and water delivery. Fresh market basil Evaluation of a Novel Shallow Aggregate Ebb- (Ocimum basilicum), for example, and-flood Culture System and Transplant Size is typically produced in hydroponic systems in which plant roots are sub- Effects on Hydroponic Basil Yield merged in nutrient solution to pro- mote maximum growth and yield 1 2 3 (Gomez et al., 2019; Resh, 2012). Samuel Doty , Ryan W. Dickson , and Michael Evans Bedding plants are often produced in soilless substrate and containers and deep flow technique, nutrient film technique, Ocimum basilicum, soilless culture periodically irrigated with a fertilizer solution using drip emitters or ebb- SUMMARY. Ornamental bedding plant operations transitioning to leafy greens and and-flood irrigation (Lieth and Oki, herb production must decide whether to invest in new hydroponic equipment or 2008). An important decision for modify existing culture systems for edible crops. In addition, common practices used bedding plant growers transitioning to increase space-use and production efficiencies during bedding plant production may be modified for hydroponic leafy greens and herbs, such as purchasing large to edible crop production is whether seedlings for transplant. The objective of the first experiment was to evaluate plant to invest in new hydroponic equip- growth in a modified and novel shallow aggregate ebb-and-flood (SAEF) system ment or modify existing culture sys- intended for bedding plant growers with an emphasis on comparing yield across four tems (Chidiac, 2017). basil (Ocimum basilicum) cultivars grown in the SAEF system to those grown using Nutrient film technique (NFT) the traditional nutrient film technique (NFT) and deep water culture (DWC) hy- and deep water culture (DWC) are droponic systems. The second experiment objective was to evaluate basil seedling size common hydroponic systems used and the time of transplant to NFT hydroponic systems to determine effects on the final commercially for the production of yield. ‘Genovese’ basil seedlings were grown in trays with cell counts of 32, 50, 72, leafy greens and herbs (Gomez et al., 105, and 162 cells with corresponding root volumes per plant of 98.1, 50.2, 38.5, 2019; Resh, 2012; Walters and 19.6, and 16.3 cm3, respectively. Seedlings were transplanted to NFT systems at 14, 21, and 28 days after sowing and were harvested at 35 days. In the first experiment, Currey, 2015a; Wolf et al., 2005). overall basil shoot fresh and dry weights per plant were intermediate in the SAEF The NFT systems contain plants within system (90.4 and 8.3 g) compared with the DWC (102.6 and 9.1 g) and NFT (75.8 narrow gutters or troughs, where root and 6.6 g) hydroponic systems. In the second experiment, final shoot fresh and dry systems are exposed to a continually weight per plant increased as seedling root volume increased from 16.3 cm3 [72.8 and flowing thin film of nutrient solution. 5.5 g (162-cell tray)] to 98.1 cm3 [148.5 and 12.2 g (32-cell tray)]. Transplanting Alternatively, DWC systems expose seedlings at later dates decreased yield across tray size and root volume treatments. plant roots to a relatively large volume Differences in yield between culture systems may have resulted from differences in of nutrient solution, typically ranging nutrient supply and availability for plant uptake. Transplant of large seedling plugs to from 6 to 8 inches in depth, where hydroponic culture was not shown to increase space-use efficiency after transplant roots are completely submerged in without compromising yield, likely because root zone factors limited growth during seedling production. Further investigation into maximizing plant growth during nutrient solution. With both systems, seedling production and evaluating the effects of seedling size and transplant prac- commercial producers maintain strict tices are needed to determine the potential for increasing space-use and production control over solution pH, nutrient efficiencies. concentrations, oxygen levels, and pathogens to ensure optimal plant growth and yield (Currey, 2017; Resh, rnamental bedding plant op- 2012). The NFT systems are popular erations in the United States among bedding plant growers transi- Received for publication 24 Apr. 2020. Accepted for Oare continually transitioning tioning to leafy greens and herb pro- publication 31 July 2020. to the production of edible crops duction, partially because NFT systems Published online 27 August 2020. (Chidiac, 2017), particularly high- are relatively low-cost and troughs are 1Department of Biology, UT Valley University, value leafy greens and herbs. How- at a comfortable working level for em- Orem, UT 84058 ever, culture systems used to produce ployees (Walters and Currey, 2015b). 