A method for repairing lightly to moderately cadmium-contaminated paddy soil using mugwort-rice intercropping

Abstract

The present invention discloses a method for repairing light to moderate cadmium contaminated paddy soil using mugwort-rice intercropping, the steps are: 1) paddy preparation; 2) mugwort seedling cultivation; 3) rice variety selection and seedling cultivation; 4) establishing an intercropping system: mugwort with a plant height of about 15-20 cm and rice seedlings are transplanted into a prepared field, and a row of mugwort is intercropped with a row of rice, with a plant spacing of 18-25 cm × 18-25 cm; 5) water management; 6) above-ground part harvest. Among them, mugwort selects Qi mugwort produced in Qichun, Hubei. The present invention is simple, easy to operate and manage. Compared with single-crop mugwort or rice, intercropping improves the enrichment capacity of mugwort and rice to cadmium, and heavy metal removal efficiency is relatively high. Calculated by harvesting 2 crops per year, 4.1 g cadmium can be removed per mu of mugwort per year.

Description

Technical Field

[0001] The present invention belongs to the technical field of agricultural environmental conservation and restoration, and more specifically relates to a method for restoring lightly to moderately cadmium-contaminated paddy field soil by intercropping mugwort and rice. Background Art

[0002] The 2014 National Soil Pollution Survey Bulletin showed that 16.1% of soil pollutants nationwide exceeded standards, with 11.2% of sites experiencing slight, 2.3% experiencing mild, and 1.5% experiencing moderate pollution. Inorganic pollutants were the primary source of pollution, accounting for 82.8% of all sites experiencing these levels. Among all inorganic pollutants, cadmium had the highest rate of exceeding standards, reaching 7.0%. Crops grown on cadmium-contaminated soil often exceed standards, particularly in southern China, where excessive cadmium levels in rice are particularly severe. This poses a threat to agricultural product safety and human health, and has drawn significant public attention.

[0003] Currently developed soil remediation technologies include physical remediation techniques such as soil importation and electroremediation, chemical remediation techniques such as leaching and chemical fixation, and bioremediation techniques using microorganisms, plants, and animals. Phytoremediation, among others, is a remediation technology with great potential for application, not only because it can be implemented in situ but also because it is low-cost and environmentally friendly. Currently, over 20 cadmium-accumulating plant species have been discovered in China, including Vetiver, Sedum alfredii, Asteraceae, Phytolacca americana, Solanum nigrum, and Bidens pilosa. However, these species suffer from low biomass and demanding growth conditions. For example, Sedum alfredii has a strong cadmium accumulation capacity but is heat-resistant and cannot survive summer in southern China, hindering its widespread application in southern China. Furthermore, most of the cadmium-accumulating plants discovered so far have low economic value and lack potential for resource utilization. Consequently, while significant investment in farmland remediation is required, economic value is not generated, limiting the widespread application of phytoremediation in southern rice-growing regions.

[0004] Mugwort (Artemisia argyi H. Lév. & Vaniot) is a perennial herb or slightly subshrubby plant of the genus Artemisia in the Asteraceae family. It is widely distributed throughout the country, primarily growing in wastelands, riverbanks, and hillsides at low to medium altitudes. It has a prominent taproot, well-developed lateral roots, and often underground rhizomes. Stems are solitary or few, generally 80-150 cm tall. Mugwort is a traditional Chinese herbal medicine, and the entire plant can be used as medicine, with properties such as warming the meridians, removing dampness, dispelling cold, stopping bleeding, reducing inflammation, relieving asthma, relieving coughs, stabilizing pregnancy, and combating allergies. Mugwort leaves are dried and crushed to produce "mugwort wool," which is used to make moxa sticks for moxibustion. Therefore, mugwort is an important resource plant and cash crop.

[0005] A search on the China Patent Network and related paper websites revealed that there are currently some reports on the enrichment and restoration of heavy metal contaminated soils by Artemisia argyi. Peng Kejian et al. found that the Cd content in the leaves of wild Artemisia argyi exceeded 100 mg / kg when they surveyed and sampled plants in the lead and zinc mining area in Hunan Province [Peng Kejian, et al. 2009. Compositae plants and their accumulation of heavy metals in the lead and zinc mining area in western Hunan. Journal of Subtropical Resources and Environment, 4(4):11-19]. Ren Xiujuan et al. found that the Cd content in the aboveground parts of Artemisia argyi grown in the non-ferrous metal mining area in Hunan Province was 14.09 mg / kg [Ren Xiujuan, et al. 2014. Research on screening of cadmium-accumulating plants. Resource Development and Market, 30(08):961-962+980]. Bai Jie et al. found that the Cd content in the aboveground parts of Artemisia argyi under Cd contaminated conditions was 15.94 mg / kg through potted experiments [Bai Jie. 2019. Analysis of the effect of Artemisia argyi on restoring heavy metal cadmium contaminated soil. New Agriculture, 49(11):17]. It can be seen that Artemisia has a strong ability to enrich cadmium and has the potential to repair cadmium-contaminated soil.

