Rice planting method based on rice straw returning to field

Abstract

The invention provides a rice planting method based on rice straw returning, and belongs to the technical field of agricultural planting. The rice planting method comprises the following steps that 1, astragalus sinicus is sown 5-10 days before rice is harvested, and then harvested rice straw is smashed and returned to the field; and (2) turning and returning the astragalus sinicus and the astragalus sinicus with pods, which grow to the full-bloom stage, and rice straws to the field, applying a base fertilizer and an adsorbent after turning and returning to the field for 30-50 days, performing rotary tillage, then irrigating, transplanting rice seedlings after 5-10 days, and planting rice. The rice planting method provided by the invention has the effects of saving the fertilizer consumption, promoting recycling of farmland waste resources, improving the soil fertility, reducing the content of heavy metals in soil, increasing the rice yield and the like.

Description

Technical Field

[0001] This invention relates to the field of agricultural planting technology, specifically to a rice planting method based on returning rice straw to the field. Background Technology

[0002] Rice is a major food crop in my country, accounting for approximately 18% of the world's total rice cultivation area, ranking among the world's top and playing a crucial role in the stability of global food production. While producing a large amount of rice, rice cultivation also generates a significant amount of rice straw, which accounts for about 50% of the total biomass of rice production and is an important byproduct of rice cultivation. With the continuous improvement of agricultural production levels, the yield of rice straw has shown a year-on-year increasing trend. Statistics show that my country is one of the world's highest producers of rice straw; however, the utilization rate of rice straw in my country is low, with a large amount becoming agricultural waste. To facilitate agricultural production and reduce the land area occupied by agricultural waste, some rice farmers often use on-site burning, which not only wastes the nutrient resources in the rice straw but also causes serious pollution to the ecological environment.

[0003] Studies have shown that rice straw is rich in organic carbon and various nutrients such as nitrogen, phosphorus, and potassium, which are essential for crop growth. After being applied to the soil and decomposed, it can provide nutrients for the next crop. The organic matter in rice straw can also provide a habitat and energy source for the growth and reproduction of beneficial microorganisms in the soil, improving their activity and soil structure, making it a valuable organic fertilizer. Therefore, returning rice straw to the field for recycling and reusing it in crop production has gradually become a research hotspot. Rice farmers often use large amounts of chemical fertilizers or pesticides to increase yields. However, chemical fertilizers usually contain heavy metals such as lead, mercury, and cadmium. Long-term and excessive use of chemical fertilizers can easily lead to excessive levels of heavy metals in the soil. Furthermore, research has found that most pesticides used in agricultural production contain high concentrations of heavy metals, such as insecticides and antibacterial agents, which typically contain copper, mercury, lead, manganese, and arsenic. Once soil is contaminated with heavy metals, it is very difficult to restore it to its original state. High concentrations of heavy metals such as copper, cadmium, chromium, mercury, arsenic, and lead can accumulate in plant tissues, enter the food chain, and accumulate in the human body, causing irreversible damage to health. Biochar is a carbonaceous material produced by the pyrolysis of biomass. Rich in porous structures, it can adsorb heavy metals from soil through physical adsorption, ion exchange, complexation reactions, and chemical precipitation reactions. Therefore, biochar is widely used in the field of heavy metal removal from soil. The removal rate of heavy metals is usually directly proportional to the amount of biochar applied; that is, to improve the heavy metal removal rate, the amount of biochar applied needs to be increased. However, applying large amounts of biochar inevitably increases the environmental burden.

[0004] How to improve the adsorption capacity of biochar while increasing rice yield and reducing fertilizer use, and solve the problem of heavy metal ion pollution, is a technical challenge that needs to be addressed. Summary of the Invention

[0005] In view of this, the present invention provides a rice planting method based on returning rice straw to the field, comprising the following steps:

[0006] (1) Sow milkvetch 5-10 days before harvesting rice, and then crush the harvested rice straw and return it to the field;

[0007] (2) Plow the milkvetch and milkvetch with pods that have grown to full bloom into the field with rice straw. After 30-50 days of plowing, apply base fertilizer and adsorbent, till the soil, then irrigate. After 5-10 days, transplant rice seedlings and plant rice.

