A method for improving soil quality of acidified red paddy soil by using carbon-rich amendment

Abstract

This invention discloses a method for improving the soil quality of acidified red soil paddy fields using carbon-enriched amendments, belonging to the field of agricultural soil improvement technology. Targeting acidified red soil paddy fields, this invention uses at least one of rice straw, sheep manure organic fertilizer, microbial organic fertilizer, and biochar as a carbon-enriched amendment, applying it as a base fertilizer in the field according to the specified ratio, and evenly mixing it into the 0-20 cm soil tillage layer. The biochar is obtained by anaerobic pyrolysis of rice straw at 300-500 °C, and each carbon-enriched amendment has a defined and appropriate application dosage. This invention, through the precise application of multiple carbon-enriched amendments, can effectively reduce soil bulk density, increase soil pH, reduce the content of exchangeable acids and active aluminum in the soil, replenish soil basic ions and organic matter nutrients, optimize the soil bacterial community structure, and significantly improve the overall soil quality of acidified red soil paddy fields. The method is standardized, easy to replicate, and highly applicable, suitable for large-scale promotion and application in acidified red soil paddy areas.

Description

Technical Field

[0001] This invention belongs to the field of agricultural soil improvement technology, and in particular relates to a method for improving the soil quality of acidified red soil paddy fields using a carbon-rich soil conditioner. Background Technology

[0002] In South my country, most paddy fields are acidic red soil. Under the long-term continuous rice cultivation model, there are widespread problems such as aggravated soil acidification, high bulk density, nutrient imbalance, lack of base ions, and prominent aluminum toxicity. This leads to the decline of arable land fertility and low paddy field productivity, resulting in large areas of acidic and low-yield paddy fields, which seriously restricts the stable and high yield of rice and the sustainable use of arable land.

[0003] Conventional methods of increasing yields by relying on chemical fertilizers can easily exacerbate soil acidification, compaction, and nutrient loss, failing to fundamentally improve the soil properties of acidic, low-yield paddy fields. Carbon-rich soil conditioners possess multiple functions, including increasing soil organic carbon content, regulating soil pH, passivating active aluminum ions, replenishing basic nutrients, improving soil pore structure, and regulating soil microbial community structure. They are ideal materials for improving acidified red soil and enhancing paddy field soil quality. However, current technologies lack standardized and replicable operational methods for the appropriate application and dosage ratios of different types of carbon-rich soil conditioners in acidified red soil paddy fields, hindering large-scale promotion and application. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for improving the soil quality of acidified red soil paddy fields using carbon-rich soil conditioners. This method solves the problems of existing technologies, such as the lack of unified standards for the appropriate application methods and dosage ratios of carbon-rich soil conditioners, non-standard operation, and difficulty in large-scale promotion, thereby achieving the improvement of acidified red soil, enhancement of soil fertility, and optimization of the micro-ecology.

[0005] This invention provides a method for improving the soil quality of acidified red soil paddy fields using a carbon-rich amendment, comprising: applying a carbon-rich amendment to the soil of the acidified red soil paddy field, and uniformly mixing the carbon-rich amendment into the tillage layer as a base fertilizer; wherein the carbon-rich amendment is at least one of rice straw, sheep manure organic fertilizer, microbial organic fertilizer, and biochar.

[0006] Furthermore, the initial soil pH of the acidified red soil paddy field is ≤5.5.

[0007] Furthermore, the carbon-rich amendment is incorporated into the topsoil layer at a depth of 0–20 cm.

[0008] Furthermore, the biochar is prepared by pyrolysis of rice straw under anaerobic conditions at 300–500°C.

[0009] Furthermore, the application rate of rice straw is 5 to 10 tons per hectare.

[0010] Furthermore, the application rate of the biochar is 5 to 10 tons per hectare.

[0011] Furthermore, the application rate of the microbial organic fertilizer is 8–15 tons per hectare.

[0012] Furthermore, the application rate of the sheep manure organic fertilizer is 10-18 tons / hectare.

[0013] The present invention also provides an application of the above-mentioned carbon-rich soil conditioner in improving the soil quality of acidified red soil paddy fields.

[0014] Compared with the prior art, the beneficial effects of the present invention are:

[0015] 1. Significantly alleviates soil acidification and reduces aluminum toxicity.

[0016] It can effectively increase the pH of acidic red soil, reduce the content of exchangeable acid, exchangeable hydrogen and exchangeable aluminum in the soil, eliminate the toxicity of aluminum ions to rice roots, and significantly enhance the soil's acid buffering capacity.

[0017] 2. Comprehensively improve soil physical and chemical properties and enhance soil fertility.

[0018] It significantly reduces soil bulk density and optimizes soil structure; it also significantly increases soil organic matter, available nitrogen, available phosphorus, available potassium, and exchangeable calcium and magnesium content, thereby enhancing nutrient supply capacity and cation exchange capacity, and fundamentally improving the soil quality of degraded paddy fields.

