Method for cultivating lettuce in plant factory and illumination control system thereof

Abstract

The invention discloses a method for cultivating lettuce in a plant factory and an illumination control system thereof. According to the method, at least three stages S1-S3 are set after field planting, and operation is carried out according to the linkage relation that the light period is gradually decreased section by section and PPFD is gradually increased section by section; the time interval is 14-20 h, the time interval is 14-18 h, and the time interval is 12-16 h; the first part and the second part are located in the interval of 150-250, the interval of 200-300 and the interval of 250-350 respectively; a full cycle cumulative illumination integral (CLI) is controlled within a target interval comparable to a constant illumination reference condition. The system is composed of an LED lighting assembly, a controller and a sensing recording unit. According to the method, the fresh weight, the dry weight and the soluble protein are improved under the condition of no enrichment, the light energy utilization efficiency and the electric energy utilization efficiency are synchronously improved, the unit output energy consumption is reduced, and the method is suitable for industrial large-scale production of the lettuce.

Description

Technical Field

[0001] This invention relates to the field of facility horticulture and plant factory cultivation control technology, specifically to a phased light regulation cultivation method for lettuce and its lighting control system, belonging to the field of LED artificial light environment optimization and energy efficiency management technology in plant factories. Background Technology

[0002] Lettuce (Lactuca sativa) belongs to the genus Lactuca in the family Asteraceae. It is an annual herbaceous plant and is popular for its crisp texture and rich nutrition. Due to its short growth cycle, strong adaptability, and rapid harvesting characteristics (Bantis et al., 2018), lettuce has become an ideal model crop for plant factories.

[0003] In the multi-dimensional environmental parameter regulation system of plant factories, light environment management constitutes a core limiting factor. Light quality, PPFD, and photoperiod jointly regulate photomorphogenesis, photosynthetic efficiency, and quality formation in plants (Yan et al., 2020; Lamet et al., 2021). While existing research has confirmed the response effects of crops such as spinach, lettuce, arugula, strawberry, and tomato under static regulation by a single light factor (Elmardy et al., 2021; Li et al., 2021; Nguyen et al., 2021; Guiamba et al., 2022; Zhang et al., 2024), most studies have neglected the adaptive needs of plants to dynamic changes in the light environment at different growth stages. The light requirements of crops differ significantly during the seedling, vegetative growth, and reproductive stages (Let et al., 2007), making it difficult to match this biological law with fixed light parameter strategies.

[0004] Furthermore, since plant factory crops rely entirely on artificial lighting, the lighting system typically constitutes the primary energy-consuming unit. Data shows that electricity consumption accounts for 25%–30% of the total production cost of a plant factory, with approximately 60%–80% of that electricity used for lighting (Kozai et al., 2013; Kozai et al., 2019). Therefore, optimizing light regulation strategies to improve light utilization efficiency (LUE) and electrical energy utilization efficiency (EUE) is a key approach to reducing energy consumption and saving production costs in plant factory operations. Summary of the Invention

[0005] This invention provides a staged light control method and a matching lighting control system for lettuce in plant factories, aiming to solve the problem that existing constant light parameter or single-factor control methods cannot simultaneously achieve yield, quality, and energy efficiency, and without adding enrichment... The core idea is to address the issues of insufficient reproducibility and energy consumption control under certain conditions. After planting, at least three growth stages (S1, S2, S3) are set sequentially according to the cultivation cycle. A linkage relationship of "gradually decreasing photoperiod and gradually increasing PPFD" is adopted. Within each stage, the photoperiod and PPFD are limited to a preset range. Through closed-loop compensation of the daily cumulative PPFD / stage CLI, the cumulative light integral (CLI) of the whole cycle is kept comparable to the constant light reference condition. This achieves the improvement of fresh weight / dry weight and soluble protein under the same light integral, and simultaneously improves light energy utilization efficiency and electrical energy utilization efficiency.

