A method for treating farmland with severe heavy metal composite pollution in saline-alkali areas of arid irrigation areas

Abstract

The present invention discloses a method for treating saline-alkaline heavy metal compound polluted farmland in a drought-stricken sewage irrigation area, which includes: screening the fields to be treated, determining the soil pollution depths of the high-step fields and the low-step fields, stripping the surface polluted soil of each step field and piling it up on one side of the low-step field, excavating trenches on the stripped low-step field and piling up the excavated soil of the trenches on the other side, layer-by-layer filling all the stripped polluted soil into the trenches, covering the excavated soil of the trenches on the surface of the filled polluted soil to form a new surface soil, setting soil and groundwater environmental monitoring points in the landfill area, implementing soil improvement measures such as soil fertilization on the new surface soil of each step, and planting corn varieties with low cadmium accumulation to complete the treatment of polluted soil. The method of the present invention can significantly reduce the ecological risk of heavy metal compound pollution in saline-alkaline cultivated land in the sewage irrigation area through multi-technology collaborative treatment, and realize the safe reclamation of farmland severely polluted by heavy metals.

Description

Technical Field

[0001] The present invention relates to the technical field of soil regeneration, and specifically relates to a method for treating saline-alkali heavy metal composite polluted farmland in arid contaminated irrigation areas. Background Technique

[0002] Heavy (metalloid) elements such as cadmium, arsenic, lead, and copper have strong biological toxicity. The elements such as cadmium in the heavy metal composite polluted soil in the contaminated irrigation area mainly come from sewage irrigation and atmospheric deposition, and enter the food chain through agricultural products, threatening ecological safety and human health. Therefore, there is an urgent need to repair and treat the heavy metal composite polluted farmland soil in the contaminated irrigation area to ensure the safety of agricultural products and human health.

[0003] In recent years, the in-situ remediation strategies for heavy metal polluted farmland soil mainly include the following categories: enhancing the adsorption and fixation of heavy metals on soil particles by adding soil conditioners; removing excessive heavy metals in the soil by using hyper-accumulating plants; planting low-accumulating crops to reduce the content of heavy metals in the edible parts of crops. The saline-alkali soil area is vast and is an important area for food production, but the soil in some areas has very serious heavy metal pollution. Compared with acidic soil, saline-alkali soil has higher adsorption and precipitation properties for heavy metals. If the ideas and methods for treating acidic heavy metal composite polluted soil are used to treat saline-alkali heavy metal composite polluted soil, it may cause further degradation of soil environment, health and fertility quality. Therefore, it is very necessary to explore and develop scientific and reasonable remediation technologies for saline-alkali heavy metal composite polluted farmland soil.

[0004] Deep ploughing is a common technology for treating and repairing polluted farmland soil. Research shows that the pollutant content in the heavy metal composite polluted farmland soil is still exceeded after deep ploughing. This may be because deep ploughing only mixes the surface soil with a higher pollutant content with the subsurface soil with a relatively lower pollutant content. In the heavy metal composite polluted soil, this method has limited effect on reducing the pollutant content in the surface soil. If the ex-situ remediation method is used to treat the polluted soil, a large amount of transportation and treatment costs need to be invested. Therefore, there is currently a lack of a soil treatment method that is both low-cost and has a significant pollution treatment effect. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a method for treating saline-alkali heavy metal composite polluted farmland in arid contaminated irrigation areas.

[0006] A method for treating saline-alkali heavy metal composite polluted farmland in arid contaminated irrigation areas includes the following steps:

[0007] S1. According to the pollution degree of the polluted farmland, select the plots that need to be treated on the polluted farmland;

[0008] S2. Then group the fields to be treated, classify the fields within the same slope range into one group to obtain multiple groups of fields. Each group of fields in the multiple groups of fields includes a high-step field and a low-step field; the same slope range means that the slope difference between the fields is between 0 and 10%.

[0009] S3. Then determine the depth of the contaminated soil in the high-step field and the low-step field. According to the depth of the contaminated soil, strip the contaminated soil of the fields to be treated to obtain the stripped contaminated soil, the stripped high-step field, and the stripped low-step field.

[0010] S4. For the stripped high-step field, directly apply fertilizer, plow, and then plant crops, thus completing the treatment.

[0011] Dig trenches in the stripped low-step field to obtain the soil dug out from the trenches, and use the layer-by-layer filling method to landfill the contaminated soil stripped in S3 into the trenches and compact it. Then cover the soil dug out from the trenches above the trenches and the stripped low-step field to form a treated low-step field.

