Preparation method of controlled-release fertilizer for mechanical transplanting rice seedling raising subsoil and application of controlled-release fertilizer for replacing field fertilization

Abstract

The invention discloses a preparation method of a controlled-release fertilizer for mechanical transplanting rice seedling raising subsoil and application of the controlled-release fertilizer to replace field fertilization, and belongs to the technical field of rice cultivation. A coating of the controlled-release fertilizer is prepared from the following components in parts by weight: 20 to 60 parts of low-density polyethylene resin, 10 to 20 parts of ethylene-vinyl acetate copolymer, 5 to 30 parts of synthetic resin biodegradation inducer, 3 to 15 parts of starch, 10 to 70 parts of talcum powder and 0.2 to 2 parts of nonionic surfactant. The controlled-release fertilizer comprises urea and a compound fertilizer which are respectively coated by the coating film. According to the controlled-release fertilizer for the machine-transplanted rice seedling raising subsoil, a coating material is optimized, the release inhibition period of the controlled-release fertilizer is 20-30 days, normal growth of rice seedlings is ensured, and the rice growth requirements are accurately met. When the method is used for rice planting, a seedling raising subsoil fertilizer carrying method is adopted, integration of rice transplanting and fertilization is achieved, and on the basis of ensuring high and stable yield of rice, the fertilizer application cost and the risk of nitrogen and phosphorus pollution emission in the rice field are reduced.

Description

Technical Field

[0001] The present invention relates to a method for preparing a controlled-release fertilizer for machine-transplanted rice seedling subsoil and its application in replacing field fertilization, and in particular to a naturally degradable controlled-release fertilizer, a preparation method thereof and a method for using the fertilizer in the subsoil to plant rice, belonging to the technical field of rice cultivation. Background Art

[0002] Conventional rice cultivation involves high fertilizer usage, frequent fertilization, significant environmental risks, laborious labor, and high fertilization costs. In conventional fertilization, basal tillering fertilizer (nitrogen fertilizer) typically accounts for 60%-80% or even more of the total fertilizer application, while fertilizer uptake during the early stages of rice production (from transplanting to jointing) only accounts for 35% of the total fertilizer used during the entire rice growth period. The utilization rate of basal fertilizer is 20%-25%, while the utilization rate of tillering fertilizer is only 15%-20%. This low utilization rate of basal tillering fertilizer and the large amount of fertilizer applied are serious bottlenecks that hinder the improvement of fertilizer utilization in rice production. The reason for this is that, on the one hand, rice seedlings are small after transplanting, and their roots are short, few, and shallowly distributed, resulting in a small root system. Most of the fertilizer applied is distributed outside the rhizosphere, where it is easily lost through ammonia volatilization, runoff, and leaching, posing a risk of environmental pollution. On the other hand, during the tillering stage, rice plants require a rapid increase in nitrogen content to above 3.5%, necessitating increased topdressing fertilizer application to improve the intensity of fertilizer supply to the rice root system. Therefore, developing a fertilizer that can both meet rice's nutrient needs and reduce the amount of basal tillering fertilizer applied outside the rhizosphere is an important approach to improving fertilizer utilization efficiency in rice and a new direction for efficient fertilization.

[0003] Machine transplanting of rice can ensure stable and high-quality rice production and has a high potential for increased production. If, based on key technological breakthroughs such as the safety of slow-release and controlled-release fertilizers for seedling cultivation, the precise and quantitative concentration of fertilizers in the rhizosphere, and the precise release of fertilizers in the field, most or all of the fertilizer applied during the whole rice planting season (mainly basal tillering fertilizers) can be applied as slow-release and controlled-release fertilizers and attached to the subsoil in the seedling cultivation, and the fertilizers can be simultaneously introduced into the whole rice planting season through mechanical transplanting, the fertilizers can be concentrated at the root base, and the nutrients can be precisely released to meet the nutrient needs of high-yield and high-quality rice. This will enable the integration of transplanting and fertilization at a higher level, making machine transplanting more efficient, and the fertilizers evenly concentrated in the rhizosphere, which can significantly improve fertilizer utilization. By reducing the amount and frequency of fertilizer application, the risk of nitrogen and phosphorus emissions can be reduced from 3-5 fertilizations during the whole rice planting season to no fertilization or 1 fertilization.

