Why are the crops grown in greenhouses not fragrant, melons not sweet, and the flavor is light? Why are there many diseases in greenhouse crops and poor plant disease resistance? Why can't the yield be greatly increased with sufficient water and fertilizer conditions? These problems are basically due to the fact that the concentration of carbon dioxide in the greenhouse air is low, which makes the crops produce carbon dioxide "hunger", which cannot meet the needs of crop photosynthesis.
1. Current status of carbon dioxide planting and application.
At present, China has more than 50 million acres of greenhouses, with an annual output value of about 500 billion yuan, and 80% of the output value is in winter, spring and autumn, because the output value of vegetables in these three seasons is high, but in these three seasons, due to the greenhouse has nearly 5 months of ventilation, the carbon dioxide concentration is insufficient, which seriously restricts the output of vegetables. The carbon and water content in the plant body is as high as 95%, and the nitrogen, phosphorus and potassium content is less than 5%. Over the decades, the application of nitrogen, phosphorus and potassium fertilizers has increased crop yields by more than 50%. In the dry matter of the plant body, organic matter accounts for about 90, and carbon accounts for about 40% of organic matter, which is an element with more content in the plant body. These carbons come from CO2. Therefore, CO2 is of great importance to the biological world.
2. The importance of carbon dioxide.
Carbon dioxide is one of the key factors affecting plant growth, development and function, it is not only a substrate for photosynthesis, but also a regulator of primary metabolic processes, photochemical distribution and growth, and participates in a series of biochemical reactions in plants, which has a direct impact on plant growth. The increase in carbon dioxide concentration can not only significantly improve the photosynthesis efficiency of plants, but also promote plant photosynthesis by expanding the use of light sources. The concentration of carbon dioxide in the air is relatively stable and does not change much, generally 003%--0.04%, when the concentration is below 25, with the increase of temperature, photosynthesis is enhanced, the organic matter created increases, and the crop shows a vigorous growth state; When the temperature exceeds 30, photosynthesis creates the same amount of organic matter as the organic matter consumed by the respiration of the crop, or even less than the organic matter consumed by respiration, and the crop stops growing.
3. Reasons for the lack of carbon dioxide:
In order to meet the needs of heat preservation in winter greenhouse vegetable production, the greenhouse is often in a closed state, resulting in the relative isolation of the air in the greenhouse from the outside air, and the carbon dioxide can not be replenished in time. After sunrise, as the photosynthesis of vegetables accelerates, the concentration of carbon dioxide in the shed drops dramatically, sometimes to the carbon dioxide compensation point (0.).008%--0.01%), vegetable crops can hardly carry out normal photosynthesis, which affects the growth and development of vegetables, causing diseases and reduced yields.
It has been determined that the normal concentration of carbon dioxide in the air is 300-500 ppm, and the plants absorb the carbon dioxide in the atmosphere at any time when they are cultivated in the open air. In the closed greenhouse in winter, in order to maintain a certain greenhouse temperature, a large amount of ventilation and air outside the greenhouse are difficult to communicate, and the crop absorbs carbon dioxide, resulting in the concentration of carbon dioxide in the shed dropping to a critical value, which makes it difficult for crops to have physiological reactions, and normal photosynthesis is difficult for crops, and crops cannot grow normally. Especially in the daytime, after the sun comes out, crops want to photosynthesize, although the light reaches 1000-3000 grams, they begin to absorb a large amount of carbon dioxide, in this period, if carbon dioxide can not be replenished in time, plants will weaken or stop photosynthesis due to lack of carbon dioxide, and it will affect the yield and quality of crops for a long time.
Fourth, countermeasures.
Many modern greenhouses are now equipped with CO2 monitoring points, which allow manual intervention when low CO2 concentrations are detected. The lack of carbon dioxide has proven to be one of the most important limiting factors in the production of greenhouse vegetables. Artificial supplementation of carbon dioxide is an important measure to achieve high and stable production in sheds, and there are currently carbon dioxide generator devices, filled finished carbon dioxide and so on.