Source: CORNELL UNIVERSITY submitted to NRP
DEVELOPMENT OF AQUAPONIC SYSTEMS FOR THE PRODUCTION OF LETTUCE AND STRAWBERRIES
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
COMPLETE
Funding Source
Reporting Frequency
Annual
Accession No.
1010413
Grant No.
(N/A)
Cumulative Award Amt.
(N/A)
Proposal No.
(N/A)
Multistate No.
(N/A)
Project Start Date
Oct 1, 2016
Project End Date
Sep 30, 2019
Grant Year
(N/A)
Program Code
[(N/A)]- (N/A)
Recipient Organization
CORNELL UNIVERSITY
(N/A)
ITHACA,NY 14853
Performing Department
Biological & Environmental Engineering
Non Technical Summary
New York consumers have limited access to fresh, high quality, locally grown produce at competitive pricing with imported product. It is well known at this point that consumers are placing an added value on locally produced products. This then provides an opportunity for the small scale producer and that opportunity can be partially addressed through aquaponics and product diversification. U.S. consumer demand for spring greens such as spinach has skyrocketed and been met by corresponding increases in production. However, Northeastern states contribute very little to production of these crops. New York State ranked eighth in strawberry production in 2014 with 3.2 million pounds (M lb), but falls far behind the top five states (CA 2758 M lb, FL 207 M lb, OR 15 M lb, NC 15 M lb, WA 10 M lb, MI 4.5 M lb, WI 3.8 M lb, PA 3.3 M lb) (USDA, 2014). Even during peak harvest months (July-August), only a small fraction of NYS residents have access to home-state strawberries. Most strawberries grown in NYS are sold within 50 miles of the farm, while residents of New York City never even see home-grown fruit, instead relying primarily on strawberries imported from California and Florida; from 2011 to 2014, New York experienced a 15% drop in production of leafy greens.While greenhouse production of flowers and almost all vegetable crops is commonly practiced, hydroponic production is still quite limited.The market movement towards locally produced and organic is providing new opportunities to re-visit the economic feasibility of hydroponic production in northeast climates. Aquaponic production is a very small fraction of hydroponic production, even though it affords the opportunity of increasing the overall sustainability of both fish and plant production. Some of the constraint to adapting either method is the lack of scientifically gathered information to document results, even though there is much grey-literature that supports these growing methodologies. Given the success of expanding greenhouse strawberry production in the Netherlands, we fully expect to be able to demonstrate successful designs for this same product to NY producers. The greenhouse berry market will primarily produce product using day-neutral varieties and provide fruit for market during the fall-winter-spring period when field grown berries are at their highest prices. We also expect to be able to produce higher quality berries (taste) since our proximity to market allows a harvest time closer to peak flavor than field grown berries that must be shipped and thus harvested earlier or using varieties that are lower in sugars so bruising and damage is not as prevalent (but taste quality is lost). By providing greenhouse growing methods for high value crops, NY growers will be able to extend their marketing period beyond their summer peak months, which will increase their sales and farm viability.Aquaponics combines hydroponics and aquaculture. Such systems make multiple uses of resources such as water and nutrients, and share infrastructure, management, and labor costs. Nutrient levels are highly dependent on the fish activity, fish number, and fish species. Even if the fish waste provides adequate nutrients to successfully grow high yielding plants, the hydrodynamics of the aquaponics system flow can be detrimental to the plant side of the system, e.g., excessive root zone water velocities.Half of an aquaponic system consists of the recirculating aquaculture system (RAS), which can be managed to nearly zero discharge of waste water, and typically will be less than 10% system volume per day. RAS conditions are usually quite different from those of hydroponic systems. While fish are grown in a pH range of 6.5-8.5, in freshwater systems, typically this reduces to a narrow range around pH 7. Alkalinity in a RAS is continuously consumed by nitrifying bacteria and thus needs to be replaced. Safe target levels for alkalinity, pH, and dissolved carbon dioxide in RAS systems are between 70 to 190 mg/L for alkalinity, to provide an adequate buffering capability to the system, around 7.0 for pH, and around 15 mg/L for dissolved carbon dioxide. The high carbon dioxide levels, compared to hydroponic systems, are partially responsible for maintaining the pH values around 7. A merger of hydroponic and RAS fish systems appears to face a challenge in that the normal water quality conditions for these two types of growing systems, particularly for pH and alkalinity, are quite different, as described above.Our research will be conducted in the Ken Post Laboratory (KPL) greenhouses on the Cornell campus, Ithaca, NY. Three primary types of systems will be evaluated: a) nutrient film technique (NTF) whereby plants are grown in troughs with recirculating irrigation water which provide plants with nutrients and oxygen, b) deep ponds, which are 0.3 m deep ponds of water covered with Styrofoam floats that are modified to accept rockwool plugs that support the strawberry plant (lettuce or spinach flat), and c) Dutch or Bato buckets, that are ~ 10 L buckets that are filled with media that support a root structure and are flooded on a cyclical basis. In all these systems, water is conserved and 100% recycled with the only water loss being from evapotranspiration. We currently have a 6 tank replicated deep pond system installed and operating at KPL. Continued research using deep ponds for lettuce and spinach will be conducted to look at optimizing nutrient concentrations as affected by pH conditions. Lettuce (Butterhead) will be primarily used as a baseline comparison when culturing other crops. For the high value crop of strawberries, Bato buckets will be used in combination with nutrient film and deep pond production methods.The above three systems will be constructed in triplicate for hydroponic (inorganic nutrients only) and for aquaponic conditions (nutrients supplied by fish system), so a total of 18 systems will be constructed. For the strawberry systems, at least 15 strawberry plants per system will be used (so that 3 cultivar strains using 5 plants can be tested in each system concurrently). When doing strawberries, a replicate of three lettuce systems will be constructed to provide concurrent comparative data, since we have a large amount of data from previous lettuce experiments. Day neutral varieties of strawberries will be used and the likely cultivars to be evaluated will include: Albion, Monterey, and San Andreas. All three system types will use both hydro- or aqua- ponic water and will be conducted concurrently to avoid seasonality (trial) effects when evaluating performance across system design. Our primary response variables will be yield (dry and wet weight) and elemental composition. Taste will also be evaluated using the Brix rating scale and using taste panels.We expect to make significant impact in NY by helping producers to take advantage of the market opportunity that exists now. Currently, there is only one NY producers that is producing strawberries using hydroponic or aquaponic techniques (1/3 acre at Gro-Moore Farms, Henrietta, NY; there may be some home-scale producers we are not aware of). The Gro-Moore farm is also only doing this during the conventional summer season till the first hard frost. Thus, we can measure impact by accounting for any new hydroponic or aquaponic strawberry production in NY that is created as a result of the extension outreach effort that is part of this project. If we do not see new commercial production resulting from our outreach efforts, then this project will have failed, at least temporarily. We also expect to have an impact by hosting regional workshops, and providing timely information on our website for the specific information on hydroponic berry production or aquaponic production of lettuce and spinach (see www.cornellcea.com).
Animal Health Component
40%
Research Effort Categories
Basic
20%
Applied
40%
Developmental
40%
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
20511222020100%
Knowledge Area
205 - Plant Management Systems;

Subject Of Investigation
1122 - Strawberry;

Field Of Science
2020 - Engineering;
Goals / Objectives
1. Compare productivity of lettuce and strawberries grown using hydroponic vs. aquaponic type conditions. 2. Quantify mass balances of macro and micro elements between fish and plant systems where fish feed inputs are the major source of required plant nutrients. 3. Identify constraints and solutions to successfully integrate aquaculture water quality conditions (neutral pH and moderate alkalinity) with hydroponic conditions (low pH and low alkalinity). Consideration to be given to continuous recirculation between fish culture system with plant culture system or batch delivery of fish culture water to plant system to provide required nutrients. 4. Determine the feasibility of raising lettuce and strawberries under organic standards. 5. Identify growing methods that can enhance product quality in terms of nutrition, taste or shelf life. (Time line is provided in subsequent section)
Project Methods
Objective 1 (year 1 and year 2, bulk of activity): Compare productivity of lettuce and strawberries grown using hydroponic vs. aquaponic type conditions. Three primary types of systems will be evaluated: a) nutrient film technique (NTF) whereby plants are grown in troughs with recirculating irrigation water which provide plants with nutrients and oxygen, b) deep ponds, which are 1-foot deep ponds of water covered with Styrofoam floats that are modified to accept rockwool plugs that support the strawberry (or lettuce flat), and c) Dutch or Bato buckets, that are ~ 10 L buckets that are filled with media that support a root structure and are flooded on a cyclical basis. In all these systems, water is conserved and 100% recycled with the only water loss being from evapotranspiration. We currently have a deep pond system installed and operating. This system was previously used to evaluate and compare Butterhead lettuce