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Factors Affecting the Growth ofMicrogreen Table BeetCarrie J. Murphy a , Kenneth F. Llort b & Wallace G. Pill ba New Castle County Cooperative Extension Service , Newark,Delawareb Department of Plant and Soil Sciences , University of Delaware ,Newark, DelawarePublished online: 02 Jun 2010.

To cite this article: Carrie J. Murphy , Kenneth F. Llort & Wallace G. Pill (2010) Factors Affecting theGrowth of Microgreen Table Beet, International Journal of Vegetable Science, 16:3, 253-266, DOI:10.1080/19315261003648241

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International Journal of Vegetable Science, 16:253–266, 2010Copyright © Taylor & Francis Group, LLCISSN: 1931-5260 print / 1931-5279 onlineDOI: 10.1080/19315261003648241

WIJV1931-52601931-5279International Journal of Vegetable Science, Vol. 16, No. 3, May 2010: pp. 0–0International Journal of Vegetable ScienceFactors Affecting the Growth of Microgreen Table BeetMicrogreen Table BeetC. J. Murphy et al.

Carrie J. Murphy,1 Kenneth F. Llort,2 and Wallace G. Pill2

1New Castle County Cooperative Extension Service, Newark, Delaware2Department of Plant and Soil Sciences, University of Delaware, Newark, Delaware

There are very few reports on the production of microgreens, a new category of saladcrops, the shoots of which are harvested at the seedling stage. A series of culturalstudies was conducted with the objective of lessening greenhouse production time andlowering production costs of microgreen table beet (Beta vulgaris L.). Sowing seed ballsat a commercially recommended rate (201 g·m−2; 11,256·seed balls·m−2) resulted ingreater shoot fresh weight·m−2 at 15 days after planting than sowing seed balls atlower rates, although individual shoots were lighter. Sowing seed balls that were ger-minated before sowing (pregerminated) in fine-grade exfoliated vermiculite moistenedwith 150% water (wt. per vermiculite dry wt.) for 5 days at 20°C resulted in 26%greater shoot fresh weight·m−2 at 15 days after planting than sowing nontreated seedballs. Combining preplanting fertilization of the peat-lite with calcium nitrate at 2000mg·L−1 of N (150 mL·L−1of medium) with daily postplanting solution fertilization with150 mg·L−1 of N led to a further increase in shoot fresh weight·m−2 of 21% (nontreatedseed balls) and 22% (pregerminated seed balls) compared to other fertilization regimes(excluding the check). Germinating, and extruding, seed balls in hydrophilic polymer(hydroxyethyl cellulose gel) advanced microgreen growth but not to the extent achievedwith vermiculite as the pregermination medium. Irrespective of seed ball treatment,producing microgreens in troughs using the hydroponic nutrient film technique, comparedto production in trays containing peat-lite, increased shoot fresh weight·m−2. Dependingon seed ball treatment, economic yield was increased 33% to 98% by 7 days after plant-ing and 75% to 144% by 15 days after planting. The greatest shoot fresh weight·m−2 at15 days after planting (10.14 kg·m−2) was achieved using seed balls pregerminated inmoist vermiculite and subsequent growth using the nutrient film technique.

Keywords Beta vulgaris, Beet root, Hydroponics, Microgreen, Seed germination,Soilless media, Peat-lite, Nutrient film technique, Table beet.

Microgreens have been defined as salad crop shoots harvested for consump-tion within 10 to 20 days of seedling emergence (Lee et al., 2004), and they aredevelopmentally classified between “sprouts” and “baby salads.” Though

Address correspondence to Wallace G. Pill, Department of Plant and Soil Sciences,Room 152 Townsend Hall, University of Delaware, Newark, DE 19716. E-mail:wgpill@udel.edu

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desired size of individual plants is the prerogative of the buyer/consumer,total shoot fresh weight (FW) is often the preferred yield determinant. Tech-niques that increase the speed of microgreen crop establishment would permitmore efficient use of expensive greenhouse space.

