Low-potassium lettuce capable of quantitatively controlling potassium content and cultivation method and cultivation system of low-potassium lettuce

Abstract

The invention discloses a low-potassium lettuce capable of quantitatively controlling the potassium content and a cultivation method and system thereof, and the method comprises the steps: preparing conventional potassium-containing and potassium-free high-power concentrated mother liquor, diluting the mother liquor in proportion, and continuously supplying a potassium-containing nutrient solution in the early stage of plant growth; when the fresh weight of the whole plant reaches a potassium cut-off threshold value calculated by the potassium content of the target fresh sample, the potassium content of the conventional lettuce and the fresh weight of the overground part, accurately switching to a potassium-free nutrient solution until harvesting; meanwhile, in the potassium-free stage, equimolar sodium salt / calcium salt is used for replacing sylvite to maintain conductivity and ion balance, and fine regulation and control of EC of 1.3-1.5 mS / cm and pH of 5.5-6.5 are matched, so that root system health and yield quality are ensured. The system does not need a special light source or a temperature control facility, is suitable for deep liquid flow, shallow liquid flow and aeroponic cultivation of multiple soilless platform lettuce production, stably realizes 100 + / -10mg / 100g (fresh sample) low-potassium products among batches, and has the advantages of simplicity and convenience in operation, high repeatability and high industrial popularization value.

Description

Technical Field

[0001] The present invention belongs to the technical field of factory-based vegetable cultivation, and specifically relates to a low-potassium vegetable cultivation method and system for quantitatively controlling potassium content. The method is particularly suitable for precisely regulating the potassium content of lettuce plants in a soilless or hydroponic environment to obtain low-potassium vegetable products that meet health or special dietary needs. Background Art

[0002] Chronic kidney disease (CKD) is a common disease among the elderly, and its incidence is increasing worldwide. CKD patients are prone to hyperkalemia due to their inability to excrete potassium normally. Hyperkalemia can lead to arrhythmias, muscle weakness, impaired consciousness, heart failure, and even sudden death. A potassium-restricted diet is a major control measure, such as limiting the intake of fresh vegetables, seafood, beans, and fruits. Leafy vegetables are rich in potassium, and doctors recommend that CKD patients blanch leafy vegetables before eating to avoid excessive potassium intake. However, lettuce is mostly eaten raw, and CKD patients find it difficult to eat dishes made with fresh lettuce, such as salads and sandwiches, like normal people. The development of low-potassium lettuce not only ensures limited potassium intake, but also enriches the dietary structure of CKD patients.

[0003] Because the mineral elements in the nutrient solution for soilless cultivation are highly controllable, low-potassium vegetable production is currently carried out using soilless cultivation, especially hydroponics. The cultivation method is mainly achieved by reducing the supply of potassium fertilizer in the nutrient solution during the vegetable production process. The most reported method is to supply sufficient potassium in the early stage of vegetable production and stop the supply of potassium fertilizer one or two weeks before harvest. Although the method of cutting off potassium at a certain time point can significantly reduce the potassium content in vegetables, the potassium content fluctuates greatly due to the influence of variety, season and nutrient solution formula. It is impossible to ensure that the potassium content of each batch of vegetables produced remains within a certain range, and it is difficult to form a standardized product. The Global Kidney Disease Outcomes Improvement Organization recommends that kidney patients consume foods with a potassium content of less than 100mg / 100g. Although Japan has reported that the potassium content in low-potassium lettuce can be controlled within 100mg / 100g (fresh), it must rely on the controlled environment of a fully artificial light plant factory to achieve this, and the investment and operating costs are high. Chinese patents CN106535622B and CN106577211B both use potassium depletion technology to reduce potassium, but this only reduces potassium content and fails to accurately and stably control potassium content within the target range. Furthermore, CN106577211B requires additional measures such as LED lighting, resulting in high production costs and complex operations, making it difficult to implement in conventional production systems. Currently, there is a lack of a cultivation technology that can consistently produce a quantitative potassium content in batches across multiple varieties and sizes without relying on specialized light sources or strict environmental conditions. Summary of the Invention

