Biological organic seedling raising substrate and seedling raising method

Abstract

The invention relates to the technical field of seedling culture, in particular to a biological organic seedling culture substrate and a seedling culture method. The matrix is formed by compounding modified straw particles, peat, coco coir and a bio-organic fertilizer. Wherein the modified straw particles are obtained by sequentially carrying out alkalization, two-stage etherification and calcium chloride and chitosan oligosaccharide solution treatment on wheat straw particles with specific particle sizes. The matrix synergistically improves the water-air coordination and the root lump formability. During seedling raising, the seedlings are put into a hole tray to be sown, the temperature, humidity and moisture are controlled, and strong seedlings can be cultivated within 25-30 days. The problems that a traditional substrate is prone to hardening, the root lumps are loose, and the transplanting rejuvenation period is long are effectively solved.

Description

A biological organic seedling substrate and seedling cultivation method Technical Field

[0001] This invention relates to the field of seedling technology, and in particular to a biological organic seedling substrate and a seedling cultivation method. Background Technology

[0002] Factory-style tray seedling cultivation is a crucial step in modern horticultural production, its core being to provide seedling roots with a micro-growing environment that coordinates water, air, and fertilizer. Currently, common bio-organic seedling substrates are mostly composed of peat, coconut coir, well-rotted organic fertilizer, and simply crushed crop straw. While these substrates can provide basic nutrients and form a certain degree of porosity, in practical applications, especially in small-volume tray seedling cultivation of crops such as tomatoes, peppers, and cabbages, they generally face insurmountable structural defects.

[0003] First, lignocellulosic materials such as straw and mushroom residue, which serve as the main volume filler and structural support, lack sufficient hydrophilic functional groups on their particle surfaces, making it difficult to coordinate water absorption and dehydration rates. After watering, moisture easily accumulates in the gaps between particles or on the surface, forming supersaturated water-holding zones that severely crowd out aeration pores and cause root hypoxia. Conversely, during the water evaporation stage, these particles lose water rapidly due to their weak water-holding capacity, leading to substrate shrinkage and compaction, which hinders the uniform extension and rooting of new root hairs. This contradiction of root suffocation when wet and compaction when dry stems from the lack of active water regulation capabilities in ordinary straw particles.

[0004] Secondly, even after decomposition, the particle size distribution and surface chemical properties of organic particles remain random. Within the limited volume of the seedling tray, this randomness makes it difficult for the substrate to spontaneously form and maintain an ideal spatial configuration where capillary water-holding pores and aeration macropores coexist and work synergistically. The consequences are poor seedling uniformity and uneven seedling growth in the early stages of seedling cultivation; in the middle and later stages, the roots struggle to form a tight bond with the substrate particles, resulting in loose root balls lacking strength. During transplanting, these root balls easily break apart, damaging the roots, significantly prolonging the recovery period, and even affecting the survival rate.

[0005] Therefore, the key problem with existing technologies is that conventional physical compounding and simple biological fermentation processes cannot achieve targeted design and precise control of the microstructure of the core components of the substrate. How to solve the three interconnected and mutually restrictive technical challenges of water retention stability, aeration assurance, and root ball formation within the small space of a seedling tray using an industrially feasible method is a bottleneck that urgently needs to be overcome in this field. Summary of the Invention

[0006] In view of this, the purpose of this invention is to propose a biological organic seedling substrate and seedling method to solve the problems of uneven emergence, loose root balls, and long transplanting recovery period caused by the uncontrollable microstructure of existing biological organic seedling substrates made of ordinary straw pellets, etc., which are difficult to meet the multiple needs of seedling roots for water, air and fixation under small-volume seedling tray conditions.

[0007] To achieve the above objectives, the present invention provides a bio-organic seedling substrate, prepared from the following raw materials: 550-700 parts modified straw pellets, 760-850 parts peat, 450-550 parts coconut coir, and 280-330 parts bio-organic fertilizer; furthermore, the modified straw pellets are obtained by alkalizing wheat straw lignocellulose pellets, performing two-stage etherification treatment, and then sequentially treating them with calcium chloride aqueous solution and chitosan oligosaccharide solution before drying.

[0008] Preferably, the wheat straw lignocellulose particles are particles obtained by crushing and screening wheat straw lignocellulose flakes, with a 20-mesh sieve undersize and a 40-mesh sieve oversize, and a moisture content of 9.6%-11.2% before alkalization.

[0009] Preferably, the alkalization treatment is as follows: by mass, 550-700 parts of wheat straw lignocellulose particles are added to 1750-2050 parts of 2-propanol, stirred at 24-26°C for 12-18 minutes, and then an alkaline solution prepared by 72-90 parts of sodium hydroxide and 110-130 parts of water is added within 12-16 minutes, and stirring is continued for 22-28 minutes.

