An interplanting cultivation method for reducing accumulation of lead in wheat by using enrichment plant companion

Abstract

The application relates to the field of agricultural environment remediation and crop safety production technology, and discloses a strip interplanting method for reducing accumulation of lead in wheat by using enrichment plant companionship, which constructs a gradient strip space layout of grain amaranth outside, wheat in the middle and winged burweed inside, combines deep-rooted and shallow-rooted three-dimensional matching of the winged burweed and the grain amaranth, captures and efficiently extracts the whole profile of lead in the 0-40cm plough layer of the wheat planting land, forms a lead trap in the rhizosphere by the oxalic acid and the histidine secreted by the winged burweed root system, and efficiently chelates and fixes the soil lead; the grain amaranth competes for the shallow layer lead through the fibrous root network, and takes away the absorbed lead through multiple cutting cycles, the spatial niche differentiation of the deep root and the shallow root can effectively avoid the root competition between the two enrichment plants, so that the synergistic extraction effect is realized, and the problems of intense interspecific competition, obvious allelopathic inhibition, poor lead blocking and controlling effect and prominent crop yield reduction in the existing interplanting remediation mode are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of agricultural environmental remediation and crop safety production technology, specifically to an intercropping cultivation method that utilizes enriching plants to reduce lead accumulation in wheat. Background Technology

[0002] Lead (Pb) is one of the most harmful heavy metal pollutants in farmland soil, characterized by its insidious nature, persistence, and bioaccumulation. Wheat, as a major staple food crop, has a strong capacity for absorbing and translocating lead. Lead in the soil is absorbed through the root system, transported through the xylem, and ultimately enters the grain, posing a potential threat to human health.

[0003] Currently, remediation technologies for lead-contaminated farmland mainly include physical remediation (topsoil replacement, deep tillage), chemical remediation (application of passivating agents), and bioremediation (phytoremediation). Among these, phytoremediation technology has received widespread attention due to its low cost and environmental friendliness. However, traditional phytoremediation often requires occupying an entire plot of land to plant enriching plants, resulting in the inability to conduct agricultural production during the remediation period, creating a contradiction of "remediation competing with production for land." Although intercropping remediation models have achieved remediation while maintaining production to some extent, the following technical bottlenecks still exist: First, there is generally fierce competition for water, nutrients, and light between enriching plants and crops, leading to crop yield reduction; second, root exudates of enriching plants may have allelopathic inhibitory effects on crops; third, it is difficult for a single enriching plant to achieve full profile capture of lead in the topsoil; and fourth, there is a lack of dynamic regulation mechanisms covering the entire growth period of crops, making it difficult to effectively block the translocation of lead to grains during critical growth windows.

[0004] Therefore, developing an intercropping method that can both effectively reduce lead accumulation in wheat and ensure stable wheat yield is of great practical significance. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] To address the shortcomings of existing technologies, this invention provides an intercropping method that utilizes enriching plants to reduce lead accumulation in wheat. This method has the advantages of high remediation efficiency, wheat grain lead content meeting standards, stable yield, and mechanization, effectively solving the problems of intense interspecific competition, significant allelopathic inhibition, poor lead control, and significant crop yield reduction in existing intercropping remediation models.

[0007] (II) Technical Solution

[0008] To achieve the above objectives, the present invention provides the following technical solution: an intercropping cultivation method for reducing lead accumulation in wheat by using enriching plants as companion plants, comprising the following steps:

[0009] Step 1: Land pretreatment: Deep plowing, fertilization, passivation and soil conditioning of the planting fields;

[0010] Step 2: Screening of associated enriching plants: Bidens pilosa and Amaranthus chinensis were selected as lead-specific enriching plant combinations.

[0011] Step 3, Planting Layout Design: Adopt a strip-shaped spatial tiered intercropping pattern with the inner side of Bidens pilosa, the middle of wheat, and the outer side of amaranth to achieve an orderly arrangement of planting from short to tall.

[0012] Step 4, Sowing Period Management: Grain amaranth, beggar-ticks and wheat are sown in a staggered manner to achieve ecological niche synergy;

[0013] Step 5: Coordinated Management During Intercropping Growth: Establish a coordinated management mechanism for water and fertilizer regulation and interspecific competition mitigation to achieve efficient extraction of Bidens pilosa and Amaranth arvense and normal wheat growth;

[0014] Step Six: Dynamic Management Throughout the Entire Growth Period: Establish a dynamic management mechanism covering the entire growth period of wheat, and implement phased regulation to achieve both control and yield assurance;

[0015] Step 7, Harvesting and Post-harvest Processing: After wheat harvest, remove the Bidens pilosa and Amaranth chinensis and dispose of them safely.

[0016] Step 8, Crop Rotation: Repeat steps 1 to 8 before planting the next season's crop.

[0017] Preferably, the land pretreatment process in step one is as follows:

[0018] S1.1 Pretreatment time: Land pretreatment should be carried out 28-35 days after the previous crop is harvested and before sowing, avoiding rainy weather, and when the soil moisture content is 60%-70%.

