A method for remediating cadmium contaminated soil by synergistically enhancing high-accumulation tobacco with nitrogen application and planting density

Abstract

This invention belongs to the field of phytoremediation technology, specifically relating to a method for remediating cadmium-contaminated soil by synergistically enhancing nitrogen application and planting density with high-accumulation tobacco. The method includes the following steps: S1: A high-cadmium-accumulating tobacco variety, Yuyan No. 5, was obtained through screening and comparative experiments; Yuyan No. 5 tobacco seeds were then used for seedling cultivation using the floating tray method; S2: When the seedlings reached 6 leaves and 1 heart leaf, they were transplanted; basal fertilizer was applied to the soil before transplanting; during fertilization, the form and amount of nitrogen fertilizer were adjusted, and the planting density of the tobacco was also adjusted to remediate the cadmium-contaminated soil. This remediation method has the advantages of low cost, environmental friendliness, simple operation, and high remediation efficiency, providing an efficient and feasible solution for the phytoremediation of Cd-contaminated soil, with significant environmental and ecological benefits.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of plant remediation, and particularly relates to a method for remediation of cadmium-contaminated soil by synergistically enhancing high-accumulation tobacco through nitrogen application and planting density. BACKGROUND

[0002] Cadmium (Cd) is a heavy metal with high toxicity and high mobility, which cannot be degraded in soil and is easily enriched in organisms through the food chain, causing serious harm to human health. Therefore, the remediation of Cd-contaminated soil has become a major challenge in the field of environmental governance. At present, the remediation methods for Cd-contaminated soil mainly include physical remediation, chemical remediation and biological remediation. Although physical and chemical remediation can take effect quickly, they have problems such as high cost, complex operation, easy damage to soil structure and possible secondary pollution, and are difficult to be widely applied. In contrast, plant remediation technology can become an important research direction for the remediation of Cd-contaminated farmland soil due to its advantages such as simple operation, environmental friendliness and strong sustainability.

[0003] Recent studies have found that tobacco has strong tolerance and accumulation capacity for Cd, can absorb Cd from soil and transfer it to the aboveground part, and is a relatively ideal potential remediation plant. In addition, tobacco grows rapidly, has large biomass, and its planting and management technology is mature, which is suitable for the remediation of large-area medium and heavy Cd-contaminated soil. However, the efficiency of tobacco in remediation of Cd-contaminated soil is limited by two key factors: one is how to increase the aboveground biomass (especially the leaf biomass) of plants per unit area, thereby increasing the Cd accumulation; the other is that the bioavailability of Cd in contaminated farmland soil is limited, and how to improve the soil Cd availability to increase the effective Cd content that plants can absorb and utilize in the rhizosphere soil environment. In the prior art, there are more studies on promoting tobacco growth by applying nitrogen or adjusting planting density alone, such as applying nitrogen (such as nitrogen fertilizer form or amount) (ref: Zhang J, Huang H, Yang LJ, et al. Research progress of nitrogen form on tobacco growth and quality [J]. China Planting Bulletin, 2018, 34(15): 38-43.) or adjusting planting density (ref: Sang YH, Yu FT, Luo YG, et al. Effects of different planting densities on growth and quality of flue-cured tobacco [J]. Shandong Agricultural Sciences, 2019, 51(12): 26-30) to promote tobacco growth. The existing reports mainly focus on the yield and quality of tobacco, while the purpose of the present technology is to increase the heavy metal accumulation of tobacco. Moreover, the existing methods only consider the improvement of the growth conditions of tobacco by a single technology, and fail to consider the “population-individual” resource allocation and “soil-plant” cadmium migration efficiency in a synergistic manner, which may result in limited improvement of the actual remediation efficiency.

