Cultivation method for reducing lead content of cassava tuberous roots

Abstract

The invention relates to a cultivation method for reducing the lead content of cassava tuberous roots. The method comprises the steps of land selection for planting and fertilization management. Wherein the fertilization management comprises base fertilizer application and topdressing, and specifically comprises the following steps: (1) before cassava seed stems are sown, applying base fertilizer after soil pretreatment; (2) after sowing is conducted for 4-7 months, a leaf fertilizer A and a leaf fertilizer B are adopted to conduct leaf surface spraying on cassava plants till leaves just drip water, and the application time interval of the leaf fertilizer A and the leaf fertilizer B is 5-7 days; wherein the content of calcium in the leaf fertilizer A is 150-200 mg / L, the content of magnesium in the leaf fertilizer A is 10-30 mg / L, the leaf fertilizer A is sprayed once every 15-20 days, and the leaf fertilizer A is sprayed for 2-5 times in total; the selenium content in the leaf fertilizer B is 15-60 mg / L, the leaf fertilizer B is sprayed once every 20-25 days, and the leaf fertilizer B is sprayed for 3-4 times in total; by means of the method, the cassava with the low lead content can be obtained, the edible safety of the cassava is improved, and the yield of the cassava cultivated through the method is high.

Description

Technical Field

[0001] The present invention relates to the technical field of cassava cultivation, and particularly relates to a cultivation method for reducing the lead content in cassava tubers.

Background Art

[0002] Cassava (Manihot esculenta Crantz) is a plant of the genus Manihot in the Euphorbiaceae family.

[0003] Lead in food has various harms to human health, especially to children and pregnant women. Therefore, reducing lead and controlling the lead content in food are important measures to ensure public health. The national food safety standard for limits of contaminants in food (GB2762-2022) stipulates that the lead limit for tubers is fresh tubers < 0.2 mg / kg. Affected by growth characteristics, surrounding soil, air, water and other environments, some cassava varieties are prone to accumulate lead in their tubers, resulting in the produced edible cassava not meeting the national standard for the lead content limit in fresh tubers.

[0004] Reducing the lead content in cassava tubers by cultivation techniques is of great significance for improving the safety of edible cassava and accelerating the process of cassava foodization. There is no relevant research report yet. In view of this, this application proposes a cultivation method for reducing the lead content in cassava to solve the above problems.

Summary of the Invention

[0005] In view of the above, it is necessary to provide a cultivation method for reducing the lead content in cassava tubers. Through this method, cassava with a low lead content can be obtained, improving the edible safety of cassava, and the cassava under this cultivation method has a high yield.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A cultivation method for reducing the lead content in cassava, the method includes land selection and planting and fertilization management;

[0008] Among them, the fertilization management includes applying basal fertilizer and top dressing, specifically: (1) applying basal fertilizer before sowing cassava seed stems and after soil pretreatment; (2) after sowing for 4-7 months, spraying foliar fertilizer A and foliar fertilizer B on the seedlings until the leaves are just dripping, and the application time interval between foliar fertilizer A and foliar fertilizer B is 5-7 days; among them, the calcium content in foliar fertilizer A is 150-200 mg / L, the magnesium content is 10-30 mg / L, spraying once every 15-20 d, and spraying 2-5 times in total; the selenium content in foliar fertilizer B is 15-60 mg / L, spraying once every 20-25 d, and spraying 3-4 times in total.

[0009] Further, the base fertilizer is mainly composed of the following raw materials in parts by weight: 60-80 parts of organic compost, 1-3 parts of urea, 5-9 parts of calcium magnesium phosphate fertilizer, and 3-8 parts of potassium chloride; the application method of the base fertilizer is: mixing the base fertilizer with the soil in the planting hole, and the application rate of the base fertilizer is 700-750 kg / mu.

