Preparation method of water-retention expanded compound organic fertilizer

Abstract

The invention discloses a preparation method of a water-retention expanded compound organic fertilizer, and relates to a preparation method of a compound organic fertilizer. The invention aims to solve the problem that the existing organic fertilizer has poor water retention or water storage capacity after improving soil. The preparation method comprises the following steps: carrying out hydrophobic treatment on attapulgite and humic acid, carrying out functional modification on the attapulgite by utilizing active functional groups such as carboxyl and phenolic hydroxyl of the humic acid, and compounding with an acrylic acid-acrylamide copolymer, a modified expanding agent, the humic acid, mushroom bran and the attapulgite to form the water-retaining expanded composite organic fertilizer. The surface of calcium carbide in the modified expanding agent is provided with a coating layer formed by xanthan gum, and after the modified expanding agent is applied to soil, the gel generates volume expansion, so that the water storage space is increased, and the water storage capacity is further improved. Due to the use of the expanding agent, the use amount of the acrylic acid acrylamide copolymer is remarkably reduced, the cost is remarkably reduced, and the expanding agent has relatively good practicability and can be popularized.

Description

Technical Field

[0001] The present invention relates to a preparation method of a compound organic fertilizer. Background Art

[0002] Drought disasters are one of the most serious natural disasters affecting the land. Due to the uneven distribution of water resources in time and space, the critical period of crop growth does not match the distribution of annual precipitation, resulting in significant seasonal drought characteristics in the agricultural field. Once it occurs, the impact on the social and economic system, especially on agricultural production, is extremely significant and cannot be underestimated. At the same time, after long-term high-intensity utilization and unreasonable tillage, some black soils have become "thin" and "less", with serious soil compaction and degradation, reduced soil fertility and productivity, and weakened resistance to drought and cold damage. Therefore, it is necessary to explore an agricultural management measure that can improve soil fertility, increase soil nutrient content, and enhance the drought resistance and moisture retention ability of black soils in Northeast China.

[0003] Agricultural superabsorbent resins play an irreplaceable role in water-saving agriculture and ecological restoration. As an efficient water-saving material, agricultural superabsorbent resins have a unique three-dimensional network structure, can absorb and store water, and show significant advantages in improving soil moisture, enhancing water resource utilization efficiency, and promoting crop growth. They have now become an important technical means in the fields of modern agriculture and ecological restoration.

[0004] In the agricultural field, the application of superabsorbent resins has significantly promoted the root development of crops such as corn and wheat, and increased the crop yields in arid and semi-arid regions. Early superabsorbent resins were mainly acrylic polymers, which had strong water absorption but high costs and were difficult to degrade, easily causing soil residues. In recent years, the research and development of biodegradable water-retaining agents has become a hot topic. Many studies usually incorporate some renewable resources and inexpensive natural substances into the resins. For example, environmentally friendly products based on natural polymers such as starch and cellulose not only have a high water absorption rate (up to hundreds of times their own weight), but also can be naturally degraded in the soil, reducing environmental pollution. In addition, composite superabsorbent resins further enhance the soil fertility regulation and disease resistance functions by adding mineral elements or microbial agents. For example, a water-retaining agent co-cultured with Bacillus subtilis can inhibit diseases such as tobacco black shank.

[0005] The water retention or water storage capacity of the soil improved by a single organic fertilizer is limited. Although the above-mentioned superabsorbent resins have significant effects in the fields of drought resistance and moisture retention, soil fixation and improvement, etc., the cost of such superabsorbent resins is high, making it difficult to promote their application on a large scale. Summary of the Invention

[0006] In order to solve the problem that the existing organic fertilizer has poor water retention or water storage capacity after improving the soil, the present invention provides a preparation method of a water-retaining expanded composite organic fertilizer.

