Medium-free cultivation method for pasture in low-light-intensity environment

Abstract

The invention discloses a medium-free cultivation method for forage grass in a low-light-intensity environment, the cultivation method comprises five steps of seed treatment and initiation, sowing, germination acceleration, planting in a growing period and harvesting, the method cancels a planting medium, uses a planting disc without holes at the bottom, reduces the material investment of forage grass water culture, and improves the yield of forage grass water culture. The labor input of the pasture hydroponics in the steps of sowing, harvesting, planting plate cleaning and the like is reduced; forage grass is planted by using lower light intensity, so that the electricity expenditure for forage grass production is saved, the forage grass cellulose content is reduced, the forage grass protein content is improved, and the palatability of forage grass is better; a running water planting mode is adopted, conventional spraying irrigation is abandoned, the environment humidity is lower, and the disease and pest propagation capacity and the facility and equipment damage risk are reduced.

Description

Technical Field

[0001] The present invention relates to a medium-free cultivation method for forage grass in a low light intensity environment, and belongs to the field of soilless cultivation. Background Art

[0002] With the continuous development of China's animal husbandry, the gap in feed supply is constantly expanding. Traditional breeding relies on natural forage grass, which is greatly affected by natural environmental factors, with unstable quality, uneven yields in different seasons, and severely restricts the development of animal husbandry. During the forage grass growing season, farmers usually adopt the methods of free-range grazing in wild pastures or cutting forage grass for centralized penning; during the forage grass withering season, farmers harvest and reserve forage grass in advance for livestock to eat. Natural forage grass is greatly affected by natural environmental factors, with unstable yields and quality in different seasons, and severely restricts the development of animal husbandry.

[0003] Traditional artificial forage grass is cultivated using substrates, with a large amount of preparatory work in the early production stage. Single-layer planting results in relatively low yields per unit area. During the production process, there is a lack of facility protection, and the quality of forage grass is easily interfered by the external environment and pests and diseases, with low production efficiency and unable to meet the feed demand of animal husbandry.

[0004] Plant factories have the characteristics of three-dimensional planting, controllable environment, and annual production, and are very suitable for the hydroponic cultivation of artificial forage. In recent years, the hydroponic cultivation of forage has developed rapidly. In the initial stage, it borrowed the cultivation methods of other edible vegetables in plant factories, including top spraying, strong light irradiation, perforated planting trays, etc. However, in the actual cultivation process, it was found that there are relatively large differences in the planting methods between hydroponic forage and edible vegetables. Completely copying them easily leads to a decline in forage quality and consumes a large amount of manpower and material resources. The forage cultivation in plant factories generally adopts a high-density and short-cycle cultivation mode. The selection of sowing medium and sowing tray is one of the difficulties in hydroponic forage cultivation. For example, when cultivating edible vegetables, the top spraying irrigation method is adopted, and the cultivation area is humid for a long time, which easily leads to short circuits in equipment circuits and damage to supplementary lighting lamps, posing a risk of production accidents; when using perforated planting trays for tender sprouts, it is convenient for the roots of seeds to pass through the planting trays and contact the nutrient solution. The cycle of tender sprouts is longer, and the roots are not harvested as the edible part, so perforated planting trays are applicable. However, hydroponic forage is usually cultivated by using a moisturizing medium such as gauze in combination with a cultivation device such as a bottom-hollowed planting tray. The consumption of the moisturizing medium is large, and the treatment and recycling of waste media are difficult, which is not conducive to the sustainable development of hydroponic forage; the roots of forage are tightly wound around the bottom hollow of the planting tray, which is difficult to clean and easily causes damage to the planting tray. The growth cycle of forage is short, the roots are edible, and the planting scale is large. Therefore, convenient harvesting is required, and perforated planting trays cannot meet the actual hydroponic needs. Conventional hydroponic cultivation of forage uses strong light, consumes a large amount of electricity, the forage ages quickly, the fiber increases, the palatability is poor, and the tips of the forage are prone to drying out and the quality declines in the later growth stage. Moreover, strong light requires high waterproof performance for lamps and facilities and equipment. There are many problems such as complex forage cultivation techniques, fine production management requirements, difficult recycling of waste media, large power consumption, high costs, and large labor input, which restrict the popularization and application of hydroponic forage in plant factories. Summary of the Invention

[0005] In view of the above problems existing in the prior art, the object of the present invention is to obtain a medium-free cultivation method for forage in a low light intensity environment.