[0010] Further, foliar fertilizer A is obtained by adding calcium nitrate and chelated calcium into water, stirring until completely dissolved, adding magnesium sulfate, chelated magnesium, boric acid and chelated zinc, stirring until completely dissolved, then successively adding polyoxyethylene ether, glycerol and citric acid, stirring evenly, and then adjusting the pH to 6.5; the mass ratio of calcium nitrate, chelated calcium, magnesium sulfate, chelated magnesium, boric acid, chelated zinc, polyoxyethylene ether, glycerol and citric acid is 10-15:8:3-5:1-2:2:3:0.1-0.5:0.5-1:0.2.

[0011] Further, foliar fertilizer B is prepared by mixing sodium selenite, selenomethionine, urea, zinc sulfate and brassinolide in a mass ratio of 1:2:2-3:1-2:0.1, and adding them into deionized water and stirring well.

[0012] Further, the site selection and planting specifically include: selecting a plot with a low soil background value, no heavy metal pollution, deep soil layer, and convenient drainage and irrigation as the planting land, applying a composite soil conditioner to the soil after land preparation, and the application rate is 400-600 kg / mu; then using mature cassava stems as sowing materials, sowing and planting in a flat or inclined insertion manner from mid-to-late March to early April, the planting row spacing is 0.8-1.2 m, and the ridge surface and furrow are covered with silver-black double-color plastic film.

[0013] Further, the land preparation is completed by machine tillage, the tillage depth is 30-40 cm, so as to be deep, loose, fine, broken, flat and weed-free, ridges are formed according to the planting row spacing, and one ridge can be planted in double rows or single rows, the ridge height is 10-15 cm, and drainage ditches are dug around.

[0014] Further, the composite soil conditioner is obtained by mixing goethite-humic acid complex, biochar and calcium oxide in a mass ratio of 1:2-3:1-2, granulating and drying.

[0015] Further, the preparation method of the ferrihydrite-humic acid complex comprises the following steps: 1) Dissolve ferric chloride in 100-200 times deionized water to obtain an iron salt solution, adjust the pH value of the iron salt solution to 7-8, then continuously stir and react until a reddish-brown ferrihydrite precipitate is formed. Wash the precipitate with deionized water and then dry it to obtain ferrihydrite powder; 2) Dissolve humic acid in 100-200 times deionized water to obtain a humic acid solution. Mix the two according to the mass ratio of the humic acid solution to the ferrihydrite powder of 0.5-1:1. Centrifuge the mixed solution to collect the precipitate, wash the precipitate with deionized water, and then dry it to obtain the ferrihydrite-humic acid complex.

[0016] Further, before sowing the mature cassava stem cuttings, cut the stem cuttings into 15-20 cm long segments, soak them in 1000 times solution of 50% carbendazim wettable powder for 3-5 minutes, fish them out and dry them in the air before sowing.

[0017] The present invention has at least the following beneficial effects:

[0018] 1. The cultivation method of the present application can effectively reduce the lead content in cassava tubers, and at the same time ensure the yield of fresh cassava, and a high-quality cassava with low lead content and rich selenium can be obtained.

[0019] 2. The cultivation method of the present application mainly includes land selection and planting and fertilization management. First, by selecting a suitable planting land and performing soil improvement pretreatment, it is found through experiments that by applying the composite soil improver of the present application, the soil structure can be improved. In addition, it can also effectively reduce the lead content in cassava. This may be because the active ingredients in the soil improver can reduce the bioavailability of lead in the soil, thereby reducing the absorption of lead by cassava; in addition, a base fertilizer is applied before sowing in the present application, which is rich in organic matter and promotes crop growth. At the same time, it is unexpectedly found that the base fertilizer applied in the present application can also reduce the lead content in cassava. Through a large number of experimental studies by the applicant, it is concluded that it may be that the calcium magnesium phosphate fertilizer and potassium chloride in the base fertilizer can compete with lead ions for the absorption sites of plant roots, thereby inhibiting the absorption of lead by cassava plants; after applying the base fertilizer, sow cassava stem cuttings, and then topdress at an appropriate time. Specifically, the topdressing in the present application is achieved by spraying foliar fertilizers. The foliar fertilizers include foliar fertilizer A and foliar fertilizer B. Among them, foliar fertilizer A contains rich calcium and magnesium components, and foliar fertilizer B is a selenium-rich foliar fertilizer. Spraying them at intervals can achieve the purpose of obtaining fresh cassava tubers with low lead content. Compared with spraying only one of the foliar fertilizers, the lead content of cassava is effectively reduced, which greatly improves the market competitiveness of cassava and has broad application prospects.

