Vegetable hydroponic nutrient solution and application thereof

Abstract

The application discloses a kind of vegetable hydroponic nutrient solution and application thereof, specifically relates to soilless culture and agricultural resources and environmental technical field, the application is by using 30 / 70 nitrate proportion in whole growth period, on the one hand, the competitive absorption mechanism of ammonium nitrogen and nitrate nitrogen is used to reduce nitrate accumulation from source, on the other hand, make plant in higher nitrogen utilization efficiency and antioxidant state.Based on this, preharvest water nitrogen is cut off to completely cut off exogenous nitrogen supply, forced plant consumes the nitrate stored in vacuole, and simultaneously stimulates the antioxidant defense system to induce explosive synthesis of vitamin C.The synergistic effect of the two is that: 30 / 70 ratio makes plant have "low nitrate basis" and "high VC synthesis potential", and water nitrogen is cut off to convert these potential into actual effect.

Description

Technical Field

[0001] This invention relates to the fields of soilless cultivation and agricultural resources and environment technology, specifically to a hydroponic nutrient solution for vegetables and its application. Background Technology

[0002] With the continued acceleration of global urbanization, urban areas face increasingly severe challenges of water and land scarcity, posing a significant threat to the sustainability of food production and food security. Against this backdrop, hydroponics, as an advanced soilless cultivation method, has become an important direction for modern agriculture due to its ability to operate without soil, its year-round continuous production, and its high resource utilization efficiency. However, in actual hydroponic production systems, the formulation of the nutrient solution, a core factor determining crop growth, development, and quality, still faces the bottleneck of balancing yield, quality, and environmental impact.

[0003] Currently, traditional hydroponic nutrient solution formulations (such as the classic Hoagland formulation) mainly rely on a high proportion of nitrate nitrogen (NO3). - High-nitrate nitrogen formulas are often used as a nitrogen source to promote rapid crop growth and maximize biomass. However, long-term use of such formulas can lead to excessive nitrate accumulation in leafy vegetables (such as bok choy, *Brassica rapa* sp. *Pekinensis*). When humans ingest excessive nitrates, the resulting nitrites pose a clear health risk. These accumulated nitrates are readily reduced to nitrites by bacteria in the digestive tract. Nitrites not only induce methemoglobinemia, reducing the blood's oxygen-carrying capacity, but also combine with amines in the acidic environment of the stomach to form nitrosamines, potent carcinogens. Long-term consumption of nitrites significantly increases the risk of digestive tract diseases such as stomach and esophageal cancer.

[0004] Meanwhile, traditional formulations often neglect the environmental impact of the production process. Because crops have limited absorption and utilization rates of high-concentration nitrate nitrogen, the discharged wastewater contains a large amount of residual nutrients, which requires a massive amount of freshwater to dilute in environmental assessments in order to meet discharge standards, resulting in an extremely high "grey water footprint," which seriously violates the original intention of green agriculture.

[0005] To address the aforementioned issues, existing research has attempted to improve vegetable quality through pre-harvest treatment. For example, Chinese patent CN108812266A discloses a method for reducing nitrate content in hydroponic lettuce. Three to five days before harvesting, the light intensity is increased by 20%-40%, while simultaneously reducing the nitrogen concentration in the nutrient solution to 1 / 5-3 / 4 of its original concentration. While this method can reduce nitrate to some extent, it has the following significant shortcomings: (1) It requires increased light intensity, increasing energy consumption and equipment investment costs; (2) It only focuses on nitrate reduction, without addressing the improvement of antioxidant nutrients such as vitamin C; (3) It does not assess the water pollution load during the production process, especially the greywater footprint. Other improvement methods, such as Chinese patent CN112321373A, often sacrifice yield by adjusting the nutrient solution formulation. Therefore, how to simultaneously achieve low nitrate, high vitamin C, and low water footprint without increasing energy consumption remains a pressing technical challenge in the field of hydroponics, hence this invention. Summary of the Invention

[0006] The technical problem to be solved by this invention is how to resolve the contradiction in existing hydroponic production between "high yield and low nitrate" and "high production efficiency and low environmental impact".

[0007] The present invention solves the above-mentioned technical problems through the following technical means:

[0008] This invention proposes a hydroponic nutrient solution for vegetables, wherein the nutrient solution includes nitrate nitrogen (NO3). - ) and ammonium nitrogen (NH4) + The nitrate nitrogen is nitrate NO3. - Nitrogen forms, ammonium nitrogen is ammonium ion NH4. + Nitrogen forms, including NO3 - / NH4 + The ion concentration ratio is 30:70.

[0009] As a further preferred technical solution, NO3 in the nutrient solution - / NH4 + An ion concentration ratio of 30:70 indicates that the total nitrogen concentration in the nutrient solution is 4 mmol / L, and the NO3 concentration is 70 mmol / L. - The ion concentration is 1.2 mmol / L, NH4+ + The ion concentration was 2.8 mmol / L.

[0010] Preferably, the vegetable hydroponic nutrient solution comprises the following raw materials: Ca(NO3)2·4H2O, CaSO4, (NH4)2SO4, KH2PO4, MgSO4·7H2O, K2SO4, H3BO3, CuSO4·5H2O, ZnSO4·7H2O, MnCl2·4H2O, H2MoO4·4H2O, and Fe-EDTA.

