Small watermelons are highly favored by consumers for their superior quality and compact size, typically weighing between 1 to 3 kilograms. However, traditional open-field cultivation is vulnerable to adverse weather conditions such as early spring frosts, summer typhoons, and autumn cold waves, which can lead to low yields and inefficient production. To address these challenges, from 1999 to 2000, Yangxi Township in Meilie District, Sanming City, under the guidance of Director Liu Shizhe from the Soilless Cultivation Research Center at South China Agricultural University, implemented a plastic greenhouse system for growing small watermelons during spring and autumn. This method proved highly effective, significantly improving yield and quality. The following outlines the key techniques and experiences gained from this project.
1. **Greenhouse Structure**
1.1 The greenhouse is a 6.5m x 30m galvanized steel arch structure with four vertical slots and a height of 3.2 meters. The eaves height is 2.0 meters, and a plastic film covers the top. In summer and autumn, insect nets are installed for ventilation and cooling, while insulating plastic films are used in winter to maintain temperature.
1.2 **Planting Troughs**
The greenhouse contains four horizontal planting troughs, each measuring 14.25 meters in length and 1 meter in width. A 50 cm wide working path is placed at both ends and along the center of the greenhouse. Each trough is constructed using three bricks stacked flat, reaching about 18 cm in height. The bottom of the troughs is filled with sand, preferably river sand with particles larger than 1.5 mm, making up over 80% of the mix. A layer of 0.2 mm thick plastic film is placed beneath the sand to prevent nutrient solution leakage.
1.3 **Nutrient Solution Delivery System**
1.3.1 A 5m x 1m cement reservoir is built for storing water and preparing nutrient solutions.
1.3.2 Drip irrigation is used, with observation ports placed in each planting tank to monitor liquid flow. The system includes capillary tubes, drippers, and filters to ensure even distribution. Main and branch pipelines (PE pipes) deliver the nutrient solution to the capillary tubes, which then drip directly into the sand around the plants.
1.3.3 A self-priming pump and filter system are used to ensure clean nutrient delivery. The filter has a 100-mesh screen to prevent clogging, and the system is designed to provide consistent and efficient irrigation.
2. **Cultivation Management Techniques**
2.1 **Variety Selection**
Suitable varieties include 'Crown', 'Golden Beauty', 'Jialing', 'Early Spring Red Jade', and 'Whelan'. These varieties are chosen for their early maturity, disease resistance, and high quality, making them ideal for greenhouse cultivation.
2.2 **Sowing and Harvesting Schedule**
In spring, sowing takes place from late February to early March, with harvesting from late May to early June. Autumn planting occurs from late August to early September, with harvests from late November to early December. During summer, leafy vegetables can be grown to maximize greenhouse usage.
2.3 **Seedling Preparation**
A seedling substrate made of fine sand and mushroom compost in a 1:1 ratio is used. Fertilizers such as calcium superphosphate, ammonium nitrate, potassium sulfate, and magnesium sulfate are added and mixed thoroughly. After sterilization with formalin, the mixture is dried and ready for use.
2.4 **Germination and Transplanting**
Watermelon seeds are soaked in 0.4% formalin for an hour, then rinsed and soaked in clean water for 8–10 hours. After removing the outer layer, the seeds are wrapped in a damp cloth and kept warm for germination. Once sprouted, they are planted in seedling bags or plugs, ensuring proper depth and spacing. Seedlings are transplanted when they have 2–3 true leaves, with a spacing of 50 cm between plants.
2.5 **Nutrient Management**
The nutrient solution formula includes calcium nitrate (826 mg/L), potassium sulfate (607 mg/L), potassium dihydrogen phosphate (181 mg/L), magnesium sulfate (370 mg/L), and trace elements. This balanced solution ensures optimal plant growth and fruit development. Regular monitoring and adjustment of the nutrient solution are essential for maintaining high-quality yields.
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