Combined phytoremediation method for strictly controlling cadmium pollution of cultivated land

Abstract

The invention discloses a combined phytoremediation method for strictly controlling cadmium pollution of farmland, and belongs to the technical field of farmland heavy metal pollution treatment and chelating induced plant extraction remediation. Aiming at the problems of low cadmium pollution remediation efficiency, high cost, poor economic benefit, high soil secondary pollution risk and the like of strictly controlled cultivated land, a biodegradable and environment-friendly efficient chelating agent is screened, economic crops with agricultural regulation and large biomass and the like are combined to carry out enhanced plant extraction remediation, a traditional single static remediation measure is broken through, and the remediation effect is good. Dynamic regulation and control are conducted according to nutrient requirements of plants in different growth periods, remediation and fertilization are both considered, planting structure adjustment is achieved, production, remediation and income can be achieved at the same time, and secondary pollution to soil cannot be caused. The method has higher repairing efficiency, lower repairing cost and better economic benefits, and has a good market application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of farmland heavy metal pollution control and chelation-induced plant extraction and restoration, and specifically relates to a combined plant restoration method for strictly controlled cadmium pollution in cultivated land. Background Art

[0002] According to the Agricultural Land Soil Pollution Risk Control Standards (GB15618-2018), depending on the soil pH, cadmium content >1.5~4.0 mg / kg is strictly controlled arable land; this type of arable land is heavily polluted by heavy metals in the soil, posing a high risk to the quality and safety of agricultural products, crop growth or soil ecological environment, and it is difficult to reduce the risk through agricultural land safe utilization measures.

[0003] Chelate-induced phytoextraction is a typical chelating agent enhanced remediation measure, that is, through the artificial addition of chelating agents (EDTA, etc.), heavy metals bound by the soil solid phase are released again and enter the soil, becoming dissolved or easily soluble, thereby effectively improving the absorption or enrichment efficiency of heavy metals by plants. Phytoextraction remediation technology has the advantages of being in situ, green, low cost, and having little environmental disturbance. It is a remediation technology that can reduce the total amount of heavy metals in cultivated soil. Chelate-induced phytoextraction remediation technology is widely used in the phytoextraction enhancement process of heavy metal contaminated soil because of its rapid effect and low cost. Among them, the selection of chelating agents and the screening of remediation plants are two important factors affecting the efficiency of chelating-induced phytoextraction remediation.

[0004] At present, commonly used chelating agents are mainly divided into two categories: polycarboxyl amino acids and natural low molecular weight organic acids. The first type of commonly used polycarboxyl amino acid chelating agents such as EDTA, EGTA, etc. are promoted for their strong chelating ability, but they have great limitations in practical applications due to their environmental persistence, poor biodegradability, and high risk of heavy metal leaching. The other type is natural low molecular weight organic acids (LMWOAs), mainly citric acid, oxalic acid, malic acid, etc. LMWOAs have the advantages of being environmentally friendly, biodegradable, and free of secondary pollution, but the chelating effect is far inferior to that of polycarboxyl amino acid chelating agents, and it will aggravate soil acidification.

[0005] The key to plant extraction and remediation is to select appropriate cadmium (super)accumulators, which are plants that can absorb excessive amounts of heavy metals and transport them to the aboveground parts. Although superaccumulators have a strong ability to extract heavy metals, there are still many problems in their application in farmland management, including strong regional distribution, low biomass, harsh agricultural growth conditions, and low economic value, which makes it difficult to promote large-scale planting in the wild.

[0006] At the same time, due to the multi-source, hidden and complex nature of soil heavy metal pollution, as well as the differences in soil types, external conditions and pollution levels in different regions, the remediation effect of a single strengthening measure is often difficult to achieve the expected goal. Agronomic measures are currently the most environmentally friendly and lowest-cost auxiliary measures that can strengthen plant remediation from both plant and soil aspects. Nitrogen (N) is the most important macronutrient in crop production and plays an important role in plant growth and development metabolism, such as photosynthesis, nutrient allocation, biomass and yield formation. A large number of studies have shown that compared with other elements such as phosphorus, potassium, calcium, magnesium, manganese, zinc and copper, the absorption, transport and accumulation of cadmium in plants are highly regulated by nitrogen. However, nitrogen fertilizer is currently generally regarded as a plant nutrient source, and the specific effects of its different forms on the migration and transformation of heavy metals have not been fully explored, ignoring the dual functions of nitrogen fertilizer "nutrition-remediation".