[0011] Preferably, the vegetable hydroponic nutrient solution is composed of 0.6-2.4 mg / L Ca(NO3)2·4H2O, 0.4-1.6 mg / L CaSO4, 1.4-5.6 mg / L (NH4)2SO4, 0.5-2 mg / L KH2PO4, 1-4 mg / L MgSO4·7H2O, 1-4 mg / L K2SO4, 1.43-5.72 mg / L H3BO3, 0.04-0.16 mg / L CuSO4·5H2O, 0.11-0.44 mg / L ZnSO4·7H2O, 0.905-3.62 mg / L MnCl2·4H2O, 0.045-0.18 mg / L H2MoO4·4H2O, and 3.823-15.29 mg / L Fe-EDTA.

[0012] More preferably, the vegetable hydroponic nutrient solution is composed of 1.2 mg / L Ca(NO3)2·4H2O, 0.8 mg / L CaSO4, 2.8 mg / L (NH4)2SO4, 1.0 mg / L KH2PO4, 2.0 mg / L MgSO4·7H2O, 2.0 mg / L K2SO4, 2.86 mg / L H3BO3, 0.08 mg / L CuSO4·5H2O, 0.22 mg / L ZnSO4·7H2O, 1.81 mg / L MnCl2·4H2O, 0.09 mg / L H2MoO4·4H2O, and 7.645 mg / L Fe-EDTA.

[0013] Preferably, the EC range of the hydroponic nutrient solution for vegetables is 1.5-2.5 mS / cm, and the pH is 6.0-6.5.

[0014] Preferably, the vegetables include, but are not limited to, one of the following: Chinese cabbage, bok choy, spinach, romaine lettuce, lettuce, chives, coriander, celery, water spinach, amaranth, garland chrysanthemum, baby bok choy, kale, and shepherd's purse.

[0015] Chinese cabbage is the preferred choice.

[0016] This invention also proposes a method for preparing the above-mentioned hydroponic nutrient solution for vegetables, comprising the following steps: Dissolve calcium-containing compounds Ca(NO3)2·4H2O and CaSO4 in deionized water to prepare solution A; dissolve sulfate and phosphate-containing compounds (NH4)2SO4, KH2PO4, MgSO4·7H2O, and K2SO4 in deionized water to prepare solution B; dissolve H3BO3, CuSO4·5H2O, ZnSO4·7H2O, MnCl2·4H2O, H2MoO4·4H2O, and Fe-EDTA in deionized water to prepare solution C; add solutions A, B, and C to a fixed volume of water in a ratio of 10:10:1000, stir thoroughly, and then adjust the pH to 6.0-6.5 with 0.1 mol / L NaOH or HCl.

[0017] This invention also proposes the application of the above-mentioned vegetable hydroponic nutrient solution in reducing the nitrate content and ash water footprint of hydroponic vegetables.

[0018] This invention proposes a cultivation method to reduce the nitrate content and ash water footprint of hydroponic vegetables, which includes hydroponically cultivating vegetable seedlings using the above-mentioned vegetable hydroponic nutrient solution and culturing them in clean water before harvesting.

[0019] The synergistic mechanism of this invention is as follows: A 30 / 70 ammonium-nitrate ratio is used throughout the entire growth period. On the one hand, the competitive absorption mechanism between ammonium and nitrate nitrogen reduces nitrate accumulation at the source; on the other hand, it keeps the plants in a state of high nitrogen use efficiency and antioxidant capacity. Based on this, pre-harvest nitrogen deprivation completely cuts off the supply of exogenous nitrogen, forcing the plants to consume the nitrate stored in their vacuoles, while simultaneously stimulating the antioxidant defense system to induce a surge in vitamin C synthesis. The synergistic effect of both is manifested in the following ways: the 30 / 70 ratio endows the plants with a "low nitrate baseline" and "high vitamin C synthesis potential," while nitrogen deprivation through water translates these potentials into tangible results.

[0020] Preferably, the cultivation method specifically involves: using a sponge substrate for germination cultivation in a standardized incubator; after germination, transplanting the germination material into the aforementioned vegetable hydroponic nutrient solution for hydroponics; and culturing in clean water before harvest.

[0021] Preferably, the germination culture conditions are cultured at 20-25℃ for 15-20 days.

[0022] Preferably, LED plant lights are used for hydroponics, with a red-to-blue light intensity ratio of 1:(2-3); blue light peak value of 440-460nm and red light peak value of 650-680nm.

[0023] A further preferred ratio is 1:3 for red to blue light intensity; with a blue light peak of 440nm and a red light peak of 660nm.

[0024] Preferably, the light intensity for hydroponics is 180-200 µmol·m - ²·s -¹, photoperiod (14-16) h light / (8-10) h darkness, light source 30-50 cm from the canopy.

[0025] Further optimization of the light intensity to 200 µmol·m - ²·s - ¹, photoperiod 14h light / 10h darkness, light source 30cm from the canopy.

[0026] Preferably, the hydroponic conditions are a daytime temperature of 24-25℃ / nighttime temperature of 15-16℃, a relative humidity of 70%-80%, and CO2 is natural air with a volume concentration of 400-500 ppm.

[0027] Preferably, the pre-harvest water culture method is to use deionized water or tap water with EC < 0.1 mS / cm and pH 6.0-6.5 for culture.

[0028] Preferably, the number of days of water culture before harvest is 0-10 days.

[0029] Preferably, the pre-harvest judgment standard is that, under the cultivation cycle of hydroponic bok choy of about 40 days, when the plants enter the maturity window, 20 plants are randomly selected from each cultivation trough. If the plants meet the following conditions, such as plant height of 17-22cm, 6-8 fully unfolded true leaves, and leaf cluster spread of 18-25cm, they are judged to be in a harvestable state.