[0012] S5. Set soil sampling points at 0.2 m, 0.5 m, and 2.0 m outside the trenches of the treated low-step field respectively, and set groundwater sampling wells at 0.5 m, 3.0 m, and 30 m outside the outer edge of the treated low-step field respectively. Regularly sample and monitor the soil at the soil sampling points and the groundwater in the groundwater sampling wells. If it is monitored that the pollutant concentration in the soil at the soil sampling points or the groundwater in the groundwater sampling wells increases with time, take anti-diffusion measures. If it is monitored that the pollutant concentration in the soil at the soil sampling points or the groundwater in the groundwater sampling wells does not increase with time, it indicates that no pollutant diffusion has occurred in the contaminated soil in the trenches on the low-step field, and proceed to the next step of treatment.

[0013] S6. Apply fertilizer, plow, and then plant crops on the low-step field where no pollution diffusion has occurred, thus completing the treatment.

[0014] Note: The above method strips and landfills the severely contaminated plow layer soil, and conducts environmental monitoring at the landfill site. The newly formed plow layer after stripping can restore soil productivity and improve soil quality through improvement measures such as soil fertilization. Specifically, through the grouping setting of high- and low-gradient fields and the corresponding design of trenches, and stripping and landfilling the surface contaminated soil, the distribution of heavy metals in the newly formed plow layer soil can be reduced. This method can significantly reduce the ecological risk of heavy metal combined pollution in saline-alkali cultivated land in sewage irrigation areas through multi-technology collaborative treatment, and achieve safe reclamation of severely heavy metal contaminated farmland.

[0015] Further, in S1, screening out the plots to be treated on the contaminated farmland according to the contamination degree of the contaminated farmland includes: investigating the soil contamination status of the contaminated farmland, and taking the plots where the cadmium, lead, arsenic, and copper contents in the soil exceed the screening value or control value as the plots to be treated.

[0016] Note: The above-mentioned screening value or control value refers to the "Soil Environmental Quality - Risk Control Standards for Soil Pollution of Agricultural Land (Trial)" (GB15618-2018). Among them, the safe utilization range value of cadmium does not exceed the control value in the standard, and the safe utilization range values of lead, arsenic, and copper do not exceed the screening value in the standard.

[0017] Further, in S2, the height difference between the high-step plots and the low-step plots in each group of the multiple groups of plots is 1.0 - 3.0 m, and the relative height between the stripped low-step plots and the high-step plots remains unchanged.

[0018] Note: By limiting the setting of maintaining the relative height between the high-step plots and the low-step plots, it is possible to avoid changing the local terrain and water flow direction.

[0019] Further, in S3, determining the depth of contamination in the high-step plots and the low-step plots includes: sampling and detecting the soil at multiple depths to obtain the cadmium, lead, arsenic, and copper contents in the soil at multiple depths. The multiple depths include the first depth, the second depth... and the nth depth from the surface layer downward. The distance between every two adjacent depths is 20 cm. When the average contents of cadmium, lead, arsenic, and copper in the soil at the nth depth do not exceed the screening value or control value, the value of the nth depth is taken as the depth of the contaminated soil.

[0020] In S3, the stripping method is: for each group of plots in the multiple groups of plots, strip the contaminated soil layer by layer from the surface soil at a rate of 10 cm per layer for the high-step plots and the low-step plots until the depth value to be stripped, and stack the stripped contaminated soil on the stripped low-step plots.

[0021] Note: By using the above method to confirm the depth layer by layer, it is possible to confirm the depth that can be safely utilized. The screening value or control value refers to the "Soil Environmental Quality - Risk Control Standards for Soil Pollution of Agricultural Land (Trial)" (GB15618-2018). Among them, the safe utilization range value of cadmium does not exceed the control value in the standard, and the safe utilization range values of lead, arsenic, and copper do not exceed the screening value in the standard.

[0022] Further, in S4, the distance between the position of the trench and the edge of the low-step field block after stripping is greater than 2.0 m. The relationship between the depth of the trench, the excavation area of the trench, the depth of the contaminated soil, and the area of the field block to be treated is as follows:

[0023] ;

[0024] In the formula, is the depth of the trench, is the excavation area of the trench; is the depth of the contaminated soil, is the area of the field block to be treated, is the conversion coefficient of earthwork volume, is the reserved coefficient of the trench opening.