[0006] To achieve one of the above-mentioned invention objects, the technical solution of the medium-free cultivation method for forage in a low light intensity environment adopted by the present invention is as follows:

[0007] The medium-free cultivation method for forage in a low light intensity environment of the present invention includes the following steps:

[0008] a) Seed treatment and priming

[0009] Soak the seeds in warm water at 45 - 65 °C for 5 - 25 min, dry them after priming with a priming agent for later use; before sowing, soak the seeds in normal temperature RO water for 6 - 12 h, and rub and wash the seeds 3 - 5 times;

[0010] b) Sowing

[0011] Put the seeds cleaned in step a) into a planting tray with no holes at the bottom and uneven surface, and plant them evenly without medium. The total seeding density is 48,000 - 100,000 seeds / m 2 , and cover the seeds in the planting tray with 2 - 5 layers;

[0012] c) Germination acceleration

[0013] Spray water on the seeds evenly planted in step b) until they are in a moist state. The germination acceleration temperature is 23 - 28 °C, the humidity is 70% - 100%, and after 24 - 48 h of dark germination acceleration, the forage grass germinates. Continue dark germination acceleration or place it in a dark environment for 12 - 24 h, then take it out and spray water to keep it moist;

[0014] d) Planting during the growth period

[0015] The forage grass after germination acceleration is hydroponically planted with a low light intensity of 50 - 200 μmol / m 2 / s; put the planting tray into the nutrient solution tank, and the nutrient solution tank adopts the way of flowing water planting. The liquid level of the hydroponic nutrient solution is in a state of submerging the roots and being flush with the convex part of the planting tray; the air temperature during the light period is 20 - 25 °C, and the air temperature during the dark period is 16 - 20 °C; the air humidity is 10 - 100%, the light duration is 14 - 18 hours per day, and the carbon dioxide concentration is 350 - 1200 ppm; the EC value is 0.5 - 2.0, the nutrient solution temperature during the light period is 20 - 25 °C, and the nutrient solution temperature during the dark period is 16 - 24 °C;

[0016] e) Harvesting

[0017] Harvest the whole tray of forage grass that has grown for 7 - 15 days. After harvesting, soak the planting tray for disinfection, rinse and dry it for later use.

[0018] Preferably, the initiator includes potassium nitrate or calcium chloride solution.

[0019] During seed treatment and priming, since the hydroponic seeding of forage grass is dense and the amount of seeds used is large, it is very easy to cause the spread of diseases. To ensure product quality, it is necessary to conduct pre-sowing treatment on forage grass seeds to reduce the growth of germs during the growth period. Soak the seeds in warm water at 45 - 65 °C for 5 - 25 min, which can effectively kill the germs carried by the seeds. To improve the seed vigor and the emergence uniformity rate, use initiator solutions such as potassium nitrate and calcium chloride for seed priming, control the seeds to slowly absorb water, make the seeds stay in the second stage of water absorption, complete the physiological and biochemical metabolism and repair of pre-germination. After the priming is completed, the life activities required for germination inside the seeds are vigorous, and the seeds are dried again for later use. Before sowing, soak the seeds in normal temperature RO water for 6 - 12 h to make the seeds fully absorb water inside, promote the rapid germination of the seeds. Finally, rub and wash the seeds 3 - 5 times to remove the mucus secreted on the seed surface and keep the seed surface clean.

[0020] Preferably, the planting tray is a planting tray with side openings and a sealed bottom surface. The side openings are generally 1-10, and the number of openings is determined by the diameter of the openings.

[0021] Furthermore, the bottom of the planting tray is provided with uneven partitions or separated by fences, and the height difference of the uneven partitions or fence divisions is 2-5 mm.

