A method for improving soil phosphorus availability and tobacco leaf quality based on low molecular weight organic acids

Abstract

The application provides a method for improving soil phosphorus availability and tobacco leaf quality based on low-molecular-weight organic acids, and belongs to the technical field of bio-agriculture. The application can significantly improve the availability of phosphorus in soil by applying specific low-molecular-weight organic acids to soil, promote the absorption and utilization of phosphorus nutrients by tobacco plants, and thus make the tobacco plants grow healthily and the leaf development good. After being applied to flue-cured tobacco cultivation, the yield, output value and proportion of superior tobacco of flue-cured tobacco are significantly improved, and the economic benefits of tobacco farmers are greatly increased. The application is simple in operation, low in cost and friendly to the environment, and can be widely used in the production of tobacco and other crops of similar soil types, and has significant values in soil improvement, quality improvement, yield increase and income increase.

Description

Technical Field

[0001] This invention relates to the field of soil improvement technology, and in particular to a method for improving soil phosphorus availability and tobacco quality based on low molecular weight organic acids. Background Technology

[0002] Phosphorus is one of the essential macronutrients for plant growth and development, directly participating in key physiological processes such as energy metabolism, nucleic acid synthesis, cell membrane construction, and signal transduction. In agricultural production, the availability of soil phosphorus is often a significant factor limiting crop yield. Large areas of brown soil and calcareous soils are generally neutral to slightly alkaline and rich in metal ions such as calcium and magnesium. In these soil environments, applied phosphate fertilizers readily combine with calcium ions to form insoluble phosphate precipitates such as calcium phosphate, octacalcium phosphate, and hydroxyapatite, or are strongly adsorbed by iron, aluminum oxides, and clay minerals, forming occluded phosphorus. These forms of phosphorus are difficult for crop roots to directly absorb and utilize, resulting in a persistent deficiency of available phosphorus concentration despite a high total phosphorus content in the soil.

[0003] For a long time, the main means of addressing insufficient phosphorus supply in agricultural production has been the excessive application of chemical phosphate fertilizers. However, the utilization rate of phosphate fertilizers in alkaline or slightly alkaline soils is typically only 10%–25% in the current season, with the vast majority of phosphorus being converted into an ineffective form shortly after application. This not only results in a huge waste of phosphate rock resources and increases agricultural production costs, but also leads to soil degradation and risks to agricultural product safety due to the accumulation of heavy metals (such as cadmium, lead, and arsenic) in the soil year after year, which are associated with phosphate fertilizer production. In addition, excessive phosphorus application enters water bodies through surface runoff and leaching, becoming one of the important agricultural non-point source pollution sources causing eutrophication of lakes and rivers.

[0004] To address this issue, scholars both domestically and internationally have conducted extensive research on the regulation of soil phosphorus activation. Common physicochemical improvement measures include applying acidic substances such as sulfur, aluminum sulfate, and ferrous sulfate to lower the rhizosphere soil pH and promote phosphate dissolution; or applying ion exchange materials such as gypsum and zeolite to compete for adsorption sites and reduce phosphorus fixation. In terms of biological measures, screening and inoculating phosphorus-solubilizing microorganisms (such as phosphorus-solubilizing bacteria and fungi) has become a research hotspot in recent years. These microorganisms can convert insoluble phosphorus into soluble phosphorus by secreting metabolites or producing phosphatases. Furthermore, reasonable crop rotation systems, planting green manure, and applying organic materials have also been proven to improve soil phosphorus availability. However, the above methods generally suffer from limitations such as high cost, complex operation, unstable effects, or susceptibility to environmental conditions, making it difficult to achieve large-scale, standardized application in vast tobacco-growing areas.

[0005] Therefore, developing a soil phosphorus activation technology that is easy to operate, low in cost, and has stable effects is of great significance for improving the phosphorus supply capacity of typical tobacco-growing soils and the quality of tobacco leaves. Summary of the Invention

[0006] The purpose of this invention is to provide a method for improving soil phosphorus availability and tobacco quality based on low molecular weight organic acids, which solves the technical problems of poor effective phosphorus in neutral to alkaline brown soils due to strong phosphorus fixation, resulting in poor growth and development of flue-cured tobacco and poor tobacco quality.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] The present invention provides a method for improving soil phosphorus availability, comprising applying an aqueous solution of a low molecular weight organic acid to the soil, wherein the low molecular weight organic acid is selected from one or more of malic acid, citric acid, succinic acid, and oxalic acid.

[0009] A method for improving tobacco leaf quality is also provided, comprising irrigating the rhizosphere soil of flue-cured tobacco with a low molecular weight organic acid aqueous solution, wherein the low molecular weight organic acid is selected from one or more of malic acid, citric acid, succinic acid, and oxalic acid.

[0010] Preferably, the concentration of the low molecular weight organic acid in the aqueous solution is 0.5-5.0 g·L. -1 .

