Method for repairing heavy metal contaminated soil through lettuce-sunflower intercropping

Abstract

The invention relates to the technical field of phytoremediation of heavy metal contaminated soil, in particular to a method for remedying facility vegetable field heavy metal cadmium contaminated soil through lettuce-sunflower intercropping. Biochar is applied to improve the structure and performance of greenhouse soil, then vegetable crop lettuce and portulacaceae ornamental plant sunflower are intercropped, the heavy metal cadmium in the soil is removed or remarkably reduced through the effects of absorption, complexation, stabilization and the like under the interaction effect of plant combinations, and the heavy metal cadmium is enriched at the roots of the ornamental plants and prevented from entering a food chain. The method is environment-friendly, has the advantages of being easy to operate, low in cost, free of fallow, free of influence on normal production activity and the like, and is suitable for in-situ remediation of agricultural soil polluted by medium-low-concentration cadmium.

Description

Technical Field

[0001] The invention relates to the research field of agricultural soil heavy metal pollution restoration, and specifically is a method for restoring agricultural cadmium-contaminated soil by intercropping vegetable crops with sunflowers, an ornamental plant of the Portulacaceae family. Background Art

[0002] my country's facility agriculture has developed rapidly, and its area and output are both ranked first in the world. Facility cultivation has improved the shortcomings of traditional agricultural production being affected by seasons and greatly increased crop yields. However, due to the planting mode of continuous production in facility agriculture throughout the four seasons, the soil environment has changed, resulting in a decrease in soil pH, salt accumulation, and reduced stability of soil aggregates, which in turn cause soil degradation and continuous cropping obstacles. In order to increase yields and improve crop quality, the amount of pesticides and fertilizers applied has increased year by year, resulting in uneven soil fertility and soil nutrient enrichment in facility farmland. At the same time, the accumulation of heavy metals and heavy metal pollution in the soil are caused during the application of large amounts of fertilizers, organic fertilizers and pesticides. The excessive heavy metal Cd in my country's facility agriculture is the most serious, with the excessive levels reaching 41.7%, 54.5% and 11.1% in the south, north and northwest. During the planting process, due to the absorption, transportation and enrichment of plants, heavy metals accumulate in crops, affecting crop quality and yield. Moreover, heavy metals can enter the human body through the food chain, posing a threat to human health.

[0003] Therefore, seeking safe, green and efficient methods for remediating heavy metal pollution in facility agriculture soil is an effective way to ensure the sustainable development of facility agriculture and the ecological environment governance of facility agriculture. Due to the large amount of farmland with moderate to light heavy metal pollution, from the perspective of economy and promotion, farmland with moderate to light heavy metal pollution is currently mainly used for safety. Through agronomic control measures, mainly including the screening of low-accumulation varieties of crops, intercropping or rotation of different types of crops, soil improvement and other methods, the bioavailability of heavy metals in the soil is reduced, thereby reducing the absorption and accumulation of heavy metals in the edible parts of crops. This method has become one of the most economical and feasible remediation measures for facility farmland with moderate to light heavy metal pollution.

[0004] Existing studies have shown that the absorption and enrichment capacity of heavy metals varies greatly between different plant species and between different varieties of the same species. Therefore, the key to remediating heavy metals in facility agricultural contaminated soil through intercropping is the screening of plants and the determination of intercropping combinations. The effects and feasibility of different intercropping patterns are comprehensively evaluated by analyzing indicators such as the heavy metal content in the edible part of crops, crop yield, and enrichment coefficient, combined with the removal or reduction rate of heavy metals in the soil. Therefore, the use of appropriate plant intercropping patterns combined with soil improvement measures to repair heavy metal-contaminated facility farmland soil is not only low-cost, easy to operate, no damage to soil structure, and no secondary pollution, but also mainly reduces the content or bioavailability of heavy metals in the soil, inhibits its entry into the food chain, or changes the ability of crops to absorb heavy metals in the soil, while fully utilizing land resources to ensure the safe production of agricultural products. Summary of the invention

[0005] The present invention aims to provide a method for preparing a method for preparing a vegetable-sunflower ( Portulaca grandiflora ) Intercropping method for remediation of heavy metal contaminated soil.