[0007] Based on this, it is of great significance to study a restoration method that maintains soil health while improving the efficiency of phytoremediation and taking into account both restoration and fertilization. Summary of the invention

[0008] In view of the problems raised in the background technology, the purpose of the present invention is to provide a combined plant restoration method for cadmium pollution in strictly controlled cultivated land. The method is aimed at the restoration of cadmium pollution in strictly controlled cultivated land, and a multi-factor synergistic restoration model of "materials-nutrients-soil-ramie" is constructed, which can significantly increase the biomass of ramie, and the cadmium content of its bast fiber can be controlled within the relevant standard range of textile raw materials, while the cadmium accumulation of stems and leaves is significantly increased, thereby improving the efficiency of plant restoration, and taking into account restoration and fertilization. The present invention fully exploits the "nutrition-restoration" regulatory function of nitrogen fertilizer, takes into account environmental benefits, economic benefits and social benefits, and has good application prospects.

[0009] The present invention provides a combined phytoremediation method for cadmium pollution in strictly controlled cultivated land, comprising the following steps: S1. Apply compound fertilizer to the cultivated land and then plough it, then spread the chelating agent; S2. Transplant ramie seedlings, apply chelating agent and ammonium nitrogen fertilizer at the first ramie seedling stage, apply chelating agent and nitrate nitrogen fertilizer at the row closing stage, and apply chelating agent and amide nitrogen fertilizer at the second and third ramie growth stages; S3. Harvesting ramie.

[0010] Furthermore, the tillage depth in S1 is 30 cm, and after tillage, the chelating agent can be evenly spread together with wood ash and dry soil into the cultivated land to be restored.

[0011] Furthermore, the chelating agents in S1 and S2 are both polyaspartic acid.

[0012] Furthermore, the variety of ramie described in S2 is "Zhong Zhu No. 1", and the ramie seedlings are tender shoot cuttings with primary radish roots grown in soil.

[0013] Furthermore, the ammonium nitrogen fertilizer in S2 is ammonium sulfate, the nitrate nitrogen fertilizer is potassium nitrate, and the amide nitrogen fertilizer is urea.

[0014] Nitrate nitrogen fertilizer and ammonium nitrogen fertilizer are both quick-acting fertilizers and are not suitable for use as base fertilizers. Polyaspartic acid is a biodegradable chelating agent with a degradation cycle of about 20-30 days. It has a strong chelating ability. Applying it before planting can form a stable water-soluble chelate with cadmium in the soil, effectively activating the cadmium in the soil, increasing the mobility of cadmium in the soil, and making it easier for ramie to absorb and enrich it.

[0015] Furthermore, the amount of the chelating agent added is 5-10 kg / mu per year, and the annual application amount of pure nitrogen is 20-30 kg / mu.

[0016] Furthermore, the application ratio of chelating agents and different forms of nitrogen fertilizers in different periods is as follows: before transplanting ramie, the applied compound fertilizer accounts for 10%-20% of the annual application of pure nitrogen, and the broadcast chelating agent accounts for 20% of the added amount; during the emergence period of ramie, the applied chelating agent accounts for 20% of the added amount, and ammonium nitrogen fertilizer accounts for 10%-20% of the annual application of pure nitrogen; during the closure period of ramie, the applied chelating agent accounts for 20% of the added amount, and nitrate nitrogen fertilizer accounts for 10%-20% of the annual application of pure nitrogen; after the harvest of ramie, the applied chelating agent accounts for 20% of the added amount, and amide nitrogen fertilizer accounts for 20%-30% of the annual application of pure nitrogen during the growth period of the second ramie, and the applied chelating agent accounts for 20% of the added amount, and amide nitrogen fertilizer accounts for 20%-30% of the annual application of pure nitrogen during the growth period of the third ramie.

[0017] The pH value of polyaspartic acid (PASP) aqueous solution is about 6-7, which will not affect the background pH value of the soil. However, the existing technology has been applying a single form of nitrogen fertilizer for a long time, ignoring the synergistic / antagonistic effect of the combined restoration of polyaspartic acid and different forms of nitrogen fertilizers, and cannot give full play to the synergistic restoration effect of PASP and nitrogen fertilizers. The key reasons are: first, when ammonium nitrogen fertilizer is applied together with PASP, ammonium ions are prone to compete with cadmium in the soil, affecting the chelating properties of PASP and weakening the activation effect of PASP on soil cadmium. In addition, ammonium nitrogen fertilizer is a physiologically acidic fertilizer. During nitrification and plant absorption, it will undergo protonation reaction and release H +, significantly reducing soil pH, and long-term application can easily cause soil acidification; second, compared with ammonium nitrogen fertilizer, single nitrate nitrogen fertilizer has a significant passivation effect on cadmium in the soil, which also weakens the activation effect of PASP on soil cadmium. In addition, nitrate nitrogen fertilizer has a short fertilizer effect and is easy to leaching and loss, and the restoration cost is higher than that of ammonium nitrogen fertilizer and urea; third, amide nitrogen fertilizer urea needs to be gradually decomposed into ammonia and carbon dioxide under the action of urease, and then undergo a series of chemical reactions to be converted into ammonium nitrogen and nitrate nitrogen that can be directly absorbed by plants. It takes a long time to take effect, which is not conducive to the fertilizer supply needs of plants during the rapid growth period.