[0004] Therefore, developing a method to enhance the remediation of Cd-contaminated soil by tobacco through the synergistic regulation of nitrogen application and planting density can not only significantly increase the biomass and Cd accumulation capacity of tobacco, but also enhance the bioavailability of Cd by influencing soil physicochemical properties, promoting the absorption and accumulation of Cd by tobacco in the soil. This achieves efficient, economical, and environmentally friendly remediation of Cd-contaminated soil. This synergistic remediation method has significant scientific and application value, providing a feasible solution for the remediation of large-scale Cd-contaminated soil and promoting the widespread application of phytoremediation technology in the field of heavy metal pollution control in soil. Summary of the Invention

[0005] To achieve the above objectives, this invention provides a method for synergistically enhancing the remediation of cadmium-contaminated soil by tobacco through nitrogen application and planting density, comprising the following steps:

[0006] S1: Yuyan No. 5 was obtained through screening and comparison, and the Yuyan No. 5 tobacco seeds were raised using the floating tray method.

[0007] S2: Select tobacco seedlings for transplanting when they have grown to 6 leaves and 1 heart; fertilize the soil before transplanting; adjust the amount of nitrogen applied to the tobacco during the fertilization process, and then adjust the planting density of the tobacco to remediate the cadmium-contaminated soil.

[0008] Furthermore, the fertilizers used in the fertilization process described in S2 include nitrogen fertilizer, superphosphate, and potassium sulfate. The nitrogen fertilizer forms include ammonium nitrogen, nitrate nitrogen, and amide nitrogen. The ammonium nitrogen is ammonium bicarbonate, the nitrate nitrogen is potassium nitrate, and the amide nitrogen is urea. The ammonium bicarbonate contains 17% N; the potassium nitrate contains 13.5% N and 44.5% K2O; and the urea contains 46% N.

[0009] Furthermore, the fertilization process described in S2 involves the application of basal fertilizer and topdressing. The basal fertilizer comprises 80% nitrogen and potassium fertilizer and all of the phosphorus fertilizer, while the topdressing comprises 20% nitrogen and potassium fertilizer.

[0010] Furthermore, the nitrogen application rate described in S2 is 60-180 kg per hectare.

[0011] Furthermore, the planting density described in S2 is 16,500-28,500 plants per hectare.

[0012] Beneficial effects

[0013] This invention provides a method for synergistically enhancing tobacco remediation of cadmium-contaminated soil through nitrogen application and planting density. This synergistic regulation significantly improves remediation efficiency: by optimizing nitrogen application and planting density, the biomass and Cd accumulation capacity of tobacco are significantly increased. Simultaneously, this regulation method significantly increases the total amount of Cd extracted by tobacco per unit area, achieving highly efficient remediation of Cd-contaminated soil.

[0014] This method is simple to operate and low in cost: The present invention uses conventional nitrogen fertilizer (such as ammonium bicarbonate, potassium nitrate, urea) and phosphorus and potassium fertilizer in the same ratio, combined with field planting density control. It does not require complicated equipment or high investment, and is simple and easy to operate, making it suitable for large-scale promotion and application.

[0015] Environmentally friendly and highly sustainable: This invention is based on phytoremediation technology, which relies entirely on natural processes such as photosynthesis, requires no power, and avoids disturbance to soil structure and secondary pollution of the ecological environment.

[0016] This remediation method has a wide range of applications and strong scalability: the tobacco variety Yuyan No. 5 used in this invention has high tolerance and accumulation capacity for Cd, and its planting and management techniques are mature, making it suitable for the remediation of large-scale Cd-contaminated soils in different regions. By adjusting the type of nitrogen fertilizer, the optimal nitrogen application rate, and the planting density, it can flexibly adapt to different soil types and environmental conditions, demonstrating broad applicability and promotional value. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] In the picture:

[0019] Figure 1 These are the root Cd absorption time-kinetic characteristics of the two types of tobacco materials of the present invention;

[0020] Figure 2 This is a diagram showing the effect of nitrogen fertilizer forms of the present invention on soil pH;

[0021] Figure 3 This is a diagram showing the effect of nitrogen fertilizer forms of the present invention on the content of available Cd in the soil;

[0022] Figure 4 This is a diagram showing the effect of nitrogen fertilizer forms of the present invention on the total Cd content of soil;

[0023] Figure 5 This is a diagram showing the effect of nitrogen fertilizer forms on the proportion of Cd chemical forms in soil according to the present invention.