[0007] The preparation method of the water-retaining expanded compound organic fertilizer of the present invention is carried out according to the following steps:

[0008] Step 1: Prepare a modified composite filler;

[0009] The preparation method of the modified composite filler is as follows: Mix dimethyl silicone oil, attapulgite clay and humic acid, then place them in a reaction kettle at 350-360 °C and react for 80-90 minutes. After the reaction is completed, cool down to room temperature, then transfer the reaction product to a ball mill for ball milling to obtain a 0.5-0.8 μm mixture, and finally dry it to obtain the modified composite filler;

[0010] The mass ratio of the dimethyl silicone oil, attapulgite clay and humic acid is 0.05:1:1-1.1;

[0011] Step 2: Place the container containing acrylic acid in a water bath environment, add sodium hydroxide solution to acrylic acid until the neutralization degree of acrylic acid reaches 80%; then add acrylamide and stir and react in the water bath environment for 5-10 minutes to obtain a reaction solution; Mix the modified composite filler obtained in Step 1 with the reaction solution, then add a modified swelling agent, N,N'-methylenebisacrylamide and ammonium persulfate, react for 2-6 minutes, and then add humic acid, mushroom bran and attapulgite clay, and continue to stir and react in the water bath environment for 60-70 minutes to obtain a primary water-retaining compound organic fertilizer;

[0012] The mass ratio of the acrylic acid, acrylamide and modified composite filler is 2-3:1:10;

[0013] The preparation method of the modified swelling agent is as follows: Mix calcium carbide, xanthan gum and methanol, and carry out ball milling in a ball mill under nitrogen protection. After the reaction is completed, air-dry to remove methanol; The mass ratio of calcium carbide, xanthan gum and methanol is 2-3:1:3;

[0014] The mass ratio of the acrylic acid, modified swelling agent, humic acid, mushroom bran and attapulgite clay is 0.05:0.08:7.5:2:2-2.5;

[0015] Step 3: Crush the primary water-retaining compound organic fertilizer to a particle size of 0.5-0.8 cm to obtain the water-retaining expanded compound organic fertilizer.

[0016] The principle and beneficial effects of the present invention are as follows:

[0017] After the present invention mixes dimethyl silicone oil, attapulgite, and humic acid and conducts a high-temperature reaction, the organic distillation products generated by humic acid at high temperature are fully miscible with dimethyl silicone oil and infiltrate into the pores of attapulgite and humic acid in the form of organic vapor at high temperature, realizing the hydrophobic treatment of attapulgite and humic acid, and using the active functional groups such as carboxyl groups and phenolic hydroxyl groups in humic acid to functionalize and modify attapulgite to obtain a modified composite filler; the modified composite filler is then compounded with polyacrylate acrylamide copolymer, modified expander, humic acid, mushroom bran, and attapulgite to form a water-retaining expanded composite organic fertilizer. The surface of calcium carbide in the modified expander has a coating layer formed by xanthan gum. After being applied to the soil, as the water in the soil infiltrates into the water-retaining expanded composite organic fertilizer, the coating layer formed by xanthan gum dissolves and exposes calcium carbide. Calcium carbide reacts with water to generate gas, which in turn causes the polyacrylate acrylamide copolymer gel to expand in volume, increasing its water storage space and thus improving the water storage capacity.

[0018] The present invention utilizes the fact that humic acid contains abundant active functional groups such as carboxyl groups and phenolic hydroxyl groups, which can form hydrogen bonds with water molecules, thereby increasing the water absorption of the fertilizer; the aromatic ring structure in humic acid also forms an interpenetrating network with mushroom bran cellulose through π-π stacking, further optimizing the pore distribution and synergistically enhancing the water retention ability, thus achieving a better water retention effect. Mushroom bran helps improve the water holding capacity of the fertilizer due to its porous structure; attapulgite has good cation exchange capacity and a large specific surface area, and its layered structure can adsorb a large amount of water molecules, having excellent water absorption and water retention characteristics. The hydrophobic treatment of attapulgite in the organic fertilizer improves the migration ability of water molecules in the organic fertilizer, improves the water storage efficiency and water capture efficiency of the organic fertilizer, increases the capillary porosity of the soil, and realizes efficient and rapid water storage.

[0019] The water-retaining composite organic fertilizer of the present invention is in a gel state after water absorption is stable. The hydrophobic treatment improves the migration ability of water molecules in the organic fertilizer, and the soil around the organic fertilizer forms a water flow channel due to the migration of a large number of water molecules, thereby increasing the capillary porosity of the soil and enhancing the water holding capacity of the soil. After the water-retaining composite organic fertilizer of the present invention is applied to the soil, it significantly improves the distribution of aggregates, and improves the soil's anti-erosion and nutrient storage capabilities.