[0004] In response to the above technical defects, the present invention proposes a low-potassium lettuce with quantitatively controlled potassium content and its cultivation method and cultivation system. First, according to the target fresh sample potassium content at harvest and the fresh sample potassium content of lettuce under conventional potassium-containing conditions, two sets of conventional potassium-containing and potassium-free nutrient solution mother solutions are prepared and diluted to use liquid according to the concentration multiple. In the early growth stage after the lettuce is planted, a conventional potassium-containing nutrient solution is continuously supplied to ensure the normal growth and development of the plant; when the fresh weight of the whole plant reaches the switching threshold calculated by the formula Y=A×X / B, the supply of potassium-containing nutrient solution is stopped, and the potassium-free nutrient solution is continuously supplied until harvest. Through the above-mentioned dynamic switching based on the fresh weight quantitative threshold, accurate control of the final fresh sample potassium content is achieved. This method does not need to rely on a fixed time node or a special light source environment. Combined with the consistent mother solution dilution multiple and potassium-free background between batches, the fresh sample potassium content of the lettuce can be stably controlled within the target range under the premise of ensuring yield and quality, and has good repeatability and industrial promotion potential.

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

[0006] According to the potassium content target, prepare conventional potassium-containing nutrient solution mother solution and potassium-free nutrient solution mother solution;

[0007] The two nutrient solution mother solutions were diluted into working solutions according to the concentration multiples, and the conventional potassium-containing nutrient solution was continuously used in the early growth period after the lettuce was planted.

[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 potassium-free nutrient solution until harvest:

[0009]

[0010] Wherein, X is the fresh weight of the aboveground part of lettuce at harvest; Y is the fresh weight of the whole lettuce plant when potassium is deprived; A is the target potassium content of the fresh sample at harvest; and B is the potassium content of the fresh sample of lettuce under normal 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 of the potassium-free nutrient solution is less than 0.5 mg / L.

[0012] In some technical solutions, the concentration multiple of the nutrient solution mother solution 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.

[0013] The use of 100-200 times concentrated mother liquor to prepare the working solution not only greatly reduces the volume of the mother liquor and reduces 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 accuracy of final potassium content control.

[0014] In some technical solutions, during 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, and the conductivity of the nutrient solution is preferably 1.4 mS / cm.

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

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

[0017] During the potassium-free stage, the potassium salt in the conventional nutrient solution is replaced with sodium salt or calcium salt on an equimolar basis to maintain the conductivity of the nutrient solution and the balance of major anions and cations, avoiding the stress of simple potassium removal on the plants and ensuring normal absorption and metabolism during the low potassium period.

[0018] Some technical solutions are suitable for deep liquid flow and shallow liquid flow hydroponics.

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

[0020] In a second aspect, the present invention further provides low-potassium lettuce produced by the above-mentioned cultivation method.

[0021] In a third aspect, the present invention further provides a low-potassium lettuce cultivation system for implementing the above-mentioned cultivation method, comprising:

[0022] Nutrient solution preparation unit, used for preparing and storing conventional potassium-containing nutrient solution mother solution and potassium-free nutrient solution mother solution;

[0023] The dilution and delivery unit is in fluid communication with the nutrient solution preparation unit and is used to automatically prepare the nutrient solution according to the concentration multiple and to circulate or quantitatively deliver the solution;

[0024] a cultivation module for supporting vegetable plants and delivering liquid for use;

[0025] Online monitoring and control unit, equipped with EC sensor, pH sensor and potassium ion sensor, connected to the dilution and delivery unit to automatically adjust the dilution ratio and rehydration rate;

[0026] Harvesting modules for automatic or semi-automatic harvesting after the potassium-free period.

