Preparation method of intelligent controlled-release fertilizer driven by water to open iron switch

Abstract

The application relates to the technical field of soil improvement, and discloses a preparation method of intelligent controlled-release fertilizer driven by water-driven iron switch. The controlled-release fertilizer is of a core-shell structure, wherein the core is a porous carrier loaded with nutrient elements, and the core shell is an iron mineral film layer. The controlled-release fertilizer provided by the application loads the nutrient elements on the porous carrier, and then coats the iron mineral film layer on the outside of the carrier. The controlled-release fertilizer can combine with soil moisture conditions, induce soil microorganisms to change the pore size of the iron mineral film layer on the material surface, thereby regulating the release rate of the nutrient elements and promoting the efficient utilization of the nutrient elements. Meanwhile, the porous carrier has the functions of keeping soil moisture and increasing soil pores, so that the controlled-release fertilizer can also optimize soil structure, and enhance soil aeration and water retention. The raw material of the controlled-release fertilizer is easy to obtain, the cost is low, the controlled-release fertilizer is environment-friendly, the preparation method is simple, energy consumption is low, no solid waste is generated, and the controlled-release fertilizer is suitable for popularization and use.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soil improvement, in particular to a preparation method of intelligent controlled-release fertilizer using water-driven iron switch. BACKGROUND

[0002] Fertilizer is an important source of nutrients for crop growth, and its input accounts for about 50% of the total agricultural production input, and is an important part of agricultural production. Fertilizer is easy to lose in farmland, in order to ensure that crops can fully obtain nutrients, a large amount of fertilizer needs to be applied, which leads to the problem of over-fertilization, which not only causes resource waste, but also causes a series of environmental problems such as non-point source pollution and soil compaction. Therefore, developing smart agriculture and developing an efficient and low-cost intelligent fertilizer is of great significance to promote the development of high-quality agriculture.

[0003] Controlled-release fertilizer is a kind of fertilizer that changes the release rate of effective components in fertilizer through physical, chemical or biological methods to meet the long-term nutrient needs of agricultural crops. Most of the existing controlled-release fertilizers cannot balance safety, harmlessness and low cost. For example, CN 109928823A discloses a preparation method of a coated controlled-release fertilizer. The technical solution uses polyvinyl alcohol and methyl cellulose and other materials to prepare an organic controlled-release coating, which has good effect, but the use of polyvinyl alcohol and other non-degradable organic matters in farmland soil may cause a series of environmental negative effects; CN 116425588 A discloses a microelement amino acid chelate / urea-formaldehyde controlled-release fertilizer and its reaction extrusion preparation. The technical solution uses plant oil and starch as basic materials for coating, which has the advantage of being green and environmentally friendly, but the raw materials are more expensive than general materials. In addition, crops have different nutrient needs under different environmental conditions, and most of the existing controlled-release fertilizers can only slow down the release rate of nutrients in disorder, and cannot control the release of nutrients according to the growth of crops and nutrient needs. SUMMARY

[0004] The present application aims to solve at least one of the above technical problems in the prior art. To this end, one of the purposes of the present application is to provide a controlled-release fertilizer; the second purpose of the present application is to provide a preparation method of the controlled-release fertilizer; and the third purpose of the present application is to provide an application of the controlled-release fertilizer.

[0005] In order to achieve the above-mentioned purposes, the technical solution adopted by the present application is:

[0006] The first aspect of the present application provides a controlled-release fertilizer, which has a core-shell structure, wherein the core is a porous carrier loaded with nutrient elements, and the shell is an iron mineral film layer.

[0007] In some embodiments of the present application, the porous carrier is selected from at least one of diatomite, bentonite, zeolite, montmorillonite, expanded vermiculite, sepiolite or attapulgite.

[0008] In some embodiments of the present application, the porous carrier is diatomite.

[0009] In some embodiments of the present application, the particle size of the porous carrier is less than 50 μm.

[0010] In some embodiments of the present application, the particle size of the porous carrier is less than 48 μm.

[0011] In some embodiments of the present application, the water content of the porous carrier is 60%-80%.

[0012] In some embodiments of the present application, the water content of the porous carrier is 60%-75%.

[0013] In some embodiments of the present application, the nutrient element includes at least one of an essential nutrient element and a beneficial nutrient element required for plant growth.

[0014] In some embodiments of the present application, the essential nutrient element includes at least one of zinc, phosphorus, and potassium.

[0015] In some embodiments of the present application, the essential nutrient element is phosphorus and potassium.

[0016] In some embodiments of the present application, the beneficial nutrient element includes selenium.

[0017] In some embodiments of the present application, the slow-release fertilizer includes the following raw materials: a porous carrier, a ferrous salt, a binder, a microbial activation induction auxiliary agent, a nutrient element salt, water, and a lye.

