Jun 29, 2018
Light is essential for plants as a source of energy for photosynthesis and the accumulation of organic matter. Green plants containing chlorophyll are able, with the help of radiant energy, to synthesize and accumulate organic substances and form fruits. The formation of chlorophyll, vitamins, enzymes and other substances that play an important role in the life of plants depends on the intensity of illumination and its spectral composition. Especially important for plants is the visible region of the spectrum of solar radiation, which is called photo-synthetically active radiation. In its composition, red, orange, blue and violet rays have the greatest influence on plants. It is the intensity of active radiation that determines the yield of vegetable crops.
Sunlight consists of visible and invisible rays. Especially important are visible rays, which take part in photosynthesis, photoperiodic reactions, movement of substances in the process of growth and development of plants. Most of the energy necessary for the flow of photosynthesis is provided by the
Vegetable plants react unequally : intensity of light, its spectral composition, duration of daylight. With increasing light intensity, photosynthesis and accumulation of organic matter intensify, the development of plants accelerates, in cloudy weather, on the contrary, sugars and dry substances accumulate poorly. For most plants, the optimal illumination is about 20-30 thousand lux.
In the open ground for their growth and development, plants use only solar energy. In sheltered ground, plants are sometimes grown with refreshing or completely under artificial lighting.
Fruit cultures of the families of pumpkin, nightshade, legumes are the most demanding for light intensity;less demanding - cabbage, root crops, onion and green crops.
On demanding light intensity sufficient for the formation of productive organs, vegetable plants are divided into the following three groups:
- strongly demanding for light - tomato, pepper, eggplant, cucumber, corn, beans, peas, melon, watermelon, pumpkin;
- medium-light to light - garlic, onion, cabbage, root vegetable crops, spinach, perennial crops;- lightly demanding light - outgrowing cultures: onions, parsley, celery, sorrel, asparagus, chicory, lettuce, in which the leaves are formed even in very low illumination due to the supply of nutrients in the underground part of the plant( bulbs, root crops, rhizomes).
Less demanding light exposure may suffer from excessive exposure to thermal rays in the spectrum, resulting in reduced assimilation and deterioration in product quality. To improve the quality sometimes obscure the individual organs of plants: in cauliflower - the head, asparagus and leek grow productive organs.
Vegetable plants that form vegetative productive organs in the form of root crops, rhizomes, bulbs, when growing seeds from them, need good lighting, and when forcing out in winter they can grow with a lack of light, sometimes even without it.
The ratio of time during which a plant receives solar energy( day) and processes it( night) is called a photoperiod. By the length of the day, vegetable crops are not the same. For vegetable plants, the duration of illumination is important. By reaction to the length of the day, vegetable plants are divided into three groups:
1. Long day plants - cabbage( species), parsnip, rutabaga, radish, radish, carrots, parsley, onions, lettuce, sorrel, spinach, dill, vegetable peas, beet, turnip - of the northern origin, in conditionsFor a prolonged daylight hours, they quickly proceed to the formation of generative organs, begin to blossom and bear fruit.
2. Short day plants( pumpkin), pumpkin, cucumber, pepper, eggplant, tomato varieties, corn, zucchini, patisson, beans. The factor of darkness is necessary at the beginning of their life( vegetation), and in the future they can successfully develop and bear fruit in a long day.
3. Neutral to the length of the day plants - watermelon, asparagus, some varieties of tomato, cucumber, peas, beans, bred in the temperate and northern latitudes of the country. These cultures do not react to the change in the length of the day, that is, the period of the plant's receipt of solar energy.
By adjusting the length of a daylight, it is possible to exert the necessary effect on crops. Lengthening or shortening the light day, you can change the timing of flowering of vegetable crops and get higher yields. So that there is no rifling and blossoming, for a radish, lettuce, spinach, onion grown on greens in the open ground, artificially create a shorter day. For this purpose, light frames of wire or thin wooden slats are installed on the ridges and at certain hours attached to them material that does not allow light, thus creating a semblance of a screen.
To shorten the light day, the plants in the beds are usually closed from 20 to 8 hours the following day. In the morning, the material is removed from the frame and the plant turns from shading into full sunlight. In late sowing, when the duration of the day decreases, lettuce, radish, onions on the green leaf do not bloom and yield good yields.
Light is the most difficult to control factor in the complex of the main conditions of plant growth. The light regime at the site can be regulated by observing the timing of sowing, its optimum density, timely weeding of weeds and thinning of plants in the nest, since adverse lighting conditions can be created with large thickening of plants and shading with weeds. The higher the air temperature, the more quickly the plants react to the lack of light. To maximize the use of solar energy in growing vegetable crops, the ridges should be placed where possible in the most illuminated southern and south-western parts of the site.
In the protected ground it is quite possible to regulate the light mode. When there is a lack of lighting, use the lightening with the help of various light sources or to shade the plants at certain hours of the day to create a shorter day. In addition, it is possible to grow plants completely under artificial lighting. Especially you should carefully monitor the light regime when growing seedlings in a closed ground. Weak illumination at high air temperature affects the plants negatively: the degree of assimilation decreases, the consumption of plastic substances on breathing increases, and as a result the quality of seedlings, especially in light-loving plants, decreases, it becomes pale, elongated.
Excessive thickening of crops reduces their illumination, which adversely affects the development of plants, and then on the harvest of vegetables and the speed of production.
The period after emergence is the most important moment when growing seedlings in protected soil. It is at this time, as a result of the consumption of seed nutrients, that plants are most in need of light. Insufficient lighting also affects the root system: in shaded plants, it develops worse than plants that receive enough light.
To maximize the use of solar energy for growing vegetables in sheltered soil, greenhouses are placed on the southern slope of the site.