[0018] Therefore, the present invention uses polyaspartic acid as a fertilizer synergist, and can significantly promote the root growth and development of ramie seedlings in combination with ammonium nitrogen fertilizer at the seedling stage, and the short-term use of ammonium nitrogen fertilizer is small and is not easy to cause soil acidification; in the closed row period, it can quickly take effect in combination with nitrate nitrogen fertilizer to promote the increase of ramie biomass; in the fiber maturity period, it can significantly improve the utilization efficiency of nitrogen fertilizer in combination with urea. The present invention applies PASP in small amounts and multiple times during the whole growth period of ramie, fully exerts the water and fertilizer conservation effect of PASP, greatly increases the biomass of ramie, and improves the restoration efficiency.

[0019] Furthermore, in S3, only the above-ground part of ramie is harvested, and the ramie is planted continuously until the total cadmium content in the soil drops to the standard for safe utilization, and then the roots of the ramie are removed as a whole.

[0020] Furthermore, the harvested ramie stalks are peeled by machine, the ramie skin is sold after drying, the ramie stalks and leaves are burned in a centralized manner, and the fly ash from the burning is treated as hazardous waste. Compared with the roots, the cadmium enrichment ratio of the aboveground part of ramie is not high, and the cadmium content of the economically valuable ramie skin can be controlled within the relevant standards for textile raw materials; the ramie stalks and leaves, as well as the ramie roots that need to be dug out later, can be collected and sent to the nearest municipal waste incineration power plant for incineration in consideration of transportation costs. Ramie stalks, leaves, and roots all have a certain calorific value, and are transported to the incinerator for incineration with domestic waste at a blending ratio of 1%-5%. Cadmium has a low boiling point (about 767°C) and is easily vaporized and enters the flue gas at high temperatures (850-1200°C) in the incinerator. During the condensation and cooling process of the flue gas (200-400°C), gaseous cadmium will be adsorbed on the surface of fly ash particles (especially fine particles with a particle size of <10 μm) through homogeneous nucleation or heterogeneous condensation, and about 85%-98% of the cadmium will eventually enter the fly ash. At present, the incineration fly ash of various domestic waste incineration power plants has been included in the hazardous waste management as required, which can eliminate the secondary pollution risk of the incineration ash of cadmium-containing ramie waste to the greatest extent.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. The combined plant restoration method developed by the present invention has the advantages of strong heavy metal chelating ability, biodegradability, improved nitrogen fertilizer utilization efficiency, water and fertilizer conservation, low cost, and no impact on agricultural production.

[0022] 2. The present invention applies different forms of nitrogen fertilizer + chelating agent combinations at different stages: application before planting is conducive to maximizing the chelating properties of polyaspartic acid and effectively activating cadmium in the soil; in the seedling stage, combined with ammonium nitrogen fertilizer can significantly promote the growth and development of ramie seedling root system; in the row closing stage, combined with nitrate nitrogen fertilizer can quickly take effect and promote the increase of ramie biomass; in the fiber maturity stage, combined with urea can significantly improve the utilization efficiency of nitrogen fertilizer, as well as the nutrition of available phosphorus, potassium and other mineral elements in the soil, and has the effect of retaining water and fertilizer. The present invention fully explores the "nutrition-repair" dual regulatory effects of PASP and different forms of nitrogen fertilizers, and constructs a "material-nutrient-soil-ramie" multi-factor synergistic repair model.

[0023] 3. In the restoration method of the present invention, PASP combined with nitrogen fertilizers in different forms can significantly increase the biomass of ramie at different growth stages, greatly improve the plant restoration efficiency of strictly controlled cadmium-contaminated farmland, and will not affect the background pH value of the soil, thus achieving "production, restoration, and profit at the same time". BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This paper compares the effects of polyaspartic acid combined with different forms of nitrogen fertilizer on soil pH and available cadmium content in strictly controlled cultivated land.