[0006] According to a first aspect of the present invention, a method for cultivating lettuce in a plant factory is provided, comprising: sequentially executing at least three growth stages S1, S2, and S3 according to a cultivation cycle after transplanting, setting a photoperiod and PPFD for each stage, and satisfying the following relationship: (1) The optical periods of S1, S2, and S3 decrease sequentially, that is... > > ; (2) The PPFD of S1, S2, and S3 increase sequentially, that is < < ; (3) , , They are located in the intervals of 14–20 h, 14–18 h, and 12–16 h, respectively; , , Located at 150–250, 200–300, and 250–350 respectively Within the range; (4) The cumulative light integral of the entire cultivation cycle is controlled within the preset target range to be comparable to the constant light reference conditions, thereby improving growth yield and quality and reducing energy consumption while maintaining a comparable light integral.

[0007] In some technical solutions, S1, S2, and S3 correspond to the 20%–40%, 30%–40%, and 20%–40% periods of the cultivation cycle, respectively.

[0008] In some technical solutions, the optical cycle and PPFD for each stage are: S1 is 17–18 h and 175–250. S2 is 15.5–16.5 h and 225–300 S3 is 14.5–15.5 h and 275–350. .

[0009] In some technical solutions, S1, S2, and S3 correspond to days 1–10, 11–20, and 21–30 of the cultivation cycle, respectively.

[0010] Some technical solutions use LED light sources, which include at least red light with a center wavelength of 660 nm and blue light with a center wavelength of 450 nm, with a red-blue light power ratio of 8:2.

[0011] In some technical solutions, the vertical distance between the LED light source and the lettuce canopy is 10–15 cm, and is adjusted periodically according to the growth stage of the plant to maintain the measured PPFD of the canopy within the target range of the corresponding stage.

[0012] In some technical solutions, the planting density is no higher than 40 plants / m². 2 .

[0013] Some technical solutions employ tray seedling cultivation and use rock wool blocks for cultivation during the treatment period.

[0014] In some technical solutions, environmental parameters include: air temperature 21±2℃, relative humidity 70%–80%. The concentration is at natural levels. The nutrient solution is used for irrigation every 2–3 days, with a pH of 5.8–6.0 and an electrical conductivity of 1.8–2.2 mS / cm.

[0015] In some technical solutions, the constant illumination reference condition includes a photoperiod of 15–17 h and a PPFD of 225–275. One or more groups.

[0016] In some technical solutions, growth indicators and energy efficiency indicators are recorded and archived in steps of 5–10 days. The growth indicators include at least fresh weight and dry weight, and the energy efficiency indicators include at least light energy utilization efficiency and electrical energy utilization efficiency. Based on this, the daylight hours or PPFD limit in subsequent stages are adaptively corrected.

[0017] According to a second aspect of the present invention, a plant factory lighting control system is further provided, comprising: LED lighting components are used to output red and blue light and provide target PPFD at each stage; The controller is electrically connected to the LED lighting components and stores a stage parameter table, which includes the target light period and target PPFD range for each of S1, S2 and S3, as well as the target range of cumulative illumination integration. The sensing and recording unit is used to collect PPFD at the canopy, the cumulative PPFD of the day, and the phase CLI, and to record the running data according to the set step size; The controller is configured to synchronously execute the decrease of optical period and the increase of PPFD during phase switching, and to trigger closed-loop compensation for optical period or PPFD based on the deviation of the cumulative PPFD of the day from the threshold in any phase, so as to keep the cumulative illumination integral of the whole cycle within the target range.

[0018] The present invention, by employing the above technical solution, has at least the following beneficial effects: 1. This invention achieves a synergistic improvement in yield and quality by implementing a coordinated strategy of "gradually decreasing photoperiod and gradually increasing PPFD" throughout the entire cycle, while maintaining the cumulative light integral (CLI) comparable to the constant light reference condition. Specifically, the longer photoperiod in the early stages facilitates rapid canopy expansion and leaf area accumulation, while the increased PPFD in the middle and later stages under shorter photoperiods enhances carbon assimilation efficiency and dry matter accumulation per unit time, resulting in a simultaneous increase in fresh weight, dry weight, and soluble protein content, demonstrating unexpected combined benefits under equal CLI conditions.

