For the germination of vegetable seeds, firstly the seeds themselves have the ability to germinate, and secondly, they require suitable environmental conditions, including temperature, oxygen, and moisture.
(1) Intrinsic conditions for seed germination The intrinsic conditions for seed germination mainly refer to two aspects. First, the seed itself has the ability to germinate (germination potential), that is, the seed is alive rather than dead.
Second, seeds can germinate when given the conditions required for their germination. Therefore, whether it is direct seeding or seedling raising, it must be a viable seed. However, many vegetable crop seeds (such as onions, leeks, etc.) have a short seed life. When they are stored indoors for more than one year, they almost lose their ability to germinate. Therefore, for vegetable crops with short seed life, use new seeds for sowing, and try not to use stale seeds.
Even for vegetable crops with a long seed life, such as tomatoes and cabbage, it is best to check the germination rate before planting. On the other hand, even if some vegetable seeds are vigorous and given suitable germination conditions, they sometimes still do not germinate. This situation is called dormancy. In order to enable the seeds to germinate and emerge smoothly after sowing, the seeds with dormant characteristics are Before sowing, measures should be taken to relieve its dormancy.
(2) External conditions for seed germination. Seeds have high requirements for environmental conditions during the germination process. Under suitable conditions, seeds can germinate quickly and grow strong seedlings in a short period of time. If it cannot be satisfied, it will affect the quality of seed germination to varying degrees.
Adequate moisture, suitable temperature and sufficient oxygen are the three basic conditions (that is, the three elements of germination) essential for seed germination. In addition, light, carbon dioxide and other factors also affect seed germination. ① Moisture.
Moisture is the most basic condition for seed germination. Only after the seeds have absorbed a large amount of water, can the stored nutrients be transformed into substances necessary for life activities.
Water can also soften the seed coat, increase air permeability, and accelerate the water-absorbing germination of seeds. Before the seeds germinate, they must absorb a certain amount of water.
However, the amount of water absorption and the speed of water absorption are different depending on the type of vegetable, which mainly depends on the structure of the seed coat and the nutrient composition of the seed storage. Generally, seeds with more protein absorb water faster and more, seeds with more starch absorb water slowly and less, and seeds with more fat are somewhere in between.
Seeds with good seed coat permeability will absorb water faster, while seed coats will be dense, while seeds with poor water permeability will absorb water slowly. The seed coats of cruciferous, leguminous, tomato, cucumber and other vegetable seeds have better water permeability; the seed coats of vegetable seeds such as Umbelliferae, eggplant, pepper, watermelon, wax gourd, bitter gourd, onion, and spinach are more difficult to permeate.
Therefore, the time should be reasonably controlled according to these characteristics when soaking the seeds; if the swelling time is too long, it will cause the nutrient extravasation of the seed and the decline of the seed vigor. In addition, the germination rate of vegetable seeds is closely related to the soil moisture content after sowing. The soil moisture content should be grasped according to the type of vegetables.
②Temperature. The seeds require an appropriate temperature during germination.
The lowest, highest and most suitable temperature for seed germination of different vegetable species are different. Generally, temperature-loving vegetables (melons, solanaceous fruits and some beans) require a higher temperature, the suitable temperature is 20~30℃, the highest temperature is 35~40℃, and the lowest temperature is 10℃.
The suitable temperature for germination of cold-tolerant and semi-cold-resistant vegetables (cabbage, cabbage, mustard greens, etc.) is 15~25°C, the highest temperature is about 30~35°C, and the lowest temperature is 0~4°C. However, most vegetable seeds can germinate well within the range of 15-30°C. Among them, some vegetable seeds have a wider temperature range suitable for germinating, such as cabbage vegetables; some are narrower, such as lettuce.
Under normal circumstances, within a suitable temperature range, the seed germination rate is higher and the germination time is shorter. If the temperature is higher than the suitable temperature, although the seeds germinate faster, the quality of the buds is poor (some vegetable seeds cannot germinate when the temperature is higher than the suitable temperature, especially lettuce and celery seeds); and if the temperature is lower than the suitable temperature, the seeds The germination time is prolonged and the germination rate is also low (even causing seed rotten when the humidity is high), and the seedling growth is relatively weak.
Some kinds of seeds do not germinate well under constant temperature conditions as well as under variable temperature conditions. For example, eggplant is a typical vegetable crop that needs to change temperature to germinate well. The best germinating effect is when the temperature difference between day and night is 8~10℃, that is, day temperature. 30°C/night temperature 20°C variable temperature. In fact, after sowing, vegetable seeds are always under a certain temperature difference between day and night.
③Oxygen. Oxygen is an extremely important condition for seed germination.
During the storage of seeds, the respiration is extremely weak and the oxygen demand is small, but when the seeds absorb water to germinate, the respiration is gradually vigorous, so the demand for oxygen increases sharply. If there is no oxygen or insufficient oxygen when the seeds germinate, the seeds will not germinate or even fail to germinate.
If the air permeability is poor during soaking and accelerating germination or the covering soil is too thick after sowing, especially if the seedbed is too wet, the lack of oxygen will cause the seeds to germinate poorly and even cause rotten seeds. Special attention should be paid to this problem after sowing legume vegetables and some melon vegetables.
④Light. The effect of light on the germination of vegetable seeds varies from species to species, but most vegetable seeds are not sensitive to light response during germination.
According to the sensitivity of seed germination to light, vegetable seeds can be divided into three categories: the first category is light-needing seeds, that is, seeds need a certain amount of light when they germinate, and cannot germinate or germinate poorly under dark conditions. Such as cabbage, cabbage, lettuce, celery, carrots, etc.
The second category is phobia seeds, that is, seeds can only germinate under dark conditions, and poorly germinate if there is light. Such as melons, amaranth, green onions, leeks and so on.
The third category is medium-light seeds, which can germinate normally under light or dark conditions. Most vegetable seeds, such as beans, fall into this category.
To understand the effect of light on seed germination, corresponding measures can be taken during sowing or accelerating germination to improve the germination rate and emergence rate of seeds.