[0004] Resin coating regulates the fertilizer nutrient release rate by the pore size and quantity of the film, and relies on the excellent characteristics that are not affected by other environmental conditions such as acidity, alkalinity, moisture, microorganisms, etc. except temperature, becoming the most common coating method of current slow-release fertilization. However, current resin-coated fertilizers cannot realize the delayed release during the seedling raising period and the slow-release after the rice seedlings are planted, so there is no successful case of resin-coated fertilizers for rice seedling raising. In addition, the degradability of the resin coating residual film after the fertilizer nutrient release is also the research and development direction of the new product of resin-coated controlled-release fertilizer. A slow-release fertilizer prepared by large-particle (particle diameter 2-5mm) urea and composite fertilizer of vegetable oil base coating is disclosed in current CN 114133298 B to carry out rice seedling raising, to realize the integration of transplanting and fertilizing. However, to ensure rice yields, the seedling trays must hold a significant amount of fertilizer. A standard seedling tray (60cm×30cm×2.6cm outer dimensions) requires at least 1.9kg of slow-release fertilizer, and some require up to 2.7kg. Due to the limited space in the trays, the amount of subsoil required for the seedlings is extremely limited. Large, round particles of slow-release fertilizer make it difficult to form a capillary structure like the subsoil, resulting in poor water retention. This not only complicates seedling management and severely limits seedling quality, but also hinders the formation of a mat-like root system, complicating machine transplanting and limiting transplanting efficiency.

[0005] To this end, a method of subsoil fertilizer loading for machine-transplanted rice seedlings based on efficient, safe, and naturally degradable controlled-release fertilizers is provided to replace the conventional fertilization method, which is of great significance for the development of high-yield, high-efficiency, high-quality, and low-drainage rice cultivation. Summary of the Invention

[0006] Objectives of the invention: The first objective of the present invention is to provide a naturally degradable controlled-release fertilizer and a method for preparing the same. The second objective of the present invention is to provide a method for growing rice using the naturally degradable controlled-release fertilizer as a subsoil fertilizer alternative to conventional fertilization.

[0007] Technical solution: The naturally degradable controlled-release fertilizer of the present invention has a coating composed of the following components: 20-60 parts of low-density polyethylene resin, 10-20 parts of ethylene-vinyl acetate copolymer, 5-30 parts of synthetic resin biodegradation inducer, 3-15 parts of starch, 10-70 parts of talc, and 0.2-2 parts of non-ionic surfactant; the controlled-release fertilizer includes urea and compound fertilizer respectively coated by the above coating.

[0008] Furthermore, the nonionic surfactant has an ethylene oxide addition number EO=6 and a cloud point CP=52°C.

[0009] Furthermore, the coating rate of the urea and compound fertilizer is 9-20%.

[0010] Furthermore, the compound fertilizer is one or more combinations of potassium dihydrogen phosphate, monoammonium phosphate, diammonium phosphate, potassium nitrate, potassium chloride, and potassium sulfate.

[0011] Furthermore, the ratio of nitrogen (N), phosphorus (P2O5) and potassium (K2O) in the controlled-release fertilizer is 30:6:6.

[0012] Furthermore, the envelope also includes a pigment.

[0013] The method for preparing the naturally degradable controlled-release fertilizer of the present invention comprises the following steps:

[0014] (1) mixing a low-density polyethylene resin, an ethylene-vinyl acetate copolymer, a synthetic resin biodegradation inducer, starch, talc, a nonionic surfactant, and a pigment, and dissolving the mixture in tetrachloroethylene to obtain a coating solution;

[0015] (2) The coating solution is coated on urea and compound fertilizer respectively, and the coated urea and compound fertilizer are mixed to obtain a naturally degradable controlled-release fertilizer.

[0016] Furthermore, the solid content of the coating solution in step (1) is 4-7%.

[0017] Furthermore, the dissolution condition in step (1) is stirring at 100° C. for 1 hour.

[0018] Furthermore, the coating conditions of the urea in step (2) include: hot air temperature of 60-80° C.; coating time of 38-50 minutes; and the coating conditions of the compound fertilizer include: hot air temperature of 60-80° C.; coating time of 47-61 minutes.

[0019] The method for planting rice by using subsoil fertilizer instead of topsoil fertilizer according to the present invention comprises the following steps:

[0020] (1) Mixing the above-mentioned naturally degradable controlled-release fertilizer with subsoil, sowing rice in a standard rice seedling tray, and raising rice seedlings;

[0021] (2) Transplant the rice seedlings into the field after they are 20 to 25 days old.

[0022] Furthermore, the amount of the naturally degradable controlled-release fertilizer in step (1) is 340 to 680 g per standard seedling tray.

[0023] Furthermore, step (2) further includes the step of applying 50-100% ear fertilizer.

[0024] Furthermore, when the rice sowing site is in the Northeast region, the dosage of the naturally degradable controlled-release fertilizer is 340g / standard seedling tray; when the rice sowing site is in the middle and lower reaches of the Yangtze River, the dosage of the naturally degradable controlled-release fertilizer is 600-680g / standard seedling tray.

