Green manure and charcoal-based yellow soil improvement method

Abstract

The invention relates to the technical field of soil improvement, in particular to a yellow soil improvement method based on green manure and charcoal. The yellow soil improvement method based on green manure and charcoal comprises the following steps: planting common vetch in yellow soil in the fourth quarter of the first year; in the second quarter of the next year, the grown vicia sativa seedlings and the charcoal are turned and pressed together, base fertilizer is applied, and preliminary improvement of the yellow soil is achieved; crops are planted into the yellow soil after preliminary improvement, first topdressing is applied after a first time interval to achieve secondary improvement of the yellow soil, second topdressing is applied after a second time interval to achieve tertiary improvement of the yellow soil, and nutrients, aggregate stability and enzyme activity of the yellow soil are obviously improved through the tertiary improvement. The problems that existing yellow soil is viscous and heavy in texture, poor in tilling performance, low in natural fertility, high in acidity and relatively low in water and fertilizer retention capacity, soil exchangeable salt bases are remarkably lacked, the salt base saturation degree is generally smaller than 20%, and the nitrogen leaching loss phenomenon of the yellow soil is serious are solved.

Description

Technical Field

[0001] This invention relates to the field of soil improvement technology, specifically to a method for improving yellow soil based on green manure and biochar. Background Technology

[0002] Yellow soil is an important zonal soil in my country, and one of the key soil types for agricultural production in the southwestern mountainous areas, especially widely distributed in the karst mountains of Guizhou Province. It is a core arable resource for maintaining food security and ecological stability in this region. Yellow soil has unique physicochemical properties, mainly characterized by its heavy texture, poor tilth, low natural fertility, and high acidity. Its water and fertilizer retention capacity is relatively weak, and it is significantly lacking in exchangeable bases, with base saturation generally less than 20%, significantly lower than that of red soil. Although the surface organic matter content of yellow soil is relatively high, nitrogen leaching is particularly severe. Long-term irrational application of nitrogen fertilizer not only exacerbates nitrogen runoff and leaching losses but also leads to increasingly serious soil acidification, causing a series of ecological and environmental problems such as soil biological function degradation, nutrient imbalance, and increased agricultural non-point source pollution. Therefore, how to systematically improve yellow soil fertility, simultaneously achieve efficient nitrogen utilization and acidity control, and construct a sustainable fertility enhancement technology system has become a key technological bottleneck that urgently needs to be overcome in the ecologically fragile karst areas. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide a method for improving yellow soil based on green manure and biochar, in order to solve the problems of existing yellow soil, such as heavy texture, poor tilth, low natural fertility, high acidity, relatively weak water and fertilizer retention capacity, significant lack of exchangeable bases, base saturation generally less than 20%, and serious nitrogen leaching loss.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for improving yellow soil based on green manure and biochar includes the following steps: S1. Plant arrowhead peas in yellow soil in the fourth quarter of the first year; S2. In the second quarter of the second year, the growing arrowhead pea seedlings were turned over as green manure together with biochar, and then base fertilizer was applied to achieve the initial improvement of the yellow soil. S3. Transplant crops into the initially improved yellow soil. Apply the first top dressing after the first interval to achieve the second improvement of the yellow soil. Apply the second top dressing after the second interval to achieve the third improvement of the yellow soil. After the three improvements, the nutrients, aggregate stability and enzyme activity of the yellow soil are significantly improved, and the yield of crops grown in the yellow soil after the three improvements is significantly increased.

[0005] Based on the above technical means, comprehensive improvement of yellow soil is achieved through the synergistic effect of multiple mechanisms including "biological-chemical-physical": ① During the fourth quarter growing season, *Vicia sativa* can biologically fix nitrogen and penetrate deeply, increasing the soil nitrogen pool and secreting organic acids, activating insoluble basic ions such as P, K, and Ca. Simultaneously, its fresh stalks, when returned to the field, provide fresh organic matter with a high C / N ratio. ② In the second quarter of the following year, fresh *Vicia sativa* stalks are used as green manure and combined with biochar for incorporation. Biochar instantly provides a porous framework, increases pH buffering capacity and CEC (cation exchange capacity), while *Vicia sativa* residues, as an easily decomposable carbon source, stimulate microbial proliferation. The two form the core of a "charcoal-organic matter-microorganism" aggregate, promoting the rapid formation of large aggregates and significantly reducing viscosity and bulk density. ③ The combined action of charcoal and stubble stimulates microorganisms to secrete polysaccharides and globulin, enhancing aggregate stability. Simultaneously, the negatively charged surface of biochar reacts with the Ca released by *Vicia sativa*. 2+ Mg 2+ The formation of a "surface complex-bridging" structure by basal ions increases the saturation of exchangeable bases and effectively inhibits Al. 3+ and H + ④ The "gradual fertilization" model of base fertilizer + two top dressings matches the improved physical structure, reducing nitrogen leaching and increasing the activity of soil urease, catalase, and acid phosphatase, ensuring a continuous supply of nutrients throughout the crop's growth period; ⑤ Under the comprehensive effect, the pH of the yellow soil increases, organic matter increases, and ultimately crop yield increases by more than 25%, achieving targeted improvement of yellow soil fertility and a leap in productivity. This solves the problems of existing yellow soil, such as heavy texture, poor tilth, low natural fertility, high acidity, relatively weak water and fertilizer retention capacity, significant lack of exchangeable bases, base saturation generally less than 20%, and severe nitrogen leaching loss.

[0006] Compared to planting arrow peas and corn at the same time, this invention improves the biomass and nutrients of arrow peas by planting them in the fourth quarter of the previous year and then turning them back into the field as green manure and biochar before transplanting corn in the following year. This makes the nutrients decomposed at the same time more easily absorbed by crops.

[0007] Among these methods, using arrowhead pea as green manure in synergistic application with biochar not only provides abundant available mineral nutrients and organic matter, improves soil microbial community and diversity, and enhances enzyme activity, thereby increasing crop yield and quality, but also improves the ecological environment. While biochar and green manure alone can increase crop yield and soil fertility, they also pose potential risks. Synergistic application of biochar and green manure addresses these potential problems, creating a "carbon-nitrogen complementarity" and optimizing the carbon-nitrogen ratio. This approach can stimulate soil organic carbon mineralization while simultaneously increasing the soil's stable carbon pool and microbial availability.

[0008] Preferably, the method for improving yellow soil based on green manure and biochar further includes the following steps: S4. In the fourth quarter of the second year, the arrowhead peas were planted again in the yellow soil; S5. In the second quarter of the third year, the growing arrowhead pea seedlings were turned over as green manure and biochar, and then base fertilizer was applied to achieve secondary preliminary improvement of the yellow soil. S6. Transplant crops into the yellow soil that has undergone two preliminary improvements. Apply the first top dressing after the first interval to achieve four improvements to the yellow soil. Apply the second top dressing after the second interval to achieve five improvements to the yellow soil. After six improvements, the nutrients, aggregate stability and enzyme activity of the yellow soil are significantly improved, and the crops grown in the yellow soil that has undergone six improvements have higher yields.

[0009] Preferably, the biochar is prepared by carbonizing straw at a temperature of 380~400℃ under low oxygen conditions for 20 minutes to obtain biochar.

[0010] Preferably, the ratio of arrowhead peas to biochar during compaction is 22.5 t / hm. 2 7.5t / hm 2 And return it to the field in one go.

[0011] Preferably, the base fertilizer consists of nitrogen fertilizer, phosphorus fertilizer, and potassium fertilizer; The fertilizers applied during the first and second topdressing were nitrogen fertilizers.

[0012] Preferably, the total amount of nitrogen fertilizer applied as base fertilizer, nitrogen fertilizer applied as the first topdressing, and nitrogen fertilizer applied as the second topdressing is 391.3 kg / hm². 2 ; The application rate of superphosphate is 1000 kg / hm². 2 ; The application rate of potassium sulfate is 300 kg / hm². 2 .

[0013] Preferably, the mass ratio of nitrogen fertilizer applied in the base fertilizer, nitrogen fertilizer applied in the first topdressing, and nitrogen fertilizer applied in the second topdressing is 4:4:2.

[0014] Preferably, the nitrogen fertilizer is selected from urea, and the nitrogen (N) content in the nitrogen fertilizer is 46% by mass, that is, the total amount of N applied is 180 kg / hm. 2 ; The phosphate fertilizer is selected from superphosphate and phosphorus pentoxide (P2O5), and the mass percentage of phosphorus pentoxide (P2O5) in the phosphate fertilizer is 12%, that is, the application rate of P2O5 is 120 kg / hm. 2 ; The potassium fertilizer is selected from agricultural potassium sulfate and potassium oxide (K2O), and the potassium oxide (K2O) content in the potassium fertilizer is 50% by mass, that is, the application rate of K2O is 150 kg / hm. 2 .

