Nutrient solution suitable for soilless sand culture of small watermelons and culture method

Abstract

The invention relates to the field of soilless culture, and particularly discloses a nutrient solution suitable for soilless sand culture of small watermelons, which comprises a formula A for the vine stretching period of the small watermelons, a formula B for the flowering and fruit setting period and a formula C for the fruit expanding period, all of which take deionized water as a solvent. According to the formula A, every 1 L of deionized water is prepared from 50 mg to 60 mg of humic acid, 50 mg to 480 mg of Ca (NO). 4HO4, 80 mg to 300 mg of KSO4, 80 mg to 90 mg of NHHPO, 150 mg to 170 mg of MgSO.7HO, 12 mg to 14 mg of Fe-EDTA, 1.0 mg to 1.2 mg of HBO, 0.5 mg to 0.6 mg of MnCl. 4HO, 0.25 mg to 0.3 mg of ZnSO.7HO, 0.1 mg to 0.12 mg of CuSO. 5HO, 0.08 mg to 0.1 mg of NaMoO. 2HO and 30 mg to 40 mg of seaweed extract; according to the formula B, every 1 L of deionized water is prepared from 60 mg to 70 mg of humic acid, 550 mg to 580 mg of Ca (NO). 4HO, 20 mg to 340 mg of KNO3, 110 mg to 120 mg of KHPO4, 180 mg to 200 mg of MgSO. 7HO, 15 mg to 17 mg of Fe-EDTA, 1.3 mg to 1.5 mg of HBO, 0.7 mg to 0.8 mg of MnCl. 4HO, 0.35 mg to 0.4 mg of ZnSO. 7HO, 0.13 mg to 0.15 mg of CuSO. 5HO and 0.11 mg to 0.13 mg of NaMoO. 2HO; by adopting the technical scheme, sand culture characteristics can be fitted, different growth stages can be adapted, and accumulation of autotoxic substances is reduced.

Description

Technical Field

[0001] This invention relates to the field of soilless cultivation, and in particular to a nutrient solution suitable for soilless sand culture of watermelons and melons. Background Technology

[0002] Soilless cultivation, as a highly efficient planting technology in modern agriculture, is widely used in the production of watermelons and cantaloupes. Among them, sand culture has become an important mode for high-quality cultivation of watermelons and cantaloupes due to its loose, breathable, clean, and pollution-free substrate, which meets the industrial needs of areas rich in sandy resources. However, in the current sand culture production of watermelons and cantaloupes, there are significant pain points in nutrient solution formulation and management technology, which make it difficult to meet the special needs of the sand culture scenario.

[0003] Current nutrient solutions for watermelons and melons mostly follow the formulation systems of soil cultivation or other substrates (such as coconut coir and rock wool), without considering the characteristics of sand culture substrates, such as weak water and fertilizer retention capacity, easy nutrient leaching, and easy salt accumulation. For example, traditional all-inorganic nutrient solutions (such as the Yamazaki cucumber formula and the South China Agricultural University fruit and vegetable formula) are prone to loss of nitrogen, potassium, and other macronutrients due to irrigation leaching in sand culture, which not only reduces fertilizer utilization but also causes substrate salt imbalance, leading to problems such as premature aging of watermelon and melon roots and insufficient sugar accumulation in fruits in the later stages. While some organic ecological nutrient solutions reduce the amount of chemical fertilizers used, the solid fertilizer topdressing method requires increased labor costs, and the release rate of organic fertilizer in sand substrates is difficult to control, which can easily lead to nutrient excess in the seedling stage and nutrient deficiency in the fruiting stage of watermelons and melons.

[0004] The nutrient requirements of watermelons and melons vary significantly at different growth stages (vine extension, flowering and fruit setting, and fruit enlargement). For example, melons require high nitrogen during the vine extension stage and a surge in potassium during the fruit enlargement stage, while watermelons are more sensitive to calcium and magnesium requirements. However, most existing nutrient solutions use a one-size-fits-all formula and do not adjust the nutrient ratios for different stages.

[0005] When watermelons and melons are continuously cropped in sand, the decomposition products of residual roots in the sandy substrate can easily trigger autotoxicity, and the inorganic nutrient residues in traditional nutrient solutions can easily lead to an imbalance in the soil microbial community. Although some studies have used grafting technology to alleviate the obstacles of continuous cropping, it has not been combined with the nutrient solution formula, so it cannot reduce the accumulation of autotoxic substances from the nutrient supply level; at the same time, existing formulas mostly rely on chemical fertilizers, and long-term use can easily cause the sandy substrate to compact, destroying its permeability advantage.

[0006] In summary, current nutrient solutions for watermelon and melon sand culture suffer from poor substrate compatibility, insufficient targeting of growth stages, and weak sustainability. There is an urgent need to develop a specialized nutrient solution that fits the characteristics of sand culture, is suitable for different growth stages, and reduces the accumulation of autotoxic substances, so as to improve the yield, quality, and resource utilization efficiency of watermelon and melon sand culture. Summary of the Invention

[0007] This invention provides a nutrient solution suitable for soilless sand culture of watermelons and melons, which can conform to the characteristics of sand culture, adapt to different growth stages, and reduce the accumulation of autotoxic substances.