[0019] 3. Optimize the structure of soil microbial communities

[0020] It enhances soil bacterial diversity and abundance, promotes the proliferation of beneficial nutrient-producing bacteria, inhibits acid-tolerant oligotrophic harmful bacteria, improves the soil micro-ecological environment, and strengthens nutrient cycling and transformation efficiency.

[0021] 4. Significant improvement in soil quality and stable yield increase.

[0022] It can significantly improve the soil quality index (SQI), which is significantly positively correlated with rice yield; without increasing fertilizer input, it can significantly increase rice yield, and the yield increase effect is stable and sustainable.

[0023] 5. The improved method is green, efficient, and highly applicable.

[0024] It uses readily available, low-cost, and environmentally friendly carbon-rich amendments such as rice straw, biochar, microbial organic fertilizer, and sheep manure organic fertilizer. The application method is simple and suitable for large-scale application in acidified red soil paddy fields in the south, combining ecological and economic benefits. Attached Figure Description

[0025] Figure 1 The monthly average variations in precipitation and temperature during the experiment;

[0026] Figure 2 Scanning electron microscope image of the changes in surface structure of straw after straw is returned to the field;

[0027] Figure 3 In this context, A represents the decomposition rate of the straw. Figure 3 B represents the average daily decomposition rate of straw; different lowercase letters indicate significant differences between groups (p < 0.05).

[0028] Figure 4 In section A, the effect of different carbon-rich soil conditioners on soil bulk density is shown. Figure 4 B represents the effect of different carbon-enriched modifiers on pH;

[0029] Figure 5 In section A, different carbon-enriched amendments affect soil NH4+. + The effect of -N; Figure 5 B represents the effects of different carbon-enriched amendments on NO3. - The effect of -N; Figure 5 C represents the effect of different carbon-enriched amendments on available phosphorus in the soil;

[0030] Figure 6 The effect of carbon-rich modifiers on bacterial α-diversity; Figure 6 In the figure, A represents the number of bacterial amplicon sequence variants (ASVs); Figure 6 B represents Good's coverage. Figure 6 C represents the Shannon index; Figure 6 D represents the Chao1 index;

[0031] Figure 7 The relative abundance of soil bacteria at the phylum level after application of carbon-rich soil conditioner;

[0032] Figure 8 Changes in bacterial β-diversity after application of carbon-rich amendment; Figure 8 In the middle, A represents nonmetric multidimensional scaling (NMDS). Figure 8 Principal coordinate analysis (PCoA) in B;

[0033] Figure 9 The relationship between environmental factors and bacterial communities; Figure 9 In the middle, A represents canonical correlation analysis (CCA). Figure 9 B represents the Pearson correlation coefficient between the dominant bacterial community (top 10) and environmental factors; * indicates significant difference (P < 0.05), ** indicates extremely significant difference (P < 0.01).

[0034] Figure 10 In Figure A, the effect of carbon-rich amendments on the soil quality index (SQI) is represented. Figure 10 In the middle, B represents the correlation between SQI and rice yield;

[0035] Figure 11 Model analysis of the impact of carbon-rich soil conditioners on soil quality; Figure 10 In the model A, the main factors affecting soil quality are represented by a random forest model. Figure 11 In section B, the structural equation model for the regulation of soil quality by carbon-rich amendments is used; soil quality is characterized by the soil quality index; the numbers next to the arrows are standardized path coefficients, and the thickness of the arrows corresponds to the magnitude of the path coefficients; blue arrows represent positive effects, red arrows represent negative effects, and dashed lines represent no significant effect; R 2 This represents the proportion explained by variance. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] Example 1

[0038] 1. Materials and Methods

[0039] 1.1 Test Site

[0040] This experiment was conducted from December 2023 to December 2025 at the Heyuan Branch Field Experiment Station of the Guangdong Provincial Laboratory of Lingnan Modern Agricultural Science and Technology, with geographical coordinates of 24°6′19″N, 114°46′35″E. The experimental site is located in northeastern Guangdong Province, within the South Asian subtropical monsoon climate zone. The region has an average annual temperature of 20.7℃, average annual precipitation of 1700 mm, annual sunshine duration of 1687 hours, annual accumulated temperature of 7436℃, and a frost-free period of 305 days. Monthly temperature and precipitation variations during the experimental period are shown in [Figure number missing]. Figure 1 .

[0041] The experimental field is a long-term continuous cropping paddy field, where single-season rice has been planted for 15 consecutive years, with an average yield of approximately 7.5 tons per hectare under conventional cultivation. -1 The tested soil is classified as red soil in the Chinese soil classification system; according to the classification standard of the International Union of Soil Sciences (IUSS) (2014), it belongs to the ferroaluminous rudimentary soil, and the parent material of the soil is Quaternary red weathered sediments.

