Lignin sulfonate modified water-soluble fertilizer, and preparation method and application thereof

Abstract

The present application provides a kind of lignin sulfonate modified water-soluble fertilizer and its preparation method and application, belong to fertilizer processing technical field.The preparation method of the present application includes the following steps: lignin sulfonate, organic acid, copper sulfate and water are mixed, 170-185 DEG C is reacted under high pressure closed environment 45-100 min, after cooling, strong oxidizing agent is added, again 180-185 DEG C is reacted under high pressure closed environment 120-150 min, after cooling, solid-liquid separation, liquid is lignin sulfonate modified water-soluble fertilizer.The present application breaks the macromolecular chain of lignin sulfonate by acid, hydrolysis process, so that its molecular weight is significantly reduced, and the final product has obvious growth-promoting effect, promotes crop growth, and improves crop yield.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer processing technology, and particularly relates to a lignin sulfonate modified water-soluble fertilizer, its preparation method and application. Background Technology

[0002] Lignosulfonates, also known as sulfonated lignin, are a byproduct of sulfite pulping and are linear polymers. In agricultural production, the adsorption and slow-release properties of lignin sulfonates effectively maintain the effectiveness of chemical fertilizers and allow for their slow release, making them an excellent slow-release material for organic compound fertilizers. These polycyclic organic polymers, containing many negatively charged groups, have a strong affinity for high-valence metal ions in the soil. Using lignin sulfonates as fertilizer carriers to adsorb or encapsulate fertilizers achieves the goal of slow fertilizer release.

[0003] Regarding the development and application of lignin sulfonate water-soluble fertilizer, invention patent application number 201010621733.9 discloses a clean and high-value utilization method for preparing fulvic acid and fertilizer from papermaking black liquor (the main component of which is lignin sulfonate). Specifically, various straws or wood are used as raw materials for alkaline pulping. The obtained black liquor is concentrated and evaporated. Peracetic acid and hydrogen peroxide solution are used as oxidants and reacted with the concentrated black liquor at 50-90℃ for 30-90 minutes to degrade it. The reaction solution is adjusted to pH 4-6 with acid, and then fulvic acid solution is obtained through solid-liquid separation. In this technology, papermaking black liquor can be completely utilized as a resource, which not only completely eliminates the pollution of black liquor, but also converts it into high-value fulvic acid. At the same time, other solid waste generated in the papermaking process is prepared into fertilizer, realizing the clean and high-value utilization of waste resources. US Patent 7198805 B2 discloses a method for producing humates in a continuous manner with high yield of useful products. The method produces humates by liquid-phase oxidation of a mixture of alkaline reagents and lignin-containing plant raw materials (lignin or lignin sulfonate). The resulting polymer compounds have carboxyl groups around their periphery, which facilitates the dissolution of the oxidation products in alkali, making them similar to natural humic acid and humic acid produced from other raw materials.

[0004] Because lignin sulfonates possess resistance to acids and hard water, they are often marketed as "plant fulvic acid." However, lignin sulfonates have a large molecular weight, exceeding 20,000 Daltons, which contradicts the definition of fulvic acid. Furthermore, once in the soil, lignin sulfonates have fewer functional groups, resulting in weaker ion-chelating ability compared to mineral-derived potassium fulvicate. Consequently, their ability to activate soil nutrients and promote growth is also significantly weaker than that of mineral-derived fulvic acid. This leads to a much higher dosage of lignin sulfonates in drip irrigation compared to mineral-derived fulvic acid. For example, the typical dosage of lignin sulfonates is 5-10 kg / acre, while 200-300 g / acre of mineral-derived fulvic acid can produce a good growth-promoting effect.

[0005] Therefore, research on how to improve the oxygen-containing functional groups in the structure of lignin sulfonate, while transforming macromolecular structures into small molecules, to enhance the effectiveness of lignin sulfonate in crop applications has great potential. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a lignin sulfonate modified water-soluble fertilizer, its preparation method and application, which breaks the macromolecular chain of lignin sulfonate through acid and hot water hydrolysis, thereby significantly reducing its molecular weight, and the final product has a significant growth-promoting effect.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] A method for preparing a lignin sulfonate modified water-soluble fertilizer includes the following steps: mixing lignin sulfonate, organic acid, copper sulfate and water, reacting at 170-185℃ for 45-100 min under high pressure and closed environment, adding a strong oxidant after cooling, and reacting again at 180-185℃ for 120-150 min under high pressure and closed environment, and separating the solid and liquid after cooling, the liquid being the lignin sulfonate modified water-soluble fertilizer.