2Department of Horticulture, University of Arkansas, edible and ornamental crops tend to Chidiac (2017) designed a novel Fayetteville, AR 72701 differ in system design and nutrient soilless substrate system—a shallow 3School of Plant and Environmental Sciences, Virginia Tech University, Blacksburg, VA 24061 We thank the University of Arkansas Department of Horticulture and Arkansas Division of Agriculture for supporting for this research. We also thank Kevin Thompson of the University of Arkansas Agricultural UnitsTo convert U.S. to To convert SI to U.S., Statistics Department for statistical advice and con- SI, multiply by U.S. unit SI unit multiply by sulting. 29.5735 fl oz mL 0.0338 The use of trade names in this publication does not 3.7854 gal L 0.2642 imply endorsement of the products named or criticism of similar ones not mentioned. 2.54 inch(es) cm 0.3937 25.4 inch(es) mm 0.0394 R.W.D. is the corresponding author. E-mail: ryand@ 16.3871 inch3 cm3 0.0610 uark.edu. 0.0254 mil(s) mm 39.3701 This is an open access article distributed under the CC 1 mmho/cm mSÁcm–1 1 BY-NC-ND license (https://creativecommons.org/ 28.3495 oz g 0.0353 licenses/by-nc-nd/4.0/). 1 ppm mgÁL–1 1 https://doi.org/10.21273/HORTTECH04635-20 ( F – 32) O 1.8 F C( C · 1.8) + 32
• October 2020 30(5) 585 aggregate ebb-and-flood (SAEF) with DWC, based on previous re- molÁm–2Ád–1 of photosynthetically ac- system—for bedding plant growers search comparing plant growth of tive radiation, and the outside average transitioning to edible crop produc- hydroponic and substrate cultures daily temperatures were 21.5 ± 3.5, tion. The SAEF system consists of (Blok et al., 2017). The objective of 22.4 ± 3.0, and 1.6 ± 7.6 C, re- modifying traditional ebb-and-flood the second experiment was to evalu- spectively; these temperatures were irrigation systems by adding a layer of ate the effect of seedling size and the measured using a weather station clay aggregate substrate to the bot- time of transplant to NFT hydroponic (WatchDog 2900ET; Spectrum Tech- tom of the flood table. Seedlings are systems on final yield. Large seedlings nologies, Aurora, IL). transplanted and grown directly in of bedding plants are typically grown NUTRIENT SOLUTION. The hy- the substrate, which is periodically in trays with relatively low cell counts droponic nutrient solution was the subirrigated with nutrient solution, and large root volumes to avoid root same across all three systems and similar to ebb-and-flood irrigation restriction (Fisher et al., 2006); there- consisted of (in mgÁL–1) 195.1 nitro- with container crop production. The fore, seedling size in this study is gen (N), 34.1 phosphorus (P), 267.2 SAEF system is intended to allow discussed in terms of tray cell count potassium (K), 171.0 calcium (Ca), bedding plant growers to easily mod- and root volume. We hypothesized 60.6 magnesium (Mg), 75.8 sulfur ify ebb-and-flood systems for food that basil seedlings grown in the (S), 4.5 iron (Fe), 1.0 manganese crop production without having to largest root volume would have the (Mn), 0.5 boron (B), 0.1 copper purchase NFT and DWC systems greatest yield as a result of decreased (Cu), and 0.1 zinc (Zn) formulated (Chidiac, 2017). However, the viabil- restriction of root growth. using commercial-grade calcium ni- ity of modifying an ebb-and-flow trate, potassium nitrate, potassium system in this manner for edible crops Materials and methods sulfate, monopotassium phosphate, needs to be evaluated by comparing Expt. 1: Basil growth in a novel magnesium sulfate heptahydrate, plant growth and yield of SAEF sys- SAEF system compared with iron-diethylenetriaminepentaacetic tems to those of traditional NFT and DWC and NFT hydroponic acid [DTPA (11%)], manganese sulfate DWC hydroponics. systems monohydrate, zinc sulfate heptahy- Bedding plant growers some- EXPERIMENTAL DESIGN. The ex- drate, boric acid, copper sulfate penta- times purchase and transplant large periment was a split-plot factorial hydrate, and ammonium molybdate seedling plugs to finishing containers with culture system (NFT, DWC, tetrahydrate mixed intapwater.Solu- as a strategy to improve production and SAEF systems) as the whole plot tion electrical conductivity (EC) and and space-use efficiencies (Fisher factor and basil cultivars (Genovese, pH were monitored in each system and et al., 2006). A similar strategy may Mrs. Burns Lemon, Cinnamon, and maintained at 1.4 ± 0.05 mSÁcm–1 and also apply to edible crop seedlings Sweet Thai) as the split-plot factor, 5.9 ± 0.2, respectively, by daily adjust- transplanted