[0030] The beneficial effects of this invention are as follows: 1. The vegetable hydroponic nutrient solution provided by this invention can solve the uncoupling problem of "biomass growth and harmful substance accumulation" in hydroponic vegetables: In existing technologies, nitrogen supply often manifests as a single input of nitrate nitrogen fertility. While this promotes rapid crop growth, it leads to nitrate reduction metabolism within the plant failing to keep pace with absorption, resulting in excessive nitrate accumulation in vacuoles. This invention aims to explore a nitrogen source ratio balance point by introducing an appropriate amount of ammonium nitrogen (NH4). + ) and nitrate nitrogen (NO3) - The synergistic effect aims to reduce the initial nitrate uptake flux of crops from a physiological level by utilizing the ammonium-nitrate competition mechanism without harming the health of the plant's root system, thereby achieving simultaneous optimization of growth rate and food safety.

[0031] 2. The cultivation method for reducing nitrate content and ash water footprint in hydroponically grown vegetables proposed in this invention can solve the bottleneck of "high moisture content and low antioxidant quality" during crop harvesting: Conventional hydroponic vegetables often exhibit characteristics of abundant water but low levels of functional components (such as vitamin C) due to excessive nutrient supply, and are highly susceptible to oxidative spoilage after harvest. This invention aims to cut off the external nitrogen source by inducing a short-term, nutrient-deprived physiological process before harvest, forcing the plant into a state of transient nitrogen metabolism reorganization. This process not only aims to consume residual nitrates in the plant but also to stimulate the plant's antioxidant defense system, inducing a surge in vitamin C (ascorbic acid) synthesis, thereby significantly improving the product's nutritional shelf life and health benefits.

[0032] 3. The cultivation method proposed in this invention for reducing nitrate content and ash water footprint in hydroponically grown vegetables can solve the environmental burden problem of excessively high "ash water footprint" in facility agriculture production: In existing hydroponic production, the limited nitrogen assimilation efficiency (NUE) of crops to high-nitrate nitrogen formulations leads to a significant environmental burden caused by the large amount of residual nitrogen in the wastewater after it is discharged into water bodies. This invention aims to address how to improve root absorption efficiency through precise formulation, thereby reducing the concentration of pollutants in the wastewater at its source. By quantitatively studying the impact of different formulations on the water footprint, this invention aims to provide a production scheme that can significantly reduce the amount of freshwater required to dilute waste pollutants, thus achieving a harmonious balance between agricultural production and ecological environmental protection.

[0033] 4. The cultivation method for reducing nitrate content and ash water footprint in hydroponic vegetables proposed in this invention can solve the problem of precise coordination between "resource input and output efficiency" in hydroponic production: Traditional hydroponic management often maintains a high concentration of nutrient solution throughout the entire life cycle. This not only leads to inefficient fertilizer consumption but also increases the difficulty of wastewater treatment later on. This invention aims to solve the problem of maximizing the biological contribution of fertilizers without increasing additional equipment investment through a phased management strategy (optimizing the nitrogen ratio during the peak growth period + withdrawing nutrients before harvest). By employing a synergistic logic of "pre-control and post-disposal," it addresses the resource waste and product quality imbalances caused by continuously high fertilizer supply.

[0034] 5. The cultivation method for reducing nitrate content and ash water footprint in hydroponic vegetables proposed in this invention can solve the problem of "maintaining physiological homeostasis and marketability" in hydroponic leafy vegetables under complex growth environments: Single nitrogen sources often exhibit poor physiological stability in response to environmental fluctuations. This invention aims to improve the morphological structure of plants (such as increasing the number, length, and width of leaves) by modifying the ammonium-nitrate ratio, thereby enhancing their physiological resilience in the later stages of growth. Simultaneously, pre-harvest water induction treatment aims to address the potential risk of nitrite conversion commonly seen in vegetables before harvesting, ensuring that vegetables entering the market meet optimal commercial standards in terms of color, taste, and safety.

[0035] 6. The cultivation method for reducing nitrate content and ash water footprint in hydroponic vegetables proposed in this invention can solve the problem that existing pre-harvest nitrate reduction technologies must increase light energy consumption: Existing pre-harvest nitrate reduction technologies (such as Chinese patent CN108812266A) require a 20%-40% increase in light intensity to reduce nitrogen concentration before harvesting, resulting in additional energy consumption and equipment investment costs. This invention, under constant low light conditions without altering the lighting, achieves a synergistic effect of nitrate reduction, vitamin C enhancement, and water footprint reduction simply by combining a 30 / 70 ammonium nitrate nutrient solution throughout the entire growth period with pre-harvest nitrogen depletion using clean water. This is done without increasing light energy consumption, meeting energy conservation and carbon reduction requirements.