[0027] The present invention adopts the above technical solution to have at least the following beneficial effects:

[0028] 1. The present invention uses the formula Y=A×X / B as the potassium-free threshold, and calculates the potassium-free fresh weight (Y) of the whole plant by multiplying the fresh weight (X) of the plant during its growth period by the ratio of the target potassium content to the potassium content under normal potassium-containing conditions (A / B). This feature tightly couples the timing of "potassium-free" with the plant's growth state: early nutrient supply fully ensures cell division and leaf expansion. When the fresh weight reaches Y, potassium transport tends to balance. Switching to a potassium-free nutrient solution can maximize potassium absorption without damaging the root-crown distribution mechanism, thereby accurately locking the fresh sample potassium content within the A±tolerance range in each batch, significantly reducing the potassium drift between batches caused by variety differences, growth stages, or environmental fluctuations.

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

[0030] 3. This method takes into account the redistribution of potassium by the root system under potassium-deficient conditions. When calculating the potassium-deficient threshold, the root fresh weight is incorporated into the total plant fresh weight Y, while only the aboveground fresh weight X is counted during actual harvest. This method fully reflects the dynamics of potassium distribution between the root and crown: during the initial stages of potassium deficiency, the root system continues to release stored potassium to new leaves, after which the aboveground potassium content stabilizes. This precise calculation of the dual fresh weight indicators allows for more rigorous prediction of the final edible potassium content, significantly improving product safety and data reliability.

[0031] 4. Based on a single dynamic formula, this invention allows users to customize the potassium threshold (Y) based on different target harvest weights (X), enabling low-potassium production of lettuce in multiple sizes (e.g., 50g, 100g, and 150g). This flexibility ensures that fresh sample potassium content ≤ A can be harvested at any time within a week of potassium withdrawal. Producers can freely schedule shifts based on market demand and packaging specifications without having to retest recipes or modify processes, significantly 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, eliminating the need for expensive light sources or temperature control equipment. Combined with online sensing and an automated liquid dispensing system, this method enables one-touch potassium-free switching and mother liquor proportioning in a variety of soilless platforms, including deep flow, shallow flow, and aeroponics, making it suitable for lettuce cultivation. This feature not only lowers the production threshold but also enhances the feasibility and economic benefits of technology transfer and industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the nutrient solution stage management method in different ways based on Example 1 and Comparative Examples 1 to 4 in Comparative Experiment 1 of the present invention;

[0034] Figure 2 This is a comparison chart of different treatment forms 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 aboveground parts under different treatments based on Example 1 and Comparative Examples 1 to 4 in Comparative Experiment 1 of the present invention;

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

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

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

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

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

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

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

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

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

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

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

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

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

[0049] Figure 17 This is a comparison chart of free amino acid contents in different treatments based on Example 1 and Comparative Examples 1 to 4 in Comparative Experiment 2 of the present invention. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present invention are described clearly and completely below. Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0051] Example 1

[0052] According to the concentrations in Tables 1 and 2, a conventional potassium concentration nutrient solution and a potassium-free nutrient solution were prepared. The potassium concentration in Formula A was less than 4 mmol / L, and the potassium concentration in Formula C was 0. The potassium concentrations were replaced with equal amounts of sodium salts. Except for the different potassium and sodium contents, the contents of the remaining elements were the same. Potassium-efficient "Huihe Green Mosaic Leaf" lettuce varieties were used as test materials. When the seedlings grew to 2 leaves and 1 heart, they were planted in hydroponic planting boxes. Each planting box was planted with 6 plants, and the box nutrient solution volume was 7 L. The fresh weight of the aboveground part of the lettuce at harvest was set at 40 g (letter X in the formula), the potassium content of lettuce cultivated at normal potassium concentration 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). According to 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, use a nutrient solution with normal potassium concentration to cultivate lettuce until the fresh weight of the whole plant reaches 10g, pour out the nutrient solution, replace it with a potassium-free nutrient solution, and then cultivate it until the fresh weight of the aboveground part of the lettuce reaches 40g.

[0053] During the cultivation period, the corresponding formula of concentrated solution was used to regulate the EC of the nutrient solution, and the EC was maintained at 1.4mS·cm -1 The pH of the nutrient solution is maintained at 5.5-6.5. When the pH is higher than this range, use nitric acid or phosphoric acid to adjust it. When the pH is lower than this range, use sodium hydroxide to adjust it.

