Detailed Explanation of Key Techniques for Off-Season Cultivation of Edamame

Edamame, also called vegetable soybean, is a type of soybean crop grown specifically for its fresh tender pods as a vegetable. Edamame is simply fresh soybeans in their pods. Edamame is an annual crop; its stems are thick and hard with fine hairs, and its pods are flat in shape, also covered with fine hairs, which is why people call it edamame. When fresh, the pods are tender green and delightfully verdant.

Off-season cultivation of edamame can maximize the planting benefits of edamame, so how can off-season cultivation of edamame be achieved? Below we introduce the two most critical techniques in off-season edamame cultivation: transplanting and double-film seedling raising.

Transplanting:

1. Field preparation. Edamame is not suitable for continuous cropping and should be grown in rotation. Therefore, choose a field where edamame has not been planted for at least two years, and which also has convenient drainage and irrigation, with few weeds. 3-4 days before transplanting edamame, plow and prepare the field, generally to a depth of 17-20 cm. In combination with plowing, apply sufficient base fertilizer; per 667 sq m, apply 2000-2500 kg of decomposed barnyard manure, 25-30 kg of superphosphate, 100-150 kg of plant ash or 20-25 kg of potassium sulfate fertilizer, to meet the edamame's need for phosphorus and potassium fertilizers during growth. If the soil is too acidic, also apply an appropriate amount of lime to neutralize the acidity. After fertilizing and preparing the land, promptly carry out chemical weed control on the field surface; generally per 667 sq m, use 100-150 ml of 72% trifluralin emulsifiable concentrate mixed with 40-50 kg of water for field spraying, to control the vast majority of annual grass weeds as well as some annual broadleaf weeds and sedges. When applying the herbicide, it must be uniform and thorough, without re-spraying or missing spots, to facilitate complete sealing. If the ground surface is relatively dry, first irrigate to moisten the topsoil, then spray the herbicide. In dry conditions without irrigation, increase the application rate. After applying the herbicide, the field can immediately be covered with plastic film according to the edamame transplanting spacing, waiting for hole-punching and transplanting.

2. Timely transplanting and rational close planting. Edamame has weak root regeneration ability and low tolerance to transplanting injury. Generally, transplanting can be done 2-3 days before or after the first pair of true leaves of the edamame seedlings unfolds. At the latest, it must not wait until the first compound leaf emerges, otherwise the seedlings will have a long recovery period in the field, easily causing stunted seedlings that fail to grow or even leading to seedling death. Generally, with only plastic film mulching, transplanting can be done from late March to early April; with plastic film plus small arch shelter covering, the suitable transplanting period can be advanced to early-to-mid March; if edamame is transplanted into medium or large tunnels, the transplanting period can be advanced to late February to early March, and tender pods can be harvested in early May.

For early-maturing or off-season edamame cultivation, rational close planting is needed to increase pod yield. Generally, wide-narrow row planting is adopted, that is, wide row spacing of 36-42 cm and narrow row spacing of 22-26 cm, with an average row spacing of 30-34 cm for edamame and a plant spacing of 16-22 cm. Edamame can also be planted with equal row spacing, that is, row spacing of about 30 cm and plant spacing of about 20 cm. Generally, about 10,000 hills are planted per 667 sq m, with 20,000-25,000 plants retained per 667 sq m. Varieties with many branches, and fields with high soil fertility and good fertilizer and water supply, should be planted more sparsely; otherwise, more densely. After the plastic film is laid, hole-punching and transplanting can be carried out. The planting depth of seedlings should be such that the cotyledons are about 1.5 cm above the ground. If planted too shallow, the hypocotyl of the seedling is exposed too high above the ground; for edamame grown only with plastic film, it is then vulnerable to cold wind, the tissue becomes stiff, and it easily breaks in strong winds. If planted too deep, the soil temperature at depth rises slowly, which is unfavorable for root development. After transplanting the edamame seedlings, water once with a small amount to help recovery, or apply a dilute manure water at about 10% concentration to promote recovery and root growth.

Double-film seedling raising

1. Seed treatment before sowing. Before sowing edamame, choose sunny and warm weather to sun-dry the seeds for 1-2 days, then sieve or winnow to remove impurities such as mud and dust. To prevent disease, cultivate strong seedlings, and increase yield, seed treatment with chemicals and inoculation with rhizobia can also be carried out before sowing.

Chemical treatment of edamame seeds is mainly aimed at seed fields where relatively serious disease occurred during the pod-filling stage, causing the seeds to carry pathogens. Generally, seed dressing with chemicals or seed soaking in chemical solution is adopted. For powder dressing, 50% thiram wettable powder or 50% carbendazim wettable powder can be directly mixed and stirred with dry seeds, or a small amount of clean water can be sprayed on the seed surface before mixing. The amount of powder used is generally 0.2%-0.3% of the seed weight. For liquid soaking, seeds can be soaked in 1% formalin, 1% copper sulfate aqueous solution, or similar solutions for 5-20 minutes, then removed, rinsed clean with water, and then sown.