[0009] Preferably, the lignin sulfonate is a byproduct of sulfite pulping and includes one or more of ammonium lignin sulfonate, sodium lignin sulfonate, and calcium lignin sulfonate.

[0010] Preferably, by weight, the lignin sulfonate comprises 50-80 parts, the organic acid 5.5-8.8 parts, the copper sulfate 0.01-0.05 parts, and the water 800-1000 parts.

[0011] More preferably, by weight, the organic acid comprises 5-8 parts of acetic acid, 0.3-0.5 parts of oxalic acid, and 0.2-0.3 parts of maleic acid.

[0012] Preferably, the amount of the strong oxidant added is 20-30 parts by weight.

[0013] Preferably, the reaction is carried out in a hydrothermal reactor, and the stirring speed of the hydrothermal reactor is 150-250 rpm.

[0014] Preferably, the rotation speed for solid-liquid separation is 3000-3500 rpm.

[0015] The present invention also provides a lignin sulfonate modified water-soluble fertilizer prepared by the aforementioned preparation method.

[0016] This invention also provides the application of the lignin sulfonate modified water-soluble fertilizer in fertilizer preparation and its application in crop cultivation.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] This invention provides a method for preparing lignin sulfonate modified water-soluble fertilizer. Through hot water hydrolysis and thermal oxidation processes, the weight-average molecular weight of the lignin sulfonate raw material is significantly reduced to only 45.5% of that of the raw material, while about 5% of pure lignin in the raw material is removed.

[0019] This invention significantly increases the O / C ratio of lignin sulfonate, and increases the number of chemical functional groups such as carbonyl, carboxylic acid, phenolic hydroxyl and ester, resulting in stronger ion exchange and adsorption capabilities.

[0020] The lignin sulfonate modified water-soluble fertilizer prepared by this invention requires a small amount, such as only 1 kg per acre per application when drip irrigating crops. It has a significant effect on promoting plant growth and can also improve the plant's nutrient absorption and crop yield. Attached Figure Description

[0021] Figure 1 Fourier transform infrared spectra of lignin sulfonate raw material (CK) and modified lignin sulfonate raw material (CK).

[0022] Figure 2 To illustrate the effects of different fertilizer treatments on the aboveground and underground growth of maize seedlings, the figures, from left to right, show cow manure compost extract treatment, lignin sulfonate treatment, lignin sulfonate modified water-soluble fertilizer treatment, and control (CK).

[0023] Figure 3 The figure shows the effects of different fertilizer treatments on maize growth. The left side represents the control (CK), and the right side represents the treatment with lignin sulfonate-modified water-soluble fertilizer. Detailed Implementation

[0024] This invention provides a method for preparing lignin sulfonate-modified water-soluble fertilizer to improve the application effect of lignin sulfonate, comprising the following steps:

[0025] (1) Mix lignin sulfonate, organic acid, copper sulfate and water.

[0026] In this invention, lignin sulfonate is preferably a byproduct of sulfite pulping, including one or more of ammonium lignin sulfonate, sodium lignin sulfonate, and calcium lignin sulfonate, including but not limited to waste products remaining after papermaking using wheat straw, rice straw, or other wood as the main raw material. When the above-mentioned lignin sulfonate is applied directly as a water-soluble fertilizer, its large molecular weight (over 20,000 Daltons) and fewer binding sites for oxygen-containing functional groups compared to mineral-derived humic acid result in relatively weak ion-binding buffering capacity, leading to problems such as large application amounts and insignificant effects. This invention utilizes organic acids and copper ions to modify it, optimizing its application effect.

