Source: LINCOLN UNIVERSITY submitted to
NUTRIENT MANAGEMENT IN SUSTAINABLE SMALL-SCALE HYDROPONIC SYSTEMS: YIELD AND QUALITY RESPONSE OF SPECIALTY AND EXOTIC LEAFY VEGETABLES TO NUTRIENT SOLUTION NITROGEN COMPOSITION
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
REVISED
Funding Source
Reporting Frequency
Annual
Accession No.
1018002
Grant No.
(N/A)
Project No.
MOLUHYDROPONICS-05
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Oct 17, 2018
Project End Date
Sep 30, 2022
Grant Year
(N/A)
Project Director
EGILLA, JO, N.
Recipient Organization
LINCOLN UNIVERSITY
(N/A)
JEFFERSON CITY,MO 65101
Performing Department
Agriculture
Non Technical Summary
The aim of this project is to determine nitrogen nutrition requirements and appropriate composition of nitrogen in the hydroponic nutrient solution for optimum marketable yield and quality of specialty and exotic leafy vegetables, culinary or medicinal herb species. In addition, develop science-based cultural practices with practical application in managing crop nitrogen nutrition in small-scale hydroponic production of specialty and exotic leafy vegetables, culinary or medicinal herb species for limited resource growers in Missouri and the NCR. Unstable produce prices, the dominance of the market for traditional commercial horticulture crops (tomatoes, cucumbers, lettuce, sweet peppers, strawberries and cut-flowers), by larger farms, and the reduction of government price stabilizing tools, threatens the viability of limited resource farm enterprises in Missouri and the NCR. Increased concentration among food processing companies that demand consistent supply of dependable quality is more favorable to large-scale operations, causing limited resource growers to lose control over their economic security. Hydroponic production of specialty crops under greenhouses and other protected structures provides an alternative approach to field production and conventional greenhouse crop production, which is often constrained by good seedling stand establishment of warm season crops, limited control over adverse weather, pests and diseases. Hydroponic systems can potentially increase opportunities for year-round production, ensuring a steady market supply of high quality fresh produce and continuous cash flow for the grower. Sustained cash-flow system is essential for the economic viability of limited resource growers. This project will focus on evaluating specialty and exotic leafy green vegetables, culinary or medicinal herb cultivars in a nutrient recirculating hydroponic systems.
Animal Health Component
0%
Research Effort Categories
Basic
50%
Applied
35%
Developmental
15%
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
10214991010100%
Goals / Objectives
Goals: The goals of this research are to 1) expand the range of hydroponically grown leafy vegetables to include specialty and exotic vegetables, culinary or medicinal herbs; and 2) sustain the high yield and quality potential of the latter through efficient use of nitrogen in fertilizer formulations for hydroponic nutrient solution.Objective 1: To evaluate the effect of nitrate source and composition of the hydroponic nutrient solution on the growth, marketable yield and post-harvest quality of selected specialty and exotic leafy vegetables, culinary or medicinal herbs in NFT hydroponic culture.Objective 2: To compare the effect of different ratios of nitrate-N (NO3-N) to ammoniacal-N (NH4+-N) of the hydroponic nutrient solution on the growth, marketable yield and postharvest quality of selected specialty and exotic leafy vegetables, culinary or medicinal herbs grown in NFT hydroponic culture.
Project Methods
Facility and Equipment Needed. All experiments will be conducted in an existing 134 sq. meters (1,440 sq. ft.) controlled environment hydroponic greenhouse at the George Washington Carver Memorial Research Farm of Lincoln University of Missouri. Studies will be conducted with replicated modules of a closed-loop nutrient recirculating hydroponic system (NFT). These modules are representative of those used for the commercial production of leafy vegetables in the hydroponic industry.The NFT Hydroponic System. The NFT hydroponic system is a recirculating nutrient solution based plant culture in which the solution flows down channels or gullies and re-circulated through crop roots continuously. The NFT hydroponic system available for this project is comprised of a set of six PVC Hydro-Troughs™ (American Hydroponics Co., Arcata, California) 5.1 x 10.2 x 365.76 cm (2" x 4" x 144") with 4.45 cm (1.75") diameter holes, spaced 20 cm (8") apart along the troughs. Each set of six PVC Hydro-Troughs™ (channels) are mounted on a metal framework with a two percent slope allowing the a thin film of nutrient solution (~2 mm deep) to flow back by gravity into 3-inch PVC or laminated plastic catchment collectors positioned perpendicularly across the lower ends of the growing channels. The nutrient solution is pumped through a ¾"-hose to headers that are located at the high end of the NFT channels, by a 300 gal/h pump from the recirculating nutrient solution reservoirs. The nutrient solution discharges from the headers into the channels through flexible trip tubes, and bathes the roots consistently as it flows down into the collectors. The catchment collector returns the nutrient solution back to the recirculating reservoir.Plant Culture: Seedling Propagation. For all experiments, selected specialty and exotic leafy vegetables, culinary or medicinal herbs will be grown. Crops will be propagated from seed in slabs of Oasis "Rootcubes™ (Smithers-Oasis North America, Kent, OH), or in rockwool cubes (Grodan Inc., Milton, ON L9T 6W3, Canada) inserted into standard horticulture flats. After seed germination, seedlings will be fertigated with a hydroponic nutrient solution prepared to supply 100 mg N liter-1, until they are transferred into the NFT hydroponic culture at the 2 to three true leaf stage. Seedlings will be grown to market maturity, while monitoring, and using data from nutrient-solution chemistry (pH, EC, N, K and Ca) and petiole-sap nitrogen concentration data to determine how regularly the nutrient solutions need to be refreshed (renewed) in order to optimize growth and yield. Daily pH data collection will guide the adjustment of the hydroponic nutrient solution to the physiological pH appropriate for the crop species using hydrochloric acid, while the EC will determine the frequency and time to renew the solution.Harvesting and Tissue Preparation. Crops will be harvested at market maturity (the end of every cropping cycle) for fresh weight record, and dry weight determination after drying to constant weight at 75o C in air forced oven. Leaves will be ground to pass through a 2-mm mesh for laboratory chemical analysis to determine the essential element composition of crops from each experiment. Several preliminary experiments will be conducted to screen the various specialty and exotic leafy vegetables, culinary or medicinal herbs for their requirements in hydroponic culture a base Steiner nutrient solution at standard nitrogen concentration. Subsequently, the experimental treatments will employ base Steiner nutrient solution with various modifications of the nitrogen form and concentration.