[0010] Preferably, based on 550-700 parts by weight of wheat straw lignocellulose particles, the two-stage etherification treatment is as follows: first, a first-stage etherification solution formed by 92-110 parts by weight of sodium chloroacetate and 190-230 parts by weight of 2-propanol is added, and the reaction is carried out at 43-48°C for 35-45 minutes; then, a second-stage etherification solution formed by 22-30 parts by weight of sodium hydroxide, 28-35 parts by weight of water, 40-50 parts by weight of sodium chloroacetate and 110-130 parts by weight of 2-propanol is added, and the reaction is carried out at 53-58°C for 22-28 minutes.

[0011] Preferably, based on 550-700 parts by weight of wheat straw lignocellulose particles, the calcium chloride aqueous solution treatment and chitosan oligosaccharide solution treatment are as follows: the two-stage etherified particles are washed with 2-propanol aqueous solution until the pH of the filtrate is 8.2-8.6; then the washed particles are added to a solution formed by 9-13 parts by weight of calcium chloride dihydrate and 900-1100 parts by weight of water, and immersed at 23℃-26℃ for 12-18 min, followed by draining for 4-6 min; then a solution formed by 10-14 parts by weight of chitosan oligosaccharide, 7-9 parts by weight of glacial acetic acid and 760-850 parts by weight of water is added, and the mixture is stirred at 23-26℃ for 18-22 min; then the particles are washed with water, and finally dried until the moisture content of the particles is 11.8%-13.3%.

[0012] Preferably, the molecular weight of the chitosan oligosaccharide is not greater than 3000 Da.

[0013] Furthermore, the present invention also provides a seedling raising method using a biological organic seedling substrate for plug tray seedling raising, comprising the following steps: filling the biological organic seedling substrate into 72-128-cell plug trays, sowing one vegetable seed in each cell, covering with substrate 3-5mm, spraying water onto each plug tray after sowing until water just seeps into the bottom of the plug tray; maintaining a temperature of 24-28℃ before emergence, and 20-26℃ during the day and 14-18℃ at night after emergence; when the moisture content of the biological organic seedling substrate drops to 45%-50%, spraying water to 60%-65%, and raising seedlings for 25-30 days.

[0014] Preferably, the vegetable seeds are tomato seeds, pepper seeds, or cabbage seeds.

[0015] The beneficial effects of this invention are as follows: It significantly improves the water-air coordination of the substrate. By performing surface-confined carboxymethylation on straw lignocellulose particles, a hydrophilic modification zone rich in carboxyl groups is constructed on the outer layer of the particles. This structure allows the outer layer of the particles to rapidly adsorb and slowly release water, while the core of the particles remains rigid, avoiding the problem of compressed aeration pores due to overall collapse in a moist state. Thus, a stable coexistence of water-holding pores and aeration pores is achieved at the microscale, creating a moist but not waterlogged, well-aerated growth environment for the roots.

[0016] This method effectively enhances the integrity and mechanical strength of the root ball: a sequential treatment process is employed, first introducing calcium ions and then low-molecular-weight chitosan oligosaccharides. Calcium ions preferentially bind to the carboxyl groups on the particle surface, forming a dense ionic cross-linking network on the inner side, providing basic skeletal support. Subsequently, the chitosan oligosaccharide molecules on the outer side further adhere through hydrogen bonding and other interactions, forming a flexible moisture-regulating and adhesive layer. This rigid support-flexible moisture-regulating dual-layer gradient structure from the inside out significantly enhances the interfacial bonding force between particles and between particles and other components (peat, coconut coir), resulting in a dense and elastic root ball structure that is less prone to disintegration during transplanting, thus protecting the integrity of the root system.

[0017] The optimization of the microstructure of the granules directly translates into superior macroscopic seedling performance, significantly improving both seedling quality and transplanting efficiency. The substrate exhibits a more gradual rhythm of water absorption and loss, along with excellent rewetting properties, reducing the difficulty of water management. The stable root ball structure not only promotes robust seedling growth and uniform emergence within the seedling trays but also ensures that the root ball can withstand the necessary mechanical stress during transplanting. This allows seedlings to be planted with an intact root ball, thereby significantly shortening the recovery period, increasing transplant survival rate, and laying a solid foundation for later crop growth. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0019] Figure 1 is an infrared spectrum of the modified straw pellets provided in Example 1 of the present invention. Detailed Implementation

[0020] 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.

[0021] The specific implementation method uses the following raw material sources: wheat straw lignocellulose raw material is JRS wheat straw pulp, in flake form; peat is Pindstrup Peat Moss, 0-10mm particle size; coconut coir is RIOCOCO CF104 coconut coir blocks; bio-organic fertilizer is "Gulin" general-purpose bio-organic fertilizer; chitosan oligosaccharide is Zhejiang Jinke Pharmaceutical's agricultural-specific chitosan oligosaccharide, with a molecular weight ≤3000Da.

