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Photosynthesis is the main material basis for the growth, development, and yield formation of vegetable crops. Green leaves convert carbon dioxide absorbed from the air, as well as water and inorganic salts absorbed from the soil, into organic substances through photosynthesis, and store solar energy in the form of chemical energy within them. Photosynthesis produces organic matter that accounts for 90% to 95% of the total dry weight of vegetable crops; only 5% to 10% of this matter comes from soil and fertilizers. The elements \"carbon\" and \"oxygen\", which constitute the largest proportion of the dry weight of vegetable crops, are primarily obtained from carbon dioxide. It can be seen that carbon dioxide is one of the important factors required for the growth and development of vegetable crops. The concentration of carbon dioxide in the air is about 0.03% (i.e., 300 milligrams per kilogram), with little variation generally. After the sun rises, photosynthesis causes the carbon dioxide concentration in the greenhouse to drop rapidly; by noon it falls to 85 milligrams per kilogram, which is less than one-third of the carbon dioxide concentration in the air outside the greenhouse, and it continues to decline in the afternoon as well. Around noon, both temperature and light intensity reach their peaks, making it the ideal time for photosynthesis. However, at this time the carbon dioxide concentration inside the greenhouse is already very low. In other seasons, this issue can be addressed by ventilation, but during the cold winter months, ventilation causes the temperature inside the greenhouse to drop, thereby affecting the growth of vegetable crops there. At this point, the only way to address the lack of carbon dioxide in solar greenhouses is to apply carbon dioxide fertilization. Using biogas combustion to supply carbon dioxide to vegetable greenhouses not only replenishes the carbon dioxide needed for plant growth but also raises the temperature inside the greenhouses, achieving two benefits at once. Generally, the combustion of 1 cubic meter of biogas produces 0.975 cubic meters of carbon dioxide and releases 21,520 kilojoules of heat. It is better to use a intermittent application method, applying it every 10–15 minutes with a 20-minute interval in between. In winter, it usually starts around 9 o’clock when there is sufficient light, and stopping takes place 30 minutes before airing the space or around 4 p.m. By noon, although the light intensity remains unchanged, the accumulation of photosynthetic products within the leaves leads to a decrease in photosynthetic efficiency; at this point, the application of carbon dioxide can be stopped. Research data show that increasing carbon dioxide levels after planting tomatoes and green peppers yields a significant increase in yield. Tomatoes yielded an average increase of 21.5% compared to the control, while green peppers showed an increase of 36%.