[0008] Preferably, in step (1), the stubble of the harvested rice is 35-50cm long, and the length of the crushed rice straw is 4-8cm.

[0009] Preferably, the amount of milkvetch seeded in step (1) is 3-4.5 kg / mu.

[0010] Preferably, the turning depth in step (2) is 25-30 cm, the rotary tillage depth in step (2) is 15-20 cm, the watering depth is 3-5 cm, the water depth is maintained at 3-5 cm during the transplanting of seedlings, the turning amount of milkvetch in step (2) is 1200-2300 kg / mu, and the turning amount of dried rice straw is 380-420 kg / mu.

[0011] Preferably, the base fertilizer in step (2) includes 10-12 kg / mu of nitrogen fertilizer, 5.3-6.8 kg / mu of phosphorus fertilizer, and 6-9 kg / mu of potassium fertilizer.

[0012] Preferably, the amount of adsorbent used in step (2) is 2.5-3.8 kg / mu.

[0013] Preferably, the method for preparing the adsorbent in step (2) is as follows:

[0014] S1. First, mix magnetic microalgae biochar and calcium nitrate solution at a mass-volume ratio of 1-3:200-500 until homogeneous. Then, add sodium dihydrogen phosphate dihydrate solution to adjust the pH of the system to 10-11. After stirring evenly, let it stand for 10-15 hours and then centrifuge to obtain the intermediate product.

[0015] S2. The intermediate product is washed, dried, and ground, then mixed with xanthan gum and dispersed under ultrasonic assistance for 1-1.5 hours to obtain a mixture.

[0016] S3. The mixture is added dropwise into a calcium nitrate solution, cross-linked and hardened for 8-12 hours to form composite microspheres, precipitated for 24-26 hours, washed with water, and freeze-dried to obtain the adsorbent.

[0017] Preferably, the concentration of the calcium nitrate solution in step S1 is 0.5-1 mol / L.

[0018] Preferably, the concentration of the sodium dihydrogen phosphate dihydrate solution in step S1 is 0.5-0.8 mol / L.

[0019] Preferably, the mass ratio of the sodium dihydrogen phosphate dihydrate solution to the calcium nitrate solution in step S1 is 1:1.2-1.5.

[0020] Preferably, the centrifugation speed in step S1 is 1000-2000 rap / min.

[0021] Preferably, the preparation method of the magnetic microalgae biochar in step S1 is as follows: microalgae powder and potassium ferrate are mixed and ground at a mass ratio of 1:3-5 for 8-15 minutes, then pyrolyzed at 300-450 degrees Celsius for 0.5-1 hours, cooled to room temperature, washed with water, and dried to obtain magnetic microalgae biochar.

[0022] Preferably, the drying temperature in step S2 is 90-120 degrees Celsius.

[0023] Preferably, the mass ratio of xanthan gum to intermediate product in step S2 is 1:2-5.

[0024] Preferably, the ultrasonic power in step S2 is 320-450W.

[0025] Preferably, the concentration of calcium nitrate in step S3 is 0.2-0.3 mol / L.

[0026] Preferably, the freeze-drying temperature in step S3 is -60 to -70 degrees Celsius, and the freeze-drying time is 10 to 18 hours.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The purple clover sown in this invention can form root nodules in symbiosis with rhizobia, converting atmospheric nitrogen into ammonia that can be used by plants. By turning it over into the field, it decomposes and thus significantly increases the nitrogen content of the soil.

[0029] This invention solves the problem of environmental pollution caused by burning rice straw by returning it to the field. It can also replace some nitrogen fertilizer, save fertilizer usage, promote the recycling of agricultural waste resources, improve soil, and contribute to sustainable agricultural development.

[0030] This invention improves the adsorption capacity of magnetic microalgae biochar for various heavy metal ions by modifying the magnetic microalgae biochar.

[0031] The adsorbent prepared by this invention has the effects of easy recovery, improving soil fertility, and increasing rice yield. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0033] Unless otherwise specified, the test methods or experimental methods described in the following examples are conventional methods; the raw materials and agents, unless otherwise specified, are obtained from conventional commercial sources or prepared by conventional methods.

[0034] The milkvetch variety used in the following examples or comparative examples is "Yujiang Daye", and the rice variety is "Xiangliangyou 6218".