[0036] Of course, implementing any product or method of the present invention does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the cultivation process of the present invention; Figure 2 This invention describes the growth characteristics of Chinese cabbage under different nitrogen fertilizer ratios (N1, N2, N3, N4), including plant height and number of leaves. The values ​​are expressed as mean ± standard deviation (n=6). For the same index, different lowercase letters indicate significant differences between treatments (P<0.05), while the same lowercase letter indicates no significant differences between treatments (P>0.05). The Duncan method was used for comparison. Figure 3 This invention relates to the SPAD values ​​of pakchoi under different nitrogen fertilizer ratios (N1, N2, N3, N4); using... Minolta SPAD-502 Chlorophyll was measured using a chlorophyll meter. The upper, middle, and lower parts of three functional leaves on the same seedling were measured, and the average value was taken. The values ​​are expressed as mean ± standard deviation (n=6). For the same index, different lowercase letters indicate significant differences between treatments (P<0.05), and the same lowercase letter indicates no significant differences between treatments (P>0.05). The Duncan method was used for comparison. Figure 4 The values ​​represent the nitrate concentrations of Chinese cabbage under different nitrogen fertilizer ratios (N1, N2, N3, N4) and under nutrient-free treatments (0, 4, 7, 10) with nitrogen deprivation. Different letters indicate significant differences between treatments (P<0.05), and the values ​​represent the mean ± standard deviation (n=3). Figure 5 The values ​​represent the vitamin C concentrations of Chinese cabbage under different nitrogen fertilizer ratios (N1, N2, N3, N4) and under nitrogen-deprived days (0, 4, 7, 10) nutrient-free treatments according to this invention; different letters indicate significant differences between treatments (P<0.05), and the values ​​represent the mean ± standard deviation (n=3). Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical terms used below have the same meaning as understood by those skilled in the art.

[0039] Unless otherwise specified, the test materials and reagents used in the following examples are commercially available or prepared by known methods.

[0040] Unless otherwise specified, all techniques or conditions described in the embodiments can be performed in accordance with the techniques or conditions described in the literature in this field or in the product manual. Unless otherwise specified, the quantitative experiments in the following embodiments are all repeated three times or more, and the results are averaged.

[0041] Example 1: A hydroponic nutrient solution for vegetables is composed of 1.2 mg / L Ca(NO3)2·4H2O, 0.8 mg / L CaSO4, 2.8 mg / L (NH4)2SO4, 1.0 KH2PO4, 2.0 mg / L MgSO4·7H2O, 2.0 mg / L K2SO4, 2.86 mg / L H3BO3, 0.08 mg / L CuSO4·5H2O, 0.22 mg / L ZnSO4·7H2O, 1.81 mg / L MnCl2·4H2O, 0.09 mg / L H2MoO4·4H2O, and 7.645 mg / L Fe-EDTA.

[0042] The preparation method of the above-mentioned hydroponic nutrient solution for vegetables includes the following steps: Dissolve calcium-containing compounds Ca(NO3)2·4H2O and CaSO4 in deionized water to prepare solution A; dissolve sulfate and phosphate-containing compounds (NH4)2SO4, KH2PO4, MgSO4·7H2O, and K2SO4 in deionized water to prepare solution B; dissolve H3BO3, CuSO4·5H2O, ZnSO4·7H2O, MnCl2·4H2O, H2MoO4·4H2O, and Fe-EDTA in deionized water to prepare solution C; add solutions A, B, and C to a fixed volume of water in a ratio of 10:10:1000, stir thoroughly, and then adjust the pH to 6.0-6.5 with 0.1 mol / L NaOH or HCl.

[0043] To reduce the nitrate content and ash water footprint of hydroponic vegetables using the above-mentioned vegetable hydroponic nutrient solution, the following steps are included: Step 1: Seedling raising and transplanting Chinese cabbage was cultured in a standardized container using a sponge substrate at 23°C. Brassica rapa Seeds of *Var. chinensis* were cultured for 15 days to induce germination. After germination, healthy and uniform seedlings were transplanted into a nutrient solution for further cultivation. The nutrient solution contained NO3-. - / NH4 + The ratio is 30 / 70, see Table 1 for details. The culture tanks are made of PVC material, 800mm long, 550mm wide, and 90mm high. 15 seedlings are planted in each culture tank; before harvesting, they are cultured in deionized water with EC < 0.1 mS / cm and pH 6.5 for 7 days.

[0044] Step 2: Prepare the nutrient solution Nutrient solution was prepared with a basic nitrogen concentration of 8 mmol / L in the nitrogen source.

[0045] The basal nutrient solution is a modified Hoagland nutrient solution, with the following macro-element content: K + 5 mmol / L, Mg² + 2 mmol / L, PO4³ - 1 mmol / L, Ca² + 2 mmol / L (as shown in Table 1); the content of trace elements (per liter) is 2.86 mg / L H3BO3, 0.08 mg / L CuSO4·5H2O, 0.22 mg / L ZnSO4·7H2O, 1.81 mg / L MnCl2·4H2O, 0.09 mg / L H2MoO4·4H2O, and 7.645 mg / L Fe-EDTA. The pH was then adjusted to 6.5 with diluted 0.1 mol / L HCl or NaOH. The selection of raw materials fully considered the balance of anions and cations and the risk of precipitation. The supply of each macro-element (N, P, K, Ca, Mg, S) and micro-element (Fe, Mn, Zn, Cu, B, Mo) in this formula is within the optimal absorption range for plant physiology.

[0046] To avoid precipitation between macroelements (such as Ca²⁺) + With SO4² - PO4³ -The preparation of the stock solution uses a separation-based method: KNO3 and Ca(NO3)2·4H2O (containing calcium, and CaSO4 from N3 and N4) are dissolved in deionized water to prepare a 10-fold stock solution (Solution A); (NH4)2SO4, KH2PO4, MgSO4·7H2O, and K2SO4 (containing sulfate and phosphate) are dissolved in deionized water to prepare a 10-fold stock solution (Solution B). Trace elements and Fe-EDTA are dissolved in deionized water to prepare a 1000-fold stock solution (Solution C). Before use, solutions A, B, and C are added to a fixed volume of water in the specified proportions, thoroughly mixed, and then the pH is adjusted to 6.5 with 0.1 mol / L NaOH or HCl, and the EC is adjusted to 2.5 mS / cm. All stock solutions are stored at 4℃ protected from light.