[0006] Regarding the use of remediation plants intercropped with crops to improve soil remediation efficiency, Zhao Qiuguo et al., in "A method for phytoremediation of cadmium-contaminated soil by intercropping Solanum nigrum with corn" [CN202010295705.6], noted that phytoremediation technology using Solanum nigrum intercropping with corn can reduce the content of heavy metals such as cadmium in soil and achieve a certain grain yield. However, Solanum nigrum is a common farmland weed that competes with crops for light, water, and fertilizer and has no economic value. Deng Tianlong et al., in "A method for phytoremediation of contaminated soil" [CN200310110757.8], mentioned methods that rotate the Chinese medicinal herb Chuanxiong and the remediation plant soybean (Glycine max (L.) Merr.), and intercrop the Chinese medicinal herb Chuanxiong (Ligusticum chuanxiong Hort) with the remediation plant Nephrolepis auriculata (L.) Triman, as methods that are beneficial for removing harmful elements from contaminated soil. However, this method has a relatively narrow scope of application, and Nephrolepis auriculata lacks potential for resource utilization. Therefore, it is extremely important and urgent to establish a "repair and production at the same time" phytoremediation method suitable for cadmium-contaminated rice fields in southern China. Summary of the Invention

[0007] In response to the technical difficulties of high investment, low returns and poor stability in the existing technology for cadmium-contaminated soil remediation, the present invention provides a method for remediating cadmium-contaminated paddy soil using mugwort-rice intercropping. The method is simple to operate and manage, and has a high efficiency in removing cadmium metal, meeting the needs of remediation and treatment of lightly to moderately cadmium-contaminated paddy soil in southern China.

[0008] The technical solution adopted by the present invention to solve its technical problem is:

[0009] A method for repairing lightly to moderately cadmium-contaminated paddy soil by intercropping mugwort and rice, comprising the following steps:

[0010] 1) Rice field preparation: Apply 1.0-1.5 tons of decomposed organic fertilizer per mu as base fertilizer, harrow and level the soil and fertilizer, and then irrigate the field to make the soil moisture reach the field water holding capacity.

[0011] The decomposed organic fertilizer is a commercial organic fertilizer with an organic matter content of ≥45% and a total nitrogen, phosphorus and potassium content of ≥5.0%.

[0012] 2) Selection of Artemisia argyi varieties and seedling cultivation: Collect underground rhizomes of Artemisia argyi from the wild, cut the long rhizomes into rhizome segments with a length of 6-8 cm with scissors, each rhizome segment has a complete internode and an axillary bud, and soak them in 2g / L rooting powder solution for 2 hours. Mix equal volumes of fine sand and peat soil to prepare a culture medium, and spread it on the seedbed with a thickness of 10 cm. Dig shallow trenches in the seedbed with a row spacing of 30 cm, and place the rhizome segments soaked in rooting powder obliquely upward along the trench wall with a spacing of 30 cm, with the buds facing upward, while covering with soil, fill the trench, and cover with soil to a thickness of 1 cm. Water the soil to saturate the water content, absorb it dry, and then water it again.

[0013] When choosing mugwort, choose Qi Ai, a national geographical indication product. This variety has a large biomass, is resistant to mowing, and has a rich aroma. Its thick, papery leaves and dense, thick hairs make it suitable for making moxa sticks, moxa cones, essential oils, and textiles.

[0014] 3) Rice variety selection and seedling cultivation: Select varieties with low cadmium accumulation.

[0015] The early rice varieties include Xiang Zao Xian 42, Xiang Zao Xian 45, Zhu Liang You 189, Zhong Jia Zao 17, Zhu Liang You 819, and Zhu Liang You 729; the medium rice varieties include Y Liang You 2108, Y Liang You 488, Y Liang You 9918, C Liang You 386, Y Liang You 19, C Liang You 651, C Liang You 755, Jian Liang You Hua Zhan, and Lu You 9803; and the late rice varieties include Xiang Wan Xian 12 and Xiang Wan Xian 13.