[0022] More preferably, there are no requirements for the shape, direction, or number of the concave and convex settings, as long as a high area utilization rate is guaranteed, including but not limited to the following schemes: ① The square grid lines are raised, and the area enclosed by the grid lines is concave for sowing; ② The circular grid lines are raised, and the other areas are concave for sowing; ③ Parallel to the width direction, the strips are raised, and the strips are concave for sowing; ④ Parallel to the length direction, the strips are raised, and the strips are concave for sowing; ⑤ Origami shape, with convexity at the peaks and concave at the valleys for sowing.

[0023] Protrusions of other geometric shapes derived from the present invention should also fall within the protection scope of the present invention. Protrusions of a single shape and a combination of protrusions of different shapes can be used, as long as the protrusions provided in the planting tray can meet the planting needs.

[0024] After the initiation treatment and soaking, the internal life activities of the forage seeds are vigorous and need to be sown as soon as possible. In order to prevent the roots of the forage from penetrating the planting tray, a planting tray with no holes at the bottom is preferred. After sowing, the seeds are loosely piled up and easily slide during transportation, resulting in uneven seed distribution. It is preferred to have a planting tray with an uneven bottom or grids, and the planting tray is divided into several small pieces. After sowing, the seeds in the concave areas are blocked by the protrusions, and the excess seeds on the top are unobstructed. With continuous shaking, they are dispersed to the surroundings until all the concave areas are filled. The evenly distributed seeds are distributed in all areas of the planting tray, and the number of seeds in each area differs by less than 20%. It can not only solve the problem that the seeds tend to be distributed on one side after shaking the flat and smooth planting tray, but also prevent the accumulation of water on one side due to the uneven germination and planting equipment. It can also be multi-layered stacked for germination, improve the utilization efficiency of the germination box, and reduce the intensity of manual management.

[0025] Forage grass plants are slender and weak, and are prone to lodging, which affects the normal growth of forage grass. In order to prevent the lodging of forage grass seedlings, further improve production efficiency and reduce production costs, plant factories should increase the sowing density as much as possible on the basis of ensuring yield and quality. The total sowing density is 48,000-100,000 seeds / m 2(Seed covering planting tray, 2 - 5 layers). Conventional planting techniques require the use of media such as gauze for sowing. The seeds adhere closely to the gauze and are not easily movable, with very high requirements for sowing uniformity. This patent adopts a media - free sowing mode. After sowing, simply shaking the sowing tray can evenly distribute the seeds, saving time and effort. The use of a culture tray with no holes at the bottom and a cultivation method of harvesting with roots ensures the possibility of high - density planting, reduces the lodging of forage grass, and increases the yield of forage grass.

[0026] During germination, to place the seeds in a suitable germination environment, avoid seed floating, movement, and oxygen - deficient rotting, after sowing, evenly spray water to ensure that the seeds are moist but not waterlogged. In the hydroponic germination of forage grass in plant factories, materials such as plastic film are usually used for covering or irregularly spraying water for moisture retention, which is time - consuming and laborious. In this solution, to save germination materials and simplify the germination process, the planting trays are stacked layer by layer. Utilizing the characteristics of the bottom of the planting tray being uneven or having grids to closely fit but not squeeze the seeds, it ensures that the seeds are in a closed and moist micro - environment during germination. By extending the germination time, promoting the rapid entanglement of the forage grass roots, and avoiding seed displacement caused by external impacts, set the germination temperature at 23 - 28 °C, humidity at 70% - 100%. After 24 - 48 h of dark germination, the forage grass begins to germinate. To avoid seed displacement caused by collision and vibration during seedling tray handling and water flow impact after placing it in the planting trough, continue dark germination or place it in a dark environment for 12 - 24 h. This dark environment has no requirements for temperature and humidity, and it can maintain the original conditions or be adjusted to existing conditions that can ensure the continuous growth of the roots. At this time, the roots grow rapidly, spread, and entangle with each other to form a whole, and external impacts are not sufficient to affect the whole forage grass. The adjusted germination process can promote the entanglement of the forage grass roots before exposure to light, making the seeds not easily movable, facilitating the handling of seedling trays and coping with water flow impacts. After germination is completed, transfer the forage grass to the cultivation area.