[0008] To solve the above-mentioned technical problems, this application provides the following technical solution: A nutrient solution suitable for soilless sand culture of watermelons and melons includes Formula A for the vine extension stage, Formula B for the flowering and fruit setting stage, and Formula C for the fruit enlargement stage, all using deionized water as a solvent. Formula A contains the following per 1L of deionized water: 50-60mg humic acid, 450-480mg Ca(NO3)2·4H2O, 280-300mg K2SO4, 80-90mg NH4H2PO4, 150-170mg MgSO4·7H2O, 12-14mg Fe-EDTA, 1.0-1.2mg H3BO3, 0.5-0.6mg MnCl2·4H2O, 0.25-0.3mg ZnSO4·7H2O, 0.1-0.12mg CuSO4·5H2O, 0.08-0.1mg Na2MoO4·2H2O, and 30-40mg seaweed extract. Formula B per 1L of deionized water includes: 60-70mg humic acid, 550-580mg Ca(NO3)2·4H2O, 320-340mg KNO3, 110-120mg KH2PO4, 180-200mg MgSO4·7H2O, 15-17mg Fe-EDTA, 1.3-1.5mg H3BO3, 0.7-0.8mg MnCl2·4H2O, 0.35-0.4mg ZnSO4·7H2O, 0.13-0.15mg CuSO4·5H2O, 0.11-0.13mg Na2MoO4·2H2O, 40-50mg seaweed extract, and 15-20mg chitosan oligosaccharide. Formula C contains the following per 1L of deionized water: 70-80mg humic acid, 50-60mg seaweed extract, 450-480mg KNO3, 130-140mg KH2PO4, 80-400mg Ca(NO3)2·4H2O, 10-230mg MgSO4·7H2O, 10-12mg Fe-EDTA, 0.9-1.1mg H3BO3, 0.4-0.5mg MnCl2·4H2O, 0.2-0.25mg ZnSO4·7H2O, 0.08-0.1mg CuSO4·5H2O, 0.09-0.11mg Na2MoO4·2H2O, and 25-30mg K2SiO3.

[0009] The basic principles and beneficial effects of the solution are as follows: When applying, nutrient solutions A, B, and C all need to be diluted with water at a ratio of 1:2-3 for drip irrigation. Sand culture substrates (such as river sand) have large interparticle gaps and weak adsorption capacity. Traditional nutrient solutions are prone to leaching during irrigation, leading to the loss of large amounts of elements such as nitrogen and potassium. In this invention, humic acid and seaweed extract are added to formulas A, B, and C. Humic acid contains a large number of functional groups such as carboxyl and hydroxyl groups, which can enhance the adsorption capacity of the sand substrate for Ca²⁺, K⁺, and NH⁴⁺ through ion exchange and complexation, reducing nutrient leakage loss. Seaweed extract contains polysaccharides, mannitol, and other components, which can form a thin film on the surface of sand substrate particles, reducing the rate of water evaporation and extending the stable moisture content period of the sand substrate by 1-2 days, alleviating the problem of frequent alternation between dry and wet conditions in sand culture.

[0010] Potassium silicate enhances the buffering capacity of sandy substrate. The K2SiO3 added in Formula C (fruit enlargement period) can form SiO3²⁻ after dissolution, which can combine with Fe³⁺ and Al³⁺ in the sandy substrate to form a stable complex, reducing the stimulation of roots by free metal ions in the sandy substrate. At the same time, it enhances the buffering capacity of sandy substrate against salt, avoiding salt damage caused by high potassium formula (KNO3+KH2PO4) during fruit enlargement period, reducing the EC value of sandy substrate, and increasing root dry weight compared to conventional silicon-free formula.

[0011] The core advantage of sand culture is its high aeration, but excessively high salt content in the nutrient solution can clog substrate gaps and inhibit root respiration. In this invention, formulas A, B, and C use a low-salt-index combination of macroelements, avoiding the use of high-concentration strong electrolytes such as NaCl and KCl. Low-salt-index compounds such as Ca(NO3)2·4H2O and K2SO4 are preferentially selected, resulting in low EC values. When used, with a dilution ratio of 1:2-3, the EC value of the sand substrate after drip irrigation can be stabilized within a suitable range for the roots, ensuring normal aerobic respiration, reducing premature aging caused by root hypoxia, and improving the root-to-shoot ratio of watermelons and melons.

[0012] During the vine extension stage (Formula A), high nitrogen promotes vegetative growth. Watermelons and melons require a large amount of nitrogen during this stage to promote stem and leaf development, laying the photosynthetic foundation for subsequent flowering and fruit setting. In Formula A, Ca(NO3)2·4H2O and NH4H2PO4 provide a high total nitrogen content, and the ratio of NH4⁺ to NO3⁻ is 1:3.5, which satisfies the root system's preference for absorbing different forms of nitrogen while avoiding root poisoning caused by NH4⁺ alone. At the same time, the addition of MgSO4·7H2O ensures chlorophyll synthesis, resulting in an increase in leaf area and photosynthetic rate during the vine extension stage compared to the general formula.

[0013] During the flowering and fruit-setting period (Formula B), calcium and boron are added to promote pollination and fruit setting. The demand for calcium and boron surges during the flowering and fruit-setting period of watermelons and melons. Calcium enhances the stability of flower organ cell walls, while boron promotes pollen germination and pollen tube elongation. Formula B contains a higher amount of Ca(NO3)2·4H2O and a higher concentration of H3BO3 compared to Formula A. Simultaneously, chitosan oligosaccharides are added. Chitosan oligosaccharides can induce the production of disease-resistant enzymes (such as chitinase) during the flowering period of watermelons and melons, reducing the occurrence of fungal diseases (such as powdery mildew) in sand-cultured environments, thus increasing the fruit-setting rate and reducing flower and fruit drop.

[0014] During the fruit enlargement stage (Formula C), high potassium promotes sugar accumulation. The potassium requirement during this stage accounts for over 60% of the total potassium requirement for watermelon and melon fruit growth. Potassium activates key enzymes such as sucrose synthase and sucrose phosphate synthase, accelerating the transport of photosynthetic products to the fruit. Formula C provides a high total potassium content from KNO3 and KH2PO4, while reducing nitrogen application (Ca(NO3)2·4H2O is less than in Formula B), avoiding excessive nitrogen leading to vegetative growth and fertilizer depletion. Combined with the transport-promoting effect of seaweed extract, this increases the soluble solids content of the fruit, increases the weight of individual fruits, and improves the uniformity of fruit coloring.