[0016] 4) Establish an intercropping system: Transplant mugwort plants about 15-20 cm tall with rice seedlings into the prepared field. Intercrop one row of rice with one row of mugwort, with a spacing of 18-25 cm x 18-25 cm.

[0017] 5) Water management: Use alternating wet-dry cycles. Water the field to a depth of 0.5-1cm, then allow the soil to dry naturally.

[0018] 6) Harvesting of above-ground parts: When the rice is ripe, harvest the mugwort and rice separately; harvest the above-ground parts of the mugwort 8-10 cm above the ground, and remove the dead branches and leaves in the field from the rice field.

[0019] Among the six steps mentioned above, the second step solves the problem of Artemisia argyi variety selection. Artemisia argyi has a strong ability to absorb cadmium, large biomass, and is resistant to mowing, and has broad prospects for resource utilization; the third step solves the problem of rice variety selection. By selecting rice varieties with low cadmium accumulation, the absorption of cadmium by rice can be reduced, which is an important step in achieving standard rice production; the fourth step is to establish an intercropping system, which can make full use of the interaction between the Artemisia argyi and rice roots to improve the absorption and accumulation of cadmium; the sixth step solves the problem of cadmium-rich plants rotting and decomposing in the fields, and the stems and leaves absorb the accumulated cadmium and return it to the soil again.

[0020] Through the above steps, a method for repairing lightly and moderately cadmium-contaminated paddy field soil was established in the southern part of the country, which is low-cost, environmentally friendly, widely applicable, easy to operate and manage, and has the advantages of being easy to operate and manage.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] (1) Easy to operate and manage. Artemisia argyi has strong adaptability to climate and soil, prefers warm and humid climate, grows well in southern rice-growing areas, and the cultivation technology is easy to master.

[0023] (2) Compared with single-cropping mugwort or rice, intercropping increased the cadmium accumulation capacity of mugwort and rice. The cadmium content in the stems and leaves of mugwort increased from 10.19 mg / kg in single-cropping to 13.27 mg / kg in intercropping; the cadmium content in the stems and leaves of rice increased from 3.68 mg / kg in single-cropping to 16.82 mg / kg in intercropping; and the cadmium content in brown rice increased from 0.46 mg / kg in single-cropping to 3.34 mg / kg in intercropping. Therefore, compared with single-cropping mugwort or rice, more cadmium can be removed from the soil through mugwort-rice intercropping.

[0024] Artemisia roots secrete small molecule organic acids such as malic acid and citric acid to activate cadmium in the soil, converting ineffective cadmium in the soil into effective cadmium, which is beneficial for plant absorption and removes more cadmium from the soil, thereby reducing the total cadmium content in the soil.

[0025] (3) Heavy metal removal efficiency is high. Test results show that in soil with a cadmium content of 0.95 mg / kg, the dry weight of mugwort stems and leaves in the intercropping system can reach 154.82 kg / mu, and the cadmium content of the stems and leaves is 13.27 mg / kg. Mugwort is a perennial plant with a strong regeneration capacity. Based on two harvests per year, 4.1 g of cadmium can be removed per mu of mugwort per year (see Example 1).

[0026] (4) The prospect of resource utilization is broad. After harvest, mugwort can be processed and used for non-food purposes such as making moxa sticks, textiles, and extracting essential oils. Although the cadmium content of brown rice is significantly increased and cannot enter the food chain, it can be used as a raw material for ethanol production. Therefore, through intercropping mugwort and rice, it is possible to achieve certain economic benefits while repairing cadmium-contaminated farmland. DETAILED DESCRIPTION

[0027] Below, the applicant will further explain the present invention in detail with reference to the example of using mugwort-rice intercropping to repair mildly to moderately cadmium-contaminated paddy soil at the Long-term Positioning Observation and Experimental Center for Heavy Metal Pollution in Cultivated Land (Beishan Town, Changsha County, Hunan Province). The purpose is to enable those skilled in the art to have a more detailed understanding and recognition of the present invention. The following examples should not be understood as limiting the scope of protection claimed in the present invention to any extent.

[0028] Example 1:

[0029] This example was conducted in a test field at the Long-term Positioning Observation and Experimental Station for Heavy Metal Pollution in Cultivated Land (Beishan Town, Changsha County, Hunan Province, referred to as Beishan Experimental Station). A method for remediating mildly to moderately cadmium-contaminated paddy soil using mugwort-rice intercropping was developed, comprising the following steps:

[0030] Step 1: Prepare the rice fields: Apply 1.0 ton of decomposed organic fertilizer per mu (approximately 1 acre) of the harvested rice fields as base fertilizer. Harrow and level the soil and fertilizer, then water until the soil reaches its field capacity.