[0018] In some embodiments of the present application, the ferrous salt is selected from at least one of ferrous sulfate, ferrous chloride, ferrous perchlorate, ferrous ammonium sulfate, and ferrous oxalate.

[0019] In some embodiments of the present application, the concentration of the binder is 0.5wt%-1.5wt%.

[0020] In some embodiments of the present application, the binder is selected from at least one of chromatographic silica gel and silica sol.

[0021] In some embodiments of the present application, the concentration of the microbial activation induction auxiliary agent is 1.5wt%-2.5wt%.

[0022] In some embodiments of the present application, the microbial activation induction auxiliary agent is selected from at least one of glucose, sodium acetate, and sodium lactate.

[0023] In some embodiments of the present application, the microbial activation induction adjuvant is used to assist in inducing the activation of iron-reducing bacteria in the soil.

[0024] In some embodiments of the present application, the nutrient element salt comprises phosphate, inorganic selenium salt, inorganic zinc salt.

[0025] In some embodiments of the present application, the phosphate comprises diammonium hydrogen phosphate, dipotassium hydrogen phosphate, monopotassium phosphate, tripotassium phosphate, superphosphate, monocalcium phosphate.

[0026] In some embodiments of the present application, the inorganic selenium salt comprises sodium selenite, potassium selenate, potassium selenite.

[0027] In some embodiments of the present application, the inorganic zinc salt comprises zinc sulfate, zinc nitrate, zinc chloride, zinc carbonate.

[0028] In some specific embodiments of the present application, the nutrient element salt is monopotassium phosphate or sodium selenate.

[0029] In some embodiments of the present application, the concentration of the lye is 5-10 mol / L.

[0030] In some embodiments of the present application, the alkali source of the lye comprises alkali metal hydroxide, alkali metal carbonate, alkali metal bicarbonate.

[0031] In some embodiments of the present application, the alkali source of the lye is selected from at least one of sodium bicarbonate, sodium carbonate, potassium hydroxide, sodium hydroxide.

[0032] In some embodiments of the present application, the mass ratio of the porous carrier, the binder, the microbial activation induction adjuvant, the nutrient element salt, the ferrous salt, and water is (400-600):(10-20):(20-30):(1-300):(40-60):1000.

[0033] In some specific embodiments of the present application, the mass ratio of the porous carrier, the binder, the microbial activation induction adjuvant, the nutrient element salt, the ferrous salt, and water is (450-550):(10-15):(22-28):(1-300):(45-55):1000.

[0034] In some specific embodiments of the present application, when the nutrient element salt is phosphate, the mass ratio of the porous carrier, the binder, the microbial activation induction adjuvant, the nutrient element salt, the ferrous salt, and water is (450-550):(10-15):(22-28):(220-290):(45-55):1000.

[0035] In some embodiments of the present application, when the nutrient element salt is an inorganic selenium salt, the mass ratio of the porous carrier, the binder, the microbial activation induction auxiliary agent, the nutrient element salt, the ferrous salt, and water is (450-550):(10-15):(22-28):(1-2):(45-55):1000.

[0036] The second aspect of the present application provides a preparation method of the controlled-release fertilizer according to the first aspect of the present application, comprising the following steps:

[0037] S1, dissolving the nutrient element salt in water, adding the binder and the microbial activation induction auxiliary agent, and then adding the porous carrier in batches to obtain the porous carrier loaded with the nutrient element;

[0038] S2, adding the ferrous salt, adjusting the pH of the system to 6.8-7.2 by adding alkali solution, solid-liquid separation, and collecting the solid phase to obtain the controlled-release fertilizer.

[0039] In some embodiments of the present application, the temperature for dissolving the nutrient element salt in water is 20-30℃.

[0040] In some embodiments of the present application, when the nutrient element salt is a phosphate salt, the phosphate salt needs to be dissolved in water and in a supersaturated state, and the precipitation is generated and does not disappear after stirring for 5-10 min.

[0041] In some embodiments of the present application, the process of dissolving the nutrient element salt is assisted by stirring; and the stirring speed is 150-200 rpm.

[0042] In some embodiments of the present application, the process of adding the binder and the microbial activation induction auxiliary agent is assisted by stirring; the stirring speed is 150-200 rpm, and the stirring time is 8-15 min.

[0043] In some embodiments of the present application, the process of adding the porous carrier is assisted by stirring; and the stirring speed is 80-120 rpm.

[0044] In some embodiments of the present application, the batch addition amount of the porous material is 1 / 5-1 / 4 of the total amount.

[0045] In some embodiments of the present application, the interval time of batch addition of the porous material is 3-8 min.

[0046] In some embodiments of the present application, after the addition of the porous material is completed, a step of stirring for 25-35 min is further included.