[0020] In the present invention, functional components are introduced while acrylic acid and acrylamide are copolymerized, so that complex interpenetrating polymer network structures are formed between acrylic acid and acrylamide and functional components such as attapulgite and humic acid. The molecular chains penetrate each other inside the organic fertilizer, improving the stability and water retention capacity of the organic fertilizer; after the organic fertilizer of the present invention is applied to the soil, it combines with soil particles, improves the soil aggregate structure, increases the soil porosity, promotes the formation of aggregate structure, reduces soil compaction, effectively reduces the soil bulk density, improves the soil structure, and enhances the soil fertility.

[0021] The use of the swelling agent of the present invention significantly reduces the dosage of acrylic acid-acrylamide copolymer, significantly reduces the cost, and has good practicability and popularization potential. Description of the Drawings

[0022] Figure 1 Micrograph of the water-retaining composite organic fertilizer prepared in Example 1;

[0023] Figure 2 Curve graph of the soil water retention rate of the water-retaining composite organic fertilizer. Detailed Embodiments

[0024] The technical solution of the present invention is not limited to the following specific embodiments listed, and also includes any reasonable combination between the specific embodiments.

[0025] Specific Embodiment 1: The preparation method of the water-retaining swelling composite organic fertilizer in this embodiment is carried out according to the following steps:

[0026] Step 1: Prepare a modified composite filler;

[0027] The preparation method of the modified composite filler is as follows: Mix dimethyl silicone oil, attapulgite clay and humic acid, then place them in a reaction kettle at 350-360 °C for reaction for 80-90 minutes. After the reaction is completed, cool down to room temperature, and then transfer the reaction product to a ball mill for ball milling to obtain a 0.5-0.8 μm mixture, and finally dry it to obtain the modified composite filler;

[0028] The mass ratio of the dimethyl silicone oil, attapulgite clay and humic acid is 0.05:1:1-1.1;

[0029] Step 2: Place the container containing acrylic acid in a water bath environment, add sodium hydroxide solution to acrylic acid until the neutralization degree of acrylic acid reaches 80%; then add acrylamide, and stir and react in the water bath environment for 5-10 minutes to obtain a reaction solution; Mix the modified composite filler obtained in Step 1 with the reaction solution, then add a modified swelling agent, N,N'-methylenebisacrylamide and ammonium persulfate, react for 2-6 minutes, and then add humic acid, mushroom bran and attapulgite clay, and continue to stir and react in the water bath environment for 60-70 minutes to obtain a primary water-retaining composite organic fertilizer;

[0030] The mass ratio of the acrylic acid, acrylamide and the modified composite filler is 2-3:1:10;

[0031] The preparation method of the modified swelling agent is as follows: Mix calcium carbide, xanthan gum and methanol, and carry out ball milling in a ball mill under nitrogen protection. After the reaction is completed, air-dry to remove methanol; The mass ratio of calcium carbide, xanthan gum and methanol is 2-3:1:3;

[0032] The mass ratio of the acrylic acid, modified swelling agent, humic acid, mushroom bran, and attapulgite clay is 0.1:0.08:7.5:2:2 to 2.5;

[0033] Step 3: Crush the primary water-retaining composite organic fertilizer to a particle size of 0.5 - 0.8 cm to obtain the water-retaining expanded composite organic fertilizer.

[0034] In this embodiment, after mixing dimethyl silicone oil, attapulgite clay, and humic acid for high-temperature reaction, the organic distillation products generated by humic acid at high temperature are fully miscible with dimethyl silicone oil and infiltrate into the pores of attapulgite clay and humic acid in the form of organic vapor at high temperature, realizing the hydrophobic treatment of attapulgite clay and humic acid, and using the active functional groups such as carboxyl groups and phenolic hydroxyl groups in humic acid to functionalize and modify attapulgite clay to obtain a modified composite filler; the modified composite filler is then compounded with acrylate-acrylamide copolymer, modified swelling agent, humic acid, mushroom bran, and attapulgite clay to form a water-retaining expanded composite organic fertilizer. The surface of calcium carbide in the modified swelling agent has a coating layer formed by xanthan gum. After being applied to the soil, as the water in the soil infiltrates into the water-retaining expanded composite organic fertilizer, the coating layer formed by xanthan gum dissolves to expose calcium carbide, and calcium carbide reacts with water to generate gas, which in turn causes the acrylate-acrylamide copolymer gel to expand in volume, increasing its water storage space and thus improving the water storage capacity.