[0035] The dry matter content of fresh milkvetch is 10.2%, the total nitrogen content by dry weight is 3.3%, the total phosphorus content is 0.5%, and the total potassium content is 3.5%.

[0036] The dry matter content of rice straw is 6.1 t / hectare, with a total nitrogen content of 1.5%, total phosphorus of 0.7%, and total potassium of 1.2%.

[0037] Example 1

[0038] A rice cultivation method based on returning rice straw to the field, the specific steps of which are as follows:

[0039] (1) Seven days before the rice is ready to be harvested, the seed of milkvetch is sown at a rate of 3.5 kg / mu. Then, the rice straw is mechanically harvested and crushed to 6 cm, and returned to the field in full. The straw is then manually spread evenly to avoid accumulation. After harvesting, the rice stubble is left at 38 cm to provide a suitable field environment for the growth of milkvetch.

[0040] (2) The milkvetch and milkvetch with pods that have grown to the full flowering stage are plowed into the field with rice straw. The plowing depth is 27 cm. The amount of milkvetch plowed is 1800 kg / mu and the amount of dried rice straw plowed is 400 kg / mu. After plowing into the field for 40 days, apply base fertilizer (nitrogen fertilizer 12 kg / mu, phosphorus fertilizer 5.8 kg / mu, potassium fertilizer 7 kg / mu) and adsorbent (2.8 kg / mu). Use a tractor to rotary till into the soil. The rotary tilling depth is 17 cm. Then irrigate to a water depth of 4 cm. Transplant rice seedlings 6 days later. During the transplanting process, keep the water depth at 4 cm and plant rice.

[0041] The preparation method of the adsorbent in step (2) is as follows:

[0042] S1. First, microalgae powder and potassium ferrate are mixed and ground at a mass ratio of 1:4 for 12 min. Then, the mixture is pyrolyzed at 350°C for 0.8 h. After cooling to room temperature, it is washed with water and dried to obtain magnetic microalgae biochar. The magnetic microalgae biochar is mixed with a 0.7 mol / L calcium nitrate solution at a mass-volume ratio of 1:300. Then, a 0.6 mol / L sodium dihydrogen phosphate dihydrate solution is added. The mass ratio of sodium dihydrogen phosphate dihydrate solution to calcium nitrate solution is 1:1.3. The pH of the system is adjusted to 10 using a 1 mol / L sodium hydroxide solution. After stirring evenly, the mixture is allowed to stand for 13 h and then centrifuged at 1500 rap / min to obtain the intermediate product.

[0043] S2. The intermediate product is thoroughly washed with deionized water, dried at 110 degrees Celsius, ground to 80 mesh, and then mixed with xanthan gum at a mass ratio of 3:1. The mixture is ultrasonically dispersed at 380W for 1.2 hours to obtain the mixture.

[0044] S3. The mixture is added dropwise to a calcium nitrate solution with a concentration of 0.2 mol / L, and cross-linked and cured at -4 degrees Celsius for 10 h to form composite microspheres. After standing for 25 h, the microspheres are washed with water and freeze-dried at -65 degrees Celsius for 13 h to obtain the adsorbent.

[0045] Example 2

[0046] A rice cultivation method based on returning rice straw to the field, the specific steps of which are as follows:

[0047] (1) Five days before the rice is ready to be harvested, the seed of milkvetch is 3 kg / mu. Then the rice straw is mechanically harvested and crushed to 4 cm, and returned to the field in full. The straw is then manually spread evenly to avoid accumulation. After harvesting, the rice stubble is left at 35 cm to provide a suitable field environment for the growth of milkvetch.

[0048] (2) The milkvetch and milkvetch with pods that have grown to the full flowering stage are plowed into the field with rice straw. The plowing depth is 25 cm. The amount of milkvetch plowed is 1200 kg / mu and the amount of dried rice straw plowed is 380 kg / mu. After plowing into the field for 30 days, apply base fertilizer (nitrogen fertilizer 10 kg / mu, phosphorus fertilizer 5.3 kg / mu, potassium fertilizer 6 kg / mu) and adsorbent (2.5 kg / mu). Use a tractor to rotary till into the soil. The rotary tilling depth is 15 cm. Then irrigate to a water depth of 3 cm. After 5 days, transplant rice seedlings. During the transplanting process, keep the water depth at 3 cm and plant rice.

