Vegetable Soybean Cultivation

AVRDC Extension Materials

Suggested
Cultural
Practices for Vegetable
Soybean

Contents

Introduction	Water management
Climate and soil	Weed control
Field preparation	Disease control
Sowing	Insect pest control
Nutrient management	Harvest

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Introduction

Vegetable soybean is popular in Japan, Korea, China and Taiwan, and consumption is increasing very rapidly. Although the vegetable-type varieties of soybean are preferred, the green-shelled beans as well as whole tender green pods of grain soybean can also be used as a vegetable. Grain soybean is already widely cultivated in many countries of the tropics and subtropics, so the production of vegetable soybean can be readily adopted.

The cultivation practices for vegetable soybean and grain soybean are similar except that vegetable soybeans are harvested when the pods are still green and full. Generally, the green seeds of vegetable soybean are larger, more tender and sweet. Green-shelled beans can be cooked to make a tasty and nutritious meal or snack.

Vegetable soybean has excellent potential for enriching the human diet. It is a rich source of Vitamin A and a good source of carbohydrates, protein and iron. Vegetable soybean is more nutritious than vegetable green peas. The pods of vegetable soybean are harvested when they are still green, just before the seeds turn yellow.

In addition to domestic consumption, vegetable soybean also has export potential. Export market requirements are: hundred seed weight (dry): 30 g or more; number of seeds per pod: 2 or more; gray pubescence on pod, good flavor, slightly sweet taste. The pods should cook quickly and they should be easy to squeeze open after cooking. Frozen vegetable soybeans are popular in supermarkets of Japan and Taiwan.

Climate and soil requirements

The best planting date of vegetable soybean differs with season and location depending upon temperature and daylength. The optimum temperature range of soybean cultivation is 20-30ºC with short daylength (14 hours or less). However, planting should be avoided at cooler temperatures during winter. Loam soil with pH of 6.0-6.5 is suitable for its cultivation, but the field should be well drained.

Field preparation

Land tillage makes the soil friable for good germination, increases soil porosity and aeration for healthy plant growth. Tillage kills weeds to control weed-crop competition for soil nutrients, moisture and light. This in turn helps plant productivity. Plow and rototill the field.

The soil should not be too dry at the time of seedbed preparation. Inadequate moisture will result in poor seed germination. At AVRDC, we irrigate the field 3-4 days prior to sowing to ensure sufficient moisture in the soil for good germination of seed. Prepare 20-cm raised beds spaced one meter apart from center of one bed to the center of the next.

Sowing

The seed is treated with protectant fungicides such as captan or thiram at 3-g a.i./kg seed for protection against soilborne fungal diseases. Spacing between rows is 45 cm and between plants 5-10 cm depending upon seed size and season. Two to three seeds are sown in each hill. However, spacing between rows varies with variety and season. Usually seeding (60-80 kg seed/ha) is required to obtain a population of 400,000 plants per hectare. Sow seeds by hand, or by a hand-operated planter.

Nutrient management

Basal fertilizer application:
Have soil samples analyzed. The fertilizer requirements are determined on the basis of the soil test. The higher the soil nutrient level, the lesser will be the quantity of fertilizer needed. To get a good harvest (7-10 tons green pods per hectare) and maintain soil nutrient status of consistent productivity, a fertilizer mix containing N, P2O5 and K2O at the rate of 20-30, 60 and 80 kg/ha respectively, is applied by broadcast as a basal dose. The fertilizer is incorporated into the soil by harrowing.

Use of Rhizobium inoculation:
Usually Rhizobium inoculation is not required in fields where legumes are cultivated. But newly opened lands need Rhizobium bacteria inoculations at 10 g per kilogram of seed. The use of Rhizobium bacteria culture will promote nodule formation and nitrogen fixation by the plant roots.

Top dressing of fertilizer:
The first top dressing is done at the rate of 20-kg N + 25 kg K2O per hectare along plant rows at flowering for higher pod set. A second application of 20-kg N per hectare is done at the beginning of the pod filling stage to improve seed size.

