Rice stubble flue-cured tobacco straw returning carbon sequestration fertilizing method

Abstract

The invention discloses a rice stubble flue-cured tobacco straw returning-to-field carbon sequestration fertilizing method which comprises the steps of straw pretreatment, calculation of returning-to-field amount, protective ditching below furrows, quantitative deep burying of straw, layered covering, pressing and burying and controllable compaction of sub-topsoil and topsoil, shallow rotary cleaning of surface stubbles, ditch position alternation and the like and parameter cooperation. The directional input and stable retention of a rice straw carbon source to a 15-30cm subsurface layer are realized, the organic carbon content and organic carbon reserve of tobacco field soil are improved, the soil structure and nutrient conversion capability are improved, the growth and quality formation of flue-cured tobaccos are promoted, and meanwhile, the environmental pressure caused by open-air treatment of straws is reduced; the method is suitable for carbon sequestration, fertilization and green sustainable cultivation in tobacco-rice rotation area rice stubble flue-cured tobacco production.

Description

Technical Field

[0001] This invention relates to the field of agricultural planting technology, and in particular to a method for returning rice stubble and tobacco straw to the field for carbon sequestration and fertilization. Background Technology

[0002] In the rice-tobacco rotation area of ​​Fujian, tobacco production has long faced the core problem of soil organic carbon pool degradation. Due to the pursuit of short-term tobacco yields, this region generally suffers from excessive application of chemical fertilizers and insufficient input of organic matter. Furthermore, traditional tillage methods, primarily rotary tillage to a depth of about 10 cm, have led to the continuous depletion of soil organic carbon and a year-on-year decline in carbon pool reserves. The organic carbon content in the subsurface layer (15-30 cm) is particularly scarce, making it difficult to support the long-term carbon source requirements for flue-cured tobacco growth. Simultaneously, the previously used "straw dissolution" technology, while achieving straw return to the field, suffers from insufficient anaerobic decomposition under the low winter temperatures. Straw carbon is difficult to efficiently convert into stable soil organic carbon and is easily lost in gaseous form, further weakening the soil carbon pool function. The degradation of the soil organic carbon pool directly triggers a chain reaction: on the one hand, insufficient carbon pool leads to unstable soil aggregate structure, increased bulk density, and decreased aeration and water retention capacity, restricting deep root development in flue-cured tobacco; on the other hand, carbon source scarcity limits microbial activity, causing an imbalance in the soil carbon-nitrogen ratio and reduced nutrient conversion efficiency. This affects both tobacco yield and quality and fails to meet the carbon sequestration and emission reduction needs of tobacco fields. Therefore, there is an urgent need to innovate straw return-to-field carbon enrichment and fertilization technologies and strengthen the construction of soil organic carbon pools, which is the key to solving the degradation of tobacco field soil in this region and promoting the green and sustainable development of tobacco agriculture.

[0003] The existing implementation schemes most similar to this invention include the traditional rice straw leaching technology (mainstream application in Fujian tobacco-growing areas): This technology is a straw return and soil conservation technology that was previously widely used in Fujian tobacco-rice rotation areas. Its core principle is to use the rice straw remaining after rice harvest to create an anaerobic environment through field irrigation, promote the decomposition of rice straw and release nutrients, and improve soil structure at the same time.

[0004] Existing technologies similar to this invention have significant drawbacks in their application in the Fujian tobacco-rice rotation area, and none of them can address the core needs for soil organic carbon pool construction in this region. The traditional rice straw dissolution technique (the mainstream application in Fujian tobacco-growing areas) suffers from low organic carbon conversion efficiency and easy loss: in the low-temperature winter environment, anaerobic microbial activity is weak, rice straw decomposes incompletely, and straw carbon is difficult to efficiently convert into stable soil organic carbon, instead being partially lost in gaseous form; moreover, the organic carbon produced by decomposition is mostly concentrated in the 0-10 cm topsoil layer, easily lost with runoff during rainfall or irrigation, failing to replenish the organic carbon in the subsurface 15-30 cm layer, and thus failing to improve the overall storage capacity of the soil organic carbon pool. Furthermore, this technology only acts on the surface soil, failing to address the problem of shallow topsoil caused by traditional rotary tillage, thus not increasing the effective soil pool capacity, limiting the retention and accumulation of organic carbon in deeper soil layers, and making it difficult to support the long-term carbon source requirements for flue-cured tobacco growth. Summary of the Invention

[0005] To address the long-standing problems in rice-tobacco rotation areas (especially rice-stubble flue-cured tobacco ridge cultivation areas) such as soil organic carbon pool degradation, lack of organic carbon in the subsurface layer (15-30cm), and insufficient decomposition, low carbon conversion efficiency, and easy loss of straw under low winter temperatures, traditional straw return methods such as "straw dissolution" provide a method for carbon sequestration and fertilization by returning rice-stubble flue-cured tobacco straw to the field. Through the coordinated process of "straw pretreatment - calculation of return amount - protective ditching below the ridge - quantitative deep burial of straw - layered covering and compaction of topsoil / subsurface soil and controlled compaction - shallow rotary cleaning of surface stubble - ditch rotation", straw carbon is directionally migrated to the subsurface layer of the soil, efficiently converted and stably retained, improving the soil organic carbon pool and fertilization capacity of tobacco fields, compatible with flue-cured tobacco ridge cultivation layout, and meeting the needs of carbon sequestration, emission reduction and green production in tobacco fields.