[0022] Example 1: Step 1: 600g of wheat straw lignocellulose flakes were crushed and sieved. The portion passing through a 20-mesh sieve and passing through a 40-mesh sieve was dried at 50℃ for 4 hours to reduce the moisture content to 10.2%. The 600g wheat straw lignocellulose particles were then added to 1800g of 2-propanol and stirred at 25℃ for 15 minutes. Then, an alkaline solution consisting of 80g sodium hydroxide and 120g water was added in portions over 15 minutes, and stirring was continued for another 25 minutes to obtain an alkalized particle suspension. Step 2: The first etherification solution consisting of 100g sodium chloroacetate and 200g 2-propanol was added to the alkalized particle suspension obtained in Step 1 and reacted at 45℃ for 40 minutes. Subsequently, a solution consisting of 25g sodium hydroxide, 30g water, 45g sodium chloroacetate, and 120g sodium hydroxide was added. The second etherification solution formed by 2-propanol was reacted at 55℃ for 25 min, and the solid and liquid were separated after the reaction. In step 3, the wet granules obtained in step 2 were washed with an 80% 2-propanol aqueous solution until the pH of the filtrate dropped to 8.5. The washed wet granules were then directly added to a calcium salt solution formed by 11 g of calcium chloride dihydrate and 1000 g of water, and soaked at 25℃ for 15 min. After soaking, the filtrate was drained for 5 min. In step 4, the wet granules treated in step 3 were directly added to a chitosan oligosaccharide solution formed by 12 g of chitosan oligosaccharide, 8 g of glacial acetic acid, and 800 g of water, and stirred at 25℃ for 20 min. Subsequently, the granules were washed twice with 1000 g of deionized water, and finally dried at 50℃ until the granule moisture content was 12.5%, yielding modified straw granules. Step 5: Pre-wet 600g of modified straw pellets with 120g of water for 10 minutes, then add 800g of peat, 500g of expanded coconut coir adjusted to 15% moisture content, and 300g of bio-organic fertilizer. Continue to add 130g of water, mix and stir for 10 minutes, seal and let stand for 12 hours, then stir for 5 minutes to obtain bio-organic seedling substrate; Step 6: Fill the bio-organic seedling substrate into 72-cell trays. Taking tomatoes as an example, sow one seed per cell, cover with substrate 3-5mm, and spray 150g of water after sowing until there is just a small amount of seepage at the bottom of the tray; maintain 25-28℃ before emergence, 22-26℃ during the day and 16-18℃ at night after emergence. When the substrate moisture content drops to 45%-50%, spray irrigation to 60%-65%, and raise seedlings for 25 days.

[0023] Example 2: Step 1: 550g of wheat straw lignocellulose flakes were crushed and sieved. The portion passing through a 20-mesh sieve and passing through a 40-mesh sieve was dried at 48℃ for 3.5h to reduce the moisture content to 9.6%. The 550g wheat straw lignocellulose granules were then added to 1750g of 2-propanol and stirred at 24℃ for 12min. Then, an alkaline solution consisting of 72g sodium hydroxide and 110g water was added in portions over 12min, and stirring was continued for 22min to obtain an alkalized granule suspension. Step 2: 92g sodium chloroacetate and 190g sodium hydroxide were added to the alkalized granule suspension obtained in Step 1. The first etherification solution formed from 2-propanol was reacted at 43°C for 35 min; then the second etherification solution formed from 22 g sodium hydroxide, 28 g water, 40 g sodium chloroacetate, and 110 g 2-propanol was added, and the reaction was carried out at 53°C for 22 min. After the reaction, solid and liquid were separated. Step 3: The wet particles obtained in step 2 were washed with a 78% (w / w) 2-propanol aqueous solution until the pH of the filtrate dropped to 8.2. The washed wet particles were then directly added to a calcium salt solution formed from 9 g calcium chloride dihydrate and 900 g water, and soaked at 23°C for 12 min. After soaking, the filtrate was drained for 4 min. Step 4: The wet particles treated in step 3 were directly added to a chitosan oligosaccharide solution formed from 10 g chitosan oligosaccharide, 7 g glacial acetic acid, and 760 g water, and stirred at 23°C for 18 min. Then, they were washed twice with 900 g deionized water. The modified straw pellets were dried at 48℃ until the moisture content of the pellets reached 11.8%. Step 5: 550g of modified straw pellets were pre-wetted with 100g of water for 8 minutes, then 760g of peat, 450g of expanded coconut coir with a moisture content adjusted to 14%, and 280g of bio-organic fertilizer were added. 120g of water was added, and the mixture was stirred for 9 minutes. The mixture was then sealed and left to stand for 10 hours, and then stirred for another 4 minutes to obtain the bio-organic seedling substrate. Step 6: The bio-organic seedling substrate was filled into 72-cell seedling trays. Taking pepper as an example, one seed was sown in each cell, and the substrate was covered with 3-4mm. After sowing, 145g of water was sprayed until a small amount of water seeped into the bottom of the tray. Before emergence, the temperature was maintained at 25-27℃. After emergence, the temperature was maintained at 23-25℃ during the day and 16-17℃ at night. When the moisture content of the substrate dropped to 46%-48%, it was sprayed to 60%-62%. Seedlings were raised for 28 days.