[0024] Figure 6 This is a diagram showing the effect of nitrogen fertilizer forms of the present invention on soil enzyme activity;

[0025] Figure 7 This is a graph showing the effect of nitrogen application rate and planting density on the Cd content of tobacco according to the present invention;

[0026] Figure 8 This is a graph showing the effect of nitrogen application rate and planting density on Cd extraction yield per hectare of tobacco according to the present invention; Detailed Implementation

[0027] The following will describe in conjunction with embodiments 1-10 of the present invention and the appendix. Figures 1-8 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] This embodiment is for screening nitrogen fertilizer forms;

[0030] A Cd-contaminated soil test area was selected, with a soil pH of 5.76 and a total Cd concentration of 1.44 mg / kg. -1 Effective Cd 0.26 mg / kg -1 The high-Cd-accumulating tobacco variety, Yuyan No. 5, was used. Seedlings were raised using the conventional floating tray method. When the seedlings reached 6 leaves and 1 heart, uniformly growing seedlings were selected for transplanting. 80% nitrogen and potassium fertilizer were applied as base fertilizer. Fifteen days after transplanting, the remaining nitrogen and potassium fertilizer were applied as top dressing. Three different forms of nitrogen fertilizer (CO(NH2)2, NH4HCO3, and KNO3) were used. A control group (CK) was also established without nitrogen application. The nitrogen application rate was set at the conventional 120 kg / hm². -2 The planting density was set at 16,500 plants per hectare. -2 After transplanting, tobacco can be managed using conventional methods. Samples were taken at the tobacco maturity stage to determine its Cd content. The effects of nitrogen fertilizer forms on the Cd content and accumulation of tobacco were obtained.

[0031] Using the results from Example 1 to screen nitrogen fertilizer forms, it was found that all three nitrogen fertilizer forms promoted the growth and development of tobacco. The order of tobacco plant height and biomass was: CO(NH2)2 > NH4HCO3 > KNO3 > CK (no nitrogen application). Under urea application, plant height and total biomass increased by 19.40% and 69.99% respectively compared to the control.

[0032] Regarding the effect of nitrogen fertilizer form on the Cd content of tobacco, it can be concluded that there was no significant difference in Cd content between the thinning roots and stems under the treatment, while the Cd content of tobacco leaves under the control condition was 10.00 mg / kg. -1 The Cd content in leaves was significantly higher under both ammonium nitrogen and amide nitrogen application conditions than under nitrate nitrogen application conditions, with the highest Cd content reaching 13.45 mg / kg under amide nitrogen application conditions. -1 This represents a 34.50% increase compared to the control group.

[0033] The effects of nitrogen fertilizer forms on Cd accumulation in tobacco plants showed that all three nitrogen fertilizer forms significantly increased Cd accumulation in all parts of the tobacco plant. The order of Cd accumulation in different parts of the tobacco plant was: CO(NH2)2 > NH4HCO3 > KNO3 > CK. Specifically, the Cd accumulation in the entire tobacco plant under the application of amide nitrogen was significantly higher than that under the other two nitrogen fertilizer treatments, reaching a maximum of 2263.08 μg / plant. -1 This represents an increase of 104.89%.

[0034] Example 2

[0035] S1: Select the cadmium-accumulating tobacco variety Yuyan No. 5. This variety has a strong tolerance and accumulation capacity for cadmium. Use the floating tray method to raise seedlings of Yuyan No. 5 tobacco seeds.