[0006] The technical solution provided by this invention is as follows:

[0007] A method for returning rice stubble and flue-cured tobacco straw to the field for carbon sequestration and fertilization includes the following steps:

[0008] S1: After rice harvest, rice straw is collected and pre-treated to obtain rice straw to be returned to the field;

[0009] S2: Determine the organic carbon content of tobacco field soil, organic carbon content of rice straw, and decomposition conversion rate; calculate the amount of rice straw returned to the field based on the soil carbon deficit and straw carbon conversion efficiency.

[0010] S3: Before ridging the tobacco, dig a burial trench along the direction of the ridge and below the furrow. The soil dug out from the trench is piled up separately as topsoil and subsoil for subsequent layering and covering.

[0011] S4: Place the rice straw to be returned to the field into the straw burying trench according to the calculated amount and bury it deeply. Then, cover it with subsoil and topsoil in layers and compact it in a controlled manner so that the straw can be in full contact with the soil while taking into account the air permeability.

[0012] S5: After covering and compacting the soil, perform shallow rotary tillage to clear the surface stubble in order to obtain a good tillage layer that meets the requirements of subsequent ridge cultivation.

[0013] S6: During the tobacco-rice rotation process, the location of the straw burial trench is rotated to ensure that the carbon input from the straw is evenly distributed within the tobacco field.

[0014] Further, in step S1, the pretreatment step is as follows: after screening and removing impurities, the rice straw is dried and the moisture content is controlled so that the straw moisture content is 15%-20%, and the straw is quantitatively bundled into small bundles; or the straw is crushed and compressed into cakes as an alternative.

[0015] Further, in step S2, the soil carbon deficit calculation formula is: Carbon deficit (kg / acre) = (Target organic carbon content - Measured organic carbon content) × Soil bulk density × Soil layer thickness (30cm) × 667㎡ × 10 -3 The amount of rice straw returned to the field is calculated according to the following formula: Straw returned to the field (kg / mu) = carbon deficit ÷ (straw organic carbon content × decomposition conversion rate).

[0016] Furthermore, in step S2, the amount of straw returned to the field is determined by combining the organic carbon enhancement requirements of the target soil layer (e.g., 0-30cm) with the organic carbon content and decomposition conversion rate. The actual amount of straw returned to the field can be controlled at 300-500 kg / mu to balance carbon input and decomposition capacity and avoid excessive straw causing nitrogen fixation.

[0017] Furthermore, in step S3, the grass-burying trench is parallel to the direction of the ridge and located below the ridge furrow, with a trench width of 20cm, a depth of 30cm, and a spacing of 2m; and a chain trenching machine can be used to open the trench, and positioning measures can be used to ensure that the direction and depth of the trench are uniform.

[0018] Furthermore, in step S4, after the straw is placed, a layered covering method of "subsoil priority covering - topsoil covering" is adopted, and light compaction is carried out within 1-2 days after covering. When covering in layers, a certain proportion of decomposed organic fertilizer can also be mixed into the subsoil layer to accelerate decomposition and improve the carbon retention of the subsoil layer.

[0019] Furthermore, in step S5, the shallow rotary tillage depth is controlled to be 0-5cm, and it is carried out 3-5 days after the soil covering and compaction are completed, in order to achieve the removal of surface stubble and the fine fragmentation of surface soil.

[0020] Furthermore, in step S6, the location of the burial trench can be rotated using methods such as alternating rows or checkerboard rotation, so that full field coverage can be achieved within 3-5 years, thereby avoiding soil structure disturbance and uneven distribution of organic carbon caused by trenching in the same location for a long time.

[0021] Beneficial effects:

[0022] This invention addresses the problems of traditional methods like "straw dissolution" which involve directional excavation of straw-burying trenches beneath furrows to enrich and deeply bury rice straw, combined with layered subsoil / topsoil covering and controlled compaction. This allows the straw carbon source to be directionally inputted and stably retained in the 15-30cm subsoil layer, improving upon the shortcomings of traditional methods such as straw dissolution. These methods often fail to replenish subsoil organic carbon, resulting in shallow topsoil and easy carbon loss. Experimental results show that the organic carbon content in the 15-30cm subsoil layer can be increased by approximately 1.2-1.4 times compared to comparative technologies, while the organic carbon level in the topsoil layer remains relatively stable.

[0023] This invention employs a layered soil covering method of "subtopril priority covering + topsoil re-covering," followed by light compaction 1-2 days after covering. This promotes close contact between straw and soil, accelerates decomposition and transformation, while simultaneously ensuring aeration and water retention, reducing the loss of straw carbon in gaseous form or through runoff, thereby increasing the overall storage capacity of the soil organic carbon pool. Experimental results show that the organic carbon storage capacity in the 15-30cm subtopril layer can be increased by approximately 1.2-1.35 times compared to comparative technologies, and exhibits good stability.

[0024] This invention sets up a calculation and verification process for the amount of straw returned to the field, so that the amount of carbon input from straw matches the carbon deficit and microbial decomposition capacity of the tobacco field soil, and controls the deviation between the actual amount of straw returned to the field and the calculated value within a small range. This reduces the risks of excessive straw return to the field causing nitrogen fixation and insufficient return to the field leading to insignificant fertilization effects, thereby achieving precise fertilization and stable carbon fixation.

[0025] The straw-burying trench of this invention is located below the furrow and parallel to the direction of the ridge, which protects the tobacco ridge and does not damage the cultivation layout. At the same time, it can be combined with shallow rotary tillage to remove stubble in the top 0-5cm layer, which can reduce the impact of stubble on the quality of ridging / transplanting and the risk of rotary tillage blade entanglement, and facilitate mechanized field operations and large-scale promotion.