[0047] In some embodiments of the present application, the porous material is pretreated before use, and the pretreatment comprises the following steps: sieving the porous material to remove impurities, washing the porous material with deionized water to remove soluble ions, and filtering the porous material to remove water.

[0048] In some embodiments of the present application, the process of adding ferrous salt is assisted by stirring, and the stirring speed is 180-220 rpm.

[0049] In some embodiments of the present application, the alkali solution is added at a speed of (5-15) mL / min.

[0050] In some embodiments of the present application, after the solid phase is collected, the process further comprises the steps of filtering and drying.

[0051] In some embodiments of the present application, the drying temperature is greater than or equal to 25℃.

[0052] The third aspect of the present application provides the application of the controlled-release fertilizer of the first aspect of the present application in soil improvement.

[0053] In some embodiments of the present application, the soil improvement comprises supplementing nutritional elements, enhancing soil aeration, and enhancing water retention.

[0054] The principle of the soil improvement of the controlled-release fertilizer of the present application is as follows:

[0055] 1) The present application uses porous materials such as diatomite as carriers, and fixes nutrients such as selenium, zinc, phosphorus, and potassium required for plant growth in the pores and surfaces of the carriers, and forms an iron mineral film layer by the secondary mineral precipitation formed by the oxidation of ferrous iron, which wraps the porous carrier loaded with nutrients to form a controlled-release fertilizer. The iron mineral film layer formed by the oxidation of ferrous iron can directionally control the release rate of nutrients according to the water content of the environment. Specifically, in an anaerobic environment with high water content (50%-100%), especially in a flooded environment, the biological iron reduction process is enhanced, the iron mineral film layer is gradually eroded by microorganisms to form a large number of pores, resulting in rapid release of nutrients in the controlled-release fertilizer; in soil with low water content (<50%), especially after drainage, the iron oxidation process is enhanced, and the oxidation of ferrous iron causes the iron mineral film layer to be reformed and the pores to be blocked, resulting in a significant decrease in nutrient release.

[0056] 2) The surface of the porous material has a three-dimensional pore structure, which, combined with silica gel with chelation and adhesion, can fix a large amount of nutrients, promote the long-term release and persistent application of nutrients in the soil, and further supplement iron elements for the soil in the dissolution process of the iron mineral film layer on the surface of the controlled-release fertilizer.

[0057] 3) Slow-release fertilizer uses porous materials such as diatomaceous earth as the core carrier, which has the advantages of maintaining soil moisture and increasing soil porosity. Therefore, in addition to providing nutrients, this slow-release fertilizer can also improve the physical and chemical properties of the soil and enhance soil vitality during use. That is, the slow-release fertilizer provided by this invention can simultaneously achieve the directional regulation and release of nutrients and the improvement of soil physical and chemical properties, thereby achieving soil improvement.

[0058] In some embodiments of the present invention, the physicochemical properties of the soil include at least one of the following:

[0059] 1) pH is 4-8;

[0060] 2) The cation exchange capacity is 5-30 cmol / kg;

[0061] 3) The total organic matter content is 10-50 g / kg;

[0062] 4) Total iron content is 50-300g / kg.

[0063] In some embodiments of the present invention, soil is classified into high moisture content soil (50%-100% moisture content) and low moisture content soil (<50% moisture content) according to its moisture content.

[0064] In some embodiments of the present invention, the amount of the controlled-release fertilizer is 10-50 kg / mu.

[0065] Compared with the prior art, the beneficial effects of the present invention are:

[0066] 1) The controlled-release fertilizer provided by this invention has nutrients loaded onto a porous carrier, and the carrier is coated with an iron mineral membrane. This controlled-release fertilizer can, in combination with soil moisture conditions, induce soil microorganisms to change the pore size of the iron mineral membrane on the surface of the material, thereby regulating the release rate of nutrients and promoting the efficient utilization of nutrients. At the same time, because the porous carrier has the function of retaining soil moisture and increasing soil porosity, this controlled-release fertilizer can also optimize soil structure and enhance soil aeration and water retention.

[0067] 2) The method for preparing controlled-release fertilizer provided by this invention uses readily available raw materials, is low in cost, is environmentally friendly, is simple to prepare, consumes little energy, does not generate solid waste, and is suitable for widespread use.