to hydroponic systems. with three replications per culture ments to the fertilizer concentration in For bedding plants, large seedlings system–cultivar treatment combina- the replenishment solution (same as finish rapidly after being transplanted tion. Replication was achieved by the starting hydroponic nutrient solu- to containers because plants are de- conducting three separate experi- tion) and additions of 0.1 N sulfuric velopmentally mature, thus reducing mental runs; each experimental run acid (H2SO4). the time between transplant and a fin- served as one replication and con- PLANT CULTURE. Untreated seed ished crop and allowing for additional tained all hydroponic systems and foreachcultivar(Johnny’sSelected crop cycles (Fisher et al., 2006). cultivars. System locations were re- Seeds, Waterville, ME) were sown However, large seedlings require ad- randomized between experimental in 162-cell rockwool sheets (A/O ditional time for adequate root and runs. Placement of cultivar groups sheets; Grodan, Roermond, The shoot growth during propagation, as was randomized within each system Netherlands) as three seeds per cell well as trays with larger root volumes for each replication. Each experi- andgerminatedonagreenhouse to avoid issues with root restriction mental run started with the transfer bench. During germination and and excessive drying of the root zone of basil seedlings to the different early plant growth, rockwool sheets (Fisher et al., 2006; Latimer, 1991; culture systems, which occurred on were subirrigated for 2 min every van Iersel, 1997). There is a need to 19 May 2017, 14 Aug. 2017, and 1 hourusingthesamenutrientsolu- investigate the potential of trans- Jan. 2018. tion described previously. Basil seed- planting large seedling plugs to hy- The experiment was conducted lings were transplanted to hydroponic droponic systems to reduce the time in a controlled environment (glass- systems 14 d after sowing, when all between transplant and harvest with- glazed) greenhouse at the Univer- plants had at least two true leaves. out compromising yield. sity of Arkansas in Fayetteville (lat. HYDROPONIC SYSTEMS. The NFT The objective of the first experi- 36.0764 N, long. 94.1608 W). Green- system consisted of 12 separate 150 · ment was to evaluate edible crop house heating and cooling set points 10 · 5-cm polypropylene hollow gut- growth in a novel SAEF culture sys- were 23 and 27 C, respectively. All ters (AM Hydro, Arcata, CA) posi- tem using basil as a model crop, with plants in the experiment were grown tioned on a 2.5% slope across the an emphasis on comparing basil under ambient light and photoperiod top of the greenhouse bench. Plants growth and morphology to plants conditions. The outside daily light were transferred to 2-inch-diameter produced in traditional NFT and integral for the three experimental holes drilled in the top of each gut- DWC hydroponic systems. We hy- runs were (mean ± SD) 40.0 ± 12.3 ter so that the rockwool cube and pothesized that basil yield would be (19 May 2017), 35.1 ± 7.9 (14 Aug. root system were located within the lower in the SAEF system compared 2017), and 12.9 ± 6.5 (1 Jan. 2018) gutter interior. Hydroponic nutrient
586 • October 2020 30(5) solution was continually pumped recommendations for optimal lettuce shoot tissue was oven-dried at 70 C from a reservoir tank below the bench (Lactuca sativa) yield by Chidiac for 2 d for dry weight determination. and into each gutter at 1.26 LÁmin–1, (2017). The SAEF system held a total Total leaf area was measured before where the nutrient solution flowed of 80 plants (40 plants per tank), and shoot tissue was oven-dried using over plant roots before draining back plants were oriented in 16 rows with a leaf area meter (LI-3050C; LI- into the reservoir. The nutrient solu- five plants per row. Each cultivar COR, Lincoln, NE). tion depth in each system was occupied four adjacent rows (4 rows STATISTICAL ANALYSIS. An analy- 1 mm. Each gutter held eight basil · 5 plants per row = 20 total plants per sis of variance using PROC GLIM- plants, and individual plant spacing cultivar), and plant spacing was the MIX (SAS version 9.4; SAS Institute, between and within gutters was main- same as that used for the NFT system. Cary, NC) was used to evaluate cul- tained at 20 cm. Three gutters were DATA COLLECTION. Plants were ture system and cultivar effects on used for each cultivar for a total of 24 harvested 21 d after seedlings were shoot fresh weight, shoot dry weight, basil plants per cultivar (3 gutters · 8 transferred to the different culture leaf SPAD chlorophyll content, leaf plants per gutter = 24 total plants