[0042] The soil samples were collected from the 0-20 cm topsoil layer of local low-yield paddy fields. After pretreatment, the soil samples were used for pot experiments, and their basic physicochemical properties were measured. The results are shown in Table 1.

[0043] Table 1. Basic physical and chemical properties of the tested soil.

[0044]

[0045] 1.2 Experimental Design

[0046] The experiment employed a completely randomized block design, with each treatment replicated three times to ensure the reliability and reproducibility of the experimental data. A total of five treatment groups were set up, as follows: ① Chemical fertilizer control (CK); ② Straw return to the field (JG); ③ Microbial organic fertilizer (effective viable bacteria count ≥10). 9 g-1, YPY); ④ Sheep manure compost (YF); ⑤ Straw biochar (SWT). The basic physicochemical properties of each carbon-enriching amendment (straw, biochar, microbial organic fertilizer, sheep manure compost) are shown in Table 2. Each experimental plot was 30m². 2 (6 m × 5 m) Isolation ridges with a width of 50 cm and a height of 30 cm are set between the small areas to effectively prevent fertilizer migration and water flow between different small areas and avoid cross-contamination.

[0047] The fertilization plan strictly followed local rice cultivation standards and combined with the experimental design requirements: chemical fertilizers were applied to both the CK and JG treatments according to local conventional fertilization rates, specifically 180 kg / hm² of nitrogen fertilizer. 2 P2O5 60 kg / hm 2 K2O 80 kg / hm 2 Chemical fertilizers used include urea (containing 46% N), superphosphate (containing 12% P2O5), and potassium chloride (containing 60% K2O). No additional chemical fertilizers were applied to the YPY, YF, and SWT treatments. Fertilization was carried out in stages: nitrogen fertilizer (N) was applied in three applications: 50% as basal fertilizer, 30% as tillering fertilizer, and 20% as heading fertilizer; phosphorus fertilizer (P2O5) was applied entirely as basal fertilizer in one application; potassium fertilizer (K2O) was applied in two applications: 60% as basal fertilizer and 40% as heading fertilizer. Basal fertilizer was applied at the beginning of June each year during tillage, tillering fertilizer was applied at the beginning of July, and heading fertilizer was applied at the beginning of August.

[0048] The application rate of each carbon-enriching amendment was determined based on the unified standard for organic carbon input (9.19 kg of organic carbon input per plot). Considering the local low-yield paddy field yield and the rice-to-straw ratio in Guangdong Province (1:1.06), the amount of rice straw returned to the field for the JG treatment was set at 8 t / hm². 2 The application rates were as follows: 24 kg of rice straw per plot; the application rates of carbon-enriched amendments for SWT, YPY, and YF treatments were 19.13 kg, 31.11 kg, and 40.43 kg per plot, respectively. The sources of each amendment were clearly defined: the rice straw was taken from low-yield paddy fields surrounding the experimental site; the straw biochar was prepared by pyrolysis of rice straw under anaerobic conditions at 350-400℃; the microbial organic fertilizer was purchased from Yipinyun Farm Technology (Shenzhen) Co., Ltd.; and the sheep manure compost was purchased from Gansu Jinzihua Agriculture and Animal Husbandry Co., Ltd.

[0049] Table 2 Characteristics of Carbon-Rich Modifiers

[0050]

[0051] The experimental rice variety used was Meixiangzhan 2. Throughout the two-year experimental period, the sowing, transplanting, and harvesting times remained consistent: sowing in mid-June, transplanting in early July, and harvesting at the end of October each year. The planting density was 25 cm × 20 cm, with 5 seedlings transplanted per hill. From transplanting to harvest, field management measures, including pest and disease control and weed control, strictly followed local rice production standard operating procedures to ensure consistent field management conditions across treatments and minimize interference from irrelevant factors on the experimental results.

[0052] Rice straw pretreatment and application methods: After the rice straw is naturally air-dried, it is cut into 3-5 cm pieces using a rice straw shredder to facilitate subsequent plowing and decomposition. During field tillage in early June each year, the rice straw and other carbon-rich soil amendments are evenly spread on the field surface. Then, a reverse straw tiller (model 1GFM-220) is used to evenly compact and mix it into the 0-20 cm topsoil layer, ensuring full contact between the amendments and the soil.

[0053] The dynamic monitoring of rice straw decomposition employed the nylon mesh bag method: 10 cm × 8 cm nylon mesh bags with a mesh diameter of 0.15 mm were used, each containing 10.00 g of dry rice straw and sealed with nylon thread. On the day of field tillage, the mesh bags were horizontally buried in the soil of the JG treatment plots to a depth of 15 cm, with 15 mesh bags placed in each plot, ensuring no overlap. Sampling was conducted in early July, early August, early September, early October, and early November each year, with 3 mesh bags removed from each plot each time. The collected rice straw samples were rinsed with deionized water to remove surface soil particles and plant roots, then dried in a 70℃ oven for 48 hours until constant weight. After weighing, the samples were ground and used for observing changes in the microstructure and analyzing the decomposition characteristics of the rice straw.