[0068] 3) The controlled-release fertilizer provided by this invention is applied to soil improvement. Because the mineral membrane has water-responsive characteristics, the release rate of nutrients can be adjusted according to the water content in the soil. This can not only improve the utilization rate of nutrients, avoid excessive fertilization, save resources, and reduce the adverse effects of excessive fertilization on the soil, but also enhance soil aeration and water retention by utilizing the special structure of the porous carrier. Attached Figure Description

[0069] Figure 1 SEM images of diatomite (a) and diatomite-iron mineral film layer composite (b) in Example 1;

[0070] Figure 2 Ferrous ion concentration change graph of different reaction stages in Example 1;

[0071] Figure 3 SEM images of slow / controlled release fertilizer in Example 2;

[0072] Figure 4 Kinetic change graph of dissolved selenium (a) and organically bound selenium (b) of different reaction stages in Example 2;

[0073] Figure 5 SEM images of slow / controlled release fertilizer in Example 3;

[0074] Figure 6 Kinetic change graph of hydrochloric acid extractable phosphorus (a) and available phosphorus (b) of different reaction stages in Example 3. DETAILED DESCRIPTION

[0075] The content of the present application is further described in detail through specific examples. The raw materials, reagents or devices used in the examples, unless otherwise specified, can be obtained from conventional commercial channels or can be obtained by existing technical methods. Unless otherwise specified, the test or test method is a conventional method in the art.

[0076] Example 1

[0077] In this example, a diatomite-iron mineral film layer composite without nutrient elements is prepared. By changing the culture conditions of the system, the periodic changes of anaerobic-aerobic conditions caused by changes of high and low water conditions in the soil are simulated. By measuring the change of ferrous ion concentration, the change of iron mineral film layer is evaluated to evaluate whether the release rate of nutrients can be regulated by changing the water condition. The specific steps are as follows:

[0078] (1) Iron-reducing bacteria culture:

[0079] The iron-reducing bacteria Shewanella oneidensis MR-1 (abbreviated as MR-1) is purchased from the China Marine Microbial and Enzyme Center, with the preservation number 1A01706, and is stored in a -80℃ refrigerator.

[0080] Prepare 200 mL of LB medium, and after adjusting the medium pH to 7.0-7.2, use a sterilized pot for high-temperature and high-pressure sterilization.

[0081] The MR-1 strain stored in a refrigerator at -80°C was thawed at room temperature. The LB medium and the strain were placed in a sterile operating table, MR-1 was inoculated into the LB medium using an inoculation needle, and then cultured at 30°C under constant temperature conditions in the dark at a speed of 180 rpm on a shaker for 16-18 h to form a bacterial solution. After the end of the culture, the bacterial solution was centrifuged using a centrifuge, the solid bacteria were precipitated, and the OD value was adjusted to 0.1 using 30 mmol / L piperazine-1,4-bisethanesulfonic acid with a pH of 7.0. 600

[0082] (2) Synthesis of diatomite-iron mineral film layer composite material:

[0083] Take 450 g of diatomite and place it on a 300-mesh sieve. Shake at a speed of 50 rpm for 30 min to remove large particles and other impurities with larger particle sizes. After shaking, pour into a beaker and wash 2-3 times with deionized water. After removing the dissolved ions in the diatomite, use a suction filter and a 0.45 μm filter membrane to remove the water. After filtration, the moisture content of the diatomite is about 60%.

[0084] Take a 2L beaker and add 1000 mL of deionized water. Insert the stirrer into the water and stir at a speed of 180 rpm. Add 13 g of chromatographic silica gel (mass fraction about 1%) and 25 g of glucose (mass fraction about 2%), continue to stir for 10 min until the solution is uniform and translucent. Reduce the stirring speed to 100 rpm, add 100 g of wet diatomite, stir for 5 min, then add another 100 g of wet diatomite, repeat the steps until 500 g of wet diatomite is added, and continue to stir for 30 min.

[0085] After the addition of diatomite, increase the stirring speed to 200 rpm and add 50 g of ferrous sulfate heptahydrate. After mixing evenly, use a syringe to gradually add 5.0 mmol / L sodium hydroxide solution at a rate of 10 mL / min, while using a pH meter to monitor the pH of the system in real time, and control the final pH of the system between 6.8 and 7.2. After the pH is stable, stop stirring and let it stand for 30 min. A large amount of yellow-brown precipitate accumulates at the bottom of the solution, indicating that the diatomite-iron mineral film layer composite material has been initially formed.

[0086] Discard the supernatant and filter the remaining solid using a suction filter and a 0.45 μm filter membrane to remove the water. Then lay the wet diatomite-iron mineral film layer composite material sample flat to dry indoors. The indoor environment should be cool and well ventilated, with a temperature not lower than 25°C. At the same time, the material should be stirred every 12 h to speed up the drying and promote the dispersion of the material, avoiding clumping. After drying for 48 h, the diatomite-iron mineral film layer composite material is obtained.

[0087] Figure 1 ​The scanning electron microscope images of diatomite (a) and diatomite-iron mineral film layer composite (b) in Example 1 are shown in Figure 1 It can be seen that the original diatom surface is smooth, has no attachments, and contains many voids; in the composite material prepared in Example 1, the iron mineral is coated on the surface of the diatomite, and the diatomite surface pores are significantly reduced, indicating that the iron mineral film is formed.

