A low potassium content lettuce with a quantitatively controlled potassium content and a cultivation method and cultivation system thereof

Abstract

A kind of low potassium content of quantitative control of potassium content and its cultivation method and cultivation system, the method is: two sets of high concentration mother liquor of conventional potassium content and no potassium are prepared, after dilution, potassium-containing nutrient solution is continuously supplied in the early stage of plant growth;When the fresh weight of the whole plant reaches the potassium threshold value calculated from the target fresh sample potassium content, conventional lettuce potassium content and aboveground fresh weight, accurately switch to no potassium nutrient solution until harvest;At the same time, replace potassium salt with equimolar sodium salt / calcium salt to maintain conductivity and ion balance during the no potassium stage, fine control with 1.3-1.5 mS / cm EC and 5.5-6.5 pH, ensure root health and yield quality.The system does not require special light source or temperature control facilities, suitable for deep liquid flow, shallow liquid flow and aeroponic multiple soilless platform lettuce production, batch stable to achieve 100±10 mg / 100 g (fresh sample) of low potassium product, with the advantages of simple operation, strong repeatability and high industrialization promotion value.

Description

Technical Field

[0001] This invention belongs to the field of vegetable factory cultivation technology, specifically relating to a method and system for quantitatively controlling potassium content in low-potassium vegetable cultivation. It is particularly suitable for precisely adjusting the potassium content of lettuce plants in hydroponic or soilless cultivation environments to obtain low-potassium vegetable products that meet health or special dietary needs. Background Technology

[0002] Chronic kidney disease (CKD) is a common disease among the elderly, and its incidence is increasing globally. CKD patients are prone to hyperkalemia because they cannot properly excrete potassium. Hyperkalemia can lead to arrhythmias, muscle weakness, altered consciousness, heart failure, and even sudden death. A potassium-restricted diet is a primary control measure, such as limiting the intake of fresh vegetables, seafood, legumes, and fruits. Leafy greens are rich in potassium, and doctors recommend that CKD patients blanch them before consumption to avoid excessive potassium intake. However, lettuce is mostly eaten raw, making it difficult for CKD patients to consume fresh lettuce dishes like salads and sandwiches as easily as healthy individuals. Developing low-potassium lettuce recipes would ensure limited potassium intake while enriching the dietary options for CKD patients.

[0003] Because the mineral elements in the nutrient solution of hydroponics are highly controllable, low-potassium vegetable production currently all adopts hydroponics, especially hydroponics. The cultivation method mainly achieves this by reducing the supply of potassium fertilizer in the nutrient solution during vegetable production. The most commonly reported method is to supply sufficient potassium in the early stages of vegetable production and then stop potassium fertilizer supply one or two weeks before harvest. While this method of stopping potassium supply at specific times can significantly reduce the potassium content in vegetables, it is greatly affected by variety, season, and nutrient solution formula, resulting in significant fluctuations in potassium content. It is impossible to guarantee that the potassium content of each batch of vegetables will remain within a certain range, making it difficult to standardize products. The Global Kidney Disease Outcome Improvement Organization recommends that kidney disease patients consume foods with a potassium content of less than 100 mg / 100g. Although Japan has reported controlling the potassium content of low-potassium lettuce to below 100 mg / 100g (fresh), this requires a fully artificial light plant factory with a controlled environment, resulting in high investment and operating costs. Chinese patents CN106535622B and CN106577211B both employ potassium reduction technology, but they only achieve a decrease in potassium content, failing to precisely and stably control it within the target range. Furthermore, CN106577211B requires auxiliary measures such as LED lighting, resulting in high production costs and complex operation, making it difficult to promote and apply in conventional production systems. Currently, there is a lack of cultivation technology that can stably output quantitative potassium content in batches of vegetables of various varieties and specifications without relying on special light sources or strict environmental conditions. Summary of the Invention

[0004] To address the aforementioned technical deficiencies, this invention proposes a method and system for quantitatively controlling the potassium content of low-potassium lettuce. First, based on the target potassium content of fresh samples at harvest and the potassium content of lettuce fresh samples under conventional potassium conditions, two sets of nutrient solutions—one conventionally potassium-containing and one potassium-free—are prepared and diluted to the desired concentration. During the early growth stage after transplanting, the conventional potassium-containing nutrient solution is continuously supplied to ensure normal plant growth and development. When the total fresh weight reaches the switching threshold calculated by the formula Y = A × X / B, the supply of the potassium-containing nutrient solution is stopped, and the potassium-free nutrient solution is continuously supplied until harvest. Through this dynamic switching based on the quantitative threshold of fresh weight, precise control of the final fresh sample potassium content is achieved. This method does not rely on fixed time points or special light environments. Combined with consistent batch-to-batch dilution ratios of the nutrient solution and a potassium-free background, it can stably control the potassium content of lettuce fresh samples within the target range while ensuring yield and quality, and possesses good repeatability and industrial-scale application potential.