[0035] In this embodiment, humic acid contains rich active functional groups such as carboxyl groups and phenolic hydroxyl groups that can form hydrogen bonds with water molecules, thereby increasing the water absorption of the fertilizer; the aromatic ring structure in humic acid also forms an interpenetrating network with mushroom bran cellulose through π-π stacking, further optimizing the pore distribution and synergistically enhancing the water retention ability, thus achieving a better water retention effect. Mushroom bran has a porous structure that helps improve the water holding capacity of the fertilizer; attapulgite clay has good cation exchange capacity and a large specific surface area, and its layered structure can adsorb a large amount of water molecules, having excellent water absorption and water retention characteristics. The hydrophobic treatment of attapulgite clay in the organic fertilizer improves the migration ability of water molecules in the organic fertilizer, improves the water storage efficiency and water capture efficiency of the organic fertilizer, increases the capillary porosity of the soil, and realizes efficient and rapid water storage.

[0036] In this embodiment, the water-retaining composite organic fertilizer is in a gel state after water absorption is stable. The hydrophobic treatment improves the migration ability of water molecules in the organic fertilizer, and the soil around the organic fertilizer forms a water flow channel due to the migration of a large number of water molecules, thereby increasing the capillary porosity of the soil and enhancing the water holding capacity of the soil. After the water-retaining composite organic fertilizer of this embodiment is applied to the soil, it significantly improves the distribution of aggregates and enhances the soil's anti-erosion and nutrient storage capabilities.

[0037] In this embodiment, functional components are introduced while acrylic acid and acrylamide are copolymerized, forming a complex interpenetrating polymer network structure between acrylic acid, acrylamide and functional components such as attapulgite and humic acid. The molecular chains penetrate each other inside the organic fertilizer, improving the stability and water retention capacity of the organic fertilizer. After the organic fertilizer of this embodiment is applied to the soil, it combines with soil particles, improves the soil aggregate structure, increases the soil porosity, promotes the formation of aggregate structure, reduces soil compaction, effectively reduces the soil bulk density, improves the soil structure, and enhances the soil fertility.

[0038] The use of the swelling agent in this embodiment significantly reduces the dosage of the acrylic acid-acrylamide copolymer, significantly reduces the cost, and has good practicability and popularization.

[0039] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that: the particle size of the attapulgite described in Step 1 is 75-100 μm.

[0040] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that: the drying process described in Step 1 is: drying at 30°C to 40°C for 1-1.5 h.

[0041] Specific Embodiment 4: The difference between this embodiment and any one of Specific Embodiments 1 to 3 is that: the mass ratio of dimethyl silicone oil, attapulgite and humic acid described in Step 1 is 0.05:1:1.05.

[0042] Specific Embodiment 5: The difference between this embodiment and any one of Specific Embodiments 1 to 4 is that: the mass ratio of acrylic acid, acrylamide and modified composite filler described in Step 2 is 2.5:1:10.

[0043] Specific Embodiment 6: The difference between this embodiment and any one of Specific Embodiments 1 to 5 is that: the addition amount of N,N'-methylenebisacrylamide described in Step 2 is 1.5% of the mass of acrylic acid, and the addition amount of ammonium persulfate is 2% of the mass of acrylic acid.

[0044] Specific Embodiment 7: The difference between this embodiment and any one of Specific Embodiments 1 to 6 is that: the preparation method of the modified swelling agent described in Step 2 is: mixing calcium carbide, xanthan gum and methanol, and carrying out ball milling in a ball mill under nitrogen protection, and air-drying to remove methanol after the reaction; the mass ratio of calcium carbide, xanthan gum and methanol is 2.5:1:3.

[0045] Specific Embodiment 8: The difference between this embodiment and any one of Specific Embodiments 1 to 7 is that: the mass fraction of the sodium hydroxide solution described in Step 2 is 30% to 45%.

[0046] Embodiment 9 in detail: The difference between this embodiment and any one of Embodiments 1 to 8 is that: the temperature of the water bath environment in Step 2 is 35°C to 40°C.

[0047] Embodiment 10 in detail: The difference between this embodiment and any one of Embodiments 1 to 9 is that: the particle size of the attapulgite clay in Step 2 is 75 to 100 μm.