[0015] Sand-based substrates have weak adsorption capacity for trace elements, leading to their easy loss through water seepage. In this invention, all trace elements in the formulation are in EDTA chelated form (Fe-EDTA, Mn²⁺ latent chelate). EDTA can form stable complexes with trace elements, ensuring improved absorption rates. Specifically, high Fe levels during the vine-spreading stage prevent yellowing of new leaves, high B levels during flowering ensure pollination, and moderately reduced Fe levels during fruit enlargement prevent abnormal fruit coloring. This forms a precise micronutrient supply system throughout the growth cycle, reducing physiological disorders such as poor netting development and blossom-end rot in watermelons and melons caused by micronutrient deficiencies, thus lowering the incidence of disease.

[0016] When watermelons and melons are continuously cropped in sand, phenolic acids (such as p-hydroxybenzoic acid and ferulic acid) secreted by the roots tend to accumulate in the sandy substrate, inhibiting the growth of subsequent plants. In this invention, humic acid and seaweed extract can reduce the accumulation of autotoxic substances. The porous structure of humic acid can adsorb free phenolic acids in the sandy substrate, reducing their effective concentration; the fucoidan in the seaweed extract can promote the proliferation of beneficial microorganisms (such as Pseudomonas and Bacillus) in the sandy substrate. These microorganisms can secrete esterases, oxidases, etc., to degrade autotoxic substances. Long-term application of this nutrient solution can maintain the content of autotoxic substances in the sandy substrate below the safe threshold after two consecutive crops, and the single fruit weight of watermelons and melons after two consecutive crops is still similar to that of the first crop, which is superior to conventional sand-culture nutrient solutions without the addition of slow-release synergists.

[0017] The chitosan oligosaccharide in formula B and the K2SiO3 in formula C form a dual-resistance system. The chitosan oligosaccharide induces systemically acquired resistance (SAR) in watermelons and melons, enhancing their resistance to fungal diseases (such as anthracnose) and bacterial diseases (such as angular leaf spot). K2SiO3 forms a siliceous layer on the leaf surface, physically blocking feeding by piercing-sucking pests such as aphids and whiteflies. After applying this nutrient solution, the incidence of anthracnose in watermelons and melons decreased, aphid populations decreased, and the amount of chemical pesticides used was reduced, aligning with the needs of green agriculture.

[0018] Humic acid and seaweed extract provide carbon and nitrogen sources for beneficial microorganisms in the sandy substrate, promoting the proliferation of rhizobia and actinomycetes while inhibiting the growth of pathogens (such as Fusarium). After applying this nutrient solution, the proportion of beneficial microorganisms in the sandy substrate increases, while the proportion of pathogens decreases, forming a benign symbiotic relationship between nutrients, microorganisms, and roots. This improves the root absorption efficiency of watermelons and melons and significantly enhances their resistance to adverse conditions (such as drought and low temperature).

[0019] By precisely supplying nutrients during the growth period and adapting the design to the characteristics of sand culture, this invention can increase the yield per acre of watermelons and melons, and significantly improve the stability of their quality: the coefficient of variation of soluble solids content in the fruit is reduced, the rate of fruit cracking is reduced (especially suitable for the thin-skinned characteristics of small watermelons), and the rate of first-grade fruit is increased, giving it a clear commercial advantage over conventional sand culture nutrient solutions. At the same time, the nutrient solution is free of heavy metals and high-residue chemicals, and the nitrate content in the watermelon and melon fruits is reduced, meeting the requirements for green food.

[0020] In summary, this invention achieves the effects of conforming to the characteristics of sand culture, adapting to different growth stages, and reducing the accumulation of autotoxic substances.

[0021] Furthermore, Fe and Mn are chelated in the form of EDTA, and Zn and Cu are chelated in the form of DTPA; the Fe²⁺ content in the EDTA chelated iron is ≥13%, the Mn²⁺ content in the EDTA chelated manganese is ≥12%, the Zn²⁺ content in the DTPA chelated zinc is ≥14%, and the Cu²⁺ content in the DTPA chelated copper is ≥15%.

[0022] Furthermore, in formula C, each 1L of deionized water also includes a compound bacterial agent of Bacillus subtilis and Bacillus amyloliquefaciens, with a bacterial agent concentration of 10. 8 -10 9 CFU / L; The Bacillus subtilis and Bacillus amyloliquefaciens compound bacterial agent is a powder that has been freeze-dried at low temperature and is added after being reconstituted with deionized water before use.

[0023] Bacillus subtilis can secrete antibacterial substances such as subtilisin, which can inhibit the reproduction of pathogens such as Fusarium oxysporum and Rhizoctonia solani in sandy substrates, degrade autotoxic substances such as p-hydroxybenzoic acid and coumaric acid produced by continuous cropping, and improve the root micro-ecological environment. Bacillus amyloliquefaciens can secrete highly active amylase, protease and phytase, which can decompose large molecular organic nutrients (such as humic acid-bound phosphorus and seaweed polysaccharide-bound potassium) in nutrient solution into small molecular soluble nutrients (PO4³⁻, K⁺). At the same time, it secretes auxin (IAA) to promote the germination of lateral roots and increase the root absorption area.

[0024] When used together, the small molecule nutrients decomposed by Bacillus amyloliquefaciens can reduce the nutrient competition pressure on Bacillus subtilis and promote its secretion of antibacterial substances; the root microenvironment improved by Bacillus subtilis can increase the colonization rate of Bacillus amyloliquefaciens; the extracellular polysaccharides secreted by both can form a root-bacterial membrane complex, reducing nutrient loss caused by salt leaching in sandy substrates, while enhancing the root's resistance to salt stress (alleviating the risk of root burn under high EC values).

[0025] Furthermore, the EC values ​​for formulation A are 2.8-3.0 mS / cm, for formulation B 3.0-3.2 mS / cm, and for formulation C 3.2-3.5 mS / cm.