[0036] S2: Optimize nitrogen fertilizer application by selecting three different forms of nitrogen fertilizer: ammonium nitrogen, nitrate nitrogen, and amide nitrogen. Specific nitrogen fertilizer types include ammonium bicarbonate (containing 17% N), potassium nitrate (containing 13.5% N and 44.5% K2O), and urea (containing 46% N). Phosphate fertilizer is applied as a one-time basal application. 80% of the nitrogen and potassium fertilizers are used as basal fertilizers, and the remaining 20% ​​of nitrogen and potassium fertilizers are applied as top dressing 15 days later, depending on the tobacco growth, to optimize nutrient supply and promote tobacco growth. Fix the nitrogen application rate and planting density to ensure that each tobacco plant receives sufficient nutrients and growing space. The nitrogen application rate is 60 kg per hectare, and the planting density is 16,500 plants per hectare. Through the absorption and accumulation of cadmium by tobacco, the cadmium content in the soil is significantly reduced, achieving efficient remediation of cadmium-contaminated soil.

[0037] Example 3

[0038] S1: The steps are the same as in Example 2.

[0039] S2: The steps are the same as in Example 2, except that the nitrogen application rate is 60 kg per hectare and the planting density is 22,500 plants per hectare.

[0040] Example 4

[0041] S1: The steps are the same as in Example 2.

[0042] S2: The steps are the same as in Example 2, except that the nitrogen application rate is 60 kg per hectare and the planting density is 28,500 plants per hectare.

[0043] Example 5

[0044] S1: The steps are the same as in Example 2.

[0045] S2: The steps are the same as in Example 2, except that the nitrogen application rate is 120 kg per hectare and the planting density is 16,500 plants per hectare.

[0046] Example 6

[0047] S1: The steps are the same as in Example 2.

[0048] S2: The steps are the same as in Example 2, except that the nitrogen application rate is 120 kg per hectare and the planting density is 22,500 plants per hectare.

[0049] Example 7

[0050] S1: The steps are the same as in Example 2.

[0051] S2: The steps are the same as in Example 2, except that the nitrogen application rate is 120 kg per hectare and the planting density is 28,500 plants per hectare.

[0052] Example 8

[0053] S1: The steps are the same as in Example 2.

[0054] S2: The steps are the same as in Example 2, except that the nitrogen application rate is 180 kg per hectare and the planting density is 16,500 plants per hectare.

[0055] Example 9

[0056] S1: The steps are the same as in Example 2.

[0057] S2: The steps are the same as in Example 2, except that the nitrogen application rate is 180 kg per hectare and the planting density is 22,500 plants per hectare.

[0058] Example 10

[0059] S1: The steps are the same as in Example 2.

[0060] S2: The steps are the same as in Example 2, except that the nitrogen application rate is 180 kg per hectare and the planting density is 28,500 plants per hectare.

[0061] Depend on Figure 1 It was found that the Cd content in both the aboveground and underground parts of the two types of tobacco materials increased significantly with increasing Cd treatment concentration. Under the same Cd concentration treatment, the Cd content in both the aboveground and underground parts of Yuyan No. 5 was significantly higher than that of the control variety RG11, by 29.6%–40.0% and 64.9%–50.6%, respectively.

[0062] Depend on Figure 2 It can be seen that the soil pH under the control condition was 5.73. The soil pH under the application of ammonium nitrogen and amide nitrogen was significantly lower than that under the control condition. The soil pH was the lowest under the application of amide nitrogen, which was 5.69. Nitrate nitrogen had no significant effect on soil pH.

[0063] Depend on Figure 3 It can be seen that the available Cd content in the soil under the control conditions was 0.21 mg / kg.-1 Under both ammonium nitrogen and amide nitrogen treatments, the available Cd content in the soil was significantly higher than that in the control. Specifically, the highest available Cd content in the soil reached 0.24 mg / kg under amide nitrogen treatment. -1 The concentration was significantly higher than the control, increasing by 14.3%, which is beneficial for tobacco to absorb Cd from the soil.

[0064] Depend on Figure 4 It can be seen that the total Cd content in the soil under the control condition was 0.68 mg / kg. -1 All three nitrogen fertilizer treatments showed a decrease in total Cd content compared to the control, with the total Cd content decreasing to the lowest level of 0.61 mg / kg under the amide nitrogen application condition. -1 The levels were significantly lower than the control, decreasing by 11.5%. This indicates that the nitrogen fertilizer treatment had the most significant promoting effect on tobacco absorption and accumulation of soil Cd, reducing the amount of Cd in the soil due to crop absorption and translocation.