[0015] Preferably, S2 includes: in the second quarter of the second year, 5 to 10 days before crop transplanting, turning in the growing arrowhead pea seedlings as green manure together with biochar, and then applying base fertilizer to achieve preliminary improvement of the yellow soil.

[0016] Preferably, S5 includes: in the second quarter of the third year, and 5 to 10 days before crop transplanting, turning in the growing arrowhead pea seedlings as green manure together with biochar, and then applying base fertilizer to achieve secondary preliminary improvement of the yellow soil.

[0017] Preferably, step S3 includes: transplanting crops into the preliminarily improved yellow soil, applying the first topdressing after an interval of 19-21 days to achieve the second improvement of the yellow soil, and applying the second topdressing after an interval of 41-45 days to achieve the third improvement of the yellow soil. After the three improvements, the nutrients, aggregate stability and enzyme activity of the yellow soil are significantly improved, and the yield of crops grown in the yellow soil after the three improvements is significantly increased.

[0018] Preferably, step S6 includes: transplanting crops into the yellow soil after two preliminary improvements, applying the first topdressing after an interval of 19-21 days to achieve four improvements to the yellow soil, applying the second topdressing after an interval of 41-45 days to achieve five improvements to the yellow soil. After six improvements, the nutrients, aggregate stability and enzyme activity of the yellow soil are significantly improved, and the yield of crops grown in the yellow soil after six improvements is higher.

[0019] Preferably, the crop is corn.

[0020] Preferably, the transplanting density of the corn is 5.423 × 10⁶. 5 Plant / hm 2 .

[0021] The beneficial effects of this invention are: This invention relates to a method for improving yellow soil based on green manure and biochar. This method achieves comprehensive improvement of yellow soil through a synergistic "biological-chemical-physical" multi-mechanism approach: ① During the fourth quarter growing season, *Vicia sativa* (arrow-footed pea) can biologically fix nitrogen and penetrate deeply, increasing the soil nitrogen pool and secreting organic acids, activating insoluble basic ions such as P, K, and Ca. Simultaneously, its fresh stalks, when returned to the field, provide fresh organic matter with a high C / N ratio. ② In the second quarter of the following year, fresh *Vicia sativa* stalks are used as green manure and combined with biochar for incorporation. Biochar instantly provides a porous framework, increases pH buffering capacity and CEC, while *Vicia sativa* residues, as an easily decomposable carbon source, stimulate microbial proliferation. The two form a core of "charcoal-organic matter-microorganism" aggregates, promoting rapid formation of large aggregates and significantly reducing bulk density and viscosity. ③ The combined action of charcoal and root stubble stimulates microorganisms to secrete polysaccharides and globulin, enhancing aggregate stability. Simultaneously, the negatively charged surface of biochar interacts with the Ca released by *Vicia sativa*. 2+ Mg 2+ The formation of a "surface complex-bridging" structure by basal ions increases the saturation of exchangeable bases and effectively inhibits Al. 3+ and H + ④ The "gradual fertilization" model of base fertilizer + two topdressings matches the improved physical structure, reducing nitrogen leaching and increasing the activities of soil urease, catalase, and acid phosphatase, ensuring a continuous supply of nutrients throughout the crop's growth period; ⑤ Under the comprehensive effect, yellow soil is improved, organic matter increases, and ultimately crop yield increases by more than 25%, achieving targeted improvement and productivity leap in strongly acidic, low-fertility yellow soil. It has promotional and application value in the field of soil improvement technology. Attached Figure Description

[0022] Figure 1 Distribution of aggregate composition for mechanical stability in yellow soil obtained by different methods; Figure 2 Distribution of water-stable aggregates in yellow soil obtained by different methods; Figure 3 The graph shows the correlation analysis results of carbon components in yellow soil. Figure 4 The graph shows the correlation analysis results between carbon components and aggregate stability indices in yellow soil. Figure 5 The graph shows the correlation analysis results between carbon components and enzyme activity in yellow soil. Figure 6 Figures showing maize yields in yellow soil improved using different methods; Figure 7 Figure showing the results of maize biomass planted in yellow soil improved by different methods (2023). Figure 8 Figure showing the results of maize biomass planted in yellow soil improved by different methods (2024). Figure 9 Figure showing the nitrogen accumulation results of maize planted in yellow soil improved by different methods (2023). Figure 10 Figure showing the nitrogen accumulation results of maize planted in yellow soil improved by different methods (2024). Detailed Implementation

[0023] The following description, with reference to preferred embodiments, illustrates the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are merely illustrative of the present invention and not intended to limit the scope of protection of the present invention.

[0024] The following examples were all conducted in a field experiment on yellow soil at the Guiyang Scientific Observation and Experiment Station of the Guizhou Academy of Agricultural Sciences in Guiyang City, Guizhou Province. This region has a subtropical humid and temperate climate, with an average temperature of 15.3℃, an average annual humidity of 77%, and an average annual rainfall of 1094.1 mm during the experiment. The soil in the experimental field was typical dry yellow soil of Guizhou, with the following basic physicochemical properties: pH 6.65, organic matter 44.45 g / kg, total nitrogen 2.00 g / kg, available phosphorus 33.95 mg / kg, and available potassium 219.89 mg / kg.

[0025] The maize variety tested was the tall-stalked maize variety 'Nongfa 710', provided by the Dryland Grain Research Institute of Guizhou Academy of Agricultural Sciences; the fertilizers tested were urea (containing 46% N), superphosphate (containing 12% P2O5), and potassium sulfate (containing 50% K2O).

[0026] Example 1 A method for improving yellow soil based on green manure and biochar includes the following steps: S1. On October 23, 2022, arrowhead peas were planted in yellow soil; S2. On April 21, 2023, corn seedlings were started. On April 25, 2023, the grown arrowhead pea seedlings were used as green manure and biochar at a rate of 22.5 t / hm². 2 7.5t / hm 2 The soil was plowed in the same proportion and returned to the field in one go. Then, on the day the corn seedlings were transplanted, May 2, 2023, base fertilizer was applied to achieve initial improvement of the yellow soil. The preparation method of biochar is as follows: straw is carbonized continuously at a temperature of 390℃ for 20 minutes under low oxygen conditions. The base fertilizer consists of nitrogen fertilizer, phosphorus fertilizer, and potassium fertilizer. The nitrogen fertilizer is urea, with a nitrogen (N) mass percentage of 46%. The phosphorus fertilizer is superphosphate and phosphorus pentoxide (P2O5), with a phosphorus pentoxide (P2O5) mass percentage of 12%. The potassium fertilizer is agricultural potassium sulfate and potassium oxide (K2O), with a potassium oxide (K2O) mass percentage of 50%. The application rate of nitrogen (N) is 72 kg / hm². 2 The application rate of nitrogen (N) is 4.8 kg / mu; the application rate of phosphorus pentoxide (P2O5) is 120 kg / hm. 2 The application rate of phosphorus pentoxide (P2O5) is 8 kg / mu; the application rate of potassium oxide (K2O) is 150 kg / hm. 2 That is, the application rate of potassium oxide (K2O) is 10 kg / mu; S3. Transplant the corn seedlings into the preliminarily improved yellow soil at a planting density of 5.423 × 10⁶. 5 Plant / hm 2 The first topdressing was applied on May 22, 2023, to achieve the second improvement of the yellow soil. The second topdressing was applied on July 3, 2023, to achieve the third improvement of the yellow soil. The corn was harvested on September 3, 2023. The yield of corn planted in the yellow soil after the three improvements was significantly higher than that of corn planted in the unimproved yellow soil. The fertilizer applied for both the first and second topdressing was urea. The nitrogen (N) application rate for the first topdressing was 72 kg / hm². 2 The amount of nitrogen (N) applied for the second top dressing is 36 kg / hm². 2 The nitrogen fertilizer is selected from urea, and contains 46% N by mass.