[0025] Note: Through the above formula, the appropriate trench size can be calculated according to the amount of contaminated soil to ensure that the field block after stripping remains flat. At the same time, under this design, the contaminated soil is buried reasonably, reducing the risk of pollutant diffusion in the soil.

[0026] Further, the layer-by-layer filling method is as follows: The stripped contaminated soil is filled and compacted into the trench in layers of 10 cm each until the distance between the stripped contaminated soil and the top of the trench is 40 - 60 cm. Then, the soil dug out from the trench is filled into the trench in layers of 10 cm each until it is flush with the top of the trench, and the remaining soil dug out from the trench is evenly spread on the low-step field block after stripping.

[0027] Note: Through the treatment method of layer-by-layer filling and compaction, the contaminated soil can be buried more concentratedly, reducing the risk of heavy metal pollutant diffusion.

[0028] Further, in S4, the thickness of the soil dug out from the trench and filled into the trench is 40 - 60 cm.

[0029] Further, the tillage depth is 18 - 25 cm, and the crop is corn;

[0030] Note: The above thickness and tillage depth are more practical. Compared with local main crops such as wheat, soybeans, and flax, corn has a good effect of low cadmium accumulation, which can reduce the cadmium accumulation in grains.

[0031] Further, at a distance of 0.5 - 2 m from the edge of the trench, an isolation trench with a width of 0.2 - 0.4 m and a depth the same as that of the trench is dug, and a filler is filled in the isolation trench. The filler, by weight, includes 100 parts of quicklime and 100 parts of attapulgite.

[0032] Description: By setting isolation ditches, the diffusion and migration of heavy metals in polluted soil can be avoided; by adjusting the raw materials and ratios in the filling filler, the precipitation and adsorption performance of the composite filler can be improved, the heavy metal ions in the soil can be fixed stably, and their migration and diffusion in the environment can be reduced.

[0033] Further, it also includes installing a plurality of geocells (40 cm × 40 cm × 15 cm) at the edge of the treated low terraced fields in S4, planting plants such as tall fescue in each geocell, then covering non-woven fabric on the geocells and watering and maintaining them regularly, wherein the geocell is a grid-like structure made of plastic material.

[0034] Description: Geocells can effectively fix the soil and prevent soil loss caused by rain erosion. The roots of tall fescue plants can further enhance the soil stability and reduce erosion. The geocell increases the shear strength of the soil through its grid structure and improves the overall stability of the slope. Covering non-woven fabric can reduce the impact of wind erosion on the slope soil, and at the same time can play a role in heat preservation and moisture retention of the soil, prevent the rapid evaporation of water, and promote the rooting and germination of plants.

[0035] The beneficial effects of the present invention are:

[0036] The method of the present invention restores the soil productivity and improves the soil quality by stripping and landfilling the severely polluted plough layer soil, setting soil and groundwater environmental monitoring points in the landfill area, and implementing soil fertility improvement and other improvement measures on the newly formed surface soil, and realizes the safe reclamation of severely heavy metal polluted farmland by planting corn varieties with low cadmium accumulation. Through the collaborative treatment of multiple technologies, this method can significantly reduce the ecological risk of severe heavy metal combined pollution in saline-alkali cultivated land in sewage irrigation areas and ensure the sustainable utilization of polluted farmland. Description of the Drawings

[0037] Figure 1 It is the distribution data diagram of total Cd in polluted soil in Example 2 of the present invention;

[0038] Figure 2 It is the change data diagram of Cd content before and after stripping of polluted soil in Example 2 of the present invention;

[0039] Figure 3 It is the distribution data diagram of total Pb in soil in Example 2 of the present invention;

[0040] Figure 4 It is the change data diagram of Pb content before and after stripping of polluted soil in Example 2 of the present invention;

[0041] Figure 5 It is the distribution of total As in soil and its change before and after stripping in Example 2 of the present invention;

[0042] Figure 6 It is the change data graph of As content before and after stripping contaminated soil in Example 2 of the present invention;

[0043] Figure 7 It is the distribution of total Cu in soil and its changes before and after stripping in Example 2 of the present invention;

[0044] Figure 8 It is the change data graph of Cu content before and after stripping contaminated soil in Example 2 of the present invention;

[0045] Figure 9 It is the Cd content in corn kernels after conventional deep plowing and soil stripping in Example 2 of the present invention. Specific implementation manners

[0046] To further elaborate on the methods adopted and the effects achieved by the present invention, the following describes in detail a method for treating saline-alkali heavy metal compound contaminated farmland in arid polluted irrigation areas provided by the present invention with specific embodiments. Obviously, the present invention is not limited to the implementation manners of the embodiments, and various changes can be made without departing from the purpose of the present invention within the knowledge scope of those of ordinary skill in the art.

