Method for treating saline-alkaline severe heavy metal combined pollution farmland in drought pollution irrigation area

Abstract

The invention discloses a method for treating saline-alkaline severe heavy metal combined pollution farmland in a drought pollution irrigation area. Comprising the following steps: screening a field to be treated, determining the soil pollution depth of a high-step field and a low-step field, stripping polluted soil on the surface layer of each step field, stacking the polluted soil on one side of the low-step field, digging a groove in the stripped low-step field, digging soil out of the groove, and stacking the soil on the other side, filling all stripped polluted soil into the groove layer by layer, covering the surface layer of the filled polluted soil with soil dug out of the groove to form new surface soil, arranging soil and groundwater environment monitoring points in a landfill area, and implementing improvement measures such as soil fertility improvement on the new surface soil of each step. And planting a corn variety with low cadmium accumulation to complete polluted soil treatment. According to the method, through multi-technology cooperative treatment, the ecological risk of heavy metal combined pollution of the saline-alkaline cultivated land in the sewage irrigation area can be remarkably reduced, and safe second ploughing of the heavily heavy metal polluted farmland is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of soil regeneration, and in particular to a method for treating farmland with severe saline-alkali and heavy metal complex pollution in arid wastewater irrigation areas. Background Art

[0002] Heavy metal elements such as cadmium, arsenic, lead and copper have strong biological toxicity. Cadmium and other elements in soil contaminated by heavy metals in sewage irrigation areas mainly come from sewage irrigation and atmospheric deposition, and enter the food chain through agricultural products, threatening ecological security and human health. Therefore, it is urgent to repair and treat farmland soil contaminated by heavy metals in sewage irrigation areas to ensure the safety of agricultural products and human health.

[0003] In recent years, the in-situ remediation strategies for heavy metal-contaminated farmland soils mainly include the following categories: adding soil conditioners to enhance the adsorption and fixation of heavy metals on soil particles; using hyper / high-accumulation plants to remove excess heavy metals in the soil; planting low-accumulation crops to reduce the content of heavy metals in the edible part of crops. The saline-alkali soil area is vast and is an important area for grain production, but the soil in some areas is seriously polluted by heavy metals. Compared with acidic soils, saline-alkali soils have higher adsorption and precipitation properties for heavy metals. If the ideas and methods for treating acidic heavy metal compound-contaminated soils are used to treat saline-alkali heavy metal compound-contaminated soils, it may cause further degradation of the soil environment, health and fertility quality. Therefore, it is very necessary to explore and develop scientific and reasonable saline-alkali heavy metal compound-contaminated farmland soil remediation technologies.

[0004] Deep tillage is a common technology for the treatment and remediation of farmland soil pollution. Studies have shown that the pollutant content of farmland soil with severe heavy metal compound pollution still exceeds the standard after deep tillage. This may be because deep tillage only mixes the surface soil with higher pollutant content with the sub-surface soil with relatively lower pollutants, and in soil with severe heavy metal compound pollution, this method has limited effect on reducing the pollutant content in the surface soil. If an ex situ remediation method is used to treat contaminated soil, a large amount of transportation and treatment costs will be required. Therefore, there is currently a lack of a soil treatment method that is both low-cost and has significant pollution control effects. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for treating farmland with severe salinity and heavy metal complex pollution in arid wastewater irrigation areas.

[0006] A method for treating farmland with severe saline-alkali and heavy metal compound pollution in arid wastewater irrigation areas comprises the following steps: 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 plots to be managed, grouping the plots in the same slope range into one group, and obtaining multiple groups of plots, each of the multiple groups of plots including a high-step terraced plot and a low-step terraced plot; the same slope range means that the slope difference between the plots is between 0 and 10%; 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 pollution spread has occurred, and then plant crops to complete the treatment.