[0027] Preferably, the total time of dark germination and / or dark environment in the germination step is 48 h - 72 h.

[0028] During the growth period, the improved planting method of the present invention combines low light intensity with media - free flowing water. The forage grass grown after hydroponic germination with a low light intensity of 50 - 200 μmol / m 2 / s is placed in a nutrient solution tank. The nutrient solution tank adopts flowing - water planting, with the water flow velocity ≤ 5 m / s, and it is changed approximately once every 2 - 7 days. The replacement standard of the nutrient solution is to add nutrient solution when the EC or pH value of the nutrient solution is lower than the set value, and just replace it in a timely manner to ensure the growth needs of the forage grass.

[0029] The main cultivation environment parameters during the growth period are as follows: the air temperature during the light period is 20 - 25°C, and the air temperature during the dark period is 16 - 20°C. The air humidity is 10 - 100%, the light duration is 14 - 18 hours per day, and the carbon dioxide concentration is 350 - 1200 ppm. The EC value is 0.5 - 2.0, the nutrient solution temperature during the light period is 20 - 25°C, and the nutrient solution temperature during the dark period is 16 - 24°C. The original light intensity for forage cultivation was borrowed from the relatively high light intensity of 250 - 350 μmol / m 2 / s for leafy vegetable growth, which led to the rapid growth of hydroponic forage, making it extremely easy to be too close to the lights, resulting in yellowing and withering of the leaf tips and affecting the normal growth of the forage. In addition, the relatively strong light intensity is likely to cause too high a cellulose content in hydroponic forage and a reduction in the content of nutrients such as protein, resulting in poor palatability of the forage and a decline in economic benefits. This cultivation scheme uses a lower light intensity (50 - 200 μmol / m 2 / s) for hydroponic forage, which can not only greatly reduce the electricity cost for supplementary lighting, but also make the forage tender, juicy, with good palatability, and higher contents of polysaccharides and proteins, and can be directly fed to livestock or stored after drying.

[0030] Moreover, in the early stage, hydroponic forage was usually planted using water-absorbing media such as gauze. The consumption of the media was large, the recycling and treatment were difficult, and it had a greater impact on the ecological environment. In addition, the forage roots were tightly wound around the media, and a large amount of manpower was required for both pruning and harvesting or tearing and harvesting methods, resulting in serious forage losses. Recently, the forage spraying hydroponic mode has developed rapidly. The disadvantage of this method is that it causes the cultivation area to remain in a high humidity state for a long time, which is prone to the spread of various pests and diseases, and this method has higher waterproof performance requirements for facilities and equipment such as lamps, otherwise it is easy to cause production accidents such as short circuits. This scheme uses the method of flowing water cultivation in a nutrient solution tank, and the nutrient solution only submerges the forage roots, which can reduce the humidity of the cultivation area and avoid production accidents. To ensure the normal growth of forage leaves and roots and avoid the growth of green algae or the penetration of roots through the planting tray, after the germination of the forage is completed, the forage is taken out and the nutrient solution is added. It is preferably to use a scheme of a planting tray with a small number of holes on the side and a sealed bottom. The planting tray is placed in the nutrient solution tank, and the liquid level of the nutrient solution is adjusted to a state where it submerges the roots and does not submerge the forage stalks.

[0031] The main improvement of the present invention lies in the protection of the forage medium-free flowing water cultivation method. Therefore, the spectral ratio of the low light intensity and the formula of the nutrient solution are not within the protection scope of the present invention. The LED spectral ratio of the present invention is set with reference to Patent CN201910270563.5, and the nutrient solution formula is prepared with reference to Patent CN201910989303.3.

[0032] Harvesting is the last step in forage cultivation. However, this step is inefficient and costly when cultivating in the original medium. The forage of the present invention grows rapidly in a low light intensity environment and can be harvested 7 - 15 days after being planted under a lamp. At this time, the roots of the forage are tightly intertwined, and all the forage forms a whole, allowing the forage with roots to be easily separated from the planting tray. When planted using this method, the harvesting efficiency is greatly improved, there is no yield loss, and it can meet the product requirements of livestock practitioners for harvesting the entire tray of forage. After harvesting, there is no impurity residue on the planting tray. It only needs to soak the planting tray for disinfection, rinse and dry it before it can be used again.