[0054] 1.3 Straw decomposition and microstructure analysis

[0055] The decomposition rate of the recycled rice straw was determined using the above-mentioned method. This decomposition rate was determined by the weight loss method (Gao et al., 2025).

[0056] The calculation formula is as follows:

[0057] (1)

[0058] In the formula, SD represents the decomposition rate of straw (%), m0 is the initial weight of straw (g), and m t The residual weight of the straw (g).

[0059] The microstructure of straw surface was observed using a Zeiss MultiSEM 706 scanning electron microscope. After vacuum drying and vacuum gold sputtering pretreatment, straw samples were scanned and imaged at an accelerating voltage of 2 kV and a magnification of 1000–2000x to obtain the surface morphology characteristics of the straw.

[0060] 1.4 Analysis of Soil Physicochemical Properties

[0061] A five-point sampling method was used to collect soil samples from the 0–20 cm topsoil layer at five key growth stages of rice: mid-tillering (MT), initial panicle differentiation (PI), heading (HD), grain-filling (FI, 20 days after heading), and physiological maturity (PM, 7 days before harvest). Fresh soil samples were passed through a 2 mm sieve and extracted with 1 mol / L KCl solution. Soil ammonium nitrogen (NH4+) was determined using a continuous flow analyzer (SAN++, Skalar, Netherlands). + -N), nitrate nitrogen (NO3) - -N content.

[0062] Fresh soil samples at each growth stage were extracted using 0.03 mol / L NH4F–0.025 mol / L HCl, and the available phosphorus content in the soil was determined using a flow analyzer. After rice harvest, three 100 cm³ soil samples were randomly collected from the 0–20 cm soil layer in each treatment plot. 3 Uncirculated soil cores are used for soil bulk density determination; soil bulk density is calculated as the ratio of the mass of soil dried at 105℃ to the volume of the soil core.

[0063] After rice harvest, topsoil samples from the 0-20 cm layer were collected from each plot using a 2.5 cm diameter soil auger and a five-point sampling method. The samples were then mixed to prepare a composite soil sample. After removing plant roots, organic residues, and gravel from the fresh soil sample, it was divided into two portions: one portion was sieved through a 2 mm sieve and stored at −80℃ for soil microbial community characteristic analysis; the other portion was sieved through an 8 mm sieve, air-dried naturally, and then sieved through 2 mm and 0.25 mm sieves respectively for the determination of conventional soil nutrients and trace elements.

[0064] Soil pH, organic matter (SOM), total nitrogen (TN), total phosphorus (TP), alkaline nitrogen (AN), and available potassium (AK) were determined according to conventional agricultural chemical analysis methods. Soil pH was measured using a FE20 pH meter (Mettler-Toledo, Switzerland) with a soil-to-water ratio of 1:5 (w / v); soil organic matter was determined using the potassium dichromate titration method; total nitrogen was determined using the semi-micro Kjeldahl method; total phosphorus was determined using the molybdenum-antimony colorimetric method; alkaline nitrogen was determined using the alkaline diffusion method; and available potassium was determined using ammonium acetate extraction.

[0065] Soil exchangeable acid (EA), exchangeable aluminum (EA1) 3+ ), exchangeable hydrogen (EH) +After extraction with 1 mol / L KCl, the soil exchangeable calcium (ECa) was determined by titration with 0.02 mol / L NaOH. 2+ Exchangeable magnesium (EMG) 2+ Extracted with 1 mol / L NH4OAc and determined by inductively coupled plasma mass spectrometry (ICP-MS).

[0066] 1.5 Determination of bacterial characteristics in soil

[0067] This embodiment only collected soil samples from rice at the physiological maturity stage in 2025 for soil bacterial community diversity analysis. 500 mg of fresh soil sample was weighed and stored at −80℃. Following the kit instructions, total DNA was extracted from each soil sample using the FastDNA™ SPIN Soil Genomic DNA Extraction Kit (MP Biomedicals, USA). The extracted DNA was tested for integrity by 1% agarose gel electrophoresis; DNA concentration and purity were determined using a NanoDrop NC2000 spectrophotometer (Thermo Fisher Scientific, Waltham, Massachusetts, USA). After passing the tests, the samples were stored at −20℃ for later use.

[0068] Total DNA extracted from qualified soil samples was sent to Novogene Biotechnology Co., Ltd. for PCR amplification and high-throughput sequencing analysis. Specific primers for the V4–V5 region of the bacterial 16S rRNA gene, 515F / 806R, were used. The primer sequences were: 515F: 5′-GTGCCAGCMGCCGCGGTAA-3′, 806R: 5′-GGACTACHVGGGTWTCTAAT-3′.