[0024] Example 3: Step 1: 650g of wheat straw lignocellulose flakes were crushed and sieved. The portion passing through a 20-mesh sieve and passing through a 40-mesh sieve was dried at 50℃ for 4 hours to reduce the moisture content to 10.8%. The 650g wheat straw lignocellulose particles were then added to 1900g of 2-propanol and stirred at 25℃ for 15 minutes. Then, an alkaline solution consisting of 84g sodium hydroxide and 125g water was added in portions over 14 minutes, and stirring was continued for 26 minutes to obtain an alkalized particle suspension. Step 2: The first etherification solution consisting of 105g sodium chloroacetate and 210g 2-propanol was added to the alkalized particle suspension obtained in Step 1 and reacted at 46℃ for 42 minutes. Subsequently, a solution consisting of 27g sodium hydroxide, 32g water, 48g sodium chloroacetate, and 125g sodium hydroxide was added. The second etherification liquid formed by 2-propanol was reacted at 56℃ for 26 min, and the solid and liquid were separated after the reaction. Step 3: The wet granules obtained in step 2 were washed with an 80% (w / w) 2-propanol aqueous solution until the pH of the filtrate dropped to 8.4. The washed wet granules were then directly added to a calcium salt solution formed by 12 g of calcium chloride dihydrate and 1000 g of water and soaked at 25℃ for 16 min. After soaking, the filtrate was drained for 5 min. Step 4: The wet granules treated in step 3 were directly added to a chitosan oligosaccharide solution formed by 13 g of chitosan oligosaccharide, 8 g of glacial acetic acid and 820 g of water and stirred at 25℃ for 21 min. Then, the granules were washed twice with 1000 g of deionized water and finally dried at 50℃ until the moisture content of the granules was 12.9%, thus obtaining modified straw. Step 5: Pre-wet 650g of modified straw pellets with 130g of water for 10 minutes, then add 780g of peat, 470g of expanded coconut coir adjusted to 15% moisture content, and 320g of bio-organic fertilizer. Continue to add 135g of water, mix and stir for 10 minutes, seal and let stand for 12 hours, then stir for 5 minutes to obtain bio-organic seedling substrate; Step 6: Fill the bio-organic seedling substrate into 105-cell trays. Taking cabbage as an example, sow one seed per cell, cover with substrate 3-4mm, and spray 148g of water after sowing until a small amount of water seeps into the bottom of the tray; maintain 24-26℃ before emergence, and 20-24℃ during the day and 14-16℃ at night after emergence. When the substrate moisture content drops to 45%-47%, spray irrigation to 60%-63%, and raise seedlings for 30 days.

[0025] Example 4: Step 1: 700g of wheat straw lignocellulose flakes were crushed and sieved. The portion passing through a 20-mesh sieve and passing through a 40-mesh sieve was dried at 52℃ for 4.5h to reduce the moisture content to 11.2%. The 700g wheat straw lignocellulose particles were then added to 2050g of 2-propanol and stirred at 26℃ for 18min. Then, an alkaline solution consisting of 90g sodium hydroxide and 130g water was added in portions over 16min, and stirring was continued for 28min to obtain an alkalized particle suspension. Step 2: The first etherification solution consisting of 110g sodium chloroacetate and 230g 2-propanol was added to the alkalized particle suspension obtained in Step 1 and reacted at 48℃ for 45min. Subsequently, a solution consisting of 30g sodium hydroxide, 35g water, 50g sodium chloroacetate, and 130g sodium hydroxide was added. The second etherification solution formed by 2-propanol was reacted at 58℃ for 28 min, and the solid and liquid were separated after the reaction. Step 3: The wet granules obtained in step 2 were washed with an 82% (w / w) 2-propanol aqueous solution until the pH of the filtrate dropped to 8.6. The washed wet granules were then directly added to a calcium salt solution formed by 13g of calcium chloride dihydrate and 1100g of water, and soaked at 26℃ for 18 min. After soaking, the filtrate was drained for 6 min. Step 4: The wet granules treated in step 3 were directly added to a chitosan oligosaccharide solution formed by 14g of chitosan oligosaccharide, 9g of glacial acetic acid and 850g of water, and stirred at 26℃ for 22 min. Then, the granules were washed twice with 1100g of deionized water, and finally dried at 52℃ until the moisture content of the granules was 13.3%, to obtain modified straw. Step 5: Pre-wet 700g of modified straw pellets with 140g of water for 12 minutes, then add 850g of peat, 550g of expanded coconut coir adjusted to 16% moisture content, and 330g of bio-organic fertilizer. Continue to add 140g of water, mix and stir for 11 minutes, seal and let stand for 14 hours, then stir for 6 minutes to obtain the bio-organic seedling substrate; Step 6: Fill the bio-organic seedling substrate into 128-cell trays. Taking tomatoes as an example, sow one seed per cell, cover with substrate 3-5mm, and spray 155g of water after sowing until a small amount of water seeps into the bottom of the tray; maintain 25-28℃ before emergence, and 22-25℃ during the day and 15-17℃ at night after emergence. When the substrate moisture content drops to 46%-50%, spray irrigation to 61%-65%, and raise seedlings for 26 days.