Lee et al. (2004) examined several seed treatments to advance greenhouseestablishment of table beet and chard, both Beta vulgaris L., microgreens.Seed ball treatments were matric priming (−1.0 MPa at 12°C for 6 days in finevermiculite) or various soaks (water, 20°C for 48 h; hydrogen peroxide, 0.3%[v/v] at 20°C for 48 h; hydrogen chloride, 0.3 M at 20°C for 2 h; or sodiumhypochlorite, 4% [v/v] at 20°C for 3 h). Though germination percentage waslittle affected, appreciable germination advancement in both crops wasachieved using all seed treatments. The most pronounced seedling emergenceadvancement was gained by germinating seed balls in fine-grade exfoliatedvermiculite (150% water [wt. per vermiculite dry wt.] for 3 days at 27°C) andsowing the germinated seed ball vermiculite mixture. Murphy and Pill (2010)found that presowing germination (pregermination) of arugula/rocket seeds(Eruca vesicaria subsp. sativa) in fine-grade exfoliated vermiculite moistenedwith 200% water (wt. per vermiculite dry wt.) for 1 day at 20°C increasedshoot FW at 14 days after planting (DAP) by 21%. Sowing pregerminatedseeds compared to sowing nontreated seeds in order to gain earlier andgreater yields was the logic behind a sowing technique termed fluid drilling inwhich germinated seeds are suspended and transferred to the seedbed in a gelcarrier (Pill, 1991). There appears to be no microgreen production literatureon use of hydrophilic gel as both a seed germination medium and a deliverymechanism to the seed bed.

Preplanting media fertilization and/or postemergence solution fertiliza-tion can affect microgreen growth rate. Nitrate or ammonium salts can serveas N sources for plant growth, although for most plant species, nitrate-Nresults in greater vegetative and/or reproductive growth than ammoniacal-N(Barker and Mills, 1980). In confirmation of this, shoot FW·m−2 and per plantof arugula microgreens was influenced in the order calcium nitrate > ammo-nium nitrate > urea when these fertilizer solutions were mixed in peat-lite at150 mL·L−1 of peat-lite before planting (Murphy and Pill, 2010). These N sourcesresulted in greater shoot FW·m−2 than preplanting ammonium sulfate, whichresulted in similar shoot FWs as media that received no preplant fertilizer.Irrespective of N source, increasing N rate from 500 to 4000 mg·L−1 quadraticallyincreased shoot FW·m−2 or per plant, with the greatest growth occurring with2000 mg·L−1 of N.

Application of soluble fertilizer through the irrigation water (solution fer-tilization, “fertigation”) is a widely practiced method of fertilizing horticulturalcrops. Compared with 100 mg·L−1 of N, 400 mg·L−1 of N as solution fertilizationtwice daily increased shoot dry weight of celery (Apium graveolens L.), lettuce(Lactuca sativa L.), broccoli (Brassica oleracea var. italica Plenck), and tomato

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Microgreen Table Beet 255

(Solanum lycopersicon Mill.) transplants by 37%, 38%, 61%, and 38% respec-tively, at 30 DAP (Masson et al., 1991). Soundy et al. (2005) evaluated lettucetransplant growth in response to 0, 30, 60, 90, or 120 mg·L−1 of N solution fer-tilized every 1, 2, 3, or 4 days. As N concentration increased, shoot dry weightand leaf N concentration increased, and root:shoot ratio decreased. Cornillon(1999) observed that increasing N concentration of daily solution fertilizationincreased tomato transplant shoot FW but had little effect on shoot dryweight. Murphy and Pill (2010) determined that shoot FW m−2 of microgreenarugula at 15 DAP increased as daily N solution fertilization concentrationincreased to 150 mg·L−1 of N. They found that the two most economical fertili-zation treatments to promote shoot FW·m−2 were daily solution fertilizationwith 150 mg·L−1 of N or daily solution fertilization with 75 mg·L−1 of N pluspreplant media incorporation of 1000 mg·L−1 of N from Ca(NO3)2 (150 mL·L−1

of peat-lite).Only one report documents the effect of seed sowing rate on emergence

and growth of microgreen seedlings (Murphy and Pill, 2010). In that reportsowing arugula seeds at 55 g·m−2 (31,845 seeds·m−2) resulted in the greatestshoot FW·m−2 but lighter individual shoots at 13 DAP than sowing seeds at25%, 50%, or 75% of this rate.

There are few reports comparing growth of any plant species in nutrientfilm technique (NFT) hydroponics and in soilless solid media such as peat-based media. Widely varying media components and fertilization regimesmake valid comparisons difficult. Correa et al. (2008) found that the numberof potato (Solanum tuberosum) tubers per plant was 147% to 286% higher inNFT than in a commercial medium containing soil, peat, and vermiculite.With the same species, Muro et al. (1997) found that total potato tuber pro-duction (number and weight) was greater with a perlite–NFT system than ina peat plus sand medium. Oswiecimski et al. (1992) observed markedly higherearly and total tomato fruit weights when plants were grown in rockwool–NFTthan in peat plus bark medium. Succop and Newman (2004) found little or nodifference in shoot FW of sweet basil (Ocimum basilicum L.) in rockwool–NFT,perlite–NFT, or peat plus compost.