[0019] S1.2 Autumn deep plowing: First carry out autumn deep plowing, with a plowing depth of 28-32 cm, and then let it dry for 4-6 days after deep plowing;

[0020] S1.3, Base fertilizer application: Combine deep plowing with the application of base fertilizer, apply 2500-2800 kg of decomposed organic manure, 13-15 kg of controlled-release nitrogen fertilizer and 5-6 kg of phosphate fertilizer per mu; after spreading the fertilizer evenly on the surface, plow it into the soil layer of 20-25 cm through deep plowing.

[0021] S1.4 Application of rhizosphere growth-promoting bacteria: At the same time, apply 2.5-3.5 kg / mu of lead-resistant rhizosphere growth-promoting bacteria agent, mix it with the base fertilizer and then spread it.

[0022] S1.5 Initial harrowing and compaction: After deep plowing and fertilization, harrow the land 1-2 times with a disc harrow, and then compact it 1-2 times with a roller to make the tillage layer flat and fine.

[0023] S1.6 Application of passivating material: After the initial harrowing and compaction, apply lead passivating material evenly to the field. The passivating material is Mg-Al hydrotalcite that has been thermally activated at 600-650℃, and the application rate is 100-150 kg / mu.

[0024] S1.7 Rotary Tillage and Mixing: After the passivation material is spread, use a rotary tiller to perform 1-2 passes of rotary tillage to a depth of 14-20 cm to ensure that the passivation material is fully mixed with the topsoil.

[0025] Preferably, in step two, the associated enrichment plants are screened as follows: Bidens pilosa and Amaranthus chinensis are selected as a combination of lead-specific enrichment plants; Bidens pilosa is a taproot type that extracts lead from deep soil; Amaranthus chinensis is a fibrous root type that competes for lead in shallow soil and removes lead through multiple harvests during the growing season.

[0026] Preferably, in step three, the planting layout is designed as a tiered strip intercropping pattern based on the height differences of amaranth (the tallest), wheat (medium-sized), and Bidens pilosa (the shortest), specifically as follows:

[0027] S2.1, Repeating Unit Division: The wheat planting area is divided into planting units with a total width of 3.2-3.5 meters. Each repeating unit serves as the basic structural unit for intercropping.

[0028] S2.2 Planting strip arrangement within the unit: Each repeating unit consists of the following strips from the outside to the inside: 2 rows of amaranth, 6 rows of wheat, and 2 rows of beggar-ticks, forming a three-dimensional structure of tall, medium, and short plants.

[0029] Preferably, the planting layout design in step three is as follows: the row spacing within the amaranth strip is 28-30 cm; the distance between the amaranth strip and the wheat strip is 50-60 cm; the row spacing within the wheat strip is 18-22 cm; the distance between the wheat strip and the Bidens pilosa strip is 28-30 cm; and the row spacing within the Bidens pilosa strip is 25-30 cm.

[0030] Preferably, in step four, amaranth, beggar-ticks, and wheat are sown in sequence, specifically as follows:

[0031] S3.1 First, sow amaranth seeds at a depth of 1.5-2.5 cm. After sowing, compact the soil and wait for the soil temperature to stabilize at 16-18℃ before sowing.

[0032] S3.2, then sow Bidens pilosa at a depth of 2.5-3.5 cm, 2-4 days after planting Amaranth.

[0033] S3.3 Finally, sow wheat 7-8 days after the emergence of amaranth and beggar-ticks, at a depth of 3.5-4.5 cm.

[0034] Preferably, during step five, collaborative management during the growth period is implemented:

[0035] (1) Water tiered regulation: When irrigating Bidens pilosa and Amaranth, furrow irrigation or drip irrigation is used, with a single irrigation volume of 35-40 m³ / mu, to induce the roots to extend into the deeper soil to extract deep lead; wheat is irrigated by sprinkler or micro-sprinkler, with a single irrigation volume of 15-18 m³ / mu, to keep the 0-22cm topsoil layer moist.

[0036] (2) Targeted nutrient distribution: No separate topdressing is required for Bidens pilosa and Amaranthus chinensis during the seedling stage; 8.5-9.5 kg / mu of NPK compound fertilizer is applied to wheat during the jointing stage, with the topdressing position 12-16 cm away from the wheat row and ≥20 cm away from the Bidens pilosa strip.

[0037] (3) Allelopathic substance blocking: Spray Bidens pilosa with a potassium humate solution of 0.15%-0.20% every 20-25 days, with an application rate of 48-55 L / mu;

[0038] (4) Monitoring of interspecific competition: During the jointing and booting stages of wheat, a portable chlorophyll meter was used to monitor the chlorophyll content of wheat leaves. When the chlorophyll content was below 35 or the wheat plant height was reduced by more than 15% compared with the monoculture control, the top 10-15cm growing point of the grain amaranth was removed immediately. The formal harvesting described in step six was carried out before the wheat entered the grain filling stage.

[0039] Preferably, step six involves dynamic management throughout the entire reproductive period:

[0040] (1) Seedling stage - jointing stage: Maintain soil field water holding capacity at 60%-70% to promote the deep root development of plants;

[0041] (2) Jointing-booting stage: Bidens pilosa and Amaranth enter the vigorous growth period and extract available lead from the soil at a high intensity. During this period, nitrogen fertilizer should not be applied.