[0019] 2. This invention employs red / blue LEDs (preferably red:blue ≈ 8:2), which helps to reduce energy waste in ineffective spectral bands while ensuring effective chloroplast excitation and canopy penetration, thereby improving light utilization efficiency (LUE) and electrical energy utilization efficiency (EUE). Compared with fixed light parameter schemes, this invention achieves "increased production without increased light, and improved quality without increased consumption" under the same light integration constraint, effectively reducing unit output power consumption and unit output light consumption.

[0020] 3. The method of this invention does not depend on Enriched throughout, only in nature Under these conditions, significant improvements in production capacity and quality can be achieved, reducing reliance on gas enrichment systems and operational complexity, minimizing safety and compliance risks, and lowering system construction costs and maintenance difficulty. If production requires further pursuit of maximum capacity, this method can also be combined with phased, low-dose... When used in conjunction with collaborative strategies, they offer excellent scalability.

[0021] 4. The stage divisions (S1 / S2 / S3) and parameter ranges (photoperiod and upper and lower limits of PPFD) of this invention are given in the form of "range + monotonic relationship", which allows the process to have a margin of adaptability to different lettuce varieties, different planting densities and lighting output capabilities. The operator can make small-scale parameter adjustments without departing from the technical concept of this invention to match different batches of seedlings, facility conditions or target markets (such as more emphasis on protein / flavor or more emphasis on appearance / yield), demonstrating strong adaptability and deployment flexibility.

[0022] 5. At the engineering implementation level, this invention only requires adding or calling the controller's software logic and basic PPFD monitoring to the existing LED lighting system for implementation. It requires no changes to the main cultivation process, resulting in low modification costs and a short path to effectiveness. Simultaneously, the gradual transition and intraday amplitude limit control during phase switching avoid physiological stress caused by sudden changes in light parameters, improving plant health and marketability, and reducing quality defects and scrap caused by stress.

[0023] 6. At the production and operation level, this invention brings higher output value returns per unit time and per unit facility investment by improving LUE / EUE and output per unit area; combined with equal CLI constraints, it can also be coupled with time-of-use pricing strategies to allocate more light time to low electricity price periods without sacrificing stage objectives, thereby further reducing the overall cost per kilowatt-hour and enhancing the economic feasibility and market competitiveness of plant factories. Attached Figure Description

[0024] Figure 1 This is a diagram of the experimental environment for light processing and a diagram of the controller panel of the device in an embodiment of the present invention; Figure 2 This is a comparison chart of growth index results between the light-treated CK group and the DLS group in an embodiment of the present invention; Figure 3 This is a top view of lettuce in the light-treated CK group (control group) and DLS group (dynamic light control) in an embodiment of the present invention; Figure 4 This is a comparison chart of chlorophyll, fluorescence, and photosynthetic parameters between the light-treated CK group and the DLS group in this embodiment of the invention. Figure 5 This is a comparison chart of protein content between the light-treated CK group and the DLS group in an embodiment of the present invention; Figure 6 This is a comparison chart of energy consumption analysis between the CK group and the DLS group in the embodiments of the present invention. Detailed Implementation

[0025] To illustrate the technical content, objectives, and effects of this invention in detail, the following description will be provided in conjunction with embodiments and accompanying drawings. Unless otherwise stated, the experimental methods used in the following embodiments are conventional experimental methods; the materials and reagents used, unless specifically noted, are products that can be obtained through conventional commercial channels.

[0026] According to one embodiment of the present invention, a method for cultivating lettuce in a plant factory is provided, comprising: after transplanting, sequentially executing at least three growth stages S1, S2 and S3 according to the cultivation cycle, setting the photoperiod and PPFD for each stage, and satisfying the following relationship: (1) The optical periods of S1, S2, and S3 decrease sequentially, that is... > > ; (2) The PPFD of S1, S2, and S3 increase sequentially, that is < < ; (3) , , They are located in the intervals of 14–20 h, 14–18 h, and 12–16 h, respectively; , , Located at 150–250, 200–300, and 250–350 respectively Within the range; (4) The cumulative light integral of the entire cultivation cycle is controlled within the preset target range to be comparable to the constant light reference conditions, thereby improving growth yield and quality and reducing energy consumption while maintaining a comparable light integral. (5) S1, S2 and S3 correspond to the 20%–40%, 30%–40% and 20%–40% periods of the cultivation cycle, respectively.