[0026] Furthermore, L-proline is added to the B formulation at an amount of 8-10 mg / L; the L-proline is a food-grade crystal with a purity of ≥99%.

[0027] A method for soilless sand culture of watermelon and cantaloupe includes the following steps: S1. Sand substrate pretreatment: Select river sand with a particle size of 0.2-2.0mm, soak it in hot water at 50-60℃ for 2 hours, drain it, and lay it in the substrate bag as sand substrate. First, lay a 10-15cm thick gravel layer with a particle size of 5-10mm in the substrate bag, and then fill the gravel layer with sand substrate to a thickness of 35-40cm. S2. Transplanting preparation: One day before transplanting watermelon and cantaloupe seedlings, drip irrigation of clean water into the sand substrate until the water content reaches 60%-65% of the field water holding capacity. Transplant 1-3 seedlings into each substrate bag according to its size. Cover with black mulch after transplanting. S3. Nutrient solution application: Start applying nutrient solution on the second day after transplanting, switching formulas according to the growth stages of watermelon and melon: use formula A during the vine extension stage, formula B during the flowering and fruit setting stage, and formula C during the fruit enlargement stage; dilute the nutrient solution with water at a ratio of 1:2-3. During the vine extension stage, drip irrigate once every 2-3 days, using 0.8-1.0L per plant each time; during the flowering and fruit setting stage, drip irrigate once every 1-2 days, using 1.0-1.2L per plant each time; during the fruit enlargement stage, drip irrigate once a day, using 1.2-1.5L per plant each time. S4. Field Management: During the vine extension stage, prune the vines to a single vine, leaving the main vine and one lateral vine; during the flowering stage, perform artificial pollination, leaving 2-3 fruits per plant; during the fruit enlargement stage, thin the fruit in a timely manner, leaving 1-2 healthy fruits; stop applying nutrient solution 7 days before harvest, and only drip irrigate with clean water.

[0028] Furthermore, the sand culture container adopts a bag-type structure.

[0029] Furthermore, in S1, organic fertilizer is laid on top of the gravel layer in the substrate bag.

[0030] Furthermore, in S3, each substrate bag is drip-irrigated independently.

[0031] Furthermore, each substrate bag has a volume of 15-45L. Attached Figure Description

[0032] Figure 1 This is a flowchart of a soilless sand culture method suitable for watermelons and melons. Detailed Implementation

[0033] The following detailed description illustrates the specific implementation method: Example 1

[0034] A nutrient solution suitable for soilless sand culture of watermelons and melons includes Formula A for the vine extension stage, Formula B for the flowering and fruit setting stage, and Formula C for the fruit enlargement stage, all using deionized water as a solvent. Formula A contains the following per 1L of deionized water: 50-60mg humic acid, 450-480mg Ca(NO3)2·4H2O, 280-300mg K2SO4, 80-90mg NH4H2PO4, 150-170mg MgSO4·7H2O, 12-14mg Fe-EDTA, 1.0-1.2mg H3BO3, 0.5-0.6mg MnCl2·4H2O, 0.25-0.3mg ZnSO4·7H2O, 0.1-0.12mg CuSO4·5H2O, 0.08-0.1mg Na2MoO4·2H2O, and 30-40mg seaweed extract. Formula B per 1L of deionized water includes: 60-70mg humic acid, 550-580mg Ca(NO3)2·4H2O, 320-340mg KNO3, 110-120mg KH2PO4, 180-200mg MgSO4·7H2O, 15-17mg Fe-EDTA, 1.3-1.5mg H3BO3, 0.7-0.8mg MnCl2·4H2O, 0.35-0.4mg ZnSO4·7H2O, 0.13-0.15mg CuSO4·5H2O, 0.11-0.13mg Na2MoO4·2H2O, 40-50mg seaweed extract, and 15-20mg chitosan oligosaccharide. Formula C contains the following per 1L of deionized water: 70-80mg humic acid, 50-60mg seaweed extract, 450-480mg KNO3, 130-140mg KH2PO4, 80-400mg Ca(NO3)2·4H2O, 10-230mg MgSO4·7H2O, 10-12mg Fe-EDTA, 0.9-1.1mg H3BO3, 0.4-0.5mg MnCl2·4H2O, 0.2-0.25mg ZnSO4·7H2O, 0.08-0.1mg CuSO4·5H2O, 0.09-0.11mg Na2MoO4·2H2O, and 25-30mg K2SiO3.

[0035] In practical use: First, prepare deionized water and raw materials as follows: calcium nitrate tetrahydrate (Ca(NO3)2·4H2O, purity ≥99%), potassium sulfate (K2SO4, purity ≥98%), ammonium dihydrogen phosphate (NH4H2PO4, purity ≥99%), magnesium sulfate heptahydrate (MgSO4·7H2O, purity ≥98%), potassium nitrate (KNO3, purity ≥99%), potassium dihydrogen phosphate (KH2PO4, purity ≥99%), and potassium silicate (K2SiO3, purity ≥98%).

[0036] EDTA chelated iron (Fe-EDTA, Fe²⁺ content 13.5%), EDTA chelated manganese (Mn-EDTA, Mn²⁺ content 12.2%), DTPA chelated zinc (Zn-DTPA, Zn²⁺ content 14.3%), DTPA chelated copper (Cu-DTPA, Cu²⁺ content 15.1%), boric acid (H₃BO₃, purity ≥99%), sodium molybdate dihydrate (Na₂MoO₄·2H₂O, purity ≥98%).

[0037] Humic acid (molecular weight 5000-10000 Da, organic matter content ≥70%), seaweed extract (brown algae source, polysaccharide content ≥40%), chitosan oligosaccharide (degree of polymerization 6-8, purity ≥95%), L-proline (food grade, purity 99.2%), and a compound bacterial agent of Bacillus subtilis and Bacillus amyloliquefaciens (low-temperature freeze-dried powder, viable count ratio of the two is 1:1, viable count 1.2×10⁻⁶). 9 CFU / g).