Progress 10/01/20 to 09/30/21

Outputs
Target Audience:The target audiences reached during this reporting period include (1)small scale limited resource hydroponics / aquaponics farmers; (2) greenhouse producers of vegetables, herbs and spices for local farmers markets; (3) undergraduate and graduate students of Lincoln University and the University of Missouri-Columbia; and (4)K-12 middle and high school students from central Missouri, and 5) Master Gardeners from Southeastern Missouri. Changes/Problems:As requested during the previous reporting period, research objective 2 will be dropped from the current project due to inadequate time and technical support to complete the required experiments for the investigation. The completion of objective 2 requires the conduct of several additional experiments that will extend over a project period of at least two years. What opportunities for training and professional development has the project provided?This project trained a Research Technician in the agriculture department of Lincoln University to conduct crop plantnutrition and management research on hydroponics crop production under a controlled environment agriculture facility, and the use of related apparatus, nutrient solution analysis instrumentation, as well as data collection from different hydroponic systems.This project also trained an undergraduate student at Lincoln University. Students on this project are being trained in science-based hydroponics crop production technology, and the use of hydroponic research tools and instrumentation. How have the results been disseminated to communities of interest?Research objectives and methodology as well as findings essential to commercial hydroponics crop production technology from the current research projects weredisseminated to the public (current and prospective hydroponic and aquaponic growers)-through onsite educational presentations during visits to the hydroponic research center at Lincoln University's George Washington Carver Memorial Research Farm in Jefferson City, Missouri. The center received over 100 visitors during the current reporting period. Training in NFT hydroponic production of Collards on hydroponic production methods were provided to the Boys & Girls Club (fourth and fifth grade students) and Master Gardeners from Cole and neighboring counties in Missouri, as well as Master Gardeners and Farmers from Southeastern Missouri. What do you plan to do during the next reporting period to accomplish the goals?My plan is to conclude the collection of crop growth data from Collards in NFT hydroponic culture including leaf chlorophyll concentration and evaluate postharvest storage quality of leaves from the different nitrogen treatments during the remaining project period. I would continue to process all harvested plant tissue, statistically analyze all crop yield and nutrient concentration data, and prepare manuscripts for conference presentations and peer review journal publications.The ongoing education of hydroponics growers, Lincoln University students, K-12 students and teachers, and agricultural audiences about sustainable hydroponic crops production and managementwill continue until September 31, 2022.