[0027] In the preferred implementation, the optical period and PPFD for each stage are: S1 is 17–18 h and 175–250. S2 is 15.5–16.5 h and 225–300 S3 is 14.5–15.5 h and 275–350. S1, S2, and S3 correspond to days 1–10, 11–20, and 21–30 of the cultivation cycle, respectively.

[0028] In practice, an LED light source is used, which includes at least red light with a center wavelength of 660 nm and blue light with a center wavelength of 450 nm, with a red-blue light power ratio of 8:2.

[0029] As a preferred embodiment, the vertical distance between the LED light source and the lettuce canopy is 10–15 cm, and is adjusted periodically according to the growth stage of the plant to maintain the measured PPFD of the canopy within the target range of the corresponding stage.

[0030] As a preferred option, the planting density should not exceed 40 plants / m². 2 .

[0031] As a preferred option, seedling trays are used for cultivation, and rock wool blocks are used for cultivation during the treatment period.

[0032] As a preferred option, the environmental parameters include: air temperature 21±2℃ and relative humidity 70%–80%. The concentration is at natural levels. The nutrient solution is used for irrigation every 2–3 days, with a pH of 5.8–6.0 and an electrical conductivity of 1.8–2.2 mS / cm.

[0033] As a preferred embodiment, the constant illumination reference condition includes a photoperiod of 15–17 h and a PPFD of 225–275. One or more groups.

[0034] As a preferred approach, growth indicators and energy efficiency indicators are recorded and archived in steps of 5–10 days. The growth indicators include at least fresh weight and dry weight, and the energy efficiency indicators include at least light energy utilization efficiency and electrical energy utilization efficiency. Based on this, the daylight hours or PPFD limit in subsequent stages are adaptively corrected.

[0035] According to another embodiment of the present invention, a plant factory lighting control system is further provided, comprising: LED lighting components are used to output red and blue light and provide target PPFD at each stage; The controller is electrically connected to the LED lighting components and stores a stage parameter table, which includes the target light period and target PPFD range for each of S1, S2 and S3, as well as the target range of cumulative illumination integration. The sensing and recording unit is used to collect PPFD at the canopy, the cumulative PPFD of the day, and the phase CLI, and to record the running data according to the set step size; The controller is configured to synchronously execute the decrease of optical period and the increase of PPFD during phase switching, and to trigger closed-loop compensation for optical period or PPFD based on the deviation of the cumulative PPFD of the day from the threshold in any phase, so as to keep the cumulative illumination integral of the whole cycle within the target range.

[0036] To better understand and apply the above scheme and to effectively demonstrate its corresponding benefits, the following describes a method for cultivating lettuce in a plant factory provided by the present invention in conjunction with specific embodiments.

[0037] First, the CK group was set to a 16-hour photoperiod and a PPFD of 250. The illumination settings for the DLS group were as follows: In the initial phase (days 1-10), the photoperiod was 17.5 hours, and the PPFD was 200. During the mid-stage of cultivation (days 11–20), the photoperiod is 16 hours and the PPFD is 250. During the later stages of cultivation (days 21–30), the photoperiod is 15 hours and the PPFD is 300. .

[0038] 1. Experimental materials and environmental conditions This invention was conducted in a plant factory (31.34°N, 121.41°E) at the Chongming Base of the National Engineering Research Center for Facility Agriculture, using the lettuce variety "Elegance". Before formal treatment, seeds were sown in rock wool substrate in 240-cell foam trays. All seedlings were kept under a photoperiod of 16 h / 8 h and a PPFD of 250. Under a red-to-blue light ratio of 8:2, plants were cultured uniformly for 15 days (plant height reached 4 cm), and then transplanted to the treatment group for continuous treatment for 30 days.