[0033] Compared with the prior art, the present invention cancels the planting medium in forage hydroponics for the first time, breaking through the dependence on the planting medium in traditional forage hydroponics. It uses a planting tray without holes at the bottom, reducing the material input in forage production and the labor costs in links such as sowing, harvesting, and cleaning. Combined with planting in a low light intensity environment, it reduces the power consumption in forage production, improves the quality and palatability of the forage, and solves the problems of large production materials, supplementary lighting power, and high labor input in forage planting in plant factories. On this basis, the germination promotion process is adjusted to make the roots of the forage intertwined before exposure to light, the seeds are not easy to move, facilitating the handling of the seedling tray and coping with the impact of water flow. The method of flowing water planting is used to avoid problems such as the spread of pests and diseases and damage to facilities and equipment caused by high humidity in the environment due to spray irrigation. The environmental humidity is lower, the ability to spread pests and diseases and the risk of damage to facilities and equipment are reduced, and the problems that are not conducive to industrial promotion such as complex forage cultivation technology and fine production management in plant factories are completely solved. Description of the Drawings

[0034] Figure 1A It is a planting process diagram of barley grass provided by the present invention planted in gauze + planting tray A;

[0035] Figure 1B It is a planting process diagram of barley grass provided by the present invention planted in cotton felt + perforated partition + planting tray B;

[0036] Figure 1C It is a planting process diagram of barley grass provided by the present invention planted in no medium + planting tray C;

[0037] Figure 2 It is a diagram showing four planting trays provided by the present invention, including circular protrusion A, square grid line protrusion B, origami shape protrusion C, and strip protrusion D;

[0038] Figure 3 is a schematic diagram of the use of the circular protrusion planting tray provided by the present invention, including illustration A of evenly distributed forage seeds, stacked illustration B for use with a germination box, and illustration C for use with a nutrient solution tank. Detailed Embodiments

[0039] The following further elaborates and completely describes the method for soilless cultivation of forage grass in low light intensity environments provided by the present invention in conjunction with embodiments. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as a limitation of the present invention.

[0040] In the experimental methods in the following embodiments, unless otherwise specified, they are all conventional methods. Unless otherwise specified, the experimental materials used in the following embodiments are all obtained through market purchase.

[0041] Example 1

[0042] Study the effect of different media on yield. Soak barley grass seeds in 65°C warm water for 25 minutes and perform seed priming with a 2% potassium nitrate solution. Before sowing, soak the seeds in normal temperature RO water for 12 hours, rub and wash the seeds 5 times, and the sowing density is 100000 seeds / m 2 (The seeds cover 5 layers of the planting tray). Keep the temperature at 28°C and the humidity at 100%. After dark germination for 72 hours, take out and spray water to keep moist. The main cultivation environment parameters during the growth period are as follows: the air temperature during the light period is 25°C, and the air temperature during the dark period is 20°C. The air humidity is 100%, and the carbon dioxide concentration is 1200 ppm. Use different media for planting (gauze + planting tray A, cotton felt + perforated partition + planting tray B, soilless + planting tray C). The LED spectrum ratio is set with reference to Patent CN201910270563.5, the light intensity is 100 μmol / m2 / s, and the light duration is 18 h / d. The EC value is 2.0, the nutrient solution temperature during the light period is 25°C, and the nutrient solution temperature during the dark period is 24°C. The nutrient solution formula is prepared with reference to Patent CN201910989303.3, and the nutrient solution level is adjusted to submerge the roots and be flush with the protrusions of the planting tray. Harvest after 15 days of planting under the lamp.

[0043] Table 1 Effect of different media on yield

[0044]

[0045] The results are as Figures 1A - 1C shown in Table 1. The roots of barley grass are closely intertwined with the gauze or cotton felt and are difficult to separate. The harvesting time of barley grass planted using the soilless method is significantly shortened, and the production efficiency is significantly improved.

