Organic liquid fertilizer based on straw enzymatic hydrolysate and preparation method thereof

Abstract

This invention relates to the field of fertilizer technology, specifically to an organic liquid fertilizer based on straw enzymatic hydrolysate and its preparation method. The method includes: pretreating corn straw with potassium hydroxide, followed by enzymatic hydrolysis with cellulase and xylanase to obtain the enzymatic supernatant; sequentially treating the supernatant with an ultrafiltration membrane with a molecular weight cutoff of 3000 Da and a nanofiltration membrane with a molecular weight cutoff of 500 Da to collect oligosaccharides with a molecular weight window of 500-3000 Da; partially stabilizing the reducing end of the oligosaccharides with sodium borohydride; pre-complexing with boric acid at pH 8.4-8.8; then sequentially adding relatively low molecular weight sodium polyglutamate, calcium chloride dihydrate aqueous solution, and ultra-high molecular weight sodium polyglutamate to construct a sequential complexation system; subsequently adding potassium nitrate and citric acid aqueous solution; and finally, after filtration at 5 μm and heat treatment at 70℃, obtaining the organic liquid fertilizer. This fertilizer has a high proportion of 500-3000 Da oligosaccharides and a low reducing sugar equivalent, inhibiting storage precipitation and browning, and improving the retention rate of extractable oligosaccharides in the soil.

Description

Technical Field

[0001] This invention relates to the field of fertilizer technology, and in particular to an organic liquid fertilizer based on straw enzymatic hydrolysate and its preparation method. Background Technology

[0002] Straw and other lignocellulosic biomass resources are rich in organic carbon, making them potential raw materials for the preparation of organic liquid fertilizers. Current technologies typically employ alkali pretreatment combined with enzymatic hydrolysis using cellulase and / or xylanase to convert cellulose and hemicellulose in straw into soluble sugars, thereby preparing liquid organic fertilizers or biostimulants. While these methods improve straw utilization, the resulting enzymatic hydrolysates have a complex composition, containing a wide molecular weight distribution ranging from monosaccharides to polysaccharides and even lignin degradation products, posing significant drawbacks for direct use in liquid fertilizer preparation.

[0003] First, components with excessively large molecular weights (e.g., greater than 3000 Da) in the enzymatic hydrolysate are prone to aggregation and sedimentation during storage, leading to decreased product uniformity and posing a risk of clogging in drip irrigation applications. On the other hand, monosaccharides or oligosaccharides with excessively small molecular weights (e.g., less than 500 Da) are prone to non-enzymatic browning such as Maillard reactions during storage due to their high reducing end activity, resulting in darker product color and deteriorated appearance. Furthermore, these small molecules are easily consumed by microorganisms after being applied to the soil, failing to provide continuous rhizosphere stimulation for crops.

[0004] Secondly, existing technologies typically focus on increasing the total organic matter content in the enzymatic hydrolysate or performing simple filtration and concentration, lacking effective enrichment and stabilization design for specific active oligosaccharide windows (such as 500-3000 Da). Even if components within a specific molecular weight range are obtained through membrane separation technology, their unstable reducing ends are not modified, leading to problems such as browning and excessively rapid bioavailability during storage and subsequent applications.

[0005] Furthermore, to enhance the functionality of fertilizers, water-retaining agents such as sodium polyglutamate or trace elements are sometimes added to the system. However, existing methods of addition often overlook the timing of interactions between components. For example, if the complexation process between calcium ions and sodium polyglutamate is not performed in the correct order, it may fail to form an ideal spatial structure, affecting the viscosity and stability of the system, and failing to provide long-term protection and a slow-release carrier for the active oligosaccharides. Simultaneously, how to construct a mild microenvironment that can stabilize the active ingredients without introducing harsh conditions such as high temperatures during subsequent processing that could damage their structure is also an aspect that current technologies have not adequately considered.

[0006] Therefore, developing a method for preparing organic liquid fertilizer that can precisely enrich the active oligosaccharide window from straw enzymatic hydrolysate, effectively inhibit its storage browning, achieve continuous and slow release into the soil, and maintain excellent physical stability has become a technical problem that needs to be solved in this field. Summary of the Invention

[0007] In view of this, the purpose of this invention is to propose an organic liquid fertilizer based on straw enzymatic hydrolysate and its preparation method, so as to solve the comprehensive problems in the prior art of preparing organic liquid fertilizer from straw enzymatic hydrolysate, which are prone to browning and precipitation during storage, poor viscosity stability, and insufficient continuous supply of active components after application to the soil, due to the wide molecular weight distribution of active oligosaccharides, unstable reducing end, and unreasonable addition sequence of functional adjuvants.

[0008] To achieve the above objectives, the present invention provides an organic liquid fertilizer based on straw enzymatic hydrolysate. The raw materials for preparing the organic liquid fertilizer, by mass parts, include: 650-750 parts of end-group stabilized oligosaccharide solution, 1.5-2.5 parts of boric acid, 2-4 parts of low molecular weight sodium polyglutamate, 40-60 parts of calcium chloride dihydrate aqueous solution, 0.6-1.4 parts of ultra-high molecular weight sodium polyglutamate, 25-35 parts of potassium nitrate, and 196-220 parts of citric acid aqueous solution.

[0009] The calcium chloride dihydrate aqueous solution is prepared by 1.5-2.5 parts calcium chloride dihydrate and 38.5-57.5 parts deionized water, and the citric acid aqueous solution is prepared by 0.8-1.2 parts citric acid monohydrate and 195.2-218.8 parts deionized water.

[0010] The terminal-stabilized oligosaccharide solution is obtained by sequentially treating the supernatant of corn straw enzymatic hydrolysis with an ultrafiltration membrane (with a molecular weight cutoff of 3000 Da) to collect the permeate, and then treating it with a nanofiltration membrane (with a molecular weight cutoff of 500 Da) to collect the retentate. The resulting oligosaccharides with a molecular weight window of 500-3000 Da are then subjected to reducing-end stabilization treatment with sodium borohydride.

[0011] In preparing the organic liquid fertilizer, boric acid is added to the end-group stabilized oligosaccharide solution at pH 8.4-8.8 for pre-complexation, followed by the sequential addition of the relatively low molecular weight sodium polyglutamate, the calcium chloride dihydrate aqueous solution, and the ultra-high molecular weight sodium polyglutamate, and then the potassium nitrate and the citric acid aqueous solution to obtain the organic liquid fertilizer.