Impacts
What was accomplished under these goals? Research Objective Consistent with objective 1, this study evaluated the effect of hydroponic nutrient solution nitrate-nitrogen composition on leaf yield of Collards (Brassica oleracea L. Acephala Group) cv. Champion in NFT hydroponic culture. Cultivars of Collards are like Kale but differ mainly in leaf shape and flavor. Collards are cool-season vegetable greens that are rich in vitamins A and C and minerals. Collards are grown for their abundant foliage, which is usually consumed as a cooked vegetable or as an ingredient in other foods. In the United States, collards are very popular in the southern states where the majority of the commercial as well as home garden production occurs. Collards grow better in warm weather and can tolerate more cold weather in the late fall than any other member of the cabbage family. The growing of Collards in NFT hydroponic system is a novel horticultural practice that will facilitate year-round intensive production in cooler regions of the USA. Research Approach Hydroponic System. The hydroponic design consists of a Nutrient Film Technique (NFT) which the solution flows down channels or gullies and re-circulated through crop roots continuously. The NFT hydroponic system used for this study is comprised of three sets of six PVC Hydro-Troughs™ (American Hydroponics Co., Arcata, California) 5.1 x 10.2 x 365.76 cm (2" x 4" x 144") with 4.45 cm (1.75") diameter holes that are spaced 20 cm (8") apart along the troughs. The rows of PVC troughs are set on metal frames (bays) 0.91-1.22 m (3-4 ft.) high, and at a spacing of 28 cm (11"). Seedling Production & Crop Culture. Collards cv. Champion was propagated from seed in slabs of 2.5 × 2.5 × 2.5 cm (1" × 1" × 1") A025/40™ Rockwool cubes. "Rootcubes™ (Grodan (ROXUL Inc. 8024 Esquesing Line Milton, ON L9T 6W3, Canada). After seed germination, seedlings were fertigated with a solution of Oasis Hydroponic Fertilizer (16N-1.75P-14.1K); J. R. Peters, Inc., Allentown, PA]), prepared to supply 100 mg N liter-1, until they are transferred into the NFT hydroponic culture at the second true leaf stage. Seedlings were grown to market maturity at mean greenhouse ambient day/night temperature and relative humidity of 23.8/12.5 C and 78.6/65.2%, respectively, during the cropping cycle. The NFT hydroponic solution comprised of modified Steiner nutrient solution without NaNO3 (NaN0, control) or with 2.0 mM NaNO3 [NaN2]) or 5.0 mM NaNO3 (NaN5), supplying 13.25% and 33.22% of the total nitrate nitrogen in Steiner's nutrient solution, respectively. The control nutrient solution contained 39.44% of the total nitrogen as ammonium nitrogen from Ammonium Sulfate and 66.44% as nitrate nitrogen from Calcium Nitrate. During NFT hydroponic culture nutrient-solution chemistry (pH, EC) as well as the N concentration was recorded weekly to determine the regularly of nutrient solution renewal to optimize growth and yield. Both pH and EC of the nutrient solution were measured daily in situ with the Hanna HI98130 pH/EC/TDS meter (Hanna Instruments, Ltd., Bedfordshire, England). Hydroponic solution nitrate concentration was measured with the LAQUAtwin Nitrate Ion Meter (Horiba Instruments Incorporated, 9755 Research Drive, Irvine California 92618 USA). Daily pH data was used to guide the maintenance of the hydroponic nutrient solution between 6.8 and 7.2, while the EC data was used to determine the frequency and time to renew the hydroponic nutrient solution. Fully expanded Collards leaves were harvested sequentially at market maturity (36, 57 and 92 days after transfer into NFT hydroponic culture), leaves from each plant were excised and counted, and leaf fresh weight (LFW) was recorded immediately at harvest. Leaves from each plant were placed in paper sacks and dried for 96 hours in an air-forced oven set at 75o C, and leaf dry weight (LDW) was recorded subsequently.