per systems for each experimental run. area, plant height, node number, and cultivar), and gutters containing the Culture systems differed in the total internode length. Mean separation same cultivar were adjacent. number of basil plants per cultivar; was performed using Tukey’s hon- The DWC system consisted of however, the experimental units used estly significant difference (HSD)at two separate polypropylene tanks for data collection were identical a = 0.05. measuring 90 · 175 · 15-cm (Bota- across systems. Each experimental nicare, Chandler, AZ) positioned on unit consisted of six basil plants per Expt. 2: Basil seedling root top of two adjacent greenhouse cultivar and culture system treatment, volume and transplant date benches and filled with hydroponic where harvested plants were taken effects on NFT hydroponics nutrient solution. Each tank held a 90 from the center of each group of EXPERIMENTAL DESIGN. The ex- · · 175 5-cm polystyrene foam board cultivars within each system. The ex- periment followed a randomized (Dow, Midland, MI) that floated on tra plants surrounding those har- complete block design. It started on the surface of the nutrient solution vested for data collection served as 3 May 2019, with the sowing of basil contained within each tank. Basil buffer plants and were not used. seed and a five root volume · three transplants were transferred to 2- Measurements across the six har- transplant date factorial. Seedling inch-diameter net cups (one trans- vested plants per treatment were av- trays differed in tray cell count and plant per cup) that fit into holes eraged and data were reported and root volume per plant, with cell drilled in the polystyrene foam board. analyzed on a per-plant basis. counts of 32, 50, 72, 105, and 162 Roots were submerged and allowed The leaf chlorophyll index was cells per tray and corresponding root to grow in the nutrient solution, measured nondestructively using volumes of 98.1, 50.2, 38.5, 19.6, which was continually aerated using a portable Soil Plant Analysis Devel- and 16.3 cm3, respectively (Table 1). electric air pumps (Tetra Whisper Air opment (SPAD) meter (Minolta Basil seedlings from each tray type Pump 10–30 gal; Spectrum Brands Corp., Tokyo, Japan); each measure- were transplanted to NFT systems at Pet, Blacksburg, VA). The DWC sys- ment was the average leaf chlorophyll 14, 21, and 28 d after sowing, when tem held a total of 80 plants (40 measured across three randomly se- each seedling had at least two, four, or plants per tank), and plants were lected and fully expanded leaves per six true leaves, respectively. The ex- arranged in 16 rows with 5 plants plant. The plant height and number periment was conducted in a green- per row. Each cultivar occupied four of nodes were measured, and the house with heating and ventilation set · adjacent rows (4 rows 5 plants per average internode length was calcu- points of 19 and 23 C, respectively. row = 20 total plants per cultivar), and lated by dividing the height by the During the experiment, the green- plant spacing was the same as that number of nodes per plant. house average daily temperature was used for the NFT system. Shoots were cut at the base of the (mean ± SD) 23.3 ± 1.3 C and the The SAEF systems consisted of stem and just above the rockwool daily light integral was 25.6 ± 7.2 two separate polypropylene tanks surface and immediately weighed for molÁm–2Ád–1 of photosynthetically ac- · · measuring 125 250 15 cm (Bot- fresh weight determination. Fresh tive radiation; these were recorded anicare) positioned on top of two adjacent greenhouse benches and partially filled with expanded round clay aggregate (Mother Earth Hydro- Table 1. Characteristics of tray types used for seedling transplant production of ton; National Garden Wholesale Sun- basil in Expt. 2. Tray cell count refers to the number of cells and plants per tray. Cell diameter, cell height, and cell volume refer to the cylindrical paper-wrapped light Supply, Vancouver, WA) to substrate contained within each tray cell. a depth of 3.8 ± 0.5 cm. Hydroponic nutrient solution was pumped from Tray cell count (no./tray)z Cell diam (cm)y Cell ht (cm) Cell vol (cm3)y a reservoir tank below the benches 162 2.2 4.5 16.3 and into both tanks simultaneously at 105 2.5 4.0 19.6 –1 126 mLÁmin for 2 min every 2 h, 72 3.5 4.0 38.5 allowing the nutrient solution to 50 4.0 4.0 50.2 cover the roots before draining back 32 5.0 5.0 98.1 into the reservoir. Aggregate depth zTray count values indicate the number of cells per standard 1.6-ft2 (0.15-m2) tray area. y 3 3 and irrigation practices followed the 1 cm = 0.3937 inch; 1 cm = 0.0610 inch .