[0031] Step 2, Artemisia argyi variety selection and seedling cultivation: Artemisia argyi produced in Qichun, Hubei Province is selected. The underground rhizomes of Artemisia argyi are dug out from the wild, kept moist, and transported to Beishan Experimental Station.

[0032] Artemisia seedling cultivation method: Use scissors to cut the long rhizomes of Artemisia collected from the wild into 8 cm long rhizome segments. Each rhizome segment has a complete internode and an axillary bud, and soak them in 2g / L rooting powder solution for 2 hours. Mix equal volumes of fine sand and peat soil to prepare a culture medium, and spread it on the seedbed with a thickness of 10cm. Dig shallow trenches in the seedbed with a row spacing of 30cm, and place the rhizome segments soaked in rooting powder at an upward angle along the trench wall with a spacing of 30cm, with the buds facing upward. Cover the trenches with soil and fill them with a thickness of 1cm. Water the soil to saturate it with water, then absorb it and water it again.

[0033] Step 3. Rice variety selection and seedling cultivation: The rice selected is the "Zhongzao 35" indica conventional rice, which is one of the main cultivated varieties of the Beishan Experimental Station in 2022 and will be uniformly cultivated by the Beishan Experimental Station.

[0034] Rice seedling raising method: The seedbed of the "Zhongzao 35" conventional indica rice selected above is set up on flat land with fertile soil and sheltered from the wind. The width of the seedbed is 2m and the length is 6m. A black polyethylene soft seedling tray (270 holes) with a length of 80m and a width of 40cm is used for seedling raising. After 5-6 rice seeds are sown in each hole, it is covered with 0.5cm of soft and fertile soil. A moist seedling raising method is adopted to keep the entire seedling raising process in an alternating dry and wet environment. Each time watering is performed, the shallow water layer in the seedling tray is 1cm until it dries up naturally. A film shed is set up on each seedbed to keep the temperature inside the shed not lower than 12°C. When the rice seedlings grow to the three-leaf stage and the seedling height is about 12cm, the heat preservation shed is removed and the rice seedlings are transplanted two days later.

[0035] Step 4: Establish an intercropping system: Transplant the mugwort seedlings (approximately 15 cm tall) grown in Step 2 and the rice seedlings (approximately 15 cm tall) grown in Step 3 into the prepared field. Intercrop one row of rice seedlings with one row of mugwort seedlings, with a spacing of 20 cm x 20 cm between rows.

[0036] Step 5: Water management: Use alternating wet-dry cycles during the growing season. When the field becomes dry, water it to a depth of 1 cm, then allow it to drain naturally.

[0037] Step 6: Harvest the aboveground parts: Harvest the mugwort and rice separately when the rice is ripe. Harvest the aboveground mugwort plants 8 cm above the ground and remove any dead branches and leaves from the rice field.

[0038] The results of Example 1 are as shown in Table 1 and Table 2. The result shows that, in the moderately polluted paddy field of Beishan Town, Changsha County, Hunan Province (soil cadmium content is 0.95mg / kg on average), the stem and leaf dry weight of Artemisia argyi can reach 154.82kg / mu, and the stem and leaf cadmium content reaches 13.27mg / kg. By removing the stem and leaves above the ground of Artemisia argyi, 2.05g cadmium can be removed from the moderately polluted paddy field soil at a single time. More importantly, the enrichment coefficient of Artemisia argyi stem and leaves can reach 17.22, and the transport coefficient can reach 1.56, which can transport the cadmium absorbed by the root system to the aboveground part of the plant by powerful transport capacity, and accumulate in the stem and leaves. In addition, in the intercropping system, the cadmium content of rice stem and leaves and brown rice also significantly increases, and the stem and leaf cadmium content increases to 16.82mg / kg from 3.68mg / kg, and the cadmium content of brown rice increases to 3.34mg / kg from 0.46mg / kg. Therefore, through mugwort-rice intercropping, the harvesting of mugwort stems and leaves, as well as rice stems and leaves and brown rice, can remove more cadmium from the soil. After a single mugwort-rice intercropping restoration, the total cadmium content in the soil decreased from 0.95 mg / kg to 0.76 mg / kg, with a significant restoration effect.

[0039] As can be seen from Table 2, the roots of Artemisia argyi secrete small molecule organic acids such as malic acid and citric acid to activate the cadmium in the soil, converting the ineffective cadmium in the soil into effective cadmium, increasing the effective cadmium content in the soil, which is beneficial for plant absorption and removes more cadmium in the soil, thereby reducing the total cadmium content in the soil.