[0088] (3) Assessing the change of iron mineral film layer with moisture content

[0089] In a 120 mL erlenmeyer flask, 50 mL of OD 600 The MR-1 bacterial solution with OD of 0.1 was added with 0.5 mL of 1000 mmol / L sodium lactate solution, and 0.5 g of diatomite-iron mineral film layer composite, and the concentration of the composite material was initially about 10 g / L.

[0090] First, the solution was aerated with nitrogen for 40 min to remove oxygen, and the erlenmeyer flask was sealed with a rubber plug and an aluminum cap to simulate an anaerobic environment in high-moisture soil. The reaction time was 96 h. After the high-moisture soil simulation condition was completed, the rubber plug and aluminum cap of the erlenmeyer flask were removed, and the bottle was sealed with a 0.22 μm sterile air-permeable membrane to prevent other bacteria from entering. The erlenmeyer flask was placed in a shaker at a speed of 180 rpm, at which time the moisture in the erlenmeyer flask was in contact with the outside atmosphere, and the moisture gradually evaporated into a low-moisture soil simulation environment. The reaction time was 54 h.

[0091] Figure 2 The ferrous ion concentration change diagram of different reaction stages in Example 1 is shown in Figure 2 It can be seen that in the high-moisture soil simulation environment, the total concentration of ferrous ion gradually increased, indicating that the iron reduction process occurred, and that the iron mineral film layer was gradually eroded in the high-moisture environment, which was conducive to the formation of pores on the surface of the material. With the increase of reaction time, the cumulative amount of ferrous ion gradually increased, reaching 75 mg / L at 96 h. This result indicates that the added material can adapt to the high-moisture soil simulation environment for a long time, and induce iron-reducing microorganisms to carry out the iron reduction process, thereby increasing the release rate of nutrient elements.

[0092] After the culture condition was changed from high water content soil simulation environment to low water content soil simulation environment, the ferrous ion concentration decreased rapidly from 75 mg / L to 1.3 mg / L at 105 h (i.e., 9 hours after the reaction condition was changed), and to about 0 mg / L in the subsequent reaction time. The rapid decrease of ferrous ion concentration indicated that the reduced iron element on the iron mineral film layer was oxidized again, converted from dissolved state to solid state, indicating that the iron mineral film layer was regenerated. This result indicates that the added material can quickly adapt to the low water content soil simulation environment, induce the regeneration of the iron mineral film layer, and thus inhibit the release rate of nutrient elements. The results of the high water content and low water content soil environment simulation experiments in Example 1 show that the iron mineral film layer has a water response characteristic, and its structure can change according to the change of water content.

[0093] Example 2

[0094] In this example, a slow / controlled release fertilizer containing selenium element is prepared, and by changing the culture condition of the system, the periodic change of anaerobic-aerobic caused by the change of high water content and low water content in soil is simulated, and by measuring the change of selenium concentration, the change of iron mineral film layer is evaluated to evaluate whether the release rate of nutrients can be regulated by changing the water content:

[0095] (1) Preparation of slow / controlled release fertilizer, steps as follows:

[0096] S11, take 550 g of diatomite and place it on a 300 mesh sieve, shake at a rate of 50 rpm for 30 min to remove large particles and other impurities with larger particle size. After shaking, pour into a beaker, wash 3 times with deionized water, remove the dissolved ions in the diatomite, and then filter with a suction filter and a 0.45 μm filter membrane to remove water. The moisture content of the filtered diatomite is about 65%.

[0097] S12, take a 2 L beaker and add 1000 mL of deionized water, insert a stirrer into the water and stir at a rate of 180 rpm. Add 1.5 g of sodium selenate until it is completely dissolved. After the solution is stable, add 13 g of chromatographic silica gel (mass fraction of about 1%) and 25 g of glucose (mass fraction of about 2%), continue to stir for 10 min until the solution is uniform and translucent. Reduce the stirring rate to 100 rpm, add 100 g of wet diatomite, stir for 5 min, then continue to add 100 g of wet diatomite, repeat the steps until 500 g of wet diatomite is added, and continue to stir for 30 min;

[0098] S21, after the diatomite is added, the stirring speed is increased to 200 rpm, and 50 g of ferrous sulfate heptahydrate is added. After mixing, a 5.0 mmol / L sodium hydroxide solution is gradually added at a rate of 10 mL / min using a syringe, and the pH of the system is monitored in real time using a pH meter, so that the final pH of the system is controlled between 6.8 and 7.2. After the pH is stable, stop stirring and stand for 30 min, a large amount of yellow-brown precipitate accumulates at the bottom of the solution, indicating that the slow-release fertilizer is initially formed;

[0099] S22, discard the supernatant, and filter the remaining solid using a filter press and a 0.45 μm filter membrane to remove water. Then spread the wet sample indoors to dry. The indoor environment needs to be cool and ventilated, and the temperature should not be lower than 25°C, and at the same time, the material is stirred once every 12 hours to speed up the drying and promote the dispersion of the material, avoiding clumping. After 48 hours of drying, the final synthesized sample is obtained.

