Carol A. Miles, Ph.D., Agricultural Systems Specialist
We have been conducting variety trials of vegetable soybean (edamame) in Chehalis, southwest Washington since 1995. In 1998 we also began a spacing and nitrogen fertilizer trial in collaboration with Del Hemphill at the Oregon State University North Willamette Research Station. It is our goal to test the performance of commercially available edamame varieties and to fine-tune the production recommendations for this new crop. The purpose of this web page is to provide the reader with photographic images of vegetable soybean and its production and harvest potential.
Vegetable soybean plants have a growth habit very similar to green beans. They are approximately the same height, 1 ½ – 2 feet tall, and do not require staking or other support. Plant spacing in the row is 2–4 inches, and spacing between rows is 18–24 inches. Pods grow along the stem of the plant (Figure 1) and are covered in fine hairs which vary in color from a translucent white to a dark brown. Generally, the lighter colored pod hairs are preferred by Asian customers, however hair color appears to have no direct relationship with flavor or other taste qualities.
|Figure 1. Vegetable soybean plants in the field (enlarged picture).|
Pods of the vegetable soybean are not edible. The beans must be shelled before eating. Generally, only pods with 2 or more beans per pod are marketable (Figure 2).
|Figure 2. Vegetable soybean pods on the plant (enlarged picture).|
It has beenour observation that plant stands of vegetable soybean can be variable (Figure 3). Edamame seed is not size graded, and larger seed can block the seed plate. Calibrate the seed plate for the largest size seed to avoid this problem. Due to the high expense of vegetable soybean seed ($6-$20 per pound), it is not advisable to over-seed a field.
|Figure 3. Poor vegetable soybean plant stands (enlarged picture).|
Currently in southwest Washington, we have not used mechanical harvesting equipment for vegetable soybean. Our research plots are small and we utilize hand harvest techniques to evaluate yields. Taiwan, a major vegetable soybean producing country, utilizes an FMC green bean harvester to harvest vegetable soybeans (Figure 4). This FMC harvester has been specially adapted to harvest vegetable soybean and has a relatively clean pick potential (Figure 5).
|Figure4. FMC green bean harvester harvesting vegetable soybean in Taiwan (enlarged picture).|
|Figure 5.Vegetable soybean picking potential of FMC harvester (enlarged picture).|
Vegetable soybeans are generally marketed in the pod. Although the pod is not eaten, pod characteristics are extremely important in the Asian market. Unacceptable pods include: pods with only one bean, blemished pods, and pods which have been damaged in harvest (Figure 6). It is interesting to note that this photograph was taken of a package of frozen vegetable soybean bought from a Tokyo food store in November 1997. Although Japanese marketers talk fervently about the absolute importance of pod quality (and product from the USA has been rejected because it does not meet these standards), the vegetable soybean product currently marketed in Japan does not meet these high standards.
|Figure 6. Vegetable soybean pod damage. (enlarged picture).|
In the United States, where the average consumer is not familiar with vegetable soybean, a new market potential is for shelled vegetable soybeans. In Japan, vegetable soybeans are most frequently purchased as a snack accompaniment to beer. The vegetable soybeans are cooked in the pod and the consumer shells each bean before eating it. In the USA, where we have no cultural affiliation for consuming vegetable soybeans in this fashion, it seems likely that shelled vegetable soybean marketed as a vegetable will have greater consumer appeal.
Shelling vegetable soybeans by hand before they have been cooked is extremely difficult and is not recommended as the parchment clings to the bean (Figure 7). However, a simple vegetable soybean sheller is used at the Asian Vegetable Research and Development Center (AVRDC) in Taiwan (Figure 8). Uncooked vegetable soybean pods are shaken down a grooved runway and are gently squeezed between two rubber-coated roller bars. The beans then fall into a trough and are gravity-fed into a collection container, shown at the right side of the sheller in this photograph. The pod falls to the floor and is discarded.
|Figure 7. Vegetable soybeans showing parchment (beans at right). (enlarged picture).|
|Figure 8. Vegetable soybean sheller at AVRDC in Taiwan. (enlarged picture).|
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, Washington State University Department of Crops and Soils.
Funding for 1995 research was from Phil Crawford, WSU Agriculture and Natural Resources. Funding for 1996-1997 research was from Tom Lumpkin and the WSU IMPACT Center. Funding for our 1998-1999 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