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Edamame Production For Southwest Washington

By: Carol A. Miles, Ph.D., Agricultural Systems Agent, and Leslie Zenz, Technical Assistant,
WSU Cooperative Extension, 360 NW North St., Chehalis, WA
Phone: 360-740-1295, Email: milesc@wsu.edu

<http://www.localaccess.com/wsulc/edam.htm>

About Edamame
Edamame (green vegetable soybean) have been a favorite vegetable in Asia since their first recorded use in 200 BC. Edamame (pronounced ed-ah-mah-may) consumption in the United States is growing due to an increasing Asian American population as well as a rise in popularity of Asian restaurant cuisines. Edamame are specialty varieties of soybean, Glycine max, which are eaten at the green stage as a vegetable (Figure 1).

Figure 1. Plate full of edamame pods (click here for the enlarged picture).

Edamame are more digestible than field soybeans and have lower levels of trypsin-inhibitor, making them easily digestable with only a short cooking time. Edamame are highly nutritious and contain about 16% protein, almost twice that of lima beans, and are also rich in calcium and Vitamins A and B. Large-seeded types are consumed as a green vegetable or as a snack, and small-seeded types are used for sprouts. Edamame plants are very similar to bush beans in height (Figure 2), however the pods are not edible and only the bean is eaten. Cooked edamame have a sweet nutty flavor, and in China and Korea they are traditionally eaten as a vegetable in stir-fries. In Japan, edamame are eaten as a snack with beer - much as Americans eat peanuts

Figure 2. Edamame plants in the field (click here for the enlarged picture).

Edamame Quality Factors
Several quality factors are associated with edamame for the Asian market. At least two beans per pod are required and four is preferred. Pods with only one bean are not marketable. Edamame pods, like all soybeans, are covered with fine pubescence or hairs (Figure 3). The color of the hairs is critical to the Asian market. Only white or a very light brown hairs are acceptable whereas dark brown hairs are not. Pod blemishes are also not acceptable on the Asian market. Finally, pod color at harvest is critical to quality edamame production. Pods must be bright green in color with no yellowing.

Figure 3. Edamame beans on the plant (click here for the enlarged picture).

The fresh market in Asia traditionally sells whole edamame plants (stalks, leaves and pods), although modern demands have increased the sale of pre-picked pods. Because fresh soybeans are only available seasonally, much like sweet corn or peas, the frozen food industry in Asia has stepped in to make edamame available year-round. In the United States, there could be a great opportunity for edamame production for the frozen food industry.

Variety Evaluation for Southwest Washington
Over a period of two years, 1995 and 1996, we evaluated a total of 18 commercial edamame varieties at an on-farm location in Chehalis, southwest Washington. Edamame varieties have not been tested extensively or developed specifically for production in southwest Washington. Environmental factors in the area, such as acid soils and low heat unit accumulation, influence variety performance. Commercial varieties currently available in the USA were evaluated for production in southwest Washington. The farmer prepared the field for planting and provided irrigation when requested. Planting, maintenance, harvesting, and evaluation of the edamame trial were all done by Dr. Carol A. Miles, WSU Extension Agricultural Systems, and technical assistant, Leslie Zenz. This trial will be repeated in 1997.

Spacing and Fertilizer
In our studies, the final spacing in the row was 2-inches and the spacing between the rows was 18-inches. Planting depth was appoximately 1 inch, but a good rule of thumb for all seed is that the planting depth should be equal to approximately twice the seed size. All plots were fertilized with a 10-20-20 N-P-K formulation, applied at the rate of approximately 500 lbs/A, or 50 lbs actual N/A, six weeks after planting, as stated in the edamame production guidelines from Asian Vegetable Research and Developement Center. This timing and rate of fertilizer application is recommended in order to enhance pod color. Soil pH was about 6.0 and this seems adequate for good edamame production. We have not tested soil pH effects but would suggest to lime to bring soil pH up to at least 6.0.
Planting and Emergence
Plots were planted on May 26, 1995, and May 28, 1996 (Figure 4). Both years we intended to plant in mid-May, but due to field conditions were not able to do so. We would suggest an earlier planting date, early-May, if soil conditions allow. Plant emergence in 1996 occured in two weeks whereas in 1995 emergence occured in three weeks. In 1995, soil conditions were dry and no rainfall occurred following planting. In 1996, soil conditions were moist at planting and slight rainfall occurred before emergence. Soil moisture played a key role to time of emergence, and moisture is necessary for good, rapid emergence. With adequate soil moisture at planting, edamame can be expected to emerge within two weeks.

