Method for remedying light and medium cadmium polluted rice field soil by utilizing mugwort-rice intercropping

Abstract

The invention discloses a method for repairing light and medium cadmium polluted rice field soil by utilizing mugwort-rice intercropping. The method comprises the following steps: 1) preparing a rice field; 2) growing seedlings of mugwort; 3) rice variety selection and seedling raising; 4) establishing an intercropping system: transplanting the mugwort with the plant height of about 15-20cm and rice seedlings into the prepared field, intercropping a row of mugwort with a row of rice, and setting the plant row spacing to be (18-25cm) * (18-25cm); 5) water management; and 6) harvesting the overground part. Wherein the Chinese mugwort is Chinese mugwort produced in Qichun of Hubei province. The method is simple and easy to implement and easy to operate and manage, compared with single mugwort or rice cropping, the cadmium enrichment capacity of mugwort and rice is improved through intercropping, the heavy metal removal efficiency is high, and 4.1 g of cadmium can be removed from each mu of mugwort every year according to the fact that two crops are harvested every 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 paddy field soil with mild to moderate cadmium pollution by intercropping mugwort and rice. Background Art

[0002] The "National Soil Pollution Survey Bulletin" released in 2014 shows that the total soil pollution rate in China exceeds the standard by 16.1%, of which the proportions of slightly, mildly and moderately polluted points are 11.2%, 2.3% and 1.5% respectively. The pollution type is mainly inorganic, and the number of points exceeding the standard accounts for 82.8% of all points exceeding the standard. Among all inorganic pollutants, cadmium has the highest rate of exceeding the standard, reaching 7.0%. The cadmium content of crops grown on cadmium-contaminated soil often exceeds the standard, especially in southern China, where the problem of excessive cadmium in rice is relatively serious, endangering the safety of agricultural products and human health, and has attracted close attention from the society.

[0003] The soil remediation technologies currently developed include physical remediation technologies such as the soil-injection method and electric remediation, chemical remediation technologies such as leaching and chemical fixation, and biological remediation technologies through microorganisms, plants, animals, etc. Among them, phytoremediation can not only be implemented in situ, but also has low cost and is green and environmentally friendly. It is a remediation technology with great application potential. At present, more than 20 cadmium-accumulating plants found in China include vetiver, southeastern sedum, blue sedum, American pokeweed, nightshade, Bidens pilosa, etc. However, there are problems such as low biomass and relatively harsh requirements for growth conditions. For example, southeastern sedum has a strong ability to enrich cadmium, but it is not resistant to high temperatures and cannot survive the summer in the southern region, so it is difficult to be widely used in the southern region. In addition, most of the cadmium-accumulating plants currently discovered have low economic value and no prospect for resource utilization. Therefore, when a large amount of cost is invested in the restoration of cultivated land, economic value cannot be generated, which limits the large-scale promotion and application of phytoremediation in the southern rice-growing areas.

[0004] Mugwort (Artemisia argyi H.Lév.&Vaniot) is a perennial herb or slightly semi-shrubby plant of the genus Artemisia in the Asteraceae family. It is widely distributed naturally, almost all over the country, mostly growing in wastelands, riverbanks and hillsides in low to medium altitudes. Mugwort has a distinct taproot, well-developed lateral roots, and often has underground rhizomes. The stems are solitary or a few, generally 80-150 cm high. Mugwort is a traditional Chinese herbal medicine, and the whole plant can be used as medicine. It has the effects of warming the meridians, removing dampness, dispelling cold, stopping bleeding, anti-inflammatory, relieving asthma, relieving cough, stabilizing pregnancy, and anti-allergic. Mugwort leaves are dried and crushed to obtain "mugwort wool", which is made into moxa sticks for moxibustion. Therefore, mugwort is an important resource plant and economic crop.

[0005] According to the search on China Patent Network and related paper websites, there are some reports on the enrichment and restoration of heavy metal contaminated soil 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 investigated and sampled plants in the lead and zinc mining area in Hunan Province [Peng Kejian, et al. 2009. Asteraceae 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 part 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-enriching plants. Resource Development and Market, 30(08):961-962+980]. Bai Jie et al. found that the Cd content in the aboveground part of Artemisia argyi under Cd pollution conditions was 15.94 mg / kg through potted experiments [Bai Jie. 2019. Analysis of the effect of Artemisia argyi in repairing 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] In terms of using remediation plants and crops to intercrop to improve soil remediation efficiency, Zhao Qiuguo et al. mentioned in "A method for remediating cadmium-contaminated soil by intercropping Solanum nigrum and corn" [CN202010295705.6] that the phytoremediation technology of intercropping Solanum nigrum and corn can reduce the content of heavy metals such as cadmium in the soil and achieve a certain grain yield, but 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. mentioned in "A method for phytoremediation of contaminated soil" [CN200310110757.8] that the method of rotating the Chinese medicinal material Chuanxiong and the remediation plant soybean (Glycine max (L.) Merr.), and intercropping the Chinese medicinal material Chuanxiong (Ligusticum chuanxiong Hort) and the remediation plant Nephrolepis auriculata (L.) Triman is conducive to the removal of harmful elements in contaminated soil, but the scope of application of this method is relatively narrow, and Nephrolepis auriculata lacks the 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 view of the technical difficulties of high investment, low return and poor stability in the prior art for the remediation of cadmium-contaminated soil, the present invention provides a method for remediating cadmium-contaminated paddy soil using mugwort-rice intercropping. The method is simple to operate, easy to 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 light to moderate 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 the soil and fertilizer evenly, and irrigate 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 mugwort varieties and seedling cultivation: Collect underground rhizomes of mugwort 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 matrix, and spread it on the seedbed with a thickness of 10 cm. Dig shallow furrows in the seedbed with a row spacing of 30 cm, and place the rhizome segments soaked in rooting powder obliquely upward along the furrow wall with a spacing of 30 cm, with the buds facing upward, and cover them with soil while placing them, filling the furrows with a thickness of 1 cm. Water the soil to saturate the water content, and water it again after drying it.