[0038] Then, the formulation is prepared (based on 1L of deionized water). The steps for preparing formulation A (vine extension stage) are as follows: Weigh out 465 mg of Ca(NO3)2·4H2O, 290 mg of K2SO4, 85 mg of NH4H2PO4, and 160 mg of MgSO4·7H2O, and dissolve them in 500 mL of deionized water to form a macro-element solution; weigh out 13 mg of Fe-EDTA, 1.1 mg of H3BO3, Mn-EDTA (equivalent to 0.55 mg of MnCl2·4H2O), Zn-DTPA (equivalent to 0.28 mg of ZnSO4·7H2O), Cu-DTPA (equivalent to 0.11 mg of CuSO4·5H2O), and 0.09 mg of Na2MoO4·2H2O, and sonicate them in 100 mL of deionized water to form a trace element solution; weigh out 55 mg of humic acid and 35 mg of seaweed extract, and dissolve them in 100 mL of deionized water to form a synergist solution. The three solutions were mixed, the pH was adjusted to 6.1 with 1 mol / L H2SO4, and the volume was brought to 1 L. The EC value was measured to be 2.9 mS / cm. The preparation steps for Formula B (flowering and fruit setting period) are as follows: Weigh 565 mg Ca(NO3)2·4H2O, 330 mg KNO3, 115 mg KH2PO4, and 190 mg MgSO4·7H2O, and dissolve them in 500 mL of deionized water to form a macro-element solution; Weigh 16 mg Fe-EDTA, 1.4 mg H3BO3, Mn-EDTA (equivalent to 0.75 mg MnCl2·4H2O), Zn-DTPA (equivalent to 0.38 mg ZnSO4·7H2O), Cu-DTPA (equivalent to 0.14 mg CuSO4·5H2O), and Na2MoO4·2H2O. 0.12 mg was ultrasonically dissolved in 100 mL of deionized water to form a trace element solution; 65 mg of humic acid, 45 mg of seaweed extract, 18 mg of chitosan oligosaccharide, and 9 mg of L-proline were weighed and dissolved in 100 mL of deionized water to form a synergist solution. After mixing, the pH was adjusted to 5.9 with 1 mol / L KOH, and the volume was brought to 1 L. The EC value was 3.1 mS / cm. The preparation steps for Formula C (fruit enlargement stage) are as follows: Weigh 465mg KNO3, 135mg KH2PO4, 390mg Ca(NO3)2·4H2O, 220mg MgSO4·7H2O, and 28mg K2SiO3, and dissolve them in 500mL of deionized water to form a macro-element solution; Weigh 11mg Fe-EDTA and H3BO3... 1.0 mg of Mn-EDTA (equivalent to 0.45 mg of MnCl2·4H2O), Zn-DTPA (equivalent to 0.23 mg of ZnSO4·7H2O), Cu-DTPA (equivalent to 0.09 mg of CuSO4·5H2O), and 0.10 mg of Na2MoO4·2H2O were ultrasonically dissolved in 100 mL of deionized water to form a trace element solution. 75 mg of humic acid and 55 mg of seaweed extract were weighed, and 0.1 g of a compound bacterial agent of Bacillus subtilis and Bacillus amyloliquefaciens (with a viable count ratio of 1:1) was reconstituted in 10 mL of deionized water for 10 min to form a synergist solution. After mixing, the pH was adjusted to 6.3 with 1 mol / L phosphoric acid, and the volume was brought to 1 L. The EC value was 3.3 mS / cm.

[0039] Suitable cultivation methods for hydroponics of watermelons and melons (such as...) Figure 1 As shown in the figure, during planting, the sand substrate pretreatment is carried out first (S1). River sand with a particle size of 0.5-1.5mm is selected, stirred and washed, and drained to a moisture content of 15%-20%. A PE black substrate bag with a volume of 20L (40cm×30cm×25cm, with 8 drainage holes of 5mm at the bottom of the bag) is used. A 12cm thick gravel layer with a particle size of 8mm is laid in the bag first (1kg of decomposed sheep manure is laid on the gravel layer). The sand substrate is then filled on the gravel layer and sheep manure layer to a thickness of 38cm (bulk density 1.65g / cm³).

[0040] Then, prepare for transplanting (S2). Soak the netted melon seeds in 55℃ hot water for 15 minutes and germinate them at 30℃ for 24 hours. Sow them in a peat moss:perlite = 3:1 substrate and cultivate them until they reach the 3-leaf and 1-heart stage (seedling age 30 days). One day before transplanting, drip irrigate with clean water until the moisture content of the sand substrate is 62%. Transplant one seedling into each substrate bag, with a hole depth of 10cm, and cover with a 20cm diameter black mulch film.

[0041] Next is the application of nutrient solution (S3). The nutrient solutions of formula A, formula B, and formula C are stored in separate storage tanks and are quantitatively prepared when used (of course, due to the inconsistent drip irrigation time, a single storage tank can also be used, and quantitative preparation can be carried out at the appropriate time) to avoid sedimentation. Drip irrigation is carried out using a drip irrigation system. The storage tank is equipped with a stirrer, pH / EC sensor, Φ25mm PE main pipe (each group of 10 bags with a flow valve), Φ8mm labyrinth drip tape (one per bag, insertion depth 8cm, distance from root 10cm, drip flow rate 2L / h), and linkage timer.