Figure 4. Planting edamame trial (click here for the enlarged picture).

Weed Control
In both 1995 and 1996, plots were hand-weeded three times during the growing season, mid-June, mid-July, and mid-August. Early weed control is essential, and once the edamame canopy covers the space between the rows, the demand for weed control drops. The plant canopy closed in mid-August both years.

Earliness
During the growing season in southwest Washington, approximately 1700 heat units are accumulated (with a base temperature of 50^o F). This is 70% the heat unit accumulation of the mid-west, and has a significant impact on crop maturity. Both years, all varieties were harvested in southwest Washington more than 40 days later than their advertised days to maturity. For example, White Lion, Gion, Lucky Lion, and Early Hakucho are advertised as maturing in 70, 72, 75, and 75 days, respectively. However, in our studies, these four varieties matured, on average, in 113, 123, 119, and 114 days, respectively (Table 1).
One variety, Fiskby V flowered and matured substantially earlier than all other varieties. This variety, however, is a small-seeded edamame type and is not suitable for the fresh vegetable market. The varieties Yusuzumi and Mikawashima 202 were late flowering (first flower after 75 days) and did not mature by the end of the season. Of those varieties which reached maturity, first flowering occured by July 31 (69 days after planting), and plants were harvested by September 17 (118 days after planting).
Earliness is a key factor affecting suitability of edamame for southwest Washington. Varieties which are advertised to mature in more than 75 days will not reach maturity in southwest Washington before rains and frost make harvesting impossible.

Irrigation
Seasonal precipitation, measured from late May until the end of September, was 4.04 and 5.63 inches in 1995 and 1996, respectively. In 1995, plots were not irrigated and bean weight was quite small
(Table 2). In 1996, plots were irrigated twice, July 9 and August 23, and bean weight increased dramatically. At each irrigation, approximately 2 inches of water was applied to the plots.
Whole pod (bean + pod) weight did not change in 1996 as compared to 1995, whereas bean weight doubled in 1996 as compared to 1995. Bean weight is an essential indicator of suitability for the fresh vegetable market. The weight of 25 beans should equal approximately 20 grams in order to meet the criteria for large-seeded edamame types which are marketed as a fresh, green vegetable. Varieties which do not meet this weight criteria may be used for sprouts. In 1995, none of the varieties produced beans which were suitable for the vegetable category, whereas in 1996 all the varieties produced beans which were suitable for the vegetable category. It appears irrigation is essential in southwest Washington for the production of large-seeded vegetable-type edamame.

Yield and Timing of Harvest
Thirteen varieties reached maturity, and four varieties, White Lion, Shironomai, Butterbeans, and Lucky Lion, were high yielding both years (Table 3). Gion yielded well in 1995 but in 1996 low plant stands resulted in poor yields. Two varieties, JSM0168 and JSY1004, yielded very well in 1996 but were not included in our trials in 1995 therefore insufficient data is available for accurate performance assessment.
It is evident that time of harvest is very critical for quality edamame production. Edamame must be harvested when the pods are at least 85% filled but before they start to turn from a bright green to a yellowed color. The harvest window appears to be close to one week in southwest Washington. Once edamame pods gain a yellowish tinge they are no longer acceptable to fresh market buyers.

