Profitability of tobacco production has dropped since the withdrawal of the federal price support program and soybean (Edamame) as a cash crop is an ideal substitute when marketed as a high value vegetable. This project addressed the need for improved supply to meet increased US demand for fresh edamame. This research found that harvest window for fresh edamame can be increased with combination of different production systems and appropriate selection of cultivars to grow. Growth season extension techniques that combine high tunnel, plasti-culture, and selection cultivars of appropriate maturity groups allowed for extended period of fresh edamame availability.
Edamame, a vegetable soybean, is harvested at R6 to R7 growth stage when seeds are still green (Fehr et al., 1971). Edamame contains high protein, monounsaturated fatty acids, and multiple minerals such as iron, zinc and phosphorus as well as vitamins such as B1 and B2 (Miles et al., 2000; Kelley and Sanchez, 2005). Edamame has been rapidly incorporated in American diet due to ethnic population growth and people’s awareness of edamame nutritional qualities. Edamame appears in grocery stores, farmers’ markets, and even Ruby Tuesday’s salad. The demand of edamame in the U.S. was estimated 14,877 tons annually (Johnson, 2000; Zhang and Kyei-Boahen, 2007).
Edamame is a promising opportunity in the specialty crop market. Over 70% of the edamame sold in supermarkets across the U.S. is imported from China and Taiwan, and is mainly marketed frozen. However, the quality of frozen edamame drops quickly in storage. Commercial frozen edamame may contain harmful bacteria such as Escherichia coli and Listeria monocytogenes (Pao et al., 2008). In addition, consumers raise the concern of edamame source of safety and start to seek locally grown fresh edamame (Montri et al., 2006).
Lack of long-term, local supply has become a barrier for successfully marketing of edamame in the U.S. because it has a very narrow field harvest window of only a few days. There is very limited information available of extending edamame harvest window though season extension production techniques in Virginia. Park et al. (2001) cultivated two Japanese edamame cultivars in Korea in plastic film house culture, plastic film tunnel. By planting from February 15 to September 25, they were able to harvest crop from May 25 to December 3. In the U.S., an intensive research was conducted to extend edamame harvest window in 2003 and 2004 at University of Kentucky (Bec et al., 2005). Four Gardensoy series edamame cultivars from MG I to IV were planted in greenhouses and transplanted into the field either covered by plastic film or no protection on April 1, 15, and 29 in Kentucky (Bec et al., 2005). The crop was harvested for fresh pods from June 17 (GardenSoy 11, MG I) to August 10 (GardenSoy 41, MG IV). In addition, GardenSoy 11 had lower marketable yield than other cultivars at all transplanting dates, which means that MG I cultivars may not be feasible for early production by transplanting in Kentucky.
Because of lack of sufficient research data on extending fresh edamame harvest window in Mid-Atlantic region, growers are looking after superior edamame cultivars with high stability and adaptability. The findings from this project will provide information on potential approaches to increase Virginia growers’ on-farm income through off-season supply and marketing of edamame. Compared to current situation, the viability and adoption of these production techniques may benefit edamame related business in future by supplying fresh edamame over a longer period.
The objectives of this project were; 1) To extend the edamame harvest window through season extension techniques; and 2) To identify edamame cultivars that can be grown in combination at each growing season to optimize yield.
To meet the objectives of this project, experiment was carried out at Randolph Research and Demonstration Farm, Virginia State University. The study was laid out as a randomized complete block design with three replications. Four edamame cultivars of different maturity groups (MG) where used: GardenSoy 31 (MG III), GardenSoy 41 (MG IV), Moon Cake (MG V) and Randolph (MG VI. Edamame planting in early- and mid-spring was done in a high tunnel (a polyethylene-covered semi-circular structure). Black plastic material was used to cover the seed beds for this early planted to increase root-zone temperature. Planting date varied because of unforeseen weather conditions, however, it was categorized into early-spring (Before April 21), mid-spring (April 21-May 21) and late spring (May 21- June 21), and late summer (Aug 21-Sept 21). During early-spring planting, all four edamame cultivars; Gardensoy 31, Gardensoy 41 and Moon cake were grown in a high tunnel under plasti-culture. However, during the second planting in the high tunnel, all four cultivars were also established in the field on non-plastic and plastic covered seed beds. Another planting in the field with or without plasti-culture was carried out in late spring. Also in late August-early September, crop was established in the high tunnel to protected crop from cold temperatures later in the fall.
