound microbial agent usage is 45 L / ha. Everything else is the same as in Embodiment 1.

[0026] Example 3 The difference between this embodiment and Embodiment 1 is that the straw usage is 14 t / ha (dry basis), the compound microbial agent usage is 45 L / ha, the top surface of the salt barrier layer is buried at a depth of 17 cm and a thickness of approximately 5 cm, and the planting density is 60,000 plants / hectare. Everything else is the same as in Embodiment 1.

[0027] Comparative Example 1 (Shallowly buried salt barrier layer but without inoculation with microbial agent) The difference between this comparative example and Example 1 is that only an equal amount of water was sprayed onto the straw (without adding compound microbial agents), thus constructing a shallow-buried straw salt-barrier layer without exogenous functional microorganisms. Other steps and parameters are the same as in Example 1.

[0028] Comparative Example 2 (inoculated with microbial agent but with full-layer rotary tillage and mixing of straw) The difference between this comparative example and Example 1 is that the salt-barrier layer structure was eliminated. 8 t / ha of straw inoculated with an equal amount of compound microbial agent was rotary tilled and mixed into the entire soil layer from 0 cm to 20 cm using a rotary tiller, thus eliminating the concentrated salt-barrier layer. Other steps and parameters were the same as in Example 1.

[0029] Control group (CK) (unmodified blank control) The control plots were not treated with straw salt barrier layer and microbial agent, but were treated with the same amount of fertilization, sowing and field management as in Example 1. The corn variety and planting density were the same as in Example 1.

[0030] Test results Each treatment method was replicated three times, with an experimental area of ​​60 m², arranged in a randomized block design. Soil salinity and fertility indices in the 0-20 cm soil layer, straw decomposition rate in the salt-barrier layer, and maize emergence rate and yield were measured at the maize harvest in 2024. The results are shown in Tables 3 and 4.

[0031] Table 3. Soil parameters and straw decomposition status at depths of 0-20 cm after one year of improvement using different treatment methods. Table 4. Maize emergence rate, yield, and yield components for each treatment. As shown in Tables 3 and 4, the salt content of the 0 cm to 20 cm soil layer in Examples 1 to 3 decreased by 56.9% to 63.0% compared with the control CK, the pH decreased by 0.89 to 1.10 units, and the alkalinity decreased by 14.9 to 17.5 percentage points. Under the same straw usage and the same shallow-buried salt-barrier layer construction conditions, Example 1 showed a 1.68 g / kg lower salt content, a 31.1 percentage point higher straw decomposition rate, a 16.0 percentage point higher seedling emergence rate, and a 58.2% higher yield compared to Comparative Example 1 (without inoculation). This indicates that the compound microbial agent, by accelerating decomposition, producing acid to neutralize alkalinity, and fixing nitrogen, solubilizing phosphorus, and solubilizing potassium, not only enhanced the salt-barrier and soil-improving effect but also overcame the inherent drawback of nitrogen competition from shallow-buried straw decomposition. Example 1 also showed a 2.26 g / kg lower salt content and a 73.2% higher yield compared to Comparative Example 2 (inoculated but fully mixed in), indicating that the physical blockage of capillary action by the continuous salt-barrier layer is key to salt suppression, and the two work synergistically. Examples 1-3 were completed and yielded high yields in the same year, without the need for fallow periods.

[0032] Two consecutive years of locational observation (2024-2025) showed that the salt content of the soil layer from 0 cm to 20 cm in Example 1 was 2.42 g / kg and 2.56 g / kg, respectively, with an average annual salt return rate of about 0.14 g / kg, significantly lower than the 0.52 g / kg / year of Comparative Example 1; the corn yield was 7593 kg / ha and 7880 kg / ha, respectively, with good yield stability. In the third year, a straw salt-blocking layer (6 t / ha) can be laid once in steps one to four to maintain the soil improvement effect. Based on the input of straw of 40-59 yuan, microbial agent of 42-63 yuan, and machinery of 80-120 yuan per mu, the total cost is 162-242 yuan / mu. The yield increased by 296.2 kg / mu compared with the control in the same year (corn at 2.4 yuan / kg), with a profit of about 711 yuan / mu. The cost can be recovered in the same year and a net increase of 469-549 yuan / mu can be achieved.