[0026] Comparative Example 1: The difference from Example 1 is that in step 2, the first etherification solution is replaced with 300g of 2-propanol, and the second etherification solution is replaced with 25g of sodium hydroxide, 30g of water and 165g of 2-propanol, without the addition of sodium chloroacetate; the other conditions are the same as in Example 1.

[0027] Comparative Example 2: The difference from Example 1 is that after adding the second etherification solution in step 2, the reaction time at 55°C was extended from 25 min to 60 min; the other conditions are the same as in Example 1.

[0028] Comparative Example 3: The difference from Example 1 is that in step 3, the calcium salt solution is made from 1000g of water, and 11g of calcium chloride dihydrate is not added. The solution is soaked at 25°C for 15min, and then drained for 5min after soaking. The other conditions are the same as in Example 1.

[0029] Comparative Example 4: The difference from Example 1 is that in step 4, the chitosan oligosaccharide solution was changed to be formed by 8g of glacial acetic acid and 812g of water, and 12g of chitosan oligosaccharide was not added. The mixture was stirred at 25°C for 20min. The other conditions were the same as in Example 1.

[0030] Comparative Example 5: The difference from Example 1 is that the order of steps 3 and 4 is reversed. That is, after the wet particles obtained in step 2 are washed until the pH of the filtrate is 8.5, a chitosan oligosaccharide solution consisting of 12g chitosan oligosaccharide, 8g glacial acetic acid and 800g water is added first, and the mixture is stirred at 25°C for 20min. Then, it is washed twice with 1000g deionized water, and a calcium salt solution consisting of 11g calcium chloride dihydrate and 1000g water is added. The mixture is then soaked at 25°C for 15min, drained for 5min after soaking, and finally dried at 50°C until the moisture content of the particles is 12.5%. The remaining conditions are the same as in Example 1.

[0031] Comparative Example 6: The difference from Example 1 is that the chitosan oligosaccharide used in step 4 was replaced with chitosan oligosaccharide with a molecular weight of 8000 Da, the amount was still 12g, the amount of glacial acetic acid was still 8g, the amount of water was still 800g, and the mixture was stirred at 25°C for 20min; the other conditions were the same as in Example 1.

[0032] Performance Testing: Sample Preparation: Modified straw pellets and bio-organic seedling substrates prepared in Examples 1-4 and Comparative Examples 1-6 were selected as test samples. The intrinsic characterization of the pellets was performed using the pellets obtained in step 4 of each sample; the physicochemical properties and application performance of the substrates were tested using the substrates obtained in step 5 of each sample. Three batches of each sample were prepared independently, and three parallel determinations were performed for each batch. The bio-organic fertilizer used in step 5 was from the same batch as in Example 1, and its quality requirements met NY 884-2012. The plug seedling experiment used 72-cell plug trays conforming to NY / T 4203-2022. The tomato seeds used were from the same batch of commercial seeds, and the seed quality met the requirements of GB 16715.3-2010. Sowing, temperature and humidity management, irrigation control, and seedling determination were carried out uniformly according to NY / T 2119-2012 and NY / T 2312-2013. Each sample was replicated in 4 trays, with 72 seeds per tray and 1 seed per cell. The substrate covering was 4 mm thick. After sowing, 150 g of water was sprayed until a small amount of water seeped into the bottom of the plug tray. The temperature was maintained at 25-28℃ before emergence, and 22-26℃ during the day and 16-18℃ at night after emergence. When the substrate moisture content dropped to 45%-50%, the water was sprayed to 60%-65%. The seedling period was 25 days. To evaluate transplant recovery, after the seedlings matured, another batch of seedlings from the same batch were transplanted into plastic pots with a diameter of 12cm and a height of 11cm. Each pot was filled with 650g of the same batch of soil that had been sieved through a 2mm sieve. The initial moisture content of the soil was adjusted to 60%. After transplanting, the seedlings were placed in an environment with a daytime temperature of 23-27℃ and a nighttime temperature of 16-20℃ and managed according to the same watering procedure.

[0033] Particle size distribution of modified straw particles: determined according to GB / T 6003.1-2022. Particles obtained in step 4 of each sample were dried at 50℃ to a moisture content of 12.5% ​​± 0.3%. 100.0 g of each sample was taken and sieved using 850 μm, 600 μm, and 425 μm woven wire mesh sieves assembled from top to bottom for 10 min. The mass of the material remaining on and under the sieves was weighed, and the mass fraction of the 850-425 μm particle size range was calculated.