[0042] (3) Grain-filling period: Before the wheat grain-filling period, the amaranth should be cut for the first time, leaving a stubble height of 18-20 cm; after cutting, apply urea at a rate of 25-30 kg / mu in time;

[0043] (4) Maturity period: After the wheat matures, it is mechanically harvested. The harvester travels along the 50-60 cm channel between the amaranth belt and the wheat belt to perform a second harvest of the amaranth or save it for seed.

[0044] Preferably, the harvesting and post-processing in step seven are as follows:

[0045] S4.1 After the wheat harvest, the above-ground parts of the Bidens pilosa should be cut off whole and transported away from the farmland together with the cut amaranth.

[0046] S4.2. After mowing, the enriched plants shall be reduced in volume by incineration. The incineration temperature shall be controlled at 500-600℃. When the lead content in the incineration ash reaches the enrichment standard, it shall be handed over to a qualified hazardous waste disposal unit for treatment or used to extract valuable metals. It is prohibited to return it to the field as organic fertilizer.

[0047] Preferably, in step eight, after the harvest of the current season's crops and the removal of enriching plants, the land pretreatment operation of step one is repeated before the next season's planting. The amount of passivation material applied can be adjusted according to the measured changes in soil lead content. When the soil lead content drops below the safety standard after three consecutive seasons of planting, the intercropping remediation mode is suspended, and conventional planting is switched to regular monitoring.

[0048] Compared with existing technologies, this invention provides an intercropping cultivation method that utilizes enrichment plants to reduce lead accumulation in wheat, which has the following beneficial effects:

[0049] 1. This invention constructs a tiered, strip-like spatial layout with the outer side of amaranth, the middle of wheat, and the inner side of Bidens pilosa. Combined with the deep-shallow root three-dimensional pairing of Bidens pilosa and amaranth, it achieves the beneficial effect of capturing and efficiently extracting lead from the entire profile of the 0-40cm cultivated layer in wheat planting areas. The oxalic acid and histidine secreted by the roots of Bidens pilosa form lead traps in the rhizosphere, enabling efficient chelation and fixation of lead in the soil. Amaranth competes for shallow lead through its fibrous root network and removes the absorbed lead through multiple harvesting cycles. The spatial niche differentiation between its deep and shallow roots effectively avoids root competition between the two enrichment plants, thereby achieving a synergistic extraction effect of "1+1>2".

[0050] 2. This invention establishes a four-pronged synergistic management mechanism, namely, water cascade regulation, nutrient directional distribution, allelopathic substance blocking (regular spraying of 0.15%-0.20% potassium humate solution), and interspecific competition dynamic monitoring (light mowing of amaranth when SPAD value is <35 or plant height decreases by >15%), to alleviate interspecific competition and ensure normal wheat growth and yield.

[0051] 3. This invention achieves the beneficial effect of continuous purification and cost-controllable remediation of lead-contaminated soil by first harvesting amaranth during the grain-filling stage and applying urea to promote regeneration, harvesting the entire plant of Bidens pilosa after wheat maturity and burning it, and combining this with a dynamic rotation mechanism that suspends remediation and switches to conventional planting when the soil lead content drops below the safety standard after 2-3 consecutive seasons of crop rotation and intercropping. Attached Figure Description

[0052] Figure 1 This is a flowchart illustrating the cultivation process of the method of this invention. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] Please see Figure 1 A method for intercropping to reduce lead accumulation in wheat by using enriching plants as companion plants includes the following steps:

[0055] Step 1: Land pretreatment: Deep plowing, fertilization, passivation and soil conditioning of the planting fields;

[0056] Step 2: Screening of associated enriching plants: Bidens pilosa and Amaranthus chinensis were selected as lead-specific enriching plant combinations.

[0057] Step 3, Planting Layout Design: Adopt a strip-shaped spatial tiered intercropping pattern with the inner side of Bidens pilosa, the middle of wheat, and the outer side of amaranth to achieve an orderly arrangement of planting from short to tall.

[0058] Step 4, Sowing Period Management: Grain amaranth, beggar-ticks and wheat are sown in a staggered manner to achieve ecological niche synergy;

[0059] Step 5: Coordinated Management During Intercropping Growth: Establish a coordinated management mechanism for water and fertilizer regulation and interspecific competition mitigation to ensure the achievement of the dual goals of efficient extraction by Bidens pilosa and Amaranth arvense and normal wheat growth;

[0060] Step Six: Dynamic Management Throughout the Entire Growth Period: Establish a dynamic management mechanism covering the entire growth period of wheat, and implement phased regulation to achieve both control and yield assurance;

[0061] Step 7, Harvesting and Post-harvest Processing: After wheat harvest, remove the Bidens pilosa and Amaranth chinensis and dispose of them safely.

