Edamame, an edible version of soybean (Glycine max), is emerging in popularity in North America. A nutritious and appetizing vegetable with a sweet, nutty flavor (Miles et al., 2000), edamame is harvested when pods are bright green and immature seeds are at their maximum size (Shanmugasundaram et al., 1991). The protein-rich seed is attractive to health-conscious consumers (Rao et al., 2002). Edamame seed also contains cholesterol-free fat (5.7%), phosphorus (158 mg per 100 g), calcium (78 mg per 100 g), vitamin B1 (0.4 mg per 100 g), vitamin B2 (0.17 mg per 100 g), isoflavones and tocopherols (Shanmugamsundaram and Yan, 2004).
The United States is second in global grain-type soybean production, accounting for 122.5 million metric tons in 2018 (USDA-NASS, 2019). However, an estimated 70% of the edamame consumed in the U.S. is imported from China (Barlow, 2018). Cultivar evaluation trials conducted across the United States—including the Mid-Atlantic, Mississippi delta, upper Plains, and Midwest—attest to the adaptability of edamame (Duppong and Hatterman-Valenti, 2005; Hunsberger et al., 2007; Zhang and Kyei-Boahen, 2007). An economic analysis revealed that edamame returns five times per hectare more than grain-type soybean grown in a 2-year rotation with corn (Karlen et al., 2004). To meet growing consumer demand for domestic product in the past decade, several U.S. vegetable processors are growing edamame (Crawford et al., 2018).
Several challenges to expanding commercial edamame production exist, including voids in best management practices for growing the crop. Recent research has reduced some barriers, including registration of certain herbicides (Williams and Nelson, 2014; Williams et al., 2017, 2019), developing nonchemical weed control tactics (Crawford and Williams, 2018; Crawford et al., 2018), and identifying optimal seeding depth (Crawford and Williams, 2019; Zhang et al., 2013). For other crop production practices, the vegetable industry relies heavily on established grain-type soybean management guidelines; however, research to confirm or deny their appropriateness is lacking.
One fundamental decision for growing a crop is to determine the target plant population density, hereafter called simply “plant density.” Selecting the appropriate plant density is an important crop management decision in commercial edamame production where plant architecture determines efficiency of mechanical harvest (Zandonadi et al., 2010). Studies on grain-type soybean report that plant density influences plant height (Matsuo et al., 2018; Mehmet, 2008), number of main stem branches (Agudamu and Shiraiwa, 2016; Board and Kahlon, 2013), and plant biomass (Matsuo et al., 2018). Companies selling edamame seed identify seeding rates ranging from 197,600 plants/ha (Wannamaker Seeds, Saluda, NC) to 344,200 plants/ha (Johnny’s Selected Seeds, Winslow, ME), which is similar to recommendations for grain-type soybean (Nafziger, 2009). However, peer-reviewed literature to develop such recommendations appears to be nonexistent. In addition, edamame seed is more expensive, ranging from $25 to $50 per kg for edamame (Fedco Seeds, Clinton, ME; Johnny’s Selected Seeds, Winslow, ME; Wannamaker Seeds, Saluda, NC) compared with $2.5 per kg for conventional grain soybean. Conventional grain soybean cost (per kilogram) were calculated based on grain soybean cost of $57.40 per acre (USDA-ERS, 2019) and seeding rate assumed 22.68 kg (50 lbs) per acre.
The vegetable industry would benefit from research-based information on edamame response to plant density, including horticultural performance and an economic analysis. We define the EOPD as the plant density that maximizes grower profits when accounting for seed cost. The objectives of this study were to a) evaluate edamame plant morphology and yield response to plant density and b) determine the EOPD of machine-harvested edamame.