[0054] Table 1. Conventional potassium content and macronutrient content of potassium-free nutrient solution formula (unit: mmol / L)

[0055]

[0056] Table 2. Trace element content of conventional potassium and potassium-free nutrient solution formula (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 to test whether its yield and quality were significantly affected compared to conventionally cultivated lettuce. A nutrient solution with a conventional potassium concentration, Formula A, was prepared in Example 1. Unlike Example 1, Formula A was used throughout the entire lettuce cultivation process in Comparative Example 1, with no changes to the formula. The lettuce was harvested 35 days after planting.

[0060] Comparative Example 2

[0061] Comparative Example 2 is one of the common methods for producing low-potassium lettuce, used for comparison with the method of the present invention. A low-potassium nutrient solution was prepared according to the macroelement formula in Table 3 and the trace element formula in Example 1. Unlike Example 1, Formula B was used throughout the entire lettuce cultivation process in Comparative Example 2, without changing the formula midway. 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 content is approximately 400 mg / 100 g, it was explored whether the potassium content of lettuce could reach 1 / 4 of that of lettuce cultivated with conventional potassium nutrient solution when the potassium content of the nutrient solution was 1 / 4 of that of the conventional potassium content. Harvested 35 days after planting.

[0062] Table 3. Content of macroelements in low potassium nutrient solution formula (unit: mmol / L)

[0063]

[0064] Comparative Example 3

[0065] Comparative Example 3, a commonly used method for producing low-potassium lettuce, was designed based on the nutrient solution cultivation model of prior invention CN106577211B (Application Number: CN201610918218.4) for comparison with the present method. Unlike Example 1, the potassium-free nutrient solution was replaced at a fixed time, two weeks before harvest, regardless of the current fresh weight of the lettuce. Harvest was completed 35 days after planting.

[0066] Comparative Example 4

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

[0068] Unlike Example 1, nutrient solution management did not rely on EC values. Instead, the corresponding fertilizer was added weekly (7 days apart) according to the weekly fertilizer absorption pattern of conventional potassium formula lettuce. The amount of elements added weekly is shown in Tables 4 and 5. Harvest was carried out 35 days after planting.

[0069] Table 4. Weekly addition 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 addition (unit: μmol / 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 test 1

[0074] 1 Materials and Methods

[0075] The potassium efficient utilization type 'Huihe Green Flower Leaf' lettuce variety was used as the test material, and the management methods of Example 1 and Comparative Examples 1, 2, 3, and 4 were used ( Figure 1 ), with different colors and letters representing the corresponding recipes in the examples above. Cultivation was performed using a late-night flow cultivation model. The lettuce plants obtained in Example 1 and Comparative Examples 1, 2, 3, and 4 were measured for their aboveground fresh weight, potassium content, soluble sugar, soluble protein, vitamin C, free amino acids, and nitrate content. The applicability and advancement of the present invention in specific implementations were explored.

[0076] 2 Results and Analysis

[0077] 2.1 Effects of different low potassium nutrient solution treatments on the growth of hydroponic lettuce

[0078] like Figure 2 As shown, under the deep liquid flow mode, after the lettuces were grown under different treatments for 35 days, there was no significant difference in morphology between the lettuces of Example 1, Comparative Example 2 and Comparative Example 3 and those of the normal potassium supply (Comparative Example 1), and the growth of Comparative Example 4 was significantly weaker than that of the other four treatments. Figure 3 It was shown that compared with Comparative Example 1, the low potassium treatment methods all affected the yield of lettuce to a certain extent. There was no significant difference between the lettuces of Example 1, Comparative Example 2 and Comparative Example 3 and Comparative Example 1, indicating that these three low potassium treatment methods had greater advantages in yield and morphology.