[0049] The preparation method of the adsorbent in step (2) is as follows:

[0050] S1. First, mix and grind microalgae powder and potassium ferrate at a mass ratio of 1:3 for 8 minutes. Then, pyrolyze at 300 degrees Celsius for 0.5 hours. After cooling to room temperature, wash with water and dry to obtain magnetic microalgae biochar. Mix the magnetic microalgae biochar with a 0.5 mol / L calcium nitrate solution at a mass-volume ratio of 1:200. Then, add a 0.5 mol / L sodium dihydrogen phosphate dihydrate solution, where the mass ratio of sodium dihydrogen phosphate dihydrate solution to calcium nitrate solution is 1:1.2. Adjust the pH of the system to 10 using a 1 mol / L sodium hydroxide solution. After stirring evenly, let stand for 10 hours and centrifuge at 1000 rap / min to obtain the intermediate product.

[0051] S2. The intermediate product is thoroughly washed with deionized water, dried at 90 degrees Celsius, ground to 80 mesh, and then mixed with xanthan gum at a mass ratio of 2:1. The mixture is ultrasonically dispersed at 320W for 1 hour to obtain the mixture.

[0052] S3. The mixture is added dropwise to a calcium nitrate solution with a concentration of 0.2 mol / L, and cross-linked and cured at -4 degrees Celsius for 8 hours to form composite microspheres. After standing for 24 hours, the microspheres are washed with water and freeze-dried at -60 degrees Celsius for 10 hours to obtain the adsorbent.

[0053] Example 3

[0054] A rice cultivation method based on returning rice straw to the field, the specific steps of which are as follows:

[0055] (1) Sow milkvetch seeds 10 days before rice is ready to be harvested. The amount of milkvetch seeds sown is 4.5 kg / mu. Then, mechanically harvest rice straw and crush it to 8 cm. Return all of it to the field and manually spread it evenly to avoid accumulation. After harvesting, leave 50 cm of rice stubble to provide a suitable field environment for milkvetch growth.

[0056] (2) The milkvetch and milkvetch with pods that have grown to the full flowering stage are plowed into the field with rice straw. The plowing depth is 30 cm. The amount of milkvetch plowed is 2300 kg / mu and the amount of dried rice straw plowed is 420 kg / mu. After 50 days of plowing, apply base fertilizer (nitrogen fertilizer 12 kg / mu, phosphorus fertilizer 6.8 kg / mu, potassium fertilizer 9 kg / mu) and adsorbent (3.8 kg / mu). Use a tractor to rotary till the soil to a depth of 20 cm. Then irrigate to a water depth of 5 cm. After 10 days, transplant rice seedlings. During the transplanting process, keep the water depth at 5 cm and plant rice.

[0057] The preparation method of the adsorbent in step (2) is as follows:

[0058] S1. First, mix and grind microalgae powder and potassium ferrate at a mass ratio of 1:5 for 15 min. Then, pyrolyze at 450 degrees Celsius for 1 h. After cooling to room temperature, wash with water and dry to obtain magnetic microalgae biochar. Mix the magnetic microalgae biochar with a 1 mol / L calcium nitrate solution at a mass-volume ratio of 3:500. Then, add a 0.8 mol / L sodium dihydrogen phosphate dihydrate solution, where the mass ratio of sodium dihydrogen phosphate dihydrate solution to calcium nitrate solution is 1:1.5. Adjust the pH of the system to 11 using a 1 mol / L sodium hydroxide solution. After stirring evenly, let stand for 15 h and centrifuge at 2000 rap / min to obtain the intermediate product.

[0059] S2. The intermediate product is thoroughly washed with deionized water, dried at 120 degrees Celsius, ground to 200 mesh, and then mixed with xanthan gum at a mass ratio of 5:1. The mixture is ultrasonically dispersed at 450W for 1.5 hours to obtain the mixture.