[0047] Cultivation Environment: Cultivation was carried out in PVC hydroponic tanks (800 mm long × 550 mm wide × 90 mm high), each tank containing 10 L of nutrient solution. Fifteen seedlings were planted and secured with polystyrene foam boards. The nutrient solution was completely replaced weekly. Each tank was equipped with two oxygen pumps to maintain dissolved oxygen ≥5 mg / L. LED plant lights were used, with a red-to-blue light intensity ratio of 1:3 (blue light peak 440 nm, red light peak 660 nm), and a light intensity of 200 µmol·m⁻¹. - ²·s - ¹, the photoperiod was 14 h light / 10 h darkness, with the light source 30 cm away from the seedling canopy; daytime temperature 25℃ / nighttime temperature 15℃, relative humidity 80%, and CO2 was from ambient air (500 ppm). During the water treatment period, deionized water (EC < 0.1 mS / cm) was used, and the pH was adjusted to 6.5, without changing the light, temperature, humidity, or other conditions.

[0048] Table 1. Different NO3 - / NH4 + Proportion of nutrient sources

[0049] Basic background constant element concentration (modified Hoagland): K + 5 mmol / L, Mg² + 2 mmol / L, PO4³ - 1 mmol / L, Ca² + 2 mmol / L.

[0050] Comparative Example 1: The difference between this comparative example and Example 1 is that the NO3 in the nutrient solution... - / NH4 + The ratio is 100 / 0, see Table 1 for details, and the remaining steps are the same as in Example 1.

[0051] Comparative Example 2: The difference between this comparative example and Example 1 is that the NO3 in the nutrient solution... - / NH4 + The ratio is 60 / 40, see Table 1 for details, and the remaining steps are the same as in Example 1.

[0052] Comparative Example 3: The difference between this comparative example and Example 1 is that the NO3 in the nutrient solution... - / NH4 + The ratio is 0 / 100, see Table 1 for details, and the remaining steps are the same as in Example 1.

[0053] Example 2: The difference between this embodiment and Embodiment 1 is that: The prepared nutrient solution had an EC of 1.5 mS / cm and a pH of 6.0. Cultivation conditions: Germination culture was carried out at 20℃ for 20 days; LED plant lights were used for hydroponics, with a red-to-blue light intensity ratio of 1:2; the blue light peak was 460nm, and the red light peak was 680nm; the light intensity for hydroponics was 180 µmol·m⁻¹. - ²·s - ¹, Photoperiod: 16h light / 8h darkness, light source 50cm from the canopy; Hydroponic conditions: daytime temperature 24-25℃ / nighttime temperature 15-16℃, relative humidity 70%-80%, CO2: ambient air (450 ppm); Pre-harvest water culture: tap water with EC < 0.1 mS / cm and pH 6.0. The remaining steps are the same as in Example 1.

[0054] Example 3: The difference between this embodiment and Embodiment 1 is that: Cultivation conditions: Germination culture was carried out at 25℃ for 18 days; LED plant lights were used for hydroponics, with a red-to-blue light intensity ratio of 1:2; the blue light peak was 450nm, and the red light peak was 650nm; the light intensity for hydroponics was 190 µmol·m⁻¹. - ²·s - ¹, the photoperiod was 15 hours of light / 9 hours of darkness, with the light source 40 cm above the canopy; the hydroponic conditions were a daytime temperature of 24°C / nighttime temperature of 16°C, a relative humidity of 70%, and natural air CO2 (400 ppm); before harvesting, the water culture method used was tap water with EC < 0.1 mS / cm and a pH of 6.5. The remaining steps were the same as in Example 1.

[0055] Example 4: The difference between this embodiment and Embodiment 1 is that: The hydroponic nutrient solution for vegetables consisted of 0.6 mg / L Ca(NO3)2·4H2O, 0.4 mg / L CaSO4, 1.4 mg / L (NH4)2SO4, 0.5 mg / L KH2PO4, 1 mg / L MgSO4·7H2O, 1 mg / L K2SO4, 1.43 mg / L H3BO3, 0.04 mg / L CuSO4·5H2O, 0.11 mg / L ZnSO4·7H2O, 0.905 mg / L MnCl2·4H2O, 0.045 mg / L H2MoO4·4H2O, and 3.8225 mg / L Fe-EDTA. The rest was the same as in Example 1.

[0056] Example 5: The difference between this embodiment and Embodiment 1 is that: The hydroponic nutrient solution for vegetables consisted of 2.4 mg / L Ca(NO3)2·4H2O, 1.6 mg / L CaSO4, 5.6 mg / L (NH4)2SO4, 2 mg / L KH2PO4, 4 mg / L MgSO4·7H2O, 4 mg / L K2SO4, 5.72 mg / L H3BO3, 0.16 mg / L CuSO4·5H2O, 0.44 mg / L ZnSO4·7H2O, 3.62 mg / L MnCl2·4H2O, 0.18 mg / L H2MoO4·4H2O, and 15.29 mg / L Fe-EDTA. The rest was the same as in Example 1.

[0057] Determination of the production quality and ascorbic acid (VC) content of Chinese cabbage: Record the plant height, maximum leaf length (from the base of the petiole to the tip of the terminal leaflet), maximum leaf width (measured from the edge of the two leaflets), and number of leaves of each treatment group of nine plants weekly.