[0026] This invention can promote a balanced supply of nutrients and improve the quality of flue-cured tobacco by strengthening the organic carbon pool in tobacco field soil, improving aggregate structure and nutrient conversion function, and thus driving economic benefits. The test results show that this invention has shown a trend of increasing yield, output value and the proportion of medium and high grade tobacco in different test sites, and has good application and promotion value. Attached Figure Description

[0027] Figure 1 : Soil organic carbon content of test site 1 (Guangze County, Nanping City).

[0028] Figure 2 : Soil organic carbon content of test site 2 (Jianyang District, Nanping City).

[0029] Figure 3 : Soil organic carbon storage at test site 1 (Guangze County, Nanping City).

[0030] Figure 4 : Soil organic carbon storage at test site 2 (Jianyang District, Nanping City). Detailed Implementation

[0031] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available. The substantive content of the present invention is described in detail below with reference to embodiments, but this does not limit the scope of protection of the present invention.

[0032] This invention addresses the unique characteristics of flue-cured tobacco ridge cultivation and the low-temperature environment in winter in the tobacco-rice rotation area of ​​Fujian Province. It innovatively designs a "deep soil compaction and fertilization technology for rice straw in tobacco-rice rotation areas." Through a collaborative design of the entire process—"straw pretreatment - calculation of fertilization amount - protective ditching - layered soil covering and burying - surface stubble removal - ditch rotation"—it achieves the directional migration, efficient conversion, and stable retention of straw carbon to the subsoil layer, while also being compatible with tobacco field cultivation layouts. The specific technical solution is described in detail in the following embodiments:

[0033] Example 1. Straw Pretreatment

[0034] To address the problems of uneven decomposition and impurity contamination that easily occur with traditional straw returning to the field, standardized pretreatment is carried out after rice harvest, with the following steps:

[0035] Straw collection and screening: Use a combine harvester with a straw collection device to collect all rice straw in the field. Manually remove mixed soil clods (diameter > 5cm), pest and disease residues, and weed roots and stems to avoid bringing harmful substances into the soil.

[0036] Sun-drying and moisture control: Spread the screened straw flat in the field to dry (20-30cm thick), turning it over 1-2 times a day to ensure that the straw moisture content drops to 15%-20%. This moisture condition can prevent the straw from becoming moldy and ensure the activity of subsequent decomposing microorganisms.

[0037] Quantitative baling: Using a small straw baler, the straw is baled into cylindrical bundles with a diameter of 20cm and a length of 30-40cm. The weight of each bundle is controlled at 5-8kg to ensure uniform baling tightness, which facilitates precise subsequent burial and control of the amount returned to the field.

[0038] Alternative for straw pretreatment: Straw can be crushed and compressed into cakes, eliminating the need for complete bale formation. This still allows for moisture control, avoidance of impurities, and ensures uniform decomposition during subsequent deep burial.

[0039] Example 2: Calculation of the Amount of Returned Rice to the Field

[0040] To ensure that the amount of straw carbon input matches the demand for increasing the soil organic carbon pool in tobacco fields and the nutrient absorption patterns of flue-cured tobacco, and to avoid excessive straw leading to soil nitrogen fixation or deficiency that affects fertilization, a calculation model for the amount of straw returned to the field based on "soil carbon deficit - straw carbon efficiency" is designed. The specific steps are as follows:

[0041] Basic parameter determination: After rice harvest and before tobacco planting, soil samples were collected from tobacco fields using a five-point sampling method to determine the soil organic carbon content; at the same time, the organic carbon content of rice straw (the carbon content of conventional rice straw is 40%-45%, and this plan uses the measured value as the standard) and the decomposition conversion rate (in combination with the low temperature environment in Fujian winter, the annual decomposition rate of straw under anaerobic-aerobic synergistic conditions was set at 35%-40%).

[0042] Target carbon increment setting: Referencing the soil organic carbon standard of high-quality tobacco fields in the Fujian tobacco-rice rotation area (target soil organic carbon content in the 0-30cm layer to increase to 18-22g / kg), calculate the "carbon gap" per unit area of ​​soil. The formula is: Carbon gap (kg / mu) = (target organic carbon content - measured organic carbon content) × soil bulk density × soil layer thickness (30cm) × 667㎡ × 10⁻³.

[0043] Calculation of straw return to the field: Based on the carbon deficit and straw carbon conversion efficiency, the amount of rice straw returned to the field per mu is derived. The formula is: Straw return to the field (kg / mu) = Carbon deficit ÷ (Straw organic carbon content × Decomposition conversion rate).

[0044] Method for determining organic carbon content in straw: The rice straw sample was dried to constant weight at 65℃, crushed and passed through a 0.25mm sieve, and the organic carbon content in straw was determined by potassium dichromate oxidation-external heating method as described in "Soil Agrochemical Analysis" (edited by Bao Shidan, third edition).

[0045] Soil bulk density determination method: Soil bulk density is determined using the ring sampler method, following the procedure outlined in NY / T 1121.4-2006 "Soil Testing Part 4: Determination of Soil Bulk Density". Specifically, a ring sampler of known volume (100 cm³) is vertically pressed into the target soil layer to collect a sample. After extraction, the sample is dried at 105℃ to constant weight. The mass of dry soil per unit volume is then calculated, which is the soil bulk density (g / cm³).