[0047] As can be seen from the foregoing background technology, after heavy metals such as cadmium enter alkaline soil, they are mainly adsorbed, precipitated and retained in the plough layer (0 - 20 cm) soil for a long time, while their content in the deep layer (> 20 cm) soil is relatively low. The salts in the soil can increase the mobility and bioavailability of heavy metals, thus significantly changing the environmental and health risks of heavy metal pollution in saline-alkali soil. Research shows that there is a complex interaction relationship between heavy metals such as Cd and salt ions. For example, salts such as Na + in the soil can displace the heavy metal ions adsorbed on the soil surface through ion exchange, thereby increasing the mobility and bioavailability of soil heavy metals.

[0048] In summary, the complexity of saline-alkali heavy metal compound contaminated soil increases the difficulty of remediation. In the actual remediation process, various methods such as soil improvement, phytoremediation and chemical remediation need to be comprehensively considered.

[0049] To reduce the degree of heavy metal compound pollution in saline-alkali soil and at the same time achieve safe crop production, the embodiments of the present invention provide a feasible method as follows:

[0050] Example 1: A method for treating saline-alkali heavy metal compound contaminated farmland in arid polluted irrigation areas, comprising:

[0051] S1. Select the plots to be treated on the polluted farmland according to the pollution degree of the polluted farmland. Specifically, it includes: investigating the soil pollution status of the polluted farmland, and taking the plots where the content of any one of cadmium, lead, arsenic and copper in the soil exceeds the screening value or the control value as the plots to be treated.

[0052] S2. Then group the plots to be treated, and group the plots within the same slope range into one group. The same slope range means that the slope difference between the plots is between 0 and 10% (for example, 5%); multiple groups of plots are obtained, and each group of plots in the multiple groups includes a high-step plot and a low-step plot; the height difference between the high-step plot and the low-step plot in each group of the multiple groups is 2.0 m.

[0053] S3. Then determine the depth of the polluted soil in the high-step plot and the low-step plot. According to the depth of the polluted soil, strip the polluted soil of the plots to be treated to obtain the stripped polluted soil, the stripped high-step plot and the stripped low-step plot.

[0054] Determining the depth of the polluted soil in the high-step plot and the low-step plot includes:

[0055] Sampling and detecting the soil at multiple depths to obtain the contents of cadmium, lead, arsenic and copper in the soil at multiple depths. The multiple depths include the first depth, the second depth... and the nth depth from the surface layer downward. The distance between every two adjacent depths is 20 cm. When the average contents of cadmium, lead, arsenic and copper in the soil at the nth depth do not exceed the screening value or the control value, take the value of the nth depth as the depth of the polluted soil.

[0056] The stripping method is: for each group of plots in the multiple groups of plots, strip the polluted soil layer by layer from the surface soil at a layer thickness of 10 cm for both the high-step plot and the low-step plot until the depth of the polluted soil, and stack the stripped polluted soil on the stripped low-step plot.

[0057] S4. For the stripped high-step plot, directly apply fertilizer, plow, and then plant crops, and the treatment is completed.

[0058] Dig trenches on the stripped low-step plot to obtain the excavated soil from the trenches, and use the method of layer-by-layer filling to landfill the polluted soil stripped in S3 into the trenches and compact it. Then cover the excavated soil from the trenches above the trenches and the stripped low-step plot to form the treated low-step plot.

[0059] The distance between the position of the trench and the edge of the stripped low-step plot is 3.0 m; the relationship between the depth of the trench, the excavation area of the trench, the depth of the polluted soil, and the area of the plot to be treated is as follows:

[0060] ;

[0061] In the formula, is the depth of the trench, is the excavation area of the trench; is the depth of the contaminated soil, is the area of the field to be treated, is the conversion coefficient of earthwork volume, is the reserved coefficient at the trench opening;

[0062] refers to the ratio of the actual volume of the soil after ramming and filling to the original volume of the soil, reflecting the compression characteristics and ramming effect of the soil during the ramming process, is related to factors such as soil type and soil moisture content (the value range is 0.67 - 1.0). In the embodiments of the present invention, takes 0.87; is related to the root distribution of plants, and its value needs to be greater than or equal to the depth of the root distribution of plants. For example, if the plant roots are distributed in the soil at 0.2 m, in order to prevent the plant roots from growing into the contaminated soil, 0.4 m is taken;