[0006] To achieve the above object, the technical solution adopted by the present invention is: A method for repairing heavy metal contaminated soil using lettuce-sunflower intercropping: vegetable crops lettuce and sunflowers, ornamental plants of the Portulaceae family, are planted in an intercropping mode in facility vegetable field soil contaminated with heavy metal cadmium, and biochar, a soil conditioner, is applied. During the plant growth process, cadmium in the soil is removed or significantly reduced through mutual absorption between plant combinations and rhizosphere complexation, while not affecting production and economic income.

[0007] In the method for repairing heavy metal-contaminated soil by intercropping lettuce and sunflowers, the cadmium concentration of the facility agricultural soil used for growing lettuce and sunflowers is 0.3-2.0 mg / kg.

[0008] In the method for repairing heavy metal-contaminated soil by intercropping lettuce and sunflowers, biochar is first applied to the soil and fully mixed, and then allowed to equilibrate at room temperature for 15-30 days. The biochar is straw biochar, and the application amount is 1.0-3.0%.

[0009] In the method of repairing heavy metal-contaminated soil by intercropping lettuce and sunflowers, nitrogen, phosphorus and potassium compound fertilizer (N:P2O5:K2O=18:18:18) is first applied to the soil as base fertilizer before sowing, and the amount of compound fertilizer applied is 1.0-1.5g base fertilizer / kg soil.

[0010] The method of using lettuce-sunflower intercropping to repair heavy metal contaminated soil includes the following planting methods: firstly selecting lettuce and sunflower seeds with mature, plump and insect-free seeds, moistening the soil before sowing, and then sowing the lettuce seeds and sunflower seeds in the cadmium contaminated soil in an intercropping mode, and then covering the soil with 0.5-1 cm.

[0011] The method of repairing heavy metal contaminated soil by intercropping lettuce and sunflowers is that after the plants are planted, regular watering, weeding and pest control are carried out according to conventional management methods of facility agriculture, and the field water holding capacity is maintained at 40-70%.

[0012] The vegetable crop used in the present invention is lettuce, an annual herbaceous plant of the genus Lactuca in the family Asteraceae, which has large, oval leaves with wrinkles on the leaf surface, short, hard, vertically extending roots, and prefers slightly acidic soil. Portulaca grandiflora ), also known as pine leaf peony, is a fleshy herbaceous flower of the genus Portulacaceae. It is an annual herb, 10-30cm tall, with a procumbent or oblique stem, many branches, and dense leaves at the branch ends. It is resistant to barrenness and has strong adaptability. The flowers are solitary or clustered at the branch ends, with a diameter of 2.5-4cm, open during the day and close at night, and are widely used in gardening or environmental landscaping.

[0013] The advantages of the present invention are as follows: 1. The present invention uses biochar to improve the soil structure and performance of facility agriculture that has been planted for many years, adjusts the soil pH, and then intercrops lettuce with ornamental plants such as sunflowers to achieve the reduction and treatment of cadmium in the soil without affecting vegetable production. The method has the advantages of simple operation, low investment, low technical requirements, no damage to vegetable fields, and can be used for in-situ repair, and does not affect the normal production activities of facility agriculture; 2. The present invention intercrops lettuce and sunflower in the soil of a facility vegetable field contaminated by heavy metal cadmium. When the cadmium concentration in the soil is 0.3-2.0 mg / kg, the intercropping pattern of the two plants significantly promotes the growth of lettuce. After 60 days of planting, the biomass of the aboveground stems and leaves of lettuce increases by 14-15 times compared with when lettuce is planted alone, indicating that this intercropping pattern can promote the growth of lettuce without affecting the normal production of facility agriculture; 3. The present invention uses lettuce and ornamental plant sunflower to interplant to repair heavy metal cadmium contaminated soil. This method has a high cadmium reduction rate. After 60 days, the cadmium reduction rate in the T3 treatment soil of lettuce + sunflower + biochar application reached 68%. In addition, the cadmium content in the aboveground stems and leaves of lettuce is reduced to 0.096 mg / kg, and the cadmium reduced in the soil is mainly enriched in the roots of sunflower (0.194 mg / kg). The cadmium content in the aboveground stems and leaves of lettuce is far lower than the limit of 0.2 mg / kg of heavy metal cadmium in leafy vegetables stipulated in my country's "National Food Safety Standard-Limit of Contaminants in Food" (GB2762-2012), and it can be eaten safely. Therefore, it is feasible to select suitable plant combinations for interplanting, and at the same time combine reasonable soil conditioners to repair cadmium-contaminated facility agricultural soil and promote its application.