[0069] The PCR amplification program was set as follows: 98℃ pre-denaturation for 1 min; followed by 30 cycles, each cycle consisting of 98℃ denaturation for 10 s, 53℃ annealing for 30 s, and 72℃ extension for 30 s; and a final extension at 72℃ for 5 min. The PCR amplification products were purified by 2% agarose gel electrophoresis, and the purified amplification products were mixed in equimolar proportions and subjected to paired-end high-throughput sequencing using the Illumina NovaSeq sequencing platform.

[0070] Sequencing data were analyzed using QIIME2 software for bacterial microbiome bioinformatics. The DADA2 plugin embedded in QIIME2 was used for sequence quality filtering, noise reduction, splicing, and chimera removal. Amplicon sequence variants (ASVs) were classified according to 100% sequence similarity, and bacterial ASV sequence species classification and annotation were performed using the Silva_138_1 database.

[0071] 1.6 Soil Quality Assessment

[0072] Soil quality was comprehensively evaluated using the Soil Quality Index (SQI) method established by Song et al. (2026). Representative soil physicochemical and biological indicators were selected to construct a minimal soil quality assessment dataset (MDS). To eliminate dimensional differences and achieve comparability among indicators, linear membership functions were used to standardize the measured values ​​of each indicator to the 0-1 scoring range.

[0073] Based on the impact of indicators on soil productivity and overall soil quality, the indicators are divided into two categories: positive indicators are standardized using a membership function where higher is better; negative indicators are standardized using a membership function where lower is better. The soil quality index (SQI) is calculated using a weighted summation method, and the calculation formulas are as follows:

[0074] (2)

[0075] (3)

[0076] (4)

[0077] In the formula, X, Xmin, and Xmax represent the measured true value, minimum value, and maximum value of the soil index in this embodiment, respectively; Wi represents the weight of each index; Si represents the index score; and n represents the total number of indexes.

[0078] 1.7 Rice Yield Measurement

[0079] During the physiological maturity stage of rice, three sampling points were randomly selected within each experimental plot (avoiding edge rows and soil sampling rows to prevent edge effect interference). Rice from a 3 m² area was harvested from each sampling point, and the yield per unit area was measured (converted to t / hm²). After harvest, the rice grain moisture content was corrected to 14% (standard moisture content) as the actual yield. Simultaneously, based on the average number of tillers in each plot, nine representative plants were selected to determine the theoretical yield and yield components such as panicle number, number of spikelets per panicle, seed setting rate, and thousand-grain weight.

[0080] 1.8 Statistical Analysis

[0081] The analysis of soil microbial data and the creation of related charts were all completed using the cloud analytics platform provided by Novogene Biotechnology Co., Ltd. (Beijing). At the ASV level, soil bacterial α-diversity was assessed by calculating Good's coverage, number of observed species, Chao1 index, and Shannon diversity index; β-diversity analysis was used to clarify the differences in soil microbial community structure among different treatments; and the differences in soil bacterial community composition were assessed based on unweighted Unifrac distance combined with principal component analysis (PCA). Principal coordinate analysis (PCoA) and nonmetric multidimensional scaling (NMDS) were used to visualize the differentiation characteristics of microbial community structure; and heatmaps were used to visualize the correlation between the top 10 dominant bacterial phyla in the soil and various environmental factors.

[0082] Except for soil microbial data, other soil physicochemical and rice yield-related data showed consistent trends over the two-year experimental period; therefore, the two years' data were combined for statistical analysis. All experimental data were processed and preprocessed using Microsoft Excel 2019. Statistical analysis was performed using SPSS Statistics 22.0 software (IBM Corporation, USA). One-way ANOVA combined with Tukey's multiple comparison test was used to analyze differences between treatments, with a statistical significance level set at p < 0.05. Data normality was verified by the Shapiro-Wilk test, and homogeneity of variance was assessed by the Levene test. All data are expressed as mean ± standard error (SE) of six replicates. All experimental charts were created using Origin 2025 software.

[0083] 2. Results and Analysis

[0084] 2.1 Straw decomposition and straw surface structure

[0085] During the rice growth period, the decomposition of rice straw in the soil showed a dynamic trend of rapid decomposition in the early stage and slowdown in the later stage. The overall decomposition rate of rice straw reached 68.78% throughout the entire experimental period. Figure 3 A). The decomposition rate was fastest in the first month after rice straw application, with an average daily decomposition rate of 0.107 g. d -1 As the decomposition process progresses, the rate gradually decreases, reaching an average daily decomposition rate of 0.007 g by the fifth month. d -1 ( Figure 3 B).

[0086] The microstructure of rice straw surface changes significantly during the decomposition process. Figure 2The original rice straw surface is smooth and dense, covered with a non-porous waxy layer; in early July, signs of decomposition begin to appear on the surface of the rice straw, the smoothness is damaged, and the dense structure becomes loose; in early August, the waxy siliceous layer gradually thins, a large number of cavities appear on the surface, and the underlying epidermal tissue is exposed; in early September, the surface cavities completely disappear; in early October, the highly lignified mechanical tissue and epidermal tissue begin to decompose and break; in early November, the overall structure of the rice straw is severely damaged, the basic tissue is completely decomposed, and the remaining lignified structure also shows obvious breakage.