[0058] After 42 days of growth, the plants were harvested and separated into roots and above-ground edible parts. The roots were washed with deionized water and blotted dry with coarse filter paper. Fresh weight (FW) was measured immediately, and dry weight (DW) was measured after drying in an oven at 65°C for 72 hours.

[0059] The average value was obtained by measuring the upper, middle, and lower parts of three functional leaves on the same seedling. The ascorbic acid (VC) content in Chinese cabbage was determined by titration. 10 grams of fresh leaves were cut into small pieces and ground using a mortar and pestle. 2% HCl (20 ml) was added to the mortar, and the mixture was ground thoroughly until homogenized. The homogenate was filtered into a 50 ml volumetric flask and shaken for 30 minutes. The mixture was then filtered through filter paper and repeatedly extracted with 2% HCl. The extract was then diluted to 50 ml in a volumetric flask. 5 ml of the extract was added to a 50 ml volumetric flask and titrated with sodium 2,6-dichlorophenolindophenol until a stable, colorless red solution was obtained within 15 seconds. Nitrate was determined using ultraviolet spectrophotometry. Approximately 1 g of fresh plant sample (including leaves and petioles) was placed in 10 ml of deionized water and heated in boiling water for 30 minutes. The sample was then filtered and diluted to 50 ml. Take 0.1 ml of the extract and mix it with 0.4 ml of 5% salicylic acid-sulfuric acid solution. Let it stand at room temperature for 20 minutes, then mix it with 9.5 ml of 8% sodium hydroxide solution and shake well. After cooling to room temperature, measure the final solution at 410 nm.

[0060] Measurement of greywater footprint: Grey water footprint is an indicator of water pollution absorption capacity. According to the Global Water Footprint Standard, grey water footprint is calculated based on nitrogen in waste nutrient solutions. Considering the differences in cultivation time and yield between traditional soil cultivation and hydroponics, this paper introduces a time dimension to identify the water footprint per unit of crop production. The water footprint assessment in hydroponics considers both growth time and yield; the grey water footprint calculation formula is shown in formula (1): Formula (1), Grey -WF Represents greywater footprint (m³ / kg / d). Y This represents the yield (kg) of bok choy. d This indicates the number of days of cultivation after transplanting. L N [mg / L] indicates the total nitrogen (TN) concentration in the waste nutrient solution, determined by a total organic carbon analyzer (TOC-L CPH / CPN). V Indicates the volume (L) of the waste nutrient solution. c max_N This indicates the maximum acceptable total nitrogen concentration. c nat_N This indicates the total nitrogen concentration in natural water.

[0061] Results analysis: like Figure 1 The diagram shown illustrates the cultivation and screening process of this invention.

[0062] 1. Analysis of plant yield gain Table 2 shows the fresh yield of pak choy under different nitrogen ratios and nitrogen-deprivation days according to the present invention; N represents the nitrogen ratio; D represents the number of days without nutrient treatment; different uppercase letters (A, B, C, D) indicate significant differences between nitrogen ratios (P<0.05); different lowercase letters (a, b, c, d) indicate significant differences between the number of days of nitrogen deprivation before harvest (P<0.05). Values ​​are expressed as mean ± standard deviation (n=3), and comparisons were made using the Duncan method.

[0063] Table 2. Fresh weight (FW, g / plant) of Chinese cabbage under different nitrogen ratios and pre-harvest nitrogen deprivation days.

[0064] Note: All data in the table are standard values ​​± standard deviation; different uppercase letters after the data in the same column indicate significant differences in different nitrogen ratios (P<0.05), and lowercase letters indicate significant differences in different nitrogen-free days (P<0.05). The Duncan method was used for comparison.

[0065] Table 3 shows the dry weight of pak choy under different nitrogen ratios and nitrogen-deprivation days according to the present invention; N represents the nitrogen ratio; D represents the number of days without nutrient treatment; different uppercase letters (A, B, C, D) indicate significant differences between nitrogen ratios (P<0.05); different lowercase letters (a, b, c, d) indicate significant differences between the number of days of nitrogen deprivation before harvest (P<0.05). Values ​​are expressed as mean ± standard deviation (n=3), and comparisons were performed using the Duncan method.

[0066] Table 3. Dry weight (DW, g / plant) of Chinese cabbage under different nitrogen ratios and pre-harvest nitrogen deprivation days.

[0067] Note: All data in the table are standard values ​​± standard deviation; different uppercase letters after the data in the same column indicate significant differences in different nitrogen ratios, and lowercase letters indicate significant differences in different nitrogen-free days (P<0.05). The Duncan method was used for comparison.

[0068] Tables 2 and 3 show the fresh weight and dry weight of pak choi under different nitrogen source ratios and short-term nutrient-free conditions. The highest fresh weight and dry weight were observed in the N3 treatment with 0 days of nutrient-free conditions, at 88.95 g / plant and 12.94 g / plant, respectively. Before harvest, there were significant differences in fresh weight and dry weight of pak choi under different nitrogen source ratios and short-term nutrient-free conditions (P<0.05). The fresh weight and dry weight of pak choi under the N3 treatment were significantly higher than those under N1, N2, and N3 (P<0.05). Similarly, the fresh weight and dry weight of pak choi under the 0-day nutrient-free condition were also significantly higher than those under the 4, 7, and 10-day nutrient-free conditions before harvest (P<0.05).