[0013] When choosing mugwort varieties, choose Qi Ai, a national geographical indication product. This variety has a large biomass, is resistant to mowing, and has a strong aroma. Its leaves are thick and papery, and its hairs are dense and thick, making 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 Xiangzaoxian 42, Xiangzaoxian 45, Zhuliangyou 189, Zhongjiazao 17, Zhuliangyou 819, and Zhuliangyou 729; the medium rice varieties include Yliangyou 2108, Yliangyou 488, Yliangyou 9918, Cliangyou 386, Yliangyou 19, Cliangyou 651, Cliangyou 755, Jianliangyou Huazhan, and Luyou 9803; and the late rice varieties include Xiangwanxian 12 and Xiangwanxian 13.

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

[0017] 5) Water management: Use alternating wet and dry water management. Water the field surface to a depth of 0.5-1cm, and then let it dry naturally.

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

[0019] Among the above six steps, the second step solves the problem of mugwort variety selection. Mugwort has a strong ability to absorb cadmium, large biomass, and is resistant to mowing, and its resource utilization has broad prospects; 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 mugwort 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 absorbing the accumulated cadmium and returning 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 paddy field with low cost, environmental friendliness, wide application range, and easy operation and management.

[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 mugwort or rice monoculture, 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 monoculture to 13.27 mg / kg in intercropping; the cadmium content in the stems and leaves of rice increased from 3.68 mg / kg in monoculture to 16.82 mg / kg in intercropping; the cadmium content in brown rice increased from 0.46 mg / kg in monoculture to 3.34 mg / kg in intercropping. Therefore, compared with mugwort or rice monoculture, more cadmium can be removed from the soil through mugwort-rice intercropping.

[0024] 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, which is beneficial for plant absorption and removes more cadmium in the soil, thereby reducing the total cadmium content in the soil.

[0025] (3) The heavy metal removal efficiency is high. The test results show that in the soil with a cadmium content of 0.95 mg / kg, the dry weight of the stems and leaves of mugwort 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 ability. Based on the calculation of 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 being harvested, 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 producing ethanol. Therefore, through intercropping mugwort and rice, it is possible to achieve certain economic benefits while repairing cadmium-contaminated farmland. DETAILED DESCRIPTION

[0027] The applicant will further explain the present invention in detail below in conjunction with an 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 embodiments should not be understood in any way as limiting the scope of protection claimed for the present invention.

[0028] Embodiment 1:

[0029] This embodiment was conducted in the test field of the Long-term Positioning Observation and Experimental Center for Heavy Metal Pollution in Cultivated Land (Beishan Town, Changsha County, Hunan Province, referred to as Beishan Experimental Station). A method for repairing mildly to moderately cadmium-contaminated paddy soil using mugwort-rice intercropping is described, and the steps are:

[0030] Step 1: Rice field preparation: Apply 1.0 ton of decomposed organic fertilizer per mu of harvested rice field as base fertilizer. After raking and leveling the soil and fertilizer, irrigate the field to make the soil moisture reach the field water holding 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] Seedling raising method of mugwort: The long rhizomes of mugwort collected from the wild are cut into 8cm long rhizome segments with scissors. Each rhizome segment has a complete internode and an axillary bud, and soaked in 2g / L rooting powder solution for 2 hours. Mix equal volumes of fine sand and peat soil to make a culture matrix, and spread it on the seedbed with a thickness of 10cm. Dig shallow furrows in the seedbed with a row spacing of 30cm, and place the rhizome segments soaked in rooting powder obliquely upward along the furrow wall with a plant spacing of 30cm, with the buds facing upward, and cover with soil while placing, fill the furrows, and cover with soil with a thickness of 1cm. Water the soil to saturate the water content, and water it again after drying.

