What are the main reasons for watermelons having little flesh

What are the main reasons for watermelons having little flesh? How should it be prevented?

First, insufficient fertilizer and water supply during the watermelon expansion period. The process of watermelon expansion is a process in which the tissue cells of the rind and flesh continuously increase in number and size. Especially in the flesh part of the watermelon, apart from the seeds and the connected vascular bundles, it is entirely composed of parenchyma cells. After the cell walls of the parenchyma cells expand, if the fertilizer and water supply is insufficient, the cells cannot obtain sufficient water and nutrients, the cell walls rupture, and cavities form.

Second, temperatures that are too low or too high during the watermelon fruit-setting period and fruit expansion period. In the early stage of watermelon development, vertical growth predominates, while in the later stage, horizontal growth predominates. When the temperature in the early development stage of greenhouse watermelons is relatively low (below 20°C), under low temperature or drought and insufficient light, the vertical growth of the fruit will be weakened or even stop prematurely. Then, upon entering the later development stage, when the greenhouse temperature is relatively high (above 35°C) and the light is strong, the horizontal development of the fruit will be very rapid. In this way, the internal growth of the watermelon is unbalanced, and hollow watermelons are easily produced.

Third, improper fertilization during the watermelon fruit-setting period and expansion period, with excessive application of nitrogen fertilizer. The ratio of nitrogen, phosphorus, and potassium absorbed throughout the entire growth period of watermelon is about 3:1:4. Before fruit setting, during the vine extension period and flowering period, the absorption of nitrogen and phosphorus is relatively high, while after fruit setting, potassium absorption predominates. If too much nitrogen fertilizer is applied at this stage, it will cause the plants to grow excessively, with long vines but no fruit, and the photosynthetic products and nutrients of the watermelon will be insufficient, easily causing hollow heart.

Preventive measures: First, water and fertilize reasonably, and avoid drastic changes in soil dryness and moisture. Watering during the watermelon growth period should gradually increase from less to more. Second, control the amount of nitrogen fertilizer and increase the application of potassium fertilizer. When the young fruit is the size of an egg, apply fruit-swelling fertilizer, using 5-10 kg of potassium sulfate or potassium dihydrogen phosphate per mu. Finally, properly regulate the temperature during the watermelon fruit-setting period and fruit expansion period. When the temperature is low in the early stage, take insulation measures such as double-film covering, and control the temperature at 22-25°C during the seedling stage and 25-28°C during the vine extension stage. After entering the fruiting stage, lower the greenhouse temperature to 28-32°C by covering with shade nets, splashing mud slurry, and other measures.