[0039] The CK and DLS groups were identical in all cultivation management conditions except for the light strategy: temperature 21±2℃, relative humidity (RH) 70–80%. Maintain the concentration at natural levels (without enrichment). Irrigate with the nutrient solution every 2–3 days, precisely controlling the pH at 6.0 and keeping the EC value constant at 2.0. The specific planting rack and control panel are as follows: Figure 1 As shown.

[0040] 2. Test indicators of this patent (1) Measurement and analysis of growth indicators Every 5 days, 5 plants were randomly selected from each treatment for destructive sampling, and plant height, plant width, number of leaves, leaf area, fresh weight, and dry weight were measured. Specific measurement methods: plant height was measured with a measuring tape (from the base of the rock wool block to the highest point of the plant); plant width was measured using a measuring tape to determine the maximum width of the above-ground portion of the plant; leaf area was analyzed using ImageJ software; and fresh and dry weights were measured using an electronic analytical balance (above-ground portion only). The results of these measurements are as follows: Figure 2 As shown.

[0041] Results analysis: Compared with the control group, the DLS group showed significant differences in plant height, plant width, number of leaves, leaf area, and dry and fresh weight starting from day 10. By day 30, the fresh weight and dry weight of the DLS group increased by 40.98% and 31.95% respectively compared with the control group. This result indicates that the DLS treatment is more beneficial to the growth of lettuce.

[0042] (2) Top view of the experimental lettuce from Figure 3 As shown in the top view, the growth of lettuce in the DLS group was significantly better than that in the CK group.

[0043] (3) Measurement and analysis of chlorophyll, photosynthetic parameters and fluorescence parameters of leaves The chlorophyll content in the leaves of the plants used in this invention was measured using a miniature plant photosynthetic pigment detector (HPL-B3; Shaanxi Hanpu Optoelectronic Technology Co., Ltd.). Photosynthetic parameters were measured using a CIRAS-3 portable photosynthesis system (PP Systems, Amesbury, MA 01913, USA). During measurement, the leaves were placed in a leaf chamber and provided with 1000... Constant PPFD, obtaining net photosynthetic rate (Pn), intercellular... Concentration (Ci), stomatal conductance (Gs), and transpiration rate (Tr) were measured. Fluorescence parameters were also measured using a plant efficiency analyzer (PEA) (Hansatech Instruments Ltd., King's Lynn, UK). Leaves were subjected to a 30-minute dark treatment before measurement to stabilize the fluorescence signal. The maximum photochemical efficiency (Fv / Fm) was finally determined. The above results are as follows: Figure 4 As shown.

[0044] Results analysis: Total chlorophyll content ( Figure 4 A) Significant differences were only observed at day 20, with the DLS group showing significantly higher values ​​than the CK group. Fluorescence parameter Fv / Fm ( Figure 4 B) Throughout the entire experimental period, no significant differences were observed between the two groups, and the values ​​remained above 0.8, indicating that neither group of plants was subjected to significant environmental stress. Changes in photosynthetic parameters are shown below. Figure 4 As shown in C–F: During the first 20 days, the Pn value of the DLS group was generally higher than that of the CK group, but the difference was not significant; the E value of the DLS group was significantly higher than that of the CK group on day 10, and in the subsequent stages, the E value of the CK group was higher than that of the DLS group. There was no significant difference in Ci between the two groups throughout the entire experimental period; the trend of stomatal conductance gs was basically consistent with that of E.

[0045] (4) Determination and analysis of protein content The soluble protein content was determined using the Coomassie Brilliant Blue method (Blakesley and Boezi, 1977). The results are analyzed as follows: Figure 5 As shown, the protein content in the DLS group was significantly higher than that in the CK group, increasing by 23.72% compared to the CK group.

[0046] (5) Energy consumption analysis Light energy use efficiency (LUE) and electrical energy use efficiency (EUE) are calculated using the following formulas (Thimijan and Heins, 1983; Kozai 2013): (1) (2) In the formula: f represents the chemical energy per unit dry matter (20 MJ / kg); D represents the increase in dry matter per unit cultivation area ( PAR represents the cumulative photosynthetically active radiation over the cultivation period ( E represents the cumulative electrical energy input per unit cultivated area. Experimental setup: Planting density 40 plants / m²; 5 LED tubes used, each with a rated power of 25 W; measured PPFD of the system was 250. The power is linearly related to PPFD (Yan et al., 2020).