Publications


    Progress 10/01/19 to 09/30/20

    Outputs
    Target Audience:The target audiences reached during this reporting period include (1)small scale limited resource hydroponics/aquaponics farmers; (2) greenhouse producers of vegetables, herbs, and spices for local farmers markets; (3) undergraduate and graduate students of Lincoln University and the University of Missouri-Columbia; and (4)K-12 middle and high school students and teachers, master gardeners, and extension educators from central Missouri. Changes/Problems:Request for Changes to Project-Accession # 1018002 1. I am requesting a one year extension of this project until the reporting period ending September 30, 2022, because of delays to the completion of various components of the experiments required. These delays were caused by COVID-19 imposed limitations on technical and student worker support for an extended time during the project execution period. 2. I am requesting that objective number 2 be dropped from the current project due to inadequate time and technical support to complete the required experiments for the investigation. The completion of objective 2 requires the conduct of several additional experiments that will extend over a project period of at least two years. Objective 2: To compare the effect of different ratios of nitrate-N (NO3-N) to ammoniacal-N (NH4+-N) of the hydroponic nutrient solution on the growth, marketable yield and postharvest quality of selected specialty and exotic leafy vegetables, culinary or medicinal herbs grown in NFT hydroponic culture. What opportunities for training and professional development has the project provided?This project continueto train a Research Technician in the agriculture department of Lincoln University to conduct crop plantnutrition and management research in a controlled environment agriculture hydroponic the system, and the use of related apparatus, nutrient solution analysis instrumentation, as well as data collection from different hydroponic systems.This project is currently permitted by the host institution to resume the training of an undergraduate student at Lincoln University. Students on this project were trained on science-based, crop plantnutrition,the use of hydroponic research tools and instrumentationandmethods of hydroponic crop production. How have the results been disseminated to communities of interest?Research objectives and methodology as well as findings from all ongoing research projects weredisseminated to the public (current and prospectivehydroponic and aquaponic growers) through onsite educational presentations during visits to the hydroponic research center at Lincoln University's George Washington Carver Memorial Research Farm in Jefferson City, Missouri. The center received about 15 visitors during the current reporting period. Training in NFT hydroponic production of lettuce in addition to classroom instruction on hydroponic production methods were provided to seventh and eighth grade students and teachers at a local school in Jefferson City, Missouri. What do you plan to do during the next reporting period to accomplish the goals?My plan is to continue the screening and evaluation of more specialtyleafy vegetables for nitrogen nutrition efficiency throughout the current project period and in future project years. I would continue to process all harvested plant tissue, statistically analyze all crop yield and nutrient concentration data, and prepare manuscripts for conference presentations and peer review journal publications.The ongoing education of hydroponics growers, Lincoln University students, K-12 students and teachers, and agricultural audiences about sustainable hydroponic crops production and managementwill continue.

