Edamame (vegetable green soybean)
by Vong
Q. Nguyen*
Introduction
Vegetable green soybean (Glycine max [L.] Merr.) is one of the most important
high protein vegetable crops in Asia. The soybean has been cultivated
for a long time, probably from 4,000-5,000 years in China for food and
medicines. Immature green beans of soybeans have been consumed as a vegetable
as long as the dry soybean has been used as a bean crop. The cultural
practices for green soybean are identical with ordinary soybean except
that the green pods are harvested at the mature green stage when the pods
are almost filled. It is evident from recent studies that green soybean
can be grown in New South Wales and Victoria for the January to April
markets. November and December are the ideal times to grow green soybean
for the highest pod yield which is comparable to the average yield of
8 t/ha in Japan. Green pods from November and December plantings could
also be marketed in January, February and March, which would coincide
with the most favourable period for export to Japan. However, since Japanese
quarantine restrictions prohibit entry of fresh green soybean from mainland
Australia, green soybean targeted for Japan must be in the processed form.
Only fresh-market green soybean produced in Tasmania, is allowed to be
exported to Japan. Markets and marketing issues International trade in
green soybean focuses on supplying Japan where total demand is approximately
160,000 t per year. There are two import markets in Japan: fresh-market
green soybean and frozen green soybean.
1. Imported fresh-market green soybean: Imported fresh-market green soybean
mainly came from Taiwan. China, Thailand and the Philippines also supplied
freshmarket green soybean to Japan but occupied a very low proportion
(only 10%) of the whole import market. In 1993, Japan imported 5,617 t
of fresh-market green soybean. Of this, 850 t was sent to the Tokyo markets.
Monthly imported volumes and landed prices are shown in Table 2 (not available
in this html version). The landed prices varied monthly but the peak occurred
in March and was ¥648/kg. However, average prices for the five-year period
1990-1994 showed that January, February and March are the best times for
green soybean with February being the time for highest prices in the Tokyo
market (Table 3- not available in this version).
2. Imported frozen green soybean: In 1993, Japan imported 51,250 t of
frozen green soybean of which 75% or 38,229 t came from Taiwan and 22%
or 11,088 t came from China. The remaining 3% came from Thailand (1,805
t), USA (107 t) and South Korea (21 t). Average landed prices from these
sources were: Taiwan ¥210/kg China ¥174/kg Thailand ¥185/kg USA ¥196/kg
South Korea ¥190/kg Most of these imports were sold to the food service
section at an average landed price of ¥201/kg. (Table 5 - not available
in this html version). In Japanese supermarkets, frozen green soybean
imported from China is sold at ¥228/400 g (or ¥570/kg.) while the Taiwanese
product generally commanded a higher price of ¥300/400 g (or ¥750/kg).
The price difference is due to poorer quality product from China. Recently,
the Chinese product has improved in quality as Taiwanese companies have
transferred their processing technology to China, resulting in a larger
volume of frozen green soybean being shipped to Japan in 1995 (Table 5
- not available in this html version).
3. Imported seed of vegetable green soybean: There is a small market for
import of seed of green soybean into Japan. Hokkaido, the major seed production
area for the Japanese green soybean market, has decreased in area from
476 ha in 1987 to 422 ha in 1992, resulting in short supply of approximately
200 t of seed. In Australia, seed of green soybean would be produced in
the southern coastal areas of New South Wales and on the east coast of
Victoria. Pod shattering when ripening is the major problem for production
in hot, dry inland areas. Production requirements Green soybean is a summer
crop which has adapted to the warm or hot conditions of the New South
Wales coastal weather. Soil temperatures greater than 15°C are needed
for effective germination and seedling growth, but the most rapid rate
of germination occurs at 20°C to 25°C. Plants are grown successfully on
a wide range of soil types, from black self-mulching clays and red-brown
earths of the inland river valleys to the light-textured sandstones of
the New South Wales coast. Vegetable green soybean prefers well-drained
soils and under irrigation they are easily managed to produce high yields.
Green soybean can be harvested within 68-86 days depending on planting
time. Varieties € Cultivars - Commercial cultivars should have high-yielding
pods with an average of 40-50 pods per plant with pod length >4.5 cm and
pod width 1.3 cm and no more than 175 pods weighing 500 g. They should
also have a fresh green colour, be of large size (2.5-3.0 g fresh weight
per pod), preferably with white pubescence, colourless hilum, high ratio
of two to three seeds per pod and be of good eating quality. Of 22 cultivars
imported from Japan, two (GSB-1 and GSB-4) have shown promise, having
achieved more than 9 t/ha on the New South Wales Central Coast in the
December planting. The average yield in Japan is 8 t/ha. The planting
time is from November to early January for the January to April markets.
Sowing from mid-January is not recommended due to the risk of unfilled
pods caused by cool weather in April. The tested cultivars which were
used in this study were unsuitable in the Murrumbidgee Irrigation Area
of New South Wales. Seed samples are available at the Gosford Horticultural
Research and Advisory Station (Phone: (043) 481900; Fax: (043) 481910).