[0011] Preferably, the amount of the low molecular weight organic acid aqueous solution applied per unit area of ​​soil or per plant is 0.5-2.0L per square meter or 0.5-2.0L per plant.

[0012] Preferably, the root irrigation treatment specifically involves uniformly irrigating the low molecular weight organic acid aqueous solution within a 5-10 cm radius around the base of the tobacco plant roots.

[0013] Preferably, the application time to the rhizosphere soil of flue-cured tobacco is 25-45 days after transplanting.

[0014] Preferably, the application process also includes a soil pretreatment step, which includes deep plowing to a depth of 25-30 cm, removing weeds and stubble, and leveling the field.

[0015] Preferably, the method also includes the step of transplanting flue-cured tobacco seedlings in a pit-like manner, wherein the row spacing is 1.0-1.5m and the plant spacing is 0.4-0.6m.

[0016] Preferably, no other soil conditioners, phosphorus activators, exogenous organic acid preparations, or plant growth regulators are applied throughout the entire growth period.

[0017] Preferably, the soil is slightly alkaline, with a pH of 7.0-7.8 and an available phosphorus content of less than 10 mg / kg. -1 Brown soil.

[0018] The beneficial effects of this invention are:

[0019] This invention significantly enhances the availability of phosphorus in the soil by applying specific types of low-molecular-weight organic acids, promoting the absorption and utilization of phosphorus nutrients by tobacco plants, thereby resulting in robust plant growth and well-developed leaves. When applied to flue-cured tobacco cultivation, sensory indicators such as the appearance, color, oil content, and chroma of the cured tobacco leaves are significantly optimized; physical processing properties such as filling value and stem content are improved; key chemical components such as reducing sugars and potassium tend to be more balanced; the total amount of neutral aroma substances increases; and the aroma quality and quantity in sensory quality are significantly improved, while off-odors and irritation are reduced. Ultimately, this results in a significant increase in flue-cured tobacco yield, output value, and the proportion of high-grade tobacco, leading to a substantial increase in the economic benefits for tobacco farmers. This invention is simple to operate, low in cost, and environmentally friendly, and can be widely used in tobacco and other crop production in similar soil types, demonstrating significant value in soil improvement, quality enhancement, yield increase, and income generation. Attached Figure Description

[0020] Figure 1 This is a technical roadmap of the present invention;

[0021] Figure 2 The effects of different treatments on the available phosphorus content in soil;

[0022] Figure 3 The effects of different treatments on soil acid phosphatase activity;

[0023] Figure 4 The effect of different treatments on the content of petroleum ether extract in tobacco leaves;

[0024] Figure 5 The effects of different treatments on the photosynthetic characteristics of tobacco leaves;

[0025] Figure 6 The effects of different treatments on the content of xylose pigments in tobacco leaves;

[0026] Figure 7 The effects of different treatments on the activity of key enzymes in tobacco carbon metabolism;

[0027] Figure 8 The effects of different treatments on the activity of key enzymes in nitrogen metabolism in tobacco leaves;

[0028] Figure 9 The effects of different treatments on the activity of phenylalanine ammonia-lyase in tobacco leaves;

[0029] Figure 10 The effects of different treatments on the activity of lipoxygenase in tobacco leaves;

[0030] Figure 11 The effects of different treatments on the morphology and density of glandular trichomes in tobacco leaves. Detailed Implementation

[0031] This invention provides a method for improving soil phosphorus availability, comprising applying an aqueous solution of a low molecular weight organic acid to the soil. The low molecular weight organic acid is selected from one or more of malic acid, citric acid, succinic acid, and oxalic acid. In this invention, low molecular weight organic acids refer to organic compounds with a molecular weight typically less than 500 Daltons, containing one or more carboxyl functional groups, and are widely found in plant root exudates, microbial metabolites, and intermediates in the decomposition of organic materials. Malic acid, also known as 2-hydroxysuccinic acid, is a naturally occurring four-carbon dicarboxylic acid with two carboxyl groups and one hydroxyl group. It is commonly found in fruits and tobacco as L-malic acid and can be produced through the citric acid cycle. Citric acid, also known as citric acid, is a tricarboxylic acid compound containing three carboxyl groups and one hydroxyl group. It is widely found in citrus fruits and has a strong ability to complex metal ions. Succinic acid, also known as succinic acid, is a dicarboxylic acid compound and an intermediate product of the tricarboxylic acid cycle, often existing as a microbial fermentation product. Oxalic acid, also known as ethanedioic acid, is the simplest dicarboxylic acid with strong acidity. It is widely found in plants such as spinach and amaranth and can form insoluble calcium oxalate with calcium ions. All four organic acids mentioned above are commercially available, such as food-grade or industrial-grade products, typically with a purity of over 98%. They can also be prepared through bio-fermentation or chemical synthesis. In this invention, depending on soil type, phosphorus fixation level, and target crop, a single organic acid can be selected for application, or two or more can be mixed in any proportion. The mixing ratio can be optimized based on the acidity constant and complexing ability of each organic acid; for example, the mass ratio of malic acid to citric acid can be 1:1 to 3:1.