[0046] Example 2

[0047] Study the effect of different germination times on yield. Soak barley grass seeds in 55°C warm water for 15 minutes. Before sowing, soak the seeds in normal temperature RO water for 10 hours, rub and wash the seeds 4 times, and the sowing density is 80000 seeds / m 2(4 - layer seed - covering planting tray). Keep the germination temperature at 25 °C, humidity at 90%, and in a dark environment. Set the germination times for 5 treatments: 24h, 48h, 60h, 72h, and 84h. After dark germination, take them out and place them in the light for growth. The cultivation environment parameters during the growth period are as follows: the air temperature during the light period is 23 °C, and the air temperature during the dark period is 18 °C. The air humidity is 50%, and the carbon dioxide concentration is 700 ppm. The LED spectrum ratio is set with reference to Patent CN201910270563.5, the light intensity is 50 μmol / m 2 / s, and the light duration is 16h / d. The EC value is 1.0. The nutrient solution temperature during the light period is 23 °C, and the nutrient solution temperature during the dark period is 20 °C. The nutrient solution formula is prepared with reference to Patent CN201910989303.3, and adjust the nutrient solution level to submerge the roots and be flush with the raised part of the planting tray. Harvest after 10 days of planting under the lamp. From the data in Table 2, it can be seen that as the germination time increases, the fresh weight of barley grass increases. Under dark conditions, barley grass grows spindly and its height increases rapidly. After being moved to the light for growth and then carrying out normal photosynthesis and growth, on the basis of the relatively high height caused by spindly growth, it is easier to obtain high yields. However, the dark germination time cannot be too long. 84h of dark germination has already caused excessive spindly growth of barley grass, resulting in a decrease in yield instead. Therefore, the optimal germination time is 48h - 72h. Another advantage of dark germination is that under the condition of not moving, the roots grow rapidly and entangle with each other, playing a fixing role. When taking out from the germination chamber and placing it on the cultivation rack and adding water, collisions and vibrations during the handling of the seedling tray or the impact of water injection into the planting trough on the seeds will cause the seeds to move and be unevenly distributed, directly affecting the subsequent growth. Therefore, the seeds start to germinate after 48h, and when germinated for 60h, the seeds can stop moving and the seed distribution can be made uniform.

[0048] Table 2 Effects of different germination times on the yield of barley grass

[0049]

[0050] Example 3

[0051] Study the effects of different irrigation methods on the yield. Soak the seeds in 45 °C warm water for 5 min and conduct seed priming with 0.1% calcium chloride solution. Before sowing, soak the seeds in normal - temperature RO water for 6 h, rub and wash the seeds 3 times, and the sowing density is 48000 seeds / m 2(2 - layer seed - covering planting tray). Keep the germination temperature at 23 °C, humidity at 70%, and germinate in the dark for 48 - 72 h, then take out and spray water to keep moist. The main cultivation environment parameters during the growth period are as follows: the air temperature during the light period is 18 °C, and the air temperature during the dark period is 15 °C. The air humidity is 10%, and the carbon dioxide concentration is 350 ppm. The LED spectrum ratio is set with reference to Patent CN201910270563.5, the light intensity is 10 μmol / m2 / s, and the light duration is 14 h / d. The EC value is 0.5, the nutrient solution temperature during the light period is 20 °C, and the nutrient solution temperature during the dark period is 16 °C. The nutrient solution formula is prepared with reference to Patent CN201910989303.3. Adopt different irrigation methods (top spraying + side drainage, side inlet + side drainage, regular liquid supplement + no drainage), adjust the nutrient solution level to submerge the roots and be flush with the raised part of the planting tray, and harvest after 7 days of planting under the lamp.

[0052] Table 3 Effects of Different Irrigation Methods on Yield

[0053]

[0054] As shown in Table 3, when using the methods of top spraying + side drainage and side inlet + side drainage, the harvest yields are relatively high. When using the method of regular liquid supplement + no drainage, the roots turn yellow - black and the growth is restricted, and the yields of alfalfa and barley grass are poor when using this method.

[0055] Example 4

[0056] This example discloses illustrations of four planting trays without holes at the bottom and with partitions, as Figure 2 shown, including circular convexity A, square grid - line convexity B, origami - shaped convexity C, and strip - shaped convexity D. Figure 3 takes the planting tray with circular convexities as an example, showing the illustration A of evenly distributed forage seeds, the stacking illustration B when used with the germination box, and the illustration C when used with the nutrient solution tank.