[0025] Beneficial Effects: Compared with the prior art, the present invention has the following significant advantages: The naturally degradable controlled-release fertilizer of the present invention optimizes the coating material, resulting in a release inhibition period of 20-30 days, ensuring the normal growth of rice seedlings. After 30 days, the fertilizer is gradually released, and the release continues for 90 days after sowing, precisely matching the growth needs of rice. When used for rice cultivation, the fertilizer is loaded into the bottom soil of the seedlings, which can replace the conventional fertilization method. By coating conventional nitrogen, phosphorus, and potassium fertilizers with biodegradable resin, the nutrient release is controlled, so that the fertilizer is concentrated only in the crop root layer, reducing nutrient loss in non-root areas. The seedlings have a mat-like rooting capacity comparable to conventional seedlings, ensuring efficient seedling management and transplanting operations. At the same time, the slow-release design ensures continuous fertilizer supply throughout the entire growth period. Even a one-time application or a small amount of topdressing of ear fertilizer can meet crop needs. The utilization rate of base tiller fertilizer is less than 25% when broadcast, but increases to over 58% when applied to the root layer. This method realizes the integration of transplanting and fertilization, and reduces the cost of fertilizer application and the risk of nitrogen and phosphorus pollution emissions from rice fields while ensuring high and stable rice yields. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 : Nitrogen release rate test results of the controlled-release fertilizer coated with Formula B prepared by the present invention.

[0027] Figure 2 : The controlled release fertilizer of formula B coating prepared by the present invention ( Figure 2 Left) and conventional resin coated controlled release fertilizer ( Figure 2 Right) Comparison of rice seedling raising safety.

[0028] Figure 3 : The present invention's subsoil loaded with resin-coated controlled-release fertilizer and conventional rice seedling growth

[0029] Figure 4 : The subsoil of the present invention is loaded with resin-coated controlled-release fertilizer and the root growth of conventional rice seedlings. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0031] Example 1 Preparation of delayed-release coating material

[0032] (1) Weigh 55 g of low-density polyethylene (LDPE) (melt index MI = 8, density D = 0.916), 15 g of ethylene-vinyl acetate copolymer (EVA) (melt index MI = 2, density D = 0.940, vinyl acetate content = 18%), 15 g of corn starch, and 95 g of talc (average particle size: 10 μm) and dissolve them in tetrachloroethylene solvent (TCE, purity ≥ 99%) at a solid content of 5%.

[0033] (2) Material I: 2 g of a nonionic surfactant NIS (fatty alcohol polyoxyethylene ether-6, AOE-6, produced by Zibo Zhongcheng Chemical Co., Ltd.) with an ethylene oxide addition number EO=6 and a cloud point CP=52°C was added to the solution prepared in step (1) to form a delayed-release coating material.

[0034] Material II: Add 2 g of a nonionic surfactant (fatty alcohol polyoxyethylene ether-9, AOE-9, produced by Zibo Zhongcheng Chemical Co., Ltd.) with an ethylene oxide addition number EO=9 and a cloud point CP=70°C to the solution prepared in step (1) to form a delayed-release coating material.

[0035] Material III: Directly use the solution prepared in step (1) as the delayed-release coating material.

[0036] (3) The three coating materials, Material I, Material II and Material III, were placed at 100°C and stirred for about 1 hour until completely dissolved to prepare a coating solution. The coating solution was then applied to the urea surface in a ratio such that the amount of coating material was the weight of the coated urea, i.e., the coating rate was 12%. The organic solvent was then removed by drying to complete the coating and obtain coated urea.

[0037] Example 2 Nitrogen release test of urea coated with different coating materials

[0038] 10 g of each of the three different coated ureas in Example 1 was added to 250 ml of distilled water and incubated at 25° C. for 30 days. 1 ml of the sample was taken every 10 days and the total nitrogen content in the water was measured using a Kjeldahl analyzer (Kjeltec analyzer 2300) to calculate the nitrogen release.

[0039] As shown in Table 1, the nitrogen release of urea coated with Material II and Material III reached over 28% in 20 days and over 36% in 30 days, while the nitrogen release of urea coated with Material I was only 8.7% in 30 days. Therefore, Material I is preferred as the delayed-release coating material.

[0040] Table 1 Cumulative release of urea nitrogen from different delayed-release coating materials

[0041] deal with 10 days 20 days 30 days Materials I 3.60％ 4.80％ 8.70％ Materials II 5.80％ 28.30％ 36.50％ Materials III 11.30％ 35.40％ 46.20％

[0042] Example 3 Preparation of resin-coated controlled-release fertilizer

[0043] (1) Coating formula

[0044] According to the delayed-release coating formula prepared by Material I in Example 1, a synthetic resin biodegradation inducer BDP and a pigment were added, and the proportions of the components were adjusted to prepare a degradable coating material, as shown in Table 2.