[0007] Note: The above method strips the heavily polluted arable layer soil and then buries it, and conducts environmental monitoring at the landfill site. The new arable layer after stripping can restore soil productivity and improve soil quality through the implementation of soil fertilization and other improvement measures. Specifically, by setting high and low gradient field groups and corresponding trench design, and stripping and burying the surface contaminated soil, the distribution of heavy metals in the newly generated arable layer soil can be reduced. This method can significantly reduce the ecological risk of heavy metal complex pollution in saline-alkali farmland in polluted irrigation areas through multi-technical coordinated governance, and achieve safe reclamation of farmland with severe heavy metal pollution.

[0008] Furthermore, in S1, according to the pollution degree of the polluted farmland, the fields that need to be treated are screened out on the polluted farmland, including: investigating the soil pollution status of the polluted farmland, and identifying the fields whose cadmium, lead, arsenic and copper contents in the soil exceed the screening value or the control value as the fields that need to be treated.

[0009] Note: The above screening values ​​or control values ​​refer to the "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard (Trial)" (GB15618-2018). Among them, the safe use range value of cadmium does not exceed the control value in the standard, and the safe use range values ​​of lead, arsenic and copper do not exceed the screening value in the standard.

[0010] Furthermore, in S2, the height difference between the high-step terrace blocks and the low-step terrace blocks in each of the multiple groups of fields is 1.0-3.0 m, and the relative height between the low-step terrace blocks and the high-step terrace blocks after stripping remains unchanged.

[0011] Note: By limiting the relative height between the high-step terrace blocks and the low-step terrace blocks, changes in local terrain conditions and water flow directions can be avoided.

[0012] Furthermore, in S3, determining the depth of pollution 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, the distance between each two adjacent depths is 20 cm, and 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.

[0013] 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 required for stripping, and the stripped contaminated soil is piled on the stripped low-step terraced fields.

[0014] Note: The above method is used to confirm the depth layer by layer to determine the depth that can be safely utilized. The screening value or control value refers to the "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard (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.

[0015] Furthermore, 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: ; In the formula, 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 managed, is the earthwork volume conversion coefficient, Reserve factor for the groove mouth.

[0016] Note: Through the above formula, the appropriate trench size can be calculated according to the amount of contaminated soil to ensure that the field remains flat after stripping. At the same time, the contaminated soil is buried reasonably under this design, reducing the risk of contaminants spreading in the soil.

[0017] Furthermore, the layer-by-layer filling method is: the stripped contaminated soil is buried and compacted into the trench in 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 dug out from the trench is buried in the trench in a layer of 10 cm until it is level with the top of the trench, and the remaining soil dug out of the trench is evenly spread on the stripped low-step terraced fields.

[0018] Note: Through the treatment method of filling and compacting layer by layer, the contaminated soil can be buried in a more concentrated manner, reducing the risk of diffusion of heavy metal pollutants.

[0019] Furthermore, in S4, the thickness of the trench excavated soil covering the trench is 40-60 cm.

[0020] Furthermore, the tillage depth is 18-25 cm, and the crop is corn; Note: The above thickness and tillage depth are more practical. Compared with local main crops such as wheat, soybeans and sesame, corn has a good low cadmium accumulation effect and can reduce the accumulation of cadmium in grains.

[0021] Furthermore, an isolation ditch with a width of 0.2-0.4 m and a depth equal to the depth of the ditch is dug out at a distance of 0.5-2 m from the edge of the ditch, and a filler is filled in the isolation ditch. The filler comprises 100 parts of quicklime and 100 parts of attapulgite by weight.

[0022] Description: The setting of isolation trenches can avoid the diffusion and migration of heavy metals in contaminated soil; by adjusting the raw materials and proportions in the filling material, the precipitation and adsorption properties of the composite filler can be improved, the heavy metal ions in the soil can be stabilized, and their migration and diffusion in the environment can be reduced.

[0023] Furthermore, it also includes installing a plurality of geocells (40cm×40cm×15cm) at the edge of the low-step terraced field blocks treated in S4, and planting plants such as tall fescue in each geocell, and then covering the geocell with non-woven fabric and watering it regularly for maintenance, wherein the geocell is a grid-like structure made of plastic.