[0027] In this invention, preferably, by weight, the composition is 50-80 parts of lignin sulfonate, 5.5-8.8 parts of organic acid, 0.01-0.05 parts of copper sulfate, and 800-1000 parts of water; more preferably, the organic acid includes 5-8 parts of acetic acid, 0.3-0.5 parts of oxalic acid, and 0.2-0.3 parts of maleic acid; more preferably, the composition is 70 parts of lignin sulfonate, 8 parts of acetic acid, 0.3 parts of oxalic acid, 0.2 parts of maleic acid, 0.05 parts of copper sulfate, and 800 parts of water. The lignin sulfonate contains a large amount of cellulose, hemicellulose residues, and lignin (unsulfonated) bound to its macromolecules. Through hydrolysis catalyzed by a specific ratio of organic acids and copper ions, the cellulose and hemicellulose residues are converted into monosaccharides such as glucose, xylose, arabinose, and galactose. Under acidic conditions, these residues are dehydrated by heating to generate furfural or its derivatives. These small molecules polymerize to form a dark brown substance (humic acid), which has a significant plant growth-promoting effect.

[0028] (2) The reaction is carried out at 170-185℃ for 45-100 min under high pressure and a closed environment, followed by cooling after the reaction is completed; preferably, the reaction is carried out at 180℃ for 75-80 min under high pressure and a closed environment; more preferably, the reaction is carried out in a hydrothermal reactor with a stirring speed of 150-250 rpm; more preferably, the stirring speed is 150-200 rpm. The high pressure mentioned in this invention is a pressure >101.325 kPa.

[0029] In this invention, the main process employed is organic acid hydrolysis. Lignosulfonate has excellent pH buffering capacity; after adding organic acid, the pH of the reaction system is 4.8-5.0. During the hydrolysis process, acetic acid primarily acts as a catalyst, promoting the hydrolysis of cellulose. It provides hydrogen ions, which, after dissociation in water, bind to the β-1,4-glucosidic bonds on the cellulose chain, causing them to break and thus decomposing cellulose into low-molecular-weight polysaccharides and monosaccharides. Oxalic acid has excellent degradation properties, degrading the amorphous structures in the lignocellulose molecular chain, thereby reducing the degree of polymerization and crystallinity of cellulose. Maleic acid hydrolyzes hemicellulose to produce xylose or other oligosaccharides. Copper ions promote the acid hydrolysis of cellulose. This invention utilizes the reaction of these three organic acids in combination with copper sulfate in a specific ratio with ligninsulfonate, achieving excellent degradation of fibers and hemicellulose while simultaneously removing lignin.

[0030] (3) After cooling in step (2), add a strong oxidant and react again at 180-185℃ for 120-150 min under high pressure and closed environment. After the reaction is completed, cool again. Preferably, the reaction is carried out in a hydrothermal reactor with a stirring speed of 150-250 rpm; more preferably, the stirring speed is 200-250 rpm.

[0031] In this invention, the strong oxidant releases oxygen during heating, utilizing the high temperature and pressure environment combined with oxygen to oxidize the substrate. Preferably, the amount of strong oxidant added is 20-30 parts by weight, more preferably 25 parts, and even more preferably, the strong oxidant is selected from one of hydrogen peroxide, ammonium persulfate, and peracetic acid.

[0032] (4) After cooling in step (3), solid-liquid separation is performed, and the liquid is lignin sulfonate modified water-soluble fertilizer. The preferred rotation speed for solid-liquid separation is 3000-3500 rpm. This invention uses the by-product of sulfite pulp papermaking as raw material. After the process is completed, about 5% lignin precipitation will occur, so it is removed by solid-liquid separation.

[0033] The present invention also provides a lignin sulfonate modified water-soluble fertilizer prepared by the above preparation method.

[0034] The present invention also provides the application of the above-mentioned lignin sulfonate modified water-soluble fertilizer in the preparation of fertilizers, including but not limited to direct processing into drip irrigation carbon fertilizer, or processing as a raw material component into other blended fertilizers. As an embodiment, the content of lignin sulfonate modified water-soluble fertilizer in the blended fertilizer is 0.1%-99.9%.

