Watermelon farming has traditionally relied on direct seeding, but as cultivation techniques and greenhouse technologies have advanced, the practice of transplanting seedlings has become more common. When using seedling transplants, preparing high-quality nursery soil is essential for growing healthy and vigorous plants.
(1) The ideal mix for nursery soil typically consists of 50% loam, 30–35% compost, 15–20% fine sand, and a small amount of wood ash or 1–2 kg of potassium sulfate per cubic meter. This combination ensures good drainage, nutrient content, and aeration, which are all crucial for strong seedling development.
(2) Applying base fertilizer is an important step in watermelon cultivation. Common methods include broadcasting, furrow application, and hole placement. On average, 15–22.5 tons of farmyard manure per hectare is recommended. After spreading, the field is plowed to incorporate the manure into the soil. Then, furrows are dug—about 50–70 cm wide and 25–40 cm deep—and the same amount of manure is placed in them. Along with it, 300–375 kg of superphosphate (with over 12% available phosphorus) and 37.5–45 kg of potassium sulfate are mixed into the soil and covered before planting.
(3) Top-dressing practices vary depending on the region and cultivation method. In northern areas, fewer top-dressings are applied, while southern regions often require more frequent applications. Young plants generally need more top-dressing than mature ones. The first top-dressing is usually done when seedlings have two true leaves (for direct-seeded crops) or after they have been transplanted and acclimated. At that point, about 150–225 kg of urea per hectare is applied, along with 105–150 kg of other nutrients. When the fruits reach 10–15 cm in diameter, another round of 150–225 kg of urea and 150–225 kg of potassium sulfate is added. During fruit enlargement and ripening, spraying 0.5% potassium dihydrogen phosphate and 0.5% calcium nitrate 2–3 times can help boost yield and improve fruit quality. However, applying only urea at this stage may lower fruit quality. If potassium sulfate is unavailable, potassium dihydrogen phosphate can be used instead. If no potassium source is available, it might be best to skip the top-dressing.
For those aiming to harvest a second crop, it's advisable to apply around 90–120 kg of urea and 150–225 kg of potassium sulfate per hectare about five days before the first harvest. This helps prevent early leaf aging and encourages the growth of the second batch of fruits.
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