    Impacts
    What was accomplished under these goals? Objective: The objective of this study is to determine whether nitrate-nitrogen (NO3---N) source: calcium nitrate [Ca(NO3)2 plus potassium nitrate (KNO3) compared to sodium nitrate (NaNO3)], and the concentration of NaNO3 in hydroponic nutrient solution can increase or decrease leaf yield and leaf nutrient element concentration of kale (Brassica oleracea Acephala Group) in nutrient Film Technique (NFT) hydroponic culture. Sodium nitrate (NaNO3) is less frequently as a NO3---N source in the formulation of hydroponic nutrient solutions compared to calcium nitrate Ca(NO3)2 or potassium nitrate (KNO3), because NaNO3 can potentially increase the Na concentration to levels that are unfavorable to plant growth. Although some leafy vegetable crops may be tolerant to moderate concentrations of Na in the root medium, the degree of sodium (Na) tolerance for most crops grown in hydroponic culture are yet to be established. This study investigates whether low to moderate concentrations of NaNO3 as NO3---N can substitute for Ca(NO3)2 and KNO3) and produce optimum yields during NFT hydroponic culture of kale. The response of leaf yield and nutrient element concentration of kale cv. Empire to two levels of NaNO3: 2.0 millimolar (mM; NaN2), or 5.0 mM (NaN5) in modified Steiner nutrient solution, was compared with a control nutrient solution without NaNO3. Kale is a non-heading leafy vegetable belonging to the family Brassicaceae, a group of vegetables that include collards, cabbage, broccoli, cauliflower, and Brussels sprouts, with a high content of health-promoting phytochemicals. Like collards, kale is a very popular leafy vegetable in southern United States, where majority of the commercial and home garden production occurs. Research Approach: Seedlings of kale cv. Empire were grown to market maturity in NFT hydroponic culture from the second true leaf stage. The NFT system uses pumps to recirculate nutrient solution through the mass of plant roots in channels or gullies continuously. The hydroponic solution comprised of modified Steiner nutrient solution without NaNO3 (NaN0; control), or with an equivalent proportion of the NO3---N substituted with 2.0 or 5.0 millimolar (mM) NaNO3 as NaN2 and NaN5; and contain 46 and 115 mg Na per liter at NaN2 and NaN5, respectively. Ca(NO3)2.4H2O and KNO3, substituted for the NO3---N composition of the control nutrient solution (NaN0). Whereas di-ammonium phosphate (NH4)2HPO4) supplied the ammoniacal-nitrogen (NH4+-N) composition in NaN2 and NaN5, NaN0 contained ammonium sulfate [(NH4)2SO4] as the sole source of NH4+-N. Mean ambient greenhouse day/night temperature and relative humidity were 24.9/7.5 C and 87.6/65.2%, respectively, during the hydroponic cropping cycle. At harvest, 35 days after seedling transfer into hydroponic culture (35-DAT), leaves were excised from each plant, and leaf fresh weight (LFW) was determined immediately after leaf count. The leaves were dried subsequently for 72 hours in an air-forced oven at 75o C for leaf dry weight (LDW) data. Ground replicate leaf samples from each treatment were analyzed chemically for macronutrient: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S); and micronutrient: iron (Fe), manganese (Mn), Zinc (Zn), copper (Cu), boron (B), molybdenum (Mo), and Na concentration. Key Findings: Leaf Yield of Kale: At 35-DAT, NaN5 increased leaf count by 4.9% over NaN2 (p = 0.0562), and by 6.3% over NaN0 (p = 0.0083), but NaN2 increased leaf count only by 1.5% compared with NaN0 (p = 0.7737). Leaf fresh weight was significantly higher at NaN5 than NaN2 and NaN0 (p <0.0001), but the difference between NaN2 and NaN0 was not significant (p = 0.7815). The response of LDW followed the trend NaN5 > NaN2 (7.4%), > NaN0 (9.2%), and NaN2 > NaN0 (2.0%); and LDW was significantly higher at NaN5 compared with NaN0 (p = 0.0051), but not NaN2 (p = 0.0669). Similar to LFW there was no significant difference in LDW between NaN2 and NaN0 (p = 0.6350). Nutrient Element Concentration of Kale Leaves: Leaf elemental concentration of kale at 35-DAT correlates with the leaf yield response to nutrient solution NaNO3 concentration. Similar to leaf fresh and dry weight, leaf nitrogen concentration was 7.0% higher at NaN5 than NaN2. However, NaN0 with similar leaf yield to NaN2, increased leaf nitrogen by 9.0% and 28.0% compared to NaN5 and NaN2, respectively, due to the relatively higher ratio of NH4+-N in the nutrient solution. Although leaf P, Ca, Mg, and S concentration were similar at all NaNO3 levels, leaf K was higher at NaN5 and NaN2 compared to NaN0: NaN5 > NaN2 (9.2%) > NaN0 (17.3%), respectively. The latter indicates that nutrient solution Na concentration at 2.0 and 5.0 mM did not depress the K uptake of kale in NFT hydroponic culture. Leaf Na concentration was 178% (NaN5) > NaN2 (170%) > NaN0, respectively, and these differences were significant (p = 0.05). At 35-DAT, leaf tissue Na concentration up to 0.41% and 0.15% of leaf DW at NaN5 and NaN2, respectively, caused no observable symptoms of Na disorder in kale. With the exception of Fe, which was 19% (NaN0), 53% (NaN2), and 71% (NaN5), below the lower limit of the sufficiency range (60 mg/g leaf DW) the leaf concentration of the other micronutrients were sufficient for optimum growth of kale, regardless of the NO3---N source, or NaNO3 concentration of the nutrient solution. However, the leaf concentration of the cation micronutrients Fe, Mn, Cu, and Zn decreased with increase in leaf Na concentration. Significance of Key Findings/Potential Impact: The supply of nitrogen as sodium nitrate in hydroponic nutrient solution up to 5.0 mM, or Na content up to 0.41% of leaf dry weight: 1) increased the leaf yield of kale, 2) did not decrease the uptake of macronutrients, and 3) cause no observable symptoms of excess sodium disorder or stress. These findings indicate that NaNO3 at moderate concentrations is a valuable substitute for other sources of nitrate nitrogen in NFT hydroponic culture of kale. Substitution of the cheaper sodium nitrate for calcium nitrate or potassium nitrate as a source of nitrate-nitrogen in the hydroponic culture of kale, and other sodium tolerant leafy vegetable crops will accrue significant savings for the hydroponic vegetable grower. The effect of sodium nitrate concentration higher than 5.0 mM in hydroponic nutrient solution on micronutrient uptake of kale requires further investigation.