The aims of the research were to establish the effect of seed ball sowingrate, preplant media fertilization, and postemergence solution fertilization onpresowing germination in vermiculite or gel and growth in peat-lite or NFT ongrowth of microgreen table beet.

MATERIALS AND METHODS

Table beet seed balls were purchased from Johnny’s Selected Seed (Winslow,Me.). These seed balls, weighing 17.9 mg each (56 ± 0.10 [mean ± SD, n = 5]seed balls g−1), were of high quality (97% germination and 2.9 days to 50%

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germination at constant 20°C). Each seed ball produced 4.1 ± 0.3 (mean ± SD,n = 200) seedlings.

Seed Ball Sowing RatePlastic trays measuring 17 × 12 × 4 cm (601 inserts with bottom drainage)

were filled to 2.5 cm depth with peat-lite growth medium (Jiffy Mix 901, JiffyProducts of America, Norwalk, Ohio). A waxed paper ring (10.8 cm dia × 2 cmdepth; 92 cm2) cut from a waxed paper tub was pressed into the growthmedium at the center of each tray with about 1 cm above the growth mediumsurface. This ring provided a subset for seedling harvest with seedlings withinthe ring free of border effects.

The seed ball sowing rate used by a commercial grower (201 g m2; 11,256seed balls·m−2) resulted in a very high seedling population density, so weselected more economical rates that were 0.25, 0.50, 0.75 of this commercialrate. Seed balls are fruit comprised of several highly compressed achenes,each achene having the potential to germinate resulting in 3 to 5 plants(Copeland and McDonald, 2001). Seed balls were broadcast evenly onto thesurface of the peat-lite and covered with 2 mm of peat-lite. Four replications(trays) of each seed sowing rate were arranged in randomized complete blocksin a greenhouse (22/20°C day/night) under natural light (during April–May).Trays were sprinkle-irrigated daily with water. Other than the nutrientsinherent in the peat-lite, no fertilizer was applied. Seedlings were harvestedat 15 DAP when the lamina of the first true leaves were ca. 2 cm long. Shootsof all seedlings within the ring were cut at the peat-lite surface and their FWswere determined. The number of seedling shoots was counted to calculateshoot fresh weight per seedling. The lamina length of the first true leaf wasmeasured. Data were subjected to analysis of variance (ANOVA).

Seed Ball Pregermination in VermiculiteSeed balls were mixed in very fine (grade 5), moist exfoliated vermiculite

(W.R. Grace, Cambridge, Mass.). The volume of vermiculite was based on thearea of the tray and the commercially recommended seeding rate. Because 5 Lof the vermiculite permitted easy distribution of the seed ball–vermiculitemixture in 25 × 260 × 4-cm-deep commercial troughs at ARC Greenhouses,Shiloh, N.J., 157 mL of vermiculite was required per 17 × 12 × 2 cm tray. Intothe vermiculite was mixed 4.1 g of seed balls (equivalent to 201 g seed balls·m−

2). Water was mixed in the vermiculite–seed ball mixture at 100%, 150%,200%, or 250% water (wt. per vermiculite dry wt.) within lidded 100-mL plas-tic cups. Nontreated seed were sown on double layers of germination paper(Germination blotter No. 385; Seedburo, Chicago, Ill.) moistened with 15 mLof deionized water contained within 125 × 80 × 20-mm transparent polysty-rene boxes. The four water concentrations (cups) and nontreated seed balls

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Microgreen Table Beet 257

(boxes) were replicated four times for each 2-, 3-, 4-, or 5-day incubation periodin darkness at 20°C. After the incubation periods, percentage germinationwas determined and radicle length measured with a Vernier caliper on 100-seed ball subsamples. If more than one achene per seed ball germinated, onlythe one with the longer(st) radicle, the first to germinate, was counted. Theangular transformation of percentage germination (arcsine.√%; to ensure anormal distribution) and radicle length were subjected to ANOVA.