Specific Embodiments

[0020] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following provides a detailed description of the specific embodiments of the present invention. Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0021] Example 1:

[0022] This example provides a cultivation method for reducing the lead content in cassava tubers, and the method includes the following steps:

[0023] (1) Site selection and planting:

[0024] Site selection and land preparation: Select a plot with a low soil background value, no heavy metal pollution, deep soil layer, and convenient drainage and irrigation as the planting land. After site selection, use mechanical tillage to complete land preparation, with a tillage depth of 40 cm, achieving deep, loose, fine, broken, flat, and weed-free. Ridges are formed according to the planting row spacing, and one ridge can be planted with two rows or one row. The ridge height is 15 cm, and drainage ditches are dug around.

[0025] Soil improvement: After land preparation, apply a composite soil conditioner to the soil, with an application rate of 600 kg / mu. The composite soil conditioner is obtained by uniformly mixing ferrihydrite-humic acid complex, biochar, and calcium oxide in a mass ratio of 1:3:2, granulating, and drying. The preparation method of the ferrihydrite-humic acid complex includes the following steps: 1) Dissolve ferric chloride in 200 times deionized water to obtain an iron salt solution, adjust the pH value of the iron salt solution to 8, and then continuously stir and react until a reddish-brown ferrihydrite precipitate is formed. Wash the precipitate with deionized water and then dry to obtain ferrihydrite powder; 2) Dissolve humic acid in 200 times deionized water to obtain a humic acid solution, mix the two according to the mass ratio of the humic acid solution to the ferrihydrite powder of 1:1, centrifuge the mixture to collect the precipitate, wash the precipitate with deionized water, and then dry to obtain the ferrihydrite-humic acid complex.

[0026] Sowing: Then use mature cassava stems as sowing materials. Before sowing, cut the stems into 20 cm long stem segments, soak them in a 1000-fold solution of 50% carbendazim wettable powder for 5 minutes, fish them out and dry them for sowing. Then, from mid-to-late March to early April, sow and plant in a flat or inclined insertion manner, with a planting row spacing of 1.2 m, and cover the ridge surface and ridge ditch with silver-black double-color plastic film.

[0027] (2) Fertilization management: It includes applying basal fertilizer and top dressing, specifically: 1) Applying basal fertilizer before sowing cassava seed stems and after soil pre-treatment; the basal fertilizer is mainly composed of the following raw materials by weight: 80 parts of organic compost, 3 parts of urea, 9 parts of calcium magnesium phosphate fertilizer, and 8 parts of potassium chloride; the application method of the basal fertilizer is: mixing the basal fertilizer with the soil in the planting hole, and the application rate of the basal fertilizer is 750 kg / mu; 2) After sowing for 4 - 7 months, that is, from early July to mid-October, foliar fertilizer A and foliar fertilizer B are sprayed on the seedlings; the application time interval between foliar fertilizer A and foliar fertilizer B is 7 days; among them, the calcium content in foliar fertilizer A is 200 mg / L, the magnesium content is 30 mg / L, and it is sprayed once every 20 days for a total of 5 times; the selenium content in foliar fertilizer B is 60 mg / L, and it is sprayed once every 25 days for a total of 4 times; foliar fertilizer A is obtained by adding calcium nitrate and chelated calcium to water, stirring until completely dissolved, adding magnesium sulfate, chelated magnesium, boric acid, and chelated zinc, stirring until completely dissolved, then successively adding polyoxyethylene ether, glycerol, and citric acid, stirring evenly, and then adjusting the pH to 6.5; the mass ratio of calcium nitrate, chelated calcium, magnesium sulfate, chelated magnesium, boric acid, chelated zinc, polyoxyethylene ether, glycerol, and citric acid is 10:8:3:1:2:3:0.1:0.5:0.2; foliar fertilizer B is prepared by mixing sodium selenite, selenomethionine, urea, zinc sulfate, and brassinolide in a mass ratio of 1:2:2:2:0.1, and adding it to deionized water and stirring well.