[0048] Example 1:

[0049] The preparation method of the water-retaining expanded compound organic fertilizer in this example is carried out according to the following steps:

[0050] Step 1, prepare a modified composite filler;

[0051] The preparation method of the modified composite filler is: mix dimethyl silicone oil, attapulgite clay and humic acid, then place them in a reaction kettle at 355°C for reaction for 90 minutes, cool to room temperature after the reaction, and then transfer the reaction product to a ball mill for ball milling to obtain a 0.5-0.8 μm mixture, and finally dry it to obtain the modified composite filler;

[0052] The mass ratio of the dimethyl silicone oil, attapulgite clay and humic acid is 0.05:1:1;

[0053] The particle size of the attapulgite clay in Step 1 is 75 to 100 μm;

[0054] The drying process is: drying at 30°C for 1.5 hours;

[0055] Step 2, place the container containing acrylic acid in a water bath environment, add sodium hydroxide solution to acrylic acid until the neutralization degree of acrylic acid reaches 80%; then add acrylamide, stir and react in the water bath environment for 8 minutes to obtain a reaction solution; mix the modified composite filler obtained in Step 1 with the reaction solution, and then add a modified swelling agent, N,N'-methylenebisacrylamide and ammonium persulfate, react for 4 minutes and then add humic acid, mushroom bran and attapulgite clay, and continue to stir and react in the water bath environment for 65 minutes to obtain a primary water-retaining compound organic fertilizer;

[0056] The mass ratio of the acrylic acid, acrylamide and the modified composite filler is 2.5:1:10;

[0057] The addition amount of N,N'-methylenebisacrylamide is 1.5% of the mass of acrylic acid, and the addition amount of ammonium persulfate is 2% of the mass of acrylic acid;

[0058] The preparation method of the modified swelling agent is: mix calcium carbide, xanthan gum and methanol, and carry out ball milling in a ball mill under nitrogen protection, and air dry to remove methanol after the reaction; the mass ratio of calcium carbide, xanthan gum and methanol is 2.5:1:3;

[0059] The mass ratio of the acrylic acid, modified swelling agent, humic acid, mushroom residue, and attapulgite is 0.1:0.08:7.5:2:2.5;

[0060] The mass fraction of the sodium hydroxide solution is 45%;

[0061] The temperature of the water bath environment is 35°C;

[0062] The particle size of the attapulgite is 75 - 100 μm.

[0063] Step 3: Crush the primary water-retaining composite organic fertilizer to a particle size of 0.5 - 0.8 cm to obtain the water-retaining swelling composite organic fertilizer.

[0064] Comparative example:

[0065] The preparation method of the water-retaining swelling composite organic fertilizer in this comparative example is as follows: Place the container containing acrylic acid in a water bath environment, add a sodium hydroxide solution to the acrylic acid until the neutralization degree of the acrylic acid reaches 80%; then add acrylamide, humic acid, mushroom residue, and attapulgite. After the reactants become uniformly pasty, add 1.5% of N,N'-methylenebisacrylamide and 2.0% of ammonium persulfate based on the mass of acrylic acid, and stir and react in a water bath environment at 35°C for 65 minutes. Take out the polymer obtained after the reaction, dry it in an oven at 70°C until it reaches a constant weight, and crush it to obtain the water-retaining composite organic fertilizer.

[0066] The mushroom residue used in the present invention is the remaining culture medium after cultivating edible fungi using corn straw as the culture medium and harvesting the edible fungi. The above experiments were all carried out in the experimental field of Xinglong Township, Wuchang City. The active accumulated temperature is 2700 - 2800°C; the planting variety is the corn variety Qi 302, and the application rate of the organic fertilizer is 100 kg / 667 m 2 .

[0067] Performance and characterization tests of the water-retaining composite organic fertilizer:

[0068] 1. Determination of water absorption ratio

[0069] Accurately weigh 0.50 g of the water-retaining composite organic fertilizer sample into a beaker, add sufficient distilled water, and let it stand at room temperature until the sample is saturated with water absorption. Then, filter out the unabsorbed water using filter paper, weigh it, and calculate the water absorption ratio Q (g / g); repeat the test 10 times. After each measurement, dry it at a constant temperature of 60°C until it reaches a constant weight and then conduct the next test, and take the average value.

[0070]

[0071] In this formula, M is the total mass (g) of the water-saturated sample, m1 is the mass (g) of the initial water-retaining composite organic fertilizer, and m2 is the weight (g) of the filter paper.

[0072] The average water absorption ratio of the water-retaining composite organic fertilizer prepared in Example 1 was 140.24 g / g; while the average water absorption ratio of the comparative example was only 74.11 g / g. After repeating the test 10 times, the fluctuation of the water absorption ratio of the water-retaining composite organic fertilizer prepared in Example 1 did not exceed 5%, showing good repeated water absorption ability, and thus having good water absorption stability.