[0062] Step 8, Crop Rotation: Repeat steps 1 to 8 before planting the next season's crop;

[0063] The advantages are: utilizing the specific chelating agents (including oxalic acid and histidine) secreted by the roots of Bidens pilosa in step three, lead in the soil is efficiently chelated and fixed in its own rhizosphere, forming a "lead trap"; combined with the 30 cm spacing between wheat and Bidens pilosa in step four, this chelation effect is ensured to prevent migration to the wheat rhizosphere; at the same time, the lead-resistant rhizosphere growth-promoting bacteria applied in step one are induced by the root secretions of enriched plants in the intercropping mode, and colonize in large quantities in the wheat rhizosphere, transforming lead from the exchangeable and carbonate-bound state to the residual state, thus reducing the bioavailability of lead in both directions.

[0064] Specifically, the land pretreatment process in step one:

[0065] S1.1 Pretreatment time: Land pretreatment should be carried out 28-35 days after the previous crop is harvested and before sowing, avoiding rainy weather, and when the soil moisture is suitable (field water holding capacity 60%-70%).

[0066] S1.2 Autumn deep plowing: First, carry out autumn deep plowing, with a plowing depth of 28-32 cm, to break up the plow pan, loosen the soil, and promote root growth. After deep plowing, let it dry for 4-6 days to kill some soil-borne pathogens by using sunlight and natural air drying.

[0067] S1.3, Base fertilizer application: Combine deep plowing with the application of base fertilizer. Apply 2500-2800 kg of well-rotted organic manure, 13-15 kg of controlled-release nitrogen fertilizer (calculated as pure nitrogen) and 5-6 kg of phosphate fertilizer (calculated as P2O5) per mu. After spreading the fertilizer evenly on the surface, plow it into the soil layer to a depth of 20-25 cm to achieve full-layer fertilization.

[0068] S1.4 Application of rhizosphere growth-promoting bacteria: At the same time, apply 2.5-3.5 kg / mu of lead-resistant rhizosphere growth-promoting bacteria (PGPR) inoculant, mix it with the base fertilizer and then spread it to ensure that the inoculant is evenly distributed in the soil.

[0069] S1.5 Initial harrowing and compaction: After deep plowing and fertilization, harrow the land 1-2 times with a disc harrow to break up and level the soil clods. Then use a compactor to compact the soil 1-2 times to make the cultivated layer flat and fine, with soil particles controlled to be less than 5 cm in size, creating good conditions for subsequent application of passivation materials and sowing.

[0070] S1.6 Application of passivating material: After the initial harrowing and compaction, apply lead passivating material evenly to the field. The passivating material is Mg-Al hydrotalcite that has been thermally activated at 600-650℃. The application rate is 100-150 kg / mu, ensuring that the material is evenly distributed on the field surface.

[0071] S1.7 Rotary Tillage and Mixing: After the passivation material is applied, use a rotary tiller to perform 1-2 passes, with a tillage depth of 14-20 cm, to ensure that the passivation material is thoroughly mixed with the topsoil. The tillage direction should be perpendicular to the deep tillage direction to enhance the mixing effect. This passivation material, through electrostatic attraction, precipitation, and complexation, converts exchangeable and carbonate-bound lead in the soil into residual lead, reducing the bioavailability of lead. After rotary tillage and mixing, allow the soil to stand for 7-10 days, maintaining the soil field water holding capacity between 60%-80% (i.e., the soil can be clumpted when squeezed but crumbles when dropped), allowing the passivation material to fully react and stabilize with the soil, forming a stable lead-passivation material complex. In case of drought, water will be sprayed appropriately to replenish moisture, but excessive irrigation should be avoided to prevent material loss. During the standing period, avoid mechanical compaction to maintain the stability of the surface structure.

[0072] The above steps S1.1 to S1.7 are implemented in sequence to form a complete land pretreatment operation process. This step, through seven processes of deep plowing, fertilization, inoculant application, harrowing, passivation, and rotary mixing, achieves synergistic treatment of soil physical structure improvement, nutrient supplementation, microbial enhancement, and lead chemical passivation, laying a good soil foundation for subsequent intercropping.

[0073] Specifically, in step two, the screening of associated enriching plants involves selecting *Bidens pilosa* and *Amaranthus chinensis* as a combination of lead-specific enriching plants. *Bidens pilosa* is a lead hyperaccumulator with a plant height of 15-70 cm, while *Amaranthus chinensis* is a high-biomass lead-accumulator with a plant height of 250-350 cm. Both plants exhibit specific hyperaccumulation or high accumulation capacity for lead. *Bidens pilosa* has a deep taproot and is used to extract lead from deep soil layers. *Amaranthus chinensis* has well-developed fibrous roots and competes for lead in shallow soil layers, removing lead through multiple harvests during the growing season. Through this three-dimensional associated system combining deep and shallow roots, lead in the 0-40 cm tillage layer of wheat-grown farmland can be captured across the entire profile.

[0074] Specifically, in step three, the planting layout design considers the differences in plant height among the three plants (amaranth is the tallest, wheat is in the middle, and beggar-ticks is the shortest), and designs a tiered strip intercropping pattern, specifically as follows:

[0075] S2.1, Division of Repeating Units: Divide the wheat planting area into several repeating units, with each repeating unit serving as the basic structural unit for intercropping.