[0012] Preferably, the corn stalk enzymatic hydrolysis supernatant is prepared by the following method: Take 450-550 parts of corn stalk powder, 4200-4800 parts of deionized water and 15-25 parts of potassium hydroxide, heat to 75-85℃ under stirring and keep warm for 1.5-2.5 h, after the holding time is completed, cool down to 48-52℃, add 22-30 parts of citric acid monohydrate and continue stirring to obtain a pretreated slurry; add 12-18 parts of cellulase and 8-12 parts of xylanase to the pretreated slurry, and enzymatically hydrolyze at 48-52℃ for 12-20 h, after the enzymatic hydrolysis is completed, inactivate the enzyme, filter and centrifuge, and collect the corn stalk enzymatic hydrolysis supernatant.

[0013] Preferably, in the preparation of the terminal-stabilized oligosaccharide solution, 3800-4200 parts of the corn straw enzymatic hydrolysis supernatant are taken, first treated with a polyethersulfone ultrafiltration membrane with a molecular weight cutoff of 3000 Da and the permeate is collected, then the permeate is concentrated with a polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da and the retentate is collected, 900-1100 parts of deionized water are added to the obtained retentate for washing and filtration, and then concentrated to 800-1000 parts with a polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da to obtain the molecular weight window enzymatic hydrolysis solution.

[0014] Preferably, in the preparation of the terminal-stabilized oligosaccharide solution, 800-1000 parts of the molecular weight window enzymatic hydrolysate are taken, cooled to 4°C, and the pH is adjusted to 8.4-8.8 using a 10% potassium hydroxide aqueous solution. Under stirring, nitrogen protection, and exhaust conditions, 2-4 parts of sodium borohydride are added in 2-4 portions. After all the sodium borohydride has been added, the reaction continues for 3-5 hours. After the reaction is completed, 80-120 parts of citric acid aqueous solution are added, and the solution is then treated with a polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da. The solution is then washed with 900-1100 parts of deionized water and finally concentrated to 650-750 parts to obtain the terminal-stabilized oligosaccharide solution. The 80-120 parts of citric acid aqueous solution are prepared by 8-12 parts of citric acid monohydrate and 72-108 parts of deionized water.

[0015] Preferably, when preparing the organic liquid fertilizer, 650-750 parts of the terminal-stabilized oligosaccharide solution are taken, and the pH is adjusted to 8.4-8.8 using a 10% potassium hydroxide aqueous solution. Then, 1.5-2.5 parts of boric acid are added, and the mixture is stirred at 25°C for 55-70 minutes. Subsequently, 2-4 parts of low molecular weight sodium polyglutamate are added and stirring is continued. Then, 40-60 parts of the calcium chloride dihydrate aqueous solution are added dropwise to the system. After the addition is complete, 0.6-1.4 parts of ultra-high molecular weight sodium polyglutamate are added and stirring is continued to obtain the fertilizer mother liquor.

[0016] Preferably, the low molecular weight sodium polyglutamate is added and stirred for 30 minutes; the calcium chloride dihydrate aqueous solution is added dropwise to the system within 60 minutes; and the ultra-high molecular weight sodium polyglutamate is added and stirred for 50-70 minutes.

[0017] Preferably, 25-35 parts of potassium nitrate are added to the fertilizer mother liquor, followed by 196-220 parts of the citric acid aqueous solution. The mixture is stirred for 30 minutes, filtered through a 5μm filter, kept at 70℃ for 15 minutes, and then cooled to 25℃ to obtain an organic liquid fertilizer based on straw enzymatic hydrolysate.

[0018] Preferably, the low molecular weight polyglutamate sodium has a weight-average molecular weight of 150,000-250,000 Da, and the ultra-high molecular weight polyglutamate sodium has a weight-average molecular weight of 1,500,000-2,500,000 Da.

[0019] Preferably, the corn stalk powder is obtained by removing mud and moldy parts from corn stalks harvested at maturity, drying them to a moisture content of no more than 10%, crushing them, and passing them through a 40-mesh sieve.

[0020] This invention also provides a method for preparing an organic liquid fertilizer based on straw enzymatic hydrolysate, comprising the following steps:

[0021] (1) The corn straw powder was pretreated with alkali and then hydrolyzed with cellulase and xylanase to obtain the corn straw hydrolysate supernatant.

[0022] (2) The corn straw enzymatic hydrolysate was sequentially treated with an ultrafiltration membrane with a molecular weight cutoff of 3000 Da and a nanofiltration membrane with a molecular weight cutoff of 500 Da to obtain a molecular weight window enzymatic hydrolysate.

[0023] (3) Sodium borohydride was used to stabilize the 500-3000 Da molecular weight window oligosaccharides in the enzymatic hydrolysate to obtain an end-stabilized oligosaccharide solution.

[0024] (4) Boric acid was added to the terminal stabilized oligosaccharide solution under alkaline conditions, followed by the sequential addition of low molecular weight sodium polyglutamate, calcium chloride dihydrate aqueous solution and ultra-high molecular weight sodium polyglutamate to obtain fertilizer mother liquor.

[0025] (5) Add potassium nitrate and citric acid aqueous solution to the fertilizer mother liquor, filter and sterilize to obtain organic liquid fertilizer based on straw enzymatic hydrolysate.

[0026] The beneficial effects of this invention are:

[0027] (1) This invention uses a combination of 3000Da ultrafiltration and 500Da nanofiltration to precisely control the molecular weight window (500-3000Da) of the active components, thereby increasing the proportion of oligosaccharides in this window to 83.2%-88.7%. This design effectively removes large molecular colloids (>3000Da) that are prone to precipitation and small molecular reducing sugars (<500Da) that are prone to browning and rapid consumption, thereby reducing the precipitation rate after 30 days of accelerated storage at 45℃ to 0.2%-0.6%, and controlling the color difference ΔE to below 5.0, significantly improving the storage stability and appearance quality of the product.

[0028] (2) In this invention, sodium borohydride is used to perform a mild reducing end stabilization treatment on oligosaccharides with a window size of 500-3000 Da, thereby reducing the reducing sugar equivalent by 50%-70%. This step significantly inhibits the Maillard reaction during storage. In Example 1, after this treatment, the color difference ΔE (3.8) after 30 days of storage at 45°C was significantly reduced compared to the untreated Comparative Example 4 (17.5), effectively alleviating the browning trend of the liquid fertilizer.

