Method and technology for fertilizing watermelon
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Watermelon farming has traditionally relied on direct seeding, but as cultivation techniques and greenhouse technology have advanced, the practice of transplanting seedlings has become more common. When using transplanted seedlings, preparing high-quality nursery soil is essential for growing strong, healthy plants.
(1) The preparation of nursery soil typically involves mixing 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 crucial for early plant development.
(2) Applying base fertilizer to watermelon fields can be done through spreading, furrow application, or hole application. A common practice is to apply 15–22.5 tons of farmyard manure per hectare. After spreading, the soil is plowed to mix the organic matter thoroughly. Then, furrows are dug—about 50–70 cm wide and 25–40 cm deep—and 15–22.5 tons of manure are placed in them. Additionally, 300–375 kg of superphosphate (with over 12% available phosphorus) and 37.5–45 kg of potassium sulfate are mixed into the soil before covering it, making it ready for planting.
(3) Top-dressing practices vary depending on the region and cultivation method. In northern melon areas, fewer top dressings are applied, while southern regions often require more frequent applications. Seedlings generally need more top dressing than mature vines. Typically, the first top dressing is done when the seedlings have two true leaves (for direct-seeded crops) or after they have been acclimated (for transplanted seedlings). At this stage, urea is applied at a rate of 150–225 kg per hectare. When the plants reach about 15 cm in height, another round of 105–150 kg of urea is recommended. Once the fruits grow to 10–15 cm in diameter, 150–225 kg of urea and 150–225 kg of potassium sulfate should be applied. During fruit enlargement and ripening, spraying 0.5% potassium dihydrogen phosphate and 0.5% calcium nitrate two to three times can help improve yield and fruit quality. However, it's important not to use only urea at this stage, as it may reduce fruit quality. If potassium sulfate is unavailable, potassium dihydrogen phosphate can be used as an alternative. If no potassium-based fertilizer is available, this step may be skipped.
To prepare for a second harvest, about 90–120 kg of urea and 150–225 kg of potassium sulfate should be applied five days before the first crop is harvested. This helps prevent premature aging of the foliage and encourages the growth of the second batch of fruits.