[0027] Example 2 A method for improving yellow soil based on green manure and biochar includes the following steps: S1. Based on the improved yellow soil of Example 1, arrowhead peas were replanted in the yellow soil on October 23, 2023; S2. On April 21, 2024, corn seedlings were started. On April 25, 2024, the grown arrowhead pea seedlings were used as green manure and biochar at a rate of 22.5 t / hm². 2 7.5t / hm 2 The soil is compacted together with the corn seedlings in a single application, and then base fertilizer is applied on the day the corn seedlings are transplanted, May 2, 2024, to achieve a secondary initial improvement of the yellow soil. The preparation method of biochar is as follows: straw is carbonized continuously at a temperature of 390℃ for 20 minutes under low oxygen conditions. The base fertilizer consists of nitrogen fertilizer, phosphorus fertilizer, and potassium fertilizer. The nitrogen fertilizer is urea, with a nitrogen (N) mass percentage of 46%. The phosphorus fertilizer is superphosphate and phosphorus pentoxide (P2O5), with a phosphorus pentoxide (P2O5) mass percentage of 12%. The potassium fertilizer is agricultural potassium sulfate and potassium oxide (K2O), with potassium oxide (K2O) mass percentage of 50%. The application rate of nitrogen (N) is 72 kg / hm². 2 The application rate of nitrogen (N) is 4.8 kg / mu; the application rate of phosphorus pentoxide (P2O5) is 120 kg / hm. 2 The application rate of phosphorus pentoxide (P2O5) is 8 kg / mu; the application rate of potassium oxide (K2O) is 150 kg / hm. 2 That is, the application rate of potassium oxide (K2O) is 10 kg / mu; S3. Transplant the corn seedlings into the preliminarily improved yellow soil at a planting density of 5.423 × 10⁶. 5 Plant / hm 2 The first topdressing was applied on May 22, 2024, to achieve the fourth improvement of the yellow soil. The second topdressing was applied on July 3, 2024, to achieve the fifth improvement of the yellow soil. The corn was harvested on September 3, 2024. The increase in corn yield from yellow soil that had undergone six improvements compared to yellow soil that had not been improved was higher than the increase in corn yield from yellow soil that had undergone three improvements compared to yellow soil that had not been improved. The fertilizer applied for both the first and second topdressing was urea. The nitrogen (N) application rate for the first topdressing was 72 kg / hm². 2 The amount of nitrogen (N) applied for the second top dressing is 36 kg / hm². 2 The nitrogen fertilizer is selected from urea, and contains 46% N by mass.

[0028] Example 3 A method for improving yellow soil based on green manure and biochar includes the following steps: S1. On October 23, 2022, arrowhead peas were planted in yellow soil; S2. On April 21, 2023, corn seedlings were started. On April 25, 2023, the grown arrowhead pea seedlings were used as green manure and biochar at a rate of 22.5 t / hm². 2 7.5t / hm 2 The soil was plowed in the same proportion and returned to the field in one go. Then, on the day the corn seedlings were transplanted, May 2, 2023, base fertilizer was applied to achieve initial improvement of the yellow soil. The preparation method of biochar is as follows: straw is carbonized continuously at a temperature of 390℃ for 20 minutes under low oxygen conditions. The base fertilizer consists of nitrogen fertilizer, phosphorus fertilizer, and potassium fertilizer. The nitrogen fertilizer is urea, with a nitrogen (N) mass percentage of 46%. The phosphorus fertilizer is superphosphate and P2O5, with a phosphorus pentoxide (P2O5) mass percentage of 12%. The potassium fertilizer is agricultural potassium sulfate and K2O, with a potassium oxide (K2O) mass percentage of 50%. The nitrogen (N) application rate was 57.6 kg / hm². 2 The application rate of nitrogen (N) is 3.84 kg / mu; the application rate of phosphorus pentoxide (P2O5) is 120 kg / hm. 2 The application rate of phosphorus pentoxide (P2O5) is 8 kg / mu; the application rate of potassium oxide (K2O) is 150 kg / hm. 2 That is, the application rate of potassium oxide (K2O) is 10 kg / mu; S3. Transplant the corn seedlings into the preliminarily improved yellow soil at a planting density of 5.423 × 10⁶. 5 Plant / hm 2 The first topdressing was applied on May 22, 2023, to achieve the second improvement of the yellow soil. The second topdressing was applied on July 3, 2023, to achieve the third improvement of the yellow soil. The corn was harvested on September 3, 2023. The yield of corn planted in the yellow soil after the three improvements was significantly higher than that of corn planted in the unimproved yellow soil. The fertilizer applied for both the first and second topdressing was urea. The nitrogen (N) application rate for the first topdressing was 57.6 kg / hm². 2 The amount of nitrogen (N) applied in the second top dressing was 28.8 kg / hm². 2 The nitrogen fertilizer is selected from urea, and contains 46% N by mass.

[0029] Example 4 A method for improving yellow soil based on green manure and biochar includes the following steps: S1. Based on the improved yellow soil of Example 3, arrowhead peas were planted in the yellow soil on October 23, 2023; S2. On April 21, 2024, corn seedlings were started. On April 25, 2024, the grown arrowhead pea seedlings were used as green manure and biochar at a rate of 22.5 t / hm². 2 7.5t / hm 2 The soil is plowed in the same proportion and returned to the field in one go. Then, base fertilizer is applied on the day the corn seedlings are transplanted, which is May 2, 2024, to achieve the initial improvement of the yellow soil. The preparation method of biochar is as follows: straw is carbonized continuously at a temperature of 390℃ for 20 minutes under low oxygen conditions. The base fertilizer consists of nitrogen fertilizer, phosphorus fertilizer, and potassium fertilizer. The nitrogen fertilizer is urea, with a nitrogen (N) mass percentage of 46%; the phosphorus fertilizer is superphosphate, with a phosphorus pentoxide (P2O5) mass percentage of 12%; and the potassium fertilizer is agricultural potassium sulfate, with a potassium oxide (K2O) mass percentage of 50%. The nitrogen (N) application rate was 57.6 kg / hm². 2 The application rate of nitrogen (N) is 3.84 kg / mu; the application rate of phosphorus pentoxide (P2O5) is 120 kg / hm. 2 The application rate of phosphorus pentoxide (P2O5) is 8 kg / mu; the application rate of potassium oxide (K2O) is 150 kg / hm. 2 That is, the application rate of potassium oxide (K2O) is 10 kg / mu; S3. Transplant the corn seedlings into the preliminarily improved yellow soil at a planting density of 5.423 × 10⁶. 5 Plant / hm 2 The first topdressing was applied on May 22, 2024, to achieve the second improvement of the yellow soil. The second topdressing was applied on July 3, 2024, to achieve the third improvement of the yellow soil. The corn was harvested on September 3, 2024. The yield of corn planted in the yellow soil after the three improvements was significantly higher than that of corn planted in the unimproved yellow soil. The fertilizer applied for both the first and second topdressing was urea. The nitrogen (N) application rate for the first topdressing was 57.6 kg / hm². 2 The amount of nitrogen (N) applied in the second top dressing was 28.8 kg / hm². 2 The nitrogen fertilizer is selected from urea, and the mass percentage of N is 46%.

[0030] Example 5 A method for improving yellow soil based on green manure and biochar includes the following steps: S1. On October 23, 2022, arrowhead peas were planted in yellow soil; S2. On April 21, 2023, corn seedlings were started, and on April 25, 2023, the grown arrowhead pea seedlings were used as green manure at a rate of 22.5 t / hm². 2 The soil was plowed and compacted to achieve a one-time return to the field. Then, on the day the corn seedlings were transplanted, May 2, 2023, base fertilizer was applied to achieve initial improvement of the yellow soil. The base fertilizer consists of nitrogen fertilizer, phosphorus fertilizer, and potassium fertilizer. The nitrogen fertilizer is urea, with a nitrogen (N) mass percentage of 46%. The phosphorus fertilizer is superphosphate and phosphorus pentoxide (P2O5), with a phosphorus pentoxide (P2O5) mass percentage of 12%. The potassium fertilizer is agricultural potassium sulfate and potassium oxide (K2O), with potassium oxide (K2O) mass percentage of 50%. The application rate of nitrogen (N) is 72 kg / hm². 2 The application rate of nitrogen (N) is 4.8 kg / mu; the application rate of phosphorus pentoxide (P2O5) is 120 kg / hm. 2 The application rate of phosphorus pentoxide (P2O5) is 8 kg / mu; the application rate of potassium oxide (K2O) is 150 kg / hm. 2 That is, the application rate of potassium oxide (K2O) is 10 kg / mu; S3. Transplant the corn seedlings into the preliminarily improved yellow soil at a planting density of 5.423 × 10⁶. 5 Plant / hm 2 The first topdressing was applied on May 22, 2023, to achieve the second improvement of the yellow soil. The second topdressing was applied on July 3, 2023, to achieve the third improvement of the yellow soil. The corn was harvested on September 3, 2023. The yield of corn planted in the yellow soil after the three improvements was significantly higher than that of corn planted in the unimproved yellow soil. The fertilizer applied for both the first and second topdressing was urea. The nitrogen (N) application rate for the first topdressing was 72 kg / hm². 2 The amount of nitrogen (N) applied for the second top dressing is 36 kg / hm². 2 The nitrogen fertilizer is selected from urea, and the mass percentage of N is 46%.