[0063] Among them, the area of the trench satisfies ; a is the length of the field L - 4 m, and b is the width of the field M - 4 m;

[0064] The method of layer-by-layer filling is as follows: The stripped contaminated soil is filled layer by layer into the trench at a thickness of 10 cm per layer until the distance between the stripped contaminated soil and the top of the trench is 40 - 60 cm. Then, the soil excavated from the trench is filled into the trench layer by layer at a thickness of 10 cm per layer until it is flush with the top of the trench. The remaining soil excavated from the trench is evenly spread on the low-step field after stripping;

[0065] At a distance of 0.5 m from the outer edge of the trench, an isolation trench with a width of 0.2 m and a depth the same as the depth of the trench is dug, and an anti-pollution diffusion filler is filled in the isolation trench. The anti-pollution diffusion filler, by weight, includes 100 parts of quicklime and 100 parts of attapulgite;

[0066] Among them, the thickness of the soil excavated from the trench filled into the trench is 40 cm; the tillage depth is 20 cm, and the crop is corn;

[0067] S5. Set soil sampling points at 0.2 m, 0.5 m, and 2.0 m outside the trenches of the treated low-step terraced fields respectively, and set groundwater sampling wells at 0.5 m, 3.0 m, and 30 m outside the outer edge of the treated low-step terraced fields. Regularly sample and monitor the soil at the soil sampling points and the groundwater in the groundwater sampling wells. If it is detected that the pollutant concentration in the soil at the soil sampling points or the groundwater in the groundwater sampling wells increases over time, take anti-diffusion measures. If it is detected that the pollutant concentration in the soil at the soil sampling points or the groundwater in the groundwater sampling wells does not increase over time, it indicates that the contaminated soil in the trenches on the low-step terraced fields has not undergone pollutant diffusion, and proceed to the next step of treatment;

[0068] The anti-diffusion measures include: managing the irrigation volume to avoid excessive irrigation causing pollutants to penetrate with water, or strengthening the barrier. The methods of strengthening the barrier include replacing the filler of the isolation ditch or widening the isolation ditch;

[0069] S6. Install multiple geocells (40 cm × 40 cm × 15 cm) on the edge of the treated low-step terraced fields, and plant plants such as tall fescue in each geocell. Then cover the geocells with non-woven fabric and water and maintain them regularly. Among them, the geocell is a grid-like structure made of plastic;

[0070] S7. Fertilize and plow the low-step terraced fields where no pollution diffusion has occurred, and then plant crops, thus completing the treatment.

[0071] Example 2: Exemplarily, a method for treating saline-alkali heavy metal composite polluted farmland in a dry environment irrigation area, the specific operation method includes the following S1 - S7;

[0072] S1. According to the pollution degree of the polluted farmland, screen out the fields that need to be treated on the polluted farmland; select the cultivated land polluted by saline-alkali heavy metal composite in the irrigation area, and there are obvious steps between the selected fields; specifically, select the restoration and treatment experiment of saline-alkali heavy metal composite polluted soil in a certain place in a certain city; conduct a soil environmental quality survey on a certain area in a certain city, and it is measured that the total amount of soil salt in this area reaches 3.29 ± 0.21 g / kg; the contents of total Cd, Pb, As, and Cu in the surface 0 - 20 cm soil in this area are 71.2 ± 32.6 mg / kg, 826 ± 768 mg / kg, 43.9 ± 26.2 mg / kg, and 263 ± 159 mg / kg respectively, all exceeding the screening values or control values specified in the "Soil Environmental Quality Risk Control Standards for Agricultural Land" (GB15618 - 2018);

[0073] S2. Then group the fields to be treated, and classify the fields within the same slope range into one group to obtain multiple groups of fields. Each group of fields in the multiple groups of fields includes a high-step field and a low-step field; the height difference between the high-step field and the low-step field in each group of fields in the multiple groups of fields reaches more than 2.0 m; specifically, corn, wheat, soybeans or other crops were planted in the two plots of the high-step field and the low-step field, and the total area is about 900 m 2 , of which the high-step field is about 500 m 2 , and the area of the low-step field is about 400 m 2 ; both fields are saline-alkali heavy metal composite polluted soils; the distribution of total soil Cd, Pb, As and Cu is as shown in Figure 1 , Figure 3 , Figure 5 and Figure 7 ; the test time is from September 2021 to October 2021;