[0029] (3) This invention introduces boric acid to construct reversible borate ester microdomains and uses a specific sequential complexation process of "adding low molecular weight sodium polyglutamate first, then adding calcium ions, and finally adding ultra-high molecular weight sodium polyglutamate" to form a structure with an inner complexation layer and an outer hydration protection layer. This synergistic effect significantly improves the retention and slow release capacity of active oligosaccharides in the soil. The 30-day extractable oligosaccharide retention rate (52.6%) in soil of Example 1 is significantly higher than that of the control lacking boric acid (Comparative Example 5, 39.6%) or calcium ions (Comparative Example 9, 28.4%), and ultimately promotes the growth of tomato plants, with a root dry weight of 0.76 g / plant, showing a better agronomic effect. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0031] The corn stalk powder used in the specific implementation method is prepared as follows: Corn stalks harvested at maturity are taken, and mud, sand, and moldy parts are removed. The stalks are dried at 65℃ until the moisture content is ≤10%, then pulverized and passed through a 40-mesh sieve to obtain corn stalk powder. Cellulase C766286 from Shanghai Aladdin Biochemical Technology Co., Ltd., derived from *Trichoderma viride*, has an enzyme activity of 22000 U / g and is in powder form. Xylanase X298998 from Shanghai Aladdin Biochemical Technology Co., Ltd., expressed by *Aspergillus oryzae*, has an enzyme activity of 2800 U / g and is in powder form. Low molecular weight polyglutamate sodium is selected from Bloomage Biotechnology's Hyafactor-PGA Sodium Polyglutamate PGA-LM, powder with a weight-average molecular weight of 200000 Da. Ultra-high molecular weight polyglutamate sodium is selected from Bloomage Biotechnology's Hyafactor-PGA Super High Molecular Weight Sodium Polyglutamate PGA-SHM, granules with a weight-average molecular weight of 2000000 Da.

[0032] Example 1:

[0033] Step 1: Take 500g of corn stalk powder, 4500g of deionized water and 20g of potassium hydroxide, add them to an alkali-resistant reaction vessel with a stirrer, heat to 80℃ under stirring at 200r / min and keep warm for 2h; after the heat preservation is completed, cool down to 50℃, add 26g of citric acid monohydrate, and continue stirring for 20min to obtain the pretreated slurry;

[0034] Step 2: Add 15g of cellulase and 10g of xylanase to the pretreated slurry obtained in Step 1, and enzymatically hydrolyze it at 50℃ and 200r / min for 16h. After the enzymatic hydrolysis is completed, raise the temperature to 90℃ and keep it at 10min to inactivate the enzyme. Then filter it through a 200-mesh filter cloth and centrifuge it at 5000r / min for 10min. Collect 4000g of supernatant enzymatic hydrolysate.

[0035] Step 3: Take 4000g of the supernatant enzymatic hydrolysate obtained in Step 2, first treat it with a polyethersulfone ultrafiltration membrane with a molecular weight cutoff of 3000 Da, collect the permeate, then concentrate the permeate with a polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da, collect the retentate, add 1000g of deionized water to the retentate for one wash filtration, and then concentrate it to 900g with a polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da to obtain the molecular weight window enzymatic hydrolysate;

[0036] Step 4: Take 900g of the molecular weight window enzymatic hydrolysate obtained in Step 3, cool it to 4℃, adjust the pH to 8.6 with a 10% potassium hydroxide aqueous solution, and add 3g of sodium borohydride in 3 portions, 1g each time, with an interval of 30min between each addition, under stirring at 200r / min, nitrogen protection and exhaust conditions, and continue the reaction for 4h after all the addition is completed; after the reaction is completed, dissolve 10g of citric acid monohydrate in 90g of deionized water to obtain 100g of citric acid aqueous solution, add 100g of citric acid aqueous solution to the reaction system within 30min, then treat it with a polyamide nanofiltration membrane with a molecular weight cutoff of 500Da, wash and filter with 1000g of deionized water, and finally concentrate it to 700g to obtain the end-group stabilized oligosaccharide solution;

[0037] Step 5: Take 700g of the end-group stabilized oligosaccharide solution obtained in Step 4, adjust the pH to 8.6 with a 10% potassium hydroxide aqueous solution, add 2g of boric acid, and stir for 60min at 25℃ and 200r / min. Then add 3g of low molecular weight sodium polyglutamate and continue stirring for 30min. Next, dissolve 2g of calcium chloride dihydrate in 48g of deionized water to obtain 50g of calcium chloride dihydrate aqueous solution, and add it dropwise to the above system within 60min, maintaining stirring at 200r / min during the addition process. After the calcium chloride dihydrate aqueous solution is added, add 1g of ultra-high molecular weight sodium polyglutamate and continue stirring for 60min to obtain fertilizer mother liquor.

[0038] Step 6: Add 30g of potassium nitrate to the fertilizer mother liquor obtained in Step 5, then add 204g of citric acid aqueous solution prepared by 1g of citric acid monohydrate and 203g of deionized water, stir for 30min, filter through a 5μm filter, keep warm at 70℃ for 15min, cool to 25℃, and obtain organic liquid fertilizer based on straw enzymatic hydrolysate.

[0039] Example 2:

[0040] Step 1: Take 450g of corn stalk powder, 4200g of deionized water and 15g of potassium hydroxide, add them to an alkali-resistant reaction vessel with a stirrer, heat to 75℃ under stirring at 200r / min and keep warm for 2.5h; after the heat preservation is completed, cool down to 48℃, add 22g of citric acid monohydrate, and continue stirring for 20min to obtain the pretreated slurry;

[0041] Step 2: Add 12g of cellulase and 8g of xylanase to the pretreated slurry obtained in Step 1, and enzymatically hydrolyze it at 48℃ and 200r / min for 20h. After the enzymatic hydrolysis is completed, raise the temperature to 90℃ and keep it at 10min to inactivate the enzyme. Then filter it through a 200-mesh filter cloth and centrifuge it at 5000r / min for 10min. Collect 3800g of supernatant enzymatic hydrolysate.