[0028] Example 2:

[0029] This example provides a cultivation method for reducing the lead content in cassava tuberous roots, and this method includes the following steps:

[0030] (1) Site selection and planting:

[0031] Site selection and land preparation: Select a plot with a low soil background value, no heavy metal pollution, deep soil layer, convenient drainage and irrigation as the planting land. After site selection, use mechanical tillage to complete land preparation, with a tillage depth of 35 cm, achieving deep, loose, fine, broken, flat, and weed-free. Ridges are formed according to the planting row spacing, and it can be planted in double rows or single rows on one ridge. The ridge height is 12 cm, and drainage ditches are dug around.

[0032] Soil improvement: After land preparation, a compound soil conditioner is applied to the soil at a dosage of 500 kg per mu. The compound soil conditioner is obtained by uniformly mixing ferrihydrite-humic acid complex, biochar and calcium oxide in a mass ratio of 1:3:1, granulating and drying. The preparation method of the ferrihydrite-humic acid complex includes the following steps: 1) Dissolve ferric chloride in 150 times deionized water to obtain an iron salt solution, adjust the pH value of the iron salt solution to 7.5, then continuously stir and react until a reddish-brown ferrihydrite precipitate is formed. Wash the precipitate with deionized water and then dry to obtain ferrihydrite powder; 2) Dissolve humic acid in 150 times deionized water to obtain a humic acid solution. Mix the two according to the mass ratio of the humic acid solution to the ferrihydrite powder of 0.7:1. Centrifuge the mixed solution to collect the precipitate, wash the precipitate with deionized water, and then dry to obtain the ferrihydrite-humic acid complex;

[0033] Sowing: Then use mature cassava stems as sowing materials. Before sowing, cut the stems into 18-cm-long stem segments, soak them in a 1000-fold solution of 50% carbendazim wettable powder for 4 minutes, fish them out and dry them in the air before sowing. Then, from mid-to-late March to early April, sow and plant them in a flat or inclined insertion manner, with a planting row spacing of 1.0 m, and cover the ridge surface and ridge ditch with silver-black double-color plastic film;

[0034] (2) Fertilization management: It includes applying basal fertilizer and top dressing, specifically as follows: 1) Apply basal fertilizer before sowing cassava stem cuttings and after soil pretreatment; the basal fertilizer is mainly composed of the following raw materials in parts by weight: 70 parts of organic compost, 2 parts of urea, 7 parts of calcium magnesium phosphate fertilizer, and 6 parts of potassium chloride; the application method of the basal fertilizer is: mix the basal fertilizer with the soil in the planting hole, and the application rate of the basal fertilizer is 720 kg / mu; 2) After sowing for 4 - 7 months, that is, from early July to mid - October, spray foliar fertilizer A and foliar fertilizer B on the seedlings; the application time interval between foliar fertilizer A and foliar fertilizer B is 6 days; among them, the calcium content in foliar fertilizer A is 180 mg / L, the magnesium content is 20 mg / L, spray once every 18 days, and spray a total of 4 times; the selenium content in foliar fertilizer B is 40 mg / L, spray once every 22 days, and spray a total of 3 times; foliar fertilizer A is obtained by adding calcium nitrate and chelated calcium to water, stirring until completely dissolved, adding magnesium sulfate, chelated magnesium, boric acid, and chelated zinc, stirring until completely dissolved, then successively adding polyoxyethylene ether, glycerol, and citric acid, stirring evenly, and then adjusting the pH to 6.5; the mass ratio of calcium nitrate, chelated calcium, magnesium sulfate, chelated magnesium, boric acid, chelated zinc, polyoxyethylene ether, glycerol, and citric acid is 12:8:4:1:2:3:0.3:0.7:0.2; foliar fertilizer B is prepared by mixing sodium selenite, selenomethionine, urea, zinc sulfate, and brassinolide in a mass ratio of 1:2:2:1:0.1, and adding them to deionized water and stirring well.