Combining Seed Ball Pregermination in Vermiculite and FertilizationMurphy and Pill (2010) examined effects of preplant media fertilization

with 500, 1000, 2000, or 4000 mg·L−1 of N (150 mL·L−1 of peat-lite) preparedfrom urea, ammonium nitrate, calcium nitrate, or ammonium sulfate on thegrowth of microgreen arugula. The greatest shoot FW m−2 or per plantoccurred with preplanting Ca(NO3)2 at 2000 mg·L−1 of N of peat-lite(150 mL·L−1) plus postemergence solution fertilization with 150 mg·L−1 ofN from 21N-2.2P-16.6K (21N-5P2O5-20K2O; Peters Excel Multi-Purpose withminor elements; Scotts-Sierra Horticultural Products, Marysville, Ohio). Thisand other fertilization treatments were included in the present study; namely,none added, preplanting incorporation of Ca(NO3)2 at 2000 mg·L−1 of N(150 mL·L−1 Jiffy Mix 901 peat-lite), daily solution fertilization at 150 mg·L−1

of N until minimal drainage occurred, these two treatments combined, orthese two treatments at one-half concentration each (preplant Ca(NO3)2 at1000 mg·L−1 of N plus 75 mg·L−1 of N solution fertilization). This last treat-ment was included because combining preplant and solution fertilizationtreatments that separately maximized growth can result in excessive solublesalts that could restrict growth. Seed balls, sown at the commercially recom-mended rate of 201 g·m−2, were not treated (control) or pregerminated in moistvermiculite (150% water [wt. per dry wt. vermiculite] for 5 days at 20°C).

Two 17 × 12 × 2 cm trays with bottoms removed were placed within a stan-dard flat, and the entire flat was filled with Jiffy Mix 901. Each flat comprised afertilizer treatment, and each tray within a flat was broadcast sown with non-treated or pregerminated seed balls. Between the trays and the flat walls, con-trol seed balls were broadcast at a rate estimated to be similar to that withinthe trays. Broadcasted seeds were covered with a 2-mm layer of the peat-lite.Flats were arranged in randomized complete blocks with four replications, andthe experiment was conducted in a greenhouse set at 25/20°C (day/night) withnatural light (in mid-August). Trays were irrigated daily with water or fertilizersolution until minimal drainage occurred. At 15 DAP, all shoots within a traywere cut at the growth medium surface and weighed to provide shoot FW·m−2.Then, a subsample of 50 randomly selected shoots was weighed, from whichshoot FW per plant was calculated. The data were subjected to ANOVA.

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Seed Ball Pregermination in Vermiculite or Gel and Growth in Peat-Lite or HydroponicsSeed balls were incubated for 5 days at 20°C either in grade 5 vermiculite

(4.1 g seed balls in 157 mL of vermiculite; 150% wt. per dry wt. vermiculite) orin 2.5% (wt./wt.) hydroxyethyl cellulose (HEC) gel (N-Gel, Aqualon Group,Wilmington, Del.; 4.1 g seed balls in 20.5 mL gel water [1 g seed balls per5 mL gel]). Nontreated seed balls were included. The seed balls (germinated ingel or in vermiculite) or nontreated seeds were then planted in two culturalsystems: peat-lite or NFT hydroponics.

The peat-lite was Jiffy Mix 901 amended with preplanting Ca(NO3)2 at2000 mg·L−1 of N (150 mL·L−1 peat-lite) contained within 17 × 12 × 2 cm trays.The NFT hydroponic system consisted of 3.5-m-long × 5-cm-wide × 3.2-cm-deep hydroponic troughs (Rehau, Leesburg, Va.) at a 7% slope. Two troughssupplied by the same nutrient solution tank comprised one replication. Thenutrient solution was prepared from four salts: Hydrosol (5N-4.7P-22K;Grace-Sierra, Milpitas, Calif.), calcium nitrate (Southern Agriculture Insecti-cides, Henderson, NC), magnesium sulfate (Walgreens Apothecary, Deerfield,IL), and iron chelate (Sprint 330; Ciba-Geigy, Greensboro, N.C.) at 1.0, 1.0,0.1, and 0.04 g·L−1, respectively. This provided (in mg·L−1) N 200, Ca 129,P 48, K 210, Mg 20, S 66, Fe 4, Mn 0.5, Zn 0.15, Cu 0.15, B 0.50, and Mo 0.10.Solution electrical conductivity was 2 dS·m−1 and pH was 5.9. White 0.9-cm-thick absorbent fabric (Sure To Grow, Beachwood, Ohio) was cut to 5.1 × 40cm to fit the trough and provide the same growing area as the 17 × 12 ×2 trays. The fabric sections were randomly positioned and equally spacedwithin the two troughs of each replication. At planting, 1.5% HEC (wt./wt.) gelwas added to the gel-incubated seed balls to a total volume of 31.5 mL (1 mL/6.5 cm−2). The reduced concentration of gel resulted in a lower gel viscositythat permitted easy pouring of the gel–seed ball mixture over the peat-litesurface or the hydroponic fabric. The vermiculite–seed ball mixture wasevenly distributed over the peat-lite surface or the hydroponic fabric by shak-ing. Nontreated seed balls were broadcast evenly over the two types of sur-faces. Seed balls were gently pressed into the hydroponic fabric to ensureadequate contact for wicking of liquid. Seed balls on the peat-lite were coveredwith 2 mm of peat-lite. The nutrient solution circulated through the hydro-ponic system continuously and was replaced every 5 days. The peat-lite traysreceived sufficient volume of the 150 mg·L−1 of N daily solution fertilization toresult in minimal drainage. Treatments were arranged in split-plot designwith four replications, with culture system (peat-lite or NFT) as the mainplots and seed ball treatment the subplots. The study was conducted in agreenhouse set at 27/20°C (day/night) with natural light (in June). Withinreplications, seed ball treatments were duplicated, one for each crop harvestat 7 and 15 DAP when all shoots were cut at the peat-lite or fabric surface and