• October 2020 30(5) 587 Table 2. Cultivar and system main and interaction effects on total shoot fresh weight, total shoot dry weight, leaf Soil Plant Analysis Development (SPAD) chlorophyll content, total leaf area, average plant height, average node number, and average internode length for basil after 21 d in the first experiment. Culture systems included deep water culture (DWC) hydroponics, nutrient film technique (NFT) hydroponics, and shallow aggregate ebb-and-flood (SAEF) soilless system. Shoot Shoot Leaf SPAD Avg plant Avg internode fresh dry wt chlorophyll Total leaf area ht Avg nodes length Source wt (g)z (g) index (cm2)z (inches)z (no./plant) (inches) Cultivar Cinnamon 97.1 ay 8.2 ab 34.8 b 1700.5 a 13.8 a 6.5 b 2.1 b Genovese 104.6 a 8.7 a 32.7 c 1793.3 a 12.3 b 5.2 d 2.4 a Mrs. Burns Lemon 85.6 b 7.3 c 27.6 d 1740.5 a 14.2 a 7.2 a 2.0 b Sweet Thai 71.0 c 7.7 bc 38.8 a 1455.8 b 11.8 b 5.7 c 2.1 b Culture system DWC 102.6 a 9.1 a 33.2 a 1798.5 a 13.7 a 6.4 a 2.1 a NFT 75.8 c 6.6 c 32.5 a 1417.8 b 12.3 b 6.0 a 2.1 a SAEF 90.4 b 8.3 b 34.8 a 1801.3 a 13.1 a 6.0 a 2.2 a Cultivar *** *** *** *** ** * * Culture system *** ** NS ** ** NS NS Cultivar · system ** ** NS *** * NS NS z1 inch = 2.54 cm; 1 g = 0.0353 oz; 1 cm2 = 0.1550 inch2. yData represent least-square means of 3 and 12 replicates for culture system and cultivar, respectively. Mean separation was performed using Tukey’s honestly significant difference with a = 0.05. NS, *, **, ***Nonsignificant or significant at P £ 0.05, 0.01, or 0.0001, respectively.
using an environmental control sys- of ‘Genovese’ basil (Johnny’s Se- different substrate volumes and cell tem (GEMLink 5; QCom, Temecula, lected Seeds) were sown as one seed diameters (Table 1). Individual CA). per cell. Seeded trays were subirri- plants were spaced between and Replication was achieved during gated as needed using a commercial within gutters at 20 cm. seedling production and after trans- water-soluble nutrient formulation DATA COLLECTION. Plants were plant to hydroponic NFT systems (16.0N–1.7P–14.9K Jack’s Oasis harvested from NFT systems on 8 using a randomized complete block Hydro FeED; JR Peters, Allentown June 2019 (36 d after sowing seed), design with three replications per PA) mixed at 200 mgÁL–1 nitrogen in and data were collected and analyzed treatment. Seeds were sown in three tap water. Applied nutrient solution on a per plant basis for each root trays per tray cell count and root EC and pH were 1.3 mSÁcm–1 and volume and transplant date treatment volume; each individual tray served 5.9, respectively. combination. Within each NFT sys- as one replicate (n = 3). At each The nutrient solution used in the tem, the two plants per treatment transplant date, two plants were taken NFT systems was identical to that of served as subreplicates, and subrepli- from the center of each replicate tray Expt. 1. Solution pH and EC were cate data were averaged to provide and transferred to three NFT systems maintained within target ranges of one treatment replicate value for data positioned adjacent to each other on 5.5 to 6.5 and 1.5 to 2.0 mSÁcm–1, analysis. Total shoot height per plant a greenhouse bench. Seedlings taken respectively, by daily adjustments to was measured just before harvest. from the same replicate tray were the fertilizer concentration in the re- Shoot fresh and dry weights were transferred to the same NFT system, plenishment solution and additions measured as described above. where the three NFT systems each of 0.1 N sulfuric acid (H2SO4). In STATISTICAL ANALYSIS. An analy- served as a replication (n = 3). At each addition, nutrient solutions for each sis of variance using PROC GLM transplant date, plant positions in NFT system were fully replaced each (SAS version 9.4) was performed to each gutter were randomly assigned. week. evaluate the root volume and trans- In addition, all gutters per NFT sys- Each NFT system contained 12 plant date main and interaction ef- tem were re-randomized at the sec- separate 150 · 40 · 4-cm polypropyl- fects on shoot fresh weight, shoot dry ond and third transplant dates (21 ene gutters (AM Hydro) positioned weight, and plant height at harvest. and 28 d, respectively). Extra plants on a 2.5% slope across the top of the Mean separation was performed using not used for experimentation were greenhouse bench. The top of each Tukey’s HSD at a = 0.05. placed at the front and back of each gutter was removed and replaced gutter, as well as in additional gutters with 6-mil white-black horticultural Results along the sides of each system, as plastic film with the white side facing EXPT.1:BASIL GROWTH IN a buffer. upward. Substrate for each trans- ANOVELSAEF SYSTEM COMPARED PLANT CULTURE. Seedling trays plant was pushed through perpen- WITH DWC AND NFT HYDROPONIC contained cells with a cylindrical pa- dicularly cut slits in the plastic film. SYSTEMS. Shoot fresh weight and dry per-wrapped and peat-based soil- The purpose of the plastic slits was weight per plant at harvest differed less substrate (Ellepots; Elleguard, to hold the substrate in place within between cultivars and culture systems Storstrømsvej, Denmark), and seeds the gutter as well as accommodate [P < 0.05 (Table 2)]. Shoot fresh
