What are some practical methods for keeping vegetable greenhouses warm in winter?
1. Seedling raising in nutrient pots. Black plastic nutrient pots absorb heat during the day and keep roots warm at night. When seedlings are raised in plastic nutrient pots placed in a sun-facing seedbed, with an outside temperature of around -10°C, the temperature inside the seedbed is 6-7°C and the temperature inside the nutrient pots is around 10°C, so the seedlings can grow slowly without suffering cold damage.
2. Prepare heat-generating nutrient soil. Chicken manure is a hot manure, and cow manure is a manure rich in mucilage with good air permeability. After both are decomposed, take 20% of each and mix with 60% sun-dried soil. This kind of nutrient soil has good heat absorption and heat generation performance, provides a good ecological environment for seedlings, and produces more and longer roots with strong absorption capacity, so the plants are naturally cold-resistant and robust.
3. When transplanting seedlings, irrigate the roots with rooting hormone. Rooting hormone is made by rationally blending several nutrient elements related to root growth, such as calcium, phosphorus and zinc. Calcium determines root thickness, phosphorus determines root number, and zinc determines root growth speed and length. After use, the root system can increase by about 70%, and deep roots increase by 25%. With a well-developed root system, the absorption capacity increases by about 70%, and deep roots increase by 25%. With a well-developed root system, the absorption capacity increases by about 70%, and deep roots increase by 25%. With a well-developed root system, the absorption capacity is strong, so the vines and stems will not be frostbitten due to poor cold resistance caused by lack of water or nutrients.
4. Spray nutrients on the leaves to resist cold. In severe winter, the temperature is low and light is weak, and the root absorption capacity is weak. Spraying photosynthetic micro-fertilizer on the leaves can supplement the nutrient deficiency caused by insufficient nutrient absorption by the roots. Spraying rice vinegar on the leaves can inhibit bacteria and repel insects. Mixed with white sugar and superphosphate, it can increase the sugar content and hardness of the leaf mesophyll and improve cold resistance. After cold damage and gas damage, the leaves become alkaline and shrink; spraying vinegar can alleviate the degree of damage, and a 100-300 times dilution should be used. Use little or no growth hormones to prevent reducing cold resistance.
5. Maintain sufficient water to keep warm and prevent freezing damage. Water has a higher specific heat than air and releases heat slowly. In winter, when the indoor soil moisture content is moderate, the pores and cracks in the tillage layer are fine and dense, the roots are not suspended in air, the soil keeps warm, and the roots are not damaged by freezing. Therefore, seedling freezing damage is mostly caused by lack of water. For this reason, watering sufficiently before winter or choosing good weather (watering is possible above 20°C) and irrigating enough water can prevent freezing damage.
6. Cultivate between rows to keep warm and prevent cold. When the ground is compacted, heat from the daytime is restricted from entering the tillage layer, the soil stores less heat, and in addition the cracks in compacted soil are large and deep with poor aggregate structure, so heat is easily lost in the first half of the night, and the room temperature is low in the second half of the night, easily causing freezing damage. Shallow inter-row cultivation can break the surface and close the cracks, which can both control the heat carried away by groundwater evaporation and preserve soil moisture, keep warm, prevent cold, and protect seedlings.
7. Ventilate repeatedly on sunny days. For a standard greenhouse with good seedling hardening performance, when the outside temperature is around -10°C, the indoor maximum temperature on a sunny winter morning can reach above 32°C. Many people think this is the best period for promoting growth after a long cold spell and that it should not be ventilated. In fact, at this time it should be ventilated repeatedly to narrow the temperature difference between inside and outside, bringing it close to the room temperature of the previous few days, so that the plants slowly adapt to the environment and grow robustly, carefully avoiding a day of rapid growth and ten days of cold damage, which can cause seedling shock and freezing damage.
8. Supplement carbon dioxide. The yield-increasing effect ratio of ammonium bicarbonate for crops is 1:1, and the crop requirement ratio of carbon to nitrogen is 30:1. At present, many farmers recognize the yield-increasing effect of nitrogen but ignore the yield-increasing effect of carbon. In winter, greenhouse vegetables are prone to excessive growth and yellowing. One hour after the sun comes out, the carbon dioxide produced by crop respiration at night and decomposition by soil microorganisms can be absorbed, and by around 12 o'clock the crops are in a state of carbon starvation. When the temperature is high, the greenhouse film can be opened and closed repeatedly to let in outside carbon dioxide, improving resistance and yield. When the temperature is low, keep the greenhouse closed and artificially supplement carbon dioxide, which can enhance the cold resistance of crops and greatly increase yield.
9. Cover with straw mats in time to keep warm. Generally the wall body is 1 m thick. It absorbs heat and stores warmth during the day and releases energy at night, accounting for 50%-60% of the indoor total; soil heat absorption and release accounts for 20%-30%; and heat stored in the space accounts for 20%-30%. According to winter and that day's temperature, 1 hour after covering with straw mats the room temperature may be maintained at around 18°C. If it is above 18°C, cover later; if below 18°C, cover earlier.
10. Hang reflective film on the back wall to increase temperature. In winter production of greenhouse vegetables, they are not afraid of cold, but of light deficiency and continuous cloudy days. Therefore, around the winter solstice, hang a strip of plastic film on the back wall for reflection, which can increase the light intensity of the growing bed, allow the heat stored in the wall to be slowly released indoors at night, maintain a relatively high temperature in the second half of the night, and prevent freezing damage to seedlings.