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 crucial for growing healthy plants.
(1) The standard mix for nursery soil typically consists of 50% loam, 30–35% compost, 15–20% fine sand, and a small amount of wood ash or about 1–2 kg of potassium sulfate per cubic meter. This combination ensures good drainage, nutrient availability, and proper aeration for strong root development.
(2) For base fertilizer application, farmers often use methods such as spreading, furrow application, or hole application. A typical rate is 15–22.5 tons of farmyard manure per hectare. After spreading, the field is plowed to incorporate the organic matter. Then, furrows are dug—about 50–70 cm wide and 25–40 cm deep—and the same amount of manure is applied. 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 before covering it and preparing for planting.
(3) Top-dressing practices vary depending on the region and cultivation method. In northern watermelon regions, fewer top dressings are needed, while southern areas often require more frequent applications. Seedlings generally need more feeding than mature plants. The first top dressing is usually done when seedlings have two true leaves (for direct-seeded crops) or after they have been hardened off (for transplanted ones). At around 15 cm in height, 150–225 kg of urea per hectare is recommended, along with 105–150 kg of another source of nitrogen. When the fruits reach 10–15 cm in diameter, 150–225 kg of urea and an equal amount 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 enhance yield and improve fruit quality. However, applying only urea at this stage may reduce fruit quality. If potassium sulfate isn't available, potassium dihydrogen phosphate can be used instead. In cases where no potassium-containing fertilizer is available, this top dressing might be skipped.
To prepare for a second harvest, it's advisable to apply 90–120 kg of urea and 150–225 kg of potassium sulfate per hectare about five days before the first crop is harvested. This helps prevent early leaf yellowing and encourages the growth of a second batch of fruits.