588 • October 2020 30(5) weight was greatest for ‘Genovese’ EXPT.2:BASIL SEEDLING ROOT that across 35 basil cultivars, shoot and ‘Cinnamon’ and lowest for VOLUME AND TRANSPLANT DATE dry weight was an average of 2.6 g ‘Sweet Thai’. Dry weight was greatest EFFECTS ON NFT HYDROPONICS. Root greater per plant when grown in for ‘Genovese’ and lowest for ‘Mrs. volume and transplant date had main DWC compared with NFT systems, Burns Lemon’. Shoot fresh weight effects on, but no interaction with, whereas shoot dry weight was 2.5 g and dry weight across cultivars were final shoot fresh weight, shoot dry greater in DWC compared with NFT consistently greatest for DWC, lowest weight, and shoot height at harvest [P in this study (Table 1). Other re- for NFT, and intermediate for SAEF. < 0.05 (Figs. 1 and 2)]. Overall, shoot searchers have reported similar trends ‘Sweet Thai’ basil was the only culti- fresh weight was greatest for plants in culture systems with floriculture var with similar fresh and dry weights transferred to NFT systems at 14 crops; for example, Blok et al. in the SAEF and NFT systems (data d after sowing and lowest at 28 d after (2017) showed that growth rates for not shown), which resulted in the sowing, with 21 d after sowing being chrysanthemum (Chrysanthemum sp.) interaction effect between the culti- intermediate (Fig. 1A). Trends for decreased 12% when grown in NFT var and system (Table 2). Mean sep- shoot dry weight were similar to those instead of DWC. The same authors aration for culture system–cultivar observed for shoot fresh weight (Fig. suggested that the thin film of solu- treatment combinations were not 1B). Shoot dry weight at harvest was tion with NFT supplied water and reported because shoot weight trends greatest, intermediate, and lowest 14, nutrients (including oxygen) at in- were similar among the remaining cul- 21, and 28 d after sowing, respec- sufficient rates for chrysanthemum, tivars and the main objective of this tively (Fig. 1B). Shoot height was thereby limiting plant growth. Roots experiment was to compare overall sys- greatest for the first and second trans- can also develop into thick mats in tem effects. plant dates, and was lower for the NFT troughs, particularly with long- Total plant height and leaf area third transplant date (Fig. 1C). term crops, resulting in rapid deple- were also influenced by cultivar and Root volume had main effects on tion of nutrients in the rhizosphere culture system [P < 0.05 (Table 2)]. shoot fresh weight (P £ 0.0001), that can decrease growth (Blok et al., Cultivars Cinnamon and Mrs. Burns shoot dry weight (P £ 0.0001), and 2017; Sonneveld and Voogt, 2009). Lemon were taller than Genovese and shoot height (P £ 0.0001) at harvest Nutrient solution and root zone Sweet Thai. Overall plant height was (Fig. 2). Overall, shoot fresh weight temperature were not monitored or lower for cultivars grown in NFT than increased as root volume increased controlled in this study; however, it is in DWC and SAEF systems. Leaf area (Fig. 2), and fresh weight was greatest possible that high nutrient solution was also lower in NFT than for DWC for plants grown in 32-cell trays and and root zone temperatures reduced and SAEF, and it was lowest for lowest for 162-cell tray. Trends for plant growth in NFT systems. The ‘Sweet Thai’ compared with other shoot dry weight were similar to those temperature of the nutrient solution cultivars. Similar to trends of shoot observed for shoot fresh weight, and film passing through NFT troughs fresh and dry weights, plant height shoot dry weight increased as root can convert rapidly to the warm am- and leaf area for ‘Sweet Thai’ were volume increased (Fig. 2B). Shoot bient air temperatures in greenhouses similar in NFT and SAEF (data not height at harvest was also greatest (Resh, 2012; Sonneveld and Voogt, shown), resulting in the interaction for plants grown in 32-cell trays and 2009) and contribute to excessively effect between cultivar and system lowest for plants in 162-cell trays, high root zone temperatures. In con- (Table 2). indicating