[0069] Yield (fresh weight): The fresh weight directly reflects the commercial yield of pakchoi, indicating an increase in economic benefits.

[0070] Material accumulation (dry weight): The dry weight excludes the interference of moisture and truly reflects the net accumulation of photosynthetic products (organic matter).

[0071] Biomass is the ultimate indicator for measuring yield. The data shows that without pre-harvest treatment, the highest fresh weight in the N3 treatment group reached 88.95 g / plant, and the dry weight reached 12.94 g / plant, significantly better than the full nitrate nitrogen treatment (N1) and the full ammonium nitrogen treatment (N4).

[0072] Technical value: This breaks the conventional technical prejudice that "reducing nitrates will necessarily lead to a reduction in yield". Through optimizing the formula, this invention has achieved a counter-trend increase in yield, and the increase in dry matter accumulation also means that the taste of the vegetables is more solid and not "watery".

[0073] 2. Evaluation of water footprint The evaluation of the water footprint of hydroponic production under different nitrogen ratios and short-term nutrient-free conditions is shown in Table 3. Table 3 shows the grey water footprint evaluation results of hydroponic production under different nitrogen ratios and days (0, 4, 7, and 10 days) of nutrient-free conditions in this invention; different capital letters (A\B\C\D) indicate significant differences between different nitrogen ratios (P<0.05); different lowercase letters (a\b\c\d) indicate significant differences between different nutrient-free days before harvest (P<0.05), and the values are the mean ± standard deviation (n = 3), and the Duncan method is used for comparison.

[0074] Table 4 Grey water footprint (Grey-WF, m³ / kg / d) under different nitrogen ratios and days of nitrogen deprivation before harvest

[0075] Note: The data in the table are all standard values ± standard deviation; different capital letters after the same column of data indicate significant differences in different nitrogen ratios, and lowercase letters indicate significant differences in different days of nitrogen deprivation (P<0.05), and the Duncan method is used for comparison.

[0076] The results show that when N3 is used as the nitrogen source, the grey water footprint is significantly lower than that of N1, N2, and N4 (P<0.05), being 0.12 ± 0.01 m 3 / kg / d. The ranking of the grey water footprint is N3 < N2 < N1 < N4. After 4 days, 7 days, and 10 days of nutrient-free treatment before harvest, the grey water footprint significantly increases (P<0.05), and the water footprints of the 7-day and 10-day nutrient-free treatments are significantly higher than those of the 0-day and 4-day nutrient-free treatments (P<0.05), while there is no significant difference between the 7-day and 10-day nutrient-free treatments before harvest.

[0077] Technical Value: Grey water footprint accounts for the majority of the total water footprint. This invention significantly reduces the freshwater consumption required to dilute agricultural pollutants by minimizing the grey water footprint. This demonstrates that this technology is not only a high-yield technology, but also an environmentally friendly cultivation technique that can significantly alleviate the eutrophication pressure on receiving water bodies.

[0078] 3. Morphological analysis of bok choy like Figure 2 The figure shows the growth characteristics of pak choi under different nitrogen fertilizer ratios. The results indicate that when N3 was used as the nutrient source, the maximum leaf length, width, and number of leaves in pak choi increased significantly. Plant height increased from day 7 to 35, then decreased at day 42, while the number of leaves, maximum leaf length, and width increased continuously from day 0 to 42. After 21 days, the number of leaves in N4 was significantly lower than that in N1, N2, and N3, while there was no significant difference among N1, N2, and N3 after transplanting (P<0.05). Conversely, the maximum leaf length and width in N3 were significantly higher than those in N1, N2, and N4 (P<0.05).

[0079] Experimental results showed that the 30:70 ammonium nitrate ratio (N3 treatment) of this invention significantly promoted the morphological development of pakchoi. Compared with total nitrate nitrogen (N1), pakchoi in the N3 group showed significant advantages in maximum leaf length, maximum leaf width, and number of leaves.

[0080] Technical value: This shows that an appropriate amount of ammonium nitrogen participating in metabolism can provide more efficient growth momentum, making vegetables appear fuller and more robust in terms of commercial appearance, directly improving their market appeal.

[0081] 4. SPAD Analysis of Bok Choy like Figure 3 The SPAD values ​​of pak choi under different nitrogen fertilizer ratios are shown. Under the four nitrogen fertilizer ratios, the SPAD values ​​of pak choi increased from 7 to 21 days after transplanting and stabilized from 21 to 42 days. The SPAD values ​​of pak choi under the N2, N3, and N4 treatments were higher than those under the N1 treatment. At 7 and 14 days after transplanting, there were significant differences between the N1 and N4 treatments and the N2 and N3 treatments, while there was no significant difference between the N2 and N3 treatments (P<0.05). Similarly, from 21 to 42 days after transplanting, the SPAD value of pak choi under the N1 treatment was significantly lower than that under the N2, N3, and N4 treatments, while there was no significant difference among the three groups in the latter (P<0.05).

[0082] SPAD values ​​reflect the nitrogen nutrition status and photosynthetic potential of plants. Experiments showed that the SPAD values ​​of the N3-treated group of pakchoi remained at a high and stable level.

[0083] Value: A high SPAD value indicates abundant chlorophyll content in the leaves, resulting in stronger photosynthetic efficiency. This proves that the 30:70 ratio did not cause ammonium poisoning; on the contrary, it optimized the chlorophyll synthesis environment, making the leaves a deeper green color.