[0074] S3. Then determine the depth of the polluted soil in the high-step field and the low-step field. According to the depth of the polluted soil, strip the polluted soil of the fields to be treated to obtain the stripped polluted soil, the stripped high-step field and the stripped low-step field; specifically, in September 2021, soil samples at 0-20 cm, 20-40 cm, and 40-60 cm before stripping were collected using a soil drill according to the grid point method. Then, through a large loader, the 0-40 cm polluted soil of the high and low step fields was stripped layer by layer, with a thickness of 10 cm for each round of stripping, and a total of 4 rounds of stripping were carried out;

[0075] S4. On the stripped low-step field, use an excavator to dig a trench 2.0 m away from the edge of the low-step field, and stack the soil dug out from the trench separately from the polluted soil stripped from the surface layer; then backfill the stripped polluted soil into the trench and compact it layer by layer. When it reaches 40 cm from the trench opening, layer by layer fill and compact the soil dug out from the trench until it is flush with the trench opening, and then stop filling. Then evenly spread the remaining soil dug out from the trench on the surface layer of the low-step field. The landfill and leveling process is ensured to be flat by using a level and a grader;

[0076] S5. Soil sampling points are respectively set at 0.2 m, 0.5 m and 2.0 m outside the grooves of the treated low-step terraced fields, and groundwater sampling wells are respectively set at 0.5 m, 3.0 m and 30 m outside the outer edge of the treated low-step terraced fields. Regularly sample and monitor the soil at the soil sampling points and the groundwater in the groundwater sampling wells. If the pollutant concentration in the soil at the soil sampling points or the groundwater in the groundwater sampling wells increases over time, anti-diffusion measures shall be taken. If the pollutant concentration in the soil at the soil sampling points or the groundwater in the groundwater sampling wells does not increase over time, it indicates that no pollutant diffusion has occurred in the polluted soil in the grooves of the low-step terraced fields, and proceed to the next step of treatment;

[0077] Exemplarily, sample and monitor the soil at the soil sampling points and the groundwater in the groundwater sampling wells every two months; Further, collect relevant samples at the atmospheric particulate matter deposition collection device and the irrigation canal outlet set within the field every two months; In addition, a soil lateral seepage collection device is arranged outside the ridge of the low-step terraced field after landfilling the polluted soil, and no water samples seeping from within the field are observed during irrigation and when there is a large surface runoff;

[0078] The changes in the total amounts of Cd, Pb, As, and Cu in the surface soil (0 - 20 cm) before and after stripping are as Figure 2 、 Figure 4 、 Figure 6 and Figure 8 shown. Compared with before stripping, the contents of total Cd, Pb, As, and Cu have decreased by 95.6%, 84.7%, 51.2%, and 71.1% respectively; The results show that within the study area, after stripping the severely saline-alkali heavy metal compound polluted farmland, the degree of heavy metal pollution in the newly generated surface soil has been significantly reduced, that is, the newly generated tillage layer has the conditions for carrying out research on safe utilization; In addition, the tillage layer soil generated after stripping is maintained according to the field management specifications, including measures such as weed cleaning and winter irrigation, to optimize the soil environmental conditions and provide guarantee for the crop planting work in the second year;

[0079] S6. Install multiple geocells (40 cm × 40 cm × 15 cm) on the edges of the treated low-step terraced fields, and plant plants such as tall fescue in each geocell, then cover non-woven fabric on the geocells and water and maintain them regularly. Among them, the geocell is a grid-like structure made of plastic;

[0080] S7. Fertilize, plow the fields where no pollution diffusion has occurred, and then plant crops, that is, complete the treatment;

[0081] Specifically, the organic materials made from agricultural and forestry waste are rich in organic matter, which can improve, cultivate, and enhance soil quality, and promote crop growth. During the soil stripping process, in order to reduce the concentration of heavy metals in the plough layer soil, the original plough layer soil is stripped and landfilled, while the newly formed plough layer soil is relatively barren. Therefore, applying a large amount of organic materials can effectively improve soil quality and improve the growth environment of crops.

[0082] After the planting season begins, spread organic materials on the stripped field (which has been winter-irrigated). After ploughing, the organic materials can be fully mixed with the new plough layer soil to construct and cultivate a good new soil body, and improve the fertility and productivity of the reconstructed plough layer soil. The N:P:K content of the organic materials is 5.45±0.26 g / kg, 1.97±0.07 g / kg, and 18.75±0.92 g / kg respectively, and the organic matter content is 75.5±2.3 g / kg. The application rate of the organic materials is 6 T / mu, and it is planned to be continuously applied for three years.