[0047] Results Analysis: LUE and EUE as follows Figure 6 As shown in A and B, from day 10 onwards, the DLS group maintained the highest efficiency value. At day 30, the DLS group improved by 31.7% in both LUE and EUE compared to CK.

[0048] In summary, compared with the traditional static light strategy, the dynamic light strategy can significantly improve yield and protein content, and improve energy efficiency.

[0049] The above description is merely a preferred embodiment of the present invention. Those skilled in the art can make various corresponding improvements and modifications based on the technical solutions and concepts disclosed in this invention. All such improvements and modifications should be considered within the scope of protection of the claims of this invention.

Claims

1. A method for cultivating lettuce in a plant factory, characterized in that, include: After transplanting, at least three growth stages (S1, S2, and S3) are executed sequentially according to the cultivation cycle. For each stage, a photoperiod and PPFD are set, and the following relationship is satisfied: (1) The optical periods of S1, S2, and S3 decrease sequentially, that is... > > ; (2) The PPFD of S1, S2, and S3 increase sequentially, that is < < ; (3) , , They are located in the intervals of 14–20 h, 14–18 h, and 12–16 h, respectively; , , Located at 150–250, 200–300, and 250–350 respectively Within the range; (4) The cumulative light integral of the entire cultivation cycle is controlled within the preset target range to be comparable to the constant light reference conditions, thereby improving growth yield and quality and reducing energy consumption while maintaining a comparable light integral.

2. The cultivation method according to claim 1, characterized in that, S1, S2, and S3 correspond to the 20%–40%, 30%–40%, and 20%–40% periods of the cultivation cycle, respectively.

3. The cultivation method according to claim 1, characterized in that, The photoperiod and PPFD for each stage are as follows: S1 is 17–18 h and 175–250. S2 is 15.5–16.5h and 225–300 S3 is 14.5–15.5h and 275–350. .

4. The cultivation method according to claim 3, characterized in that, S1, S2, and S3 correspond to days 1–10, 11–20, and 21–30 of the cultivation cycle, respectively.

5. The cultivation method according to claim 1, characterized in that, The LED light source is used, which includes at least red light with a center wavelength of 660nm and blue light with a center wavelength of 450nm, with a red-blue light power ratio of 8:

2.

6. The cultivation method according to claim 5, characterized in that, The vertical distance between the LED light source and the lettuce canopy is 10–15 cm, and is adjusted periodically according to the growth stage of the plant to maintain the measured PPFD of the canopy within the target range of the corresponding stage.

7. The cultivation method according to claim 1, characterized in that, Planting density should not exceed 40 plants / m² 2 .

8. The cultivation method according to claim 1, characterized in that, Environmental parameters include: air temperature 21±2℃, relative humidity 70%–80%. The concentration is at natural levels. Irrigate with the nutrient solution every 2–3 days. The pH is 5.8–6.0 and the conductivity is 1.8–2.2 mS / cm.

9. The cultivation method according to claim 1, characterized in that, The constant illumination reference conditions include a photoperiod of 15–17 hours and a PPFD of 225–275. One or more groups.

10. A lighting control system for a plant factory, characterized in that, include: LED lighting components are used to output red and blue light and provide target PPFD at each stage; The controller is electrically connected to the LED lighting components and stores a stage parameter table, which includes the target light period and target PPFD range for each of S1, S2 and S3, as well as the target range of cumulative illumination integration. The sensing and recording unit is used to collect PPFD at the canopy, the cumulative PPFD of the day, and the phase CLI, and to record the running data according to the set step size; The controller is configured to synchronously execute the decrease of optical period and the increase of PPFD during phase switching, and to trigger closed-loop compensation for optical period or PPFD based on the deviation of the cumulative PPFD of the day from the threshold in any phase, so as to keep the cumulative illumination integral of the whole cycle within the target range.

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