[0031] Example 6 A method for improving yellow soil based on green manure and biochar includes the following steps: S1. Based on the improved yellow soil of Example 5, arrowhead peas were replanted in the yellow soil on October 23, 2023; S2. On April 21, 2024, corn seedlings were started, and on April 25, 2024, the grown arrowhead pea seedlings were used as green manure at a rate of 22.5 t / hm². 2 The soil was plowed and compacted to achieve a one-time return to the field. Then, on the day the corn seedlings were transplanted, May 2, 2024, base fertilizer was applied to achieve a secondary preliminary improvement of the yellow soil. The base fertilizer consists of nitrogen fertilizer, phosphorus fertilizer, and potassium fertilizer. The nitrogen fertilizer is urea, with a nitrogen (N) mass percentage of 46%. The phosphorus fertilizer is superphosphate and phosphorus pentoxide (P2O5), with a phosphorus pentoxide (P2O5) mass percentage of 12%. The potassium fertilizer is agricultural potassium sulfate and potassium oxide (K2O), with potassium oxide (K2O) mass percentage of 50%. The application rate of nitrogen (N) is 72 kg / hm². 2 The application rate of nitrogen (N) is 4.8 kg / mu; the application rate of phosphorus pentoxide (P2O5) is 120 kg / hm. 2The application rate of phosphorus pentoxide (P2O5) is 8 kg / mu; the application rate of potassium oxide (K2O) is 150 kg / hm. 2 That is, the application rate of potassium oxide (K2O) is 10 kg / mu; S3. Transplant the corn seedlings into the preliminarily improved yellow soil at a planting density of 5.423 × 10⁶. 5 Plant / hm 2 The first topdressing was applied on May 22, 2024, to achieve the fourth improvement of the yellow soil. The second topdressing was applied on July 3, 2024, to achieve the fifth improvement of the yellow soil. The corn was harvested on September 3, 2024. The increase in corn yield from yellow soil that had undergone six improvements compared to yellow soil that had not been improved was higher than the increase in corn yield from yellow soil that had undergone three improvements compared to yellow soil that had not been improved. The fertilizer applied for both the first and second topdressing was urea. The nitrogen (N) application rate for the first topdressing was 72 kg / hm². 2 The amount of nitrogen (N) applied for the second top dressing is 36 kg / hm². 2 The nitrogen fertilizer is selected from urea, and the mass percentage of N is 46%.

[0032] Example 7 A method for improving yellow soil based on green manure and biochar includes the following steps: S1. Corn seedlings were started on April 21, 2023, and biochar was applied at a rate of 7.5 t / hm² on April 25, 2023. 2 The soil was plowed and compacted to achieve a one-time return to the field. Then, on the day the corn seedlings were transplanted, May 2, 2023, base fertilizer was applied to achieve initial improvement of the yellow soil. The preparation method of biochar is as follows: straw is carbonized continuously at a temperature of 390℃ for 20 minutes under low oxygen conditions. The base fertilizer consists of nitrogen fertilizer, phosphorus fertilizer, and potassium fertilizer. The nitrogen fertilizer is urea, with a nitrogen (N) mass percentage of 46%. The phosphorus fertilizer is superphosphate and phosphorus pentoxide (P2O5), with a phosphorus pentoxide (P2O5) mass percentage of 12%. The potassium fertilizer is agricultural potassium sulfate and potassium oxide (K2O), with potassium oxide (K2O) mass percentage of 50%. The application rate of nitrogen (N) is 72 kg / hm². 2 The application rate of nitrogen (N) is 4.8 kg / mu; the application rate of phosphorus pentoxide (P2O5) is 120 kg / hm. 2 The application rate of phosphorus pentoxide (P2O5) is 8 kg / mu; the application rate of potassium oxide (K2O) is 150 kg / hm. 2That is, the application rate of potassium oxide (K2O) is 10 kg / mu; S2. Transplant the corn seedlings into the preliminarily improved yellow soil at a planting density of 5.423 × 10⁶. 5 Plant / hm 2 The first topdressing was applied on May 22, 2023, to achieve the second improvement of the yellow soil. The second topdressing was applied on July 3, 2023, to achieve the third improvement of the yellow soil. The corn was harvested on September 3, 2023. The yield of corn planted in the yellow soil after the three improvements was significantly higher than that of corn planted in the unimproved yellow soil. The fertilizer applied for both the first and second topdressing was urea. The nitrogen (N) application rate for the first topdressing was 72 kg / hm². 2 The amount of nitrogen (N) applied for the second top dressing is 36 kg / hm². 2 The nitrogen fertilizer is selected from urea, and the mass percentage of N is 46%.

[0033] Example 8 A method for improving yellow soil based on green manure and biochar includes the following steps: S1. On April 21, 2024, corn seedlings were raised. Based on the improved yellow soil of Example 7, biochar was again applied on April 25, 2024, at a rate of 7.5 t / hm². 2 The soil was plowed and compacted to achieve a one-time return to the field. Then, on the day the corn seedlings were transplanted, May 2, 2024, base fertilizer was applied to achieve a secondary preliminary improvement of the yellow soil. The preparation method of biochar is as follows: straw is carbonized continuously at a temperature of 390℃ for 20 minutes under low oxygen conditions. The base fertilizer consists of nitrogen fertilizer, phosphorus fertilizer, and potassium fertilizer. The nitrogen fertilizer is urea, with a nitrogen (N) mass percentage of 46%. The phosphorus fertilizer is superphosphate and phosphorus pentoxide (P2O5), with a phosphorus pentoxide (P2O5) mass percentage of 12%. The potassium fertilizer is agricultural potassium sulfate and potassium oxide (K2O), with potassium oxide (K2O) mass percentage of 50%. The application rate of nitrogen (N) is 72 kg / hm². 2 The application rate of nitrogen (N) is 4.8 kg / mu; the application rate of phosphorus pentoxide (P2O5) is 120 kg / hm. 2 The application rate of phosphorus pentoxide (P2O5) is 8 kg / mu; the application rate of potassium oxide (K2O) is 150 kg / hm. 2 That is, the application rate of potassium oxide (K2O) is 10 kg / mu; S2. Transplant the corn seedlings into the preliminarily improved yellow soil at a planting density of 5.423 × 10⁶. 5 Plant / hm2 The first topdressing was applied on May 22, 2024, to achieve the fourth improvement of the yellow soil. The second topdressing was applied on July 3, 2024, to achieve the fifth improvement of the yellow soil. The corn was harvested on September 3, 2024. The increase in corn yield from yellow soil that had undergone six improvements compared to yellow soil that had not been improved was higher than the increase in corn yield from yellow soil that had undergone three improvements compared to yellow soil that had not been improved. The fertilizer applied for both the first and second topdressing was urea. The nitrogen (N) application rate for the first topdressing was 72 kg / hm². 2 The amount of nitrogen (N) applied for the second top dressing is 36 kg / hm². 2 The nitrogen fertilizer is selected from urea, and the mass percentage of N is 46%.

[0034] Comparative Example 1 A method for growing maize in yellow soil includes the following steps: S1. Corn seedlings were started on April 21, 2023, and transplanted into yellow soil on May 2, 2023, at a planting density of 5.423 × 10⁶. 5 Plant / hm 2 The first topdressing was applied on May 22, 2023, the second topdressing was applied on July 3, 2023, and the corn was harvested on September 3, 2023. The fertilizer applied for both the first and second topdressing was urea. The nitrogen (N) application rate for the first topdressing was 72 kg / hm². 2 The amount of nitrogen (N) applied for the second top dressing is 36 kg / hm². 2 The nitrogen fertilizer is selected from urea, and the mass percentage of N is 46%.

[0035] Comparative Example 2 A method for growing maize in yellow soil includes the following steps: S1. On April 21, 2024, corn seedlings were raised. Based on the yellow soil after corn planting in Comparative Example 1, the corn seedlings were transplanted into the yellow soil on May 2, 2024, at a planting density of 5.423 × 10⁻⁶. 5 Plant / hm 2 The first topdressing was applied on May 22, 2024, the second topdressing was applied on July 3, 2024, and the corn was harvested on September 3, 2024. The fertilizer applied for both the first and second topdressing was urea. The nitrogen (N) application rate for the first topdressing was 72 kg / hm². 2 The amount of nitrogen (N) applied for the second top dressing is 36 kg / hm². 2The nitrogen fertilizer is selected from urea, and the mass percentage of N is 46%.

[0036] Comparative Example 3 A method for growing maize in yellow soil includes the following steps: S1. Corn seedlings were started on April 21, 2023, and transplanted into yellow soil on May 2, 2023, at a planting density of 5.423 × 10⁶. 5 Plant / hm 2 The corn was harvested on September 3, 2023.

[0037] Comparative Example 4 A method for growing maize in yellow soil includes the following steps: S1. Corn seedlings were started on April 21, 2024. Based on the yellow soil after corn planting in Comparative Example 3, the corn seedlings were transplanted into the yellow soil on May 2, 2024, at a planting density of 5.423 × 10⁻⁶. 5 Plant / hm 2 The corn was harvested on September 3, 2024.