[0073] 2. Determination of soil water retention capacity: Measure the actual soil water retention rate, bulk density, actual soil water content and capillary porosity two months after sowing.

[0074] ①. Take the soil and put it in a beaker, add 100 g of distilled water, and record the total mass as m0; after standing for 12 h, transfer it to a constant temperature oven at 50 °C and weigh it every day and record it as m.

[0075]

[0076] ②. Use the cutting ring method to take soil. Put the cutting ring and the soil in the cutting ring into a beaker, add distilled water until the soil sample reaches water absorption saturation, and then control the water of the saturated soil for 8 hours until all the gravitational water is lost, and weigh it again. At this time, the water absorption of the soil sample is the field water holding capacity; repeat the measurement 5 times and take the average value.

[0077]

[0078] In this formula, D is the field water holding capacity, g·cm -3 ; m3 is the total weight of the cutting ring and the soil, g; m4 is the weight of the cutting ring, g; V is the volume of the cutting ring, cm 3 .

[0079] ③. Dry the cutting ring and the soil in the cutting ring that have reached water absorption saturation, and test the capillary porosity of the soil.

[0080]

[0081] In this formula, Pc is the capillary porosity, %; m4 is the weight of the cutting ring, g; m5 is the total weight of the cutting ring and the soil when the soil sample reaches water absorption saturation, g; m6 is the total weight of the cutting ring and the soil after drying, g.

[0082] The bulk density of the soil in Example 1 was 0.54 - 0.66 g·cm -3 , and the bulk density of the soil in Comparative Example 1 was 0.71 - 0.83 g·cm -3 . The field water holding capacity of the soil in Example 1 was 52%, while the field water holding capacity of the soil in Comparative Example 1 was 45.31%. As Figure 2The 30-day soil water retention rate of the soil added with the water-retaining composite organic fertilizer prepared in Example 1 reached 57%, while the 30-day soil water retention rate of the soil added with the organic fertilizer in Comparative Example 1 was only 40.1%. The capillary porosity of the soil added with the water-retaining composite organic fertilizer prepared in Example 1 reached 49%, while the capillary porosity of the soil added with the organic fertilizer in Comparative Example 1 was only 41%.

[0083] 3. Determination of soil organic carbon: Measure the actual soil organic carbon content two months after sowing, and use the potassium dichromate-external heating method for determination; the organic carbon content of the soil added with the water-retaining composite organic fertilizer prepared in Example 1 was 27.11 g·kg -1 , while the soil added with the organic fertilizer in Comparative Example 1 was only 20.63 g·kg -1 .

[0084] 4. Aggregate determination:

[0085] Use the wet sieving method to screen the water-stable aggregates, which are divided into four particle sizes: >2 mm (coarse aggregates), 0.25 - 2 mm (fine-large aggregates), 0.053 - 0.25 mm (micro-aggregates) and <0.053 mm (silt and clay particles). Weigh the masses of the four components respectively, and calculate the mass percentage content of soil aggregates in different particle sizes.

[0086] After testing, the content of <0.053 mm aggregates in Example 1 was 2.25% - 5.66%. The content of 0.053 - 0.25 mm aggregates was 5.75% - 8.47%. The content of 0.25 - 2 mm aggregates was 10.52%, and the rest were >2 mm aggregates; while in Comparative Example 1, the content of <0.053 mm aggregates was 11.12% - 15.39%. The content of 0.053 - 0.25 mm aggregates was 13.47% - 16.31%.

[0087] 5. Saturated hydraulic conductivity: Use the constant head method. After the core soil sample is fully saturated in distilled water, a stable water head is provided by a Mariotte bottle, and the water head height is maintained at 5 cm. After starting to supply water, wait for the outflow rate to stabilize and then start timing. Record the outflow volume Q within a certain period of time, and then derive the formula for the soil saturated hydraulic conductivity Ks according to Darcy's law Q = KIA:

[0088]

[0089] In the formula, Ks is the soil saturated hydraulic conductivity, mm·min -1 ; 10 is the conversion rate from cm to mm; Q is the outflow volume within a certain period of time, ml; L is the core height, cm; H is the sum of the water head height and the core height, cm; A is the cross-sectional area of the core, cm 2 ; t is the measurement time, min.