[0065] Depend on Figure 5 It can be seen that, compared with the control, the proportions of exchangeable and carbonate-bound Cd with higher activity under the application of ammonium nitrogen and amide nitrogen showed an increasing trend, while the proportions of iron and manganese oxidized and residual Cd with lower activity showed a decreasing trend. Specifically, the proportion of exchangeable Cd reached its maximum of 25.0% under the application of amide nitrogen fertilizer, while the proportion of residual Cd was the lowest at 22.4%. The application of nitrate nitrogen fertilizer showed the opposite trend, with the proportion of exchangeable Cd decreasing to 17.4%, while the proportion of residual Cd reached its maximum of 31.6%.

[0066] Soil enzyme activity is an important indicator for evaluating soil ecological function. It can help determine the activity of soil microorganisms after nitrogen fertilizer application and reflect the soil remediation effect at different levels. Figure 6 It can be seen that the application of all three nitrogen fertilizers significantly increased the activities of soil urease, sucrase, and catalase compared to the control. Soil enzyme activity may play an important role in Cd speciation by influencing soil microbial communities and soil chemical properties. The increase in enzyme activity also indicates that nitrogen fertilizer application increased soil nitrogen nutrient levels, increased nutrient transformation efficiency of soil microorganisms, and reduced the toxic effects of Cd in the soil. Among them, the application of amide nitrogen resulted in the highest urease and catalase activities, at 7.94 and 4.16 μg, respectively. -1 g -1 h -1 Compared with the control, it increased by 3.7% and 6.4%.

[0067] Depend on Figure 7It can be seen that, under the same planting density, the Cd content in tobacco roots and stems generally shows a trend of first decreasing and then increasing with increasing nitrogen application, reaching its highest level under no nitrogen application. Regarding leaf Cd content, under the same density, it increases with increasing nitrogen application, indicating that nitrogen fertilizer application effectively increases leaf Cd content; at 180 kg / hm²... -2 The nitrogen application rate reached its maximum under the given conditions, and was significantly higher than that of 0 and 60 kg / hm. -2 The nitrogen application rate was determined. Under the same nitrogen application rate, the Cd content in the leaves was not affected by the planting density.

[0068] Depend on Figure 8 It can be seen that, under the same planting density, the amount of Cd extracted by tobacco from the soil per hectare showed a trend of first increasing and then decreasing with the increase of nitrogen application, with the lowest extraction rate at 120 kg / hm². -2 The nitrogen application rate reached its maximum value under the given conditions, and was significantly higher than that of 0 and 60 kg / hm. -2 The nitrogen application rate was determined. Under the same nitrogen application rate, Cd extraction also showed a trend of first increasing and then decreasing with increasing planting density, at 22,500 plants per hectare. -2 The density reached its maximum value under the specified conditions, and was significantly higher than that of 16,500 plants per hectare. -2 Density conditions. Overall, at 22,500 plants / hm²... -2 Under the given density conditions, apply 120 kg hm -2 Nitrogen fertilizer, the highest Cd extraction yield per hectare of tobacco can reach 39685.28 mg / hm. -2 Compared to the same planting density without nitrogen application (22,500 plants / hm²), -2 Planting density, 0 kg / hm -2 The nitrogen application rate improved by 68.5%; compared to the conventional planting density (16,500 plants per hectare) with the same nitrogen application rate. -2 Planting density, 120 kg / hm -2 The nitrogen application rate increased by 26.9%, demonstrating that the synergistic regulation of nitrogen application rate and planting density can significantly increase the total Cd extraction per unit area of ​​tobacco.

[0069] This invention provides a method for remediating cadmium-contaminated soil by synergistically enhancing nitrogen application and planting density with high-accumulation tobacco. This invention selects the cadmium-accumulating tobacco variety Yuyan No. 5 and significantly improves the absorption, translocation and accumulation of cadmium by tobacco by optimizing nitrogen fertilizer form, nitrogen application amount and planting density, thereby enhancing its remediation efficiency for cadmium-contaminated soil.