[0014] In summary, the present invention uses lettuce and sunflower intercropping in combination with straw biochar to repair and produce facility agricultural soil contaminated by heavy metal cadmium, and through continuous multiple intercropping and repetition of the above steps, effectively removes cadmium from the contaminated soil until its content reaches the environmental safety standard. The method is simple to operate, requires little investment, has low technical requirements, does not cause damage to vegetable field soil, can be used for in-situ repair, and does not affect the normal production activities of facility agriculture. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The residual amount and reduction rate of Cd in the soil of different treatment groups after 60 days provided by the embodiment of the present invention, in which: T1 is a treatment of planting lettuce alone; T2 is a treatment of intercropping lettuce + sunflower; T3 is a treatment of intercropping lettuce + sunflower + biochar; CK is a treatment without planting plants; Figure 2 Biomass diagram of aboveground stem and leaf parts of lettuce after 60 days in different treatment groups provided in the embodiment of the present invention; Figure 3 This is a graph showing the Cd content in the aboveground (stems and leaves) and underground (roots) parts of lettuce and sunflower after 60 days in different treatment groups provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0016] A method of utilizing lettuce-sunflower ( Portulaca grandiflora ) Intercropping methods for remediating heavy metal contaminated soil mainly include: Applying straw biochar to the soil of greenhouse vegetable fields contaminated with heavy metal cadmium can regulate the soil structure and physical and chemical properties, especially for greenhouse vegetable fields with long planting years and acidic soil (pH <5.8). Then, lettuce, a crop of the Asteraceae Lactuca genus, and sunflower, an ornamental plant of the Portulacaceae family, are planted in an intercropping mode. During the growth of the two plants, the heavy metals in the soil are removed or significantly reduced through mutual absorption and the synergistic effect of root secretions.

[0017] The utilization of lettuce-sunflower ( Portulaca grandiflora ) Intercropping method for repairing heavy metal contaminated soil: before sowing lettuce and sunflowers, apply straw biochar to the soil and mix it thoroughly, then leave it to equilibrate at room temperature for 15-30 days. The amount of biochar applied is 1.0-3.0%.

[0018] The method of repairing heavy metal contaminated soil by intercropping lettuce and sunflowers is as follows: nitrogen, phosphorus and potassium compound fertilizer is applied to the soil as base fertilizer before sowing seeds, the N:P2O5:K2O in the compound fertilizer is 18:18:18, and the application amount is 1.0-1.5g base fertilizer / kg soil.

[0019] The method of using lettuce-sunflower intercropping to repair heavy metal contaminated soil includes first selecting lettuce and sunflower seeds with mature, plump and insect-free seeds, then moistening the soil, sowing the lettuce seeds and sunflower seeds in the cadmium-contaminated soil in an intercropping mode, and then covering the soil with 0.5-1 cm.

[0020] The method of repairing heavy metal contaminated soil by intercropping lettuce and sunflowers requires regular watering, weeding, and pest control during the growth of lettuce and sunflowers in accordance with conventional management methods of facility agriculture, and maintaining the field water holding capacity at 40-70%.