[0025] Figure 2 This is a comparison chart of the effects of cadmium form transformation in strictly controlled cultivated land under the model of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the embodiments. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0028] Example 1: Differences in the effects of PASP compound nitrogen fertilizers in different forms on soil pH and available cadmium content in strictly controlled cultivated land 1. The test soil for this experiment was taken from the surface layer of cultivated soil (0-20cm) in the strictly controlled area of ​​Xiangdong District, Pingxiang City, Jiangxi Province. After air drying, grinding, and removing debris, it was sieved through a 5 mm sieve for use. Basic physical and chemical properties of the soil: pH 6.4, total cadmium content 19.66 mg / kg, and effective cadmium content 2.93 mg / kg.

[0029] 200 g (accurate to 0.01 g) of sieved and air-dried cadmium-contaminated original soil was weighed into a series of 500 mL plastic bowls. After one week, a mixed solution of PASP and different forms of nitrogen fertilizers was added to carry out a 45-day room temperature film-covered soil cultivation experiment, and the moisture was maintained at 60%-80% of the field water holding capacity. Deionized water was added to all samples to the initial weight by weighing method every 3 days. Destructive sampling was carried out on the 15th, 30th and 45th days of cultivation for the determination of pH value, effective cadmium content and cadmium form. CK is a blank control, NO is a nitrate nitrogen fertilizer, NH is an ammonium nitrogen fertilizer, P is PASP, PNO is PASP+nitrate nitrogen fertilizer, and PNH is PASP+ammonium nitrogen fertilizer; each group was treated 3 times.

[0030] Figure 1 The difference in the effects of PASP compound ammonium nitrogen fertilizer and nitrate nitrogen fertilizer on pH and available cadmium content in strictly controlled cadmium-contaminated soil was investigated. The results showed that single PASP could significantly increase the available cadmium content in soil. Compared with single PASP, PASP compound ammonium nitrogen fertilizer or nitrate nitrogen fertilizer would weaken the activation performance of PASP on cadmium. Therefore, before ramie planting, single PASP was applied (compound fertilizer was deeply applied after plowing, and try not to contact with PASP). Single ammonium nitrogen fertilizer or compound PASP would significantly reduce the background pH of soil and was not suitable for long-term application. However, single PASP or compound nitrate nitrogen fertilizer had no significant effect on soil pH.

[0031] Example 2: Effect of PASP compound nitrogen fertilizers in different forms on the transformation of cadmium forms in strictly controlled cultivated land soil The determination of cadmium forms refers to the BCR continuous extraction method proposed by the European Community Bureau of Reference, which divides cadmium forms into four types: weak acid extractable state (acid soluble state), reducible state, oxidizable state, and residual state.

[0032] Figure 2 This is a comparison chart of the effects of cadmium form transformation in strictly controlled cultivated land. The results show that compared with the blank control, the application of single PASP or compound nitrogen fertilizers in different forms significantly increased the content of acid-soluble cadmium that is easily absorbed by plants, and significantly reduced the content of residual cadmium that is not easily absorbed by plants. That is, PASP compound nitrogen fertilizers in different forms increased the bioavailability of cadmium in the soil.

[0033] Example 3: Accumulation and extraction efficiency of cadmium by ramie after restoration of strictly controlled cultivated land under the mode of the present invention In order to further verify the restoration effect of the restoration method of the present invention on cadmium pollution in strictly controlled cultivated land, multiple field tests were carried out. The field test site was located in a strictly controlled agricultural land area. The total annual application of PASP was 7.5 kg / mu, which was applied in 5 times on average; the total annual application of pure nitrogen was 24 kg·N / mu, which was applied in 5 times.

[0034] Before planting ramie, first spread compound fertilizer with a nitrogen, phosphorus and potassium ratio of 17-17-17 (calculated as 20% of the total annual nitrogen application), then plow and apply deep fertilizer (30 cm), and then apply polyaspartic acid (calculated as 1.5 kg / mu). In early April, soil was purchased to cultivate "Zhongzhu No. 1" ramie tender shoot cuttings with primary radish roots, and ramie seedlings with consistent growth were selected for transplanting, and the seedlings were supplemented with stumps one week after transplanting. Polyaspartic acid (1.5 kg / mu) and ammonium sulfate (nitrogen content ≥ 21.0%, calculated as 20% of the total annual nitrogen application) were applied at the seedling stage of the first hemp; polyaspartic acid (1.5 kg / mu) and potassium nitrate (nitrogen content ≥ 13.0%, K2O ≥ 45.0%, calculated as 20% of the total annual nitrogen application) were applied at the closing period; polyaspartic acid (1.5 kg / mu) and urea (nitrogen content ≥ 52.0%, calculated as 20% of the total annual nitrogen application) were applied during the inter-tillage period of the second hemp; polyaspartic acid (1.5 kg / mu) and urea (nitrogen content ≥ 52.0%, calculated as 20% of the total annual nitrogen application) were applied during the inter-tillage period of the third hemp. The first hemp and the second hemp (only the above-ground part) were harvested in June and August, and the third hemp (whole plant) was harvested in October, and soil was taken for determination.