Agronomy The seeds need to be inoculated with Bradyrhizobium japonicum
strain CB1809 and are sown at planting densities of 0.15-0.20 m ¥ 0.90
m (55,555-74,000 plants/ha) to produce a high proportion of marketable
pods which contain two and three seeds each. For seed production, planting
density of up to 130,000 plants/ha (0.10 m ¥ 0.75 m) is used to increase
seed yields. Fertilisation of green soybean in early growth of plants
should be focused to form good plant height and to produce maximum pod
numbers. The combination of N:P:K at the rate of 78 kg. N:104 kg. P:64
kg. K per ha should be applied as a basal dressing. However, to maximise
the marketable pod yield, one side dressing of potassium nitrate at the
rate of 100 kg. per ha (13N:46K) would be necessary at flowering. Lack
of nutrition at reproduction stage could lead to an increase in number
of unfilled and/or one-seed pods. Irrigation‹Green soybean requires a
large amount of water for growing, particularly at the vegetative stage,
for flower bud formation and for pod development. Insufficient water during
flowering to pod growth stage reduces flower numbers and causes pods to
drop. Pest and disease control Weed control is very important for green
soybean as weeds badly affect yield and pod quality. The herbicide that
was successfully identified for green soybean at the Somersby Research
Farm was Dacthal® (pre-emergence, 6 kg./ha). Diseases and insects‹The
most common diseases and insects that were found on the Central Coast
of New South Wales were Sclerotium crown rot (fungus Sclerotium rolfsii)
and caterpillars of budworms (Helicoverpa armigera) and cutworms (Agrotis
spp.). Warm and moist weather favours these diseases and insects. Harvesting,
packaging and postharvest handling Harvesting‹Green soybean should be
harvested within 68 to 86 days after sowing, depending on cultivars and
planting times, when 90% of the pods become filled and have a f.resh green
colour. Green soybean can be harvested three days earlier and/or later,
but the pod yield could be lost at the rate of 0.5 t/ha/day. Pod yield
of cultivars growing on the New South Wales Central Coast achieved a high
yield of 9 t/ha in the December plantings. Mechanical harvesting‹The fresh
bean harvester does a very good job in harvesting green soybean, removing
approximately 76% of beans and separating foliage and stalks. Harvest
time, using the single row machine, is approximately a quarter hectare
per hour. Approximately 7% of beans harvested by machine were bruised.
There are three types of vegetable green soybeans sold in Asian markets
which are: Attached type: (pod-bearing plant), marketed in bundle form
which is the most desirable in fresh markets as Japanese customers believe
this type keeps pod quality longer, ie. flavour and taste. The top leaves
and small damaged pods are removed while whole plants with leaves, pods,
stems and roots are packed in bundles or in 5 kg. wooden boxes or cartons.
Detached type: (pod only) is marketed in plastic net bags. Only marketable
pods (two- and three-seed pods) are selected and packed in these bags.
Attached types usually obtain higher prices than the detached types because
of better pod quality and these high prices meet the costs of transport.
Harvesting, de-podding and packaging are labour intensive and need to
be carried out in as short a time as possible to retain the freshness
of green pods. Fresh bean: (bean only) in which beans are shelled and
marketed as fresh beans. The first two types are the most popular form
in Japan while the fresh, shelled beans are most popular in the Chinese
markets such as Taiwan, Hong Kong and Singapore. Frozen green soybean,
which is the major type of green soybean imported by the Japanese markets,
is the detached type which is frozen by using Individual Quick Frozen
(IQF) technology. Specific processing requirements € With IQF technology,
both carbon dioxide (CO2) and nitrogen liquids produced a highly satisfactory
quality of frozen pods. € Blanching at 95°C constant for two minutes could
easily produce `popped' frozen green soybean. € After blanching and cooling,
it is desirable that the temperature of the bean should be less than 16°C.
€ Freezing immediately after blanching is recommended to avoid build up
of bean tem-perature which would cause a high percentage of undesirably
dark and bruised pods. The Taiwanese processing flow chart is shown in
Figure 1 (not available in this html version). Future outlook Discussion
with Japanese vegetable importers has confirmed the potential of fresh
vegetable green soybean as a cash crop for export from Australia. However,
due to quarantine problems, only green soybean grown in Tasmania is allowed
to be exported to Japan as fresh product. A previous study has shown that
many tested cultivars which are high in yield and pod quality can be promoted
by the Tasmanian vegetable industry, thus providing opportunities to target
peak periods for demand of fresh markets in Japan during January, February
and March. For frozen green soybean, investigation of Japanese markets
has shown that average wholesale prices have reduced annually since 1990
from ¥323/kg. to ¥163/kg. in 1995 (Table 4 - not available in this html
version). The price reductions may be due to an increase of Chinese and
SE Asian supplies. If the quality of Chinese supply improves, as mentioned
above, wholesale prices could drop as low as ¥150/kg because of low labour
costs in China and SE Asia. The value of Japanese Yen, which has recently
decreased to ¥88/our Australian dollar (June, 1997) is an important factor
for consideration. The break-even price for Australian frozen green soybean
is A$1.55/kg. (Table 6 - not available in this html version). Organic
green soybeans in both fresh and frozen forms are also required by Japanese
trade houses.