Claims

1. A method for improving saline-alkali land by shallow burying straw in a salt-inhibiting layer and applying a compound microbial agent, characterized in that, The method includes the following steps: Step 1: Collect straw after the autumn crop harvest, shred it to a length of 4 cm to 6 cm, and set it aside; Step 2: Determine the salt content of the 0 cm to 20 cm soil layer of the saline-alkali land to be improved, and determine the top burial depth of the straw salt-blocking layer according to the salt content: when the salt content is 3 g / kg to 5 g / kg, the burial depth is 12 cm to 15 cm; when the salt content is 5 g / kg to 8 g / kg, the burial depth is 15 cm to 18 cm; when the salt content is > 8 g / kg, the burial depth is 18 cm to 22 cm. Step 3: Spread the straw obtained in Step 1 evenly on the ground surface, with a spreading amount of 5 t / ha to 15 t / ha on a dry basis; then spray the straw surface evenly with a diluted compound microbial agent, and let it stand for 2 h to 6 h to allow the microbial solution to penetrate into the straw, thus obtaining inoculated straw. Step 4: Plow the inoculated straw obtained in Step 3 to the depth determined in Step 2 to construct a continuous straw salt barrier layer with a thickness of 2 cm to 5 cm in the soil layer; immediately after plowing, rotary tillage is carried out to loosen the soil above the top surface of the salt barrier layer to the ground surface, with a loosening depth of not less than 10 cm, and a loose soil layer with a thickness of not less than 8 cm is retained above the salt barrier layer. Step 5: In the following spring, ridging is carried out, and base fertilizer is applied and sown in one go. The sowing depth is 4 cm to 5 cm. After that, routine field management is carried out.

2. The method for improving saline-alkali land by shallow burying straw in a salt-inhibiting layer and applying a compound microbial agent according to claim 1, characterized in that, In step three, the compound microbial agent is prepared by mixing Bacillus subtilis, Bacillus licheniformis, Trichoderma harzianum, Bacillus mucilaginosa, Azotobacter chrysophagus, and Bacillus megaterium in a volume ratio of (25~35):(15~25):(15~20):(10~15):(10~15):(10~15), and the effective viable count of the compound microbial agent is not less than 5.0 × 10⁻⁶. 9 The straw cellulose degradation rate is no less than 45% after 30 days of cultivation in saline-alkali soil with a salt content of 8 g / kg and a pH of 9.5, at a concentration of CFU / mL and a pH of 6.5-7.

5.

3. A method for improving saline-alkali land by shallow burying straw in a salt-inhibiting layer and applying a compound microbial agent, as described in claim 1 or 2, characterized in that... In step one, the straw is one or a mixture of several of the following: corn straw, sunflower straw, sweet sorghum straw, wheat straw, or rice straw.

4. The method for improving saline-alkali land by shallow burying straw in a salt-inhibiting layer and applying a compound microbial agent according to claim 3, characterized in that, In step three, the dosage of the compound microbial agent is 15 L / ha to 45 L / ha. Before spraying, it is diluted with water 80 to 120 times to obtain the diluted compound microbial agent solution.

5. The method for improving saline-alkali land by shallow burying straw in a salt-inhibiting layer and applying a compound microbial agent as described in claim 4, characterized in that, In step five, the base fertilizer is compound fertilizer 15-15-15, and the dosage is 450 kg / ha to 600 kg / ha.

6. The method for improving saline-alkali land by shallow burying straw in a salt-inhibiting layer and applying a compound microbial agent as described in claim 5, characterized in that, The crop planted is corn.

7. The method for improving saline-alkali land by shallow burying straw in a salt-inhibiting layer and applying a compound microbial agent according to claim 6, characterized in that, In step five, the row spacing for crop sowing is 60 cm to 65 cm, the plant spacing is 25 cm to 30 cm, and the planting density is 55,000 plants / hectare to 65,000 plants / hectare.

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