[0005] In a first aspect, the present invention provides a method for quantitatively controlling potassium content in the cultivation of low-potassium lettuce, comprising the following steps:

[0006] Based on the potassium content target, prepare conventional potassium-containing nutrient solution stock solution and potassium-free nutrient solution stock solution;

[0007] The two nutrient solution stock solutions were diluted according to the concentration ratio to form the working solution. The conventional potassium-containing nutrient solution was continuously used in the early growth stage after the lettuce was transplanted.

[0008] When the fresh weight of the whole lettuce plant reaches the switching threshold calculated by the following formula, stop using the conventional potassium-containing nutrient solution and switch to a potassium-free nutrient solution until harvest:

[0009]

[0010] Where X is the above-ground fresh weight of lettuce at harvest; Y is the whole fresh weight of lettuce when potassium is depleted; A is the potassium content of the target fresh sample at harvest; and B is the potassium content of the fresh sample of lettuce under conventional potassium conditions.

[0011] In some technical solutions, the potassium ion concentration in the conventional potassium-containing nutrient solution is 3.0–4.0 mmol / L, and the background potassium content in the potassium-free nutrient solution is less than 0.5 mg / L.

[0012] In some technical solutions, the concentration factor of the nutrient solution mother liquor is 100 to 200 times, and the dilution ratio of the working liquid is prepared at a volume ratio of 1:100 to 1:200.

[0013] Using a 100–200 times highly concentrated mother liquor to prepare the working solution not only significantly reduces the volume of the mother liquor and lowers storage, transportation and management costs, but also improves the accuracy and consistency of nutrient solution preparation through precise quantification after high dilution, eliminating the impact of manual preparation errors on the final potassium content control precision.

[0014] In some technical solutions, the conductivity of the nutrient solution is maintained at 1.3 to 1.5 mS / cm and the pH value is maintained at 5.5 to 6.5 throughout the entire culture process, with the preferred conductivity being 1.4 mS / cm.

[0015] In some technical solutions, A is 90-110 mg / 100g, preferably 100 mg / 100g, and B is 350-450 mg / 100g, preferably 400 mg / 100g.

[0016] In some technical solutions, the potassium salt in the potassium-free nutrient solution is replaced with sodium or calcium salt in an equimolar amount to maintain ion balance.

[0017] During the potassium-free stage, the potassium salts in the conventional nutrient solution are replaced with sodium or calcium salts in equal molar amounts to maintain the conductivity and main cation-anion balance of the nutrient solution. This avoids the stress on the plants caused by simply removing potassium and ensures normal absorption and metabolism during the low potassium period.

[0018] Some technical solutions are applicable to both deep flow and shallow flow hydroponics.

[0019] In some technical solutions, lettuce can be a low-potassium tolerant variety or a low-potassium sensitive variety.

[0020] Secondly, the present invention also provides a low-potassium lettuce produced using the above-described cultivation method.

[0021] Thirdly, the present invention further provides a low-potassium lettuce cultivation system for implementing the above-mentioned cultivation method, comprising, in sequence:

[0022] Nutrient solution preparation unit, used to prepare and store conventional potassium-containing nutrient solution stock solution and potassium-free nutrient solution stock solution;

[0023] The dilution and dispensing unit is fluidly connected to the nutrient solution preparation unit and is used to automatically prepare the working solution according to the concentration factor and circulate or quantitatively dispense it.

[0024] The cultivation module is used to support vegetable plants and deliver the nutrient solution.

[0025] The online monitoring and control unit is equipped with an EC sensor, a pH sensor, and a potassium ion sensor, which are connected to the dilution and dispensing unit to automatically adjust the dilution ratio and replenishment rate.