[0032] This invention also provides a method for improving the quality of tobacco leaves, including root irrigation treatment of the rhizosphere soil of flue-cured tobacco with a low molecular weight organic acid aqueous solution, wherein the low molecular weight organic acid is selected from one or more of malic acid, citric acid, succinic acid, and oxalic acid. Here, "flue-cured tobacco" refers to a type of tobacco variety specifically used for producing tobacco leaves that have been cured and processed. Common cultivated varieties include Yunyan 87, K326, Qinyan 96, and Zhongyan 100, etc., whose tobacco leaves become raw materials for the cigarette industry after being harvested, stalked, packed, yellowed, color-fixed, and dried. "Rhizosphere soil" refers to a microenvironment that is significantly different from soil in terms of physicochemical and biological properties due to the influence of plant root activity. It usually refers to the area extending outward from the root surface by several millimeters to several centimeters. This area is rich in the types and quantities of microorganisms, and the pH value is often lower than that of non-rhizosphere soil, with active ion exchange and complexation reactions. "Root irrigation" is an agricultural practice that involves directly applying an aqueous solution to the soil around the base of the tobacco plant. Unlike foliar spraying or drip irrigation, its purpose is to concentrate the solution in the rhizosphere, reducing the loss and evaporation of active ingredients. This method can be performed using handheld sprayers, backpack sprayers (without nozzles), agricultural irrigation buckets, or drip irrigation tapes. Root irrigation should ideally be done on a sunny, windless day, in the evening or early morning, to maximize the solution's penetration and retention time in the soil.

[0033] Preferably, the concentration of the low molecular weight organic acid in the aqueous solution is 0.5-5.0 g·L. -1 In this invention, the concentration of the organic acid aqueous solution can be appropriately adjusted according to the soil alkalinity, phosphorus fixation level, climatic conditions, and crop growth stage. For example, when the soil pH is higher than 7.5 or the available phosphorus content is lower than 5 mg / kg... -1 At this time, a higher concentration such as 3.5-5.0 g·L can be selected. -1 When the soil pH is between 7.0 and 7.5 or the available phosphorus content is 5-8 mg / kg -1 At this time, a medium concentration such as 1.5-3.0 g·L can be selected. -1 When the soil is neutral or the available phosphorus content is close to 10 mg·kg -1 In such cases, a lower concentration, such as 0.5-1.2 g·L⁻¹, can be selected. -1 More preferably, the concentration is 1.5-2.5 g·L⁻¹. -1 More preferably, the concentration is 1.8-2.2 g·L⁻¹. -1 Most preferably, the concentration is 2.0 g·L⁻¹. -1 Aqueous solutions of organic acids with different concentration gradients can be prepared by adding a certain mass of organic acid powder or concentrated solution to water, stirring until completely dissolved, and then adjusting the volume. The dissolution temperature can be controlled at 20-30℃, and the stirring time is usually 5-15 minutes. After preparation, it should be used within 24 hours to prevent microbial degradation or oxidative deterioration.

[0034] Preferably, the amount of the low molecular weight organic acid aqueous solution applied per unit area of ​​soil or per plant is 0.5-2.0 L per square meter or 0.5-2.0 L per plant. In this invention, the application amount can be adjusted according to the crop type, plant spacing, soil bulk density, and rhizosphere volume. For densely planted crops such as wheat and corn, 0.5-1.0 L per square meter is preferable; for cash crops with larger plant spacing such as tobacco, tomato, and cotton, 0.8-1.5 L per plant is preferable. More preferably, the application amount is 0.8-1.5 L per square meter or 0.8-1.2 L per plant; even more preferably, the application amount is 0.9-1.1 L per plant; most preferably, the application amount is 1.0 L per plant. During application, the calculated total liquid volume can be evenly distributed to each plant or per square meter, and watered around the root base to allow the solution to seep naturally and avoid surface runoff. For sandy soils or arid conditions, the amount applied at one time can be reduced and the number of applications increased; for clay soils or areas with more rainfall, the amount applied at one time can be increased to ensure that the solution penetrates to the deep rhizosphere.

