Intercropping Cultivation Technology for Watermelon and Chinese Yam in Large Arch Sheds

In early spring, using a large arch shed for intercropping watermelon with Chinese yam can bring the harvest and market time of both watermelon and Chinese yam more than 45 days earlier than open-field cultivation, thereby achieving relatively high economic benefits.

1. Arch shed structure. The shed is 7 m wide, the arch height at the center of the shed is 2.5 m, and the shed length depends on the plot. The arch frame is generally made of precast cement components, or two bamboo poles can be used, with their lower ends buried and fixed in the soil respectively, and their upper ends bent inward into an arch shape, with the joints tightly twisted with iron wire to form the shed frame; 3 rows of upright posts are set up at the center and on the left and right sides of the shed respectively to support the frame. When covering the shed, high-quality plastic film is laid over the arch frame, and the plastic film is tightened and pressed down with iron wire. 2. Ditching and land preparation. In each large arch shed, two planting furrows need to be dug along the length of the shed, with the center points of the two planting furrows located 2.7 m to the left and right of the shed center. The furrows should be 0.8 m wide and 0.8 m deep. When digging the furrows, the subsoil and topsoil are piled separately. When backfilling, backfill the topsoil first, then the subsoil, and be careful to break up large clods at all times. When backfilling to 40 cm from the ground, apply base fertilizer: 4000 kg of high-quality decomposed organic fertilizer and 40 kg of nitrogen-phosphorus-potassium compound fertilizer per mu, mix the fertilizer evenly with the soil, and fill it in. 3. Watermelon planting. Cover the shed 10-15 days before watermelon planting to raise the temperature inside the shed. After covering the shed, water immediately to build up soil moisture. When the 5 cm soil temperature inside the shed stabilizes above 15°C, planting can begin. Watermelon should be planted in the center of the planting furrow. Seedlings can be planted when they are 40-50 days old. The plant spacing is 35 cm, so that 2 rows of watermelon are planted in each shed, with 550 plants per mu. When planting, first dig the planting holes, then take the watermelon seedlings with their soil balls out of the nutrient pots, plant them together with the soil balls into the planting holes, then fill firmly with fine soil, and after filling firmly, water each seedling lightly once. After the watermelon planting is completed, immediately cover with plastic mulch, put up a small arch shed, and at night cover the small arch shed with straw curtains for insulation. 4. Chinese yam planting. When the main vine of the watermelon grows to 40-50 cm, Chinese yam can be planted. In this way, Chinese yam is prevented from growing too early and competing with watermelon for light, water, and nutrients, while also ensuring that the fertilizer and water needs of watermelon basically match those of Chinese yam without conflicting with each other. Chinese yam is planted on the left and right sides of the watermelon, 20 cm from the watermelon row, with a plant spacing of 35 cm. Chinese yam and watermelon are planted in a staggered ‘’ shape. In this way, each planting furrow contains 1 row of watermelon and 2 rows of Chinese yam, and each shed contains a total of 2 rows of watermelon and 4 rows of Chinese yam, with 1100 Chinese yam plants per mu. When planting, first use thick steel bars to drill a vertical hole according to the plant and row spacing, with a hole depth of 60 cm, then drill a slanted hole along the row at the mouth of the hole, with the slanted hole at an angle of 15-20 degrees to the ground. Then place the Chinese yam head (the root segment with the apical bud used for propagation) into the slanted hole so that the top end is at the vertical hole opening, in order to guide the new tuber to extend vertically downward along the vertical hole, and finally press the soil gently firm with the hand. 5. Field management. 1) Temperature regulation: During the watermelon seedling recovery stage, the daytime temperature should not be too high and should be 20-25°C, with nighttime not lower than 15°C; after Chinese yam sprouts, its temperature requirements are not strict, and the shed temperature can be regulated according to the growth and development requirements of watermelon; during the watermelon flowering stage, the temperature can be slightly higher, with daytime 25-28°C and nighttime not lower than 17°C; after fruit set, as the weather warms, ventilation should be increased as appropriate during the day to lower the temperature, with daytime around 30°C and nighttime 15-20°C. Maintaining a relatively large day-night temperature difference is beneficial for improving watermelon yield and quality. 2) Fertilizer and water management: Chinese yam is relatively drought-tolerant, but suitable soil moisture can promote the growth and development of Chinese yam. In water management, watering should also be done timely and appropriately according to the water requirements of watermelon. In the early stage, the number and amount of watering should be reduced to prevent heavy watering from lowering soil temperature. If the soil is dry, water lightly; especially during the flowering and fruit-setting period, watering should be controlled to prevent excessive vine growth from affecting fruit set; during the fruit expansion period, water sufficiently to promote watermelon fruit expansion, promote Chinese yam vine growth, and increase leaf area. Before watermelon harvest, do not irrigate heavily to prevent fruit cracking. Both watermelon fruit expansion and Chinese yam growth require large amounts of nutrients, especially potassium fertilizer. During the fruit expansion period, in combination with watering, apply 30 kg of nitrogen-phosphorus-potassium compound fertilizer and 15 kg of potassium sulfate per mu. 3) Watermelon pruning and Chinese yam vine hanging: Watermelon pruning generally adopts the double-vine pruning method, leaving fruit on the main vine and no fruit on the side vine. The main vine is topped after leaving 15-18 leaves ahead of the fruit, and the side vine is topped after leaving 18-20 leaves. Secondary vines sprouting from the main vine and side vines should be removed promptly to ensure that the main and side vines extend along a single axis; after Chinese yam emerges, hang the vines promptly. A rope can be used with one end buried in the soil and the other end tied to the iron wire at the top of the shed to guide the vines to grow upward along the rope. 4) Watermelon fruit retention and pollination: For watermelon, select the 2nd female flower on the main vine for fruit retention, and pollinate the female flower retained for fruit promptly. When pollinating, gently rub the stamens of the male flower on the stigma of the female flower so that the pollen is evenly distributed on the stigma. After pollination, mark it and record the date so that the maturity period can be estimated according to the number of days for watermelon to mature. 5) Management after watermelon harvest: Watermelon in early spring large arch sheds generally matures and can be marketed in early to mid-May. After watermelon harvest, the fertilizer and water needs of Chinese yam should be met, and an additional 20 kg of nitrogen-phosphorus-potassium compound fertilizer per mu should be applied to promote Chinese yam tuber growth and increase yield. At this time, if a second crop of watermelon is to be retained, pollinate promptly, and the second crop of watermelon can be harvested after more than 20 days of fruit set; if no second crop of watermelon is to be retained, the watermelon vines can be pulled out and cowpea, cucumber, vegetable sponge, zucchini, and other summer vegetables or peanuts, corn, and other crops can be planted.

6. Chinese yam harvest: In July, Chinese yam can be harvested and marketed according to market conditions.