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

[0080] like Figure 4-8As shown, compared with Comparative Example 1, low-potassium treatment increased the soluble sugar content of hydroponic lettuce. Example 1 had the highest soluble sugar content, 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 VC content of hydroponic lettuce, with the VC content ranking from highest to lowest in the order: Comparative Example 4 > Comparative Example 2 > Example 1 > Comparative Example 3 > Comparative Example 1. Low-potassium treatment reduced the soluble protein content and nitrate content of the lettuce. There were no significant differences in free amino acid content among the five treatments. These results demonstrate that Example 1 increased the soluble sugar content, VC content, and free amino acid content of lettuce, and reduced the harmful substance nitrate content to a certain extent.

[0081] 2.3 Effects of different low potassium nutrient solution treatments on chlorophyll fluorescence dynamics of hydroponic lettuce

[0082] From the fluorescence kinetic curve ( Figure 9 ) It can be seen that among the low potassium treatments, only Example 4 had an adverse effect on the photosystem II of the hydroponic lettuce. This also shows that Example 1 had no adverse effect on the photosystem II of the hydroponic lettuce.

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

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

[0085] Table 6. Comparison of mineral elements in 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 with Comparative Example 1, the low potassium treatment methods all affect the yield of lettuce to a certain extent. There is no significant difference between the lettuces of Example 1, Comparative Example 2 and Comparative Example 3 and Comparative Example 1, indicating that these three low potassium treatment methods have greater advantages in yield and morphology. Comparative Example 4 has the greatest adverse effect on the growth of lettuce, and photosynthetic system II is damaged to a certain extent. Example 1 can increase the soluble sugar content, VC content and free amino acid content of lettuce, and reduce the content of harmful substances such as nitrate to a certain extent. All low potassium treatment methods significantly reduce the potassium content of lettuce. Only Example 1 successfully controls the potassium content of lettuce to about 100 mg / 100 g, achieving the purpose of quantitatively controlling potassium content. All low potassium treatment methods increase the content of P, Ca and Mg in hydroponic lettuce, among which Example 1 has the greatest advantage in P and Mg content.

[0089] Comparative Test 2

[0090] Unlike Comparative Experiment 1, the cultivation mode was changed to nutrient film (shallow liquid flow) hydroponics, and the number of cultivated varieties was increased to two: Huihe Green Mosaic Leaf (a low-potassium tolerant variety) and Huqian (a low-potassium sensitive variety). This study explored whether different cultivation modes and varieties affect the effectiveness of the present method.

[0091] 2 Results and Analysis

[0092] 2.1 Effects of different low potassium nutrient solution treatments on the growth of hydroponic lettuce

[0093] Similar to the results of comparative experiment 1, Figure 10 、 Figure 11 and Figure 12 As shown, under the shallow liquid flow mode, with the exception of Comparative Example 4, the other low-potassium treatments showed no significant differences in growth compared to Comparative Example 1, but all showed a certain degree of reduction in aboveground fresh weight. Among the four low-potassium treatments for the 'Huihe Green Mosaic' variety, Example 1 had 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 can achieve good performance in terms of morphology and yield under the shallow liquid flow mode.

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

[0095] like Figure 13-17As shown, compared with Comparative Example 1, low potassium treatment increased the soluble sugar content and free amino acid content of the two hydroponic lettuces. In particular, the soluble sugar content of 'Huihe Green Flower Leaf' and 'Huiqian' in Example 1, as well as the amino acid content of 'Huihe Green Flower Leaf', were significantly different from those in Comparative Example 1. Low potassium treatment can reduce the nitrate content of lettuce. Both varieties had the lowest content under the operation of Example 1. Under the conditions of Example 1, the nitrate content of 'Huihe Green Flower Leaf' was 42.92%, 14.42%, 26.89% and 16.90% lower than that of Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4, respectively. Under the conditions of Example 1, the nitrate content of 'Huiqian' was 36.33%, 35.90%, 26.89% and 13.67% lower than that of Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4, respectively.

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

[0097] As shown in Tables 7 and 8, compared with normal potassium supply (Comparative Example 1), all low-potassium treatments significantly reduced potassium content in hydroponic lettuce. For both varieties, only the treatment in Example 1 achieved a potassium content of approximately 100 mg / 100 g. Low-potassium treatment increased the contents of N, P, Ca, and Mg in hydroponic lettuce. This suggests that Example 1, like other low-potassium treatments, reduced potassium content in lettuce while simultaneously increasing the contents of other mineral elements.