[0042] Step 3: Take 3800g of the supernatant enzymatic hydrolysate obtained in Step 2, first treat it with a polyethersulfone ultrafiltration membrane with a molecular weight cutoff of 3000 Da, collect the permeate, then concentrate the permeate with a polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da, collect the retentate, add 900g of deionized water to the retentate for one wash filtration, and then concentrate it to 800g with a polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da to obtain the molecular weight window enzymatic hydrolysate;

[0043] Step 4: Take 800g of the molecular weight window enzymatic hydrolysate obtained in Step 3, cool it to 4℃, adjust the pH to 8.4 with a 10% potassium hydroxide aqueous solution, and add 2g of sodium borohydride in two portions, 1g each time, with a 30min interval between each addition, under stirring at 200r / min, nitrogen protection and exhaust conditions. After all the sodium borohydride has been added, continue the reaction for 5h. After the reaction is complete, dissolve 8g of citric acid monohydrate in 72g of deionized water to obtain 80g of citric acid aqueous solution. Add the 80g of citric acid aqueous solution to the reaction system within 30min, then treat it with a polyamide nanofiltration membrane with a molecular weight cutoff of 500Da, and wash and filter with 900g of deionized water. Finally concentrate to 650g to obtain the end-group stabilized oligosaccharide solution.

[0044] Step 5: Take 650g of the end-group stabilized oligosaccharide solution obtained in Step 4, adjust the pH to 8.4 with a 10% potassium hydroxide aqueous solution, add 1.5g of boric acid, and stir for 55min at 25℃ and 200r / min. Then add 2g of low molecular weight sodium polyglutamate and continue stirring for 30min. Next, dissolve 1.5g of calcium chloride dihydrate in 38.5g of deionized water to obtain 40g of calcium chloride dihydrate aqueous solution, and add it dropwise to the above system within 60min, maintaining stirring at 200r / min during the addition process. After the calcium chloride dihydrate aqueous solution is added, add 0.6g of ultra-high molecular weight sodium polyglutamate and continue stirring for 50min to obtain fertilizer mother liquor.

[0045] Step 6: Add 25g of potassium nitrate to the fertilizer mother liquor obtained in Step 5, then add 196g of citric acid aqueous solution prepared by 0.8g of citric acid monohydrate and 195.2g of deionized water, stir for 30min, filter through a 5μm filter, keep warm at 70℃ for 15min, and cool to 25℃ to obtain organic liquid fertilizer based on straw enzymatic hydrolysate.

[0046] Example 3:

[0047] Step 1: Take 550g of corn stalk powder, 4800g of deionized water and 25g of potassium hydroxide, add them to an alkali-resistant reaction vessel with a stirrer, heat to 85℃ under stirring at 200r / min and keep warm for 1.5h; after the heat preservation is completed, cool down to 52℃, add 30g of citric acid monohydrate, and continue stirring for 30min to obtain the pretreated slurry;

[0048] Step 2: Add 18g of cellulase and 12g of xylanase to the pretreated slurry obtained in Step 1, and enzymatically hydrolyze it at 52℃ and 200r / min for 12h. After the enzymatic hydrolysis is completed, raise the temperature to 90℃ and keep it at 10min to inactivate the enzyme. Then filter it through a 200-mesh filter cloth and centrifuge it at 5000r / min for 10min to collect 4200g of supernatant enzymatic hydrolysate.

[0049] Step 3: Take 4200g of the supernatant enzymatic hydrolysate obtained in Step 2, first treat it with a polyethersulfone ultrafiltration membrane with a molecular weight cutoff of 3000 Da, collect the permeate, then concentrate the permeate with a polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da, collect the retentate, add 1100g of deionized water to the retentate for one wash filtration, and then concentrate it to 1000g with a polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da to obtain the molecular weight window enzymatic hydrolysate;

[0050] Step 4: Take 1000g of the molecular weight window enzymatic hydrolysate obtained in Step 3, cool it to 4℃, adjust the pH to 8.8 with a 10% potassium hydroxide aqueous solution, and add 4g of sodium borohydride in 4 portions, 1g each time, with an interval of 30min between each addition, under stirring at 200r / min, nitrogen protection and exhaust conditions, and continue the reaction for 3h after all the addition is completed; after the reaction is completed, dissolve 12g of citric acid monohydrate in 108g of deionized water to obtain 120g of citric acid aqueous solution, add 120g of citric acid aqueous solution to the reaction system within 30min, then treat it with a polyamide nanofiltration membrane with a molecular weight cutoff of 500Da, wash and filter with 1100g of deionized water, and finally concentrate it to 750g to obtain the end-group stabilized oligosaccharide solution;

[0051] Step 5: Take 750g of the end-group stabilized oligosaccharide solution obtained in Step 4, adjust the pH to 8.8 with a 10% potassium hydroxide aqueous solution, add 2.5g of boric acid, and stir for 70min at 25℃ and 200r / min. Then add 4g of low molecular weight sodium polyglutamate and continue stirring for 30min. Next, dissolve 2.5g of calcium chloride dihydrate in 57.5g of deionized water to obtain 60g of calcium chloride dihydrate aqueous solution, and add it dropwise to the above system within 60min, maintaining stirring at 200r / min during the addition process. After the calcium chloride dihydrate aqueous solution is added, add 1.4g of ultra-high molecular weight sodium polyglutamate and continue stirring for 70min to obtain fertilizer mother liquor.

[0052] Step 6: Add 35g of potassium nitrate to the fertilizer mother liquor obtained in Step 5, then add 220g of citric acid aqueous solution prepared by 1.2g of citric acid monohydrate and 218.8g of deionized water, stir for 30min, filter through a 5μm filter, keep warm at 70℃ for 15min, and cool to 25℃ to obtain organic liquid fertilizer based on straw enzymatic hydrolysate.

[0053] Example 4:

[0054] Step 1: Take 480g of corn stalk powder, 4400g of deionized water and 18g of potassium hydroxide, add them to an alkali-resistant reaction vessel with a stirrer, heat to 78℃ under stirring at 200r / min and keep warm for 2.2h; after the heat preservation is completed, cool down to 50℃, add 24g of citric acid monohydrate, and continue stirring for 25min to obtain the pretreated slurry;

[0055] Step 2: Add 14g of cellulase and 9g of xylanase to the pretreated slurry obtained in Step 1, and enzymatically hydrolyze it at 50℃ and 200r / min for 18h. After the enzymatic hydrolysis is completed, raise the temperature to 90℃ and keep it at 10min to inactivate the enzyme. Then filter it through a 200-mesh filter cloth and centrifuge it at 5000r / min for 10min. Collect 3900g of supernatant enzymatic hydrolysate.

