Key Techniques for Improving the Quality of Greenhouse Watermelons
How to Improve the Quality of Greenhouse Watermelons?
(Agricultural Wealth Network) With the adjustment of the industrial structure, the cultivated area of greenhouse watermelons is growing larger and larger. But an accompanying problem is that the taste of greenhouse watermelons has become poorer. How can the quality of greenhouse watermelons be improved? Mainly pay attention to the following aspects:
Increase photosynthetic intensity The level of sweetness in watermelons is mainly determined by the amount of sugars such as sucrose, fructose and glucose, and the formation of these sugars is inseparable from photosynthesis. Therefore, the following measures can be taken to increase photosynthetic intensity. Increase light intensity: choose low-temperature-resistant, anti-aging drip-free greenhouse film, keep the film clean, wipe the film once every 7 days, remove dust on the film, and enhance light transmission. Extend the light duration: this can be achieved through artificial supplementary lighting.
Increase carbon dioxide content Ventilation: after 9 a.m. on sunny days, open the vents for ventilation. When the temperature is low, the vents should be small. Apply more carbon dioxide: horse manure can release carbon dioxide during fermentation, so fresh horse manure can be piled in the greenhouse, 5-6 kg per cubic meter; burning propane produces carbon dioxide, and burning 1.2-1.5 kg of propane in a 600 sq m greenhouse can raise the carbon dioxide concentration in the greenhouse to 0.13%; use a coke carbon dioxide generator, which can release carbon dioxide when the coke is fully burned; place concentrated hydrochloric acid in a corrosion-resistant container, then add a small amount of lime (calcium carbonate) to produce carbon dioxide through a chemical reaction; release dry ice directly in the greenhouse. The period for applying carbon dioxide is mainly during the peak growth stage of watermelons, especially the fruit development stage. The suitable time for application is around 10 a.m., and the concentration is 0.1%-0.5%.
Reduce nitrogen supply After the watermelons expand, nitrogen supply should be reduced and the amount of potassium fertilizer appropriately increased. When applying fertilizer to promote fruit swelling, apply an additional 15-20 grams of potassium sulfate per plant. In particular, the absorption of nitrogen by the plants in the late growth stage of watermelons must be controlled, because if too much nitrogen is absorbed at this time, the quality of the watermelons will be reduced. This is because the watermelons are no longer growing at this time, and the excess nitrogen accumulates in the fruit, which instead worsens the sweetness and flavor of the watermelons. During this period, an increase in side vines is a sign of excessive nitrogen.
Increase the day-night temperature difference Higher daytime temperatures can increase photosynthetic intensity, and lowering the greenhouse temperature after sunset can reduce plant respiration intensity, decrease sugar consumption, and allow more sugar to be stored in the fruit, which is conducive to the accumulation of sugars and improves watermelon sweetness. Strengthening ventilation at night in the late growth stage of watermelons can artificially increase the day-night temperature difference in the greenhouse.
Control watering before harvest From the beginning of fruit development to 2-3 days before harvest, environmental conditions and cultivation measures play a decisive role in watermelon quality. Many watermelon-producing areas have the saying that "dry melons are sweet." If it is dry and rainless before harvest, the watermelons are indeed relatively sweet, while if there is heavy rain before harvest, the watermelons taste bland and not sweet. Therefore, watering should be stopped 5 days before watermelon harvest, which can relatively increase watermelon sweetness.
Increase photosynthetic intensity The level of sweetness in watermelons is mainly determined by the amount of sugars such as sucrose, fructose and glucose, and the formation of these sugars is inseparable from photosynthesis. Therefore, the following measures can be taken to increase photosynthetic intensity. Increase light intensity: choose low-temperature-resistant, anti-aging drip-free greenhouse film, keep the film clean, wipe the film once every 7 days, remove dust on the film, and enhance light transmission. Extend the light duration: this can be achieved through artificial supplementary lighting.
Increase carbon dioxide content Ventilation: after 9 a.m. on sunny days, open the vents for ventilation. When the temperature is low, the vents should be small. Apply more carbon dioxide: horse manure can release carbon dioxide during fermentation, so fresh horse manure can be piled in the greenhouse, 5-6 kg per cubic meter; burning propane produces carbon dioxide, and burning 1.2-1.5 kg of propane in a 600 sq m greenhouse can raise the carbon dioxide concentration in the greenhouse to 0.13%; use a coke carbon dioxide generator, which can release carbon dioxide when the coke is fully burned; place concentrated hydrochloric acid in a corrosion-resistant container, then add a small amount of lime (calcium carbonate) to produce carbon dioxide through a chemical reaction; release dry ice directly in the greenhouse. The period for applying carbon dioxide is mainly during the peak growth stage of watermelons, especially the fruit development stage. The suitable time for application is around 10 a.m., and the concentration is 0.1%-0.5%.
Reduce nitrogen supply After the watermelons expand, nitrogen supply should be reduced and the amount of potassium fertilizer appropriately increased. When applying fertilizer to promote fruit swelling, apply an additional 15-20 grams of potassium sulfate per plant. In particular, the absorption of nitrogen by the plants in the late growth stage of watermelons must be controlled, because if too much nitrogen is absorbed at this time, the quality of the watermelons will be reduced. This is because the watermelons are no longer growing at this time, and the excess nitrogen accumulates in the fruit, which instead worsens the sweetness and flavor of the watermelons. During this period, an increase in side vines is a sign of excessive nitrogen.
Increase the day-night temperature difference Higher daytime temperatures can increase photosynthetic intensity, and lowering the greenhouse temperature after sunset can reduce plant respiration intensity, decrease sugar consumption, and allow more sugar to be stored in the fruit, which is conducive to the accumulation of sugars and improves watermelon sweetness. Strengthening ventilation at night in the late growth stage of watermelons can artificially increase the day-night temperature difference in the greenhouse.
Control watering before harvest From the beginning of fruit development to 2-3 days before harvest, environmental conditions and cultivation measures play a decisive role in watermelon quality. Many watermelon-producing areas have the saying that "dry melons are sweet." If it is dry and rainless before harvest, the watermelons are indeed relatively sweet, while if there is heavy rain before harvest, the watermelons taste bland and not sweet. Therefore, watering should be stopped 5 days before watermelon harvest, which can relatively increase watermelon sweetness.