[0026] The harvesting module is used to perform automatic or semi-automatic harvesting after the potassium-free stage.

[0027] The present invention, by employing the above technical solution, has at least the following beneficial effects:

[0028] 1. This invention uses the formula Y = A × X / B as the potassium depletion threshold. The whole plant's potassium-depleted fresh weight (Y) is calculated by multiplying the plant's fresh weight during its growth period (X) by the ratio of the target potassium content to the potassium content under conventional potassium conditions (A / B). This feature ensures that the timing of potassium depletion is closely coupled with the plant's growth state: early nutrient supply adequately guarantees cell division and leaf enlargement; when the fresh weight reaches Y, potassium transport tends to be balanced, and switching to a potassium-free nutrient solution can maximally block potassium absorption without damaging the root-shoot distribution mechanism. This allows for precise locking of the fresh sample potassium content within the range of A ± tolerance in each batch, significantly reducing batch-to-batch potassium content drift caused by varietal differences, growth stages, or environmental fluctuations.

[0029] 2. This invention precisely controls the conductivity of the nutrient solution to 1.3–1.5 mS / cm and the pH value to 5.5–6.5, which can maintain the ion channels and enzyme activity of root cells and prevent damage to the root system caused by salt damage or acid-base imbalance. Thus, it can maintain a growth rate and yield comparable to conventional cultivation even under low potassium conditions.

[0030] 3. This invention takes into account the redistribution of potassium in roots under potassium-deficient conditions. When calculating the potassium depletion threshold, the fresh weight of the roots is included in the total fresh weight (Y) of the plant, while only the fresh weight (X) of the aboveground parts is counted at actual harvest. This method fully reflects the dynamic distribution of potassium between the root and shoot: the roots continue to release stored potassium to new leaves in the early stages of potassium depletion, after which the potassium content in the aboveground parts tends to stabilize. Through precise calculation of these two fresh weight indicators, the potassium content of the final edible portion can be predicted more accurately, greatly improving product safety and data reliability.

[0031] 4. Based on the same dynamic formula, this invention allows users to set the potassium depletion threshold Y according to different target harvest fresh weights X, enabling low-potassium production of lettuce in various sizes (e.g., 50g, 100g, 150g). This flexibility ensures that the potassium content of fresh samples remains ≤A regardless of when harvesting is done within one week after potassium depletion. Producers can freely schedule production based on market demand and packaging specifications without needing to re-test formulas or modify processes, greatly improving production scheduling and standardization.

[0032] 5. The core steps of this invention rely solely on a simple mathematical formula and a mother liquor dilution scheme, requiring no expensive light sources or temperature control facilities. Combined with an online sensing and automatic dispensing system, it enables one-click potassium discontinuation switching and mother liquor ratio adjustments in various soilless platforms, including deep flow, shallow flow, and aeroponics, making it suitable for lettuce growth. This feature not only lowers the production threshold but also enhances the feasibility and economic benefits of technology transfer and industrialization. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the nutrient solution stage management method based on different methods in Example 1 and Comparative Examples 1 to 4 in Comparative Experiment 1 of the present invention;

[0034] Figure 2 This is a comparison diagram of different treatment methods based on Example 1 and Comparative Examples 1 to 4 in Comparative Experiment 1 of the present invention;

[0035] Figure 3 This is a comparison chart of the fresh weight of the aboveground parts based on different treatments in Example 1 and Comparative Examples 1-4 in Comparative Experiment 1 of the present invention;

[0036] Figure 4 This is a comparison chart of the soluble sugar content based on different treatments in Example 1 and Comparative Examples 1-4 in Comparative Experiment 1 of the present invention;

[0037] Figure 5 This is a comparison chart of VC content based on different treatments in Example 1 and Comparative Examples 1-4 in Comparative Experiment 1 of the present invention;

[0038] Figure 6 This is a comparison chart of the soluble protein content based on different treatments in Example 1 and Comparative Examples 1-4 in Comparative Experiment 1 of the present invention;

[0039] Figure 7 This is a comparison chart of nitrate content based on different treatments in Example 1 and Comparative Examples 1-4 in Comparative Experiment 1 of the present invention;

[0040] Figure 8 This is a comparison chart of the free amino acid content based on different treatments in Example 1 and Comparative Examples 1-4 in Comparative Experiment 1 of the present invention;