[0024] Description: Geocells can effectively fix the soil and prevent soil loss caused by rain erosion. The roots of tall fescue plants can further strengthen the stability of the soil and reduce erosion. Geocells increase the shear strength of the soil through their grid structure and improve the overall stability of the slope. Covering with non-woven fabrics can reduce the impact of wind erosion on the slope soil, and can also keep the soil warm and moist, prevent water from evaporating too quickly, and promote plant rooting and germination.

[0025] The beneficial effects of the present invention are: The method of the present invention is to strip the seriously polluted arable layer soil and then landfill it, set up soil and groundwater environmental monitoring points in the landfill area, implement soil fertilization and other improvement measures on the newly formed surface soil to restore soil productivity and improve soil quality, and plant corn varieties with low cadmium accumulation to achieve safe reclamation of heavily polluted farmland. This method can significantly reduce the ecological risk of severe heavy metal compound pollution in saline-alkali farmland in sewage irrigation areas through multi-technical synergy, and ensure the sustainable use of polluted farmland. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a graph showing the distribution of the total amount of Cd in the contaminated soil in Example 2 of the present invention; Figure 2 is a data graph showing the change in Cd content in the contaminated soil before and after stripping in Example 2 of the present invention; Figure 3 This is a graph showing the total amount of Pb distribution in soil in Example 2 of the present invention; Figure 4 is a data graph showing the change in Pb content in the contaminated soil before and after stripping in Example 2 of the present invention; Figure 5 The distribution of total As in soil and its changes before and after stripping in Example 2 of the present invention; Figure 6 is a data graph showing the change in As content in the contaminated soil before and after stripping in Example 2 of the present invention; Figure 7The total Cu distribution in the soil and the changes before and after stripping in Example 2 of the present invention; Figure 8 is a data graph showing changes in Cu content in contaminated soil before and after stripping in Example 2 of the present invention; Fig. 9 It is the Cd content of corn kernels after conventional deep tillage and soil stripping in Example 2 of the present invention. DETAILED DESCRIPTION

[0027] To further illustrate the methods and effects of the present invention, a method for treating farmland with severe heavy metal compound pollution in arid wastewater irrigation areas provided by the present invention is described in detail below in conjunction with specific embodiments. Obviously, the present invention is not limited to the embodiments of the embodiments, and various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

[0028] From the above background technology, we know that heavy metals such as cadmium will be mainly adsorbed and precipitated by the cultivated layer (0-20cm) of the soil and stay in this layer for a long time after entering the alkaline soil, while its content in the deep layer (>20cm) is relatively low. Salt in the soil can increase the mobility and bioavailability of heavy metals, thereby significantly changing the environmental and health risks of heavy metal pollution in saline-alkali soil. Studies have shown that there is a complex interactive relationship between heavy metals such as Cd and salt ions, such as Na in the soil. + Isosalt ions can replace heavy metal ions adsorbed on the soil surface through displacement, thereby improving the mobility and bioavailability of heavy metals in the soil.

[0029] In summary, the complexity of saline-alkaline and severely heavy metal-compound polluted soil increases the difficulty of remediation and management. In the actual remediation and management process, it is necessary to comprehensively consider multiple methods such as soil improvement, phytoremediation and chemical remediation.