[0035] This invention also provides the application of the above-mentioned lignin sulfonate modified water-soluble fertilizer in crop cultivation; preferably, it is used as a drip irrigation water-soluble fertilizer and applied during the seedling stage of crops; more preferably, the application rate is 1 kg / mu. As one possible implementation method, the crop is corn.

[0036] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0037] Example 1

[0038] A lignin sulfonate-modified water-soluble fertilizer, the steps are as follows:

[0039] Lignosulfonate (calcium lignosulfonate), acetic acid, oxalic acid, maleic acid, copper sulfate, and water were mixed in a specific mass ratio of 50 parts: 5 parts: 0.3 parts: 0.2 parts: 0.05 parts: 1000 parts, and placed in a sealed hydrothermal reactor. The reactor was set with a stirring speed of 200 rpm and a reaction temperature of 170°C for 45 minutes. After cooling, the reactor was opened, 20 ml of hydrogen peroxide was added, and the reactor was sealed again. The reactor was then set with a stirring speed of 250 rpm and a reaction temperature of 180°C for 120 minutes. After cooling, the reactor was opened, and centrifugation was used to separate the solid and liquid phases. The liquid was the prepared product, lignosulfonate-modified water-soluble fertilizer.

[0040] Example 2

[0041] A lignin sulfonate-modified water-soluble fertilizer, the steps are as follows:

[0042] Lignosulfonate (ammonium lignosulfonate), acetic acid, oxalic acid, maleic acid, copper sulfate, and water were mixed in a specific mass ratio of 80 parts: 8 parts: 0.5 parts: 0.3 parts: 0.01 parts: 1000 parts, and placed in a sealed hydrothermal reactor. The reactor was set with a stirring speed of 150 rpm and a reaction temperature of 180°C for 90 minutes. After cooling, the reactor was opened, 30 ml of peracetic acid was added, and the reactor was sealed again. The reactor was then set with a stirring speed of 200 rpm and a reaction temperature of 185°C for 150 minutes. After cooling, the reactor was opened, and centrifugation was used to separate the solid and liquid phases. The liquid was the prepared product, lignosulfonate-modified water-soluble fertilizer.

[0043] Example 3

[0044] A lignin sulfonate-modified water-soluble fertilizer, the steps are as follows:

[0045] Lignosulfonates (sodium lignosulfonate and calcium lignosulfonate), acetic acid, oxalic acid, maleic acid, copper sulfate, and water were mixed in a specific mass ratio of 70 parts: 5 parts: 0.5 parts: 0.3 parts: 0.01 parts: 900 parts, and placed in a sealed hydrothermal reactor. The reactor was set with a stirring speed of 200 rpm and a reaction temperature of 185°C for 100 min. After cooling, the reactor was opened, 30 ml of hydrogen peroxide was added, and the reactor was sealed again. The reactor was then set with a stirring speed of 250 rpm and a reaction temperature of 180°C for 120 min. After cooling, the reactor was opened, and centrifugation was used to separate the solid and liquid phases. The liquid was the prepared product, lignosulfonate-modified water-soluble fertilizer.

[0046] Example 4

[0047] A lignin sulfonate-modified water-soluble fertilizer, the steps are as follows:

[0048] Lignosulfonate (sodium lignosulfonate), acetic acid, oxalic acid, maleic acid, copper sulfate, and water were mixed in a specific mass ratio of 80 parts: 6 parts: 0.4 parts: 0.2 parts: 0.03 parts: 800 parts, and placed in a sealed hydrothermal reactor. The reactor was set with a stirring speed of 180 rpm and a reaction temperature of 170°C for 100 min. After cooling, the reactor was opened, 25 ml of hydrogen peroxide was added, and the reactor was sealed again. The reactor was then set with a stirring speed of 230 rpm and a reaction temperature of 185°C for 140 min. After cooling, the reactor was opened, and centrifugation was used to separate the solid and liquid phases. The liquid was the prepared product, lignosulfonate-modified water-soluble fertilizer.

[0049] Example 5

[0050] Comparison of infrared spectral characteristics between sodium lignosulfonate raw material (CK) and modified product

[0051] Sodium lignosulfonate was purchased from Shenyang Xingzhenghe Chemical Co., Ltd.; the modified treatment was the lignosulfonate-modified water-soluble fertilizer prepared in Example 4.