[0041] Figure 9 This is a comparison of fluorescence kinetic curves based on different treatments in Example 1 and Comparative Examples 1-4 in Comparative Experiment 1 of the present invention;

[0042] Figure 10 This is a graph showing the effect of different low-potassium nutrient solution management modes on lettuce morphology based on Example 1 and Comparative Examples 1-4 'Huihe Green Flower Leaf' in Comparative Experiment 2 of the present invention;

[0043] Figure 11 This is a graph showing the effect of different low-potassium nutrient solution management modes on lettuce morphology based on Example 1 and Comparative Examples 1-4 'Huqian' in Comparative Experiment 2 of the present invention;

[0044] Figure 12 This is a comparison chart of the fresh weight of the aboveground parts of the plant under different treatments in Comparative Experiment 2 of the present invention, based on Example 1 and Comparative Examples 1-4.

[0045] Figure 13 This is a comparison chart of the soluble sugar content based on different treatments in Example 1 and Comparative Examples 1-4 in Comparative Experiment 2 of the present invention;

[0046] Figure 14 This is a comparison chart of VC content based on different treatments in Example 1 and Comparative Examples 1-4 in Comparative Experiment 2 of the present invention;

[0047] Figure 15 This is a comparison chart of the soluble protein content based on different treatments in Example 1 and Comparative Examples 1-4 in Comparative Experiment 2 of the present invention;

[0048] Figure 16 This is a comparison chart of nitrate content based on different treatments in Comparative Experiment 2 of the present invention, based on Example 1 and Comparative Examples 1-4;

[0049] Figure 17 This is a comparison chart of the free amino acid content based on different treatments in Example 1 and Comparative Examples 1-4 in Comparative Experiment 2 of the present invention. Detailed Implementation

[0050] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0051] Example 1

[0052] Nutrient solutions with conventional potassium concentrations and those without potassium were prepared according to the concentrations in Tables 1 and 2. Formula A had a potassium concentration less than 4 mmol / L, while Formula C had a potassium concentration of 0 mmol / L, replaced by an equal amount of sodium salt. Except for the potassium and sodium content, the contents of all other elements were the same. The potassium-efficient 'Huihe Green Floral' lettuce variety was used as the test material. When the seedlings reached two leaves and one bud, they were transplanted into hydroponic planting boxes, with six seedlings planted in each box. The nutrient solution volume in each box was 7 L. The fresh weight of the above-ground parts of the lettuce at harvest was set at 40 g (letter X in the formula). The potassium content of lettuce cultivated at normal potassium concentrations was 400 mg / 100 g (letter B in the formula), and the target potassium content at harvest was 100 mg / 100 g (letter A in the formula). Using the formula Y = A × X / B in the invention, the fresh weight of the whole lettuce plant was calculated as Y = 100 mg / 100 g × 40 g ÷ 400 mg / 100 g = 10 g. Therefore, when lettuce is cultivated to a fresh weight of 10g using a nutrient solution with normal potassium concentration, the nutrient solution is discarded and replaced with a potassium-free nutrient solution. Then, the lettuce is cultivated to a fresh weight of 40g above ground.

[0053] During cultivation, the EC of the nutrient solution was adjusted using a concentrated solution with the appropriate formula, maintaining the EC at 1.4 mS·cm. -1 The pH of the nutrient solution should be maintained between 5.5 and 6.5. If the pH is higher than this range, adjust it with nitric acid or phosphoric acid; if the pH is lower than this range, adjust it with sodium hydroxide.

[0054] Table 1. Potassium content in standard and potassium-free nutrient solution formulations (unit: mmol / L)

[0055]

[0056] Table 2. Trace element content in conventional and potassium-free nutrient solution formulations (unit: μmol / L)

[0057] Fe B Mn Zn Cu Mo 61.03 25.90 5.35 0.43 0.18 0.40

[0058] Comparative Example 1

[0059] Comparative Example 1 served as a control for low-potassium lettuce, examining whether the yield and quality of low-potassium lettuce were significantly affected compared to conventionally cultivated lettuce. A conventional potassium concentration nutrient solution, similar to Formula A in Example 1, was prepared. Unlike Example 1, Formula A was used throughout the entire cultivation process in Comparative Example 1, without any changes to the formula. Lettuce was harvested 35 days after transplanting.