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Microgreen Table Beet 259

shoot FWs were determined. A subsample of 50 shoots from each treatment wasweighed to determine shoot FW per plant. The data were subjected to ANOVA.

RESULTS AND DISCUSSION

Seed Ball Sowing RateIncreasing seed sowing rate quadratically increased number of shoots·m−2,

linearly increased shoot FW·m−2, and quadratically decreased FW per shoot(Table 1). The decrease in individual shoot weight and increasing seeding ratelikely reflected increasing interplant competition for resources. Increasingshoot population density resulted in decreased lamina length of the first trueleaf with values of 16.0, 9.5, 4.5, and 1.5 mm for the 0.25, 0.50, 0.75, and 1.00of the commercial seeding rate (202 g·m−2), respectively (data not shown).Optimal leaf length would depend on various requirements of the marketplace. Sowing seeds at rates below the commercially used rate would result inlower yield per unit bench area and lower economic yield but would decreaseseed ball cost. In this study, shoot population density ranged from 194% to220% of the number of seed balls sown. A preliminary germination assaydetermined that seed balls produced 4.1 ± 0.3 (mean ± SD, n = 300) seedlings,about double the seedlings per seed ball achieved in this study (Table 1). Thislower than potential seedling population density may have resulted fromshading of later-emerging shoots by more vigorous shoots.

Seed Ball Pregermination in VermiculiteOne approach to reduce time to harvest is to sow germinated (pregerminated)

seed balls. With 2-day incubation in grade 5 exfoliated vermiculite at 20°C, nogermination had occurred (Table 2). With 3-day incubation, germination

Table 1: Shoot fresh weight per plant and per population and shoot population density of ‘Early Wonder Tall Top’ table beet at 15 days after planting in response to seed ball sowing rate.

Seed ball sowing ratea

Seed balls Shoot population

density (number·m-2)

Shoot fresh weight (g·m-2)

Shoot fresh weight

(mg/shoot)g·m-2 No.·m-2

0.25 50.3 2817 5478 1474 2710.50 100.5 5628 12,360 1947 1600.75 150.8 8445 14,958 1888 1301.00 201.0 11,256 21,945 2450 121Significance Linear *** *** **

Quadratic * NS ***

NS, *,**, ***Not significant or significant at P = 0.05, 0.01, or 0.001, respectively.aSeed ball sowing rate based on 1× = commercial rate of 201 g seed balls·m2 (11,256 seedballs·m2).

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260 C. J. Murphy et al.

increased quadratically from 0% in vermiculite with 100% water to 20.3%(radicles 7.3 mm long) in vermiculite with 250% water. By the fourth day ofincubation, seed balls had begun to germinate in vermiculite with 100%water (1% and radicles 0.5 mm long), and seed balls in vermiculite with 250%water had reached 65% germination (radicles 11.8 cm long). With 5 days ofincubation, germination increased quadratically from 3% (radicles 1.3 mmlong) in vermiculite with 100% water to 100% (radicles 16.3 mm long) in ver-miculite with 250% water. Increasing germination percentage and radicle lengthwith increasing water concentration in vermiculite can be attributed to increasing

Table 2: Germination percentage (and its angular transformation) and radicle length of ‘Early Wonder Tall Top’ table beet seed balls after 2 to 5 days incubation in vermiculite containing varying percentages of water (weight per dry weight vermiculite).

Incubation period

Day 2 Day 3

Germination Radical length (mm)

GerminationRadical length

(mm)Water in vermiculite (%, wt per dry weight) (%) [deg.] (%) [deg.]