[0046] Note: Considering the yield of rice straw in Fujian tobacco-growing areas (typically 500-700 kg / mu) and the carrying capacity of tobacco fields, the actual amount of straw returned to the field is controlled at 300-500 kg / mu to balance carbon input with soil microbial decomposition capacity and the nutrient requirements of flue-cured tobacco.

[0047] Example 3: Protective trenching

[0048] To achieve directional deep burial of straw in the subsurface layer without damaging the tobacco ridge / furrow structure, a directional furrowing scheme based on the ridge spacing in the tobacco field is designed, with the following steps:

[0049] Ditching location: After rice harvest and before tobacco ridging, based on the conventional ridge spacing of 1.1-1.3m in Fujian tobacco-growing areas, determine that the burying ditch is parallel to the direction of the ridge and located below the ridge furrow to ensure that the ditching operation does not disturb the foundation of the ridge and is compatible with subsequent flue-cured tobacco ridging cultivation.

[0050] Trenching equipment and parameter settings: Select a chain trencher suitable for the red soil texture of the Wuyi hilly area, with a trench width of 20cm, a trench spacing of 2m, and a trench depth of 30cm.

[0051] Trenching quality control: GPS positioning is used to assist in trenching to ensure that the burying trenches are straight and relatively uniform in depth; at the same time, the soil excavated during trenching is piled separately as topsoil and subsoil for subsequent layered covering.

[0052] Example 4: Layered covering and burying

[0053] Based on the calculated amount of straw returned to the field and the pre-treated straw baling, directional deep burial and filling are carried out to concentrate the input of straw carbon. The steps are as follows:

[0054] Straw bale burial sequence: Place the pre-treated straw bales into the burial trench in sequence, using a "single-layer flat laying + staggered stacking" method. Place 2-3 straw bales per meter of burial trench, with the ends of adjacent straw bales overlapping by 5-10cm to improve the straw filling rate in the trench (straw filling rate in the trench ≥95%, with no obvious gaps), and avoid the formation of voids after covering with soil, which would affect decomposition.

[0055] Verification of straw return to the field: After the straw burial of each tobacco field is completed, the straw return to the field is verified by the "counting method + sampling weighing method": the total length of the straw burial trench (m) × the number of straw bundles per meter × the weight of a single bundle is counted to calculate the actual straw return to the field, so that the error between the actual straw return to the field and the theoretical straw return to the field calculated in Example 2 is ≤5%, thus achieving accurate carbon input.

[0056] To accelerate straw decomposition, reduce carbon gaseous loss, and simultaneously improve the balance between soil compaction and aeration, a layered soil covering and controlled compaction scheme was designed, with the following steps:

[0057] Layered soil covering: Place the straw bales at the bottom of a 30cm deep trench, and after appropriate compaction, the actual height should be about 8-10cm. First, evenly cover the straw bales with the subsoil (15-30cm) piled up during trenching, with a soil covering thickness of 10-12cm, so that it covers the straw bales and forms a "subsoil-straw" contact layer, which is conducive to the decomposition of straw by microorganisms in the subsoil layer; then cover the subsoil with topsoil (0-15cm), with a soil covering thickness of 10-13cm, so that the total soil covering thickness in the trench is level with the ground surface, ensuring that the soil layers are consistent with the original profile and without damaging the soil structure.

[0058] Alternative to layered topsoil: During the subtopsoil backfilling stage, mix 5%-10% well-rotted organic fertilizer into the subtopsoil layer (15-30cm) when covering. This eliminates the need for pure subtopsoil, still accelerates straw decomposition, enhances carbon retention in the subtopsoil, and does not damage soil layers.

[0059] Controlled compaction: Within 1-2 days after covering with soil, lightly compact the soil above the straw burial trench; avoid rolling over the ridge during the compaction process so that the compacted soil can be in close contact with the straw without affecting soil aeration.

[0060] Example 5: Rotary tillage for clearing surface stubble

[0061] To remove loose straw (unbundled stalks, leaf sheaths, etc.) from the field and prevent stubble from affecting subsequent sowing / transplanting quality, a shallow rotary tillage treatment is designed, with the following steps:

[0062] Rotary tillage timing and equipment selection: 3-5 days after the soil covering and compaction are completed, use a small rotary tiller with a depth limit device to ensure that the tillage depth is strictly controlled within 0-5cm. The rotary tiller operates vertically along the burial furrow, chopping up and mixing loose stubble in the top 0-5cm of soil, achieving stubble removal and topsoil fine fragmentation; after rotary tillage, there is no obvious stubble accumulation on the surface soil, providing a good tillage foundation for subsequent tobacco ridging.

[0063] Example 6: Trenching Location Rotation Strategy

[0064] To avoid soil stratification and uneven organic carbon distribution caused by trenching in the same location for a long time, a periodic trenching location rotation plan is designed, with the following steps:

[0065] Rotation cycle setting: In conjunction with the tobacco-rice rotation cycle (two seasons per year, tobacco season + rice season), after the rice season ends and before the tobacco season is planted, the location of the straw burial trench is rotated so that all areas of the tobacco field can be covered with straw deep burial treatment once every 3-5 years.

[0066] Rotation pattern design: The "alternating row rotation" pattern is adopted: if the burial furrow of the previous season is located at position A on the ridge, the burial furrow of the next season will be located at position B on the ridge, with a rotation interval of 1m (matching the furrow spacing of 2m); during rotation, field marker stakes are used to assist in positioning to ensure accurate rotation position.