[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 above-selected "Zhongzao 35" conventional indica rice has a seedbed set up on a flat land with leeward and sunny conditions and fertile soil. 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 raising seedlings. After 5-6 rice seeds are sown in each hole, 0.5cm of soft and fertile soil is covered. The wet seedling raising method is adopted to make the entire seedling raising process in an alternating dry and wet environment. Each time the water is irrigated, the shallow water layer of the seedling tray is 1cm until it dries up naturally. A film shed is set up on each seedbed to keep 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 about 12cm, the insulation shed is removed and the rice seedlings are transplanted two days later.

[0035] Step 4, establish an intercropping system: transplant the mugwort seedlings grown in step 2 with a plant height of about 15 cm and the rice seedlings grown in step 3 with a plant height of about 15 cm into the prepared field. One row of rice seedlings is intercropped with one row of mugwort seedlings, with a plant spacing of 20 cm×20 cm.

[0036] Step 5: Water management: During the growing season, alternate wet and dry water management is used. When the field surface becomes dry, water the field surface to a depth of 1 cm, and then let it dry naturally.

[0037] Step 6, harvesting the aboveground part: When the rice is ripe, harvest the mugwort and rice separately. Harvest the aboveground plants of mugwort 8 cm above the ground, and remove the dead branches and leaves in the field from the rice field.

[0038] The results of Example 1 are shown in Table 1 and Table 2. The results show that in the moderately polluted paddy field (soil cadmium content is 0.95mg / kg on average) in Beishan Town, Changsha County, Hunan Province, 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 above-ground stems and leaves of Artemisia argyi, 2.05g of cadmium can be removed from the moderately polluted paddy field soil at a single time. More importantly, the enrichment coefficient of Artemisia argyi stems and leaves can reach 17.22, and the transport coefficient can reach 1.56. The cadmium absorbed by the root system can be transported to the above-ground part of the plant through a strong transport capacity, and is enriched in the stems and leaves. In addition, in the intercropping system, the cadmium content of rice stems and leaves and brown rice also increases significantly, and the stem and leaf cadmium content increases from 3.68mg / kg to 16.82mg / kg, and the cadmium content of brown rice increases from 0.46mg / kg to 3.34mg / kg. Therefore, more cadmium can be removed from the soil by intercropping mugwort and rice, harvesting mugwort stems and leaves, rice stems and leaves, and brown rice. Through a single mugwort-rice intercropping restoration, the total cadmium content in the soil dropped 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, facilitating plant absorption and removing more cadmium from the soil, thereby reducing the total cadmium content in the soil.

[0040] Table 1. Biomass and cadmium enrichment 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 restoration in Beishan Town, Changsha County, Hunan Province

[0043]

[0044] The above-mentioned embodiments only express the specific implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A method for repairing mildly 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; 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. A method for repairing mildly to moderately cadmium-contaminated paddy field 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 as base fertilizer per mu of the harvested paddy field, the soil and fertilizer are raked and tilled evenly, 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. A method for repairing mildly to moderately cadmium-contaminated paddy field soil using mugwort-rice intercropping according to claim 1, characterized in that: The mugwort variety selection and seedling raising method described in step (2) is as follows: the long rhizomes of mugwort collected from the wild are cut into rhizome segments with a length of 6-8 cm with scissors, each rhizome segment has a complete internode and an axillary bud, and are soaked in a 2g / L rooting powder solution for 2 hours; equal volumes of fine sand and peat soil are mixed to prepare a culture matrix, which is spread on a seedbed with a thickness of 10 cm; shallow furrows are opened on the seedbed with a row spacing of 30 cm, and the rhizome segments soaked in rooting powder are placed obliquely upward along the furrow wall with a plant spacing of 30 cm, with the buds facing upward, and soil is covered while placing, and the furrows are filled with soil with a thickness of 1 cm, and water is applied to saturate the soil with water, and the soil is dried and then watered again.

4. A method for repairing mildly to moderately cadmium-contaminated paddy field 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 leeward and sunny conditions and fertile soil, the width of the seedling bed is 2m and the length is 6m, and a soft seedling raising tray with 270 holes of 80m in length and 40cm in width is used for seedling raising. After 5-6 rice seeds are sown in each hole, 0.5cm of soft and fertile soil is covered, and a wet seedling raising method is adopted to make the entire seedling raising process in an alternating dry and wet environment. Each time the seedling raising tray is watered, the shallow water layer of the seedling raising tray is 1cm until it dries up naturally, and a film shed is set up 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, and the rice seedlings are transplanted two days later.

5. The method for repairing mildly to moderately cadmium-contaminated paddy field soil by intercropping mugwort and rice according to claim 1, characterized in that: The water management described 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 on the field surface 0.5-1 cm, and then the field is dried naturally.

6. The method for repairing mildly to moderately cadmium-contaminated paddy field soil by intercropping mugwort and rice according to claim 1, characterized in that: The above-ground part harvesting in step (6) is specifically to harvest mugwort and rice separately when the rice is ripe, harvest the above-ground mugwort plants 8-10 cm above the ground, and remove the dead branches and leaves in the field out of the rice field.

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