[0035] Preferably, the root irrigation treatment specifically involves uniformly watering the low molecular weight organic acid aqueous solution around the base of the tobacco plant within a 5-10 cm radius. "Uniform watering" means pouring or spraying the solution onto the target area slowly, continuously, and in a dispersed manner to avoid concentrated flushing that could lead to excessively high local solution concentrations or soil compaction. A fine-nozzle sprayer, drip irrigation tape, or watering tool with a diversion device can be used, with the watering speed controlled at 0.2-0.5 L / s. -1 This allows the solution to naturally and evenly soak into the soil. The "5-10cm radius around the root base" refers to a ring-shaped area with a radius of 5-10cm extending outwards from the base of the tobacco plant stem. This area has the densest root distribution and the strongest absorption capacity. During the flue-cured tobacco's growth stage and vigorous growth phase, the main and lateral roots are concentrated in the 0-20cm topsoil layer, with the highest density of fine roots within the 5-10cm radius around the root base. Using this area as the target area for root irrigation maximizes the contact efficiency between organic acids and the roots. More preferably, the irrigation range is 6-8cm around the root base; most preferably, it is 8cm around the root base. After irrigation, a thin layer of soil or straw can be covered to reduce water evaporation. If heavy rain occurs within 6 hours after root irrigation, a second irrigation may be necessary.

[0036] Preferably, the application period for irrigating the rhizosphere soil of flue-cured tobacco is 25-45 days after transplanting. From transplanting to harvest, flue-cured tobacco typically goes through the seedling establishment stage, root extension stage, rosette stage, vigorous growth stage, budding stage, and maturity stage. 25-45 days after transplanting roughly corresponds to the late rosette stage to the early vigorous growth stage. At this time, the root system of the tobacco plant has been initially established, the above-ground parts begin to grow rapidly, the demand for phosphorus increases significantly, root secretion capacity is enhanced, rhizosphere microorganisms are active, and the synergistic effect of exogenous organic acids is optimal. More preferably, the application period is 30-40 days after transplanting; further preferably, 33-37 days after transplanting; and most preferably, 35 days after transplanting. Root irrigation during this window period can promote the absorption of activated phosphorus by the tobacco plant, laying a nutrient foundation for leaf development and dry matter accumulation during the vigorous growth stage. If applied too early, before the root system has fully expanded, the organic acids may not be fully absorbed and may be buffered or degraded by the soil. If applied too late, the tobacco plants have entered the late stage of vigorous growth, and the peak demand for phosphorus has passed, resulting in a reduced effect. In addition to flue-cured tobacco, other crops such as corn, soybeans, and cotton can also be treated similarly during their own growth stages, such as the large trumpet stage and the early flowering stage, which are critical periods for phosphorus demand.

[0037] Preferably, the application process includes a soil pretreatment step, which includes deep plowing to a depth of 25-30 cm, removing weeds and crop residues, and leveling the field. Deep plowing refers to using a moldboard plow, rotary tiller, or subsoiler to deeply turn over or loosen the soil to a depth of 25-30 cm. This breaks up the plow pan, increases soil permeability and water retention capacity, and promotes root development. In this invention, the deep plowing depth can be selected as 26-28 cm, more preferably 27-28 cm, and most preferably 28 cm. Removing weeds and crop residues refers to removing weeds from the field by manual weeding, using a cultivator, or applying herbicides, as well as removing organic matter such as straw and stubble left from the previous crop, reducing overwintering sites for pests and diseases and competition for nutrients. Leveling the field refers to using a laser leveler, scraper, or manual rake to level the field surface, eliminating local height differences, ensuring uniform solution distribution during subsequent root irrigation, and avoiding waterlogging and runoff. Pretreatment is usually carried out 7-15 days after the previous crop is harvested and before transplanting. If the soil moisture is insufficient, appropriate irrigation can be carried out before deep plowing to make the soil moisture content reach 60%-70% of the field capacity, which is conducive to breaking up soil clods and leveling operations.

[0038] Preferably, the method also includes a step of transplanting flue-cured tobacco seedlings in a pit-like manner, where the row spacing is 1.0-1.5m and the plant spacing is 0.4-0.6m. Pit-like transplanting is a drought-resistant transplanting technique suitable for crops such as tobacco and sweet potatoes. The specific operation involves: first, drilling holes to form pit-shaped planting holes with a diameter of 8-12cm and a depth of 15-20cm; placing the tobacco seedlings in the holes, ensuring the top of the seedlings is slightly below the ground level; then watering to settle the roots; and sealing the holes after the water has seeped in. This method reduces water evaporation during the seedling stage, increases soil temperature, and promotes early and rapid growth. Row spacing refers to the vertical distance between two adjacent rows of tobacco plants. 1.0-1.5m can be adjusted according to the variety, leaf size, and terrain; for example, 1.2m can be selected in plains areas, and 1.3-1.4m can be selected on slopes. More preferably, the row spacing is 1.1-1.3m; most preferably, the row spacing is 1.2m. Plant spacing refers to the center-to-center distance between two adjacent plants within the same row, which can be selected from 0.4-0.6m. Fertile plots are suitable for sparse planting (0.5-0.6m), while infertile plots are suitable for dense planting (0.4-0.5m). A more preferable spacing is 0.45-0.55m; the most preferred spacing is 0.5m. The number of plants per acre can be calculated based on the row spacing and plant spacing. For example, with a row spacing of 1.2m and a plant spacing of 0.5m, there will be approximately 1111 plants per acre. Transplanting should be done on a cloudy day or in the evening of a sunny day. After transplanting, check and replant seedlings promptly to ensure a high survival rate.