[0100] Figure 3 For the scanning electron microscope image of the slow-release fertilizer in Example 2, from Figure 3 It can be seen that the diatomite surface is covered with a large amount of iron minerals, and the pore is significantly reduced, indicating that the selenium element loaded into the pores and surface of the diatomite is tightly wrapped by the iron mineral coating. The selenium element in the synthesized iron mineral coated selenium-rich diatomite can change the release rate with the change of the iron mineral coating.

[0101] (2) Evaluation of the release of selenium in slow-release fertilizer with changes in soil moisture content:

[0102] The soil sample was collected in Taishan City, Jiangmen City, Guangdong Province, and the soil crop was rice. The surface soil sample of 0-20 cm was collected. After the soil sample was collected, it was placed in the laboratory, dried in a cool and ventilated environment, and then the large rhizosphere, stones and other impurities were picked out, and then sieved through a 200 mesh sieve for use. The basic physicochemical properties of the soil are as follows: pH = 4.49, cation exchange capacity is 13.6 cmol / kg, total organic matter content is 46.2 g / kg, and total iron content is 40.56 g / kg;

[0103] Three 50 mL vials were prepared, each containing 5.0 g soil, 0.5 g slow controlled release fertilizer and 50 mL deionized water. The vials were sealed with rubber stoppers and aluminum caps and placed on a shaker at a speed of 240 rpm for 30 min to mix the soil, slow controlled release fertilizer and water. The vials were then placed in a 30°C constant temperature incubator in the dark, and the vials were isolated from the atmosphere so that water could not evaporate, to simulate an anaerobic environment in soil with high water content. The reaction time was 40 days. After the simulation of the high water content soil condition, the rubber stoppers and aluminum caps were removed, and the vials were sealed with 0.22 μm sterile air-permeable membranes to prevent other bacteria from entering. The vials were then placed on a shaker at a speed of 180 rpm, and air entered the vials and water evaporated, to simulate a low water content soil condition. The reaction time was 2 days.

[0104] Figure 4 The kinetic changes of dissolved selenium (a) and organic bound selenium (b) in different reaction stages in Example 2 are shown in the graphs in FIG. 2. Figure 4 As can be seen from FIG. 2, in the high water content soil simulation environment, the total concentration of dissolved selenium gradually increased, reaching 0.86 μg / L on the 40th day, indicating that selenium was released from the slow controlled release fertilizer into the soil. The concentration of selenium in the reaction system did not rapidly increase in a short time, but increased slowly, indicating that selenium was released slowly and accumulated in the soil system, further indicating that the iron mineral film layer could adapt to the soil environment and achieve the purpose of slow release of nutrients in the high water content soil environment. The change trend of organic bound selenium in the high water content soil simulation environment was similar to that of dissolved selenium, and gradually increased with the change in the culture time, reaching 6.3 μg / L on the 40th day. Both dissolved and organic bound selenium are forms that are easily absorbed by crops, indicating that the added sodium selenate in the slow controlled release fertilizer can be converted into various beneficial forms, which are beneficial to the full absorption and utilization of crops.

[0105] After the culture conditions changed from the high water content soil simulation environment to the low water content soil simulation environment, the concentrations of dissolved and organic bound selenium both decreased. On the 42nd day of the total reaction (i.e., the 2nd day of changing the reaction conditions), the concentration of dissolved selenium decreased to 0.55 μg / L, and the concentration of organic bound selenium decreased to 5.14 μg / L. The concentrations of dissolved and organic bound selenium decreased because the oxygen content was sufficient in the low water content soil environment, and the iron mineral film layer was regenerated, which on the one hand limited the further release of selenium, resulting in no accumulation of selenium, and on the other hand the regeneration of the iron mineral film layer fixed a part of the released selenium, resulting in a decrease in the concentration of selenium.

[0106] In summary, the slow controlled release fertilizer in the application can accurately control the release of selenium in the soil environment by changing the moisture conditions. In a high moisture environment conducive to plant nutrient absorption, the release of nutrients is promoted. In a low moisture environment not conducive to plant nutrient absorption, the release of selenium in the soil environment is reduced, and part of the released selenium is fixed, achieving the effect of nutrient preservation.

