How can the sugar content of thick-skinned melons grown in solar greenhouses be increased?
In recent years, the area devoted to cultivating thick-skinned melons in solar greenhouses has grown larger and larger. Because growers single-mindedly pursue yield, the sugar content of thick-skinned melons is low and prices have fallen. Therefore, how to increase the sugar content of thick-skinned melons has become a key technical measure in cultivation.
1. Choose varieties with high sugar content. Varieties such as Zhuangyuan, Mishijie, Yuanshuai, Xialong, and netted thick-skinned melons from Israel and the Netherlands can all reach a refractometer sugar content of more than 16%, and have good market prospects. When choosing a variety, in addition to considering the variety's tolerance to low temperature, tolerance to weak light, and high-yield characteristics, you should also pay attention to the important indicator of the variety's sugar content.
2. Cleverly arrange the cropping season. Because the fruit development of thick-skinned melons requires high temperature and good light. Only when the daytime temperature reaches 28-32°C, the nighttime temperature is 15-18°C, and the light is around 60,000 lx is it favorable for fruit enlargement and sugar accumulation. Therefore, when thick-skinned melons are cultivated in winter-warm solar greenhouses, it is best to choose the winter-spring season. Taking the Langfang Type 40 greenhouse as an example, it is more suitable to arrange the harvest period from March to June in spring, and to arrange the sowing period in early November of the previous year; the first crop of melons begins to be harvested in March, and the second crop of melons is uprooted in mid-June.
3. Base fertilizer should be mainly coarse fertilizer. For a greenhouse with an effective area of 6 m × 80 m, the application rate of coarse fertilizer is generally 8-10 t.
4. Control the top and promote the bottom to establish good seedlings. From seedling recovery to fruit set, persist in frequent intertillage, generally 4-5 times, and the intertillage depth is best at 2-3 cm.
5. Prune reasonably and keep a single fruit. Elizabeth is generally topped at 25 leaves; after topping, keep 2 secondary vines; after the secondary vines set fruit, select and keep 1 long-round milk melon, and remove round melons and deformed melons. It is best to complete fruit retention and fruit selection within 3-5 days, and strive for uniformity and consistency. Compared with keeping 2 or more melons, keeping 1 melon not only has a sugar content 1-2 percentage points higher, but also has good commercial quality.
6. Increase phosphorus and supplement potassium in the middle and late stages. After entering the fruit enlargement stage, topdressing chemical fertilizer should maintain a balance of nitrogen, phosphorus, and potassium. When most fruits have grown to half-size melons, promptly apply a three-element compound fertilizer; for foliar fertilization, 0.6% potassium dihydrogen phosphate can be used, and 0.6% Baolifeng (produced in Israel) can also be used, once a week, spraying 3-4 times in succession.
7. Widen the temperature difference to increase sugar. After the fruit is selected and retained, especially after entering the fruit enlargement stage, the temperature difference in the greenhouse should be widened as much as possible, keeping 30-32°C during the day for 1-2 hours, 18-15°C in the first half of the night, and 14-12°C in the second half of the night.
8. Avoid heavy watering before harvest. One week before harvest, if the relative soil humidity is less than 60%, a small amount of water can be applied appropriately. If the humidity is between 70-75%, no watering is needed. When the relative soil humidity is above 85%, the sugar content of the fruit will be somewhat affected.