[0039] Preferably, no other soil conditioners, phosphorus activators, exogenous organic acid preparations, or plant growth regulators are applied throughout the entire growth period. Soil conditioners refer to substances used to improve the physical, chemical, or biological properties of soil, including lime, gypsum, humic acid, polyacrylamide, and biochar. Phosphorus activators refer to chemical or biological agents specifically used to convert insoluble phosphorus in the soil into available phosphorus, such as phosphate rock powder, phosphorus-solubilizing bacteria, and organic acid complexes. Exogenous organic acid preparations refer to commercially available preparations containing organic acids other than the low molecular weight organic acids described in this invention, such as amino acid solutions, fulvic acid, and nucleic acid decomposition products. Plant growth regulators refer to artificially synthesized substances with plant hormone activity, such as gibberellins, auxins, cytokinins, and paclobutrazol. This invention limits the application of the above substances throughout the entire growth period to eliminate interfering factors, ensure clear attribution of technical effects, and avoid additional costs and unnecessary chemical inputs. In practical application, if the target field has severe nutrient deficiency or other obstacles, single-element fertilizers (such as boron fertilizer, zinc fertilizer) or conventional insecticides and fungicides may be appropriately supplemented without violating the core protection scope of this invention. However, it should be avoided to mix them with organic acid solutions for root irrigation. It is recommended to apply them separately at intervals of more than 7 days.

[0040] Preferably, the soil is slightly alkaline, with a pH of 7.0-7.8 and an available phosphorus content of less than 10 mg / kg. -1Brown soil, also known as brown forest soil, is a zonal soil type found in the warm temperate semi-humid and semi-arid regions of my country, mainly distributed in Shanxi, Shaanxi, Henan, Hebei, and Shandong provinces along the middle and lower reaches of the Yellow River. The parent material of brown soil is mostly loess or loess-like material. Its profile typically includes a humus layer, a clay layer, and a calcareous layer. The soil texture is mainly silty loam or light loam, with illite and montmorillonite as the main clay minerals. The cation exchange capacity is generally 15-25 cmol·kg⁻¹. -1 Typical characteristics of brown soil include: pH values ​​mostly between 7.0 and 8.0, exhibiting a neutral to slightly alkaline reaction; high calcium carbonate content, typically between 5% and 15%; and moderate to low organic matter content, generally 10-20 g / kg. -1 Phosphorus fixation capacity is strong; applied phosphate fertilizers readily combine with calcium to form calcium phosphate precipitates, and the effective phosphorus content is generally below 10 mg / kg. -1 In some older farmlands, the levels were even lower than 5 mg / kg. -1 The soil pH for which this invention is applicable is more preferably 7.2-7.6, further preferably 7.4-7.5, and most preferably 7.5; the available phosphorus content is more preferably 5-9 mg·kg. -1 Further preferred is 6-8 mg·kg -1 The optimal value is 8 mg / kg. -1 For soils with an organic matter content of less than 10 g / kg -1 For barren brown soil, before implementing this invention, 1-2 tons of well-rotted organic fertilizer per mu can be applied in conjunction with base fertilizer. -1 To enhance the synergistic effect between organic acids and soil.

[0041] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0042] Example

[0043] This embodiment provides a method for improving soil phosphorus availability and tobacco quality based on low molecular weight organic acids. The specific steps are as follows:

[0044] 1. Experimental location: Xichuan Village, Potou Township, Mianchi County, Sanmenxia City, Henan Province; soil type: brown soil; basic physicochemical properties: pH 7.52, organic matter 13.35 g·kg⁻¹ -1 Total nitrogen 1.42 g·kg -1 Available nitrogen 108.39 mg·kg -1 Available phosphorus 8.22 mg·kg -1 Available potassium 184.28 mg·kg -1 Slow-release potassium 1220.75 mg·kg -1 .

[0045] 2. Soil pretreatment: In April 2024, the soil was deeply plowed to a depth of 28cm to remove weeds and tobacco stalks from the field. The field was leveled manually to ensure that the soil was loose, uniform, and free of clods and impurities.

[0046] 3. Transplanting of tobacco seedlings: On May 1, 2024, the seedlings were transplanted using a pit-style method. The variety was Qin Yan 96. The row spacing was 1.2m and the plant spacing was 0.5m. 1100 seedlings were planted per mu. Healthy seedlings with a height of 15cm, stem diameter of 0.8cm and 4 true leaves were selected. After transplanting, the seedlings were watered in time to ensure the survival rate.