[0040] Table 1. Biomass and cadmium accumulation characteristics of mugwort and rice in the mugwort-rice intercropping experiment to restore mildly to moderately cadmium-contaminated paddy soil in Beishan Town, Changsha County, Hunan Province

[0041]

[0042] Table 2. Effect of mugwort-rice intercropping on soil cadmium reduction and remediation in Beishan Town, Changsha County, Hunan Province

[0043]

[0044] The above-described embodiments merely represent specific implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for repairing lightly to moderately cadmium-contaminated paddy soil using mugwort-rice intercropping, characterized in that: The steps include: Step (1), rice field preparation; Step (2), selecting mugwort varieties and raising seedlings, wherein the mugwort is selected from Qichun mugwort produced in Hubei Province; Step (3), rice variety selection and seedling cultivation, wherein the rice is selected as "Zhongzao 35" indica conventional rice; Step (4), establishing an intercropping system: transplanting the mugwort seedlings grown in step (2) with a plant height of 15-20 cm and the rice seedlings grown in step (3) with a plant height of 15 cm into the prepared field respectively; intercropping one row of rice seedlings with one row of mugwort seedlings, with a plant spacing of 18-25 cm × 18-25 cm; Step (5), moisture management; Step (6), harvesting the above-ground parts.

2. The method for repairing lightly to moderately cadmium-contaminated paddy soil using mugwort-rice intercropping according to claim 1, characterized in that: The paddy field preparation in step (1) is specifically as follows: 1.0-1.5 tons of decomposed organic fertilizer is applied per mu of the harvested paddy field as base fertilizer, the soil and fertilizer are raked and leveled, and then water is irrigated to make the soil moisture reach the field water holding capacity; the decomposed organic fertilizer has an organic matter content of ≥45% and a total nitrogen, phosphorus and potassium content of ≥5.0%.

3. The method for repairing lightly to moderately cadmium-contaminated paddy soil using mugwort-rice intercropping according to claim 1, characterized in that: The mugwort variety selection and seedling cultivation described in step (2) are as follows: the mugwort seedling cultivation method comprises the following steps: collecting mugwort from the wild, cutting the long rhizomes into rhizome segments with a length of 6-8 cm with scissors, each rhizome segment having a complete internode and an axillary bud, and soaking the segments in a 2g / L rooting powder solution for 2 hours; mixing equal volumes of fine sand and peat soil to prepare a culture matrix, and spreading the matrix on a seedbed with a thickness of 10 cm; making shallow furrows on the seedbed with a row spacing of 30 cm, placing the rhizome segments soaked in rooting powder obliquely upward along the furrow wall with a plant spacing of 30 cm, with the buds facing upward, covering the furrows with soil while placing the segments, filling the furrows with a covering thickness of 1 cm, watering the soil to saturate the water content, absorbing the water, and then watering it again.

4. The method for repairing lightly to moderately cadmium-contaminated paddy soil using mugwort-rice intercropping according to claim 1, characterized in that: The rice variety selection and seedling raising method described in step (3) is as follows: the selected "Zhongzao 35" indica conventional rice is set in a flat land with fertile soil and a leeward and sunny location. The width of the seedling bed is 2m and the length is 6m. A soft seedling tray with 270 holes, which is 80m long and 40cm wide, is used for seedling raising. After 5-6 rice seeds are sown in each hole, 0.5cm of soft and fertile soil is covered. A wet seedling raising method is adopted to make the entire seedling raising process in an alternating dry and wet environment. Each time watering is performed, the shallow water layer of the seedling tray is 1cm until it dries up naturally. A film shed is set on each seedling bed to make the temperature in the shed not lower than 12°C. When the rice seedlings grow to the three-leaf stage and the seedling height is 12cm, the heat preservation shed is removed. The rice seedlings are transplanted two days later.

5. The method for repairing lightly to moderately cadmium-contaminated paddy soil using mugwort-rice intercropping according to claim 1, characterized in that: The water management in step (5) is specifically to adopt dry-wet alternating water management during the growing period; when the field surface becomes dry, water is applied to make the water depth of the field surface 0.5-1 cm, and then the field is dried naturally.

6. The method for repairing lightly to moderately cadmium-contaminated paddy soil using mugwort-rice intercropping according to claim 1, characterized in that: The above-ground part harvesting in step (6) is specifically as follows: when the rice is mature, the mugwort and the rice are harvested separately, the above-ground mugwort plants are harvested 8-10 cm above the ground, and the dead branches and leaves in the field are removed from the rice field.

Images