AgudamuT.Y.ShiraiwaT.2016Branch development responses to planting density and yield stability in soybean cultivarsPlant Prod. Sci.19331339
BarlowZ.2018Soy—edamame: 70% imported from China—U.S. researchers working on U.S. bean. Virginia Tech University. 1 Nov. 2018. <https://agfax.com/2018/11/01/soy-edamame-70-imported-from-china-u-s-researchers-working-on-u-s-bean/>
BoardJ.E.2000Light interception efficiency and light quality affect yield compensation of soybean at low plant populationsCrop Sci.4012851294
CrawfordL.E.WilliamsM.M.IIWortmanS.E.2018An early-killed rye (Secale cereale) cover crop has potential for weed management in edamame (Glycine max)Weed Sci.66502507
DuppongL.M.Hatterman-ValentiH.2005Yield and quality of vegetable soybean cultivars for production in North DakotaHortTechnology15896900
EdwardsJ.T.PurcellL.C.2005Soybean yield and biomass responses to increasing plant population among diverse maturity groupsCrop Sci.4517701777
Fedco Seeds20198 Mar. 2019. <https://www.fedcoseeds.com/seeds/list-edamame>
FehrW.R.CavinessC.E.BurmoodD.T.PenningtonJ.S.1971Stage of development descriptions for soybeans, Glycine max (L.) MerrillCrop Sci.11929931
Johnny’s Selected Seeds20198 Mar. 2019. <https://www.johnnyseeds.com/vegetables/beans/soybeans/>
HunsbergerL.SimonJ.SciarappaW.J.ShenD.WuQ.L.HulmeB.2007Evaluation of edamame cultivars in New Jersey and Maryland. <https://ssrn.com/abstract=2032208>
Illinois Climate Network2019Illinois climate network: monthly and daily data. 24 June 2019. <https://www.isws.illinois.edu/warm/datatype.asp>
KarlenD.L.DelateK.TurnbullR.BoesJ.2004Organic soybean production: Challenges and perspectives of an increasing trend. Proc. VII World Soybean Research Conf. VI International Soybean Processing and Utilization Conference and III Congresso Brasileiro de Soja. 29:319–327
LiY.S.DuM.ZhangQ.Y.HashemiM.LiuX.B.HebertS.J.2013Correlation and path coefficient analysis for yield components of vegetable soybean in Northeast ChinaLegume Res.36284288
MatsuoN.YamadaT.TakadaY.FukamiK.HajikaM.2018Effect of plant density on growth and yield of new soybean genotypes grown under early planting condition in southwestern JapanPlant Prod. Sci.211625
MilesC.A.LumpkinT.A.ZenzL.2000Edamame. Food & farm connection. Wash. State Univ. Coop. Ext. Pacific Northwest Ext. Publ. PNW0525
NafzigerE.2009Soybean. Illinois Agronomy Handbook. 24th ed. Champaign IL: University of Illinois Extension. 2009:27–36
OhY.J.KimK.H.SuhS.K.KimS.D.ParkH.K.RyuJ.H.KimJ.G.WoodA.J.ChoY.2007Effects of stem lengths on seed yield and yield components of late planted soybeansWorld J. Agric. Sci.3363370
RaoM.S.S.BhagsariA.S.MohamedA.I.2002Fresh green seed yield and seed nutritional traits of vegetable soybean genotypesCrop Sci.4219501958
ShanmugasundaramS.ChengS.T.HuangM.T.YanM.R.1991Varietal improvement of vegetable soybean in Taiwan p. 30–42. In: S. Shanmugasundaram (ed.). Vegetable soybean: Research needs for production and quality improvement. Asian Vegetable Research and Development Center Taiwan
ShanmugasundaramS.YanM.R.2004Global expansion of high value vegetable soybean. Proc. VII World Soybean Conf./IV Intl. Soybean Processing and Utilization Conf./III Brazilian Soybean Congr. Foz do Iguassu Brazil 29 Feb.–5 Mar. 2004
UmburanasR.C.YokoyamaA.H.BalenaL.Dourado-NetoD.TeixeiraW.F.ZitoR.K.ReichardtK.KawakamiJ.2019Soybean yield in different sowing dates and seeding rates in a subtropical environmentIntl. J. Plant Prod.13117128
U.S. Department of Agriculture National Agricultural Statistics Service (USDA-NASS)2019Crops and plant statistics. 19 June 2019. <https://www.nass.usda.gov/Statistics_by_Subject/index.php?sector=CROPS>
U.S. Department of Agriculture Economic Research Service (USDA-ERS)2019Commodity costs and returns. 25 Sept. 2019. <ers.usda.gov/data-products/commodity-costs-and-returns/>
Wannamaker Seeds20198 Mar. 2019. <http://www.wannamakerseeds.com/order.html>
WilcoxJ.R.SediyamaT.1981Interrelationships among height, lodging and yield in determinate and indeterminate soybeansEuphytica30323326
WilliamsM.M.IIMoodyJ.L.HausmanN.E.2019Vegetable soybean tolerance to flumioxazin-based treatments for waterhemp control is similar to grain-type soybeanWeed Technol.33530534
WilliamsM.M.IINelsonR.L.2014Vegetable soybean tolerance to bentazon, fomesafen, imazamox, linuron, and sulfentrazoneWeed Technol.28601607
ZandonadiR.StombaughT.CoolongT.PfeifferT.2010Mechanical harvesting of edamame. 14 July 2017. <http://www.uky.edu/Ag/ccd/edamameharvest.pdf>
ZhangQ.Y.HashemiM.HebertS.J.LiY.S.2013Different responses of preemergence and early seedling growth to planting depth between vegetable soybean and grain soybeansLegume Res.36515521