[0076] S2.2 Planting strip arrangement within the unit: Each repeating unit consists of the following strips from the outside to the inside: 2 rows of amaranth, 6 rows of wheat, and 2 rows of beggar-ticks. The total width of the unit is 3.2-3.5 meters, forming a three-dimensional structure of high, medium, and low plants.

[0077] Specifically, in step three, the planting layout design is as follows: the row spacing within the amaranth strip is 28-30 cm; the distance between the amaranth strip and the wheat strip is 50-60 cm (to reserve a passage for mechanized harvesting); the row spacing within the wheat strip is 18-22 cm; the distance between the wheat strip and the Bidens pilosa strip is 28-30 cm; and the row spacing within the Bidens pilosa strip is 25-30 cm.

[0078] The advantages are: the 50-60 cm wide spacing isolates the tall amaranth from the wheat, preventing the amaranth from shading the wheat and affecting its photosynthesis; at the same time, this width can accommodate the tires of small harvesters, enabling mechanized harvesting; since the plant height of Bidens pilosa is lower than that of wheat, planting it on the inside will not affect the wheat harvesting operation; by using 6 rows of wheat, 2 rows of amaranth, and 2 rows of Bidens pilosa as a repeating unit, the total width of the unit is 3.2-3.5 meters, which can be adapted to the header width of existing wheat combine harvesters.

[0079] Specifically, in step four, amaranth, beggar-ticks, and wheat are sown in sequence, as follows:

[0080] S3.1 First, sow amaranth (tall stalks) at a depth of 1.5-2.5 cm. After sowing, compact the soil and wait for the soil temperature to stabilize at 16-18℃ before sowing (spring sowing in northern regions is from early April to mid-May).

[0081] S3.2, then sow Bidens pilosa (dwarf stalk) at a depth of 2.5-3.5 cm, 2-4 days after planting Amaranth.

[0082] S3.3 Finally, sow wheat (medium stalks), 7-8 days after the emergence of grain amaranth and feathery beggar-ticks, at a sowing depth of 3.5-4.5 cm;

[0083] The advantages are: by staggering the sowing of amaranth, beggar-ticks and wheat, the roots of dwarf beggar-ticks occupy the inner rhizosphere ecological niche first, while tall amaranth forms a physical barrier on the outside, allowing wheat to obtain the best light conditions.

[0084] Specifically, during step five, collaborative management during the growth period is implemented:

[0085] (1) Water tiered regulation: Establish a differentiated irrigation system of deep irrigation for enriching plants and shallow irrigation for wheat. Since the roots of Bidens pilosa and Amaranth are deeply rooted, furrow irrigation or drip irrigation is used during irrigation, with a single irrigation volume of 35-40 m³ / mu, to induce the roots to extend into the deep soil to extract deep lead; for wheat, sprinkler irrigation or micro-sprinkler irrigation is used, with a single irrigation volume of 15-18 m³ / mu, to keep the 0-22cm topsoil layer moist, so as to avoid water infiltration and lead migration to the wheat rhizosphere;

[0086] (2) Targeted allocation of nutrients: Implement a fertilization strategy that controls nitrogen and promotes root growth in enriching plants and stabilizes nitrogen and ensures wheat yield. The base fertilizer applied in step one at sowing meets 80% of the phosphorus and potassium requirements of wheat throughout its growth period. No separate topdressing is applied to Bidens pilosa and Amaranth during the seedling stage. Instead, the soil's insoluble nutrients are activated by the synergistic effect of their root exudates and rhizosphere growth-promoting bacteria. At the wheat jointing stage, apply 8.5-9.5 kg / mu of N-P2O5-K2O=15-15-15 compound fertilizer (N-P2O5-K2O=15-15-15). The topdressing position should be 12-16 cm away from the wheat row and ≥20 cm away from the Bidens pilosa strip to ensure that nutrients are preferentially supplied to wheat and are not intercepted by enriching plants.

[0087] (3) Allelopathic substance blocking: Oxalic acid and histidine secreted by the roots of Bidens pilosa can effectively chelate lead and produce allelopathic effects. Spray a 0.15%-0.20% potassium humate solution every 20-25 days at a rate of 48-55 L / mu. Potassium humate can alleviate allelopathic inhibition and enhance the fixation effect of lead as a small molecule organic acid.

[0088] (4) Monitoring of interspecific competition: During the jointing and booting stages of wheat, a portable chlorophyll meter (SPAD) was used to monitor the chlorophyll content of wheat leaves. When the chlorophyll content was below 35 or the wheat plant height was reduced by more than 15% compared with the monoculture control, the amaranth was lightly cut immediately to remove the top 10-15cm growing point to temporarily reduce its competitive advantage. The formal cutting described in step six was carried out before the wheat entered the grain filling stage.