[0067] Alternative solution: "Checkerboard rotation" can be adopted, dividing the tobacco field into 1m×1m grids, and digging ditches in adjacent grids every season, achieving full coverage in 3-5 years, replacing the alternate row rotation, still achieving uniform carbon distribution and avoiding soil structure disturbance.

[0068] The purpose of rotation is to achieve a uniform distribution of straw carbon in tobacco fields through full-area rotation, reduce the phenomenon of excessively high or low local soil organic carbon, reduce the disturbance of soil structure caused by long-term single ditching, and improve the overall storage and stability of the soil organic carbon pool in the entire tobacco field.

[0069] Example 7: The effect of this method on soil organic carbon

[0070] During the tobacco maturity period, soil samples were taken using a soil sampler at five points in each replicate plot of each treatment. After sampling, the same replicate samples were mixed and larger impurities were removed. The samples included soil samples from 0-15 cm (topsoil) and 15-30 cm (subtopsoil). Organic carbon content was determined using the concentrated sulfuric acid-potassium dichromate oxidation method and titration method, referring to "Soil Agrochemical Analysis, Third Edition" (Bao Shidan, 2000).

[0071] like Figure 1 As shown, compared with rice straw dissolution (conventional technology), straw collection and deep soil fertilization significantly improved the subsurface carbon content of the soil. The organic carbon content in the 15-30cm subsurface layer of straw collection and deep soil fertilization was 26.9g / kg, which was significantly higher than that in rice straw dissolution (22g / kg). Moreover, the subsurface carbon content of straw collection and deep soil fertilization has reached the target value of organic carbon for high-quality tobacco fields.

[0072] Topsoil organic carbon (0-15cm): The organic carbon content of the topsoil in the 0-15cm layer of straw-collected deep soil fertilization (22.4g / kg) is basically the same as that in the 0-15cm layer of rice straw-dissolved soil (19g / kg), with no "excessive concentration" phenomenon.

[0073] like Figure 2 As shown, the organic carbon content in the subsurface layer of straw at a depth of 15-30cm (22.37 g / kg) is significantly higher than that in rice straw at a depth of 15-30cm (16.12 g / kg), although the absolute value is slightly lower. Figure 1 However, it still meets the target value of organic carbon for high-quality tobacco fields, and the comparison relationship of "straw accumulation and deep fertilization > rice straw dissolution" is completely consistent. Even if there are differences in the basic carbon content of different plots (resulting in different absolute values ​​of the vertical axis), the technical logic of "directional deep burial + layered soil covering" of this invention can still stably solve the problem of "subsurface carbon deficiency", indicating that the technical effect is not affected by local soil basic conditions and is suitable for the needs of different plots in the Fujian tobacco-rice rotation area.

[0074] comprehensive Figure 1 and Figure 2 Results: The organic carbon content in the 15-30cm subsurface layer of this invention is 1.2-1.4 times that of straw-melted fields, directly solving the problems of "straw-melted fields failing to replenish subsurface carbon and shallow topsoil," providing a long-term carbon source for deep root development in flue-cured tobacco, and supporting the patent objective of "sustainable production of tobacco-rice rotation systems." The data trends in the two graphs are consistent, proving...

[0075] The entire process of "straw pretreatment → directional trenching → layered soil covering → rotation" can steadily increase the organic carbon content of the soil, and the effect is better than existing technologies, providing measured data support for the core goal of the patent "carbon enrichment and carbon sequestration and emission reduction".

[0076] Example 8: The effect of this method on soil organic carbon storage

[0077] Referring to the "Soil Carbon Storage Calculation Method" (Liu Min et al., 2018), based on the measured organic carbon content and soil bulk density data, the organic carbon storage of each soil layer was calculated using the formula C=∑(Ci×Di×ρi×10), where Ci is the organic carbon content of the i-th layer (g / kg), Di is the soil layer thickness (cm), and ρi is the soil bulk density (g / cm³).

[0078] like Figure 3 As shown, the straw-based deep fertilization method, through a combination of techniques including directional trenching (30cm) to precisely locate the subsurface layer, deep burial of straw to enrich carbon sources, and priority covering of subsurface soil to promote decomposition, increased the subsurface carbon storage to 4.00 kg / m², an increase of over 20.2% compared to the control. This resulted in a larger difference between the subsurface and topsoil storage, indicating that more carbon was transferred to deeper layers, completely filling the subsurface carbon gap and realizing the transformation of the carbon pool from "shallow concentration" to "deep retention," which aligns with the goal of "improving the overall storage of soil organic carbon."

[0079] like Figure 4 As shown, the subsurface carbon storage (15-30cm) increased significantly, proving that the technology is not affected by differences in the basic soil. The basic carbon storage in the Jianyang experimental site was higher than that in Guangze County, but the subsurface carbon storage in the straw-melting field was only 4.8 kg / m², and the difference between the topsoil (3.3 kg / m²) and subsurface carbon storage was only 1.5 kg / m², indicating a more pronounced imbalance in the deep carbon pool. Straw-collected deep fertilization, using the same technical logic (directional deep burial + layered covering), increased the subsurface carbon storage to 6.48 kg / m², an increase of approximately 1.35 times, and the difference between the topsoil and subsurface carbon storage increased, significantly improving the balance of deep carbon distribution. This indicates that regardless of the basic soil carbon storage in the tobacco field, the technology can reliably solve the problem of "subsurface carbon scarcity," adapting to the needs of different plots in the Fujian tobacco-rice rotation area.