[0035] Example 3:

[0036] This example provides a cultivation method for reducing the lead content in cassava tubers, and this method includes the following steps:

[0037] (1) Site selection and planting:

[0038] Site selection and land preparation: Select a plot with a low soil background value, no heavy metal pollution, deep soil layer, convenient drainage and irrigation as the planting land. After site selection, use mechanical tillage to complete land preparation, with a tillage depth of 40 cm, achieving deep, loose, fine, broken, flat, and weed - free. Ridges are formed according to the planting row spacing, and it can be planted in double rows or single row on one ridge. The ridge height is 15 cm, and drainage ditches are dug around.

[0039] Soil improvement: After land preparation, a compound soil conditioner is applied to the soil at a rate of 600 kg / mu. The compound soil conditioner is obtained by uniformly mixing ferrihydrite-humic acid complex, biochar, and calcium oxide in a mass ratio of 1:3:2, granulating, and drying. The preparation method of the ferrihydrite-humic acid complex includes the following steps: 1) Dissolve ferric chloride in 200 times deionized water to obtain an iron salt solution, adjust the pH value of the iron salt solution to 8, then continuously stir and react until a reddish-brown ferrihydrite precipitate is formed. Wash the precipitate with deionized water and then dry it to obtain ferrihydrite powder; 2) Dissolve humic acid in 200 times deionized water to obtain a humic acid solution. Mix the two according to a mass ratio of 1:1 of the humic acid solution and ferrihydrite powder. Centrifuge the mixed solution to collect the precipitate, wash the precipitate with deionized water, and then dry it to obtain the ferrihydrite-humic acid complex;

[0040] Sowing: Then, use mature cassava stems as sowing materials. Before sowing, cut the stems into 20-cm-long stem segments, soak them in a 1000-fold solution of 50% carbendazim wettable powder for 5 minutes, fish them out and let them dry in the air before sowing. Then, from mid-to-late March to early April, sow and plant them in a horizontal or inclined insertion manner, with a planting row spacing of 1.2 m, and cover the ridge surface and ridge ditch with silver-black double-color plastic film;

[0041] (2) Fertilization management: It includes applying basal fertilizer and top dressing, specifically: 1) Apply basal fertilizer before sowing cassava stems and after soil pretreatment. The basal fertilizer is mainly composed of the following raw materials in parts by weight: 80 parts of organic compost, 3 parts of urea, 9 parts of calcium magnesium phosphate fertilizer, and 8 parts of potassium chloride. The application method of the basal fertilizer is to mix the basal fertilizer with the soil in the planting hole, and the application rate of the basal fertilizer is 750 kg / mu; 2) After sowing for 4 - 7 months, that is, from early July to mid-October, spray foliar fertilizer A and foliar fertilizer B on the seedlings. The application time interval between foliar fertilizer A and foliar fertilizer B is 7 days. Among them, the calcium content in foliar fertilizer A is 200 mg / L, the magnesium content is 30 mg / L, and it is sprayed once every 20 days for a total of 5 times; the selenium content in foliar fertilizer B is 60 mg / L, and it is sprayed once every 25 days for a total of 4 times. Foliar fertilizer A is obtained by adding calcium nitrate and chelated calcium to water, stirring until completely dissolved, adding magnesium sulfate, chelated magnesium, boric acid, and chelated zinc, stirring until completely dissolved, then successively adding polyoxyethylene ether, glycerol, and citric acid, stirring evenly, and then adjusting the pH to 6.5. The mass ratio of calcium nitrate, chelated calcium, magnesium sulfate, chelated magnesium, boric acid, chelated zinc, polyoxyethylene ether, glycerol, and citric acid is 15:8:5:2:2:3:0.5:1:0.2. Foliar fertilizer B is prepared by mixing sodium selenite, selenomethionine, urea, zinc sulfate, and brassinolide in a mass ratio of 1:2:3:2:0.1, and adding them to deionized water and stirring well;