[0107] Example 3

[0108] In this embodiment, a slow controlled release fertilizer containing phosphorus elements is prepared, and by changing the system culture conditions, the periodic changes of anaerobic-aerobic brought by high and low moisture conditions in the soil are simulated. By measuring the change of phosphorus concentration, the change of iron mineral film layer is evaluated to evaluate whether the release rate of nutrients can be regulated by changing the moisture conditions:

[0109] (1) Prepare the slow controlled release fertilizer, the steps are as follows:

[0110] S11, take 530g of diatomite and place it on a 300 mesh sieve, shake at a speed of 50rpm for 25min to remove large particles and other impurities with larger particle size. After shaking, pour into a beaker, wash 3 times with deionized water, remove the dissolved ions in the diatomite, and then filter with a 0.45μm filter membrane using a suction filter to remove the water. The moisture content of the filtered diatomite is about 65%.

[0111] S12, take a 2L beaker and add 1000mL of deionized water, insert a stirrer into the water and stir at a speed of 180rpm. The dissolution temperature is controlled at about 30℃, add 281g of potassium dihydrogen phosphate, if the temperature is too high, the amount of potassium dihydrogen phosphate needed is gradually reduced, so that the potassium dihydrogen phosphate solution is supersaturated, a small amount of white precipitate is produced at the bottom, continue to stir for 5min, and the precipitate does not disappear. After the solution is stable, add 13g of chromatographic silica gel (mass fraction of about 1%) and 25g of glucose (mass fraction of about 2%), continue to stir for 10min until the solution is uniform and translucent. Reduce the stirring speed to 100rpm, add 100g of wet diatomite, stir for 5min, then add another 100g of wet diatomite, repeat the steps until 500g of wet diatomite is added, and continue to stir for 30min;

[0112] S21, after the diatomite is added, increase the stirring speed to 200rpm, and add 50g of ferrous sulfate heptahydrate. After mixing evenly, use a syringe to gradually add 5.0mmol / L of sodium hydroxide solution at a rate of 10mL / min, while using a pH meter to monitor the pH of the system in real time, so that the final pH of the system is controlled between 7.0. After the pH is stable, stop stirring and stand for 30min, a large amount of yellow-brown precipitate accumulates at the bottom of the solution, indicating that the slow controlled release fertilizer is initially formed;

[0113] S22, discard the supernatant, and filter the remaining solid using a suction filter and a 0.45 μm filter membrane to remove water. Then, spread the wet sample on a room to dry. The room needs to be cool and ventilated, and the temperature should be kept at no less than 25°C. At the same time, the material is stirred once every 12 hours to accelerate drying and promote material dispersion, avoiding clumping. After 48 hours of drying, the final synthesized sample is obtained.

[0114] Figure 5 The scanning electron microscope images of the slow-controlled release fertilizer in Example 3 are shown in FIG. 1. Figure 5 It can be seen that the diatomite surface is covered with a large amount of iron minerals, and the pores are significantly reduced, indicating that the phosphorus loaded in the pores and on the surface of the diatomite is tightly wrapped by the iron mineral coating. The phosphorus element in the synthesized iron mineral-coated phosphorus-rich diatomite can change the release rate with the change of the iron mineral coating.

[0115] (2) Evaluation of the release of phosphorus in the slow-controlled release fertilizer with changes in soil water content:

[0116] The soil sample was collected in Yingtan City, Jiangxi Province, and the soil crop was rice. The surface soil sample of 0-20 cm was collected. After the soil sample was collected, it was placed in a greenhouse and dried in a cool and ventilated place. After removing large rhizosphere, stones and other impurities, it was passed through a 10 mesh sieve and used. The basic physicochemical properties of the soil are as follows: pH = 4.40, total organic matter content is 44.8 g / kg, and total iron content is 17.6 g / kg;

[0117] Prepare 3 10L pots, add 5.0 kg of soil, 250 g of slow-controlled release fertilizer and mix well. Add deionized water to the soil surface to about 5 cm of accumulated water, and place it in a greenhouse for cultivation. Water every 2 days to maintain the soil surface water to about 5 cm, at which time the soil is isolated from the atmosphere to form an anaerobic environment with high soil moisture, and the reaction continues for 40 days. After the high-moisture soil reaction is completed, no more water is added, and the water in the pots is allowed to evaporate naturally. At this time, the soil environment enters an aerobic condition with low soil moisture, and the reaction time is 20 days.