[0083] Preferably, select the corn variety Jinyuan 007, which is drought-tolerant, high-yielding, has strong lodging resistance, and low cadmium absorption. Apply basal fertilizer (compound fertilizer: N-P 2 O 5 -KO 2 15-15-15) before planting, with a dosage of 40 kg / mu. When the corn has 10-12 leaves, top-dress diammonium hydrogen phosphate (2 parts) and urea mixture (1 part). The fertilization method is hole application and covering with soil, and the mixed dosage is 30 kg / mu. Before 10 am or after 4 pm on a windless and rainless day, select 55% nicosulfuron·atrazine herbicide and dilute it 150 times for spraying when the corn has 3-5 leaves, with a dosage of 200 g / mu. After winter irrigation in the previous year, raking and moisture preservation can meet the water demand during the seedling stage of corn. Subsequently, irrigate respectively after top-dressing at 10-12 leaves, jointing and booting stage, heading and flowering stage, and maturity stage. After the corn is mature, harvest the straw and grains, wash, dry, grind, and then digest them. The Cd content in the digestion solution is measured by ICP-MS. The data obtained from the experimental treatments are analyzed using Excel 2013 and SPSS 16.0 software. The difference analysis of the data between different treatments is performed by one-way ANOVA (LSD) for multiple comparisons. The changes in the Cd content in the corn grains planted after conventional deep ploughing and after land stripping are as Figure 9 shown. After the land stripping measure, the cadmium content in the newly formed plough layer is significantly reduced, and thus the cadmium content in the corn grains is also reduced.

[0084] Example 3: The difference from Example 2 is that the height difference between the high-step field plots and the low-step field plots in each of the multiple groups of field plots is 1.0 m; at a distance of 0.5 m from the edge of the trench, an isolation trench with a width of 0.2 m is dug, and the isolation trench is filled with filler; in S4, it is filled and compacted layer by layer into the trench until the distance between the stripped soil and the upper edge of the trench is 40 cm; the thickness of the soil dug from the trench covered into the trench in S4 is 40 cm; the tillage depth is 18 cm, and the crop is corn.

[0085] Example 4: The difference from Example 2 is that the height difference between the high-step field plots and the low-step field plots in each of the multiple groups of field plots is 3.0 m; at a distance of 2 m from the edge of the trench, an isolation trench with a width of 0.4 m is dug, and the isolation trench is filled with filler; in S4, it is filled and compacted layer by layer into the trench until the distance between the stripped soil and the top edge of the trench is 60 cm; the thickness of the soil dug from the trench covered into the trench in S4 is 60 cm, the tillage depth is 25 cm, and the crop is corn.

Claims

1. A method for treating farmland with severe salinity and heavy metal complex pollution in arid wastewater irrigation areas, characterized in that: The following steps are involved: S1. According to the pollution degree of the polluted farmland, selecting the fields that need to be treated on the polluted farmland; S2, then grouping the fields that need to be managed, grouping the fields in the same slope range into one group, and obtaining multiple groups of fields, each of the multiple groups of fields including a high-step terraced field and a low-step terraced field; S3, then determining the depth of the contaminated soil in the high-step terrace block and the low-step terrace block, and stripping the contaminated soil of the field block that needs to be treated according to the depth of the contaminated soil, to obtain the stripped contaminated soil, the high-step terrace block after stripping, and the low-step terrace block after stripping; S4, directly fertilizing and tilling the stripped high-step terraced fields, and then planting crops, thus completing the management; Digging a trench on the stripped low-step terrace block to obtain trench excavated soil, and filling the stripped contaminated soil in S3 into the trench in a layer-by-layer filling manner and compacting it, and then covering the trench excavated soil over the trench and the stripped low-step terrace block to form a treated low-step terrace block; S5. Set soil sampling points at 0.2m, 0.5m and 2.0m away from the outside of the groove of the treated low-step terraced field block, respectively; set groundwater sampling wells at 0.5m, 3.0m and 30m away from the outer edge of the treated low-step terraced field block, respectively; regularly sample and monitor the soil in the soil sampling points and the groundwater in the groundwater sampling wells; if it is monitored that the pollutant concentration in the soil in the soil sampling points or the groundwater in the groundwater sampling wells increases over time, take anti-diffusion measures; if it is monitored that the pollutant concentration in the soil in the soil sampling points or the groundwater in the groundwater sampling wells does not increase over time, it indicates that the pollutants in the contaminated soil in the groove on the low-step terraced field block have not diffused, and the next step of treatment is carried out; S6. Fertilize and till the low-level terraced fields where no pollutant diffusion has occurred, and then plant crops to complete the treatment.