[0080] comprehensive Figure 3 and Figure 4 The results showed that the organic carbon storage in the 15-30cm subsurface layer of the straw-collected deep fertilization treatment was 1.2-1.35 times that of the rice straw-dissolving field, and the difference in carbon storage between the topsoil and subsurface layers also increased. This solved the problem that "existing technologies cannot supplement subsurface carbon," enabling the soil carbon pool to achieve "deep accumulation" and providing long-term carbon source support for flue-cured tobacco growth. It also verified the stability and universality of the technology, meeting the requirements for large-scale application. Although there were significant differences in the basic soil carbon storage in the experimental sites of Guangze County and Jianyang District, the technical combination of "directional deep burial + layered covering + precise quantity control" of this invention consistently and steadily increased the subsurface carbon storage and stabilized the topsoil carbon content, proving that the technical effect is not affected by local soil conditions and can be promoted on a large scale in the Fujian tobacco-rice rotation area, providing experimental evidence for "supporting the sustainable production of the tobacco-rice rotation system."

[0081] Example 9: The effect of this method on tobacco leaf quality

[0082] 1.Chemical composition

[0083] One sample of B2F and C3F tobacco leaves was taken from each treatment. The routine chemical composition was determined according to the "China Tobacco Planting Regionalization". Ten indicators were selected as evaluation indicators for the chemical composition of flue-cured tobacco, including total alkaloids, total nitrogen, reducing sugar, total sugar, potassium ion, chloride ion, starch content, sugar-alkaloid ratio, potassium-chloride ratio, and two-sugar ratio. The determination methods were based on YC / T159—2002, YC / T173—2003, YC / T160—2002, and YC / T161—2002, with the YC / T162—2002 standard method as an example. The specific data are shown in Tables 1 and 2 below. (YC / T159—2002: Tobacco Industry Standard of the People's Republic of China - Determination of Water-Soluble Sugars in Tobacco and Tobacco Products - Continuous Flow Method; YC / T173—2003: Tobacco Industry Standard of the People's Republic of China - Determination of Potassium in Tobacco and Tobacco Products - Continuous Flow Method; YC / T160—2002: Tobacco Industry Standard of the People's Republic of China - Determination of Total Alkaloids in Tobacco and Tobacco Products - Continuous Flow Method; YC / T161—2002: Tobacco Industry Standard of the People's Republic of China - Determination of Total Nitrogen in Tobacco and Tobacco Products - Continuous Flow Method; YC / T162—2002: Tobacco Industry Standard of the People's Republic of China - Determination of Chlorine in Tobacco and Tobacco Products - Continuous Flow Method)

[0084]

[0085] Table 1 Chemical composition of tobacco leaves in test site 1 (Guangze County, Nanping City)

[0086]

[0087] Table 2 Chemical composition of tobacco leaves from Experimental Site 2 (Jianyang District, Nanping City)

[0088] Total alkaloids and total nitrogen are fundamental to the flavor formation of flue-cured tobacco, and their balanced content directly depends on the stability of the soil carbon-nitrogen ratio. Experimental data shows that for the K326 variety, under straw-collected deep fertilization treatment, the total alkaloid content in the upper leaves was 2.77±0.10%, basically the same as the 2.72±0.06% in straw-dissolving fields, but the total nitrogen content of 1.50±0.03% was closer to the suitable range of 1.4%-1.6% for high-quality tobacco. The total alkaloid content in the middle leaves was 1.71±0.11%, significantly improving the low content of 1.60±0.04% in the middle leaves of straw-dissolving fields, thus avoiding a bland smoke. For the Cuibi No. 1 variety, under straw-collected deep fertilization treatment, the total nitrogen in the middle leaves was 1.57±0.13%, and the total alkaloid content was 2.17±0.20%, with a ratio (1:1.38) superior to the 1:1.06 ratio in straw-dissolving fields, solving the defect of "nitrogen supply fluctuations leading to an imbalance in alkaloid accumulation" in traditional techniques.

[0089] Reducing sugars and total sugars are the core precursors of aroma substances in flue-cured tobacco (such as esters and aldehydes), while the sugar-alkali ratio (8-12 for high-quality flue-cured tobacco) directly determines the smoothness of the smoke—a ratio that is too low can easily lead to a harsh smoke, while a ratio that is too high can easily lead to a bland smoke. This invention stabilizes the soil carbon pool without changing the total amount of sugars, but optimizes the ratio of sugars to plant alkalis. The sugar-alkali ratio optimization is significant: for the middle leaves of Cuibi No. 1, the sugar-alkali ratio of straw-infused deep fertilization reaches 10.97±0.11, which is significantly higher than the 6.33±0.02 of rice straw-dissolving fields, directly entering the suitable range for high-quality tobacco; for the middle leaves of K326, the sugar-alkali ratio of straw-infused deep fertilization is 13.00±0.54, which is better than the 9.58±0.38 of rice straw-dissolving fields, effectively solving the smoke quality problem caused by the "sugar-alkali imbalance" in traditional rice straw-dissolving fields.

[0090] Potassium is a key element for improving the combustibility of flue-cured tobacco and reducing tar content, while excessive chlorine content leads to poor combustion. This invention optimizes the safety of mineral elements by increasing soil organic carbon content, enhancing the soil's adsorption and release capacity for potassium, and simultaneously inhibiting excessive chlorine absorption. High-quality tobacco requires a potassium-chlorine ratio ≥4. Under straw-based deep fertilization treatment, the potassium-chlorine ratio in the middle leaves of Cuibi No. 1 was 6.14±0.22, and in the middle leaves of K326 it was 13.00±0.54, both meeting the standard and superior to that of rice straw-soluble fields. The chlorine content of both varieties was controlled within the safe range of 0.23%-0.44%, and the availability of potassium was enhanced.