[0035] The accumulation of cadmium in ramie biomass and its various parts is shown in Table 1. The results showed that compared with the conventional method (single urea was selected as nitrogen fertilizer, the annual total amount of pure nitrogen applied was 24 kg·N / mu, applied in 5 times, and chelating agent was applied 15 days before each ramie harvest), the biomass of ramie increased significantly and the enrichment of cadmium in the body increased significantly after the application of PASP combined with different forms of nitrogen fertilizers.

[0036] Table 1 Accumulation of cadmium in ramie biomass and its various parts

[0037] The embodiments described above only express several preferred embodiments of the present invention, and the descriptions thereof are relatively specific and detailed, but are not intended to limit the present invention. It should be noted that for those skilled in the art, the present invention may also have various changes and modifications, and any modifications, equivalent substitutions, improvements, etc. made within the concept and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A combined phytoremediation method for cadmium pollution in strictly controlled cultivated land, characterized in that: The steps include: S1. Apply compound fertilizer to the cultivated land and then plough it, then spread the chelating agent; S2. Transplant ramie seedlings, apply chelating agent and ammonium nitrogen fertilizer at the first ramie seedling stage, apply chelating agent and nitrate nitrogen fertilizer at the row closing stage, and apply chelating agent and amide nitrogen fertilizer at the second and third ramie growth stages; S3. Harvesting ramie.

2. The combined phytoremediation method for cadmium pollution in strictly controlled cultivated land according to claim 1, characterized in that: The chelating agents in S1 and S2 are both polyaspartic acid.

3. The combined phytoremediation method for cadmium pollution in strictly controlled cultivated land according to claim 1, characterized in that: The variety of ramie described in S2 is "Zhong Zhu No. 1", and the ramie seedlings are soil-grown tender shoot cuttings with primary radish roots.

4. The combined phytoremediation method for cadmium pollution in strictly controlled cultivated land according to claim 1, characterized in that: The ammonium nitrogen fertilizer in S2 is ammonium sulfate, the nitrate nitrogen fertilizer is potassium nitrate, and the amide nitrogen fertilizer is urea.

5. The combined phytoremediation method for cadmium pollution in strictly controlled cultivated land according to claim 1, characterized in that: The amount of the chelating agent added is 5-10 kg / mu per year, and the annual application amount of pure nitrogen is 20-30 kg / mu.

6. The combined phytoremediation method for cadmium pollution in strictly controlled cultivated land according to claim 5, characterized in that: The application ratio of chelating agents and different forms of nitrogen fertilizers in different periods is as follows: before transplanting ramie, the applied compound fertilizer accounts for 10%-20% of the annual application of pure nitrogen, and the broadcast chelating agent accounts for 20% of the added amount; during the emergence period of ramie, the applied chelating agent accounts for 20% of the added amount, and ammonium nitrogen fertilizer accounts for 10%-20% of the annual application of pure nitrogen; during the closure period of ramie, the applied chelating agent accounts for 20% of the added amount, and nitrate nitrogen fertilizer accounts for 10%-20% of the annual application of pure nitrogen; after the harvest of ramie, the applied chelating agent accounts for 20% of the added amount, and amide nitrogen fertilizer accounts for 20%-30% of the annual application of pure nitrogen during the growth period of the second ramie, and the applied chelating agent accounts for 20% of the added amount, and amide nitrogen fertilizer accounts for 20%-30% of the annual application of pure nitrogen during the growth period of the third ramie.

7. The combined phytoremediation method for cadmium pollution in strictly controlled cultivated land according to claim 1, characterized in that: In S3, only the above-ground part of ramie is harvested, and the ramie is planted continuously until the total cadmium content in the soil drops to the standard for safe utilization, and then the roots of the ramie are removed as a whole.

8. The combined phytoremediation method for cadmium pollution in strictly controlled cultivated land according to claim 7, characterized in that: The harvested ramie stalks are peeled by machines, the husks are sold after being dried in the sun, the stalks and leaves are burned in a centralized manner, and the fly ash is disposed of as hazardous waste.

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