[0056] Step 3: Take 3900g of the supernatant enzymatic hydrolysate obtained in Step 2, first treat it with a polyethersulfone ultrafiltration membrane with a molecular weight cutoff of 3000 Da, collect the permeate, then concentrate the permeate with a polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da, collect the retentate, add 950g of deionized water to the retentate for one wash filtration, and then concentrate it to 850g with a polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da to obtain the molecular weight window enzymatic hydrolysate;

[0057] Step 4: Take 850g of the molecular weight window enzymatic hydrolysate obtained in Step 3, cool it to 4℃, adjust the pH to 8.5 with a 10% potassium hydroxide aqueous solution, and add 2.5g of sodium borohydride in three portions under stirring at 200r / min, nitrogen protection and exhaust conditions. The first addition is 0.8g, the second is 0.8g, and the third is 0.9g, with an interval of 30min between each addition. After all the additions are completed, continue the reaction for 4.5h. After the reaction is completed, dissolve 9g of citric acid monohydrate in 81g of deionized water to obtain 90g of citric acid aqueous solution. Add the 90g of citric acid aqueous solution to the reaction system within 30min, then treat it with a polyamide nanofiltration membrane with a molecular weight cutoff of 500Da, and wash the filter with 950g of deionized water. Finally, concentrate it to 680g to obtain the end-group stabilized oligosaccharide solution.

[0058] Step 5: Take 680g of the end-group stabilized oligosaccharide solution obtained in Step 4, adjust the pH to 8.5 with a 10% potassium hydroxide aqueous solution, add 1.8g of boric acid, and stir for 60min at 25℃ and 200r / min. Then add 2.5g of low molecular weight sodium polyglutamate and continue stirring for 30min. Then dissolve 1.8g of calcium chloride dihydrate in 43.2g of deionized water to obtain 45g of calcium chloride dihydrate aqueous solution, and add it dropwise to the above system within 60min, while maintaining stirring at 200r / min during the addition process. After the calcium chloride dihydrate aqueous solution is added, add 0.8g of ultra-high molecular weight sodium polyglutamate and continue stirring for 60min to obtain fertilizer mother liquor.

[0059] Step 6: Add 28g of potassium nitrate to the fertilizer mother liquor obtained in Step 5, then add 205g of citric acid aqueous solution prepared by 0.9g of citric acid monohydrate and 204.1g of deionized water, stir for 30min, filter through a 5μm filter, keep warm at 70℃ for 15min, cool to 25℃, and obtain organic liquid fertilizer based on straw enzymatic hydrolysate.

[0060] Example 5:

[0061] Step 1: Take 520g of corn stalk powder, 4600g of deionized water and 22g of potassium hydroxide, add them to an alkali-resistant reaction vessel with a stirrer, heat to 82℃ under stirring at 200r / min and keep warm for 1.8h; after the heat preservation is completed, cool down to 50℃, add 28g of citric acid monohydrate, and continue stirring for 25min to obtain the pretreated slurry;

[0062] Step 2: Add 16g of cellulase and 11g of xylanase to the pretreated slurry obtained in Step 1, and enzymatically hydrolyze it at 50℃ and 200r / min for 14h. After the enzymatic hydrolysis is completed, raise the temperature to 90℃ and keep it at 10min to inactivate the enzyme. Then filter it through a 200-mesh filter cloth and centrifuge it at 5000r / min for 10min to collect 4100g of supernatant enzymatic hydrolysate.

[0063] Step 3: Take 4100g of the supernatant enzymatic hydrolysate obtained in Step 2, first treat it with a polyethersulfone ultrafiltration membrane with a molecular weight cutoff of 3000 Da, collect the permeate, then concentrate the permeate with a polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da, collect the retentate, add 1050g of deionized water to the retentate for one wash filtration, and then concentrate it to 950g with a polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da to obtain the molecular weight window enzymatic hydrolysate;

[0064] Step 4: Take 950g of the molecular weight window enzymatic hydrolysate obtained in Step 3, cool it to 4℃, adjust the pH to 8.7 with a 10% potassium hydroxide aqueous solution, and add 3.5g of sodium borohydride in four portions under stirring at 200r / min, nitrogen protection and exhaust conditions. The first addition is 0.8g, the second is 0.9g, the third is 0.9g, and the fourth is 0.9g, with an interval of 30min between each addition. After all the additions are completed, continue the reaction for 3.5h. After the reaction is completed, dissolve 11g of citric acid monohydrate in 99g of deionized water to obtain 110g of citric acid aqueous solution. Add the 110g of citric acid aqueous solution to the reaction system within 30min, then treat it with a polyamide nanofiltration membrane with a molecular weight cutoff of 500Da, and wash the filter with 1050g of deionized water. Finally, concentrate it to 730g to obtain the end-group stabilized oligosaccharide solution.

[0065] Step 5: Take 730g of the end-group stabilized oligosaccharide solution obtained in Step 4, adjust the pH to 8.7 with a 10% potassium hydroxide aqueous solution, add 2.2g of boric acid, and stir for 65min at 25℃ and 200r / min. Then add 3.5g of low molecular weight sodium polyglutamate and continue stirring for 30min. Next, dissolve 2.2g of calcium chloride dihydrate in 52.8g of deionized water to obtain 55g of calcium chloride dihydrate aqueous solution, and add it dropwise to the above system within 60min, maintaining stirring at 200r / min during the addition process. After the calcium chloride dihydrate aqueous solution is added, add 1.2g of ultra-high molecular weight sodium polyglutamate and continue stirring for 65min to obtain fertilizer mother liquor.

[0066] Step 6: Add 32g of potassium nitrate to the fertilizer mother liquor obtained in Step 5, and then add 213g of citric acid aqueous solution prepared by 1.1g of citric acid monohydrate and 211.9g of deionized water. Stir for 30min, filter through a 5μm filter, keep warm at 70℃ for 15min, and cool to 25℃ to obtain organic liquid fertilizer based on straw enzymatic hydrolysate.

[0067] Comparative Example 1:

[0068] The difference from Example 1 is that step 3 does not involve the treatment with a polyethersulfone ultrafiltration membrane with a molecular weight cutoff of 3000 Da and a polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da. Instead, 900g of the supernatant enzymatic hydrolysate obtained in step 2 is directly used as the molecular weight window enzymatic hydrolysate in step 4, and the other conditions are the same as in Example 1.

[0069] Comparative Example 2:

[0070] The difference from Example 1 is that in step 3, only the polyethersulfone ultrafiltration membrane with a molecular weight cutoff of 3000 Da is used for treatment. After collecting the permeate, it is directly concentrated to 900 g. The concentration and washing of the polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da are not performed. The other conditions are the same as in Example 1.