During harvest, all plants were harvested and pods removed. Because day of planting, edamame maturity group, and production systems differed, harvest occurred over time. Total weight of harvested pods was determined and then sorted into pods with 1, 2, 3 or 4 seeds. The weight of pods in the individual categories was obtained. Total weight of marketable pods was obtained as weight of all pods with two or more seeds. A representative sample of the marketable pods was obtained weight and shelled. Number of seeds was obtained, and its fresh weight determined. About 100 gram of the shelled seeds were obtained and stored frozen. The seeds were later freeze tried and ground. The ground material was analyzed to determine oil, protein, and sucrose content.
Plants in high tunnel on plasti-culture in early- and mid-spring showed good growth and pod harvest was achieved as early as the beginning of July. During mid-spring, crop planted in the field on plastic-covered beds showed faster growth than those without plastic cover (Figure 1). Using the production systems (High tunnel, plastic covered seed-beds in the field, and conventional soybean production) in combination with edamame cultivars of different maturity groups, the harvest window was extended from the a few days for conventionally produced crop to several months (Table 1). Within a cultivar, harvesting occurred two weeks to a month between first and second crop in the high tunnel. In the field, crop on plastic-covered beds was harvested earlier than those without plastic. Gardensoy31 (MG III) and Gardensoy41 (MG IV) were harvested earlier than Mooncake (MG V) and Randolph (MG VI) when planted at the same time. This is not surprising since these cultivars matures earlier than those of higher maturity groups like Randolph. Because edamame cultivars were of different maturity group and planting occurred on different dates throughout the spring and late summer, pod harvest occurred from early July and continued through mid-October. However, extremely cold temperature and animal pest destroyed edamame grown in late summer for two successive years. While this crop was not included in the result, there was a potential to extend harvest into early November.
For a specific planting period and for a specific production system (high tunnel, field with or without plastic covered seed-bed), total harvested pods differed with edamame cultivars. For early spring planting in the high tunnel, total pod yield varied from 4300 kg ha-1 in Gardensoy31 to over 10,000 kg ha-1 for Randolph (Table 2). Slightly higher yields were obtained during the second planting in the high tunnel in mid- spring. Yield in a crop established in August and September in the high tunnel are not included due to loss of crops from destruction by animal pest.
In mid-spring, though not significant, marketable yield from crop established in high tunnels with plastic covered seed-bed were relatively higher than that from field without plastic cover (Table 3). While marketable yield range from a low of 4120 kg ha-1 in Gardensoy31 to 6545 kg ha-1 in Randolph under the high tunnel, it ranged from 2092 kg ha-1 in Gardensoy31 to 10,287 kg ha-1 in Randolph in uncovered field plots. The difference in yield between cultivars within a production systems could be attributed to differences in cultivar yield potentials. In field grown crop, plastic covered-bed increased yield in all cultivars. Under all the systems, marketable pods (≥ 2 seeds pod-1) were between 40-75 % of the total yield. The number of pods with at least two beans was proportionally higher than the other class categories and could explain the high proportion of marketable pod yield. Beans harvested at different time periods during first year of production showed comparable levels of sucrose, protein and oil. This could indicate that even when produced of season, edamame quality could be maintained.
There was a strong correlation between yield and yield related traits (Table 4). Total pod weight was correlated to marketable pod weight and number of pods with one, two, or three seeds. Similarly, marketable pod weight was correlated to number of pods with one, two, or three seeds.
- Table 3. Comparison of edamame cultivars total and marketable pod yield for mid-spring planting under different production systems
- Table 4. Correlation coefficients of yield and yield related traits
- Figure 1. Growth of field grown plants grown the same day in mid-spring with (a) and without plastic cover (b)
- Table 1. Planting and harvest period of edamame cultivars grown under different production systems
- Table 2. Comparison of total and marketable pod yield for edamame cultivars grown under the high tunnel at different planting dates
Educational & Outreach Activities
A student thesis write-up is ongoing. A manuscript will be written and published in refereed journals in the near future.
Farm tours and field days were used to discuss the project and its benefit to potential future producers. Knowledge acquired will be used to develop recommendation on production techniques and selection of appropriate cultivar combination for interested producer. While adoption as not occurred, this information will be available to those interested in edamame production in the future.
There is great potential to increase edamame supply in Virginia using season extension techniques. A mix of high tunnel, plastic covered seed-beds allows for early planting when field soil temperatures are still too low for root growth. This crop will be harvested in early summer and producers may be able to access market when supply is low and potential for higher prices exist. By making appropriate cultivar choices, edamame of different maturity groups allows for a sequential harvest over several months and ensure fresh pod/bean supply for extended periods.
Areas needing additional study
Economic analysis should be done to determine the viability and profitability of the production techniques used in this study. Collaborative work needs to be done with food packaging entities and consumer markets to determine the market demand and edamame supply dynamics so that timely production can be done.