[0034] Infrared spectroscopy and Ca surface / inner layer distribution of modified straw pellets: Sample pellets from Example 1 were dried, pulverized, and passed through a 200-mesh sieve. 1.0 mg of the sample was weighed and mixed with 100.0 mg of spectrally pure KBr, then compressed into tablets at 4000-400 cm⁻¹. -1 Scan within the range, with a resolution of 4cm. -1The scan was performed 32 times, and the results are shown in Figure 1. Ca elemental determination was carried out according to GB / T 17359-2023. A linear scan was performed along the outer surface inwards on the same cross-section, with a step size of 5 μm. The region 0-20 μm from the outer surface was defined as the surface region, and the region 40-80 μm from the outer surface was defined as the inner region. The average Ca atomic fraction was calculated for each region, and the ratio of the surface Ca atomic fraction to the inner Ca atomic fraction was used as the Ca surface / inner layer distribution index.

[0035] Bulk density, total porosity, aeration porosity, and water-holding porosity of the organic seedling substrate were determined according to NY / T 2118-2012 and in conjunction with GB / T 33891-2017. A substrate with an internal volume of 100 cm³ was used. 3 The sample ring was naturally filled with the mixed matrix until leveled, without compaction, and the sample mass was measured. The sample ring was then placed in shallow water to absorb water from bottom to top until completely wetted, and then soaked for 24 hours. After removal, the outer wall was wiped clean and the fully saturated mass was immediately weighed. Subsequently, it was placed on a drainage rack lined with filter paper to drain freely for 2 hours, and the mass after free drainage was weighed again. Finally, it was dried at 105℃ to constant weight and the dry mass was weighed. The bulk density was calculated using the dry mass and the volume of the sample ring. The total porosity was calculated by subtracting the water volume corresponding to the dry mass from the fully saturated mass. The water-holding porosity was calculated by subtracting the water volume corresponding to the dry mass from the mass after free drainage. The aeration porosity was calculated by subtracting the water-holding porosity from the total porosity.

[0036] Water absorption strength, 24-hour free water loss rate, and rewetting time of the bio-organic seedling substrate: Water absorption strength was determined according to HG / T6080-2022. For each sample, 50.0 g of substrate (equivalent to dry basis weight) was placed into a cylindrical sample tube with uniformly spaced small holes at the bottom. The contact depth between the bottom of the sample tube and the surface of 25℃ deionized water was controlled at 5 mm. After absorbing water for 60 min, the sample was removed, allowed to drip water for 2 min, and weighed. The water absorption strength was calculated based on the amount of water absorbed per unit dry basis weight within 60 min. For the same sample after water absorption, it was allowed to stand for 24 h at 25℃ and 60% relative humidity, and weighed again. The 24-hour free water loss rate was calculated as the percentage of water lost in 24 h relative to the amount absorbed in 60 min. Take another 50.0 g of each sample (calculated dry basis), dry it at 45℃ to a moisture content of 10.0% ± 0.5%, and then spread it evenly in a 12 cm diameter petri dish. Add 50.0 mL of deionized water evenly within 10 s. Record the time required from the start of water addition until there are no visible dry spots on the surface and all the water has entered the matrix layer as the rewetting time.

[0037] Root ball mass retention rate, root ball compressive load, 7-day survival rate after transplanting, and seedling establishment period: On the 25th day after sowing, 20 seedlings were randomly selected from each sample. After being pushed out of the bottom of the seedling tray with an 8mm diameter pusher, the root ball mass m0 was immediately weighed. The root ball was then dropped freely from a height of 30cm onto a stainless steel plate. After collecting and removing the detached substrate, the remaining root ball mass m1 was weighed. The root ball mass retention rate was calculated as m1 / m0×100%. Ten intact root balls were placed between two parallel pressure plates of an electronic universal testing machine. The preload was set to 0.2N, and the compression speed was set to 20mm / min. The peak load was recorded when the root ball height deformation was 20%, which was taken as the root ball compressive load. For the transplanting experiment, 20 normal seedlings were taken from each sample and transplanted into uniform nutrient pots. They were observed continuously for 7 days. On the 7th day, the number of surviving seedlings was counted and the survival rate after 7 days of transplanting was calculated. At the same time, the number of days required for each seedling to develop new leaves and for the leaf color to return to normal was recorded from the date of transplanting, and the average value was taken as the seedling recovery period.