[0071] Comparative Example 3:

[0072] The difference from Example 1 is that step 3 does not involve treatment with a polyethersulfone ultrafiltration membrane with a molecular weight cutoff of 3000 Da. Instead, 4000g of the supernatant enzymatic hydrolysate obtained in step 2 is directly concentrated through a polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da. The retentate is collected, and 1000g of deionized water is added to the retentate for a single wash. The retentate is then concentrated to 900g through a polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da to obtain the molecular weight window enzymatic hydrolysate. The remaining conditions are the same as in Example 1.

[0073] Comparative Example 4:

[0074] The difference from Example 1 is that in step 4, instead of adding 3g of sodium borohydride, 3g of deionized water is used instead of 3g of sodium borohydride, and the mixture is kept at 4°C, pH 8.6, stirring at 200r / min, under nitrogen protection and exhaust conditions for 4 hours. The other conditions are the same as in Example 1.

[0075] Comparative Example 5:

[0076] The difference from Example 1 is that in step 5, instead of adding 2g of boric acid, 2g of deionized water is used instead of 2g of boric acid, and the mixture is stirred for 60min at 25℃ and 200r / min. The other conditions are the same as in Example 1.

[0077] Comparative Example 6:

[0078] The difference from Example 1 is that the order of adding low molecular weight polyglutamate sodium and calcium chloride dihydrate aqueous solution in step 5 is changed to first adding 50g of calcium chloride dihydrate aqueous solution prepared by 2g of calcium chloride dihydrate and 48g of deionized water, and then adding 3g of low molecular weight polyglutamate sodium. Ultra-high molecular weight polyglutamate sodium is still added after the low molecular weight polyglutamate sodium is added and stirred for 30 minutes. The other conditions are the same as in Example 1.

[0079] Comparative Example 7:

[0080] The difference from Example 1 is that in step 5, 3g of low molecular weight polyglutamate sodium is replaced with 3g of ultra-high molecular weight polyglutamate sodium, and the 3g of ultra-high molecular weight polyglutamate sodium is added at the same time point as the low molecular weight polyglutamate sodium in Example 1. The 1g of ultra-high molecular weight polyglutamate sodium added in the latter part of the original step 5 remains unchanged, and the other conditions are the same as in Example 1.

[0081] Comparative Example 8:

[0082] The difference from Example 1 is that in step 5, 1g of ultra-high molecular weight polyglutamate sodium is replaced with 1g of low molecular weight polyglutamate sodium, and the 1g of low molecular weight polyglutamate sodium is added at the same time point as the ultra-high molecular weight polyglutamate sodium in Example 1. The 3g of low molecular weight polyglutamate sodium added at the beginning of step 5 remains unchanged, and the other conditions are the same as in Example 1.

[0083] Comparative Example 9:

[0084] The difference from Example 1 is that in step 5, instead of adding 2g of calcium chloride dihydrate, 2g of deionized water is used instead of 2g of calcium chloride dihydrate, and it is still mixed with 48g of deionized water to form 50g of water, which is then added dropwise to the above system within 60min. The other conditions are the same as in Example 1.

[0085] Performance testing:

[0086] Determination of oligosaccharide proportion and reducing sugar equivalent in molecular weight window: Take 2.00 g each of the organic liquid fertilizers obtained in the examples and comparative examples, add deionized water to make up to 50 mL, vortex mix for 2 min, filter through a 0.22 μm aqueous filter membrane and perform gel permeation chromatography analysis. The gel permeation chromatography detection program was established according to the gel permeation chromatography method of GB / T 27843-2011. An aqueous gel chromatography column was used, the column temperature was 30℃, the mobile phase was 0.10 mol / L sodium nitrate aqueous solution, the flow rate was 0.5 mL / min, the injection volume was 20 μL, and the detector was a differential refractive index detector. Calibration curves were established with 500 Da, 1000 Da, 2000 Da, 3000 Da and 5000 Da dextran standards, and the proportion of the peak area of ​​500-3000 Da to the total peak area of ​​oligosaccharides was calculated. The reducing sugar equivalent was determined according to the reducing sugar determination method in GB / T 5513-2019, using Fehling's reagent method, and expressed as glucose. The reduction rate of reducing sugar equivalent was calculated by dividing the difference in reducing sugar equivalent before and after treatment in step 4 of the same sample by the reducing sugar equivalent before treatment.

[0087] Determination of water-insoluble matter and viscosity: Take 100 mL of each of the organic liquid fertilizers obtained in the examples and comparative examples, keep them at 25℃ for 30 min, and shake thoroughly. Water-insoluble matter was determined according to NY / T 1973-2021. For the determination, take 10.00 g of sample, dilute with deionized water to 250 mL, stir for 10 min, and filter through a pre-weighed glass frit crucible. Wash the filter residue with deionized water until the filtrate has no obvious color, dry at 105℃ to constant weight, and calculate the water-insoluble matter content based on the mass difference. Viscosity was determined according to GB / T 22235-2008 using a rotational viscometer at a test temperature of 25℃ and a rotor speed of 60 r / min. Each sample was measured three times consecutively, and the average value was taken.

[0088] Organic matter content determination: Take 50 mL of each of the organic liquid fertilizers obtained in the examples and comparative examples, shake well, and determine according to NY / T1976-2010. The determination is based on the original liquid and is performed in parallel 3 times.

[0089] Accelerated storage stability determination: 100 mL of each of the organic liquid fertilizers obtained in the examples and comparative examples were placed in 100 mL transparent glass bottles, sealed, and placed in a 45℃ incubator in the dark for 30 days. Another sample from the same batch was placed at 25℃ in the dark for 30 days as a room temperature control. After storage, the samples were equilibrated at 25℃ for 2 hours. First, it was observed whether stratification, flocculation, or visible precipitation occurred. Then, 10.00 g of the sample was thoroughly shaken and centrifuged at 5000 r / min for 10 min. The supernatant was discarded, and the precipitate was dried at 105℃ to constant weight. The precipitation rate was calculated. Color difference was determined using a colorimeter, with the freshly prepared sample as a reference, and the ΔE value of the sample after 30 days of storage at 45℃ was measured.

[0090] Determination of sustained release of oligosaccharides in soil: 200g portions of air-dried loam that had passed through a 2mm sieve were placed in 250mL culture bottles. The moisture content was adjusted to 60% of field capacity. 20mL of a 500-fold dilution of the organic liquid fertilizer obtained in the examples and comparative examples was added, and the mixture was incubated at 25℃ for 30 days. On days 1, 7, 15, and 30, 10g soil samples were taken, 50mL of deionized water was added, the mixture was shaken for 30 minutes, centrifuged at 5000 rpm for 10 minutes, and the supernatant was filtered through a 0.22μm aqueous filter membrane. The 500-3000Da oligosaccharide content was determined by gel permeation chromatography. Using the 500-3000Da oligosaccharide content measured on day 1 as the initial value, the retention rate of extractable oligosaccharides on day 30 was calculated.