[0060] Comparative Example 2

[0061] Comparative Example 2 is one of the commonly used methods for producing low-potassium lettuce and is used to compare it with the method of this invention. A low-potassium nutrient solution was prepared according to the macro-element formula in Table 3 and the micro-element formula in Example 1. Unlike Example 1, in Comparative Example 2, Formula B was used throughout the entire lettuce cultivation process without any changes to the formula. The potassium content of the nutrient solution was 1 / 4 of that of a conventional nutrient solution. Since the potassium content of lettuce cultivated with conventional potassium is approximately 400 mg / 100g, this study investigated whether the potassium content of lettuce could reach 1 / 4 of that cultivated with a conventional potassium nutrient solution when the potassium content of the nutrient solution was 1 / 4 of the conventional potassium content. Harvesting was carried out 35 days after transplanting.

[0062] Table 3. Macronutrient content in low-potassium nutrient solution formulations (unit: mmol / L)

[0063]

[0064] Comparative Example 3

[0065] Comparative Example 3 is one of the commonly used methods for producing low-potassium lettuce. It was designed with reference to the nutrient solution cultivation model in the existing invention CN106577211B (application number: CN201610918218.4) and used for comparison with the method of this invention. Unlike Example 1, the replacement time with the potassium-free nutrient solution is fixed, i.e., two weeks before harvest, regardless of the current fresh weight of the lettuce. Harvesting is carried out 35 days after transplanting.

[0066] Comparative Example 4

[0067] Comparative Example 4 is one of the commonly used methods for producing low-potassium lettuce, and is used to compare it with the method of the present invention.

[0068] Unlike Example 1, nutrient solution management did not rely on EC values, but rather followed the typical potassium-based fertilizer absorption pattern of lettuce, applying the appropriate fertilizer weekly (every 7 days). The weekly amounts of elements added are shown in Tables 4 and 5. Harvesting was carried out 35 days after transplanting.

[0069] Table 4. Weekly supplementation of macro-mineral elements (unit: mmol / plant)

[0070] time serial number N P K Ca Mg S Na Week 1 Ⅰ 0.57 0.05 0.27 0.06 0.02 0.02 0.01 Week 2 Ⅱ 1.81 0.17 0.99 0.19 0.07 0.04 0.03 Week 3 Ⅲ 3.18 0.33 1.53 0.51 0.20 0.09 0.17 Week 4 Ⅳ 3.15 0.43 1.25 0.67 0.30 0.09 0.49 Week 5 Ⅴ 5.03 0.64 2.10 1.11 0.40 0.14 0.49 total 13.74 1.62 6.15 2.54 0.99 0.38 1.19

[0071] Table 5. Weekly Trace Mineral Element Supplementation (Unit: umol / plant)

[0072] serial number B Fe Mn Zn Cu Mo Week 1 Ⅰ 0.39 0.36 0.18 0.11 0.02 0.00 Week 2 Ⅱ 0.95 1.41 0.64 0.33 0.05 0.01 Week 3 Ⅲ 2.26 3.75 1.98 0.63 0.09 0.01 Week 4 Ⅳ 4.47 2.30 2.85 0.92 0.12 0.02 Week 5 Ⅴ 6.21 4.88 3.61 4.10 0.22 0.01 total 14.27 12.69 9.26 6.10 0.49 0.04

[0073] Comparative Experiment 1

[0074] 1. Materials and Methods

[0075] Using the potassium-efficient 'Huihe Green Leaf' lettuce variety as the test material, the management methods of Example 1 and Comparative Examples 1, 2, 3, and 4 were followed. Figure 1 (The different colors and letters in the diagram represent the corresponding formulas in the examples above.) The lettuce was cultivated using a late-night flow cultivation method. The aboveground fresh weight, potassium content, soluble sugar, soluble protein, vitamin C, free amino acids, and nitrate content of the lettuce plants obtained in Example 1 and Comparative Examples 1, 2, 3, and 4 were measured. The applicability and advancement of this invention in specific implementation processes were investigated.