[0091] This technology achieves synergistic optimization of key chemical composition ratios in flue-cured tobacco through subsurface carbon supplementation and precise nutrient supply. The effect is consistently demonstrated in the two mainstream varieties, directly confirming the practicality of the patented "carbon fixation and fertilization" technology and providing chemical composition-level support for the sustainable production of tobacco-rice rotation systems.

[0092] 2. Evaluation Indicators

[0093] Tobacco leaf samples were destemmed, shredded, dried, and moisture-balanced to produce cigarettes. Following the "Sensory Evaluation Methods for Tobacco and Tobacco Products" (YC / T138—1998), the cigarettes were evaluated by the expert group of the Zhengzhou Tobacco Research Institute of China National Tobacco Corporation. Evaluations were based on indicators such as aroma characteristics (aroma quality, aroma quantity), smoke characteristics (concentration, strength, aftertaste), and taste characteristics (offensiveness, irritation), using a 9-point scoring system to assign values ​​to the main evaluation indicators. This invention strengthens the soil organic carbon pool through "rice straw deep fertilization and returning to the field technology," promoting a balanced supply of nutrients to flue-cured tobacco and significantly optimizing the smoking quality of tobacco leaves (aroma, taste, smoke characteristics). This directly supports the core patent objective of "increasing carbon and fertilizing → enhancing flavor." Specific values ​​are shown in Tables 3 and 4 below.

[0094]

[0095] Table 3. Tobacco Evaluation Indicators at Experimental Site 1 (Guangze County, Nanping City)

[0096]

[0097] Table 4. Tobacco Evaluation Indicators for Experimental Site 2 (Jianyang District, Nanping City)

[0098] Aroma quality and aroma quantity are core flavor indicators of tobacco leaves, and their improvement depends on soil carbon-nitrogen balance and precise nutrient supply. Under the straw-infused deep fertilization treatment, the aroma quality of the middle leaves of K326 was 6.33±0.08a, significantly higher than 6.06±0.10b in the rice straw-melting field; the aroma quality of the middle leaves of Cuibi 1 was 6.33±0.12a, better than 6.00±0.08ab in the rice straw-melting field. The aroma quantity of both varieties remained in the excellent range above 6.0, confirming the promoting effect of subsurface carbon pool enhancement on the synthesis of aroma precursors.

[0099] Off-odors and irritation directly affect the comfort of inhalation, and straw-based deep composting effectively improves the shortcomings of traditional techniques. The off-odor of the upper leaves of Cuibi No. 1 is 5.83±0.08ab, which is better than that of rice straw melting field (5.67±0.08b). The irritation index of both K326 and Cuibi No. 1 is stable in the range of 5.8-6.2, with no obvious spiciness or unpleasant taste.

[0100] Aftertaste is a key indicator of the smoking experience, and the straw-based deep fertilization treatment shows outstanding performance. The aftertaste of the upper leaves of K326 is 6.33±0.08a, which is higher than that of rice straw-based treatment (5.83±0.12a). The aftertaste of all parts of Cuibi No. 1 is above 6.0, and the smoke concentration and strength are more coordinated, which meets the smoking standard of "mellow and full-bodied" for high-quality flue-cured tobacco.

[0101] Based on the evaluation results, it can be seen that the straw collection and deep fertilization treatment performed well in terms of aroma quality, aroma quantity and aftertaste, and the off-flavors and irritation were maintained within a relatively suitable range, indicating that this technical solution is conducive to improving the coordination of the sensory quality of tobacco leaves.

[0102] This technology achieves stable optimization of the core evaluation indicators of the two mainstream varieties through a chain reaction of subsurface carbon replenishment and coordinated accumulation of flavor substances. The effect is not affected by the basic conditions of the plot, which fully demonstrates the practicality of the patented "carbon fixation and fertilization" technology and provides sensory quality support for the sustainable production of tobacco-rice rotation systems.

[0103] Example 10: The impact of this method on the economic benefits of tobacco.

[0104] The flue-cured tobacco leaves after different treatments were stored separately, and the yield was calculated according to the GB2635-1992 standard and the local purchase price of each grade of tobacco leaves. The unit yield, unit output value, and proportion of medium and high-grade tobacco were calculated separately. The "rice straw collection and deep fertilization returning technology" of this invention achieves synergistic optimization of tobacco yield, output value, and proportion of high-quality tobacco by strengthening the soil organic carbon pool, directly supporting the core patent objective of increasing carbon and fertilization → supporting the sustainable production of the tobacco-rice rotation system, as shown in Table 5.

[0105]

[0106] Table 5. Economic Benefits of Tobacco

[0107] In Experimental Site 1 (Guangze County), the yield per mu (667 square meters) from straw-collected deep fertilization was 133.64 kg, a 3.5% increase compared to rice straw-dissolved fields (129.09 kg). In Experimental Site 2 (Jianyang District), the yield was 123.10 kg, slightly higher than rice straw-dissolved fields (122.22 kg). The output value per mu from straw-collected deep fertilization in Experimental Site 1 was 4575.55 yuan, higher than the 4448.64 yuan from rice straw-dissolved fields. The average price per mu from straw-collected deep fertilization in Experimental Site 2 was 35.24 yuan, significantly higher than the 33.20 yuan from rice straw-dissolved fields, indicating that the increased yield and quality contributed to the overall economic benefits. In Experimental Site 2, the proportion of medium-to-high-grade tobacco from straw-collected deep fertilization was 90.35%, a 3.18 percentage point increase compared to the 87.17% from rice straw-dissolved fields. In Experimental Site 1, the proportion remained above 93%, confirming the positive impact of balanced nutrients on the production of high-quality tobacco.