[0087] 2.2 Soil bulk density and pH

[0088] Applying carbon-rich soil conditioners can significantly reduce soil bulk density. Figure 4 A). Compared with the control group (CK), the soil bulk density of the JG, YPY, YF and SWT treatment groups decreased significantly by 12.83%, 9.30%, 9.09% and 13.48%, respectively; although the soil bulk density of the JG and SWT treatment groups was lower than that of the YPY and YF treatment groups, there was no significant difference in soil bulk density among the various carbon-rich amendment treatments.

[0089] Carbon-rich soil conditioners can significantly increase the pH value of acidic soils. Figure 4 B). Compared with the CK group (pH 4.37), the soil pH values ​​of the JG, YPY, YF and SWT treatment groups were significantly increased by 0.32, 0.48, 0.45 and 0.98, respectively. Among them, the soil pH value of the SWT treatment group was significantly higher than that of all other treatment groups, and the acidification effect was the best.

[0090] 2.3 Soil Nutrients

[0091] 2.3.1 Dynamics of soil inorganic nitrogen and available phosphorus

[0092] Soil ammonium nitrogen (NH4) + -N), nitrate nitrogen (NO3) - The concentrations of -N and available phosphorus both showed a gradual decreasing trend throughout the entire rice growth period. Figure 5 Compared with the control group, the YPY, YF, and SWT treatments significantly increased soil NH4 at all growth stages. + -N and NO3 - -N concentration ( Figure 5 A, B); JG treatment showed stage-specific differences, with NH4 at mid-tillering (MT) + -N and NO3 - The -N level was significantly lower than that of the CK group, but its content was higher than that of the CK group at the heading stage (HD), grain filling stage (FI), and physiological maturity stage (PM).

[0093] All carbon-enriched amendment treatments significantly increased the available phosphorus content in the soil throughout the entire rice growth period. Figure 5C), but the available phosphorus content in the JG treatment was significantly lower than that in the YPY, YF, and SWT treatments; the soil NH4 content in the SWT treatment group was lower. + -N, NO3 - The increases in -N and available phosphorus content were the largest among all treatments, and there were no significant differences among the SWT, YPY, and YF treatment groups in the HD, FI, and PM stages.

[0094] 2.3.2 Soil basic nutrient content

[0095] The application of carbon-enriched soil amendments significantly increased soil organic matter (SOM), total nitrogen (TN), carbon-nitrogen ratio (C / N), available nitrogen (AN), and available potassium (AK) content, and some treatments increased total phosphorus (TP) content (Table 3). Compared with the control group, the SOM content of each carbon-enriched soil amendment treatment significantly increased by 7.59%–14.16%; the TN content increased significantly by 5.77%, 12.65%, 7.45%, and 12.25% under the JG, YPY, YF, and SWT treatments, respectively; only the soil C / N ratio of the YF and SWT treatments was significantly higher than that of the control group; and the soil TP content was significantly higher in the YF treatment group than in the control group.

[0096] Overall, all carbon-rich soil amendments improved soil nutrient levels, with the JG treatment showing the weakest improvement. Compared to the JG treatment, the YPY, YF, and SWT treatments significantly increased the contents of soil SOM, AK, and AN: SOM increased by 6.11%, 7.70%, and 16.70%, respectively; AK increased by 11.56%, 8.64%, and 11.62%, respectively; and AN increased by 7.68%, 8.56%, and 13.68%, respectively.

[0097] Table 3. Effects of carbon-rich soil conditioner on nutrient content in acidic paddy soil.

[0098]

[0099] Note: Different lowercase letters in the same column indicate significant differences between treatments (p<0.05).

[0100] 2.4 Soil exchangeability index

[0101] The application of carbon-rich amendments can significantly improve soil exchangeability indicators, specifically by significantly increasing soil exchangeable calcium (ECa). 2+ ) and exchangeable magnesium (EMg) 2+ The content of exchangeable hydrogen (EH) was significantly reduced, while the exchangeable hydrogen content was also significantly decreased. + Exchangeable acid (EA) and exchangeable aluminum (EA1) 3+ ) level (Table 4).

[0102] Soil EH in each treatment group + With EAl3+ The content showed a consistent changing pattern, specifically ranked as follows: CK > JG > YF > YPY > SWT. The EA and EAl content of all carbon-rich amendment treatment groups... 3+ The content of these compounds was significantly lower than that of the control group, indicating that the carbon-rich amendment can effectively reduce soil acid activity and alleviate aluminum toxicity. Among them, the YF, YPY, and SWT treatments significantly reduced soil EH. + The content of EH was not significantly different between the JG treatment and the CK group; compared with the JG treatment, the YF, YPY and SWT treatments could further significantly reduce EH. + EA and EAl 3+ The content is higher, and the improvement effect is more prominent.