[0047] 4. Organic acid root irrigation: 35 days after transplanting (June 5, 2024), prepare a 2.0 g·L⁻¹ solution. -1 Apply 1L of malic acid solution evenly to the roots of each tobacco plant, watering within an 8cm radius around the base of the plant, avoiding splashing the leaves; the control group was treated with an equal amount of water.

[0048] 5. Field management: Apply 1500 kg / mu of well-rotted organic fertilizer + 50 kg / mu of tobacco-specific compound fertilizer as base fertilizer. Apply 10 kg / mu of seedling fertilizer 20 days after transplanting and 15 kg / mu of growth-promoting fertilizer 40 days after transplanting. Maintain soil moisture content of 60%–70% during the vigorous growth period and control soil moisture content of 50%–60% during the maturity period. Use yellow sticky traps to kill tobacco aphids and biological agents to control red spot disease. Do not apply other soil amendments throughout the entire growth period.

[0049] 6. Harvesting and curing: The tobacco leaves will be harvested in three stages when they mature in August and September 2024. They will be individually bundled into poles according to their processing and cured in three stages. After curing, they will be graded according to the GB2635-1992 flue-cured tobacco standard.

[0050] 7. Index determination: Soil available phosphorus, total phosphorus, and acid phosphatase activity were determined according to "Soil Agrochemical Analysis"; agronomic traits of tobacco plants were determined according to YC / T1421998; appearance quality and physical properties were determined according to flue-cured tobacco standards; conventional chemical components were determined using continuous flow analysis; neutral aroma substances were determined using GCMS; sensory evaluation was conducted according to YC / T4152011; and economic benefit indicators such as yield, output value, and proportion of high-grade tobacco were statistically analyzed.

[0051] 2. Comparison of treatments with different organic acids

[0052] Based on Example 1, four low molecular weight organic acids and three concentration control treatments were set up, for a total of 13 treatments (including the control), as follows:

[0053] Oxalic acid (OA): 1.5 g·L -1 (OA1.5), 2.0 g·L -1 (OA2.0), 2.5 g·L -1 (OA2.5);

[0054] Succinic acid (SA): 1.5 g·L -1 (SA1.5), 2.0 g·L -1 (SA2.0), 2.5 g·L -1 (SA2.5);

[0055] Citric acid (CA): 1.5 g·L -1 (CA1.5), 2.0 g·L -1 (CA2.0), 2.5 g·L -1 (CA2.5);

[0056] Malic acid (MA): 1.5 g·L -1 (MA1.5), 2.0 g·L -1 (MA2.0), 2.5 g·L -1 (MA2.5);

[0057] Control (CK): Root irrigation with plain water.

[0058] Each treatment was repeated three times in a randomized block design. All other management measures were exactly the same as in Example 1, and the measurement indicators were the same as in Example 1.

[0059] 3. Comparative Example

[0060] Comparative Example 1: Conventional cultivation (no organic acids applied, only conventional phosphate fertilizer applied)

[0061] Comparative Example 2: Application of 1.5 g·L -1 malic acid root irrigation

[0062] Comparative Example 3: Application of 2.5 g·L -1 malic acid root irrigation

[0063] Comparative Example 4: Application of 2.0 g·L -1 Citric acid root irrigation

[0064] The results showed that the present invention was effective at 2.0 g·L⁻¹. -1 Malic acid treatment significantly outperformed the control group in terms of increasing available phosphorus in the soil, optimizing tobacco quality, and increasing economic benefits. Specifically, the increase in available phosphorus in the soil was more than 35% higher than that of control group 1, and the tobacco output value was more than 30% higher than that of control group 1, resulting in the best overall effect.

[0065] The effects of each treatment on the agronomic traits, appearance quality, physical properties, conventional chemical components, neutral aroma substances, sensory quality, and economic benefits of tobacco plants are shown in Tables 1 to 7.

[0066] Table 1 Effects of different treatments on agronomic traits of tobacco plants

[0067]

[0068] Table 2 Effects of different treatments on the appearance quality of tobacco leaves

[0069]

[0070] Table 3 Effects of different treatments on the physical properties of tobacco leaves

[0071]

[0072] Table 4 Effects of different treatments on conventional chemical components of tobacco leaves

[0073]

[0074] Table 5. Effects of different treatments on neutral aroma compounds in tobacco leaves

[0075]

[0076] Table 6. Effects of different treatments on the sensory quality of tobacco leaves

[0077]

[0078] Table 7. Impact of different treatments on the economic benefits of tobacco.

[0079]

[0080] See technical route Figure 1 The effects of each treatment on soil available phosphorus, acid phosphatase activity, petroleum ether extract, photosynthetic characteristics, plastid pigments, carbon and nitrogen metabolism enzymes, nitrogen metabolism enzymes, phenylalanine ammonia-lyase, lipoxygenase, and glandular trichome morphology and density are shown in the following figures. Figures 2 to 11 .