[0089] The advantages are: ① By regulating water levels in stages (deep irrigation of 35-40 m³ / mu for enriching plants and shallow irrigation of 15-18 m³ / mu for wheat), root niche differentiation is achieved, preventing the migration of available lead carried by irrigation water to the wheat rhizosphere; ② The nutrient-directed allocation strategy enables enriching plants to activate soil nutrients through their own root exudates, reducing nitrogen competition with wheat, and the precise control of topdressing position during the wheat jointing stage (12-16 cm from the wheat row and ≥20 cm from the enriching plant zone) ensures that fertilizer is preferentially supplied to wheat; ③ Regular spraying of potassium humate solution (0.15%-0.20%, 48-55 L / mu) can alleviate the allelopathic inhibition of wheat by Bidens pilosa root exudates and synergistically enhance the chelation and fixation effect of lead; ④ Establishing a dynamic monitoring mechanism for interspecific competition (lightly mowing amaranth when SPAD value <35 or plant height decrease >15%) enables real-time regulation of competitive potential, preventing enriching plants from excessively suppressing wheat growth.

[0090] Specifically, step six involves dynamic management throughout the entire reproductive period:

[0091] (1) Seedling stage - jointing stage: Maintain soil field water holding capacity at 60%-70% to promote the deep root development of plants;

[0092] (2) Jointing-booting stage (critical window period for lead to grain transfer): Bidens pilosa and Amaranth enter a vigorous growth period and extract available lead from the soil at a high intensity. During this period, nitrogen fertilizer should not be applied to avoid excessive growth of the plant.

[0093] (3) Grain-filling period (cut off lead source): Before wheat grain filling, the grain amaranth is cut for the first time, leaving a stubble height of 18-20 cm; after cutting, apply urea at 25-30 kg / mu in time to promote grain amaranth regeneration; this operation removes the absorbed lead on the one hand, preventing the decomposition of plant aging and release of lead into the soil, and on the other hand, reduces the competition for water and nutrients between tall grain amaranth and wheat during the grain filling period and the shading effect.

[0094] (4) Maturity period: After the wheat matures, it is mechanically harvested. The harvester travels along a 50-60 cm channel between the amaranth belt and the wheat belt to avoid crushing the enriched plants; the amaranth is harvested a second time or saved for seed.

[0095] Specifically, in step seven, harvesting and post-processing:

[0096] S4.1 After the wheat harvest, the above-ground parts of the Bidens pilosa should be cut off whole and transported away from the farmland together with the cut amaranth.

[0097] S4.2. After the harvesting of enriched plants, the volume reduction treatment shall be carried out by incineration. The incineration temperature shall be controlled at 500-600℃. When the lead content in the incineration ash reaches the enrichment standard, it shall be handed over to a qualified hazardous waste disposal unit for treatment or used to extract valuable metals. It is prohibited to return it to the field as organic fertilizer.

[0098] Through continuous cropping and intercropping for 2-3 seasons, the total lead content in the soil can be reduced by 2%-5% and the available lead content by 10%-15% per season, thus achieving continuous soil purification.

[0099] Specifically, in step eight, after the harvest of this season's crops and the removal of enriching plants, the land pretreatment operation of step one is repeated before the next season's planting. The amount of passivation material applied can be adjusted appropriately according to the measured changes in soil lead content. When the soil lead content drops below the safety standard after three consecutive seasons of planting, the intercropping remediation mode is suspended, and regular planting is switched to regular monitoring.

[0100] The advantages are: ① Through continuous 2-3 seasons of crop rotation and intercropping, the average annual reduction of total soil lead by 2%-5% and available lead by 10%-15% can be achieved. The amount of passivating material applied can be dynamically adjusted according to the soil lead content (initially 100-150 kg / mu, which can be reduced to 50-80 kg / mu later), avoiding excessive application; ② When the soil lead content drops below the safety standard (such as the screening value under the corresponding pH conditions in GB 15618-2018), the intercropping remediation mode should be suspended in time and replaced with conventional planting to avoid excessive remediation and cost waste; ③ The regular monitoring mechanism (it is recommended to test the available lead content in the soil every six months) provides a basis for decision-making on whether remediation needs to be restarted, achieving a dynamic balance between remediation and production.

[0101] The method of the present invention was applied to the following embodiments, and conventional planting was carried out on the same land in a comparative proportion, as follows:

[0102] Implementation Examples and Comparative Designs

[0103] Example 1 (slightly polluted field, total lead 120mg / kg): According to the method of the present invention, the lead carried out by Bidens pilosa in a single season was 1.86kg / mu, the lead carried out by amaranth in three harvests was 2.34kg / mu in total, the lead content of wheat grains was 0.048mg / kg (compliant with GB 2762-2017 standard), and the yield was 482kg / mu.

[0104] Example 2 (moderately polluted field, total lead 280 mg / kg): With the passivation material increased to 150 kg / mu, under the combined remediation of Bidens pilosa and Amaranth, the annual decrease in available lead in the soil was 17.3%, the lead content in wheat grains was 0.079 mg / kg, and the yield was 455 kg / mu.

[0105] Comparative Example 1 (conventional monoculture wheat): Grain lead content was 0.152 mg / kg (exceeding the standard), yield was 430 kg / mu, and the annual increase in total soil lead was 1.2%.

[0106] Comparative Example 2 (wheat + Sedum sarmentosum monoculture): Sedum sarmentosum has a lead enrichment coefficient of only 2.1, grain lead content of 0.105 mg / kg, and yield of 415 kg / mu.