Water management

Maintaining proper soil moisture throughout the growing season is important for good quality pods. Usually, first irrigation is needed within a week after sowing under AVRDC soil conditions. Irrigation is done in furrows. Depending upon weather and soil moisture conditions, the irrigation is continued at 10-15 day intervals until the pods are well developed. However, irrigating the crop is essential at critical periods such as flowering and pod filling stages.

Weed control

At AVRDC, application of alachlor at 1.5 kg a.i./ha either alone or combined with pendimethalin at 0.75 kg a.i./ha as pre-emergence spray is practiced to control weeds.

Intertillage once or twice is beneficial for aeration of root system and to control weeds that emerge after the effect of chemical weedicides fades off.

	Disease control Rust may be a serious problem especially for seed production, causing up to 100% yield loss. Tan, dark brown or reddish brown lesions occur on leaves of rust-affected plants. None of the commercial cultivars are resistant to rust, but rust-tolerant breeding lines have been selected at AVRDC. Fungicides such as mancozeb or triadimefon at the rate of 2-kg a.i./ha are sprayed at 10-day intervals to control rust in susceptible cultivars.
	Downy mildew disease commonly occurs during spring and autumn seasons but it does not generally cause yield reduction. The symptoms are pale green to light yellow spots on the surface of the leaf. These spots later enlarge into pale to bright yellow lesions. The underside of the leaf shows white powdery spores. To control downy mildew, plant resistant cultivars. For susceptible cultivars, spray fungicides such as mancozeb at the rate of 2-kg a.i./ha depending upon severity of disease attack.
	Bacterial pustule can cause yield losses of up to 40% in vegetable soybean. Early symptoms of this disease are small pale green lesions that become watersoaked with bacterial ooze that dries to become white crust on upper/lower leaf surfaces. The best way to control bacterial pustule disease is by planting resistant varieties.

	Insect pest control Beanfly is a serious pest of soybean. Beanfly larvae feed inside the plant stem and their damage cannot be recognized easily. Beanfly damage is more severe in relatively cool season (e.g. autumn at AVRDC) compared to long dry weather conditions (e.g. spring at AVRDC) due to lower insect populations. Soybean must be protected against beanfly. For the autumn crop at AVRDC, monocrotophos, omethoate or dimethoate is sprayed at the rate of 0.5 kg a.i./ha at 3, 7, 14, 21, 28 and 35 days after emergence (DAE). The first three sprays are very important and should not be delayed. Spraying is stopped at 35 DAE. In spring, usually there is no serious damage by beanfly.
	Pod borers may attack soybean but usually they do not cause significant yield loss under AVRDC conditions if we use insecticides for beanfly control.
	Stink bugs commonly occur on vegetable soybeans late in spring and summer season crops. They do not cause any economic damage under AVRDC conditions. However, if you notice high population (i.e. 3 to 4 insects per meter row) uniformly over the entire field in early pod filling stage, spray insecticides such as fenvalerate at 100-g a.i./ha or deltamethrin at 30-50 g a.i./ha at weekly intervals till the insect infestation is controlled. Defoliators feed on leaves. Minor damage does not require insecticide application. However, when the attack is severe, they can also be controlled by the insecticides used for stink bug control. Stop spraying chemicals at least 10 days prior to harvest. Overuse of insecticides or fungicides is hazardous for human and animal health.

	Harvest Harvesting is done when 80% of the pods have reached physiological maturity stage. It may take 65 to 75 days after germination for vegetable soybeans to be ready for harvest depending upon variety, temperature and weather conditions. The pods are still green. In Taiwan, harvesting usually begins at midnight when dew and cool temperature help to preserve the green color and freshness of the vegetable soybeans. When harvested in daytime, the plants are kept under the shade. The pods are stripped from the plants by hand. Harvesting machines can save labor, cost and time.
	Grading is important for export of good quality vegetable soybeans. The diseases and insect-damaged pods and pods with spots and blemishes are sorted out. The good marketable yields are 7-10 t/ha of pods, 4-7 t/ha of green beans, or 18-25 t/ha of whole plants.

Taken from Vegetable Soybean Production, written by G. Lal, S.H. Lai, and S. Shanmugasundaram. 1990. Updated in 2000. Edited by T. Kalb.

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