[0042] To illustrate the effects of this application, the applicant conducted the following experiments:

[0043] The applicant compared the cassava yields, lead contents, and selenium contents in fresh cassava of the following groups, which were specifically divided into the following groups:

[0044] Group 1: The cultivation method described in Example 2;

[0045] Group 2: In fertilizer management, foliar fertilizer B was removed, and foliar fertilizer A was additionally applied at the original time for applying foliar fertilizer B, and other methods were the same as those in Example 2;

[0046] Group 3: In fertilizer management, foliar fertilizer A was removed, and foliar fertilizer B was additionally applied at the original time for applying foliar fertilizer A, and other methods were the same as those in Example 2;

[0047] Group 4: In fertilizer management, the application methods of both foliar fertilizer A and foliar fertilizer B were changed to root fertilization, and other methods were the same as those in Example 2;

[0048] Group 5: Calcium magnesium phosphate fertilizer and potassium chloride in the base fertilizer were removed, and other methods were the same as those in Example 2;

[0049] Group 6: The ferrihydrite-humic acid complex in the compound soil conditioner was removed, and other methods were the same as those in Example 2.

[0050] To compare the cultivation effects of cassava in the above groups, the cassava variety selected in this experiment was SC9, and the data were recorded as shown in Table 1:

[0051] Table 1 Comparison of Cultivation Effects of Cassava in Each Group

[0052]

[0053]

[0054] According to the results in Table 1, the cassava obtained by using the cultivation method of the present application not only has a high yield, but also has a low lead content and a high selenium content in its fresh tubers. The cultivation method of the present application can obtain a cassava with low lead and rich selenium, with high food safety and good quality. After the foliar fertilizer B was removed from the second group, the selenium content decreased sharply, and the selenium element could not be enriched. At the same time, it was found that the lead content in the second group was also relatively high, indicating that the selenium-rich foliar fertilizer can not only increase the selenium element content, but also reduce the lead content in cassava. In the third group, when foliar fertilizer A was removed, the lead element content increased significantly, and the purpose of cultivating low-lead cassava could not be achieved. In the fourth group, root fertilization was carried out, and the lead content was relatively high. It may be that the fertilizer described in the topdressing of the present application can be directly absorbed through leaf stomata and epidermal cells, with a faster absorption rate, which is conducive to competing with lead ions for the absorption sites of plant roots. After soil root application, the nutrients are slowly released, and the plant may absorb more lead elements in the soil. In addition, the cassava root system is relatively sensitive to lead absorption, but the selenium element content is relatively high, and the influence is not as large as the lead content. This is also an unexpected discovery in the applicant's cultivation experiment and is considered to have a very prominent effect. When the calcium magnesium phosphate fertilizer and potassium chloride in the base fertilizer were removed from the fifth group and the hydro-iron ore-humic acid complex was removed from the sixth group, both showed relatively high lead element contents, indicating that these components are beneficial to reducing the lead content in cassava. In summary, each step of the present application is coordinated with each other. If a certain component is removed or a certain step is changed, the effect described in the present application may not be achieved, indicating that the fertilizer used for fertilization, the fertilization method, etc. have a great impact on the growth of cassava and the enrichment of elements.