100 0 [0]aa 0 a 0 [0]d 0 d150 0 [0]a 0 a 2.5 [7.9]c 1.8 c200 0 [0]a 0 a 9.3 [17.6]b 4.8 b250 0 [0]a 0 a 20.3 [26.4]a 7.3 aControlb 0 [0]a 0 a 20.2 [26.5]a 4.3 bOne-way LSD0.05 [NS] NS [5.2]*** 1.7***Linearb [NS] NS [*] ***Quadratic [NS] NS [***] NS

Day 4 Day 5

Germination Radical length (mm)

Germination Radical length (mm)Water in vermiculite (%) (%) [deg.] (%) [deg.]

100 1.0 [3.9]c 0.5c 3.0 [7.1]d 1.3d150 32.0 [34.2]b 5.8b 50.0 [45.0]c 6.5c200 28.3 [32.1]b 8.8ab 62.5 [52.5]c 10.0b250 65.0 [54.0]a 11.8a 100.0 [90.0]a 16.3aControl 65.0 [53.9]aa 10.0a 82.3 [65.8]b 10.5bOne-way LSD0.05 [7.9]*** 3.1*** [8.3]*** 3.2***Linear [***] *** [***] ***Quadratic [**] *** [**] ***

NS, *, **, ***Not significant or significant at P = 0.05, 0.01, or 0.001, respectively.aMeans followed by the same letter within a column for a germination day are not significantlydifferent by LSD0.05.bControl = Nontreated seed balls sown on double layers of germination paper moistenedwith water.

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Microgreen Table Beet 261

matric potential. The moisture characteristic curve for grade 5 vermiculiterevealed matric potential (ψm) values of −0.4, −0.3, −0.2, and −0.1 MPa at 100%,150%, 200%, and 250% (w/w) water, respectively (Khan et al., 1992). Controlseed balls sown on moist germination blotters had germination percentagesand radicle lengths similar to, or greater than, those achieved when seed wereincubated in vermiculite with 200% water. We wished to select a seed ballpregermination treatment that would give the greatest germination percentagewith radicles under 0.75 mm long. When table beet radicles are = 0.75 mmlong, seedlings are not separable because the root hairs of touching seedlingsbecome entangled. The incubation treatment deemed optimal was 150% water invermiculite for 5 days, which gave 50% germination and radicles 6.5 mm long.

Combining Seed Ball Pregermination in Vermiculite and FertilizationPreliminary work established that shoot FW·m−2, and per plant, increased

quadratically by 15 DAP in response to increasing N concentration of dailysolution fertilization (SF; 0, 75, or 150 mg·L−1; data not shown). Othersobserved increased seedling growth with increasing N concentration in SF(Masson et al., 1991; Soundy et al., 2005). Irrespective of seed treatments,shoot FW m−2 was greatest with preplanting media incorporation of 2000mg·L−1 of N from Ca(NO3)2 (CN) at 150 mL·L−1 peat combined with SF (CN + SF),although SF alone led to greater shoot growth than CN alone (Table 3). Unlikethe observation of Murphy and Pill (2010) that FW·m−2 of microgreen arugulawas similar with both the full and one-half rates of CN + SF, shoot FW·m−2 oftable beet increased 17% by the full-rate compared to the half-rate of CN + SF(Table 3). For arugula, the full-rate of CN+SF represented luxury consump-tion, or slight toxicity although no excess salt symptoms existed. The positivegrowth response of table beet to the full rate of CN + SF (compared to the lackof response in arugula) might be expected because table beet is one of the mostsalt-tolerant vegetable species (Maas, 1986). In earlier work with microgreenarugula, shoot FW·m−2, and per plant, was influenced by preplanting addi-tions of N sources in the order calcium nitrate > ammonium nitrate > urea >ammonium sulfate (Murphy and Pill, 2010). Maynard and Barker (1969)noted that fertilizers that provide N as ammonium partly, or wholly, led toless seedling growth than fertilizers providing only nitrate-N.

Use of CN + SF compared to the check (nutrients supplied by the Jiffy Mix901, no fertilizer added) resulted in 102.2% and 104.6% increases in shootFW·m−2 for nontreated and pregerminated seed balls, respectively, whichwould lead to reduced cropping time, especially for pregerminated seed balls(6937 g·m−2) than for nontreated seeds (5469 g·m−2; Table 3). For nontreatedseed balls, fertilization treatments resulted in similar increases in shoot FWper plant (average of 280 mg) compared to the 166 mg shoot FW per plant

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achieved in nonfertilized plants. For pregerminated seed balls shoot FW perplant was in the order CN + SF > 0.5CN + 0.5SF = CN > SF. Shoot FWs ofindividual plants from pregerminated seed balls were more responsive tofertilization than those from nontreated seed balls, a response that can beattributed to the greater time available to pregerminated seed balls for nutri-ent uptake because of their developmentally advanced stage at time of plant-ing. For the greatest shoot FW per area and per plant, a response that wouldgive the shortest cropping time, seed balls pregerminated in vermiculiteshould be planted in peat-lite containing 2000 mg·L−1 of N from Ca(NO3)2.Subsequently, solution fertilization with 150 mg·L−1 of N should be applieddaily. Without tissue analysis, shoot nitrate concentration in response to thesefertilization regimes is unknown. Nitrates are implicated in the genesis ofmethaemoglobinaema and some forms of cancer (Salomez and Hofman, 2009).