[0057] Finally, it is necessary to state here that: the above examples are only used to further illustrate the technical solutions of the present invention in detail, and cannot be understood as limiting the protection scope of the present invention. Some non - essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all fall within the protection scope of the present invention.

Claims

1. A medium - free cultivation method for forage grass in low - light intensity environment, characterized in that, the cultivation method only includes forage grass seeds and nutrient solution in the planting tray, and comprises the following steps: a) Seed treatment and priming Soak the seeds in warm water at 45 - 65 °C for 5 - 25 min, dry them after priming with a priming agent for later use; before sowing, soak the seeds in normal - temperature RO water for 6 - 12 h, and rub and wash the seeds 3 - 5 times; b) Sowing Put the seeds cleaned in step a) into a planting tray with no holes at the bottom and uneven surface, and plant them evenly without medium. The total seeding density is 48,000 - 100,000 seeds / m 2 , and cover the seeds in the planting tray with 2 - 5 layers; c) Germination acceleration Spray water onto the seeds evenly planted in step b) until they are in a moist state. The germination - accelerating temperature is 23 - 28 °C, the humidity is 70% - 100%, and after dark germination for 24 - 48 h, the forage grass germinates. Continue dark germination or place it in a dark environment for 12 - 24 h, then take it out and spray water to keep it moist; d) Cultivation during the growth period Use the forage grass grown after low-light hydroponic germination at 50-200 μmol / m 2 / s. Place the planting tray into the nutrient solution tank. The nutrient solution tank adopts flowing water cultivation, with the water flow velocity ≤ 5 m / s, and it is changed about once every 2-7 days. The liquid level of the hydroponic nutrient solution is in a state of submerging the roots and being flush with the raised part of the planting tray; e) Harvesting Harvest the whole tray of forage grass that has grown for 7 - 15 days. After harvesting, soak the planting tray in disinfectant, rinse it, and dry it for later use.

2. The medium - free cultivation method for forage grass in low - light intensity environment according to claim 1, characterized in that, the planting tray is a planting tray with holes on the side and a sealed bottom.

3. The medium - free cultivation method for forage grass in low - light intensity environment according to claim 1, characterized in that, the bottom of the planting tray is provided with uneven partitions or separated by fences, and the height difference of the uneven partitions or fence partitions is 2 - 5 mm.

4. The medium - free cultivation method for forage grass in low - light intensity environment according to claim 3, characterized in that, the bottom concave - convex shape of the planting tray includes: square grid - line protrusions, circular protrusions, strip protrusions, origami - shape protrusions, or a combined protrusion of any two or more of them.

5. The medium - free cultivation method for forage grass in low - light intensity environment according to claim 1, characterized in that, the priming agent includes potassium nitrate or calcium chloride solution.

6. The medium - free cultivation method for forage grass in low - light intensity environment according to claim 1, characterized in that, the following conditions are also included during the cultivation in the growth period: the air temperature during the light period is 20 - 25 °C, the air temperature during the dark period is 16 - 20 °C; the air humidity is 10 - 100%, the light duration is 14 - 18 hours per day, the carbon dioxide concentration is 350 - 1200 ppm; the EC value is 0.5 - 2.0, the nutrient solution temperature during the light period is 20 - 25 °C, and the nutrient solution temperature during the dark period is 16 - 24 °C.

7. The medium - free cultivation method for forage grass in low - light intensity environment according to claim 1, characterized in that, the total time of dark germination and / or dark environment in the germination - accelerating step is 48 h - 72 h.

8. The medium - free cultivation method for forage grass in low - light intensity environment according to claim 1, characterized in that, in the germination - accelerating step, spray water until it is in a moist but non - water - logging state.

9. The medium - free cultivation method for forage grass in low - light intensity environment according to claim 1, characterized in that, when accelerating germination, stack the sowing trays until the roots of the forage grass are entangled and the above - ground part begins to grow or shows slight excessive growth.

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