[0103] Compared with the CK group, the ECa2+ content in the JG, YPY, YF, and SWT treatment groups was significantly increased by 44.58%, 96.38%, 43.67%, and 106.77%, respectively; EMG 2+ The contents increased significantly by 31.58%, 59.50%, 54.75%, and 71.82%, respectively. Among these, SWT treatment significantly increased the content of ECa... 2+ and EMG 2+ The treatment with biochar showed the best improvement effect, significantly better than other carbon-rich soil amendments, indicating that biochar has significant advantages in replenishing soil basic ions and improving soil acidity.

[0104] Table 4. Effects of carbon-rich amendments on exchangeable indices in acidic soils.

[0105]

[0106] 2.5 Soil bacterial diversity

[0107] Amplicon sequencing yielded 1,116,609 valid bacterial sequences from 15 soil samples after quality control, averaging 74,440.6 sequences per sample. Among the treatments, the SWT treatment had the highest number of ASVs (autoimmune viruses), reaching 1,935. There was no significant difference in ASV numbers among the SWT, YPY, and YF treatments. Figure 6 A). Compared with the control (CK), the YPY, YF, and SWT treatments significantly increased the number of soil bacteria ASVs; the ASV abundance in the JG treatment was lower than that in the CK, but the difference between the two was not significant.

[0108] Good's coverage of all soil bacteria was above 99%, indicating sufficient sequencing depth and that the sequencing results accurately reflected the composition characteristics of the soil bacterial community. Figure 6 B). α-diversity results showed that, compared to the control (CK), the YPY, YF, and SWT treatments significantly increased the Chao1 and Shannon indices of soil bacteria; there were no significant differences in the Chao1 and Shannon indices between the JG and CK treatments. Figure 6 C Figure 6 D).

[0109] The results of the horizontal community composition of the phylum indicate that ( Figure 7 The top 15 dominant bacterial phyla accounted for 97.22%–98.48% of the total community abundance. In the control treatment, Pseudomonas, Bacillus, and Thermodesulfobacterium were the absolutely dominant groups, with relative abundances of 27.29%, 18.76%, and 15.38%, respectively; Acidobacteria, Actinobacteria, Chlorconiosis, and Myxobacteria also had high abundance.

[0110] The community structure of each carbon-enriched treatment changed significantly. The dominant bacterial groups were mainly Pseudomonas (15.31%–44.57%), Bacillus (12.35%–43.42%), and Bacteroidetes (10.51%–22.20%), while Chlorocybenophyceae and Actinobacteria also maintained high relative abundance. Compared with the control (CK), carbon enrichment significantly increased the relative abundance of Bacteroidetes, while significantly decreasing the abundance of thermodesulfurized Bacteroides, Spirochetes, and Acidobacteria. Specifically, the abundance of thermodesulfurized Bacteroides in the JG, YPY, YF, and SWT treatments decreased by 71.77%, 89.42%, 72.20%, and 81.02%, respectively, compared with the CK.

[0111] 2.6 Bacterial community structure and its relationship with environmental factors

[0112] Beta diversity analysis was used to reveal the differentiation characteristics of soil bacterial community structure under different treatments. Figure 8 The results of NMDS nonmetric multidimensional scaling analysis and PCoA principal coordinate analysis based on unweighted UniFrac distance showed that the bacterial communities of each treatment were clearly separated, indicating that the application of carbon-rich soil amendments significantly changed the bacterial community structure of paddy fields.

[0113] Canonical association analysis (CCA) was used to analyze the driving effects of environmental factors on bacterial communities. Figure 9 A). The CCA1 and CCA2 axes explained 27.75% and 15.69% of the total community variation, respectively. Soil bacterial communities and exchangeable hydrogen (EH2) + Exchangeable acid (EA), exchangeable aluminum (EAl) 3+ It showed a significant negative correlation with soil pH, organic matter (SOM), total nitrogen (TN), available nitrogen (AN), available potassium (AK), and exchangeable calcium (ECa). 2+ Exchangeable magnesium (EMG) 2+ The effective phosphorus (AP) showed a significant or highly significant positive correlation.

[0114] Pearson correlation analysis of phylum-level dominant microbial communities and environmental factors can be found in [the table below]. Figure 9 B. Phylum Desulfobacteria, Phylum Acidobacteria, and EA, EH + EAl3+ Soil bulk density (BD) showed a significant positive correlation with pH, ​​SOM, TN, AK, and ECa. 2+ ,EMg 2+ AP showed a significant negative correlation; Bacteroidetes were significantly negatively correlated with EA and EH. + EAl 3+ It showed a significant negative correlation with SOM, AN, AK, TN, and EMG. 2+ AP showed a significant positive correlation. Another phylum of Bacteroides was only associated with EH. + Significantly negative correlation with SOM, AN, TN, and ECa 2+ AP and pH were significantly positively correlated; Pseudomonas was only positively correlated with EH. + Significantly positive correlation; Myxococci are only associated with E1 3+ BD is significantly positively correlated.