Seed Ball Pregermination in Vermiculite or Gel and Growth in Peat-Lite or HydroponicsAt 7 DAP, shoot yields were greater for plants grown in hydroponic cul-

ture (1446 g FW·m−2 and 174 mg FW/plant) than for those grown in peat-lite(1003 g FW·m−2 and 90 mg FW/plant; Table 4). Shoot yields were influenced byseed ball treatment in the order pregermination in vermiculite > pregermination

Table 3: Shoot fresh weight per plant and per population of ‘Early Wonder Tall Crop’ table beet at 15 days after planting in response to seed ball and fertilizer treatments.

Seed treatment (ST)Fertilization

treatment (FT)a Shoot fresh weight (g·m-2)

Shoot fresh weight (mg/shoot)

Nontreated Check 2705h 166eb

CN 4207f 268dSF 4676e 268d0.5 CN + 0.5 SF 4676e 284cdCN + SF 5469cd 299cd

Pregerminatedc Check 3391g 298cdCN 5087de 362bSF 5649c 306c0.5 CN + 0.5 SF 6294b 362bCN + SF 6937a 415a

Interaction LSD0.05 444 36SignificanceST *** ***FT *** ***ST × FT * **

*,**, ***Significant at P = 0.05, P = 0.01, or P = 0.001, respectively.aCheck = no additional fertilizer added to the peat-lite; CN = preplant addition of solidCa(NO3)2 at 2000 mg·L−1 of N (150 mL·L−1of peat-lite); SF = daily application of 150 mg·L−1 of Nsolution fertilizer from 21-5-20; 0.5 = one-half rate.bMeans within a column followed by the same letter are not significantly different by LSD0.05.cPregerminated = seed ball incubation in fine (grade 5) vermiculite with 150% water for 5days at 20°C.

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in gel > nontreated (1909 > 1126 > 638 g FW·m−2, respectively, and 175 > 122 >99 mg FW/plant, respectively). At 15 DAP, however, cultural system and seedball treatment interacted in influencing these variables. Irrespective of seedball treatment, shoot FW m−2 and per plant were greater for plants grown inhydroponic culture than for those grown in peat-lite. Within hydroponic cul-ture, seed ball pregermination in vermiculite resulted in greater shoot FW·m−

2 (10,139 g) and shoot FW/plant (1320 mg) than pregermination in gel (6523 gshoot FW·m−2 and 866 mg shoot FW/plant), with the lowest shoot yields occur-ring from nontreated seed balls (5037 g FW·m−2 and 697 mg FW/plant). Forplants grown in peat-lite, shoot FW·m−2, and per plant, followed the sameorder according to seed ball treatment as in hydroponically grown plants,although adjacent means were not different from each other; pregerminatedin vermiculite = pregerminated in gel = nontreated).

Greater table beet shoot yields in hydroponic culture than in peat-lite(solid soilless media) agree with those for potato tuber yield (Correa et al.,2008; Muro et al., 1997) and for tomato fruit yield (Oswiecimski et al., 1992)but not with Succop and Newman (2004), who found little or no difference inshoot FW of sweet basil (Ocimum basilicum) in rockwool–NFT, perlite–NFT,or peat plus compost. Using hydroponic NFT rather than peat-lite to produce

Table 4: Shoot fresh weight per per population and per plant of ‘Early Wonder Tall Crop’ table beet at 7 and 15 days after planting (DAP) seed balls pregerminated in exfoliated vermiculite or in hydroxyethyl cellulose (HEC) gel into hydroponic troughs or onto peat-lite.