[0045] Table 2 Mixing ratio of degradable coating materials

[0046]

[0047] (2) Encapsulation process

[0048] All ingredients in Table 1 were dissolved in tetrachloroethylene solvent at a solid content of 5%. The mixed degradable coating material was added to a constant temperature closed stirring tank and stirred at 100° C. for about 1 hour until completely dissolved to prepare a coating solution.

[0049] Air drawn into the intake system is then heated by a heat exchanger. This heated air passes through a porous plate, creating a specific airflow pattern that fluidizes the fertilizer granules (urea or compound fertilizer, with the compound fertilizer consisting of potassium nitrate (nitrogen (N), phosphorus (P2O5), and potassium (K2O) contents of 13.5%, 0%, and 46%), and monoammonium phosphate (nitrogen, phosphorus, and potassium contents of 14%, 44%, and 0%)). The coating solution from the constant-temperature stirring tank is pumped to a fluid nozzle, where it is atomized and sprayed onto the surface of the fluidized fertilizer granules, completing the coating process. Coating conditions are detailed in Table 3.

[0050] Table 3 Coating conditions of urea and compound fertilizer

[0051]

[0052] After coating urea and compound fertilizer respectively by the above method, the coated compound fertilizer and urea are mixed in proportion to finally prepare a controlled-release fertilizer with a nitrogen (N)-phosphorus (P2O5)-potassium (K2O) content of 30-6-6.

[0053] Example 4 Performance Test of Coating

[0054] 1. Natural decomposition rate

[0055] 5 grams of each controlled-release fertilizer prepared in Example 3 were taken and punctured individually to completely dissolve the fertilizer inside. These samples were used as test samples. The samples were buried in a turnover box (270×180×140 mm internal dimensions) with soil sieved through a 1 mm sieve. The moisture conditions simulated conventional rice cultivation. After 2 years in a constant temperature greenhouse at 25°C, the soil and fertilizer coatings were dried and passed through a 1 mm sieve. Any material that did not pass through the 1 mm sieve was considered undecomposed coating material. The natural decomposition rate of each coating material formulation was calculated.

[0056] The results are shown in Table 4. Among the formulations in Example 3, the film of formulation B can be completely decomposed naturally during the test period. Therefore, formulation B is preferably used as the final film formulation.

[0057] Table 4 Natural decomposition rate of different coating formulas

[0058]

[0059] 2. Nitrogen release rate test

[0060] To determine the nitrogen release rate of the coated controlled-release fertilizer (Formula B), 10 g of Formula B controlled-release fertilizer was added to 250 mL of distilled water at 15°C, 25°C, and 30°C. 1 mL of water was sampled daily and the total nitrogen content was measured using a Kjeldahl analyzer (2300). The nitrogen release was calculated.

[0061] The test results are shown in Figure 1 The nitrogen release rate of controlled-release fertilizer accelerates with increasing temperature. At 15℃, 25℃ and 30℃, the nitrogen release rates within 20 days of cultivation are 2.7%, 4% and 6.2% respectively, and the nitrogen release rates within 30 days of cultivation are 5.5%, 9.1% and 12.1% respectively. Therefore, it has higher seedling safety.

[0062] Example 5 Comparison of safety of raising rice seedlings

[0063] 400 g of each of the resin-coated controlled-release fertilizer (polyurethane-coated compound fertilizer, produced by Shandong Maoshi Ecological Fertilizer Co., Ltd.) widely used on the market and the controlled-release fertilizer coated with Formula B in Example 3 were selected and mixed into 1.8 L of subsoil. The subsoil was a conventional seedling raising substrate, and the seedling tray was a 9-inch (60 cm × 30 cm × 2.6 cm) plastic hard disk for blanket seedling raising.

[0064] The rice variety tested was Nanjing 5055, with a seeding rate of 140 g / tray. All treatments were uniformly raised using hard-ground micro-sprinkler irrigation, and seedling burn was observed.

[0065] Depend on Figure 2 It can be seen that the polyurethane coated controlled release fertilizer seedling treatment ( Figure 2 Right) Serious seedling burn occurred 12 days after sowing, and more than half of the seedlings showed yellowing of leaf tips or even dead leaves. However, the controlled-release fertilizer coated with Formula B in Example 3 of the present invention did not Figure 2 Left) The rice seedlings grew normally and continued to grow normally 30 days after sowing, demonstrating that the controlled-release fertilizer of the present invention is safe for rice seedling cultivation.

[0066] Example 6 Rice seedling raising and field planting test

[0067] All experiments in this example used the controlled-release fertilizer coated with Formula B in Example 3.