[0042] In other embodiments, a drip irrigation system suitable for soilless sand culture of watermelon and cantaloupe can also be used for drip irrigation, the drip irrigation system including: a storage tank, a main pipe, a stirrer, a flow valve, a drip tape and a controller; The sensors include: A pH sensor is used to collect the pH value of each nutrient solution formula in real time, with a collection frequency of once every 5 minutes, a data range of 4.0-8.0, and an accuracy of ±0.01. The collected data includes: pH value of formula A (vine extension stage), pH value of formula B (flowering and fruit setting stage), and pH value of formula C (fruit enlargement stage). The focus is on monitoring the pH change of formula C after the addition of compound microbial agent (microbial agent metabolism may cause pH fluctuations). EC sensors are used to collect the conductivity of various nutrient solutions in real time, with a sampling frequency of once every 5 minutes, a data range of 0-10 mS / cm, and an accuracy of ±0.01 mS / cm. The collected data includes: EC values ​​of the stock solution of Formula A (target 2.8-3.0 mS / cm), the stock solution of Formula B (target 3.0-3.2 mS / cm), the stock solution of Formula C (target 3.2-3.5 mS / cm), as well as the EC values ​​of the diluted nutrient solutions (Formula A: 1.1 mS / cm, Formula B: 1.5 mS / cm, Formula C: 1.1 mS / cm), and the EC value of the recovered leachate.

[0043] A flow sensor, installed at the end of each branch pipe, is used to collect the nutrient solution delivery rate of a single bag of substrate in real time, with a sampling frequency of once every 10 seconds and an accuracy of ±0.05L. The collected data includes: actual flow rate of a single irrigation and cumulative irrigation flow rate, used to determine whether the drip irrigation tape is blocked (sudden drop in flow rate) or the pipe is leaking (abnormally increased flow rate).

[0044] A temperature sensor, installed inside the nutrient solution tank, is used to collect the temperature of the nutrient solution once every 10 minutes, with a range of 5-40℃ and an accuracy of ±0.1℃. Special attention should be paid to preventing the compound microbial agent in Formula C from becoming inactive at temperatures above 30℃ or experiencing a decrease in root absorption efficiency at temperatures below 15℃.

[0045] The controller, based on data collected by pH, EC, flow rate, and temperature sensors, and combined with a nutrient requirement model for the growth stages of watermelons and melons, generates flow valve control commands to maintain the pH of each nutrient solution formula between 5.8 and 6.3, including: , in, The required volume of acid / base solution to be added is the only indicator of the amount used for acid / base adjustment. The sensor collects the current pH value of the nutrient solution, which uniquely represents the real-time acidity and alkalinity. The target pH value set for each formula (5.8-6.3 for formulas A / B / C) uniquely represents the ideal acidity or alkalinity. : Storage tank volume, uniquely representing the total amount of nutrient solution; Nutrient solution density is the unique characteristic of the mass of nutrient solution per unit volume. Nutrient solution buffer capacity (measured values: Formula A 0.02 mol / L·pH, Formula B 0.025 mol / L·pH, Formula C 0.03 mol / L·pH), uniquely characterizing the ability of a nutrient solution to resist pH changes; The concentration coefficient of acid / base is used for adjustment (0.8 for 1 mol / L H2SO4 and 0.9 for 1 mol / L KOH), which uniquely characterizes the adjustment efficiency of acid-base solutions. The pH value of the acid / base used for adjustment (0.5 for 1 mol / L H2SO4, 13.5 for 1 mol / L KOH) is the only indicator of the acidity or alkalinity of the adjusting reagent itself.

[0046] when At that time, the controller calculates And start the acid pump to inject the corresponding volume of 1mol / L H2SO4 into the storage tank; when At that time, start the alkali pump to inject 1 mol / L KOH, and at the same time, activate the stirrer to accelerate mixing until the pH returns to the target range.

[0047] This method can prevent Fe and Mn from precipitating due to excessively high pH (improving the utilization rate of trace elements) and prevent root burn due to excessively low pH (improving root survival rate).

[0048] The controller is also used to ensure that the EC value of the diluted nutrient solution meets the requirements of each growth stage and to avoid salt accumulation in the sand substrate by: , in: : The required volume of clean water to be added (unit: L), which uniquely represents the amount of dilution water used; : Current volume of nutrient solution in the storage tank (unit: L), uniquely representing the total amount of nutrient solution to be diluted; The EC value of the original solution collected by the sensor is the only indicator of the nutrient concentration of the original solution. The target EC values ​​after dilution at each growth stage (Formula A 1.1 mS / cm, Formula B 1.5 mS / cm, Formula C 1.1 mS / cm) uniquely represent the ideal dilution concentration. EC value of clean water (fixed ≤0.1mS / cm), is the only indicator of the purity of dilution water.

[0049] The controller is used for real-time comparison. and ,calculate Then, activate the clean water valve to inject the corresponding volume of clean water, and simultaneously adjust the mixing ratio of the stock solution and clean water using the flow valve. For example, if the EC of the stock solution of formula C is 3.3 mS / cm and the target dilution EC is 1.1 mS / cm, the calculated... That is, dilute at a ratio of 1:2, and the flow valve distributes the flow of the original solution and the clean water according to this ratio.

[0050] This method allows for precise control of dilution concentration (EC deviation ≤ 5%), avoids excessive water leading to nutrient leakage (which improves fertilizer utilization), and reduces the risk of excessive EC values ​​in sand substrate.

[0051] The controller is also used to adjust the amount of irrigation per irrigation based on the fertilizer requirements of watermelons and melons during their growth period and the water retention characteristics of the sandy substrate, thus avoiding alternating periods of drought and flooding. Specific details are as follows:

[0052] in: : Single plant irrigation volume per irrigation (unit: L), uniquely representing the actual liquid supply; The growth period coefficient (0.4 during vine extension, 0.55 during flowering and fruit setting, and 0.65 during fruit enlargement) uniquely characterizes the fertilizer requirement intensity at different stages. The average daily water consumption per plant (1.5L during vine extension, 2.0L during flowering and fruit setting, and 2.5L during fruit enlargement) is the only indicator of the plant's water requirements. EC value of sand matrix (determined by matrix extract, target 1.2-2.0 mS / cm), uniquely characterizes the salinity of the matrix; The ideal EC value of the matrix (fixed at 1.6 mS / cm) is the only indicator of the suitable salinity level of the matrix.