In early-maturing edamame varieties, rhizobia are generally not well developed, and rhizobia themselves form relatively little during the edamame seedling stage, with low nitrogen-fixing capacity. Therefore, inoculating edamame seeds with rhizobia can cultivate strong seedlings, so that after inoculation with rhizobial agent, edamame can improve nitrogen-fixing capacity from the seedling stage and achieve obvious yield increases. There are two methods of rhizobia inoculation. First, seed dressing with inoculant: directly use 50-75 g of purchased rhizobia powder, first spray a small amount of clean water on the seeds to make the seed surface moist, then also spray water on the inoculant so that its moisture content reaches about 35%, that is, spray 18-30 g of clean water on the inoculant, then mix the two evenly. Second, without purchasing rhizobial agent: select root nodules from the old roots of robust edamame plants harvested the previous year, cut off the nodule portions with scissors, wash off the soil clumps with clean water, dry them in a dark place, and after drying, pound them into powder and mix evenly with edamame seeds. Generally, 30-40 plants are sufficient per 667 sq m.

In addition, the trace element molybdenum can enhance the respiratory intensity of edamame seeds and improve germination vigor and germination rate. In particular, molybdenum can promote the formation and growth of root nodules, increasing their number and size and raising nitrogen fixation; molybdenum is also a component of nitrogenase, and only when molybdenum supply is normal can nitrogenase carry out nitrogen fixation. When molybdenum is deficient, root nodules develop poorly, are few in number, and are small. Therefore, in combination with rhizobia seed dressing, seeds can be dressed with a 1.5% ammonium molybdate aqueous solution; per 100 kg of seeds, 3.3 kg of diluted ammonium molybdate solution is sufficient.

2. Fertilizing the seedbed. The seedbed should be chosen in a sheltered, sunny location, on high and dry terrain, with convenient drainage and irrigation, and with relatively few pests, diseases, and weeds. Generally, the seedbed is 1.8-2 m wide, with a net width of 1.3-1.4 m. The length of the seedbed should be determined according to the field area to be transplanted, the diameter of the nutrient pots or the length of the nutrient soil blocks, and the transplanting density. In addition, appropriately increase the seedbed length by 10%-15% as a reserve seedbed for filling gaps. The seedbed can be fertilized either by preparing nutrient soil or by directly applying fertilizer to the seedbed. The nutrient soil used for seedling raising is mainly made from vegetable garden soil or pond mud that has not grown legumes, fully decomposed barnyard manure, or mud-made compost, combined with decomposed manure, plant ash, and so on. Generally, it is 6 parts soil plus 4 parts decomposed organic matter. The thickness of the culture soil in the seedbed is 5-8 cm, or filling 80% of the nutrient pots. If adopting the method of directly applying fertilizer to the seedbed, generally for every 3.3 m length of seedbed, apply 100 kg each of decomposed ash and manure, 2-2.5 kg of rapeseed cake, and 2-3 kg of high-efficiency compound fertilizer, then turn the seedbed soil upside down and mix evenly, and shape it.

3. Fine sowing. After the seedbed is fertilized, pots can be made or blocks cut for sowing. Before making pots or cutting blocks, the bed surface should be watered sufficiently to establish good moisture. The moisture of the seedbed should be such that the bed soil can be squeezed into a ball that breaks apart when dropped from chest height. Otherwise, if the bed soil is too dry, the pots or blocks made cannot hold their shape, affecting seed germination and emergence; if the bed soil is too wet, the pots or blocks made are too muddy, easily causing compaction, making it difficult for seed roots to penetrate, and easily causing seed rot and stunted seedlings. To protect the edamame root system, it is best to use nutrient pots or nutrient soil blocks for seedling raising. Nutrient soil blocks can be pressed with a machine, or the bed soil can be cut with a thin board, generally preferably 10-12 cm square, and a small wooden stick is used to poke a hole about 2 cm deep in the center for sowing. The diameter of nutrient pots is generally preferably 8-10 cm. Whether nutrient soil blocks or nutrient pots, place 2-3 seeds per hole. For off-season edamame cultivation, generally 3-3.5 kg of seed is used per 667 sq m. After sowing, cover with about 2 cm of fine soil, and then scatter a layer of black rice husk ash or plant ash on the surface, so that the soil temperature rises easily. After covering the seedbed with soil, a layer of plastic film can be laid flat over it, and then a small arch shelter can be set up for covering.

4. Seedbed management. Before edamame emerges, do not water the seedbed, to avoid causing seed rot. Generally, emergence begins 10-12 days after sowing. After 50% emergence, the plastic film should be removed. After another 10-15 days, when the first pair of true leaves of the seedlings unfolds, transplanting should be done promptly. 3-5 days before transplanting, the seedbed should be ventilated more and cooled to carry out appropriate low-temperature hardening. 1-2 days before, water thoroughly once to facilitate lifting seedlings with soil. Seedling-stage management is mainly ventilation and heat preservation. On sunny and warm days during the day, around 9 a.m., uncover the film at both ends of the arch shelter; if the seedbed is too long, also uncover part of the film in the middle, to enhance ventilation and moisture dispersal and prevent excessive humidity that causes spindly growth and tall leggy seedlings. At the same time, except before transplanting, water as little as possible or not at all during the seedling stage. When ventilating to disperse moisture, also prevent the “flash seedling” phenomenon, that is, a sudden drop in air humidity inside the seedbed, causing the bean seedlings to suddenly lose water, resulting in dry leaf edges and wilted leaves; if accompanied by cold weather, chlorophyll is destroyed, making leaf color turn white or even crack and dry. The way to avoid this is to choose sunny and warm weather and gradually uncover the film to disperse moisture. In addition, at night the seedbed should be kept warm. In cold weather, an additional layer of straw curtains can be covered outside the arch shelter to prevent the bean seedlings from prolonged low-temperature freezing injury.