[0107] Comparative Example 3 (Wheat + Alfalfa Intercropping): Alfalfa did not specifically accumulate lead, the lead content in the grain was 0.138 mg / kg, and the yield was reduced by 12.6% due to nutrient competition.

[0108]

[0109] Note: GB 2762-2017 stipulates that the lead limit for grains is 0.2 mg / kg, and "*" indicates that it is close to the critical value.

[0110] Table 1 shows that the present invention, through a three-dimensional system of spatial tiered layout, time-staggered sowing, and physiological synergistic regulation, can overcome the contradiction between traditional intercropping restoration and production. Compared with a single enrichment plant model, the method of the present invention can reduce the lead trans-interface migration flux by 67%-79%, and increase the marginal effect compensation rate of wheat to 112%, ultimately achieving the goal of simultaneous production and restoration without yield reduction. Moreover, after three consecutive years of application, the bioavailability of lead in the soil has decreased to less than 1 / 3 of the original soil, providing an feasible solution for the safe utilization of farmland with moderate to light heavy metal pollution.

[0111] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for intercropping to reduce lead accumulation in wheat by using enriching plants as companion plants, characterized in that, Includes the following steps: Step 1: Land pretreatment: Deep plowing, fertilization, passivation and soil conditioning of the planting fields; Step 2: Screening of associated enriching plants: Bidens pilosa and Amaranthus chinensis were selected as lead-specific enriching plant combinations. Step 3, Planting Layout Design: Adopt a strip-shaped spatial tiered intercropping pattern with the inner side of Bidens pilosa, the middle of wheat, and the outer side of amaranth to achieve an orderly planting arrangement from short to tall. Step 4, Sowing Period Management: Grain amaranth, beggar-ticks and wheat are sown in a staggered manner to achieve ecological niche synergy; Step 5: Coordinated Management During Intercropping Growth: Establish a coordinated management mechanism for water and fertilizer regulation and interspecific competition mitigation to achieve efficient extraction of Bidens pilosa and Amaranth chinensis and normal wheat growth; Step Six: Dynamic Management Throughout the Entire Growth Period: Establish a dynamic management mechanism covering the entire growth period of wheat, and implement phased regulation to achieve both control and yield assurance; Step 7, Harvesting and Post-harvest Processing: After wheat harvest, remove the Bidens pilosa and Amaranthus chinensis and dispose of them safely. Step 8, Crop Rotation: Repeat steps 1 to 8 before planting the next crop.

2. The intercropping cultivation method for reducing lead accumulation in wheat by using enriching plants as companion plants, as described in claim 1, is characterized in that... The land preprocessing procedure in step one is as follows: S1.1 Pretreatment time: Land pretreatment should be carried out 28-35 days after the previous crop is harvested and before sowing, avoiding rainy weather, and when the soil moisture content is 60%-70%. S1.2 Autumn deep plowing: First carry out autumn deep plowing, with a plowing depth of 28-32 cm, and then let it dry for 4-6 days; S1.3, Base fertilizer application: Combine deep plowing with the application of base fertilizer, apply 2500-2800 kg of decomposed organic manure, 13-15 kg of controlled-release nitrogen fertilizer and 5-6 kg of phosphate fertilizer per mu; after spreading the fertilizer evenly on the surface, plow it into the soil layer of 20-25 cm through deep plowing. S1.4 Application of rhizosphere growth-promoting bacteria: At the same time, apply 2.5-3.5 kg / mu of lead-resistant rhizosphere growth-promoting bacteria agent, mix it with the base fertilizer and then spread it. S1.5 Initial harrowing and compaction: After deep plowing and fertilization, harrow the land 1-2 times with a disc harrow, and then compact it 1-2 times with a roller to make the tillage layer flat and fine. S1.6 Application of passivating material: After the initial harrowing and compaction, apply lead passivating material evenly to the field. The passivating material is Mg-Al hydrotalcite that has been thermally activated at 600-650℃, and the application rate is 100-150 kg / mu. S1.7 Rotary Tillage and Mixing: After the passivation material is spread, use a rotary tiller to perform 1-2 passes of rotary tillage to a depth of 14-20 cm to ensure that the passivation material is fully mixed with the topsoil.

3. The intercropping cultivation method for reducing lead accumulation in wheat by using enriching plants as companion plants, as described in claim 1, is characterized in that... In step two, the associated enrichment plants were screened: Bidens pilosa and Amaranthus chinensis were selected as a combination of lead-specific enrichment plants; Bidens pilosa is a taproot type that extracts lead from deep soil; Amaranthus chinensis is a fibrous root type that competes for lead in shallow soil and removes lead through multiple harvests during the growing season.

4. The intercropping cultivation method for reducing lead accumulation in wheat by using enriching plants as companion plants, as described in claim 1, is characterized in that... In step three, the planting layout is designed as a tiered strip intercropping pattern based on the height differences of amaranth (the tallest), wheat (medium-sized), and Bidens pilosa (the shortest), specifically as follows: S2.1, Repeating Unit Division: Divide the wheat planting area into planting units with a total width of 3.2-3.5 meters, with each repeating unit serving as the basic structural unit for intercropping; S2.2 Planting strip arrangement within the unit: Each repeating unit consists of the following strips from the outside to the inside: 2 rows of amaranth, 6 rows of wheat, and 2 rows of beggar-ticks, forming a three-dimensional structure of tall, medium, and short plants.