2. The method for treating farmland with severe salinity and heavy metal complex pollution in arid wastewater irrigation areas according to claim 1, characterized in that: In S1, according to the pollution degree of the polluted farmland, the fields that need to be treated are screened on the polluted farmland, including: investigating the soil pollution status of the polluted farmland, and identifying the fields whose cadmium, lead, arsenic and copper content in the soil exceeds the screening value or the control value as the fields that need to be treated.

3. The method for treating farmland with severe salinity and heavy metal complex pollution in arid wastewater irrigation areas according to claim 2, characterized in that: In S2, the height difference between the high-level terraced fields and the low-level terraced fields in each of the multiple groups of fields is 1.0-3.0 m.

4. The method for treating farmland with severe saline-alkali and heavy metal complex pollution in arid wastewater irrigation areas according to claim 2, characterized in that: In S3, determining the depth of the contaminated soil in the high-step terrace blocks and the low-step terrace blocks includes: sampling and testing the soil at multiple depths to obtain the cadmium, lead, arsenic and copper contents in the soil at multiple depths, the multiple depths include a first depth from the surface layer downward, a second depth... and an nth depth, and the distance between every two adjacent depths is 20 cm. When the average contents of cadmium, lead, arsenic and copper in the soil at the nth depth do not exceed the screening value or the control value, the value of the nth depth is used as the depth of the contaminated soil.

5. The method for treating farmland with severe salinity and heavy metal complex pollution in arid wastewater irrigation areas according to claim 1, characterized in that: In S3, the stripping method is: for each group of the multiple groups of fields, the high-step terraced fields and the low-step terraced fields are separated into a layer of 10 cm each, and the contaminated soil is stripped layer by layer starting from the surface soil to the depth of the contaminated soil, and the stripped contaminated soil is piled on the stripped low-step terraced fields.

6. The method for treating farmland with severe salinity and heavy metal complex pollution in arid wastewater irrigation areas according to claim 1, characterized in that: In S4, the distance between the position of the groove and the edge of the stripped low-step terraced field is greater than 2.0 m; the relationship between the depth of the groove, the excavation area of ​​the groove, the depth of the contaminated soil, and the area of ​​the field to be treated is as follows: Where H is the depth of the groove, is the excavation area of ​​the trench, The depth of contaminated soil, is the area of ​​the field that needs to be treated, is the earthwork volume conversion coefficient, is the groove opening reserve coefficient, Related to the distribution of plant roots, The value should be greater than or equal to the depth of plant root distribution.

7. The method for treating farmland with severe salinity and heavy metal complex pollution in arid wastewater irrigation areas according to claim 1, characterized in that: The layer-by-layer filling method is: the stripped contaminated soil is buried and compacted into the trench layer by layer according to a layer of 10 cm until the distance between the stripped contaminated soil and the top of the trench is 40-60 cm, and then the soil excavated from the trench is buried in the trench according to a layer of 10 cm until it is level with the top of the trench, and the remaining soil excavated from the trench is evenly spread on the stripped low-step terraced fields.

8. The method for treating farmland with severe salinity and heavy metal complex pollution in arid wastewater irrigation areas according to claim 1, characterized in that: In S4, the thickness of the trench excavated soil covering the trench is 40-60 cm.

9. The method for treating farmland with severe salinity and heavy metal complex pollution in arid wastewater irrigation areas according to claim 1, characterized in that: At 0.5~2m away from the outer edge of the groove, an isolation ditch with a width of 0.2~0.4m and a depth equal to the groove depth is dug, and the isolation ditch is filled with pollution-proof diffusion filler, which includes 100 parts of quicklime and 100 parts of attapulgite by weight.

10. The method for treating farmland with severe salinity and heavy metal complex pollution in arid wastewater irrigation areas according to claim 1, characterized in that: The method further includes installing a plurality of geocells at the edge of the low-step terraced field blocks treated in S4, planting tall fescue plants in each geocell, and then covering the geocells with non-woven fabrics and watering them regularly for maintenance, wherein the geocells are grid-like structures made of plastic.

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