[0068] (1) Effects of different subsoil fertilizer loadings on rice seedling growth

[0069] On May 15, 2023, a subsoil fertilizer-loading seedling cultivation experiment was carried out in Jintan District, Changzhou City, Jiangsu Province.

[0070] Subsoil fertilizer loading treatment: The controlled-release fertilizer loading rate was set to three levels, namely 400g / tray, 600g / tray and 800g / tray.

[0071] Conventional seedling raising (no fertilizer added to the subsoil) was used as the control CK.

[0072] The controlled-release fertilizer was mixed into 1.8 L of subsoil. The subsoil was a conventional seedling raising substrate, and the seedling tray was a 9-inch (60 cm × 30 cm × 2.6 cm) plastic hard disk for blanket seedling raising.

[0073] The rice variety used in the experiment was Nanjing 5055, a rice variety widely grown in Jintan District, Changzhou City. The seeding rate was 140 g / tray. All treatments were uniformly raised on hard-ground micro-sprinkler irrigation.

[0074] On June 8, 2023, the above-ground and underground growth conditions of 24-day-old rice seedlings were measured.

[0075] The test results are shown in Figure 3 and Figure 4 The rice seedlings in each subsoil fertilizer treatment emerged normally without any seedling burn or death. The rooting and matting properties of the seedlings were also comparable to those of conventional seedlings.

[0076] The effects of subsoil fertilizer loading on the aboveground part of rice seedlings are shown in Table 5. Compared with conventional seedling cultivation, each subsoil fertilizer loading treatment significantly increased the plant height, stem diameter, leaf age, and aboveground dry matter weight of rice seedlings, while increasing the relative chlorophyll content in seedling leaves, but significantly reduced the seedling weight-to-height ratio.

[0077] Table 5 Effects of subsoil fertilizer loading on the aboveground part of rice seedlings

[0078]

[0079] Note: CK represents conventional rice seedling cultivation; 400 represents 400 g of subsoil fertilizer per tray; 600 represents 600 g of subsoil fertilizer per tray; and 800 represents 800 g of subsoil fertilizer per tray. The SPAD value is the relative chlorophyll content of the top leaf of rice seedlings, measured using a portable chlorophyll meter (SPAD-502PLUS, Konica Minolta, Japan).

[0080] The effects of subsoil fertilizer loading on the root system of rice seedlings are shown in Table 6. There was no significant difference in the root length of rice seedlings under different treatments. With the increase of subsoil fertilizer loading, the number of white roots, underground dry weight and root coiling force of the seedlings showed a downward trend.

[0081] When the subsoil fertilizer loading reached 800 g / tray, the number of white roots, underground dry weight and root binding capacity of rice seedlings were significantly lower than those in conventional seedling cultivation.

[0082] Table 6 Effects of subsoil fertilizer loading on rice seedling root system

[0083]

[0084] (2) Effects of different fertilization methods on rice yield and yield composition

[0085] On June 8, 2023, the seedlings grown in each treatment in (1) were transplanted mechanically in the field with a row spacing of 30 cm × 12 cm, and 18 trays were transplanted per mu in each treatment.

[0086] Conventional seedling raising treatments included application of basal fertilizer (applied before rice transplanting), tillering fertilizer (applied 7 days after transplanting when the seedlings turned green), and panicle fertilizer (applied at the jointing stage, about 50-65 days after transplanting) according to the local conventional fertilization method; in the subsoil fertilization treatments, no basal fertilizer and tillering fertilizer were applied. When applying panicle fertilizer, three levels were set for each subsoil fertilization level: no panicle fertilizer, 50% of the conventional fertilizer amount, and 100% of the conventional fertilizer amount. The application rates of total nitrogen (N), phosphorus (P2O5), and potassium (K2O) in each group are shown in Table 7.

[0087] Table 7 Nitrogen (N), phosphorus (P2O5), and potassium (K2O) application rates (kg / mu) under different fertilization treatments

[0088]

[0089] Note: CK is conventional fertilization, base fertilizer: 20kg compound fertilizer (18-7-10) (nitrogen, phosphorus, potassium content: 18%, 7%, 10%), tillering fertilizer: 10kg urea, ear fertilizer: 20kg compound fertilizer (18-7-10) + 10kg urea; 400, 600 and 800 are subsoil fertilizer 400g / tray, 600g / tray and 800g / tray respectively; 400+50%, 600+50% and 800+50% The subsoil fertilizer loading is 400g / tray and topdressing half of the conventional amount of ear fertilizer, 600g / tray and topdressing half of the conventional amount of ear fertilizer, and 800g / tray and topdressing half of the conventional amount of ear fertilizer; 400+100%, 600+100% and 800+100% are respectively the subsoil fertilizer loading is 400g / tray and topdressing the full amount of conventional amount of ear fertilizer, 600g / tray and topdressing the full amount of conventional amount of ear fertilizer, and 800g / tray and topdressing the full amount of conventional amount of ear fertilizer.