[0038] Detection and Analysis Soil fertility is a crucial indicator of soil quality, directly impacting soil productivity. It is typically assessed using chemical properties such as soil organic matter and nutrient content, as well as physical properties such as aggregate stability. Soil aggregates, as a fundamental component of soil structure, are a key factor influencing soil fertility levels. Ideal aggregates effectively promote the sequestration of organic matter, and their formation and stability are influenced by the content and properties of organic carbon in the soil. Stable soil aggregates provide a favorable environment for microbial activity, promoting increased microbial biomass and enzyme activity, thereby contributing to soil carbon mineralization.

[0039] 1) Soil nutrient content test The specific operating steps are as follows: Nutrient content tests were conducted on the yellow soils planted with maize in Examples 2, 4, 6, 8, Comparative Example 2, and Comparative Example 4. Specifically, pH was measured using a pH meter, organic matter content was determined using the potassium dichromate titration method, total nitrogen content was determined using the semi-micro Kjeldahl method, available phosphorus content was determined using the molybdenum-antimony colorimetric method, and available potassium content was determined using flame photometry. The results are shown in Table 2.

[0040] Table 2 shows the nutrient content of yellow soil after different methods of improvement. Note: Different lowercase letters indicate significant differences between different treatments (P<0.05). The same applies below.

[0041] In Table 2, 0%N corresponds to Example 4, 100%N corresponds to Example 2, 100%NM corresponds to Example 6, 100%NB corresponds to Example 8, 100%NMB corresponds to Example 2, and 80%NMB corresponds to Example 4.

[0042] Table 2 shows that the nutrient content of the yellow soil varied among different treatments. Compared with 0% N, nitrogen application (100% N) increased the contents of OM, TN, AP, and AK by 1.94 g / kg, 0.13 g / kg, 0.81 mg / kg, and 2.59 mg / kg, respectively. After biochar and green manure were applied to the field separately, the contents of soil pH, OM, TN, AP, and AK under 100% NM and 100% NB treatments all showed an increasing trend compared with 100% N, increasing by 0.04 g / kg, 7.97 g / kg, 0.30 g / kg, 0.79 mg / kg, and 8.42 mg / kg, and 0.09 g / kg, 7.92 g / kg, 0.27 g / kg, 4.64 mg / kg, and 20.66 mg / kg, respectively. After biochar was applied in conjunction with green manure (Pistacia chinensis) and returned to the field, the soil pH, OM, TN, AP, and AK contents in the 100% NMB treatment were 6.80 g / kg, 59.05 g / kg, 2.50 g / kg, 43.20 mg / kg, and 249.55 mg / kg, respectively, which were higher than other treatments. When nitrogen fertilizer application was reduced by 20%, the soil nutrient content was slightly lower than that in the 100% NMB treatment, but higher than that in the 100% NM and 100% NB treatments. The overall soil pH, OM, TN, AP, and AK contents showed the following order: 100% NMB > 80% NMB > 100% NM ≈ 100% NB > 100% N > 0% N; there was no significant difference in soil pH among the treatments.

[0043] 2) Determination of soil aggregate distribution The specific operating steps are as follows: Soil aggregate distribution tests were conducted on the yellow soils after corn planting in Examples 2, 4, 6, 8, Comparative Example 2, and Comparative Example 4.

[0044] Soil aggregate stability indices are described using mean weight diameter (MWD), mean geometric diameter (GMD), aggregate breakdown rate (PAD), and macroaggregate content (MA). MWD, GMD, and PAD values ​​characterize the stability of aggregates to water; higher MWD and GMD, and smaller PAD, indicate stronger aggregate stability. MA represents the structure of soil aggregates, and its quantity is positively correlated with soil fertility. The calculation formula is as follows: Using data on agglomerates of various particle sizes, the average weight diameter (MWD), average geometric diameter (GMD), breakdown rate (PAD), and large agglomerates (MA) were calculated, as shown in equations (I) to (III): In equations (I) to (III), MWD is the average mass diameter of soil aggregates (unit: mm); GMD is the average geometric diameter of soil aggregates (unit: mm); Xi is the average diameter of the i-th grade soil aggregates (unit: mm); Wi is the percentage of the i-th grade aggregates in the total soil mass (unit: %); Wd is the mass fraction of dry sieve aggregates with an aperture > 0.25 mm; Ww is the mass fraction of wet and dry sieve aggregates with an aperture > 0.25 mm; i represents the particle size class of the soil sieved, with sieved soil particles < 0.25 mm classified as grade 1, sieved soil particles between 0.25 and 0.5 mm classified as grade 2, sieved soil particles between 0.5 and 1 mm classified as grade 3, sieved soil particles between 1 and 2 mm classified as grade 4, sieved soil particles between 2 and 5 mm classified as grade 5, and sieved soil particles greater than 5 mm classified as grade 6. This indicates the average diameter of soil aggregates across all grades (unit: mm).

[0045] Mean weight diameter (MWD) can be divided into mean weight diameter of mechanical aggregates (MS-MWD) and mean weight diameter of water-stable aggregates (WS-MWD); mean geometric diameter (GMD) can be divided into mean geometric diameter of mechanical aggregates (MS-GMD) and mean geometric diameter of water-stable aggregates (WS-GMD); macroaggregate content (MA) can be divided into mechanical macroaggregate content (MS-MA) and water-stable macroaggregate content (WS-MA).

[0046] The results are as follows Figure 1 and Figure 2 As shown.

[0047] Figure 1 and Figure 2 In this context, 0%N corresponds to Example 4, 100%N corresponds to Example 2, 100%NM corresponds to Example 6, 100%NB corresponds to Example 8, 100%NMB corresponds to Example 2, and 80%NMB corresponds to Example 4.

[0048] from Figure 1 and Figure 2As can be seen, the particle size distributions of mechanically stable and water-stable aggregates show opposite trends. Regarding mechanically stable aggregates, the distribution of mechanically stable aggregates in each treatment shows an increasing trend with increasing particle size. Compared to 0% N, each treatment reduced the content of aggregates <0.25 mm by 5.86% (100% N), 32.33% (100% NM), 32.49% (100% NB), 45.04% (100% NMB), and 39.81% (80% NMB), respectively, while the content of aggregates 0.25–5 mm increased accordingly. Compared to 100% N, the biochar and green manure treatments reduced the content of aggregates 0.25–5 mm and increased the content of aggregates >5 mm. Regarding water-stable aggregates, the distribution of water-stable aggregates in each treatment showed a decreasing trend with increasing particle size. Compared with 100% N, the biochar and green manure return treatments reduced the content of aggregates <0.25 mm by 18.06% (100% NM), 18.09% (100% NB), 28.29% (100% NMB), and 25.27% (80% NMB), respectively, while the content of aggregates 0.25~5 mm increased accordingly.

[0049] The differences in soil aggregate stability are shown in Table 3.

[0050] Table 3 shows the average weight diameter, average geometric diameter, large aggregate content, and aggregate destruction rate of aggregates in yellow soil improved by different methods. In Table 3, 0%N corresponds to Example 4, 100%N corresponds to Example 2, 100%NM corresponds to Example 6, 100%NB corresponds to Example 8, 100%NMB corresponds to Example 2, and 80%NMB corresponds to Example 4.

[0051] Table 3 shows that the stability of yellow soil aggregates varied among different treatments. In terms of mechanical stability indices, the MS-MWD was lowest in 100% N treatment at 2.68 mm, lower than other treatments by 0.28–0.63 mm. The MS-MWD of biochar and green manure treatments was higher than that of 100% N treatment, by 0.32–0.63 mm respectively. The MS-GMD of 100% NB treatment was 2.56 mm, higher than other treatments by 0.07–0.66 mm, but not significantly different from 100% NM and 100% NMB. Aggregate distribution in all treatments was dominated by MS-MA, all above 90%, with 100% NMB showing the highest at 96.59%, higher than other treatments by 0.54–3.16 percentage points, but not significantly different from 100% NM, 100% NB, and 80% NMB. In terms of water stability indicators, WS-MWD was lowest with 100% N at 0.79 mm, which was 0.12–0.32 mm lower than other treatments. The WS-MWD of biochar and green manure treatments was higher than that of 100% N, which was 0.13–0.32 mm higher, respectively. The WS-GMD of 100% NMB was 0.66 mm, which was 0.03–0.17 mm higher than other treatments, but not significantly different from that of 80% NMB. The WS-MA was highest with 100% NMB at 64.48%, which was 1.49–14.01 percentage points higher than other treatments, but not significantly different from that of 80% NMB. The content of large aggregates >0.25 mm was slightly higher than that of microaggregates <0.25 mm in each treatment. In terms of PAD, the PAD of the 100%N treatment was 46.19%, which was significantly higher than that of other treatments by 4.47 to 12.95 percentage points. The PAD of the 100%NMB treatment was the lowest, at 33.24%, which was significantly lower than that of other treatments by 4.11 to 12.95 percentage points, except that it was not significantly different from that of the 80%NMB treatment.