that plant height also in- trast, large solution volumes and sub- The leaf chlorophyll index dif- creased as the root volume increased strate in the DWC and SAEF systems fered between cultivars at harvest (P < (Fig. 2C). help buffer against temperature fluc- 0.0001), but it was not influenced by tuations and reduce the potential for the culture system (Table 2). In this Discussion high root zone temperature stress experiment, leaf SPAD chlorophyll Results indicated that basil culti- (Resh, 2012). content values greater than 30 indi- vars differed in shoot growth and Overall shoot weights in the cated visibly green foliage. The leaf morphology. Overall, cultivars Geno- SAEF system were intermediate com- chlorophyll index was lowest for vese and Cinnamon produced greater pared with those in the commercially ‘Mrs. Burns Lemon’ (leaf chlorophyll shoot fresh weight and dry weight at used DWC and NFT hydroponic of 27.6) (Table 2). harvest compared with Mrs. Burns systems (Table 2), suggesting that Node number per plant and av- Lemon and Sweet Thai (Table 1). modifications of ebb-and-flood irri- erage internode length at harvest dif- Similar trends were reported by Wal- gation tables for edible crop produc- fered between cultivars (P < 0.05) but ters and Currey (2015a) for the same tion may be viable options for were unaffected by culture system cultivars grown in NFT and DWC bedding plant operations. Reduced (Table 2). Although statistically sig- hydroponics. Cultivars Genovese, basil growth in the SAEF system nificant, the numbers of nodes per Cinnamon, and Sweet Thai had compared with DWC may have par- plant were only slightly different be- greater leaf SPAD chlorophyll index tially resulted from an intermittent tween cultivars, ranging from 5.2 values than Mrs. Burns Lemon in this and lower supply of nutrients. The nodes for Genovese to 7.2 nodes study. same nutrient solution was applied to for Cinnamon. Similarly, internode Similar to results reported by each system, and plants grown hydro- length was slightly greater for Geno- Walters and Currey (2015a), basil ponically (DWC and NFT systems) vese compared with Cinnamon, Mrs. shoot weights were greater in DWC received a constant supply of the Burns Lemon, and Sweet Thai (Table than in NFT hydroponic systems. entire nutrient solution volume. In 2). Walters and Currey (2015a) found contrast, plants in the SAEF system
• October 2020 30(5) 589 were irrigated periodically using ebb- and-flood and excess nutrient solu- tion not held by the clay aggregate drained back into the reservoir. Therefore, roots in the SAEF system were exposed only to the nutrient solution retained by the clay aggre- gate between irrigation events (every 2 h). Incorporating substrate compo- nents with greater water-holding ca- pacity and/or adjusting applied nutrient concentrations and fertiga- tion frequency are strategies to in- crease nutrient availability and plant growth in substrate-based hydro- ponic systems (Bar-Yosef, 2008; Lieth and Oki, 2008). Shoot weights decreased for basil seedlings grown with lower root vol- umes, particularly when transplanted late to NFT hydroponics (Fig. 1). Past research of floriculture crops has shown that low root volumes can cause root restriction and reduc- tion in growth (Latimer, 1991; van Iersel, 1997). van Iersel (1997) found that salvia (Salvia sp.) seedlings grown in trays with 7.3-cm3 root volumes suffered from root restric- tion and had decreased net assimila- tion rates compared with trays with 55-, 166-, and 510-cm3 root vol- umes. Latimer (1991) also found that seedlings of marigold (Tagetes erecta) had 60% of the leaf area and shoot and root dry weights when grown in 7- cm3 compared with 44-cm3 container volumes, and further reductions in growth occurred in the landscape after transplant. Fisher et al. (2006) showed that calibrachoa (Calibrachoa ·hybrida) young plants held for 6 to 8 weeks in 144- and 125-cell trays dried quickly, resulting in air-pruning of roots and delayed growth after trans- plant. In this study, basil grown in 32- cell trays with the largest root volume per plant (98.1 cm3) still had lower shoot weights when transplanted 28 d compared with 14 d after sowing, but it did not exhibit the highly dense and matted root systems often char- acteristic of root restriction. Fig. 1. Transplant date effects on basil seedling shoot fresh weight (A), shoot dry Root zone nutrients may have weight (B), and shoot height (C) per plant at harvest 35 d after sowing seeds for become depleted between irrigation the second experiment. Transplant dates 1, 2, and 3 corresponded to 14, 21, and events and limited plant growth dur- 28 d after sowing. Data represent least-square means of 15 replicates per ing seedling production. Substrate treatment. Mean separation was performed using Tukey’s honestly significant EC averaged 0.46, 0.42, and 0.33 difference (HSD) with a = 0.05. Error bars represent 95% confidence intervals of mSÁcm–1 across tray cell count and each mean. 1 g = 0.0353 oz; 1 cm = 0.3937 inch. root volume treatments when seed- lings were transplanted at 14, 21, and 28 d after sowing, respectively (data not shown), and it was lower