[0076] 2 Results and Analysis

[0077] 2.1 Effects of different low-potassium nutrient solutions on the growth of hydroponically grown lettuce

[0078] like Figure 2 As shown, under deep liquid flow mode, after 35 days of growth of lettuce under different treatments, the lettuce of Example 1, Comparative Example 2 and Comparative Example 3 showed no significant difference in morphology compared with the normal potassium supply (Comparative Example 1), while the growth of Comparative Example 4 was significantly weaker than the other four treatments. Figure 3 The results show that, compared with Comparative Example 1, all low-potassium treatments affected the yield of lettuce to some extent. The lettuce from Example 1, Comparative Example 2, and Comparative Example 3 showed no significant difference from that of Comparative Example 1, indicating that these three low-potassium treatments have greater advantages in terms of yield and morphology.

[0079] 2.2 Effects of different low-potassium nutrient solutions on the nutritional quality of hydroponic lettuce

[0080] like Figure 4-8As shown, compared with Comparative Example 1, the low-potassium treatment increased the soluble sugar content of hydroponic lettuce. The soluble sugar content of the treatment in Example 1 was the highest, increasing by 37.10%, 20.13%, 25.98%, and 16.90% compared to Comparative Examples 1, 2, 3, and 4, respectively. All four low-potassium treatments increased the vitamin C content of hydroponic lettuce, with the vitamin C content ranking from highest to lowest as Comparative Example 4 > Comparative Example 2 > Example 1 > Comparative Example 3 > Comparative Example 1. The low-potassium treatment decreased the soluble protein and nitrate content of lettuce. There was no significant difference in the free amino acid content among the five treatments. The results indicate that Example 1 can increase the soluble sugar, vitamin C, and free amino acid content of lettuce, and to some extent reduces the content of the harmful substance nitrate.

[0081] 2.3 Effects of different low-potassium nutrient solutions on chlorophyll fluorescence dynamics in hydroponic lettuce leaves

[0082] From the fluorescence kinetic curve ( Figure 9 It can be seen that only Comparative Example 4 of the low-potassium treatment had an adverse effect on the photosystem II of hydroponic lettuce. This also indicates that Example 1 did not have an adverse effect on the photosystem II of hydroponic lettuce.

[0083] 2.4 Effects of different low-potassium nutrient solutions on the mineral content of hydroponic lettuce

[0084] As shown in Table 6, compared with normal potassium supply (Comparative Example 1), all different low-potassium treatments significantly reduced the potassium content in hydroponic lettuce. Only the potassium content in the treatment of Example 1 was approximately 100 mg / 100 g. The low-potassium treatments increased the content of P, Ca, and Mg in hydroponic lettuce, with P and Mg showing the highest values ​​in Example 1. This indicates that Example 1, like other low-potassium treatments, increased the content of other mineral elements while reducing the potassium content in lettuce.

[0085] Table 6. Comparison of mineral elements under different treatments (unit: mg / 100g fresh sample)

[0086] Processing Number K N P Ca Mg S Comparative Example 1 371.83±2.96a 274.74±4.81a 45.53±0.36b 56.78±1.23b 16.49±0.57c 11.83±0.61b Comparative Example 2 153.99±5.09c 278.77±2.09a 50.77±0.77ab 64.97±1.04b 29.97±1.6ab 10.27±0.13c Comparative Example 3 117.57±2.17d 239.65±6.81b 46.92±1.54b 60.72±0.47b 24.90±0.21b 9.87±0.76c Comparative Example 4 204.31±5.57b 279.5±15.98a 50.76±2.18ab 94.88±10.40a 25.89±2.79b 16.11±0.16a Example 1 101.52±5.16e 255.47±5.03ab 55.75±3.50a 62.23±2.00b 33.85±2.74a 9.24±0.34c

[0087] 3. Conclusion

[0088] Compared to Comparative Example 1, all low-potassium treatments affected lettuce yield to some extent. The lettuce from Examples 1, 2, and 3 showed no significant difference from Comparative Example 1, indicating that these three low-potassium treatments had greater advantages in yield and morphology. Comparative Example 4 had the greatest adverse effect on lettuce growth, and photosynthetic system II was damaged to some extent. Example 1 increased the soluble sugar, vitamin C, and free amino acid content of lettuce, and to some extent reduced the content of harmful nitrates. All low-potassium treatments significantly reduced the potassium content of lettuce; only Example 1 successfully controlled the potassium content of lettuce to around 100 mg / 100g, achieving the goal of quantitative potassium content control. All low-potassium treatments increased the content of P, Ca, and Mg in hydroponic lettuce, with Example 1 showing the greatest advantage in P and Mg content.