[0052] 3) Soil carbon composition determination The specific operating steps are as follows: Carbon composition tests were conducted on the yellow soil samples from Examples 2, 4, 6, 8, Comparative Example 2, and Comparative Example 4 after corn planting. The testing methods were as follows: Total soil carbon (TC) was determined by mass spectrometry; soil organic carbon (OC) and readily oxidizable organic carbon (ROC) were determined by potassium dichromate oxidation; soluble organic carbon (DOC) was determined by deionized water extraction-mass spectrometry; microbial biomass carbon (MBC) was determined by chloroform fumigation; and particulate organic carbon (POC) was determined by sodium hexametaphosphate extraction-potassium dichromate external heating method. Active organic carbon (AOC) was the sum of DOC, MBC, and ROC. The results are shown in Table 4.

[0053] Table 4 shows the carbon content in yellow soil improved by different methods. In Table 4, 0%N corresponds to Example 4, 100%N corresponds to Example 2, 100%NM corresponds to Example 6, 100%NB corresponds to Example 8, 100%NMB corresponds to Example 2, and 80%NMB corresponds to Example 4.

[0054] Table 4 shows that the carbon composition of yellow soil differed among different treatments. Compared with 0% N, nitrogen application increased the carbon composition of yellow soil. In 100% N soil, TC, OC, ROC, DOC, MBC, AOC, and POC increased by 0.92 g / kg, 0.12 g / kg, 0.14 g / kg, 8.35 mg / kg, 26.64 g / kg, 1.74 percentage points, and 0.54 mg / kg, respectively. When biochar and green manure were applied separately and returned to the field, the carbon composition of yellow soil in 100% NM and 100% NB treatments showed a significant increasing trend compared to 100% N. After biochar was applied in conjunction with green manure, the soil TC, OC, ROC, DOC, MBC, AOC, and POC in the 100% NMB treatment were 33.50 g / kg, 34.25 g / kg, 2.93 g / kg, 116.89 mg / kg, 507.77 g / kg, 35.55%, and 5.40 mg / kg, respectively, all higher than other treatments. When nitrogen fertilizer application was reduced by 20%, the carbon composition of the yellow soil in the 80% NMB treatment was lower than that in the 100% NMB treatment, but higher than that in the 100% NM and 100% NB treatments.

[0055] 4) Soil enzyme activity assay The specific operating steps are as follows: Enzyme activity tests were conducted on the yellow soils of Examples 2, 4, 6, 8, Comparative Example 2, and Comparative Example 4 after corn planting. The determination method was as follows: the soil superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), polyphenol oxidase (PPO), cellulase, and β-glucosidase were determined by a kit-visible spectrophotometry. The results are shown in Table 5.

[0056] Table 5 shows the enzyme activity test results of yellow soil. In Table 5, 0%N corresponds to Example 4, 100%N corresponds to Example 2, 100%NM corresponds to Example 6, 100%NB corresponds to Example 8, 100%NMB corresponds to Example 2, and 80%NMB corresponds to Example 4.

[0057] Table 5 shows that the enzyme activities in yellow soil varied among different treatments. Compared with 0% N, nitrogen application increased yellow soil enzyme activity. In 100% N soil, SOD, CAT, POD, PPO, Cellulase, and β-Glucosidase increased by 13.89 U / g, 0.77 μmol / d / g, 0.14 mol / d / g, 2.33 mg / d / g, 9.15 mg / d / g, and 8.19 μmol / d / g, respectively. When biochar and green manure were applied separately and returned to the field, the enzyme activities in yellow soil under 100% NM and 100% NB treatments showed a significant increasing trend compared to 100% N. After biochar was applied in conjunction with green manure, the levels of SOD, CAT, POD, PPO, Cellulase, and β-Glucosidase in the soil treated with 100% NMB increased by 292.06 U / g, 37.31 μmol / d / g, 24.17 mol / d / g, 33.60 mg / d / g, 258.22 mg / d / g, and 50.18 μmol / d / g, respectively, all higher than in other treatments. When nitrogen fertilizer application was reduced by 20%, the enzyme activity in the yellow soil treated with 80% NMB was lower than that in 100% NMB, but higher than that in 100% NM and 100% NB.

[0058] 5) Analysis of the correlation between soil carbon composition and aggregates, enzyme activity, and influencing factors. Correlation analysis of carbon components in yellow soil yielded the following results: Figure 3 As shown.

[0059] from Figure 3 Correlation analysis of carbon components in yellow soil revealed significant or highly significant positive correlations among different soil carbon components. Soil total carbon (TC) showed a significant positive correlation with total organic carbon (POC), and highly significant positive correlations with total organic carbon (OC), total organic carbon (ROC), total organic carbon (DOC), total organic carbon (MBC), and total organic carbon (AOC). Except for TC, all other carbon components in yellow soil showed highly significant positive correlations among themselves.

[0060] Correlation analysis was performed on the carbon components of yellow soil with aggregate stability indicators and enzyme activity, and the results are as follows: Figure 4 and Figure 5 As shown.

[0061] from Figure 4 and Figure 5Analysis showed that the carbon components of yellow soil were all significantly positively correlated with SOD, CAT, PPO, and Cellulase. Except for the significant positive correlation between TC, DOC, MBC and POD, the carbon components of yellow soil were not significantly correlated with POD. Except for the significant positive correlation between ROC, DOC and β-Glucosidase, the carbon components of yellow soil were all significantly positively correlated with β-Glucosidase. All yellow soil carbon components showed a highly significant positive correlation with MS-MA. Except for yellow soil DOC and POC, which were not correlated with WS-MWD and WS-GMD, other yellow soil carbon components showed significant or highly significant positive correlations with WS-MWD and WS-GMD. Except for soil POC, which was not correlated with WS-MA, other yellow soil carbon components showed significant or highly significant positive correlations with WS-MA. Except for yellow soil OC, which showed a highly significant positive correlation with MS-MWD, other yellow soil carbon components did not show a significant relationship with MS-MWD. Except for yellow soil DOC, MBC, and POC, which were not correlated with MS-GMD, other yellow soil carbon components showed significant or highly significant positive correlations with MS-GMD. Except for yellow soil POC, which was not correlated with PAD, yellow soil carbon components showed significant or highly significant negative correlations with PAD. The correlation between yellow soil carbon components and water-stable aggregate indicators was better than that between yellow soil carbon components and mechanical aggregate indicators. Overall, the carbon content of yellow soil showed a good correlation with enzyme activity and water-stable aggregate index. The higher the carbon content of yellow soil, the larger the water-stable aggregate index, the smaller the PAD, and the more stable the structure of yellow soil.

[0062] 6) Maize yield measurement The corn harvested in Examples 1 to 8 and Comparative Examples 1 to 4 was weighed to obtain the corn yield results as follows: Figure 6 As shown.

[0063] Figure 6 In the examples, 0%N corresponds to Comparative Example 3 and Comparative Example 4, 100%N corresponds to Comparative Example 1 and Comparative Example 2, 100%NM corresponds to Example 5 and Example 6, 100%NB corresponds to Example 7 and Example 8, 100%NMB corresponds to Example 1 and Example 2, and 80%NMB corresponds to Example 3 and Example 4.

[0064] from Figure 6 Analysis shows that maize yields varied across different years and treatments. Compared to 0% N, nitrogen application significantly increased maize yield; the yields under 100% N treatment increased by 1470.2 and 2783.2 kg / hm² in two years compared to 0% N treatment. 2 When biochar and green manure were returned to the field separately, the maize yields of 100% NM and 100% NB were 411.3 and 393.0 kg / hm² higher, respectively, than those of 100% N. 2 and 389.6, 320.9 kg / hm2 Among the various methods, green manure application was slightly more effective than biochar. After applying biochar in conjunction with green manure, the maize yields with 100% NMB (non-biologically modified) were 11082.4 and 10471.5 kg / hm² in two years, respectively. 2 It is 323.1 and 576.2 kg / hm higher than 100% NM and 100% NB, respectively. 2 and 344.8, 648.3 kg / hm 2 When nitrogen fertilizer application was reduced by 20%, the maize yields under 80% NMB (nitrogen-moistened mulch) conditions were 11050.5 kg / hm² and 10117.4 kg / hm² in two years, respectively. 2 It was 31.9 and 354.2 kg / hm lower than 100% NMB. 2 However, it is 291.2 and 222.0 kg / hm higher than 100% NM and 100% NB, respectively. 2 and 312.9, 294.1 kg / hm 2 The above results indicate that returning both biochar and green manure to the field can increase maize yield. When biochar and green manure are returned to the field in a coordinated manner, maize yield can be maintained or increased while reducing nitrogen by 20%.

[0065] The effects of different improvement methods on maize yield components of yellow soil are shown in Table 6.

[0066] Table 6 shows the components of maize yield. Note: Different lowercase letters indicate significant differences between different treatments in the same year (P<0.05). The same applies below.