[0060] S3. The mixture is added dropwise to a calcium nitrate solution with a concentration of 0.3 mol / L, and cross-linked and cured at -4 degrees Celsius for 12 hours to form composite microspheres. After standing for 26 hours, the microspheres are washed with water and freeze-dried at -70 degrees Celsius for 18 hours to obtain the adsorbent.

[0061] Example 4

[0062] A rice cultivation method based on returning rice straw to the field, the specific steps of which are as follows:

[0063] (1) Sow milkvetch seeds 6 days before rice is ready to be harvested. The amount of milkvetch seeds sown is 4.0 kg / mu. Then, mechanically harvest rice straw and crush it to 7 cm. Return all of it to the field and manually spread it evenly to avoid accumulation. After harvesting, leave 45 cm of rice stubble to provide a suitable field environment for milkvetch growth.

[0064] (2) The milkvetch and milkvetch with pods that have grown to the full flowering stage are plowed into the field with rice straw. The plowing depth is 26 cm. The amount of milkvetch plowed is 1900 kg / mu and the amount of dried rice straw plowed is 400 kg / mu. After plowing into the field for 40 days, apply base fertilizer (nitrogen fertilizer 10 kg / mu, phosphorus fertilizer 5.3 kg / mu, potassium fertilizer 6 kg / mu) and adsorbent (2.5 kg / mu). Use a tractor to rotary till into the soil. The rotary tilling depth is 15 cm. Then irrigate to a water depth of 3 cm. Transplant rice seedlings 5 ​​days later. During the transplanting process, keep the water depth at 3 cm and plant rice.

[0065] The preparation method of the adsorbent in step (2) is as follows:

[0066] S1. First, microalgae powder and potassium ferrate are mixed and ground at a mass ratio of 1:3 for 13 min. Then, the mixture is pyrolyzed at 330°C for 0.8 h. After cooling to room temperature, it is washed with water and dried to obtain magnetic microalgae biochar. The magnetic microalgae biochar is mixed with a 0.7 mol / L calcium nitrate solution at a mass-volume ratio of 1:400. Then, a 0.6 mol / L sodium dihydrogen phosphate dihydrate solution is added, with a mass ratio of sodium dihydrogen phosphate dihydrate solution to calcium nitrate solution of 1:1.5. The pH of the system is adjusted to 11 using a 1 mol / L sodium hydroxide solution. After stirring evenly, the mixture is allowed to stand for 14 h and then centrifuged at 1700 rap / min to obtain the intermediate product.

[0067] S2. The intermediate product is thoroughly washed with deionized water, dried at 90 degrees Celsius, ground to 80 mesh, and then mixed with xanthan gum at a mass ratio of 2:1. The mixture is ultrasonically dispersed at 320W for 1 hour to obtain the mixture.

[0068] S3. The mixture is added dropwise to a calcium nitrate solution with a concentration of 0.2 mol / L, and cross-linked and cured at -4 degrees Celsius for 10 h to form composite microspheres. After standing for 24 h, the microspheres are washed with water and freeze-dried at -60 degrees Celsius for 12 h to obtain the adsorbent.

[0069] Example 5

[0070] A rice cultivation method based on returning rice straw to the field, the specific steps of which are as follows:

[0071] (1) Sow milkvetch seeds 10 days before rice is ready to be harvested. The sowing amount of milkvetch seeds is 3.8 kg / mu. Then, mechanically harvest rice straw and crush it to 7 cm. Return all of it to the field and manually spread it evenly to avoid accumulation. After harvesting, leave 48 cm of rice stubble to provide a suitable field environment for milkvetch growth.

[0072] (2) The milkvetch and milkvetch with pods that have grown to the full flowering stage are plowed into the field with rice straw. The plowing depth is 30 cm. The amount of milkvetch plowed is 2300 kg / mu and the amount of dried rice straw plowed is 420 kg / mu. After 50 days of plowing, apply base fertilizer (nitrogen fertilizer 12 kg / mu, phosphorus fertilizer 6.8 kg / mu, potassium fertilizer 9 kg / mu) and adsorbent (3.8 kg / mu). Use a tractor to rotary till the soil to a depth of 20 cm. Then irrigate to a water depth of 5 cm. After 10 days, transplant rice seedlings. During the transplanting process, keep the water depth at 5 cm and plant rice.