[0098] Table 7. Comparison of mineral elements in different treatments of shallow liquid flow 'Huihe Green Flower Leaf' (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 good growth. All low-potassium treatments affected lettuce yield to some extent, but the yield of Example 1 was not much different from that of hydroponic lettuce treated with normal potassium, and was similar to or better than existing low-potassium vegetable cultivation modes. This shows that the low-potassium treatment methods of Examples 1, 2, and 3 have greater advantages in yield and morphology. Example 1 was able to increase the soluble sugar content, VC content, and free amino acid content of lettuce, and to some extent reduced the harmful substance nitrate content. All low-potassium treatments significantly reduced the potassium content of lettuce, but only Example 1 successfully controlled the potassium content of lettuce to around 100 mg / 100 g, achieving the goal of quantitatively controlling potassium content. Previously available methods, however, showed large fluctuations in potassium content under different cultivation modes and varieties, and were ineffective in quantitatively controlling potassium content. All low-potassium treatments increased the N, P, Ca, and Mg contents in hydroponic lettuce.

[0105] These results demonstrate that the present invention can quantitatively control the potassium content of lettuce under different hydroponic cultivation modes and varieties, without exhibiting potassium deficiency symptoms. Yields are comparable to those of hydroponic lettuce grown under normal potassium treatment, and are comparable to or superior to existing low-potassium vegetable cultivation modes. The lettuce produced by the present invention significantly improves its nutritional quality and mineral content, while reducing the harmful nitrate content.

[0106] Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

Claims

1. A low-potassium lettuce cultivation method for quantitatively controlling potassium content, characterized in that: The following steps are involved: According to the potassium content target, prepare conventional potassium-containing nutrient solution mother solution and potassium-free nutrient solution mother solution; The two nutrient solution mother solutions were diluted into working solutions according to the concentration multiples, and the conventional potassium-containing nutrient solution was continuously used in the early growth period after the lettuce was planted. 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 potassium-free nutrient solution until harvest: Wherein, X is the fresh weight of the aboveground part of lettuce at harvest; Y is the fresh weight of the whole lettuce plant when potassium is deprived; A is the target potassium content of the fresh sample at harvest; and B is the potassium content of the fresh sample of lettuce produced in a conventional potassium-containing nutrient solution.

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 of 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 ratio of the nutrient solution mother solution 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: During the entire cultivation process, the conductivity of the nutrient solution was maintained at 1.3-1.5 mS / cm and the pH value was maintained at 5.5-6.

5.

5. The low-potassium lettuce cultivation method according to claim 1, characterized in that: The A is 90-110 mg / 100 g, and the B is 350-450 mg / 100 g.

6. The low-potassium lettuce cultivation method according to claim 1, characterized in that: In the potassium-free nutrient solution, the potassium salt in the conventional potassium-containing nutrient solution is replaced by sodium salt or calcium salt in equal moles to maintain ion balance.

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

8. Low-potassium lettuce produced by the cultivation method according to any one of claims 1 to 7.

9. A low-potassium lettuce cultivation system for implementing the cultivation method according to any one of claims 1 to 7, characterized in that: Including in order: Nutrient solution preparation unit, used for preparing and storing conventional potassium-containing nutrient solution mother solution and potassium-free nutrient solution mother solution; The dilution and delivery unit is in fluid communication with the nutrient solution preparation unit and is used to automatically prepare the nutrient solution according to the concentration multiple and to circulate or quantitatively deliver the solution; a cultivation module for supporting the lettuce plants and delivering the use liquid; Online monitoring and control unit, equipped with EC sensor, pH sensor and potassium ion sensor, connected to the dilution and delivery unit to automatically adjust the dilution ratio and rehydration rate; Harvesting modules for automatic or semi-automatic harvesting after the potassium-free period.

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