    Publications


      Progress 10/17/18 to 09/30/19

      Outputs
      Target Audience:The target audiences reached during this reporting period include (1)small scale limited resource hydroponics/aquaponics farmers; (2) greenhouse producers of vegetables, herbs, and spices for local farmers markets; (3) undergraduate and graduate students of Lincoln University and the University of Missouri-Columbia; and (4)K-12 middle and high school students from central Missouri. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project continues to train a Research Technician (RT) in the agriculture department of Lincoln University to conduct nitrogen-nutrition and management research in a Controlled Environment Agriculture hydroponic the system, and the use of related apparatus, nutrient-solution analysis instrumentation, as well as data collection under protected agriculture conditions.This project has also been permitted by the host institution to resume the training of an undergraduate student at Lincoln University. The undergraduate studentis being trained on science-based, crop nitrogen-nutrition and managementresearch and methods of hydroponic crop production. The studentcontinues to acquire practical skills in the use of hydroponic and analytical research tools and instrumentation. How have the results been disseminated to communities of interest?Information about the research objectives and methodology was disseminated to the public (current and prospectivehydroponic and aquaponic growers)-through onsite educational presentations during visits to the hydroponic research center at Lincoln University's George Washington Carver Memorial Research Farm in Jefferson City, Missouri. The center received about 25 visitors during the current reporting period. What do you plan to do during the next reporting period to accomplish the goals?I plan to continue the screening and evaluation of more specialty and exotic leafy vegetables throughout this year and in future project years. ?I would continue to process all harvested plant tissue, statistically analyze all crop yield data and prepare manuscripts for conference presentations and peer-review journal publications. The ongoing education of hydroponics growers, Lincoln University students and the public about nitrogen use-efficiency and management in recirculating hydroponic systems will continue.