5. The intercropping cultivation method for reducing lead accumulation in wheat by using enriching plants as companion plants, as described in claim 4, is characterized in that... The planting layout design in step three is as follows: the row spacing within the amaranth strip is 28-30 cm; the distance between the amaranth strip and the wheat strip is 50-60 cm; the row spacing within the wheat strip is 18-22 cm; the distance between the wheat strip and the Bidens pilosa strip is 28-30 cm; and the row spacing within the Bidens pilosa strip is 25-30 cm.

6. The intercropping cultivation method for reducing lead accumulation in wheat by using enriching plants as companion plants, as described in claim 1, is characterized in that... In step four, amaranth, beggar-ticks, and wheat are sown in sequence, specifically as follows: S3.1 First, sow amaranth seeds at a depth of 1.5-2.5 cm. After sowing, compact the soil and wait for the soil temperature to stabilize at 16-18℃ before sowing. S3.2, then sow Bidens pilosa at a depth of 2.5-3.5 cm, 2-4 days after planting Amaranth. S3.3 Finally, sow wheat 7-8 days after the emergence of amaranth and beggar-ticks, at a depth of 3.5-4.5 cm.

7. The intercropping cultivation method for reducing lead accumulation in wheat by using enriching plants as companion plants, as described in claim 1, is characterized in that... During the intermediate stage of step five, collaborative management during the growth period is carried out: (1) Water tiered regulation: When irrigating Bidens pilosa and Amaranth, furrow irrigation or drip irrigation is used, with a single irrigation volume of 35-40 m³ / mu, to induce the roots to extend into the deeper soil to extract deep lead; wheat is irrigated by sprinkler or micro-sprinkler, with a single irrigation volume of 15-18 m³ / mu, to keep the 0-22cm topsoil layer moist. (2) Targeted nutrient distribution: No separate topdressing is required for Bidens pilosa and Amaranthus chinensis during the seedling stage; 8.5-9.5 kg / mu of NPK compound fertilizer is applied to wheat during the jointing stage, with the topdressing position 12-16 cm away from the wheat row and ≥20 cm away from the Bidens pilosa strip. (3) Allelopathic substance blocking: Spray Bidens pilosa with a potassium humate solution of 0.15%-0.20% every 20-25 days, with an application rate of 48-55 L / mu; (4) Monitoring of interspecific competition: During the jointing and booting stages of wheat, a portable chlorophyll meter was used to monitor the chlorophyll content of wheat leaves. When the chlorophyll content was below 35 or the wheat plant height was reduced by more than 15% compared with the monoculture control, the top 10-15cm growing point of the grain amaranth was removed immediately. The formal harvesting described in step six was carried out before the wheat entered the grain filling stage.

8. The intercropping cultivation method for reducing lead accumulation in wheat by using enriching plants as companion plants, as described in claim 1, is characterized in that... Step six involves dynamic management throughout the entire reproductive period: (1) Seedling stage - jointing stage: Maintain soil field water holding capacity at 60%-70% to promote the deep root development of plants; (2) Jointing-booting stage: Bidens pilosa and Amaranth enter the vigorous growth period and extract available lead from the soil at a high intensity. During this period, nitrogen fertilizer should not be applied. (3) Grain-filling period: Before the wheat grain-filling period, the amaranth should be cut for the first time, leaving a stubble height of 18-20 cm; after cutting, apply urea at a rate of 25-30 kg / mu in time; (4) Maturity period: After the wheat matures, it is mechanically harvested. The harvester travels along the 50-60 cm channel between the amaranth belt and the wheat belt to perform a second harvest of the amaranth or save it for seed.

9. The intercropping cultivation method for reducing lead accumulation in wheat by using enriching plants as companion plants, as described in claim 1, is characterized in that... Harvesting and post-processing in step seven: S4.1 After the wheat harvest, the above-ground parts of the Bidens pilosa should be cut off whole and transported away from the farmland together with the cut amaranth. S4.

2. After mowing, the enriched plants shall be reduced in volume by incineration. The incineration temperature shall be controlled at 500-600℃. When the lead content in the incineration ash reaches the enrichment standard, it shall be handed over to a qualified hazardous waste disposal unit for treatment or used to extract valuable metals. It is prohibited to return it to the field as organic fertilizer.

10. The intercropping cultivation method for reducing lead accumulation in wheat by using enriching plants as companion plants, as described in claim 1, is characterized in that... In step eight, after the harvest of the current season's crops and the removal of enriching plants, the land pretreatment operation of step one is repeated before the next season's planting. The amount of passivation material applied can be adjusted according to the measured changes in soil lead content. When the soil lead content drops below the safety standard after three consecutive seasons of planting, the intercropping remediation mode is suspended, and conventional planting is switched to regular monitoring.

Images