[0073] The preparation method of the adsorbent in step (2) is as follows:

[0074] S1. First, mix and grind microalgae powder and potassium ferrate at a mass ratio of 1:5 for 15 min. Then, pyrolyze at 300-450 degrees Celsius for 1 h. After cooling to room temperature, wash with water and dry to obtain magnetic microalgae biochar. Mix the magnetic microalgae biochar with a 1 mol / L calcium nitrate solution at a mass-volume ratio of 1:500. Then, add a 0.8 mol / L sodium dihydrogen phosphate dihydrate solution, where the mass ratio of sodium dihydrogen phosphate dihydrate solution to calcium nitrate solution is 1:1.5. Adjust the pH of the system to 10.5 using a 1 mol / L sodium hydroxide solution. After stirring evenly, let stand for 15 h and centrifuge at 2000 rap / min to obtain the intermediate product.

[0075] S2. The intermediate product is thoroughly washed with deionized water, dried at 950 degrees Celsius, ground to 200 mesh, and then mixed with xanthan gum at a mass ratio of 5:1. The mixture is ultrasonically dispersed at 450W for 1.5 hours to obtain the mixture.

[0076] S3. The mixture is added dropwise to a calcium nitrate solution with a concentration of 0.3 mol / L, and cross-linked and cured at -4 degrees Celsius for 12 hours to form composite microspheres. After standing for 26 hours, the microspheres are washed with water and freeze-dried at -70 degrees Celsius for 18 hours to obtain the adsorbent.

[0077] Comparative Example 1

[0078] The difference from Example 1 is that no milkvetch was sown.

[0079] Comparative Example 2

[0080] The difference from Example 1 is that an equal amount of corn stalks is used to replace the microalgae powder.

[0081] Comparative Example 3

[0082] The difference from Example 1 lies in the method of preparing the adsorbent, specifically:

[0083] First, microalgae powder and potassium ferrate are mixed and ground at a mass ratio of 1:4 for 12 minutes. Then, the mixture is pyrolyzed at 350 degrees Celsius for 0.8 hours. After cooling to room temperature, it is washed with water and dried to obtain magnetic microalgae biochar, i.e., adsorbent.

[0084] Comparative Example 4

[0085] The difference from Example 1 is that an equal amount of sodium alginate was used instead of xanthan gum.

[0086] Comparative Example 5

[0087] The difference from Example 1 lies in the method of preparing the adsorbent, specifically:

[0088] S1. First, microalgae powder and potassium ferrate are mixed and ground at a mass ratio of 1:4 for 12 min. Then, the mixture is pyrolyzed at 350°C for 0.8 h. After cooling to room temperature, it is washed with water and dried to obtain magnetic microalgae biochar. The magnetic microalgae biochar is mixed with a 0.7 mol / L calcium nitrate solution at a mass-volume ratio of 1:300. Then, a 0.6 mol / L sodium dihydrogen phosphate dihydrate solution is added. The mass ratio of sodium dihydrogen phosphate dihydrate solution to calcium nitrate solution is 1:1.3. The pH of the system is adjusted to 10 using a 1 mol / L sodium hydroxide solution. After stirring evenly, the mixture is allowed to stand for 13 h and then centrifuged at 1500 rap / min to obtain the intermediate product.

[0089] S2. The intermediate product is thoroughly washed with deionized water, dried at 110 degrees Celsius, and ground to 80 mesh to obtain the adsorbent.

[0090] Comparative Example 6

[0091] The difference from Example 1 is that the pyrolysis temperature is 200 degrees Celsius.

[0092] Test case

[0093] The basic conditions of the test soil are shown in Table 1.

[0094] Table 1 Group Test items (mg / kg) Test results 1 Total lead (as Pb) 60 2 Total mercury (as Hg) 4 3 Total cadmium (as Cd) 17 4 Total arsenic (as As) 40 5 Total chromium (as Cr) 210

[0095] The heavy metal removal rates of the test examples and comparative examples are shown in Table 2.