[0021] The method of using lettuce and sunflower intercropping to repair heavy metal contaminated soil is as follows: lettuce is harvested during the growth period (60-90 days), and the heavy metal cadmium content in the aboveground stems and leaves is measured. When the heavy metal content limit of leafy vegetables is lower than the limit value of heavy metal content specified in my country's "National Food Safety Standard - Limits of Contaminants in Food" (GB2762-2012), the lettuce can be sold, and at the same time, the ornamental plant sunflower that absorbs and enriches heavy metals in its roots is transplanted to achieve the purpose of reducing or removing heavy metals in the soil without affecting production. Example

[0022] The following examples can make ordinary technicians in this field understand the present invention more comprehensively, but do not limit the present invention in any way. A potted experiment was carried out in the greenhouse of Shenyang University. The soil was collected from the vegetable field of Shenbei New District, Shenyang City. The soil of the facility with a planting period of more than 10 years was collected. After analysis, the content of heavy metal cadmium in the soil ranged from 0.3 to 2.0 mg / kg, which posed a great ecological and health risk. The soil used in the potted experiment was a mixed soil of various points. The basic physical and chemical properties of the mixed soil were: pH value 5.7, organic matter content 26.5g / kg, alkaline nitrogen, available phosphorus and available potassium contents of 83.31, 90.17 and 218.69 mg / kg respectively, and the background value of cadmium in the soil was 0.492 mg / kg. Straw biochar was first applied to the potted soil and mixed thoroughly, and then placed at room temperature for 15-30 days for equilibrium, and the amount of biochar applied was 1.0-3.0%. Then, compound fertilizer (N:P2O5:K2O=18:18:18) was applied to the soil as base fertilizer at one time, with the application amount of compound fertilizer being 1.0-1.5g base fertilizer / kg soil. After the soil was fully mixed, lettuce and sunflower seeds with mature, plump, and insect-free seeds were selected, and then the soil was moistened. Lettuce seeds and sunflower seeds were sown in the cadmium-contaminated soil in an intercropping mode, and then covered with 0.5-1cm of soil. The experiment set up three different treatments, namely, the treatment group of planting lettuce alone (T1), the treatment group of planting lettuce + sunflower (T2), and the treatment group of planting lettuce + sunflower + biochar application (T3). A blank control group (i.e., no plant planting treatment CK) was also set up in the experiment. The experimental pots were 16 cm × 11.5 cm (diameter × height) round PE plastic pots. The mass of each pot soil was 1.2 kg. 15 lettuce seeds and 15 sunflower seeds were evenly sown in each pot. After their growth was stable, the seedlings were thinned out, and 2 lettuce seedlings and 2 sunflower seedlings were retained in each pot (4 lettuce seedlings were retained in the T1 treatment of planting lettuce alone). Deionized water was used for irrigation during the growth period, and each treatment was repeated 5 times. During the experiment, the irrigation frequency and water volume were controlled to prevent the loss of heavy metals and nutrients in the soil. After 60 days of planting, the aboveground stems and leaves of the plants and the underground roots were harvested, and the rhizosphere soil and the control soil without plants were collected to determine the plant biomass and the content of heavy metal cadmium in the plants and soil.

[0023] Inductively coupled plasma mass spectrometry (ICP-MS) (ELANDRC-E, PerkinElmer) was used to determine the heavy metal cadmium content in soil and plants. National standard samples and blank samples were used for quality control during the analysis.

[0024] Figure 1The figure shows the residual amount and reduction rate of Cd in the soil of different treatment groups after 60 days. In the figure, T1 is the treatment of planting lettuce alone; T2 is the treatment of intercropping lettuce + sunflower; T3 is the treatment of intercropping lettuce + sunflower + biochar; CK is the treatment of no plant planting. After 60 days, the residual amount of cadmium in the blank control treatment CK without plant planting was the highest, while the residual amount of cadmium in the soil decreased significantly after planting plants, and the residual amount of cadmium in the soil of T3 treatment with planting lettuce + sunflower + applying biochar was the lowest. After calculation, the reduction rate of cadmium in the soil of T3 treatment reached 68%.