[0091] Performance testing of tomato potted plants: The potted plant experiment was conducted indoors according to the field trial design principles of water-soluble fertilizers for macronutrients in NY / T 3552-2020. Tomato seedlings with uniform growth and at the four-leaf-one-heart stage were selected. Each pot contained 2.00 kg of air-dried loam with a soil pH of 6.8, organic matter content of 18.5 g / kg, available nitrogen of 92 mg / kg, available phosphorus of 24 mg / kg, and available potassium of 126 mg / kg. One seedling was planted per pot. The organic liquid fertilizers obtained in the examples and comparative examples were diluted 500 times and used as root irrigation solutions. 50 mL was applied per pot at 1 day, 7 days, 14 days, and 21 days after transplanting. Ten pots were set up for each treatment, randomly arranged. The greenhouse daytime temperature was 25℃ to 28℃, the nighttime temperature was 18℃ to 20℃, and the relative humidity was 60% to 70%. The watering amount was consistent for all treatments during the experiment. The fresh weight of the aboveground parts and the dry weight of the roots were measured on the 30th day after transplanting. For the dry weight of the roots, the roots were washed with deionized water, blanched at 105℃ for 30 minutes, and then dried at 75℃ to constant weight.

[0092] Table 1 Performance Test Results

[0093]

[0094] As shown in Table 1, Comparative Example 1 did not have membrane molecular weight window control, and the proportion of oligosaccharides in the 500-3000 Da range was only 42.8%, with an organic matter content of 111.8 g / L. Moreover, the precipitation rate and color difference after storage at 45℃ for 30 days were 3.8% and 13.6%, respectively, indicating that it is difficult to balance effective oligosaccharide enrichment and storage stability by directly using the full amount of enzymatic hydrolysate.

[0095] Comparative Example 2 only underwent 3000 Da ultrafiltration without removing components smaller than 500 Da. Although the organic matter content increased to 146.2 g / L, the color difference increased to 15.2 after 30 days of storage at 45℃, and the retention rate of extractable oligosaccharides in the soil after 30 days was only 21.6%. This indicates that when there are too many small molecule reducing sugars and easily consumed components, the risk of storage browning and rapid consumption in the rhizosphere is high.

[0096] Comparative Example 3, without removing components greater than 3000 Da, showed that water-insoluble matter, viscosity at 25℃, and precipitation rate increased to 4.76 g / L, 38.7 mPa·s, and 4.2%, respectively, indicating that an increase in macromolecular colloids or residual polymer components is detrimental to the homogeneity and stability of the liquid system.

[0097] Compared with the comparative examples above, Examples 1-5 formed a molecular weight window through 3000Da ultrafiltration and 500Da nanofiltration, increasing the proportion of oligosaccharides from 500-3000Da to 83.2%-88.7%, controlling water-insoluble matter at 0.43-0.68 g / L, and controlling the precipitation rate at 0.2%-0.6% after 30 days of storage at 45°C.

[0098] Based on Example 1 and Comparative Example 4, it can be seen that without partial stabilization at the reducing end, the reduction rate of reducing sugar equivalent is only 2.8%, and the color difference increases to 17.5 after 30 days of storage at 45°C; while in Example 1, the reduction rate of reducing sugar equivalent is 60.8%, and the color difference decreases to 3.8, indicating that partial stabilization at the reducing end is beneficial to reducing the browning trend during storage.

[0099] Based on Example 1 and Comparative Examples 5 and 9, it can be seen that when boric acid or calcium ions are absent, the 30-day extractable oligosaccharide retention rate in soil decreases to 39.6% and 28.4%, respectively, which is significantly lower than the 52.6% in Example 1. This indicates that both the borate ester microdomain and the calcium-polyglutamate sodium dynamic complexation help to improve the continuous extractability of oligosaccharides in soil.

[0100] Based on Examples 1 and Comparative Examples 6-8, it can be seen that changing the order of addition of low molecular weight polyglutamate (SMWPO), calcium chloride dihydrate, and ultra-high molecular weight polyglutamate (UHMWPO), or replacing SMWPO / UHMWPO with each other, resulted in varying degrees of decrease in system viscosity, sedimentation rate, and potted plant growth indicators. This indicates that the timing of SMWPO first accepting calcium ions and then UHMWPO forming hydration protection is crucial. In Example 3, the proportion of 500-3000 Da oligosaccharides, the reduction rate of reducing sugar equivalent, the retention rate of extractable oligosaccharides from the soil over 30 days, the fresh weight of the aboveground parts of the tomato, and the dry weight of the roots reached 88.7%, 68.4%, 61.4%, 39.4 g / plant, and 0.86 g / plant, respectively, representing the best levels among the examples.

[0101] In summary, this invention, through molecular weight window control, partial stabilization of the reducing end, construction of borate ester microdomains, and continuous combination of calcium-polyglutamate sodium sequential complexation, improves the storage stability of liquid fertilizer, the continuous supply of oligosaccharides in the soil, and the growth performance of tomato seedlings without simply pursuing the highest organic matter content.

[0102] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. An organic liquid fertilizer based on straw enzymatic hydrolysate, characterized in that, The raw materials for preparing the organic liquid fertilizer, by weight, include: 650-750 parts of end-group stabilized oligosaccharide solution, 1.5-2.5 parts of boric acid, 2-4 parts of low molecular weight sodium polyglutamate, 40-60 parts of calcium chloride dihydrate aqueous solution, 0.6-1.4 parts of ultra-high molecular weight sodium polyglutamate, 25-35 parts of potassium nitrate, and 196-220 parts of citric acid aqueous solution; The calcium chloride dihydrate aqueous solution is prepared by 1.5-2.5 parts calcium chloride dihydrate and 38.5-57.5 parts deionized water, and the citric acid aqueous solution is prepared by 0.8-1.2 parts citric acid monohydrate and 195.2-218.8 parts deionized water; The terminal stabilized oligosaccharide solution is obtained by sequentially passing the supernatant of corn straw enzymatic hydrolysis through an ultrafiltration membrane with a molecular weight cutoff of 3000 Da to collect the permeate, and then through a nanofiltration membrane with a molecular weight cutoff of 500 Da to collect the retentate. The resulting oligosaccharides with a molecular weight window of 500-3000 Da are then subjected to reducing end stabilization treatment with sodium borohydride. In preparing the organic liquid fertilizer, boric acid is added to the end-group stabilized oligosaccharide solution at pH 8.4-8.8 for pre-complexation, followed by the sequential addition of the relatively low molecular weight sodium polyglutamate, the calcium chloride dihydrate aqueous solution, and the ultra-high molecular weight sodium polyglutamate, and then the potassium nitrate and the citric acid aqueous solution to obtain the organic liquid fertilizer.