[0089] Comparative Experiment 2

[0090] Unlike control experiment 1, the cultivation method was changed to nutrient film (shallow flow) hydroponics, and the number of cultivated varieties was increased to two: Huihe Green Flower Leaf (low potassium tolerant variety) and Huqian (low potassium sensitive variety). This study investigated whether different cultivation methods and varieties affected the effectiveness of the method described in this invention.

[0091] 2 Results and Analysis

[0092] 2.1 Effects of different low-potassium nutrient solutions on the growth of hydroponically grown lettuce

[0093] Similar to the results of Comparative Experiment 1, combined Figure 10 , Figure 11 and Figure 12 As shown, under the shallow sap flow mode, except for Comparative Example 4, the other low-potassium treatments showed no significant difference in growth compared to Comparative Example 1, but the aboveground fresh weight was reduced to some extent in all cases. Among the four low-potassium treatments for the 'Huihe Green Leaf' variety, Example 1 showed the highest aboveground fresh weight. For the 'Huqian' variety, there were no significant differences between Example 1, Comparative Example 2, and Comparative Example 3. This indicates that both varieties in Example 1 showed good performance in terms of morphology and yield under the shallow sap flow mode.

[0094] 2.2 Effects of different low-potassium nutrient solutions on the nutritional quality of hydroponic lettuce

[0095] like Figures 13-17As shown, compared with Comparative Example 1, the low potassium treatment increased the soluble sugar and free amino acid content of both hydroponic lettuce varieties. Specifically, the soluble sugar content of 'Huihe Green Flower' and 'Huqian' varieties in Example 1, as well as the amino acid content of 'Huihe Green Flower', showed significant differences compared to Comparative Example 1. The low potassium treatment reduced the nitrate content of the lettuce. Both varieties showed the lowest nitrate content under the conditions of Example 1. Under the conditions of Example 1, the nitrate content of 'Huihe Green Flower' was 42.92%, 14.42%, 26.89%, and 16.90% lower than that of Comparative Examples 1, 2, 3, and 4, respectively. Under the conditions of Example 1, the nitrate content of 'Huqian' was 36.33%, 35.90%, 26.89%, and 13.67% lower than that of Comparative Examples 1, 2, 3, and 4, respectively.

[0096] 2.3 Effects of different low-potassium nutrient solutions on the mineral content of hydroponic lettuce

[0097] As shown in Tables 7 and 8, compared with normal potassium supply (Comparative Example 1), all different low-potassium treatments significantly reduced the potassium content in hydroponic lettuce. Only the potassium content in the treatment of Example 1 for both varieties was approximately 100 mg / 100g. The low-potassium treatment increased the content of N, P, Ca, and Mg in hydroponic lettuce. This indicates that Example 1, like other low-potassium treatments, increased the content of other mineral elements while reducing the potassium content of lettuce.

[0098] Table 7. Comparison of mineral elements in different treatments of shallow-flow 'Huihe Green Flower Leaf' varietal (unit: mg / 100g fresh sample)

[0099]

[0100]

[0101] Table 8. Comparison of mineral elements in different treatments of shallow liquid flow 'Huqian' (unit: mg / 100g fresh sample)

[0102] Processing Number K N P Ca Mg S Comparative Example 1 267.63±2.01a 166.88±1.90c 34.18±1.29b 63.36±2.77c 12.56±0.65b 16.57±0.42a Comparative Example 2 125.45±5.13bc 185.20±2.59ab 41.42±0.48a 74.36±2.55b 21.53±0.42a 8.26±0.15d Comparative Example 3 133.66±2.58b 176.60±3.58b 41.83±2.59a 69.33±1.89bc 19.43±1.26a 13.00±0.60b Comparative Example 4 119.74±1.06c 192.50±3.75ab 37.51±0.58ab 83.58±2.84a 19.72±0.59a 12.34±0.27b Example 1 93.36±1.53d 167.60±0.90c 40.17±0.35a 67.02±1.06bc 20.55±0.24a 11.06±0.08c