[0052] Tested by Shanghai Fuda Testing Technology Group Co., Ltd., report number: FT-20240819109, results are as follows: Figure 1 As shown.

[0053] according to Figure 1 It can be seen that in the range of 4000-1500cm -1 In the wavenumber band, the characteristic absorption peaks of the infrared spectra of the two samples are almost identical; in the 500-1500 cm⁻¹ range... -1 In the wavenumber band, there are some differences in the characteristic absorption peaks of the infrared spectra of the two samples, while the 500-1500 cm⁻¹ band... -1 Within the wavenumber band, vibrations and bending of matter produce absorption peaks, commonly referred to as fingerprint peaks; 900-1500 cm⁻¹ -1 Within the wavenumber band, the absorption peak is typically located between the vibrational and bending peaks; the two samples are at 990 cm⁻¹. -1 1220cm -1 The peaks show significant differences, and these peaks are usually associated with chemical functional groups such as carbonyl, carboxylic acid, phenolic hydroxyl, and ester; Simultaneously, processing at 680 cm⁻¹... -1 The presence of a specific peak indicates that the process of this invention causes structural differences in sodium lignosulfonate.

[0054] Example 6

[0055] Comparison of molecular weight distribution and elemental composition of sodium lignosulfonate raw material (CK) and modified product

[0056] Sodium lignosulfonate was purchased from Shenyang Xingzhenghe Chemical Co., Ltd.; the modified treatment was the lignosulfonate-modified water-soluble fertilizer prepared in Example 4.

[0057] The molecular weight distribution was determined by gel permeation chromatography (GPC) system (Agilent PL-GPC220) by Shanghai Fuda Testing Technology Group Co., Ltd., report number: FT-20240819109, as shown in Table 1.

[0058] Table 1. Differences in molecular weight distribution between sodium lignosulfonate raw material (CK) and modified sodium lignosulfonate.

[0059] CK 475 810 2963 17891 36249 2179 3.65802 Modification treatment 1696 1137 1349 1538 1728 1320 1.18646

[0060] In the table, Mp: peak molecular weight; Mn: number-average molecular weight; Mw: mass-average molecular weight (weight-average molecular weight); Mz: polydisperse molecular weight; Mz+1: high molecular weight; Mv: viscosity-average molecular weight; PD: molecular weight distribution index.

[0061] As shown in Table 1, the weight-average molecular weight (Mw) decreased from 2963 g / mol in the control to 1349 g / mol, a decrease of 54.5%; the molecular weight distribution index (PD) decreased from 3.66 to 1.19, with the PD value approaching 1 after treatment, indicating that the polymer molecular weight is relatively uniform. These results demonstrate that the molecular weight of sodium lignosulfonate changes after treatment using the process of this invention; the polymerized molecular chains are broken down into shorter chains, and the molecules are relatively uniform.

[0062] The elemental composition was determined using an organic elemental analyzer (UNICUBE elemental analyzer) in CHNS mode and oxygen mode, as shown in Table 2.

[0063] Table 2. Differences in elemental composition between sodium lignosulfonate raw material (CK) and modified product.

[0064]

[0065] The molar ratio of elements can characterize the degree of oxidation and aroma of lignin humic acid to a certain extent. As can be seen from Table 2, the samples treated by the process of the present invention have a high O content, a low C content, and a high O / C ratio.

[0066] Example 7

[0067] The effects of nutrient solutions from different sources on maize seedling growth were evaluated through hydroponic experiments, and the potential of lignin sulfonate-modified water-soluble fertilizer for agricultural application was assessed.

[0068] Materials and Methods

[0069] (1) Test materials

[0070] The four treatments were sodium lignosulfonate treatment (LS treatment), lignosulfonate modified water-soluble fertilizer treatment (modified LS treatment), cow manure compost extract treatment, and control (CK). The four treatments contained the same levels of N, P2O5, K2O+ trace elements.