[0081] Experimental Results and Analysis

[0082] 1. Impact on soil phosphorus availability

[0083] Root irrigation with different low molecular weight organic acids significantly improved soil phosphorus availability, with MA2.0 showing the best effect: soil available phosphorus content reached 11.73 mg·kg⁻¹ in the MA2.0 treatment. -1 The improvement was 37.51% compared to CK. The treatments were ranked as follows:

[0084] MA2.0>CA2.0>MA2.5>CA1.5>SA2.5>MA1.5>OA2.5>SA2.0>CA2.5>SA1.5>OA2.0>OA1.5>CK;

[0085] The proportion of available phosphorus to total phosphorus: the MA2.0 treatment reached 1.99%, an increase of 33.56% compared to the control (CK).

[0086] Soil acid phosphatase activity: MA2.0 treatment increased by 1.37 times compared with CK, significantly activating the soil's organic phosphorus mineralization capacity.

[0087] 2. Effects on agronomic traits of tobacco plants

[0088] MA2.0 treatment significantly optimized tobacco plant agronomic traits, with improvements compared to the control (CK):

[0089] Plant height: 90.17cm, an increase of 26.63%;

[0090] Stem circumference: 9.95cm, an increase of 9.22%;

[0091] Maximum leaf length: 65.01cm, an increase of 17.54%;

[0092] Maximum leaf width: 33.65cm, an increase of 6.12%;

[0093] Each treatment had no significant effect on the number of leaves, and the tobacco plants grew vigorously with a compact shape, spread-out leaves, and a significantly increased photosynthetic area.

[0094] 3. Impact on the appearance quality of tobacco leaves

[0095] MA2.0 treatment comprehensively improves the appearance quality indicators of tobacco leaves, with an improvement of: [Percentage missing] compared to CK.

[0096] Color: 38.90%; Maturity: 19.56%; Leaf structure: 25.68%;

[0097] Identity: 32.38%; Oil content: 50.50%; Color: 41.99%;

[0098] The cured tobacco leaves are orange-yellow in color, have good maturity, loose structure, high oil content, and rich color, and their appearance quality meets the standards for high-quality flue-cured tobacco.

[0099] 4. Effects on the physical properties of tobacco leaves

[0100] MA2.0 treatment significantly improves the physical processing properties of tobacco leaves:

[0101] Fill value: 22.12% higher than CK;

[0102] Infarct rate: 22.15% lower than CK;

[0103] Tensile strength, leaf density, and equilibrium moisture content are all significantly optimized. The leaves are loose and flexible, resulting in low processing losses and improved industrial usability.

[0104] 5. Effects on the conventional chemical composition of tobacco leaves

[0105] MA2.0 treatment harmonizes the chemical composition of tobacco leaves, meeting the requirements for high-quality flue-cured tobacco:

[0106] Reducing sugars: increased by 30.15%; Total sugars: increased by 27.73%; Potassium content: increased by 43.85%;

[0107] Chlorine content: decreased by 48.39%;

[0108] The potassium-chlorine ratio, sugar-alkali ratio, and nitrogen-alkali ratio are significantly optimized, and the chemical composition is coordinated and balanced, without defects such as being too alkaline, too sweet, or too irritating.

[0109] 6. Effects on aroma compounds in tobacco leaves

[0110] MA2.0 treatment significantly increases the content of aroma compounds in tobacco leaves:

[0111] Petroleum ether extract: 44.37% higher than CK;

[0112] Total amount of neutral aroma compounds: 42.66% higher than CK;

[0113] Carotenoid degradation products: increased by 11.06%; Neophytadiene: increased by 48.72%;

[0114] Maillard reaction products: increased by 10.80%; phenylalanine degradation products: increased by 31.66%; cephalosporin degradation products: increased by 8.71%;

[0115] Sufficient accumulation of aroma precursors lays the material foundation for the formation of high-quality aroma.

[0116] 7. Impact on the sensory quality of tobacco leaves

[0117] MA2.0 treatment significantly improved the sensory quality of tobacco leaves, with an improvement over the control (CK):

[0118] Fragrance quality: 1.60 points; Fragrance intensity: 1.43 points;

[0119] Irritation: reduced by 1.40 points; impurities reduced, aftertaste pure, smoke mellow, sensory quality reaches the level of high-grade flue-cured tobacco.

[0120] 8. Impact on the economic benefits of tobacco leaves

[0121] MA2.0 treatment significantly improves flue-cured tobacco yield and efficiency:

[0122] Production volume: increased by 13.43% compared to CK; Output value: increased by 32.28%;

[0123] The proportion of premium-grade cigarettes increased by 11.45%; the average price also increased significantly.

[0124] Profit: 42.42% higher than CK, with excellent input-output ratio, resulting in a significant increase in tobacco farmers' income.