[0053] The controller is used to collect the EC value of the sand matrix once every 2 days. Then by reducing (Reduce nutrient input) while increasing the frequency of irrigation with clean water; if Then improve (Replenishing nutrients). For example, during the fruit enlargement period. , , Calculated The controller sends a single-open instruction to the flow valve for 39 minutes (drip tape flow rate 2L / h).

[0054] This method meets the nutrient requirements of different growth stages (increasing the daily weight gain of a single fruit during the fruit expansion period) and dynamically adjusts the irrigation amount to alleviate the imbalance of substrate salt (resulting in a decrease in the rate of fruit cracking).

[0055] During the vine extension period (1-25 days): Dilute Formula A with water at a ratio of 1:2.5 (EC 1.1 mS / cm), and irrigate 0.9 L / plant every 2 days at 9 am; Flowering and fruit setting period (26-45 days): Formula B + water = 1:2 dilution (EC 1.5mS / cm), irrigate 1.1L / plant every 1.5 days from 8:30 to 9:30 am; During the fruit enlargement period (46 days to 7 days before harvest): C formula + water = 1:3 dilution (EC 1.1mS / cm), irrigate 1.3L / plant at 9 am and 4 pm every day.

[0056] During this process, field management (S4) is required. During the vine extension period, single-vine pruning is performed (retaining the main vine + 5 lateral vines at the 25th node, and topping at 25 leaves). Artificial pollination is carried out at 10 am during the flowering period, leaving 2 healthy young fruits per plant. The greenhouse temperature is 26-28℃ during the day and 16-18℃ at night, with a humidity of 65%-70%. During the later stage of fruit enlargement, the temperature is 13-15℃ at night (a day-night temperature difference of 12-15℃). Nutrient solution is stopped 7 days before harvest, and 0.8L of clean water is drip-irrigated per plant. Harvest is carried out when the soluble solids content of the fruit is ≥15%.

[0057] After implementation, the growth and quality indicators of netted melons are as follows: leaf area of ​​280cm² / plant during the vine extension period, fruit set rate of 92% during the flowering and fruit setting period, and daily weight gain of 15g per fruit during the fruit enlargement period; soluble solids of mature fruit of 15.8%, vitamin C of 65mg / 100g, fruit cracking rate of 8%, and first-grade fruit rate of 90%; after two consecutive crops on sandy substrate, the rhizosphere p-hydroxybenzoic acid content was 0.12mg / kg, and the weight of the second crop per fruit was 1.8kg (92% of the first crop).

[0058] To verify the technical effect of the present invention, four comparative examples were set up (based on the netted melon of Example 1, only a single variable was changed, and the other conditions were the same).

[0059] Comparative Example 1 (without sustained-release synergist): Humic acid and seaweed extract were removed from formulations A, B, and C, and the rest were the same as in Example 1.

[0060] Reasons for the difference in results: Without humic acid to adsorb nutrients, the nitrogen and potassium leaching loss rate increased to 45%; without seaweed extract to retain water, the sand substrate experienced frequent dry and wet cycles, which inhibited root growth, significantly reduced fruit setting rate and leaf area, and caused a surge in fruit cracking rate due to water fluctuations.

[0061] Comparative Example 2 (General Nutrient Solution, No Growth Period Formula): Commercially available general nutrient solution for watermelon and cantaloupe (no A / B / C stage formula, EC value 3.0 mS / cm) was used, with a single concentration applied throughout the entire process.

[0062] Reasons for the difference in results: insufficient nitrogen during the vine extension period leads to small leaf area, and insufficient potassium during the fruit enlargement period leads to low soluble solids; the general formula is not adapted to the percolation characteristics of sand culture, resulting in a high nutrient loss rate and a sharp drop in single fruit weight after continuous cropping.

[0063] Comparative Example 3 (without Bacillus subtilis and Bacillus amyloliquefaciens compound inoculant, continuous cropping): Bacillus subtilis and Bacillus amyloliquefaciens compound inoculant were removed from Formula C, and the rest was the same as in Example 1. The crops were continuously cropped for 2 tests.

[0064] Reasons for the difference in effect: The compound inoculant of Bacillus subtilis and Bacillus amyloliquefaciens degrades the autotoxic substances. After two consecutive crops, the content of p-hydroxybenzoic acid in the rhizosphere increases to 0.35 mg / kg (exceeding the safety threshold), inhibiting root absorption and reducing the weight of a single fruit to 70% of that of the first crop.

[0065] Comparative Example 4 (conventional drip irrigation, without adapter): ordinary field drip irrigation tape was used (without independent control, drip flow rate of 3L / h, no backflow), and the rest was the same as in Example 1.

[0066] The comparison results are shown in the table below:

[0067] Excessive drip irrigation flow leads to excessive irrigation volume per irrigation, increasing nutrient leakage and loss rate; lack of independent control results in insufficient irrigation of the edge substrate bags, reduced root dry weight, and suppressed fruit quality.

[0068] As can be seen from the comparison of the examples and comparative examples, the present invention, through the combination design of controlled-release synergist + staged formula for the growth period + compound bacterial agent of Bacillus subtilis and Bacillus amyloliquefaciens + adapted drip irrigation device, can significantly improve the growth indicators, quality indicators and continuous cropping adaptability of watermelon and cantaloupe in sand culture, and solve the problems of poor adaptability of sand culture, insufficient targeting of the growth period and continuous cropping obstacles.