[0025] Figure 2 The figure shows the biomass of the aboveground stem and leaf of lettuce in different treatment groups after 60 days. Intercropping lettuce with sunflower significantly promoted the growth of lettuce. The aboveground stem and leaf biomass of lettuce in the T1 treatment of planting lettuce alone was 0.098 g / plant. After intercropping with sunflower, the biomass of lettuce in the T2 treatment increased by 14 times. After applying biochar, the biomass of lettuce in the T3 treatment of intercropping lettuce and sunflower increased by 15 times. This shows that intercropping lettuce with sunflower can promote the growth of lettuce.

[0026] Figure 3 The following is a diagram of Cd content in the aboveground (stems and leaves) and underground (roots) parts of lettuce and sunflowers after 60 days of different treatment groups. In the treatment of planting lettuce alone, the cadmium content in the aboveground stems and leaves of lettuce was 0.203 mg / kg. After intercropping sunflowers with lettuce, the cadmium content in the aboveground stems and leaves of lettuce dropped to 0.143 mg / kg, and the cadmium content in the aboveground part was lower than that in the roots. After applying biochar to improve the soil, in the T3 treatment of intercropping lettuce and sunflowers, the cadmium content in the aboveground stems and leaves of lettuce dropped to 0.096 mg / kg, and cadmium was mainly enriched in the roots of sunflowers (0.194 mg / kg). The cadmium content in the aboveground stems and leaves of lettuce is far lower than the limit of 0.2 mg / kg of heavy metal cadmium for leafy vegetables stipulated in my country's "National Food Safety Standard-Limits of Contaminants in Food" (GB2762-2012), and it can be eaten safely.

[0027] Experiments have shown that intercropping vegetable crops lettuce with sunflowers, an ornamental plant of the Purslane family, and applying biochar to improve the soil can effectively remove heavy metal cadmium from the soil while promoting the growth of lettuce, and cadmium is mainly enriched in the roots of lettuce and sunflowers. For medium- and low-pollution facility soils, multiple rounds of intercropping are carried out until the heavy metal cadmium in the soil reaches the environmental safety standard. During the restoration period, when the cadmium content in the aboveground part of lettuce is lower than the limit specified in my country's "National Food Safety Standard - Limits of Contaminants in Food" (GB2762-2012), it can be sold and eaten normally.

Claims

1. A method for repairing heavy metal contaminated soil by intercropping lettuce and sunflowers, characterized in that: The method involves planting vegetable crops lettuce and ornamental plant sunflower of the Portulaceae family in an intercropping mode in facility vegetable field soil contaminated with heavy metal cadmium, and applying soil conditioner biochar. During the plant growth process, cadmium in the soil is removed or significantly reduced through interactive absorption between plant combinations, rhizosphere chelation, etc., without affecting agricultural production. The concentration of heavy metal cadmium in the contaminated soil is 0.3-2.0 mg / kg.

2. The method for repairing heavy metal contaminated soil by intercropping lettuce and sunflowers according to claim 1, characterized in that: Before sowing lettuce and sunflowers, biochar is applied to the soil and mixed thoroughly, and then left to equilibrate at room temperature for 15-30 days. The biochar applied is straw biochar, and the application amount is 1.0-3.0%.

3. The method for repairing heavy metal contaminated soil by intercropping lettuce and sunflowers according to claim 1, characterized in that: Before sowing, base fertilizer is applied to the soil. The base fertilizer is a nitrogen, phosphorus and potassium compound fertilizer. The N:P2O5:K2O in the compound fertilizer is 18:18:18, and the application amount is 1.0-1.5g base fertilizer / kg soil.

4. The method for repairing heavy metal contaminated soil by intercropping lettuce and sunflowers according to claim 1, characterized in that: Select lettuce and sunflower seeds with mature, plump and insect-free seeds, moisten the soil before sowing, and then sow the lettuce seeds and sunflower seeds in the cadmium-contaminated soil in an intercropping mode, and then cover the soil with 0.5-1 cm.

5. The method for repairing heavy metal contaminated soil by intercropping lettuce and sunflowers according to claim 1, characterized in that: After planting the plants, follow the conventional management methods of facility agriculture, regularly water, weed and pest control, and maintain the field water holding capacity at 40-70%.

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