[0071] Sodium lignosulfonate was purchased from Shenyang Xingzhenghe Chemical Co., Ltd.; the modified treatment was the lignosulfonate-modified water-soluble fertilizer prepared in Example 4; the cow manure compost extract was prepared by catalytic oxidation-alkali dissolution and acid precipitation method (DOI:10.19451 / j.cnki.issn1671-9212.2006.06.014.).

[0072] (2) Test methods

[0073] Sodium lignosulfonate, lignosulfonate-modified water-soluble fertilizer, and cow manure compost extract were diluted 20,000 times to prepare nutrient solutions. Potting soil was prepared for placing corn seeds, ensuring good seed-soil contact. A transparent container was placed under the potting soil and filled with an appropriate amount of nutrient solution, ensuring adequate aeration to guarantee sufficient oxygen content for root respiration. During the prescribed growth cycle, the nutrient solution was replenished regularly to maintain its concentration and cleanliness. The control (CK) was supplemented with the same amount of water.

[0074] (3) Measurement indicators

[0075] Several days after planting, the aboveground biomass (including stems, leaves, etc.) and underground biomass (roots) of corn were measured.

[0076] Experimental results.

[0077] according to Figure 2 As shown in Table 3, different treatments had different effects on the biomass of maize's aboveground and belowground parts. Under the control (CK) treatment, the aboveground weight of maize was 0.51 g. In contrast, the modified LS treatment significantly increased the aboveground weight (P<0.05), with an increase of 27.48%, showing the best performance. The cow manure compost extract treatment also had a positive effect, with an increase in aboveground weight of 12.27%, while the LS treatment had almost no effect on the aboveground weight, with an increase of only -0.27%, which can be considered as no change. For the weight of the belowground part per plant, the CK treatment was 0.04 g. Both the modified LS treatment and the cow manure compost extract treatment significantly promoted the growth of the belowground part, with an increase of about 50%. The LS treatment had no significant effect on the weight of the belowground part (P>0.05). Overall, the modified LS treatment performed the best in increasing the biomass per plant, with an increase of 29.19%. The cow manure compost extract treatment had an increase of 14.82%, showing the second best performance. The LS treatment had no significant effect on the biomass per plant.

[0078] Furthermore, the root-to-shoot ratio in the CK treatment was 0.08, indicating that under control conditions, the aboveground biomass of the plant was relatively high, while the underground biomass accounted for a small proportion. The root-to-shoot ratio in the modified LS treatment increased to 0.10, a slight increase compared to the CK. This suggests that the modified LS treatment promoted root growth, resulting in a relatively greater allocation of resources to the underground parts of the plant, thereby enhancing the growth potential of maize. The LS treatment did not change the root-to-shoot ratio, which remained the same as the CK at 0.08. The cow manure compost extract treatment had the highest root-to-shoot ratio at 0.11, indicating that the cow manure compost extract treatment significantly promoted root growth.

[0079] Table 3 Effects of different nutrient solution treatments on maize seedling growth

[0080]

[0081] In summary, the modified LS treatment and the cow manure compost extract treatment showed the best effects in promoting the growth of both aboveground and belowground parts of the plant and increasing biomass. The cow manure compost extract treatment had the most significant effect on increasing the root-to-shoot ratio. This indicates that these two treatments can improve the plant's growth by promoting root growth, while the LS treatment did not make a significant contribution to the increase of plant biomass and root-to-shoot ratio.

[0082] Example 8

[0083] By comparing and analyzing the effects of sludge humic acid, mineral humic acid, and lignin sulfonate-modified water-soluble fertilizer treatments at different concentration gradients on maize seedling biomass and nutrient absorption, this study aims to assess whether lignin sulfonate-modified water-soluble fertilizer has promising agricultural applications.

[0084] Materials and Methods

[0085] (1) Test materials

[0086] Humic acid extracts: sludge fulvic acid, mineral-derived potassium humate and lignin sulfonate modified water-soluble fertilizer (modified LS); corn seeds.

[0087] The sludge fulvic acid and mineral-derived potassium humate were purchased from Shenyang Xingzhenghe Chemical Co., Ltd.; the modification treatment was the lignin sulfonate modified water-soluble fertilizer prepared in Example 4.