[0090] During the machine transplanting operation, there was no significant difference in the transplanting efficiency between the seedlings grown with 400g / tray and 600g / tray subsoil fertilizer and the conventional seedling growing method.

[0091] The seedlings grown with 800g of subsoil fertilizer per tray have fewer roots and weak root binding force, so the seedling blanket often breaks, the seedlings are broken, and the seedlings are stuck during the machine transplanting process. In order to ensure the quality of transplanting, the efficiency is reduced by 10% to 20% compared with conventional seedling cultivation.

[0092] The rice yield and yield composition of different fertilization treatments are shown in Table 8. The yield of all subsoil fertilizer-loading treatments was lower than that of conventionally fertilized rice when no panicle fertilizer was applied. The yield of conventionally fertilized rice could be achieved by applying the full amount of conventional panicle fertilizer at a subsoil fertilizer loading of 400 g / tray and topdressing the full amount of conventional panicle fertilizer. The yield of conventionally fertilized rice could be achieved by applying half the amount of conventional panicle fertilizer at a subsoil fertilizer loading of 600 g / tray and topdressing the half amount of conventional panicle fertilizer. Although the rice yield increased with increasing the amount of subsoil fertilizer or the amount of panicle fertilizer applied, it did not reach a significant level.

[0093] In all subsoil fertilizer replacement treatments, regardless of whether topdressing of panicle fertilizer was applied or not, even in the treatment with the lowest fertilizer loading of 400 g / tray, the number of rice panicles at maturity was not significantly different from that in the conventional fertilization treatment.

[0094] However, the number of grains per ear and the fruit setting rate were significantly lower than those in the conventional fertilization treatments under all subsoil fertilization treatments without topdressing of ear fertilizer and subsoil fertilization treatments of 400g / tray with topdressing of the full conventional amount of ear fertilizer. The different fertilization methods had no significant effect on the thousand-grain weight.

[0095] Overall, from the perspective of ensuring the efficiency of rice machine planting, ensuring rice yield, and significantly reducing nitrogen fertilizer input, subsoil loading of 600g / tray and topdressing with half the amount of conventional ear fertilizer is considered to be the best subsoil loading method to replace regular field fertilization. Under the premise of ensuring the same rice yield as conventional fertilization, the application of nitrogen fertilizer can be reduced by 55%, the application of phosphorus fertilizer by 44%, and the application of potassium fertilizer by 53%.

[0096] Table 8 Rice yield and yield components under different fertilization treatments

[0097]

[0098] (3) Experiment on subsoil fertilizer loading instead of field fertilizer application in different regions

[0099] Based on the results of the above-mentioned nitrogen release rate test of controlled-release fertilizers and the effects of different fertilization methods on rice yield and yield composition, experiments on subsoil-loading fertilizers to replace mid-field fertilization were carried out in different areas of two major rice-growing areas.

[0100] Two sampling sites, Qinglongshan Farm and Tangyuan Farm, were selected in Heilongjiang Province, and four sampling sites, Yizheng City, Wujin District of Changzhou City, Changshu City and Kunshan City, were selected in Jiangsu Province.

[0101] Taking into account the temperature and fertilization characteristics of different regions, in Heilongjiang Province: the average temperature for rice seedling cultivation is around 15℃, and the conventional nitrogen fertilizer applied in rice fields is 8kg / mu to 12kg / mu; in Jiangsu Province: the average temperature for rice seedling cultivation is 25℃ to 30℃, and the conventional nitrogen fertilizer applied in rice fields is 16kg / mu to 20kg / mu.

[0102] The subsoil fertilizer loading amount at each sampling point in Jiangsu Province was set at 600 g / tray to 680 g / tray, and the subsoil fertilizer loading amount at each sampling point in Heilongjiang Province was halved to 340 g / tray. The rice varieties, sowing amounts, subsoil fertilizer loading amounts and planting spacing in different regions are detailed in Table 9.

[0103] Table 9 Rice varieties, sowing rates, subsoil fertilizer loading and planting spacing in different regions

[0104]

[0105] No other fertilizers were applied in the subsoil fertilizer treatment at each sampling point in Heilongjiang Province throughout the season; no base fertilizer and tillering fertilizer were applied at each sampling point in Jiangsu Province, and panicle fertilizer was applied in the same amount or a reduced amount according to local routine treatment. The total nitrogen, phosphorus and potassium application amounts for rice varieties in each region and different fertilization treatments are shown in Table 10.