[0084] 5. A leap forward in nutritional quality and food safety. like Figure 4 As shown, the nitrate content of pak choi increased significantly with increasing NO3 concentration in the nutrient solution (P<0.05). The highest nitrate concentration, reaching 1108.38 mg / kg, was observed under N1 and 0-day nutrient-free treatments. The lowest nitrate content, at 157.4 mg / kg, was observed under N4 and 10-day nutrient-free treatments. Short-term nutrient-free treatment before harvest significantly reduced the nitrate concentration of pak choi (P<0.05). At the same nitrogen ratio, the nitrate concentration of pak choi under the 0-day nutrient-free treatment was significantly higher than that under the 4, 7, and 10-day nutrient-free treatments before harvest, while there was no significant difference between the 4-day and 7-day nutrient-free treatments before harvest (P<0.05).

[0085] like Figure 5 The vitamin C (VC) concentration in pak choi varied significantly among the four nitrogen source ratios shown (P<0.05). Compared with treatments N1, N2, and N4, the VC content of pak choi was significantly increased when N3 was used as the nitrogen source (P<0.05). Before harvest, the VC content of pak choi under the 7-day nutrient-free treatment was significantly higher than that under the 10-day, 4-day, and 0-day nutrient-free treatments, while there was no significant difference between the 4-day and 10-day nutrient-free treatments (P<0.05). The highest VC content, reaching 50.49 mg / 100g, was achieved when N3 was used as the nitrogen source and the 7-day nutrient-free treatment was used before harvest.

[0086] Significant reduction in nitrates: Through source control using the N3 formula and 7 days of pre-harvest water treatment, the nitrate concentration in the bok choy experienced a dramatic decrease. Pre-harvest nutrient-free treatment significantly removed nitrates stored in the vacuoles, resulting in a product far exceeding food safety limits.

[0087] Significantly increased vitamin C content: Pre-harvest water treatment induced a stress response in the plants, and the vitamin C content reached a peak of 50.49 mg / 100g when the N3 formula was combined with a 7-day pre-harvest treatment.

[0088] Technological value: This combination of "one decrease and one increase" transforms ordinary vegetables into "functional vegetables" with high antioxidant value, significantly increasing the added value of the products.

[0089] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A hydroponic nutrient solution for vegetables, characterized in that, The nutrient solution comprises nitrate nitrogen and ammonium nitrogen, wherein the nitrate nitrogen is nitrate (NO3). - Nitrogen forms, ammonium nitrogen is ammonium ion NH4. + Nitrogen forms, including NO3 - / NH4 + The ion concentration ratio is 30:

70.

2. The vegetable hydroponic nutrient solution according to claim 1, characterized in that, The vegetable hydroponic nutrient solution comprises the following raw materials: Ca(NO3)2·4H2O, CaSO4, (NH4)2SO4, KH2PO4, MgSO4·7H2O, K2SO4, H3BO3, CuSO4·5H2O, ZnSO4·7H2O, MnCl2·4H2O, H2MoO4·4H2O, and Fe-EDTA; the EC range of the vegetable hydroponic nutrient solution is 1.5-2.5 mS / cm, and the pH is 6.0-6.

5.

3. The vegetable hydroponic nutrient solution according to claim 2, characterized in that, The vegetable hydroponic nutrient solution is composed of 0.6-2.4 mg / L Ca(NO3)2·4H2O, 0.4-1.6 mg / L CaSO4, 1.4-5.6 mg / L (NH4)2SO4, 0.5-2 mg / L KH2PO4, 1-4 mg / L MgSO4·7H2O, 1-4 mg / L K2SO4, 1.43-5.72 mg / L H3BO3, 0.04-0.16 mg / L CuSO4·5H2O, 0.11-0.44 mg / L ZnSO4·7H2O, 0.905-3.62 mg / L MnCl2·4H2O, 0.045-0.18 mg / L H2MoO4·4H2O, and 3.823-15.29 mg / L Fe-EDTA.

4. The application of the vegetable hydroponic nutrient solution according to any one of claims 1-3 in reducing the nitrate content and ash water footprint of hydroponic vegetables.

5. A cultivation method for reducing nitrate content and ash water footprint in hydroponic vegetables, characterized in that, This includes using the vegetable hydroponic nutrient solution described in any one of claims 1-3 to hydroponically cultivate vegetable seedlings and to cultivate them in clean water before harvest.

6. The cultivation method according to claim 5, characterized in that, The cultivation method specifically involves: using a sponge substrate for germination cultivation in a standardized incubator; after germination, transplanting the seeds into the aforementioned vegetable hydroponic nutrient solution for hydroponics; and culturing in clean water before harvest.

7. The cultivation method according to claim 6, characterized in that, Germination culture conditions are 15-20 days at 20-25℃.

8. The cultivation method according to claim 6, characterized in that, When hydroponically growing plants, use LED plant lights with a red to blue light intensity ratio of 1:(2-3); blue light peak value 440-460nm, red light peak value 650-680nm.

9. The cultivation method according to claim 6, characterized in that, Hydroponic conditions require a light intensity of 180-200 µmol·m⁻². - ²·s - ¹, Photoperiod (14-16) h light / (8-10) h darkness, light source distance from the canopy 30-50 cm; temperature 24-25℃ during the day / 15-16℃ at night, relative humidity 70%-80%, CO2 is natural air, volume concentration 400-500 ppm.

10. The cultivation method according to claim 6, characterized in that, The pre-harvest water culture method involves using deionized water or tap water with EC < 0.1 mS / cm and pH 6.0-6.5.

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