Detailed Explanation of Key Techniques for Greenhouse Cultivation of Green Asparagus

    Green asparagus is renowned worldwide for its rich nutritional and medicinal value and is listed as one of the world's ten famous vegetables. In recent years, the Yifeng Agricultural Research Institute of Hejian City, Hebei Province, has conducted experimental research on high-yield cultivation of asparagus and achieved successful technical experience, which is summarized as follows.

　　I. Establishing High-Standard Greenhouses

Select a plot with sandy soil that is sheltered from wind and facing the sun, with flat terrain, fertile soil, deep topsoil, convenient drainage and irrigation, and good aeration for building the greenhouse. The best lighting effect is achieved when the greenhouse is oriented due south with a 5-degree deviation toward the sun. The greenhouse is 50 m long from east to west, with a span of 8.2 m, a rear wall height of 2 m, a wall thickness of 1.2 m at the bottom and 0.9 m at the top, and a ridge height of 3 m. The rear slope uses double film with 20 cm thick corn stalks or wheat straw sandwiched between, and the film is covered with 45 cm thick soil. The front slope is covered with polyethylene non-drip film. A cold-proof trench of 70 cm * 70 cm is dug in front of the greenhouse, filled with corn stalks or wheat straw.

　　II. Cultivation Techniques

1. Variety selection. For green asparagus, hybrid varieties should be selected that are cold-resistant, disease-resistant, with tightly clasped scales, and green, relatively thick and uniform spears.

2. Soaking seeds in warm water. Before sowing, soak seeds in warm water at 45-50°C for 30 minutes, then replace with clean well water and soak for another 24 hours, then drain, rinse once with warm water at 30°C, and place at 25-30°C for germination. Rinse once each morning and evening with warm water at 30°C, then wash off the secretions on the seed surface to prevent mildew. When the seed germination rate reaches 15% (germination is indicated by the seed coat breaking and the white radicle showing), sowing can begin.

3. Sowing. In early March, use a small arch shed for seedling cultivation. For each mu of greenhouse, prepare two seedbeds of 1.5 m * 10 m. Apply 2.5 kg of diammonium phosphate and 1.5 kg of potassium chloride to each seedbed, then plow the soil 20 cm deep, and level and refine the seedbed. First open furrows at a row spacing of 10 cm with a depth of 5 cm, then sow at a plant spacing of 10 cm, with 1 seed per hole, cover with about 3 cm of soil, and scatter 1605 mixed with wheat bran bait on the seedbed surface to eliminate underground pests. Then cover the small arch shed with a layer of plastic film, seal it tightly, and generally do not ventilate before seedlings emerge.

4. Seedbed management. Since asparagus seeds can only germinate above 10°C, with the optimum temperature being 25-30°C, and the temperature is still low when sowing in the small shed for seedling cultivation, straw mats should be covered on the shed at night. When 60% of seedlings emerge through the soil, the plastic film should be removed in time. After all seedlings have emerged, ventilation should begin. Ventilation should be done after 11 a.m. and closed at 2 p.m., with the ventilation opening gradually increasing from small to large. As the asparagus seedlings grow, the shed film should eventually be fully removed. During the seedling stage, the daytime temperature is best controlled at 20-25°C, and the nighttime temperature should be maintained at around 18°C.

5. Transplanting. In early June, when seedlings are 50 cm tall, have 3-6 root systems and 3 young spears, they can be transplanted. The seedlings to be transplanted should be graded by size and transplanted separately. When transplanting, orient the germination surface of the asparagus root crown all toward the south. Before transplanting, clear away the residual branches and fallen leaves of the previous crop to prevent the occurrence of diseases and pests in the greenhouse. Apply sufficient base fertilizer; generally apply more than 7500 kg of farmyard manure per mu, 50-70 kg of ternary compound fertilizer, 20 kg of urea, and 30 kg of potassium chloride. Plow the soil 20 cm deep and level it. Open furrows from one side of the greenhouse in a north-south direction, with a furrow depth of 10 cm. Apply 3 kg each of Dichongjing and Dijunjing in the furrows, mix the soil and pesticide evenly, and then transplant at a row spacing of 90 cm * 30 cm. After transplanting, the first soil covering should be 3-5 cm. After 7-8 days when the seedlings have recovered, the second soil covering should be to the same depth as the original seedling soil. After the first soil covering, water thoroughly.

6. Management after transplanting. Within 1 month after transplanting, inspect seedlings and fill gaps in time. If dead seedlings are found, replant them in time, and the replanted seedlings should be larger than the original ones. After transplanting, young spears emerge within 7-8 days. Because the seedlings are tender, their resistance to diseases and pests and their regenerative ability are very poor, so timely inspection is necessary. If stem blight is found, spray 800 times diluted 50% carbendazim in time. If pests are found, spray pesticide in time for control. One month after transplanting, the young spears of the seedlings have grown to 4-5 cm high. To promote their growth and development, sufficient water and nutrients must be provided. At this time, quick-acting chemical fertilizers can be applied as a top dressing, with 10-15 kg of urea per mu, or 15-20 kg of ternary compound fertilizer. Around August 25, asparagus enters the autumn growth stage. Open furrows again and apply 3000-4000 kg of farmyard manure, 10 kg of diammonium phosphate, 15 kg of potassium chloride, and 40 kg of ternary compound fertilizer. Around October 25, cut off the asparagus stems and clear away all residual branches and fallen leaves, take them out of the greenhouse, and burn them in a centralized manner. Then carry out intertillage and loosening of the soil, open furrows, and apply 40-50 kg of ternary compound fertilizer and 20 kg of urea. In mid-November, water once. Combined with intertillage and soil loosening, apply 4 kg each of Dichongjing and Dijunjing, shape the ridges into a fish-back shape, and cover with plastic film. In mid-December, cover with straw mats at night so that the temperature inside the greenhouse is 20-28°C during the day and 18-20°C at night.

7. Harvesting. When young spears push through the soil, break the film in time to release the seedlings. When the young spears grow to 20 cm high, cut them off at ground level with a sharp asparagus harvesting knife. Put the harvested asparagus into the harvesting box immediately. After harvesting, sort the young spears, tie them in bundles by grade, pack them into boxes, cover with a wet cloth, and sell. They can be temporarily placed in a cool place, but must never be soaked in water to avoid rot and deterioration.