[0108] In summary, the technology has achieved "stable yield increase and optimized benefits" in different plots, proving its practicality and providing yield support for sustainable production of tobacco-rice rotation.

Claims

1. A method for returning rice stubble and flue-cured tobacco straw to the field for carbon sequestration and fertilization, characterized in that, It includes the following steps: S1: Collect and pre-treat rice straw to obtain rice straw to be returned to the field; S2: Based on the soil organic carbon content of the rotation tobacco field, the organic carbon content of the rice straw, and the decomposition conversion rate, and combined with the target organic carbon content of the target soil layer, calculate the amount of rice straw returned to the field based on the soil carbon deficit and straw carbon conversion efficiency. S3: Before the tobacco is ridged, dig a grass-burying trench below the ridge along the direction of the tobacco ridge. The trench is 20cm wide, 30cm deep, and 2m apart. The soil excavated from the trench is piled up separately as topsoil and subsoil. S4: Place the rice straw obtained in step S1 into the straw burying trench according to the amount of straw returned to the field calculated in step S2 and bury it deeply. Then, first cover the rice straw with the subsoil, and then cover the subsoil with the topsoil to form layers of soil covering, so that the total thickness of the soil covering in the trench is level with the ground surface. After covering the soil, lightly press the soil above the straw burying trench within 1-2 days. S5: 3-5 days after the soil covering and compaction are completed, shallow rotary tillage is carried out to clean the surface residue. The shallow rotary tillage depth is 0-5cm. S6: Rotate the location of the burial trench during the tobacco-rice rotation cycle.

2. The method for returning rice stubble and flue-cured tobacco straw to the field for carbon sequestration and fertilization according to claim 1, characterized in that, The pretreatment step in step S1 is as follows: manually remove the mixed soil clods, pest and disease residues and weed roots and stems, and dry the rice straw until the moisture content is 15%-20%. Then, bundle the rice straw into small cylindrical bundles with a diameter of 20cm and a length of 30-40cm, with each bundle weighing 5-8kg.

3. The method for returning rice stubble and flue-cured tobacco straw to the field for carbon sequestration and fertilization according to claim 1, characterized in that, The soil carbon deficit calculation formula mentioned in step S2 is: Carbon deficit (kg / acre) = (Target organic carbon content - Measured organic carbon content) × Soil bulk density × Soil layer thickness (30cm) × 667㎡ × 10 -3 ; The amount of rice straw returned to the field is calculated using the following formula: Straw returned to the field (kg / mu) = carbon deficit ÷ (straw organic carbon content × decomposition conversion rate).

4. A method for returning rice stubble and flue-cured tobacco straw to the field for carbon sequestration and fertilization according to claim 3, characterized in that, The organic carbon content of the rice straw is 40%-45%, the decomposition conversion rate is 35%-40%, and the actual amount returned to the field is controlled at 300-500 kg / mu.

5. A method for returning rice stubble and flue-cured tobacco straw to the field for carbon sequestration and fertilization according to claim 1, characterized in that, In step S3, the location of the burying trench is determined based on the tobacco ridges with a spacing of 1.1-1.3m. The burying trench is dug using a chain trencher. GPS positioning is used to assist in the trenching process to ensure that the burying trench is straight and has a uniform depth.

6. A method for returning rice stubble and flue-cured tobacco straw to the field for carbon sequestration and fertilization according to claim 2, characterized in that, In step S4, small bundles of rice straw are placed in the burying trench in a single layer and staggered arrangement. 2-3 bundles of rice straw are placed per meter of burying trench, with the ends of adjacent bundles of rice straw overlapping by 5-10cm, and the rice straw filling rate in the trench is ≥95%.

7. A method for returning rice stubble and flue-cured tobacco straw to the field for carbon sequestration and fertilization according to claim 1, characterized in that, In step S4, the thickness of the subsoil cover is 10-12 cm, and the thickness of the topsoil cover is 10-13 cm.

8. A method for returning rice stubble and flue-cured tobacco straw to the field for carbon sequestration and fertilization according to claim 1, characterized in that, In step S4, after the rice straw is placed in the field, the actual amount of straw returned to the field is verified by a combination of counting and sampling weighing methods, so that the error between the actual amount of straw returned to the field and the amount of straw returned to the field calculated in step S2 is ≤5%.

9. A method for returning rice stubble and flue-cured tobacco straw to the field for carbon sequestration and fertilization according to claim 1, characterized in that, In step S5, a rotary tiller with a depth limiting device is used to work along the vertical direction of the burial trench to chop up the stubble in the top 0-5cm of soil and mix it into the soil.

10. A method for returning rice stubble and flue-cured tobacco straw to the field for carbon sequestration and fertilization according to claim 1, characterized in that, In step S6, the location of the straw burial trench is rotated using an alternating row rotation pattern with a rotation interval of 1m, and all areas of the tobacco field are covered with straw deep burial treatment once every 3-5 years.

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