[0115] 2.7 Rice yield and yield composition

[0116] Table 6 shows the yield and composition of rice under each carbon enrichment treatment. Compared with the control (CK), carbon enrichment significantly increased the number of grains per panicle, seed setting rate, and total grain yield. The yield indicators of the YPY, YF, and SWT treatments were significantly better than those of the CK, while the JG treatment showed no significant difference from the CK.

[0117] Yield results showed that, compared to the control (CK), the YPY, YF, and SWT treatments significantly increased rice yield by 34.34%, 32.68%, and 41.26%, respectively; the JG treatment only increased yield by 7.14%, with a negligible effect. Application of carbon-enriched soil conditioner slightly increased the thousand-grain weight of rice, but the difference was not significant among treatments. The SWT treatment effectively increased the number of panicles, the number of grains per panicle, and the seed setting rate, resulting in the best yield; there was no significant difference in rice yield between the SWT and YPY treatments.

[0118] Table 6 Rice Yield and Yield Components

[0119]

[0120] 2.8 Soil Quality Index (SQI) and its Relationship with Rice Yield

[0121] Compared with the control (CK), the application of carbon-rich soil amendment significantly improved the soil quality index (SQI). Figure 10 A). The SQI of the JG, YF, YPY, and SWT treatments increased by 1.21 times, 2.79 times, 3.03 times, and 3.74 times compared with the CK, respectively; there was no significant difference in SQI between the YPY and YF treatments. Correlation analysis showed that the soil quality index SQI was significantly positively correlated with rice yield. Figure 10 B).

[0122] 2.9 Key Influencing Factors of Carbon-Rich Amendments on Soil Quality Index Regulation

[0123] A random forest (RF) model was used to incorporate 13 soil physicochemical indicators to screen the main controlling factors affecting the soil quality index (SQI). Indicators with significant increases in mean squared error (MSE) were selected as key predictors. Figure 11 A). The results show that the random forest model explains 58% of the SQI variation; among which, exchangeable magnesium EMG... 2+ Soil pH, soil organic matter (SOM), exchangeable acid (EA), available phosphorus (AP), and exchangeable calcium (ECa) 2+ It is a significant controlling factor affecting SQI (p < 0.05).

[0124] Structural equation modeling can explain 92% of the SQI variation. Figure 11 B). Application of carbon-rich amendments with EMG 2+ pH, SOM, AP, ECa 2+ It exhibits a significant positive effect and a significant negative effect with exchangeable acid EA; meanwhile, EMG... 2+ pH, SOM, ECa 2+ It has a direct positive driving effect on the Soil Quality Index (SQI). In summary, under the regulation of carbon-rich amendments, soil physicochemical properties are the core driving factors determining changes in soil quality, while soil microbial characteristics are not the dominant factor.

[0125] 3. Conclusion

[0126] The application of carbon-rich soil conditioners can effectively improve the acidification status of acidic, low-yield paddy fields, optimize soil nutrient supply, regulate bacterial community structure, and enhance soil quality and rice yield. Among these, straw biochar (SWT) and microbial organic fertilizer (YPY) show the best improvement effects and can be considered preferred soil conditioners for improving the quality of acidic, low-yield paddy fields. This invention provides a theoretical basis and practical reference for the improvement and sustainable utilization of acidic, low-yield paddy fields.

[0127] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for improving the soil quality of acidified red soil paddy fields using a carbon-rich soil conditioner, characterized in that, include: A carbon-rich soil conditioner is applied to the soil of acidified red soil paddy fields, and the carbon-rich soil conditioner is evenly mixed into the tillage layer as a base fertilizer; the carbon-rich soil conditioner is at least one of rice straw, sheep manure organic fertilizer, microbial organic fertilizer, and biochar.

2. The method according to claim 1, characterized in that, The initial soil pH of the acidified red soil paddy field is ≤5.

5.

3. The method according to claim 1, characterized in that, The carbon-rich amendment is incorporated into the topsoil layer at a depth of 0–20 cm.

4. The method according to claim 1, characterized in that, The biochar is prepared by pyrolysis of rice straw under anaerobic conditions at 300–500℃.

5. The method according to claim 1, characterized in that, The application rate of rice straw is 5 to 10 tons per hectare.

6. The method according to claim 1, characterized in that, The application rate of biochar is 5 to 10 tons per hectare.

7. The method according to claim 1, characterized in that, The application rate of the microbial organic fertilizer is 8–15 tons per hectare.

8. The method according to claim 1, characterized in that, The application rate of the sheep manure organic fertilizer is 10-18 tons / hectare.

9. The application of the carbon-rich soil conditioner according to any one of claims 1 to 8 in improving the soil quality of acidified red soil paddy fields.

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