[0055] The above examples only illustrate several embodiments of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. A cultivation method for reducing the lead content of cassava root tubers, characterized in that: The method includes site selection, planting and fertilizer management; The fertilization management includes applying basal fertilizer and topdressing, specifically: (1) applying basal fertilizer before sowing cassava seed stems and after soil pretreatment; (2) spraying the seedlings with foliar fertilizer A and foliar fertilizer B 4-7 months after sowing, and the application time interval between foliar fertilizer A and foliar fertilizer B is 5-7 days; wherein the calcium content in the foliar fertilizer A is 150-200 mg / L, and the magnesium content is 10-30 mg / L, and the foliar fertilizer is sprayed once every 15-20 days, for a total of 2-5 times; the selenium content in the foliar fertilizer B is 15-60 mg / L, and the foliar fertilizer is sprayed once every 20-25 days, for a total of 3-4 times.

2. The method according to claim 1, characterized in that The base fertilizer is mainly composed of the following raw materials in parts by weight: 60-80 parts of organic compost, 1-3 parts of urea, 5-9 parts of calcium magnesium phosphate fertilizer, and 3-8 parts of potassium chloride; the base fertilizer is applied in the following manner: mixing the base fertilizer with the soil in the planting hole, and the base fertilizer application amount is 700-750kg / mu.

3. The method according to claim 1, characterized in that The foliar fertilizer A is prepared by adding calcium nitrate and chelated calcium into water, stirring until completely dissolved, adding magnesium sulfate, chelated magnesium, boric acid and chelated zinc, stirring until completely dissolved, then sequentially adding polyoxyethylene ether, glycerol and citric acid, stirring evenly, and then adjusting the pH to 6.5 to obtain foliar fertilizer A; the mass ratio of the calcium nitrate, chelated calcium, magnesium sulfate, chelated magnesium, boric acid, chelated zinc, polyoxyethylene ether, glycerol and citric acid is 10-15:8:3-5:1-2:2:3:0.1-0.5:0.5-1:0.

2.

4. The method according to claim 1, characterized in that: The foliar fertilizer B is prepared by mixing sodium selenite, selenomethionine, urea, zinc sulfate and brassinolide in a mass ratio of 1:2:2-3:1-2:0.1, adding the mixture into deionized water, and stirring the mixture thoroughly.

5. The method according to claim 1, characterized in that The site selection and planting specifically include: selecting a plot with low soil background value, no heavy metal pollution, deep soil layer, and convenient irrigation and drainage as the planting site, applying a composite soil conditioner to the soil after land preparation, with an application amount of 400-600kg / mu; then using mature cassava stems as sowing materials, sowing and planting them in a flat or oblique manner from mid-to-late March to early April, with a planting row spacing of 0.8-1.2m, and using a silver-black two-color mulch to cover the bed surface and bed furrows.

6. The method according to claim 5, characterized in that The land preparation is completed by mechanized tillage with a tillage depth of 30-40 cm, and the land is deep, loose, fine, broken, flat and free of weeds. Ridges are formed according to the row spacing of the plants, and double rows or single row can be planted in one ridge. The ridge height is 10-15 cm, and drainage ditches are opened all around.

7. The method according to claim 5, characterized in that The composite soil conditioner is obtained by uniformly mixing ferrihydrite-humic acid complex, biochar and calcium oxide in a mass ratio of 1:2-3:1-2, granulating and drying.

8. The method according to claim 7, characterized in that The preparation method of the ferrihydrite-humic acid complex comprises the following steps: 1) dissolving ferric chloride in 100-200 times of deionized water to obtain an iron salt solution, adjusting the pH value of the iron salt solution to 7-8, and then continuously stirring the reaction to generate a reddish brown ferrihydrite precipitate, washing the precipitate with deionized water, and then drying to obtain ferrihydrite powder; 2) dissolving humic acid in 100-200 times of deionized water to obtain a humic acid solution, mixing the humic acid solution and the ferrihydrite powder in a mass ratio of 0.5-1:1, centrifuging the mixed solution to collect the precipitate, washing the precipitate with deionized water, and then drying to obtain the ferrihydrite-humic acid complex.

9. The method according to claim 5, characterized in that Before sowing, the mature cassava seed stems are cut into stem segments of 15-20 cm in length, soaked in 1000 times liquid of 50% carbendazim wettable powder for 3-5 minutes, fished out and dried before sowing.

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