[0067] In Table 6, 0%N corresponds to Comparative Example 3 (2023) and Comparative Example 4 (2024), 100%N corresponds to Comparative Example 1 (2023) and Comparative Example 2 (2024), 100%NM corresponds to Example 5 (2023) and Example 6 (2024), 100%NB corresponds to Example 7 (2023) and Example 8 (2024), 100%NMB corresponds to Example 1 (2023) and Example 2 (2024), and 80%NMB corresponds to Example 3 (2023) and Example 4 (2024).

[0068] Table 6 shows that the components of maize yield differed significantly among different treatments. Similar trends were observed in 2023 and 2024, with nitrogen-applied treatments showing a significant increase in ear row number, kernel number per row, and 100-kernel weight compared to the non-nitrogen-applied treatment. Regarding ear row number, the 100% NMB treatment had the highest number in both 2023 and 2024, at 20.00 and 19.00 rows respectively, exceeding other treatments by 0.50–2.67 and 0.25–1.92 rows respectively. When nitrogen fertilizer application was reduced by 20%, the ear row number in the 80% NMB treatment was 19.50 and 18.75 rows in the two years, lower than 100% NMB by 0.50 and 0.25 rows respectively, but higher than 100% NM and 100% NB by 0.83 and 0.25 rows respectively, and 0.92 and 0.25 rows respectively. Regarding the number of kernels per row, similar to the results for the number of rows per ear, the 100% NMB treatment had the highest number in both 2023 and 2024, at 39.46 and 37.75 kernels respectively, which were 0.46–4.00 and 0.29–5.63 rows higher than other treatments, respectively. When nitrogen fertilizer application was reduced by 20%, the number of rows per ear in maize with 80% NMB was 39.00 and 37.46 kernels in the two years, which were 0.46 and 0.29 kernels lower than with 100% NMB, but 0.67 and 0.96 kernels higher than with 100% NM and 100% NB, respectively, and 0.50 and 0.79 kernels higher, respectively. Regarding the 100-grain weight, similar to the results for ear row number and row number of kernels, the highest values ​​were observed in 2023 and 2024 with 100% NMB, at 40.89 and 37.20 g respectively, exceeding the other treatments by 0.29–5.35 and 0.08–5.48 rows respectively. When nitrogen fertilizer application was reduced by 20%, the ear row number of maize with 80% NMB was 40.60 and 37.13 g in the two years, respectively, lower than 100% NMB by 0.29 and 0.08 g, but higher than 100% NM and 100% NB by 0.85 and 0.34 g, and 0.78 and 0.44 g respectively. These findings indicate that returning both biochar and green manure to the field can improve the components of maize yield. Furthermore, with the synergistic application of biochar and green manure, a 20% reduction in nitrogen fertilizer can maintain or improve these components of maize yield.

[0069] 7) Maize biomass measurement The maize biomass harvested in Examples 1 to 8 and Comparative Examples 1 to 4 was weighed, and the maize biomass results are as follows: Figure 7 and Figure 8 As shown.

[0070] Figure 7 In the example, 0%N corresponds to Example 3, 100%N corresponds to Example 1, 100%NM corresponds to Example 5, 100%NB corresponds to Example 7, 100%NMB corresponds to Example 1, and 80%NMB corresponds to Example 3.

[0071] Figure 8In the example, 0%N corresponds to Example 4, 100%N corresponds to Example 2, 100%NM corresponds to Example 5, 100%NB corresponds to Example 8, 100%NMB corresponds to Example 2, and 80%NMB corresponds to Example 4.

[0072] from Figure 7 and Figure 8 The results show that maize biomass varied across different treatments. Compared to 0% N, nitrogen application significantly increased maize biomass; the biomass under 100% N treatment was 18672.7 kg / hm² in 2023 and 18356.0 kg / hm² in 2024. 2 The concentrations were 2071.2 and 4682.8 kg / hm higher than 0%N, respectively. 2 After biochar and green manure were returned to the field separately, the maize biomass of 100% NM and 100% NB was 1037.7 and 2727.0 kg / hm² higher, respectively, than that of 100% N. 2 and 1095.9, 2661.7 kg / hm 2 After biochar was applied in conjunction with green manure and returned to the field, the biomass of maize with 100% NMB was 20832.4 kg / hm² in two years and 22852.4 kg / hm² in two years, respectively. 2 It is 1122.0 and 1769.5 kg / hm higher than 100% NM and 100% NB, respectively. 2 and 1063.9, 1834.7 kg / hm 2 When nitrogen fertilizer application is reduced by 20%, the maize biomass under 80% NMB coverage is 20570.8 kg / hm² and 21777.5 kg / hm² in two years, respectively. 2 It was 261.6 and 1074.9 kg / hm lower than that of 100% NMB. 2 However, it is 860.4 and 694.5 kg / hm higher than 100% NM and 100% NB, respectively. 2 and 802.3, 759.8 kg / hm 2 .

[0073] 8) Measurement of nitrogen accumulation in maize The nitrogen accumulation of maize harvested in Examples 1 to 8 and Comparative Examples 1 to 4 was determined. The determination method was as follows: H2SO4-H2O2 combined digestion was used, and the total nitrogen content was determined by the Kjeldahl method. The nitrogen accumulation of each part of the maize was calculated by multiplying the nitrogen content of each part by the biomass. The sum of the nitrogen accumulation of each part was the total nitrogen accumulation of the maize. The results of the maize nitrogen accumulation are as follows. Figure 9 and Figure 10 As shown.

[0074] Figure 9In the example, 0%N corresponds to Example 3, 100%N corresponds to Example 1, 100%NM corresponds to Example 5, 100%NB corresponds to Example 7, 100%NMB corresponds to Example 1, and 80%NMB corresponds to Example 3.

[0075] Figure 10 In the example, 0%N corresponds to Example 4, 100%N corresponds to Example 2, 100%NM corresponds to Example 5, 100%NB corresponds to Example 8, 100%NMB corresponds to Example 2, and 80%NMB corresponds to Example 4.

[0076] from Figure 9 and Figure 10 The results show that the nitrogen accumulation in maize varies across different years and treatments. Compared to 0% N, nitrogen application significantly increases nitrogen accumulation in maize; the nitrogen accumulation in maize under 100% N treatment increased by 47.12 and 60.97 kg / hm² over two years compared to 0% N treatment. 2 After biochar and green manure were returned to the field separately, the cumulative nitrogen content of maize under 100% NM and 100% NB conditions was 15.66 and 31.91 kg / hm² higher, respectively, than that under 100% N conditions. 2 and 16.16, 31.88 kg / hm 2 After biochar was applied in conjunction with green manure and returned to the field, the cumulative nitrogen content of maize using 100% NMB was 237.36 kg / hm² and 232.78 kg / hm² over two years, respectively. 2 It is 18.97 and 19.10 kg / hm higher than 100% NM and 100% NB, respectively. 2 and 18.47, 19.12 kg / hm 2 When nitrogen fertilizer application was reduced by 20%, the cumulative nitrogen content of maize under 80% NMB for two years was 229.66 kg / hm² and 220.86 kg / hm², respectively. 2 It was 7.69 and 11.92 kg / hm lower than 100% NMB. 2 However, it is 11.28 and 7.18 kg / hm higher than 100% NM and 100% NB, respectively. 2 and 10.77, 7.20 kg / hm 2 .

[0077] 9) Analysis of nitrogen absorption and utilization efficiency in maize Nitrogen agronomic efficiency (AE) N = (Yield in nitrogen-treated area - Yield in non-nitrogen-treated area) / Nitrogen application rate Nitrogen Partial Productivity (PEP) N =Yield in nitrogen-applied area / Amount of nitrogen applied Nitrogen absorption and utilization efficiency (RE) N = (Total cumulative nitrogen in the nitrogen-applied area - Total cumulative nitrogen in the non-nitrogen-applied area) / Nitrogen application rate × 100% The results are shown in Table 7.