[0069] The above are merely embodiments of the present invention. The invention is not limited to the fields covered by these embodiments. Commonly known structures and characteristics in the solutions are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are able to access all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, under the guidance of this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A nutrient solution suitable for hydroponics of watermelons and melons, characterized in that, Formula A, targeting the vine extension stage of watermelons and melons; Formula B, targeting the flowering and fruit setting stage; and Formula C, targeting the fruit enlargement stage, all use deionized water as a solvent. Among them: Formula A contains the following per 1L of deionized water: 50-60mg humic acid, 450-480mg Ca(NO3)2·4H2O, 280-300mg K2SO4, 80-90mg NH4H2PO4, 150-170mg MgSO4·7H2O, 12-14mg Fe-EDTA, 1.0-1.2mg H3BO3, 0.5-0.6mg MnCl2·4H2O, 0.25-0.3mg ZnSO4·7H2O, 0.1-0.12mg CuSO4·5H2O, 0.08-0.1mg Na2MoO4·2H2O, and 30-40mg seaweed extract. Formula B per 1L of deionized water includes: 60-70mg humic acid, 550-580mg Ca(NO3)2·4H2O, 320-340mg KNO3, 110-120mg KH2PO4, 180-200mg MgSO4·7H2O, 15-17mg Fe-EDTA, 1.3-1.5mg H3BO3, 0.7-0.8mg MnCl2·4H2O, 0.35-0.4mg ZnSO4·7H2O, 0.13-0.15mg CuSO4·5H2O, 0.11-0.13mg Na2MoO4·2H2O, 40-50mg seaweed extract, and 15-20mg chitosan oligosaccharide. Formula C contains the following per 1L of deionized water: 70-80mg humic acid, 50-60mg seaweed extract, 450-480mg KNO3, 130-140mg KH2PO4, 80-400mg Ca(NO3)2·4H2O, 10-230mg MgSO4·7H2O, 10-12mg Fe-EDTA, 0.9-1.1mg H3BO3, 0.4-0.5mg MnCl2·4H2O, 0.2-0.25mg ZnSO4·7H2O, 0.08-0.1mg CuSO4·5H2O, 0.09-0.11mg Na2MoO4·2H2O, and 25-30mg K2SiO3.

2. The nutrient solution suitable for hydroponics of watermelons and melons according to claim 1, characterized in that, Fe and Mn are chelated in the form of EDTA, and Zn and Cu are chelated in the form of DTPA; the Fe²⁺ content in the EDTA chelated iron is ≥13%, the Mn²⁺ content in the EDTA chelated manganese is ≥12%, the Zn²⁺ content in the DTPA chelated zinc is ≥14%, and the Cu²⁺ content in the DTPA chelated copper is ≥15%.

3. The nutrient solution suitable for hydroponics of watermelons and melons according to claim 2, characterized in that, In formula C, each 1L of deionized water also includes a compound bacterial agent of Bacillus subtilis and Bacillus amyloliquefaciens, with a bacterial agent concentration of 10. 8 -10 9 CFU / L; The Bacillus subtilis and Bacillus amyloliquefaciens compound bacterial agent is a powder that has been freeze-dried at low temperature and is added after being reconstituted with deionized water before use.

4. The nutrient solution suitable for hydroponics of watermelons and melons according to claim 3, characterized in that, Formula A has an EC value of 2.8-3.0 mS / cm, Formula B has an EC value of 3.0-3.2 mS / cm, and Formula C has an EC value of 3.2-3.5 mS / cm.

5. The nutrient solution suitable for hydroponics of watermelons and melons according to claim 4, characterized in that, The B formulation also contains L-proline at a concentration of 8-10 mg / L; the L-proline is a food-grade crystal with a purity of ≥99%.

6. A method for soilless sand culture of watermelon and melon, characterized in that, Includes the following steps: S1. Sand substrate pretreatment: Select river sand with a particle size of 0.2-2.0mm, soak it in hot water at 50-60℃ for 2 hours, drain it, and lay it in the substrate bag as sand substrate. First, lay a 10-15cm thick gravel layer with a particle size of 5-10mm in the substrate bag, and then fill the gravel layer with sand substrate to a thickness of 35-40cm. S2. Transplanting preparation: One day before transplanting watermelon and cantaloupe seedlings, drip irrigation of clean water into the sand substrate until the water content reaches 60%-65% of the field water holding capacity. Transplant 1-3 seedlings into each substrate bag according to its size. Cover with black mulch after transplanting. S3. Nutrient solution application: Start applying nutrient solution on the second day after transplanting, switching formulas according to the growth stages of watermelon and melon: use formula A during the vine extension stage, formula B during the flowering and fruit setting stage, and formula C during the fruit enlargement stage; dilute the nutrient solution with water at a ratio of 1:2-3. During the vine extension stage, drip irrigate once every 2-3 days, using 0.8-1.0L per plant each time; during the flowering and fruit setting stage, drip irrigate once every 1-2 days, using 1.0-1.2L per plant each time; during the fruit enlargement stage, drip irrigate once a day, using 1.2-1.5L per plant each time. S4. Field Management: During the vine extension stage, prune the vines to a single vine, leaving the main vine and one lateral vine; during the flowering stage, perform artificial pollination, leaving 2-3 fruits per plant; during the fruit enlargement stage, thin the fruit in a timely manner, leaving 1-2 healthy fruits; stop applying nutrient solution 7 days before harvest, and only drip irrigate with clean water.

7. A method for soilless sand culture of watermelon and melon according to claim 6, characterized in that, The sand culture container adopts a bag-type structure.

8. A method for soilless sand culture of watermelon and melon according to claim 7, characterized in that, In S1, organic fertilizer is laid on top of the gravel layer in the substrate bag.

9. A method for soilless sand culture of watermelon and melon according to claim 8, characterized in that, In S3, each substrate bag is drip-irrigated independently.

10. A method for soilless sand culture of watermelon and melon according to claim 8, characterized in that, Each substrate bag has a volume of 15-45L.

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