[0118] Figure 6 The kinetic change diagrams of hydrochloric acid extractable phosphorus (a) and available phosphorus (b) in different reaction stages in Example 3 are shown in FIG. 2. Figure 6It can be seen that the accumulation of initial phosphorus in the reaction system is the background value of soil phosphorus. In the high moisture soil reaction condition, the concentration of hydrochloric acid extractable phosphorus gradually increases and reaches 110.4 mg / kg at the 40th day. The phosphorus concentration does not rapidly increase in a short time, but slowly increases, indicating that the phosphorus in the slow-release fertilizer is slowly released and gradually accumulated in the soil. It is further indicated that the iron mineral film layer can adapt to the soil environment and achieve the purpose of slow release of nutrients in the high moisture soil environment. The change trend of available phosphorus in the high moisture soil condition is similar to that of the change rule of hydrochloric acid extractable phosphorus. With the change of the culture time, it gradually increases and reaches 239.6 mg / L at the 40th day. Both the hydrochloric acid extractable phosphorus and the available phosphorus are phosphorus elements with high activity in the soil, which are easily absorbed and transformed by crops, indicating that the added potassium dihydrogen phosphate in the slow-release fertilizer can be converted into various beneficial forms, which is beneficial to the full absorption and utilization of crops.

[0119] After the culture condition changes from the high moisture soil reaction condition to the low moisture soil reaction condition, the concentrations of hydrochloric acid extractable phosphorus and available phosphorus decrease. At the 60th day of the total reaction (i.e. the 20th day of changing the reaction condition), the concentration of hydrochloric acid extractable phosphorus decreases to 70.0 mg / kg, and the concentration of available phosphorus decreases to 175.6 mg / L. The decrease of the concentrations of hydrochloric acid extractable phosphorus and available phosphorus is because the oxygen content is sufficient in the low moisture soil environment, and the dissolved iron mineral film layer is regenerated in the high moisture soil environment. On the one hand, the regeneration of the iron mineral film layer limits the further release of phosphorus, resulting in no increase of phosphorus. On the other hand, the regeneration of the iron mineral film layer fixes a part of the released phosphorus, resulting in the decrease of the concentration of phosphorus.

[0120] In summary, the slow-release fertilizer in the application can accurately control the release of phosphorus in the soil environment by changing the water condition. In the high moisture environment conducive to plant nutrient absorption, the release of nutrients is promoted. In the low moisture environment not conducive to plant nutrient absorption, the release of phosphorus in the soil environment is reduced, and a part of the released phosphorus is fixed, achieving the effect of nutrient preservation.

Claims

1. A slow-release fertilizer, characterized by comprising, The slow controlled release fertilizer is a core-shell structure, wherein the core is a porous carrier loaded with nutrient elements, and the shell is an iron mineral film layer; wherein the iron mineral film layer is formed by secondary mineral precipitation generated by ferrous oxidation; The slow controlled release fertilizer comprises the following preparation raw materials: a porous carrier, a ferrous salt, a binder, a microbial activation induction auxiliary agent, a nutrient element salt, water, and an alkali solution; The slow controlled release fertilizer is prepared by a method comprising the following steps: S1, dissolving the nutrient element salt in water, adding the binder and the microbial activation induction auxiliary agent, and then adding the porous carrier in batches to obtain the porous carrier loaded with nutrient elements; S2, adding the ferrous salt, adjusting the pH of the system to 6.8-7.2 by adding an alkali solution, solid-liquid separation, and collecting the solid phase to obtain the slow controlled release fertilizer.

2. The slow-release fertilizer according to claim 1, characterized in that, The porous carrier is selected from at least one of diatomite, bentonite, zeolite, montmorillonite, expanded vermiculite, sepiolite, or attapulgite; the particle size of the porous carrier is less than 50 μm; and the water content of the porous carrier is 60%-80%.

3. The slow-release fertilizer according to claim 1, characterized in that, The nutrient elements include at least one of essential nutrient elements and beneficial nutrient elements required for plant growth.

4. The slow-release fertilizer according to claim 1, characterized in that, The binder is selected from at least one of chromatographic silica gel and silica sol.

5. The slow-release fertilizer according to claim 1, wherein The microbial activation induction auxiliary agent is selected from at least one of glucose, sodium acetate, and sodium lactate.

6. The slow-release fertilizer according to claim 1, wherein The alkali source of the alkali solution includes alkali metal hydroxides, alkali metal carbonates, and alkali metal bicarbonates.

7. The slow-release fertilizer according to claim 1, wherein The mass ratio of the porous carrier, the binder, the microbial activation induction auxiliary agent, the nutrient element salt, the ferrous salt, and water is (400-600):(10-20):(20-30):(1-300):(40-60):1000.

8. Use of the slow controlled release fertilizer according to any one of claims 1-7 in soil improvement.

9. Use according to claim 8, characterized in that, The physicochemical properties of the soil include at least one of the following: 1) pH is 4-8; 2) cation exchange capacity is 5-30 cmol / kg; 3) total organic matter content is 10-50 g / kg; 4) total iron content is 50-300 g / kg.

10. Use according to claim 8, characterized in that, The dosage of the slow controlled release fertilizer is 10-50 kg / acre.

Images