[0078] Table 7 shows the nitrogen absorption and utilization efficiency of maize. Table 7 shows that there are differences in nitrogen use efficiency among different treatments in maize. N In terms of 100% N AE N The AE (acetic acid) levels for maize in 2023 and 2024 were 8.17 and 15.46 kg / kg, respectively. After biochar and green manure were returned to the field separately, the AE levels for maize were 100% NM and 100% NB for two years. N Compared to 100% N, the AE of maize was 2.28 and 2.19 kg / kg higher, and 2.16 and 1.19 kg / kg higher, respectively; after biochar was combined with green manure and returned to the field, the AE of maize with 100% NMB was significantly higher in two years. N The AE values ​​were 12.25 and 20.85 kg / kg, respectively, which were 1.80 and 3.20 kg / kg higher than those of 100% NM and 1.92 and 3.60 kg / kg higher than those of 100% NB. When nitrogen fertilizer application was reduced by 20%, the AE values ​​of 80% NMB for two years were significantly higher than those of corn. N The highest values ​​were 15.09 and 23.60 kg / kg, respectively, which were higher than the other treatments (2.84–6.92 and 2.75–8.14 kg / kg). PEP N In terms of 80% NMB two-year corn PEP N The highest values ​​were 76.74 and 70.26 kg / kg in the two years, respectively, which were significantly higher than the other treatments (15.17–19.25 and 12.08–17.47 kg / kg); 100% N maize PEP N The lowest values ​​were 57.49 and 52.79 kg / kg for the two years respectively. RE N In terms of 100% N RE N In 2023 and 2024, the percentages were 26.18% and 33.87% respectively. After biochar and green manure were returned to the field separately, the corn RE (reproductive rate) was 100% NM and 100% NB for two years. N Compared to 100% N, the percentages were 8.70, 17.73, and 8.98, 17.72 percentage points higher, respectively; after biochar was combined with green manure and returned to the field, the two-year RE of maize with 100% NMB was significantly higher. N The percentages were 45.42% and 62.21%, respectively, which were 10.54 and 10.61 percentage points higher than those of 100% NM and 10.26 and 10.62 percentage points higher than those of 100% NB. When nitrogen fertilizer application was reduced by 20%, the two-year RE (reduction rate) of corn using 80% NMB was... N The highest rates were 51.43% and 69.49%, respectively, which were 6.01–25.25 and 7.28–35.62 percentage points higher than other treatments.

[0079] In summary, the yellow soil improvement method based on green manure and biochar of this invention, compared with 0% N, shows that nitrogen application (100% N) can increase soil organic matter, total nitrogen, available phosphorus, and available potassium, indicating that fertilizer is an effective source of nutrients for improving soil fertility. Compared with 100% N, the soil nutrient levels are significantly improved when biochar and green manure (arrow-footed pea) are applied and returned to the field alone (100% NM, 100% NB), indicating that biochar and green manure can provide corresponding nutrients, thereby improving soil nutrient levels. When biochar and green manure are synergistically applied to the field, the soil organic matter, total nitrogen, available phosphorus, and available potassium contents of 100% NMB are higher than those of 100% NM and 100% NB, indicating a positive synergistic effect of biochar and green manure application. When nitrogen fertilizer application is reduced by 20%, the soil organic matter, total nitrogen, available phosphorus, and available potassium contents of 80% MNB are higher than those of 100% N, 100% NM, and 100% NB, indicating a nutrient substitution effect of biochar and green manure. Simultaneously, soil enzyme activity also shows an increasing trend after synergistic application of biochar and green manure, thus promoting the decomposition of green manure and increasing soil carbon content. Furthermore, regardless of whether biochar and green manure are applied alone or synergistically, the aggregate stability indices MWD, GMD, and MA are all higher than those of 100% N, while PAD is lower than that of 100% N, indicating that both biochar and green manure, applied alone or synergistically, can improve soil structural stability. Furthermore, regardless of mechanical stability or water stability, the MWD and GMD of 100% N soil were lower than those of 0% N soil, while PAD was higher than that of 0% N soil. This is because nitrogen addition exacerbates the decrease in the total amount of exchangeable cations in the soil. On the other hand, nitrogen application leads to a decrease in soil fungal biomass, and the formation of large aggregates is positively correlated with fungal biomass. Additionally, due to the poor water and fertilizer retention capacity of Guizhou yellow soil, this ultimately promotes the transformation of large aggregates into smaller aggregates, reducing MWD and GMD, and thus decreasing soil stability. Correlation analysis showed a good correlation between soil carbon components and WS-MWD, WS-GMD, WS-MA, PAD, and enzyme activity. This indicates that rhizosphere soil, by increasing nutrient input and aggregate stability, provides a favorable environment for microbial activity, leading to a significant increase in microbial biomass and enzyme activity, thereby promoting soil carbon mineralization. This has significant application value in the field of soil improvement technology.

[0080] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A method for improving yellow soil based on green manure and biochar, characterized in that, Includes the following steps: S1. Plant arrowhead peas in yellow soil in the fourth quarter of the first year; S2. In the second quarter of the second year, the growing arrowhead pea seedlings were turned over as green manure together with biochar, and then base fertilizer was applied to achieve the initial improvement of the yellow soil. S3. Transplant the crops into the initially improved yellow soil. Apply the first top dressing after the first interval to achieve the second improvement of the yellow soil. Apply the second top dressing after the second interval to achieve the third improvement of the yellow soil. After the three improvements, the nutrients, aggregate stability and enzyme activity of the yellow soil are significantly improved.

2. The method for improving yellow soil based on green manure and biochar according to claim 1, characterized in that, It also includes the following steps: S4. In the fourth quarter of the second year, the arrowhead peas were planted again in the yellow soil; S5. In the second quarter of the third year, the growing arrowhead pea seedlings were turned over as green manure and biochar, and then base fertilizer was applied to achieve secondary preliminary improvement of the yellow soil. S6. Transplant the crops into the yellow soil that has undergone two preliminary improvements. Apply the first top dressing after the first interval to achieve four improvements to the yellow soil. Apply the second top dressing after the second interval to achieve five improvements to the yellow soil. After six improvements, the nutrients, aggregate stability and enzyme activity of the yellow soil are significantly improved.

3. The method for improving yellow soil based on green manure and biochar according to claim 2, characterized in that, The method for preparing biochar is as follows: straw is carbonized continuously for 20 minutes in the absence of air at a temperature of 380~400℃ to obtain biochar.

4. The method for improving yellow soil based on green manure and biochar according to claim 2, characterized in that, The ratio of arrowhead peas to biochar during compaction is 22.5 t / hm. 2 7.5t / hm 2 And return it to the field in one go.

5. The method for improving yellow soil based on green manure and biochar according to claim 2, characterized in that, The base fertilizer consists of nitrogen fertilizer, phosphorus fertilizer, and potassium fertilizer; The fertilizers applied during the first and second topdressing were nitrogen fertilizers.

6. The method for improving yellow soil based on green manure and biochar according to claim 5, characterized in that, The total amount of nitrogen fertilizer applied as base fertilizer, as well as the nitrogen fertilizer applied as the first topdressing and the nitrogen fertilizer applied as the second topdressing, is 391.3 kg / hm². 2 ; The application rate of superphosphate is 1000 kg / hm². 2 ; The application rate of potassium sulfate is 300 kg / hm². 2 .

7. The method for improving yellow soil based on green manure and biochar according to claim 5, characterized in that, The mass ratio of nitrogen fertilizer applied in the base fertilizer, the nitrogen fertilizer applied in the first topdressing, and the nitrogen fertilizer applied in the second topdressing is 4:4:

2.

8. The method for improving yellow soil based on green manure and biochar according to claim 5, characterized in that, The nitrogen fertilizer is selected from urea, and the nitrogen (N) content in the nitrogen fertilizer is 46% by mass, that is, the total amount of N applied is 180 kg / hm. 2 ; The phosphate fertilizer is selected from superphosphate and phosphorus pentoxide (P2O5), and the mass percentage of phosphorus pentoxide (P2O5) in the phosphate fertilizer is 12%, that is, the application rate of P2O5 is 120 kg / hm. 2 ; The potassium fertilizer is selected from agricultural potassium sulfate and potassium oxide (K2O), and the potassium oxide (K2O) content in the potassium fertilizer is 50% by mass, that is, the application rate of K2O is 150 kg / hm. 2 .

9. The method for improving yellow soil based on green manure and biochar according to claim 2, characterized in that, S2 includes: in the second quarter of the second year, 5 to 10 days before crop transplanting, turning in the growing arrowhead pea seedlings as green manure together with biochar, and then applying base fertilizer to achieve the initial improvement of yellow soil. And / or, S5 includes: in the second quarter of the third year, and 5 to 10 days before crop transplanting, turning in the growing arrowhead pea seedlings as green manure together with biochar, and then applying base fertilizer to achieve secondary preliminary improvement of the yellow soil. And / or, S3 includes: transplanting crops into the preliminarily improved yellow soil, applying the first topdressing after an interval of 19-21 days to achieve the second improvement of the yellow soil, and applying the second topdressing after an interval of 41-45 days to achieve the third improvement of the yellow soil. After the three improvements, the nutrients, aggregate stability and enzyme activity of the yellow soil are significantly improved, and the yield of crops grown in the yellow soil after the three improvements is significantly improved. And / or, S6 includes: transplanting crops into the yellow soil after two preliminary improvements, applying the first topdressing after an interval of 19 to 21 days to achieve four improvements to the yellow soil, applying the second topdressing after an interval of 41 to 45 days to achieve five improvements to the yellow soil, and after six improvements, the nutrients, aggregate stability and enzyme activity of the yellow soil are significantly improved.

10. The method for improving yellow soil based on green manure and biochar according to claim 1, characterized in that, The crop in question is corn.

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