[0088] (2) Test methods

[0089] At the start of the experiment, soil corresponding to each treatment was evenly distributed into flowerpots, with each pot weighing 15 kg, and 5 pots per treatment. Five corn plants were planted in each pot. Nitrogen fertilizer and phosphorus and potassium fertilizer were applied as top dressing, with nitrogen fertilizer being 150 mg / kg urea and phosphorus and potassium fertilizer being 75 mg / kg potassium dihydrogen phosphate, prepared according to the air-dried soil weight to form a nutrient solution.

[0090] Lignosulfonate-modified water-soluble fertilizer and sludge fulvic acid were diluted 10,000 times and 20,000 times respectively, and mineral-derived potassium humate was diluted 15,000 times and 30,000 times respectively (designed for equal cost). Each treatment was defined as CK, low-concentration (L) sludge fulvic acid treatment, high-concentration (H) sludge fulvic acid treatment, low-concentration (L) modified LS treatment, high-concentration (H) modified LS treatment, low-concentration (L) mineral-derived potassium humate treatment, and high-concentration (H) mineral-derived potassium humate treatment. The above treatments were then mixed with nutrient solution as top dressing.

[0091] (3) Measurement indicators

[0092] Thirty days after corn planting, growth indicators (including dry weight of aboveground and underground parts) and plant nutrient content (nitrogen, phosphorus, and potassium) were measured using conventional methods. Excel 2019 was used to process the relevant data and perform significance analysis.

[0093] Experimental results.

[0094] (1) Effects of different treatments on maize seedling biomass

[0095] Table 4 shows the biomass and growth rate of maize seedlings under each treatment.

[0096] Table 4. Biomass and variation of maize seedlings under different treatments.

[0097]

[0098]

[0099] Table 4 shows that sludge fulvic acid, modified LS, and potassium humate from mineral sources all have a positive impact on the growth of plant underground parts, with varying effects at different concentrations. Modified LS treatment increased the dry weight of underground parts at both concentrations, and the increase in dry weight increased significantly from 12.08% to 14.73% with increasing concentration (P<0.05). This indicates that modified LS promotes root growth, and the effect strengthens with increasing concentration. Potassium humate from mineral sources showed the most significant effect on increasing the dry weight of underground parts, especially at high concentrations, where it increased by 26.09%, far exceeding other treatments. Sludge fulvic acid treatment increased the dry weight of aboveground parts at both concentrations, but the effect weakened with increasing concentration, with the increase decreasing from 15.28% to 11.86%. This suggests that excessively high concentrations of sludge fulvic acid may have a certain inhibitory effect on aboveground growth. The effect of modified LS treatment weakened with increasing concentration; in fact, at high concentrations, the increase in aboveground part biomass was -4.81%, making it the only treatment to show negative growth. This indicates that high concentrations of modified LS may have an inhibitory effect on aboveground part growth, suggesting the existence of an optimal concentration range. The effect of low concentrations of modified LS treatment on maize plant biomass was significantly different from the control (P<0.05), with a biomass increase exceeding 12%. Figure 3 As shown, the high concentration showed no difference compared to the control (P>0.05).

[0100] (2) Effects of different treatments on nutrient absorption in maize seedlings

[0101] Table 5 shows the nutrient absorption of maize seedlings under each treatment.

[0102] Table 5. Nutrient absorption status of maize seedlings under different treatments.

[0103]

[0104] As shown in Table 5, all three treatments had a certain impact on nutrient absorption by the plants, and many indicators showed significant differences between the treatments and the control (P<0.05). The high-concentration sludge humic acid treatment showed the best performance, with a 40%-50% increase in total nitrogen, phosphorus, and potassium absorption. The low-concentration modified LS treatment showed a 17.7%-40% increase in total nitrogen, phosphorus, and potassium absorption, with a relatively high increase in total phosphorus (40%), and increases of 17.7% and 20.15% for other nutrients, respectively. In contrast, the high-concentration modified LS treatment only showed a 3.5%-14.6% increase in total nitrogen, phosphorus, and potassium absorption. The high-concentration potassium humate treatment showed higher total nitrogen absorption, with total phosphorus and potassium absorption at 21% and 26%, respectively.