      Impacts
      What was accomplished under these goals? Objective: The objective of this study is to evaluate the effect of hydroponic nutrient solution nitrate-nitrogen composition on leaf yield of Kale (Brassica oleracea Acephala Group) cv. Empire in NFT hydroponic culture. Introduction: The effect of increasing concentrations of nitrate as sodium nitrate (NaNO3) in modified base Steiner nutrient solution on the growth and leaf yield of kale cv. Empire was compared with that composed of calcium nitrate (Ca(NO3)2.4H2O) and potassium nitrate (KNO3) in NFT hydroponic culture. Di-ammonium phosphate or ammonium sulfate supplied the ammoniacal-N (NH4+-N) composition of the nutrient solution. Kale is a non-heading leafy vegetable belonging to the family Brassicaceae, a group of vegetables that include collards, cabbage, broccoli, cauliflower, and Brussels sprouts, with a high content of health-promoting phytochemicals. Like collards, kale is a very popular leafy vegetable in the southern United States, where the majority of the commercial and home garden production occurs. Research Approach: The Hydroponic System consists of a Nutrient Film Technique (NFT), which is a nutrient solution recirculating hydroponic system that enables the flow of nutrient solution down channels or gullies and then recirculated through crop roots continuously. The NFT hydroponic system used for this study is comprised of three sets of six PVC Hydro-Troughs™ (American Hydroponics Co., Arcata, California) 5.1 x 10.2 x 365.76 cm (2" x 4" x 144") with 4.45 cm (1.75") diameter holes that are spaced 20 cm (8") apart along the troughs. The rows of PVC troughs are set on metal frames (bays) 0.91-1.22 m (3-4 ft.) high, and at a spacing of 28 cm (11"). Each set of six PVC Hydro-Troughs™ (channels) is supported by a metal framework with a two percent slope allowing a thin film of nutrient solution (~2 mm deep) to flow back by gravity into 3-inch PVC plastic catchment collectors positioned perpendicularly across the lower ends of the growing channels. The nutrient solution is pumped through three-quarter inch (¾") hoses to headers located at the high end of the NFT channels by 300 gallons per hour pumps from variable volume reservoirs. The nutrient solution discharges from the headers into the channels through flexible drip tubes and bathes the roots consistently as it flows down into the collectors. The catchment collector or pipe conducts the solution back to the recirculating nutrient solution reservoir. Seedling Production and Crop Culture: Kale cv. Empire was propagated from seed in slabs of 2.5 × 2.5 × 3.75 cm (1" × 1" × 1.5"; 162 cubes/flat) Oasis "Rootcubes™ (Smithers-Oasis North America, Kent, OH). After seed germination, seedlings were fertigated with a solution of Jack's™ CAL-MAG (15N-2.2P-12.5K; J. R. Peters, Inc., Allentown, PA]), prepared to supply 100 mg N liter-1, until they are transferred into the NFT hydroponic culture at the second true leaf stage. Seedlings were grown to market maturity at mean greenhouse ambient day/night temperature and relative humidity of 24.9/7.5 C and 87.6/65.2%, respectively, during the cropping cycle. The hydroponic solution comprised of modified Steiner nutrient solution without NaNO3 (NaN0, control) or with an equivalent proportion of the nitrate-nitrogen substituted with 2.0 (NaN2) or 5.0 millimolar (mM) NaNO3 (NaN5). During NFT hydroponic culture nutrient-solution pH, EC, as well as the N, and K concentration data was recorded weekly to determine how frequently the nutrient solution need to be refreshed (replaced) in order to optimize growth and yield. Both pH and EC of the nutrient solution were measured daily in situ with the Hanna HI98130 pH/EC/TDS meter (Hanna Instruments, Ltd., Bedfordshire, England). Daily pH data was used to guide the maintenance of the hydroponic nutrient solution between 6.8 and 7.2, while the EC data was used to determine the frequency and time to refresh the hydroponic nutrient solution. At market maturity, (35 days after transfer into hydroponic culture), leaves from each plant were excised and counted, and leaf fresh weight (LFW) was recorded immediately at harvest. Leaves from each plant were placed in paper sacks and dried for 72 hours in an air-forced oven set at 75o C, and leaf dry weight (LDW) was recorded subsequently. Results: At 35-DAT, percent frequency of leaf count were NaN5 (34.77%) > NaN2 (32.63%) > NaN0 (32.60%), respectively. This frequency corresponded to an increase in leaf count of 4.9% at NaN5 over NaN2 (p = 0.0562) and 6.3% over NaN0 (p = 0.0083). NaN2 increased leaf count only by 1.5% NaN2 compared with NaN0 (p = 0.7737). Leaf fresh weight (LFW) was significantly higher at NaN5 than NaN0 and NaN2 (p <0.0001), but the difference between NaN2 and NaN0 was not significant (p = 0.7815). The response of LDW followed the trend NaN5 > NaN2 (7.4%), > NaN0 (9.2%), and NaN2 > NaN0 (2.0%), and LDW was significantly higher at NaN5 compared with NaN0 (p = 0.0051), but not NaN2 (p = 0.0669). Similar to LFW there was no significant difference in LDW between NaN2 and NaN0 (p = 0.6350). The growth (LFW and LDW) of kale cv. Empire increased significantly at 5.0 mM compared to 2.0 mM NaNO3. This observation suggests that the supply of nitrate-nitrogen in the form of NaNO3 can contribute to a higher leaf yield of kale in hydroponic culture. The substitution of the cheaper NaNO3 for calcium nitrate (Ca[NO3].2H2O) and potassium nitrate (KNO3) as a source of nitrate-nitrogen in the hydroponic culture of kale and other sodium tolerant leafy vegetable crops will accrue significant savings for the hydroponic vegetable grower. However, further study is necessary to determine the degree of sodium tolerance in kale, and to facilitate further screening of leafy vegetable crops for their sodium tolerance in hydroponic culture.

      Publications

      • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Egilla, Jonathan N., Isabelle Nyirakabibi. 2019. Nutrient Element Interactions with Leaf Growth of Collards in Response to Hydroponic Solution Composition. HortScience 54(9): S112-113. (Abstr.)