[0030] In order to reduce the degree of heavy metal compound pollution in saline-alkali soil and achieve safe crop production, the embodiment of the present invention provides a feasible method as follows: Embodiment 1: A method for treating farmland with severe salinity and heavy metal complex pollution in arid wastewater irrigation areas, comprising: S1. According to the degree of contamination of the polluted farmland, the fields that need to be treated are screened out on the polluted farmland; specifically, the fields that need to be treated are investigated for soil contamination status of the polluted farmland, and the fields with cadmium, lead, arsenic and copper content in the soil exceeding the screening value or control value are considered as the fields that need to be treated; S2, then group the plots to be managed, and group the plots in the same slope range into one group, where the same slope range means that the slope difference between the plots is between 0 and 10% (e.g., 5%); obtain multiple groups of plots, each of which includes a high-step terraced plot and a low-step terraced plot; the height difference between the high-step terraced plot and the low-step terraced plot in each of the multiple groups of plots is 2.0 m; S3, then determining the depth of the contaminated soil in the high-step terrace blocks and the low-step terrace blocks, and stripping the contaminated soil of the fields that need to be treated according to the depth of the contaminated soil, to obtain the stripped contaminated soil, the stripped high-step terrace blocks, and the stripped low-step terrace blocks; Determining the depth of contaminated soil in high- and low-level terraces involves: 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 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, the value of the nth depth is taken as the depth of the contaminated soil; The stripping method is as follows: for each 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 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; S4. The stripped high-level terraced fields are directly fertilized, plowed, and then crops are planted to complete the management; A trench is dug on the stripped low-step terrace block to obtain trench excavated soil, and the contaminated soil stripped by S3 is filled into the trench in a layer-by-layer filling manner and compacted, and then the trench excavated soil is covered on the trench and the stripped low-step terrace block to form a treated low-step terrace block; The distance between the position of the trench and the edge of the stripped low-step terraced field is 3.0 m; the relationship between the trench depth, trench excavation area, depth of contaminated soil, and area of ​​the field to be treated is as follows: ; In the formula, 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 managed, is the earthwork volume conversion coefficient, Reserve coefficient for the groove mouth; It refers to the ratio of the actual volume of soil after tamping to the original volume of soil, reflecting the compression characteristics and tamping effect of soil during the tamping process. It is related to factors such as soil type and soil moisture content (the value range is 0.67~1.0). In the embodiment of the present invention, Take 0.87; Related to the distribution of plant roots, its value needs to be greater than or equal to the depth of plant root distribution. For example, if the plant roots are distributed in 0.2m of soil, 0.4m is used to prevent the plant roots from growing into contaminated soil. The area of ​​the groove is satisfy ; a is the length of the field L-4 m, b is the width of the field M-4 m; The layer-by-layer filling method is: the stripped contaminated soil is buried and compacted into the trench layer by layer at a rate of 10 cm until the distance between the stripped contaminated soil and the top of the trench is 40-60 cm, and then the trench excavated soil is buried into the trench at a rate of 10 cm until it is level with the top of the trench, and the remaining trench excavated soil is evenly spread on the stripped low-step terraced fields; At 0.5m from the outer edge of the trench, dig an isolation trench with a width of 0.2m and a depth equal to the depth of the trench, and fill the isolation trench with anti-pollution diffusion filler, which includes 100 parts of quicklime and 100 parts of attapulgite by weight; The soil thickness of the trench dug out to fill the trench is 40 cm; the tillage depth is 20 cm, and the crop is corn; S5. Set up soil sampling points at 0.2m, 0.5m and 2.0m from the outside of the trench of the treated low-step terraced field block, and set up groundwater sampling wells at 0.5m, 3.0m and 30m from the outer edge of the treated low-step terraced field block, and 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 at 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 at 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 trench on the low-step terraced field block have not diffused, and the next step of treatment is carried out; Anti-diffusion measures include: managing irrigation volume to avoid excessive irrigation that causes pollutants to penetrate with water, or strengthening barriers, including replacing the filler of the isolation ditch or widening the isolation ditch; S6. Install multiple geocells (40 cm × 40 cm × 15 cm) on the edge of the treated low-step terraced fields, plant tall fescue and other plants in each geocell, then cover the geocell with non-woven fabric and water it regularly for maintenance, wherein the geocell is a grid-like structure made of plastic; S7. The treatment is completed by fertilizing and tilling the low-level terraced fields where no pollution has spread, and then planting crops.