[0106] Table 10 Fertilizer application amount for each fertilization treatment in different regions

[0107]

[0108]

[0109] Note: CK represents conventional fertilization treatment in each region, and ZF represents subsoil fertilizer application instead of Honda fertilizer in each region.

[0110] The fertilizer loaded in the subsoil described in Table 10 is the resin-coated fertilizer of Formula B in Example 3 of the present invention, with nitrogen, phosphorus, and potassium contents of 30%, 6%, and 6%, respectively, and the urea nitrogen, phosphorus, and potassium contents in the tillering fertilizer and ear fertilizer are 46%, 0%, and 0%, respectively.

[0111] Among the base fertilizers described in Table 10, the conventional fertilization treatment group: the Qinglongshan and Tangyuan sample sites applied compound fertilizer (18-18-18) with nitrogen, phosphorus, and potassium contents of 18%, 18%, and 18%; the Wujin, Yizheng, and Kunshan sample sites applied compound fertilizer (15-15-15) with nitrogen, phosphorus, and potassium contents of 15%, 15%, and 15%; the Changshu sample site applied compound fertilizer (30-6-12) with nitrogen, phosphorus, and potassium contents of 30%, 6%, and 12%.

[0112] Among the tillering fertilizers described in Table 10, the conventional fertilization treatment group: the Tangyuan sample site applied compound fertilizers of 7.5 kg potassium sulfate (nitrogen, phosphorus, and potassium contents of 0%, 0%, and 50%) and 7.5 kg diammonium phosphate (nitrogen, phosphorus, and potassium contents of 18%, 46%, and 0%); the Changshu sample site applied compound fertilizer of the herbicide fertilizer Jiuxiaodan (nitrogen, phosphorus, and potassium contents of 33%, 0%, and 0%), and the Kunshan sample site applied compound fertilizer (15-15-15).

[0113] Among the ear fertilizers described in Table 10, the Qinglongshan site used potassium sulfate (nitrogen, phosphorus, and potassium contents were 0%, 0%, and 50%) as a compound fertilizer for conventional fertilization; the Tangyuan site used 7.5 kg of potassium sulfate and 7.5 kg of diammonium phosphate as a compound fertilizer for conventional fertilization; the Wujin site used compound fertilizer (15-15-15); the Yizheng site used compound fertilizer (30-0-8) with nitrogen, phosphorus, and potassium contents of 30%, 0%, and 8%. The Changshu site used compound fertilizer (16-16-16). The Kunshan site used compound fertilizer (15-15-15) as a conventional fertilization treatment, and potassium chloride (nitrogen, phosphorus, and potassium contents of 0%, 0%, and 60%) as a compound fertilizer for subsoil-loaded fertilizer instead of Honda fertilization.

[0114] Table 11 shows rice yields under different fertilization treatments in various regions. At the Qinglongshan and Tangyuan test sites in Heilongjiang Province, subsoil fertilizer loading of 340g / tray replaced all fertilization on the rice paddy field, achieving similar growth conditions and yields to conventionally fertilized rice. Nitrogen fertilizer application rates were reduced by 51% and 67%, phosphate fertilizer application rates by 83% and 92%, and potash fertilizer application rates by 90% and 93%.

[0115] At various test sites in Jiangsu Province, subsoil fertilizer loading of 600g / tray to 680g / tray achieved similar growth and yield to conventionally fertilized rice when topdressed with equal or reduced amounts of conventional ear fertilizer. Overall, nitrogen fertilizer input was reduced by 43% to 67%, phosphorus fertilizer input by 35% to 90%, and potassium fertilizer input by 44% to 83%.

[0116] Table 11 Rice yield (kg / mu) under different fertilization treatments in various regions

[0117]

[0118] Note: CK stands for conventional fertilization; ZF stands for subsoil-loaded fertilizer instead of Honda fertilization.

[0119] (4) Comparison of the cost of subsoil-loaded fertilizer instead of conventional fertilization in different regions

[0120] It can be seen from Table 12 that, while ensuring the same rice yield as conventional fertilization, the amount of chemical fertilizer applied by subsoil loading instead of regular fertilization in different regions can be reduced by 66.15% to 100%, with an average reduction of 85.85% in chemical fertilizer application, and an average reduction of 26.46 yuan per mu in fertilizer application costs; considering the comprehensive fertilizer costs and fertilization costs, the cost of subsoil loading instead of regular fertilization in different regions is reduced by 17.27% to 58.07% compared with conventional fertilization, with an average reduction of 36.63%, and an average saving of 77.47 yuan per mu.