590 • October 2020 30(5) compared with the EC of 1.3 mSÁcm–1 in the applied nutrient solu- tion. In hydroponic culture, plants also received a constant supply of nutrient solution, and root systems expanded in NFT troughs for greater exposure to nutrients and water. The combination of a large root volume and early transplant to hydroponics may have resulted in less root restric- tion and a nearly optimal supply of nutrients and water for plant growth. Past research with bedding plants has shown that the transplant of large seedling plugs to containers can increase production efficiency and reduce costs (Fisher, 2008; Fisher et al., 2006). In this study, trans- planting basil seedlings at later dates decreased harvested shoot weights across seedling tray and root volume treatments (Fig. 1), possibly because root zone factors limited growth dur- ing seedling production, as previously discussed. Final shoot weights were also greatest for seedlings grown in the largest root volume [98.1 cm3 (32 cell-count tray)] and transplanted at the earliest date (14 d after sowing). Therefore, results of this study did not suggest that transplanting large basil seedlings could increase space- use efficiency after transplant without compromising yield. However, if root zone factors could be horticulturally managed to improve basil growth during seedling production and min- imize effects on final yield, then there may still be a cost-benefit to trans- planting large seedling plugs in hy- droponic systems. Edible crop growers would likely benefit from further in- vestigations of maximizing plant growth during seedling production as well as evaluations of the effects of seedling size and transplant practices on space- use and production efficiencies. Conclusions Basil yield of the SAEF system was intermediate compared with yields of commercially used DWC and NFT hydroponic systems; the Fig. 2. Main effects of transplant seedling tray cell count on basil shoot fresh yield was greatest for DWC and low- weight (A), shoot dry weight (B), and shoot height (C) per plant at harvest 35 est for NFT. These results suggest d after sowing seed for the second experiment. Data represent least-square means that ornamental bedding plant growers of nine replicates per treatment. Mean separation was performed using Tukey’s using ebb-and-flood irrigation can honestly significant difference (HSD) with a = 0.05. Error bars represent 95% potentially modify these systems for confidence intervals of each mean. 1 g = 0.0353 oz; 1 cm = 0.3937 inch. edible crop production without hav- ing to purchase DWC and NFT hy- droponic equipment. Differences in yields between culture systems may have resulted from differences in
• October 2020 30(5) 591 nutrient supply and availability for tion rate and distribution in water-based Lieth, J.H. and L.R. Oki. 2008. Irrigation plant uptake. Increasing the substrate cultivation systems. Front. Plant Sci. 8:1– in soilless production, p. 117–144. In: M. water-holding capacity and/or adjust- 15. Raviv and J.H. Lieth (eds.). Soilless cul- ing the applied nutrient concentration ture, theory and practice. Elsevier, Lon- Chidiac, J. 2017. Shallow aggregate ebb- don, UK. and fertigation frequency are potential and-flow system for greenhouse lettuce strategies for increasing the nutrient production. MS Thesis, Univ. Arkansas, Resh, H.M. 2012. Hydroponic food supply and yield in the SAEF system. Fayetteville. production: A definitive guidebook for the advanced home gardener and the Transplanting large basil seed- Currey, C. 2017. A systematic ap- lings to NFT hydroponic systems < commercial hydroponic grower. CRC proach. 2 July 2020. https://www. Press, Boca Raton, FL. did not increase space-use efficiency producegrower.com/article/a-systematic- after transplant without compro- approach/>. Sonneveld, C. and W. Voogt. 2009. Plant mised yield. Root zone factors, par- nutrition of greenhouse crops. Springer, ticularly root volume and nutrient Fisher, P.R. 2008. What is the most Dordrecht, The Netherlands. profitable liner size? 2 July 2020.
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