[0103] 3. Conclusion

[0104] Under shallow liquid flow mode, compared with Comparative Example 1, Examples 1, 2, and 3 showed better growth. All low-potassium treatments affected lettuce yield to some extent, but the yield of Example 1 was not significantly different from that of hydroponic lettuce under normal potassium treatment, and was similar to or better than existing low-potassium vegetable cultivation methods, indicating that the low-potassium treatment methods of Examples 1, 2, and 3 have greater advantages in yield and morphology. Example 1 increased the soluble sugar content, vitamin C content, and free amino acid content of lettuce, and to some extent reduced the content of harmful substances such as nitrate. All low-potassium treatments significantly reduced the potassium content of lettuce; only Example 1 successfully controlled the potassium content of lettuce to around 100 mg / 100g, achieving quantitative control of potassium content. Previous methods showed significant fluctuations in potassium content under different cultivation modes and varieties, failing to achieve quantitative control. All low-potassium treatments increased the content of N, P, Ca, and Mg in hydroponic lettuce.

[0105] The above results indicate that this invention can achieve quantitative control of potassium content in lettuce under different hydroponic modes and with different varieties, without showing symptoms of potassium deficiency. In terms of yield, there is little difference compared to hydroponic lettuce treated with normal potassium, and it is similar to or better than existing low-potassium vegetable cultivation methods. The lettuce produced by this invention improves the nutritional quality and mineral content of lettuce to a certain extent, while reducing the content of harmful substances such as nitrates.

[0106] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for quantitatively controlling potassium content in the cultivation of low-potassium lettuce, characterized in that, Includes the following steps: Based on the potassium content target, prepare conventional potassium-containing nutrient solution stock solution and potassium-free nutrient solution stock solution; The two nutrient solution stock solutions were diluted according to the concentration ratio to form the working solution. The conventional potassium-containing nutrient solution was continuously used in the early growth stage after the lettuce was transplanted. When the fresh weight of the whole lettuce plant reaches the switching threshold calculated by the following formula, stop using the conventional potassium-containing nutrient solution and switch to a potassium-free nutrient solution until harvest: ； Wherein, X is the fresh weight of the aboveground part of the lettuce at harvest; Y is the fresh weight of the whole lettuce plant when potassium is depleted; A is the potassium content of the target aboveground part of the fresh sample at harvest; B is the potassium content of the whole lettuce plant fresh sample produced by conventional potassium-containing nutrient solution; throughout the entire cultivation process, the conductivity of the nutrient solution is maintained at 1.3–1.5 mS / cm and the pH value is maintained at 5.5–6.5; wherein A is 90–110 mg / 100 g and B is 350–450 mg / 100 g.

2. The low-potassium lettuce cultivation method according to claim 1, characterized in that, The potassium ion concentration in the conventional potassium-containing nutrient solution is 3.0–4.0 mmol / L, and the background potassium content in the potassium-free nutrient solution is less than 0.5 mg / L.

3. The low-potassium lettuce cultivation method according to claim 1, characterized in that, The concentration factor of the nutrient solution mother liquor is 100 to 200 times, and the dilution ratio of the working solution is prepared at a volume ratio of 1:100 to 1:

200.

4. The low-potassium lettuce cultivation method according to claim 1, characterized in that, In the potassium-free nutrient solution, the potassium salts in the conventional potassium-containing nutrient solution are replaced with sodium or calcium salts in equal molar amounts to maintain ion balance.

5. The low-potassium lettuce cultivation method according to claim 1, characterized in that, Suitable for both deep flow and shallow flow hydroponics.

6. Low-potassium lettuce produced using any one of the cultivation methods described in claims 1-5.

7. A low-potassium lettuce cultivation system for implementing the cultivation method according to any one of claims 1-5, characterized in that, In order, they include: Nutrient solution preparation unit, used to prepare and store conventional potassium-containing nutrient solution stock solution and potassium-free nutrient solution stock solution; The dilution and dispensing unit is fluidly connected to the nutrient solution preparation unit and is used to automatically prepare the working solution according to the concentration factor and circulate or quantitatively dispense it. The cultivation module is used to support lettuce plants and deliver the nutrient solution. The online monitoring and control unit is equipped with an EC sensor, a pH sensor, and a potassium ion sensor, which are connected to the dilution and dispensing unit to automatically adjust the dilution ratio and replenishment rate. The harvesting module is used to perform automatic or semi-automatic harvesting after the potassium-free stage.

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