Mechanical Harvesting
A possible limiting factor to large-scale edamame production in Washington is mechanical harvesting. To make edamame a profitable and manageable crop for larger growers in the state, mechanical harvesting will be essential. For small-scale growers who already hand-harvest vegetables, hand-harvesting edamame will be a viable option. A green bean harvester is used in other countries to mechanically harvest edamame for the fresh vegetable market. The same type of equipment is available in the Pacific northwest but it has not yet been tested with edamame. It is our objective in 1997 to plant a small commercial plot in southwest Washington and test a green bean harvester for harvesting edamame.

Commercial Farm Plots
In 1996, small commercial plots were planted on two farms, Hamilton Meadows in Chehalis and Shaffner Farms in Montesano, to test planting machinery and mechanical cultivation. A pea planting plate was used to plant edamame, with good success. From these plots it was apparent that weed control can pose a serious threat to edamame production. Three cultivations, in mid-June, mid-July and mid-August, were necessary to maintain low weed populations. Chemical weed control options could be available, but it is not yet clear if further agrochemical labeling is necessary to gain access to products currently labeled for use on field soybeans.

Cooking and Storing Edamame
To cook edamame, add the whole pods to boiling water. Boil the pods for five minutes, then drain and cool them slightly. By lightly squeezing one end of the pod, the beans will pop out the other end. Trying to shell the beans before cooking is an unrewarding task as the pod sticks tightly to the bean (Figure 5).

Figure 5. Edamame beans on a plate (click here for the enlarged picture).

Cooking separates the bean from the pod, enabling the beans to pop out quickly and painlessly. Edamame can also be cooked in a microwave. Rinse the pods and place them in a covered microwave-safe dish. Suggested cooking rates are 4-5 minutes on high or full power for 2 cups of pods. Edamame can be kept fresh in the refrigerator for a least 2 weeks. If you wish to store them longer, we suggest blanching the whole pods for 2-3minutes and freezing them in the pod. When using frozen edamame for a meal, cook them for 5 minutes in boiling water or 3-4 minutes in the microwave on high or full power.

Edamame Recipes
Edamame taste good eaten freshly cooked, squeezed from pod to mouth, for a delicious and nutritious snack. When adding edamame to recipes, cook them first. Edamame may be used as a substitute for lima beans or peas in any recipe. Try edamame as an accompaniment to mushroom dishes, potato and leek soup, mashed potatoes, spaghetti squash, or other savory winter vegetable recipes.
In stir-fries: Boil or microwave the pods and shell the beans as suggested above. Toss edamame beans into a stir fry with other chinese vegetables including cabbage, bean sprouts, and bamboo shoots. Or, add edamame to an American stir-fry of beets, carrots, broccoli, cauliflower, or most any other vegetable.
In rice-dishes: The delicate flavor of edamame lends itself well as an accompaniment to Basmati or Jasmine white rices. Cook the edamame and toss into cooked rice and serve.
In pasta dishes: Add edamame to Asian style pasta salads such as sesame noodles. Or add edamame to your favorite pasta salad.

Seed Sources
A list of the varietes evaluated in these trials and contact information for the supplying companies is given in Table 4.

Acknowledgements
All photographs were taken by Carol Miles and may not be reproduced without her consent.
Photographic images were scanned for web presentation by Suzanne Farrow, WSU Crops and Soils.
Funding for 1995 research was from Phil Crawford, WSU Agriculture and Natural Resources. Funding for 1996 research was from Tom Lumpkin and the WSU IMPACT Center. Funding for our 1997 research is from an IMPACT grant with Tom Lumpkin et al.
Special recognition is due to Dr. S.Shanmugasundaram, Director, International Cooperation Program AVRDC, P.O. Box 42, Shanhua, Tainan, Taiwan 741 Tel:886-6-5837801 Ext. 500, Fax:886-6-5830009, email: sundar@Netra.AVRDC.org.TW

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