7 days DAP 15 DAP

Culture systemSeed ball

treatmentaShoot fresh weight (g·m-2)(mg/shoot)

Shoot fresh weight (g·m-2)(mg/shoot)

Peat-lite Pregerminated in vermiculite

1638bb 130c 4150cd 425d

Pregerminated in HEC gel

943d 81d 3728de 364de

Nontreated 428e 60d 2612e 269eHydroponics Pregerminated in

vermiculite2180a 221a 10,139a 1320a

Pregerminated in HEC gel

1311c 163b 6523b 866b

Nontreated 846d 138c 5037c 697cLSD0.05 294 24 1481 150

SignificanceCultural system (CS) *** *** *** ***Seed treatment (ST) *** *** *** ***CS × ST NS NS *** **

NS, **, ***Not significant or significant at P = 0.01or P = 0.001, respectively.aSeed ball treatment: seed balls incubated (pregerminated) for 5 days at 20°C in exfoliatedvermiculite with 150% water (wt/wt) or in 2.5% (wt./wt.) hydroxyethyl cellulose (HEC) gel (thendelivered in 1.5% HEC gel).bMeans within a column followed by the same letter are not significantly different, LSD0.05.

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264 C. J. Murphy et al.

table beet microgreens would lessen time between planting and harvest andwould ensure that the harvested crop would be free of particulate contaminationsuch as peat fibers. Where electrical supply is unpredictable, solid soillessmedia would be a safer cultural system for microgreen production.

Sowing pregerminated seed balls in gel resulted in greater shoot FW·m−2

than sowing nontreated seed balls at both sowing dates in hydroponic cultureand for the first harvest in peat-lite (Table 4). Greater yields at the first harvestresulted from sowing seed balls pregerminated in moist vermiculite at thefirst sowing date in both cultural systems and in hydroponic NFT at achievedat the second harvest. Lower aeration of seed balls in gel than in vermiculitemay have contributed to the lower shoot yields resulting from incubatingpregerminated seeds in the gel. Preliminary results revealed that germinationof seed balls was 21% after 5 days incubation at 20°C in 2.5% gel (data notshown), whereas germination in vermiculite with 150% water (wt.) was 50.0%(Table 2). Preliminary results also indicated that 1.5%, 3.5%, and 4.5% (wt./wt.)gel resulted in lower germination percentages than occurred in 2.5% gel.Increasing the gel to seed ball ratio from 5 mL·g−1 seed balls to 7.5 or 10 mL g−1

led to lower germination percentages (data not shown). At the two higher gel-to–seed ball ratios, inadequate aeration was associated with the smell of fermen-tation. Though radish and arugula seeds had similar germination percentagesin vermiculite or gel (preliminary work), further work is needed to increasegermination percentage of seed balls in gel. Sowing pregerminated seeds com-pared to sowing nontreated seeds in order to gain earlier and greater yields wasthe logic behind a sowing technique termed fluid drilling in which germinatedseeds are suspended and transferred to the seedbed in a gel carrier (Pill, 1991).In the fluid drilling system, seeds typically are germinated in aerated waterand then mixed in gel. Germinating seed in gel would eliminate the need forthis extra step. Pill and Mucha (1994) found that germinating petunia (Petuniahybrida) seeds on the surface of hydrated gel before mixing the seedling–gelmixture and extruding it on the seed bed increased seedling number and shootFW compared to sowing nontreated seeds. It is possible that microgreen seed-ling–gel mixtures could be stored before planting because germinated tomatoseed can be stored in the gel under refrigeration for up to 12 days without loss ofactivity following extrusion of the seedling–gel mix (Pill and Fieldhouse, 1982).

Several cultural practices that can promote seedling growth and reducegreenhouse production time for microgreen table beet were examined. Sowingseed at a high rate (201g·m−2) resulted in greater economic yield than lowerrates; and if the seed balls were first germinated in moist vermiculite for5 days at 20°C before sowing the vermiculite–germinated seed mixture, eco-nomic yield was further increased. Combining preplanting fertilization of thepeat-lite with calcium nitrate at 2000 mg·L−1 of N (150 mL·L−1 of medium)with daily postplanting solution fertilization with 150 mg·L−1 of N led to a fur-ther increase in yield compared to other fertilization regimes. Germinating

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Microgreen Table Beet 265

and extruding seed balls in hydrophilic polymer advanced microgreen growthbut not to the extent achieved with vermiculite as the pregermination medium.Depending on the seed ball treatment, producing microgreens in hydroponic,compared to peat-lite, culture increased economic yield 33% to 98% by 7 daysafter planting (DAP) and 75% to 144% by 15 DAP. The highest shoot FW(10,139 g·m−2) at 15 DAP was achieved from sowing seed balls pregerminatedin moist vermiculite and from subsequent seedling growth in hydroponicnutrient film technique. This yield would equate to an annual shoot FW of243.3 kg·m−2 assuming 24 crop cycles per year.

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