[0031] Example 2: Illustrative, a method for treating farmland with severe saline-alkali and heavy metal compound pollution in arid wastewater irrigation areas, the specific operation method includes the following S1 to S7; S1. According to the degree of pollution of polluted farmland, select the fields that need to be treated on the polluted farmland; select the saline-alkali and heavy metal compound polluted farmland in the sewage irrigation area, and the selected fields have obvious steps; specifically, select the remediation and treatment test of the saline-alkali and heavy metal compound polluted soil in a certain place in a certain city; conduct a soil environmental quality survey in a certain area of ​​a certain city, and find that the total salt content of the farmland soil in the area reaches 3.29±0.21g / kg; the contents of total Cd, Pb, As and Cu in the surface 0-20cm soil of the area are 71.2±32.6mg / kg, 826±768mg / kg, 43.9±26.2mg / kg and 263±159mg / kg, respectively, which exceed the screening values ​​or control values ​​specified in the "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard" (GB15618-2018); S2. Then the plots to be managed are grouped, and the plots in the same slope range are grouped together to obtain multiple groups of plots. Each of the multiple groups of plots includes a high-step terrace plot and a low-step terrace plot. The height difference between the high-step terrace plot and the low-step terrace plot in each of the multiple groups of plots is more than 2.0m. Specifically, the high-step terrace plot and the low-step terrace plot were planted with crops such as corn, wheat or soybeans, with a total area of ​​about 900m. 2 , of which the high-level terraces are about 500m 2 The area of ​​low-level terraces is about 400m 2 ; Both fields are saline-alkaline soils with heavy metal complex contamination; the distribution of total soil Cd, Pb, As and Cu is as follows Figure 1 , Figure 3 , Figure 5 and Figure 7 As shown; the trial period is from September 2021 to October 2021; S3. Then determine the depth of contaminated soil in the high-step terrace blocks and the low-step terrace blocks, and according to the depth of the contaminated soil, strip the contaminated soil of the fields that need to be treated to obtain stripped contaminated soil, high-step terrace blocks after stripping, and low-step terrace blocks after stripping; specifically, in September 2021, use a soil drill to collect soil samples of 0-20cm, 20-40cm, and 40-60cm before stripping according to the grid point method, and then use a large loader to strip the contaminated soil of 0-40cm of the high and low-step terrace blocks layer by layer, and each round of soil stripping is 10cm thick, and a total of 4 rounds of stripping; S4. On the stripped low-step terraced field, a trench is dug by an excavator 2.0 m away from the edge of the low-step terraced field, and the soil excavated from the trench is separated from the contaminated soil stripped from the surface and piled up; the stripped contaminated soil is then backfilled into the trench and compacted layer by layer, and the soil excavated from the trench is buried layer by layer after reaching 40 cm from the trench mouth, and compacted layer by layer until it is level with the trench mouth, and the burial is stopped, and the remaining trench excavated soil is evenly spread on the surface of the low-step terraced field. The burial and leveling process is performed by using a leveler and a grader to ensure that the plot is flat; S5. Set up soil sampling points at 0.2m, 0.5m and 2.0m from the outside of the trench of the treated low-step terraced field block, and set up groundwater sampling wells at 0.5m, 3.0m and 30m from the outer edge of the treated low-step terraced field block, and 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 at 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 at 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 trench on the low-step terraced field block have not diffused, and the next step of treatment is carried out; Exemplarily, the soil in the soil sampling points and the groundwater in the groundwater sampling wells are sampled and monitored every 2 months; further, relevant samples are collected every 2 months from the atmospheric particulate matter set-up set-up in the field and the irrigation canal outlet; in addition, soil side seepage water collection devices are arranged outside the ridges of the low-step terraced fields after the landfill of contaminated soil, and no water samples seeping from the fields are observed during irrigation and when there is a large surface runoff; The changes in the total amount of Cd, Pb, As and Cu content in the surface soil (0-20cm) before and after stripping are as follows Figure 2 , Figure 4 , Figure 6 and Figure 8As shown in the figure, compared with before stripping, the contents of total Cd, Pb, As and Cu decreased by 95.6%, 84.7%, 51.2% and 71.1%, respectively; the results show that in the study area, after stripping of saline-alkali severely heavy metal compound polluted farmland, the heavy metal pollution level in the newly generated surface soil was significantly reduced, that is, the newly generated arable layer