2. The organic liquid fertilizer based on straw enzymatic hydrolysate according to claim 1, characterized in that, The corn stalk enzymatic hydrolysis supernatant was prepared by the following method: 450-550 parts of corn stalk powder, 4200-4800 parts of deionized water, and 15-25 parts of potassium hydroxide were taken, heated to 75-85℃ under stirring and kept at that temperature for 1.5-2.5 h. After the holding time was completed, the temperature was lowered to 48-52℃, 22-30 parts of citric acid monohydrate were added, and stirring was continued to obtain a pretreated slurry. 12-18 parts of cellulase and 8-12 parts of xylanase were added to the pretreated slurry, and enzymatic hydrolysis was carried out at 48-52℃ for 12-20 h. After the enzymatic hydrolysis was completed, the enzymes were inactivated, filtered, and centrifuged to collect the corn stalk enzymatic hydrolysis supernatant.

3. The organic liquid fertilizer based on straw enzymatic hydrolysate according to claim 1, characterized in that, In the preparation of the terminal-stabilized oligosaccharide solution, 3800-4200 parts of the corn straw enzymatic hydrolysis supernatant are taken, first treated with a polyethersulfone ultrafiltration membrane with a molecular weight cutoff of 3000 Da and the permeate is collected, then the permeate is concentrated with a polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da and the retentate is collected, 900-1100 parts of deionized water are added to the obtained retentate for washing and filtration, and then concentrated to 800-1000 parts with a polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da to obtain the molecular weight window enzymatic hydrolysis solution.

4. The organic liquid fertilizer based on straw enzymatic hydrolysate according to claim 3, characterized in that, In the preparation of the terminal-stabilized oligosaccharide solution, 800-1000 parts of the molecular weight window enzymatic hydrolysate are taken, cooled to 4°C, and the pH is adjusted to 8.4-8.8 using a 10% potassium hydroxide aqueous solution. Under stirring, nitrogen protection, and exhaust conditions, 2-4 parts of sodium borohydride are added in 2-4 portions. After all the sodium borohydride has been added, the reaction continues for 3-5 hours. After the reaction is completed, 80-120 parts of citric acid aqueous solution are added, and the solution is then treated with a polyamide nanofiltration membrane with a molecular weight cutoff of 500 Da. The solution is washed with 900-1100 parts of deionized water and finally concentrated to 650-750 parts to obtain the terminal-stabilized oligosaccharide solution. The 80-120 parts of citric acid aqueous solution is prepared by 8-12 parts of citric acid monohydrate and 72-108 parts of deionized water.

5. The organic liquid fertilizer based on straw enzymatic hydrolysate according to claim 1, characterized in that, In preparing the organic liquid fertilizer, take 650-750 parts of the terminal-stabilized oligosaccharide solution, adjust the pH to 8.4-8.8 using a 10% potassium hydroxide aqueous solution, add 1.5-2.5 parts of boric acid, stir at 25°C for 55-70 minutes, then add 2-4 parts of low molecular weight sodium polyglutamate and continue stirring, then add 40-60 parts of the calcium chloride dihydrate aqueous solution dropwise to the system, and after the dropwise addition is complete, add 0.6-1.4 parts of ultra-high molecular weight sodium polyglutamate and continue stirring to obtain the fertilizer mother liquor.

6. The organic liquid fertilizer based on straw enzymatic hydrolysate according to claim 5, characterized in that, After the low molecular weight sodium polyglutamate is added, stirring continues for 30 minutes; the calcium chloride dihydrate aqueous solution is added dropwise to the system within 60 minutes; after the ultra-high molecular weight sodium polyglutamate is added, stirring continues for 50-70 minutes.

7. The organic liquid fertilizer based on straw enzymatic hydrolysate according to claim 5 or 6, characterized in that, Add 25-35 parts of potassium nitrate to the fertilizer mother liquor, then add 196-220 parts of the citric acid aqueous solution, stir for 30 minutes, filter through a 5μm filter, keep warm at 70℃ for 15 minutes, and cool to 25℃ to obtain an organic liquid fertilizer based on straw enzymatic hydrolysate.

8. The organic liquid fertilizer based on straw enzymatic hydrolysate according to claim 1, characterized in that, The low molecular weight polyglutamate sodium has a weight-average molecular weight of 150,000-250,000 Da, and the ultra-high molecular weight polyglutamate sodium has a weight-average molecular weight of 1,500,000-2,500,000 Da.

9. The organic liquid fertilizer based on straw enzymatic hydrolysate according to claim 1, characterized in that, The corn stalk powder is obtained by removing mud and moldy parts from corn stalks harvested at maturity, drying them to a moisture content of no more than 10%, crushing them, and passing them through a 40-mesh sieve.

10. A method for preparing an organic liquid fertilizer based on straw enzymatic hydrolysate according to any one of claims 1-9, characterized in that, Includes the following steps: (1) The corn straw powder was pretreated with alkali and then hydrolyzed with cellulase and xylanase to obtain the corn straw hydrolysate supernatant. (2) The corn straw enzymatic hydrolysate was sequentially treated with an ultrafiltration membrane with a molecular weight cutoff of 3000 Da and a nanofiltration membrane with a molecular weight cutoff of 500 Da to obtain a molecular weight window enzymatic hydrolysate. (3) Sodium borohydride was used to stabilize the 500-3000 Da molecular weight window oligosaccharides in the enzymatic hydrolysate to obtain an end-stabilized oligosaccharide solution. (4) Boric acid was added to the terminal stabilized oligosaccharide solution under alkaline conditions, followed by the sequential addition of low molecular weight sodium polyglutamate, calcium chloride dihydrate aqueous solution and ultra-high molecular weight sodium polyglutamate to obtain fertilizer mother liquor. (5) Add potassium nitrate and citric acid aqueous solution to the fertilizer mother liquor, filter and sterilize to obtain organic liquid fertilizer based on straw enzymatic hydrolysate.

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