[0105] In summary, low-concentration treatment with modified LS can effectively increase maize seedling biomass, promote root growth, and enhance soil nutrient absorption capacity. However, high-concentration treatment has a certain inhibitory effect on maize growth. Therefore, attention should be paid to the dosage during agricultural applications.

[0106] Example 9

[0107] This study analyzed the effects of sodium lignosulfonate (LS) and lignosulfonate-modified water-soluble fertilizer (modified LS) on maize yield using drip irrigation, and assessed whether lignosulfonate-modified water-soluble fertilizer has promising agricultural applications.

[0108] Materials and Methods

[0109] (1) Test materials

[0110] Sodium lignosulfonate was purchased from Shenyang Xingzhenghe Chemical Co., Ltd.; the modified treatment was the lignosulfonate-modified water-soluble fertilizer prepared in Example 4.

[0111] (2) Test methods

[0112] Five treatments were established with the same phosphorus and potassium (P2O5 150 kg / hm2, K2O 75 kg / hm2). Treatment 1: conventional fertilization (CK); Treatment 2: conventional fertilization (CK) + 1 kg LS; Treatment 3: conventional fertilization (CK) + 5 kg LS; Treatment 4: conventional fertilization (CK) + 1 kg modified LS. After the corn seedlings had hardened off, drip irrigation fertilization was carried out on May 20th. Each treatment was repeated three times, with a plot area of ​​200 m2. 2 .

[0113] (3) Measurement indicators

[0114] After the corn matures, yield is measured, including the number of ears per mu, the number of kernels per ear, the weight of kernels per ear, and the yield per mu.

[0115] Test results

[0116] As shown in Table 6, there was no significant difference in the number of maize plants among the treatments (P>0.05). The grain weight per plant in treatments 3 and 4 was significantly greater than that in the control (CK) treatment, with treatment 4 showing the highest weight at 179.09 g / plant, significantly higher than both CK and treatment 2 (P<0.05). There was no significant difference between CK and treatment 2 (P>0.05). Compared to CK, treatments 3 and 4 significantly increased maize yield (P<0.05), with increases of 6.73% and 8.12%, respectively.

[0117] Table 6. Corn yield under drip irrigation with different water-soluble fertilizers

[0118]

[0119]

[0120] The above results indicate that modified LS can increase maize yield under drip irrigation conditions, with a significant difference in yield increase, and the yield increase effect is better than that of unmodified LS.

[0121] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a lignin sulfonate-modified water-soluble fertilizer, characterized in that, Includes the following steps: Lignosulfonate, organic acid, copper sulfate and water are mixed and reacted at 170-185℃ for 45-100 min under high pressure and closed environment. After cooling, a strong oxidant is added and reacted again at 180-185℃ for 120-150 min under high pressure and closed environment. After cooling, the solid and liquid are separated and the liquid is ligninsulfonate modified water-soluble fertilizer. By weight, the lignin sulfonate comprises 50-80 parts, organic acid 5.5-8.8 parts, copper sulfate 0.01-0.05 parts, and water 800-1000 parts; By weight, the organic acids include 5-8 parts acetic acid, 0.3-0.5 parts oxalic acid, and 0.2-0.3 parts maleic acid.

2. The preparation method according to claim 1, characterized in that, The lignin sulfonate is a byproduct of sulfite pulping and includes one or more of ammonium lignin sulfonate, sodium lignin sulfonate, and calcium lignin sulfonate.

3. The preparation method according to claim 1, characterized in that, The amount of the strong oxidant added is 20-30 parts by weight.

4. The preparation method according to claim 1, characterized in that, The reaction is carried out in a hydrothermal reactor, and the stirring speed of the hydrothermal reactor is 150-250 rpm.

5. The preparation method according to claim 1, characterized in that, The rotation speed for solid-liquid separation is 3000-3500 rpm.

6. The lignin sulfonate modified water-soluble fertilizer prepared by the preparation method according to any one of claims 1-5.

7. The application of the lignin sulfonate modified water-soluble fertilizer according to claim 6 in the preparation of fertilizers.

8. The application of the lignin sulfonate modified water-soluble fertilizer according to claim 6 in crop cultivation.

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