[0070] The core innovation of this invention is:

[0071] Application of high Cd-accumulating tobacco varieties: Yuyan No. 5, a high Cd-accumulating tobacco material, was selected. This variety has high tolerance and accumulation capacity for Cd, and can efficiently absorb and accumulate Cd in the soil, significantly improving remediation efficiency.

[0072] Nitrogen fertilizer form optimization: Multiple nitrogen fertilizers, including ammonium bicarbonate, potassium nitrate, and urea, were used in combination with a rational allocation of basal and topdressing fertilizers to optimize nutrient supply. Specifically, the application of amide nitrogen (CO(NH2)2) effectively promoted tobacco growth and development. Simultaneously, it enhanced soil enzyme activity, lowered soil pH, and promoted the migration and transformation of insoluble Cd into soluble Cd, thereby increasing the bioavailability of Cd in the soil and facilitating the absorption and accumulation of Cd by tobacco. The highest Cd accumulation in tobacco reached 2263.08 μg plant. -1 This represents an increase of 104.89% compared to the control group.

[0073] Coordinated regulation of nitrogen application rate and planting density: at a planting density of 22,500 plants per hectare -2 The application rate of amide nitrogen fertilizer is 120 kg / hm². -2 Under these conditions, the highest Cd extraction yield per unit area of ​​tobacco reached 39685.28 mg / hm. -2 Compared to no nitrogen application and conventional planting density control, the nitrogen application rate increased by 68.5% and 26.9%, respectively. This result indicates that by synergistically controlling nitrogen application rate and planting density, the absorption and accumulation capacity of tobacco for Cd can be significantly improved, thereby increasing the total amount of Cd extracted per unit area.

[0074] Remediation Mechanism: This invention promotes tobacco growth and development through the synergistic effect of nitrogen application and planting density, emphasizing the coordination between individual tobacco plants and the overall population, and increasing the aboveground biomass of tobacco. The combination of suitable nitrogen fertilizer type (amide nitrogen) and appropriate dosage can significantly reduce soil pH and increase the bioavailability of Cd, thereby significantly improving the tobacco's ability to absorb and accumulate Cd in the soil, effectively increasing the total amount of Cd extracted by tobacco per unit area, and ultimately achieving efficient remediation of Cd-contaminated soil.

Claims

1. A method for remediating cadmium-contaminated soil with high-accumulation tobacco by synergistically enhancing nitrogen application and planting density, characterized in that, Includes the following steps: S1: Yuyan No. 5 was obtained through screening and comparison, and the Yuyan No. 5 tobacco seeds were raised using the floating tray method. S2: When the tobacco seedlings have grown to 6 leaves and 1 heart, select the seedlings for transplanting; fertilize the soil before transplanting; Adjusting the nitrogen application rate of tobacco during fertilization, and then adjusting the planting density of tobacco, are used to remediate cadmium-contaminated soil. The fertilizers used in the fertilization process include nitrogen fertilizer, superphosphate, and potassium sulfate. The nitrogen fertilizer includes ammonium nitrogen, nitrate nitrogen, and amide nitrogen. The ammonium nitrogen is ammonium bicarbonate, the nitrate nitrogen is potassium nitrate, and the amide nitrogen is urea. The ammonium bicarbonate contains 17% N; the potassium nitrate contains 13.5% N and 44.5% K₂O; and the urea contains 46% N. The nitrogen application rate is 60-180 kg per hectare; the planting density is 16,500-28,500 plants per hectare.

2. The method for remediating cadmium-contaminated soil with high-accumulation tobacco by synergistically enhancing nitrogen application and planting density, as described in claim 1, is characterized in that... The fertilization process described in S2 is basal fertilizer + topdressing. The basal fertilizer includes 80% nitrogen fertilizer + potassium fertilizer and all of the phosphorus fertilizer, and the topdressing includes 20% nitrogen fertilizer + potassium fertilizer.

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