[0038] Table 1 Performance Test Results

[0039] Data Analysis: As can be seen from the data in Table 1, the bio-organic seedling substrate prepared by this invention exhibits a relatively balanced optimization trend in terms of the particle size concentration of modified straw particles, the coordination of pore structure, the rhythm of water absorption and dehydration, and the stability of root ball formation. After surface-confined carboxymethylation, the outer layer of the particles possesses good water absorption and rewetting capabilities, while the core retains the necessary structural rigidity. After sequential treatment with calcium ions and chitosan oligosaccharides, the substrate further demonstrates the characteristics of synergistic maintenance of water-holding and aeration pores, moderate free water loss, and good integrity of the root ball after pressure and drop. It is speculated that this is because the carboxyl-rich band formed on the outer layer of the particles facilitates water dispersion and entry, the inner calcium ion bridging layer inhibits softening after wetting, and the outer chitosan oligosaccharide moisture-regulating layer improves the interfacial adhesion between the particles and peat, coconut coir, and bio-organic fertilizer, thereby simultaneously achieving moisture regulation, aeration, and root fixation within small-volume pores.

[0040] As can be seen from the data in Table 1 for Example 1 and Comparative Example 1, when only the initial etherification stage is performed without the subsequent sodium chloroacetate supplementation, the particle size distribution, substrate water-holding stability, and root ball formation of the modified straw particles all decrease. Although the aeration porosity increases somewhat, this does not translate into performance advantages. The main reason is that the surface-confined carboxymethylation is insufficient, resulting in a lack of sites on the outer layer of the particles that can participate in water absorption and calcium ion binding. Consequently, the subsequent chitosan oligosaccharide cannot form a uniform moisture-regulating layer on the surface, leading to uneven distribution of water after it enters, rapid water loss, and insufficient fixation between the roots and substrate particles. Therefore, the two-stage etherification is not simply adding reaction steps, but rather providing a necessary prerequisite for the subsequent sequential construction of calcium ions and chitosan oligosaccharides.

[0041] As can be seen from the data in Example 1 and Comparative Example 2 in Table 1, significantly extending the reaction time in the second stage, while enhancing water absorption rate and rewetting ability, actually reduced aeration porosity, root ball compressive load resistance, and transplant recovery. This is presumably due to excessive reaction in the latter stage, causing the hydrophilic modification, which should have been confined to the outer layer of the particles, to extend deeper. After wetting, the particles soften more easily, leading to compression of the macroporous structure and an increase in the proportion of free water, resulting in an unbalanced state of rapid water absorption but structural instability. This indicates that the key to surface-confined carboxymethylation lies not only in introducing hydrophilic structures but also in controlling its reaction depth and spatial location.

[0042] As can be seen from the data in Table 1 for Example 1, Comparative Example 3, and Comparative Example 4, when calcium ions are omitted, the root ball mass retention rate and compressive strength decrease more significantly; when chitosan oligosaccharide is omitted, the decrease in rewetting, free water loss control, and post-transplant recovery is more pronounced. The former indicates that with only surface-bound carboxymethylation and lack of calcium ion bridging, the particles lack sufficient internal support after water absorption, making them prone to becoming loose in a wet state; the latter indicates that while calcium ions without chitosan oligosaccharide can provide some rigidity, the outer layer moisture regulation and interfacial adhesion are insufficient, making it difficult to simultaneously achieve rapid rewetting and stable water retention.

[0043] As can be seen from the data in Example 1 and Comparative Example 5 in Table 1, simply changing the treatment order of calcium ions and chitosan oligosaccharides caused a simultaneous decline in substrate aeration, root ball strength, and post-transplant recovery, indicating that the order itself has a substantial effect. The main reason is that after chitosan oligosaccharides first contact the particle surface, they preferentially occupy the outer layer sites and form a coating, making it difficult for subsequent calcium ions to continue to enter the inner region to build effective bridging. The final result is a structure that is closer to a surface-closed structure, rather than a support-humidity-regulating bilayer structure that changes from the inside to the outside.

[0044] As can be seen from the data in Example 1 and Comparative Example 6 in Table 1, although replacing the chitosan oligosaccharide with a chitosan oligosaccharide with a higher molecular weight still resulted in a certain degree of adhesion and strength on the particle surface, the air permeability, rewetting efficiency, and seedling establishment performance were no longer coordinated. It is speculated that this is because the higher molecular weight chitosan oligosaccharide has longer chain segments and higher solution viscosity in acidic aqueous systems, making it easier to form a continuous film layer on the particle surface during treatment. This leads to narrowing of the outer pores, restricting water entry and air exchange. Therefore, the result is more of a localized enhancement rather than an overall optimization that balances water retention, air permeability, and root stabilization.