has the conditions for conducting safe utilization research; in addition, the arable layer soil generated after stripping is maintained according to field management specifications, including taking measures such as weed cleaning and winter irrigation to optimize soil environmental conditions and provide guarantees for crop planting in the second year; S6. Install multiple geocells (40 cm × 40 cm × 15 cm) on the edge of the treated low-step terraced fields, plant tall fescue and other plants in each geocell, then cover the geocell with non-woven fabric and water it regularly for maintenance, wherein the geocell is a grid-like structure made of plastic; S7. Fertilize and till the fields where no pollution has spread, and then plant crops to complete the treatment; Specifically, organic materials made from agricultural and forestry wastes are rich in organic matter, which can improve, cultivate and enhance soil quality and promote crop growth. In the process of soil stripping, in order to reduce the concentration of heavy metals in the cultivated layer soil, the original cultivated layer soil is stripped and landfilled, while the newly generated cultivated layer soil is relatively poor. Therefore, the application of a large amount of organic materials can effectively improve soil quality and improve the growth environment of crops. After the planting season begins, organic materials are spread on the stripped fields (which have been winter-irrigated). After plowing, the organic materials can be fully mixed with the new tillage layer soil to build and cultivate a good new soil body and improve the fertility and productivity of the reconstructed tillage layer soil; the N:P:K content of organic materials is 5.45±0.26g / kg, 1.97±0.07g / kg and 18.75±0.92g / kg respectively, and the organic matter content is 75.5±2.3g / kg; the application rate of organic materials is 6T / mu, and it is planned to be applied continuously for three years; Preferably, the corn variety Jinyuan 007 with drought tolerance, high yield, strong lodging resistance and low cadmium absorption is selected for planting; base fertilizer (compound fertilizer: N-P2O5-KO215-15-15) is applied before planting, and the amount is 40kg / mu; when the corn has 10-12 leaves, diammonium phosphate (2 parts) and urea mixture (1 part) are applied, and the fertilization method is hole application and soil covering, and the amount after mixing is 30kg / mu; before 10 am or after 4 pm on a windless and rainless day, 55% mesotrione·atrazine herbicide is selected and diluted 150 times for spraying when the corn has 3-5 leaves, and the amount is 200g / mu; the previous year After winter irrigation, harrowing and hoeing to conserve moisture can meet the water demand of corn seedlings. Subsequently, irrigation was carried out after 10-12 leaves were fertilized, jointing and booting, heading and flowering, and maturity. After corn matured, the stalks and grains were harvested, washed, dried, ground, and digested. The Cd content in the digested solution was determined by ICP-MS. The data obtained from the experimental treatments were analyzed using Excel 2013 and SPSS 16.0 software. The differences between the data of different treatments were analyzed by multiple comparisons using variance analysis (LSD). The changes in Cd content in corn grains planted after conventional deep tillage and land stripping are shown in Figure 2. Fig. 9 As shown, after land stripping measures, the cadmium content in the newly formed tillage layer was significantly reduced, which in turn reduced the cadmium content in corn grains.

[0032] Example 3: The difference from Example 2 is that the height difference between the high-step terraced fields and the low-step terraced fields in each group of multiple groups of fields is 1.0m; an isolation ditch with a width of 0.2m is dug 0.5m away from the edge of the ditch, and the isolation ditch is filled with filler; S4 is filled and compacted into the ditch layer by layer until the distance between the stripped soil and the upper end of the ditch is 40cm; the thickness of the excavated soil covering the ditch in S4 is 40cm; the tillage depth is 18cm, and the crop is corn.

[0033] Example 4: The difference from Example 2 is that the height difference between the high-step terraced fields and the low-step terraced fields in each group of multiple groups of fields is 3.0m; an isolation ditch with a width of 0.4m is dug 2m away from the edge of the ditch, and the filler is filled in the isolation ditch; in S4, the soil is filled layer by layer and compacted into the ditch until the distance between the stripped soil and the top edge of the ditch is 60cm; in S4, the thickness of the excavated soil covering the ditch is 60cm, the plowing depth is 25cm, 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 pollution spread 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 salinity 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: ; In the formula, 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 managed, is the earthwork volume conversion coefficient, Reserve factor for the groove mouth.

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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