[0125] 9. Effects on the physiological metabolism of tobacco leaves

[0126] MA2.0 treatment comprehensively enhances the physiological and metabolic functions of tobacco leaves:

[0127] Photosynthetic characteristics: Net photosynthetic rate increased by 43.38%, transpiration rate increased by 54.73%, and stomatal conductance increased by 42.86%;

[0128] Plastoplast pigments: Chlorophyll a increased by 20.39%, chlorophyll b increased by 67.86%, and carotenoids increased by 28.13%;

[0129] Carbon and nitrogen metabolism enzymes: Sucrose synthase increased by 53.03%, sucrose phosphate synthase increased by 97.79%, nitrate reductase increased by 74.94%, and glutamine synthase increased by 65.65%;

[0130] Aroma synthase: Phenylalanine ammonia-lyase activity increased by 50.47%, and lipoxygenase activity was significantly increased;

[0131] Glandular hair density: Long-stalked glandular hair was 1.96 times that of CK, short-stalked glandular hair was 1.50 times, and total glandular hair density was 1.86 times.

[0132] As shown in the above embodiments, this invention provides a method for improving soil phosphorus availability and tobacco leaf quality based on low molecular weight organic acids. Field trials of different types and concentrations of low molecular weight organic acids verified that root irrigation during the flue-cured tobacco growing stage improved soil available phosphorus content, the proportion of available phosphorus to total phosphorus, and soil acid phosphatase activity to varying degrees, with malic acid showing the most significant effect. After applying malic acid, agronomic traits such as plant height, stem circumference, and leaf length and width were significantly improved. Appearance quality indicators of the cured tobacco leaves, such as color, maturity, oil content, and chroma, were enhanced, and physical properties such as filling value, tensile strength, and stem content were optimized. The content of reducing sugar, total sugar, and potassium in the tobacco leaves increased, while the chlorine content decreased, and the potassium-chlorine ratio, sugar-alkali ratio, and nitrogen-alkali ratio tended to be more balanced. The total amount of petroleum ether extract and neutral aroma substances increased significantly, and aroma components such as carotenoid degradation products, neophytadiene, Maillard reaction products, and phenylalanine degradation products accumulated more. Sensory quality evaluation showed improved aroma quality and aroma quantity scores, and reduced irritation. Simultaneously, the net photosynthetic rate, plastid pigment content, activity of key carbon and nitrogen metabolism enzymes, aroma synthesis enzyme activity, and leaf glandular trichome density of tobacco leaves were all significantly improved. Ultimately, yield, output value, proportion of high-grade tobacco, and profit all increased significantly. Considering all indicators, the technical solution of this invention can systematically solve the prominent problems of low phosphorus availability and poor tobacco quality in neutral to alkaline brown soil tobacco-growing areas, demonstrating stable field application effects and significant industrialization and promotion value.

[0133] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for improving soil phosphorus availability, characterized in that, This includes applying an aqueous solution of a low molecular weight organic acid to the soil, wherein the low molecular weight organic acid is selected from one or more of malic acid, citric acid, succinic acid, and oxalic acid.

2. A method for improving the quality of tobacco leaves, characterized in that, This includes irrigating the rhizosphere soil of flue-cured tobacco with a low molecular weight organic acid aqueous solution, wherein the low molecular weight organic acid is selected from one or more of malic acid, citric acid, succinic acid, and oxalic acid.

3. The method according to claim 1 or 2, characterized in that, The concentration of the low molecular weight organic acid in the aqueous solution is 0.5-5.0 g·L. -1 .

4. The method according to claim 1 or 2, characterized in that, The amount of the low molecular weight organic acid aqueous solution applied per unit area of ​​soil or per plant is 0.5-2.0L per square meter or 0.5-2.0L per plant.

5. The method according to claim 2, characterized in that, The root irrigation treatment specifically involves uniformly irrigating the low molecular weight organic acid aqueous solution within a 5-10cm radius around the base of the tobacco plant roots.

6. The method according to claim 2, characterized in that, The application time for the rhizosphere soil of flue-cured tobacco is 25-45 days after transplanting.

7. The method according to claim 2, characterized in that, Before application, the process also includes a soil pretreatment step, which includes deep plowing to a depth of 25-30 cm, removing weeds and stubble, and leveling the field.

8. The method according to claim 2, characterized in that, It also includes the step of transplanting flue-cured tobacco seedlings in a pit-like manner, wherein the row spacing is 1.0-1.5m and the plant spacing is 0.4-0.6m.

9. The method according to claim 2, characterized in that, No other soil conditioners, phosphorus activators, exogenous organic acid preparations, or plant growth regulators should be applied throughout the entire growth period.

10. The method according to claim 1 or 2, characterized in that, The soil is slightly alkaline, with a pH of 7.0-7.8 and an available phosphorus content of less than 10 mg / kg. -1 Brown soil.

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