[0090] After the water-retaining compound organic fertilizer in Example 1 was applied to the soil, the saturated hydraulic conductivity reached 2.75 - 3.70 mm·min -1 , which can significantly improve the problem of soil compaction. The saturated hydraulic conductivity of the soil added with the organic fertilizer in Comparative Example 1 was 2.55 - 2.87 mm·min -1 .

Claims

1. A preparation method of a water-retaining expanded compound organic fertilizer, characterized in that: The preparation method of the water-retaining expanded compound organic fertilizer is carried out according to the following steps: Step 1, prepare a modified composite filler; The preparation method of the modified composite filler is: mix dimethyl silicone oil, attapulgite clay and humic acid, then place them in a reaction kettle at 350-360 °C for reaction for 80-90 min. After the reaction, cool down to room temperature, and then transfer the reaction product to a ball mill for ball milling to obtain a 0.5-0.8 μm mixture, and finally dry it to obtain the modified composite filler; The mass ratio of the dimethyl silicone oil, attapulgite clay and humic acid is 0.05:1:1-1.1; Step 2, place the container containing acrylic acid in a water bath environment, add sodium hydroxide solution to acrylic acid until the neutralization degree of acrylic acid reaches 80%; then add acrylamide and stir and react in the water bath environment for 5-10 min to obtain a reaction solution; mix the modified composite filler obtained in Step 1 with the reaction solution, then add a modified swelling agent, N,N'-methylenebisacrylamide and ammonium persulfate, react for 2-6 min, and then add humic acid, mushroom bran and attapulgite clay, and continue to stir and react in the water bath environment for 60-70 min to obtain a primary water-retaining compound organic fertilizer; The mass ratio of the acrylic acid, acrylamide and modified composite filler is 2-3:1:10; The preparation method of the modified swelling agent is: mix calcium carbide, xanthan gum and methanol, and carry out ball milling in a ball mill under nitrogen protection. After the reaction, air-dry to remove methanol; the mass ratio of calcium carbide, xanthan gum and methanol is 2-3:1:3; The mass ratio of the acrylic acid, modified swelling agent, humic acid, mushroom bran and attapulgite clay is 0.1:0.08:7.5:2:2-2.5; Step 3, crush the primary water-retaining compound organic fertilizer to a particle size of 0.5-0.8 cm to obtain the water-retaining expanded compound organic fertilizer.

2. The preparation method of the water-retaining expanded compound organic fertilizer according to claim 1, characterized in that: The particle size of the attapulgite clay in Step 1 is 75-100 μm.

3. The preparation method of the water-retaining expanded compound organic fertilizer according to claim 1, characterized in that: The drying process in Step 1 is: dry at 30 °C - 40 °C for 1-1.5 h.

4. The preparation method of the water-retaining expanded compound organic fertilizer according to claim 1, characterized in that: The mass ratio of the dimethyl silicone oil, attapulgite clay and humic acid in Step 1 is 0.05:1:1.

05.

5. The preparation method of the water-retaining expanded compound organic fertilizer according to claim 1, wherein: The mass ratio of the acrylic acid, acrylamide and modified composite filler in Step 2 is 2.5:1:

10.

6. The preparation method of the water-retaining expanded compound organic fertilizer according to claim 1, wherein: The addition amount of N,N'-methylenebisacrylamide in Step 2 is 1.5% of the mass of acrylic acid, and the addition amount of ammonium persulfate is 2% of the mass of acrylic acid.

7. The preparation method of the water-retaining expanded compound organic fertilizer according to claim 1, wherein: The preparation method of the modified swelling agent in Step 2 is: mix calcium carbide, xanthan gum and methanol, and carry out ball milling in a ball mill under nitrogen protection. After the reaction, air-dry to remove methanol; the mass ratio of calcium carbide, xanthan gum and methanol is 2.5:1:

3.

8. The preparation method of the water-retaining expanded compound organic fertilizer according to claim 1, characterized in that: The mass fraction of the sodium hydroxide solution in Step 2 is 30% - 45%.

9. The preparation method of the water-retaining expanded compound organic fertilizer according to claim 1, characterized in that: The temperature of the water bath environment in Step 2 is 35 °C - 40 °C.

10. The preparation method of the water-retaining expanded compound organic fertilizer according to claim 1, characterized in that: The particle size of the attapulgite clay in Step 2 is 75-100 μm.

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