[0045] As shown in Figure 1, the modified straw pellets obtained in Example 1 have a particle size of 3420 cm⁻¹. -1 The presence of a broad and strong absorption band nearby indicates the presence of abundant hydroxyl groups and a small amount of amino hydrogen bond association in the sample; 2923 cm⁻¹ -1 and 2852cm -1 The nearby peak represents the stretching vibration of aliphatic CH molecules. (1597 cm⁻¹) -1and 1420cm -1 The presence of relatively obvious characteristic absorptions in the vicinity can be attributed to the -COO group after carboxymethylation. - Asymmetric and symmetric stretching vibrations, of which 1597cm -1 The peak shape near the center broadens slightly, indicating that the carboxyl group reacts with Ca. 2+ And there are certain ionic / hydrogen bond interactions between the amino groups of chitosan oligosaccharides; 1730cm -1 The presence of weak absorption nearby indicates the existence of a small amount of residual carbonyl structures in the straw lignocellulose. At 1160 cm⁻¹ -1 1032cm -1 and 898cm -1 Nearby, characteristic peaks related to the polysaccharide skeleton are visible, corresponding to COC and CO stretching vibrations and glycosidic bond vibrations, respectively. Overall, this spectrum retains the characteristics of the straw lignocellulose skeleton and also shows relatively obvious carboxylate-related absorption peaks, indicating that surface-confined carboxymethylation has occurred in Example 1, and that the subsequent calcium ion-chitosan oligosaccharide sequential treatment has formed a functionalized structure on the particle surface that is conducive to water absorption, water stabilization, and interfacial bonding.

[0046] 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. A biological organic seedling substrate, characterized in that, It is prepared from the following raw materials: 550-700 parts modified straw pellets, 760-850 parts peat, 450-550 parts coconut coir and 280-330 parts bio-organic fertilizer; the modified straw pellets are obtained by alkalizing wheat straw lignocellulose pellets, performing two-stage etherification treatment, and then successively treating them with calcium chloride aqueous solution and chitosan oligosaccharide solution before drying.

2. The biological organic seedling substrate according to claim 1, characterized in that, The wheat straw lignocellulose particles are particles obtained by crushing and sieving wheat straw lignocellulose flakes, which are either below a 20-mesh sieve or above a 40-mesh sieve.

3. The biological organic seedling substrate according to claim 1, characterized in that, The wheat straw lignocellulose particles had a moisture content of 9.6%-11.2% before alkalization.

4. The biological organic seedling substrate according to claim 1, characterized in that, The alkalization treatment is as follows: by mass, 550-700 parts of wheat straw lignocellulose particles are added to 1750-2050 parts of 2-propanol, stirred at 24-26℃ for 12-18 minutes, and then an alkaline solution prepared by 72-90 parts of sodium hydroxide and 110-130 parts of water is added within 12-16 minutes, and stirring is continued for 22-28 minutes.

5. The biological organic seedling substrate according to claim 1, characterized in that, Based on 550-700 parts by weight of wheat straw lignocellulose particles, the two-stage etherification treatment is as follows: first, a first-stage etherification solution formed by 92-110 parts by weight of sodium chloroacetate and 190-230 parts by weight of 2-propanol is added, and the reaction is carried out at 43-48℃ for 35-45 min; then, a second-stage etherification solution formed by 22-30 parts by weight of sodium hydroxide, 28-35 parts by weight of water, 40-50 parts by weight of sodium chloroacetate and 110-130 parts by weight of 2-propanol is added, and the reaction is carried out at 53-58℃ for 22-28 min.

6. The biological organic seedling substrate according to claim 1, characterized in that, Based on 550-700 parts by weight of wheat straw lignocellulose particles, the calcium chloride aqueous solution treatment and chitosan oligosaccharide solution treatment are as follows: the two-stage etherified particles are washed with 2-propanol aqueous solution until the pH of the filtrate is 8.2-8.6; then the washed particles are added to a solution formed by 9-13 parts by weight of calcium chloride dihydrate and 900-1100 parts by weight of water, and soaked at 23℃-26℃ for 12-18 min, followed by draining for 4-6 min; then a solution formed by 10-14 parts by weight of chitosan oligosaccharide, 7-9 parts by weight of glacial acetic acid and 760-850 parts by weight of water is added, and stirred at 23-26℃ for 18-22 min; The particles are then washed with water and finally dried until the moisture content of the particles is 11.8%-13.3%.

7. The biological organic seedling substrate according to claim 1, characterized in that, The molecular weight of the chitosan oligosaccharide is no greater than 3000 Da.

8. A seedling raising method, characterized in that, Using the bio-organic seedling substrate according to any one of claims 1-7 for tray seedling cultivation includes the following steps: filling the bio-organic seedling substrate into 72-128-cell trays, sowing one vegetable seed in each cell, covering with 3-5mm of substrate, spraying water onto each tray after sowing until water just seeps into the bottom of the tray; maintaining a temperature of 24-28℃ before emergence, and 20-26℃ during the day and 14-18℃ at night after emergence; when the moisture content of the bio-organic seedling substrate drops to 45%-50%, spraying water to 60%-65%, and cultivating seedlings for 25-30 days.

9. The seedling raising method according to claim 8, characterized in that, The vegetable seeds mentioned are tomato seeds, pepper seeds, or cabbage seeds.

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