[0121] Table 12 Comparison of fertilizer cost per mu between subsoil loading fertilizer instead of regular fertilizer and conventional fertilizer in different regions

[0122]

[0123] Note: Qinglongshan CK, Tangyuan CK, Wujin CK, Yizheng CK, Changshu CK, and Kunshan CK represent conventional rice fertilization in Qinglongshan, Tangyuan, Wujin, Yizheng, Changshu, and Kunshan, respectively. Qinglongshan ZF, Tangyuan ZF, Wujin ZF, Yizheng ZF, Changshu ZF, and Kunshan ZF represent subsoil fertilizer application in seedling nursery instead of rice field fertilization in Qinglongshan, Tangyuan, Wujin, Yizheng, Changshu, and Kunshan, respectively.

[0124] The types and amounts of fertilizers used in the various regions described in Table 12 are from Table 10.

[0125] The prices of the above-mentioned fertilizers, compound fertilizer (18-18-18), compound fertilizer (15-15-15), compound fertilizer (16-16-16), compound fertilizer (30-6-12), and compound fertilizer (30-0-8) are: 3,400 yuan / ton, 2,400 yuan / ton, 2,600 yuan / ton, 3,000 yuan / ton and 3,200 yuan / ton respectively; urea: 2,200 yuan / ton; potassium sulfate: 3,800 yuan / ton; diammonium phosphate: 3,600 yuan / ton; medicinal fertilizer Jiuxiaodan: 4,500 yuan / ton; potassium chloride 2,200 yuan / ton.

[0126] The controlled-release fertilizer described in Table 12 is the resin-coated fertilizer of Formula B in Example 3 of the present invention. Referring to the current market price range of resin-coated fertilizers of 4,800 to 10,000 yuan / ton, the average price is taken as 7,500 yuan / ton.

[0127] The fertilization cost described in Table 12 is 0.5 yuan / kg for using drones to apply fertilizer in the field.

[0128] It can be seen from the above results that the subsoil fertilizer loading method of the present application realizes the integration of transplanting and fertilization, which reduces the fertilizer application cost and the risk of nitrogen and phosphorus pollution emissions from rice fields while ensuring high and stable rice yields.

[0129] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Persons skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A naturally degradable controlled-release fertilizer, characterized in that: The coating of the controlled-release fertilizer is composed of the following components: 20-60 parts of low-density polyethylene resin, 10-20 parts of ethylene-vinyl acetate copolymer, 5-30 parts of synthetic resin biodegradation inducer, 3-15 parts of starch, 10-70 parts of talc, and 0.2-2 parts of non-ionic surfactant; the controlled-release fertilizer includes urea and compound fertilizer respectively coated by the coating.

2. The naturally degradable controlled-release fertilizer according to claim 1, characterized in that: The nonionic surfactant has an ethylene oxide addition number EO=6 and a cloud point CP=52°C.

3. The naturally degradable controlled-release fertilizer according to claim 1, characterized in that: The compound fertilizer is one or more combinations of potassium dihydrogen phosphate, monoammonium phosphate, diammonium phosphate, potassium nitrate, potassium chloride, and potassium sulfate.

4. The naturally degradable controlled-release fertilizer according to claim 1, characterized in that: The coating rate of the urea and compound fertilizer is 9-20%.

5. The method for preparing the naturally degradable controlled-release fertilizer according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) mixing a low-density polyethylene resin, an ethylene-vinyl acetate copolymer, a synthetic resin biodegradation inducer, starch, talc, a nonionic surfactant, and a pigment, and dissolving the mixture in tetrachloroethylene to obtain a coating solution; (2) The coating solution is coated on urea and compound fertilizer respectively, and the coated urea and compound fertilizer are mixed to obtain a naturally degradable controlled-release fertilizer.

6. The preparation method according to claim 5, characterized in that The solid content of the coating solution in step (1) is 4-7%.

7. The preparation method according to claim 5, characterized in that The coating conditions of the urea in step (2) include: hot air temperature of 60-80° C.; coating time of 38-50 minutes; the coating conditions of the compound fertilizer include: hot air temperature of 60-80° C.; coating time of 47-61 minutes.

8. A method for planting rice by using subsoil fertilizer instead of topsoil fertilizer, characterized in that: The following steps are involved: (1) Mixing the naturally degradable controlled-release fertilizer according to any one of claims 1 to 4 with subsoil, sowing rice in a standard seedling tray, and raising rice seedlings; (2) Transplant the rice seedlings into the field after they are 20 to 25 days old.

9. The method according to claim 8, characterized in that The amount of the naturally degradable controlled-release fertilizer in step (1) is 340 to 680 g per standard seedling tray.

10. The method according to claim 8, characterized in that The method further comprises the step of applying 50-100% ear fertilizer after step (2).

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