[0096] Table 2 Group Total lead (as Pb) (mg / kg) Total mercury (as Hg) (mg / kg) Total cadmium (as Cd) (mg / kg) Total arsenic (as As) (mg / kg) Total chromium (as Cr) (mg / kg) Standard requirements ≤50 ≤2 ≤3 ≤15 ≤150 Example 1 16 0.1 1.8 7 42 Example 2 19 0.3 2.6 9 51 Example 3 16 0.4 2.5 10 55 Example 4 20 0.2 1.4 7 48 Example 5 18 0.5 1.3 8 44 Comparative Example 1 35 1 5 22 76 Comparative Example 2 22 1.2 3.5 18 54 Comparative Example 3 55 4 10 33 176 Comparative Example 4 26 0.9 3.2 15 73 Comparative Example 5 42 3 8 29 163 Comparative Example 6 24 2.1 5.4 17 89

[0097] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A rice planting method based on returning rice straw to the field, characterized in that, Includes the following steps: (1) Sow milkvetch 5-10 days before harvesting rice, and then crush the harvested rice straw and return it to the field; (2) Plow the milkvetch and milkvetch with pods that have grown to full bloom into the field with rice straw. After 30-50 days of plowing, apply base fertilizer and adsorbent, till the soil, then irrigate. After 5-10 days, transplant rice seedlings and plant rice.

2. The rice planting method based on returning rice straw to the field according to claim 1, characterized in that, In step (1), the stubble length of the harvested rice is 35-50cm, and the length of the crushed rice straw is 4-8cm.

3. The rice planting method based on returning rice straw to the field according to claim 1, characterized in that, The seeding rate of milkvetch in step (1) is 3-4.5 kg / mu.

4. The rice planting method based on returning rice straw to the field according to claim 1, characterized in that, The turning depth in step (2) is 25-30 cm, the rotary tillage depth in step (2) is 15-20 cm, the watering depth is 3-5 cm, the water depth is maintained at 3-5 cm during the transplanting of seedlings, the turning amount of milkvetch in step (2) is 1200-2300 kg / mu, and the turning amount of dried rice straw is 380-420 kg / mu.

5. The rice planting method based on returning rice straw to the field according to claim 1, characterized in that, The base fertilizer mentioned in step (2) includes 10-12 kg / mu of nitrogen fertilizer, 5.3-6.8 kg / mu of phosphorus fertilizer, and 6-9 kg / mu of potassium fertilizer.

6. The rice planting method based on returning rice straw to the field according to claim 1, characterized in that, The amount of adsorbent used in step (2) is 2.5-3.8 kg / mu.

7. The rice planting method based on returning rice straw to the field according to claim 1, characterized in that, The method for preparing the adsorbent in step (2) is as follows: S1. First, mix magnetic microalgae biochar and calcium nitrate solution at a mass-volume ratio of 1-3:200-500 until homogeneous. Then, add sodium dihydrogen phosphate dihydrate solution to adjust the pH of the system to 10-11. After stirring evenly, let it stand for 10-15 hours and then centrifuge to obtain the intermediate product. S2. The intermediate product is washed, dried, and ground, then mixed with xanthan gum and dispersed under ultrasonic assistance for 1-1.5 hours to obtain a mixture. S3. The mixture is added dropwise into a calcium nitrate solution, cross-linked and hardened for 8-12 hours to form composite microspheres, precipitated for 24-26 hours, washed with water, and freeze-dried to obtain the adsorbent.

8. The rice planting method based on returning rice straw to the field according to claim 7, characterized in that, The concentration of the calcium nitrate solution in step S1 is 0.5-1 mol / L, the concentration of the sodium dihydrogen phosphate dihydrate solution in step S1 is 0.5-0.8 mol / L, the mass ratio of the sodium dihydrogen phosphate dihydrate solution to the calcium nitrate solution in step S1 is 1:1.2-1.5, and the centrifugation speed in step S1 is 1000-2000 rap / min.

9. The rice planting method based on returning rice straw to the field according to claim 7, characterized in that, The drying temperature in step S2 is 90-120 degrees Celsius, and the mass ratio of xanthan gum to intermediate product in step S2 is 1:2-5.

10. The rice planting method based on returning rice straw to the field according to claim 7, characterized in that, The concentration of calcium nitrate in step S3 is 0.2-0.3 mol / L, the freeze-drying temperature is -60 degrees Celsius, and the freeze-drying time is 10-18 hours.