production between hydroponic and aquaponic conditions. Continued research using deep ponds for lettuce will be done to look at optimizing nutrient concentrations as affected by pH conditions. Lettuce (Butterhead) is primarily used as a baseline comparison when doing other crops. For the high value crop of strawberries, Bato buckets (see below) will be used in combination with nutrient film and deep pond production methods (see below).The above three systems will be constructed in triplicate for hydroponic (plant nutrients only) and for aquaponic conditions (with fish nutrients), so a total of 18 systems will be constructed. For the strawberry systems, at least 15 strawberry plants per system will be used (so that 3 cultivar strains using 5 plants can be tested in each system concurrently). When doing strawberries, a replicate of three lettuce systems will be constructed to provide concurrent comparative data, since we have a large amount of performance data from previous lettuce experiments. Day neutral varieties of strawberries will be used and the likely cultivars to be evaluated will include: Albion, Monterey, and San Andreas. All three systems types will use both hydro- or aqua- ponic water and will be conducted concurrently to avoid seasonality effects when evaluating performance across system design. Data collected will include independent variables of greenhouse environmental variables (natural and supplemental light, temperature, humidity), water environments (temperature and macro and micro elements, pH, alkalinity, nitrate, ammonia, and nitrite), cultivar (type of lettuce or strawberry), and the response variables as reflected in yield (dry and wet weight) and elemental composition. Nutritional quality will be evaluated based upon elemental macro and micro element values (C, H, N, P, K, Al, As, B, Ba, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, S, Sr, Ti, V, Zn) obtained from submitting replicate (3 per growing system) samples to the Cornell Nutrient Analysis Laboratory (a nationally recognized laboratory). This data will be compared between aquaponic and hydroponically grown plants and with literature values for field grown crops.Objective 2 (year 1 and 2, concurrent with Objective 1): Mass balances. Evaluation will include doing mass balances of macro and micro elements between fish and plant systems where fish feed inputs are the major source of required plant nutrients. ANOVA and paired t-tests will be done on all data to compare treatment significance.Objective 3 (year 2 and 3, based upon results of year 1): Identify constraints and solutions to successfully integrate aquaculture water quality conditions (neutral pH and moderate alkalinity) with hydroponic conditions (low pH and low alkalinity). Based upon the results collected in Objective 1, elemental differences in plants or fruits will be compared between treatment conditions using ANOVA. Data analysis will include conducting mass balances on nutrient inputs to fish systems and what fraction of nutrient elements are assimilated by the plants that are grown. This data will be useful in identifying possible alterations to the nutrient waters used. Elemental comparisons will be made between hydroponic and aquaponic crops compared to literature data for these same crops grown using conventional ground based production systems.Follow-up experiments will be designed to address any plant deficiencies and/or yield reductions by altering nutrient water conditions or the methods that plants are integrated with aquaponic waters. Known constraints include the challenge of nutrient availability between aquaponic water quality conditions ((neutral pH ~ 7.0 and moderate alkalinity, 50 to 100 mg/L CaCO3) with hydroponic conditions (low pH ~ pH 5.8 and low alkalinity, 20 mg/L CaCO3).We will evaluate the effect of continuous recirculation between fish culture system with plant culture system or batch delivery of fish culture water to plant system to provide required nutrients. Consideration will be given to continuous recirculation between the fish culture system with the plant culture system or to a batch delivery of fish culture water to the plant systems to provide required nutrients. Batch delivery has the advantage of not returning potential disease organisms to the fish culture system. Hydraulic retention time (HRT) is one way to characterize mixing rates, which can also affect root zone water velocity. Various HRT rates will be investigated since at some point, high HRT values will cause root stress due to excessive velocity. A currently operating fish production and aquaponic system is in place to generate aquaponic waters for growing target crops.Objective 4 (year 3, 6 months). Determine the feasibility of raising lettuce and strawberries using an US organic standard. Based upon data and analysis obtained from the proposed research and previous studies, this data will be used to develop an economic model to evaluate feasibility of the various crops. The economic model will include risk assessment along with possible market premiums that can be obtained from organic and/or locally grown attributes. Risk will be differentiated based upon choice of system design (deep ponds are known to be less risky to failure than NFT). Economic model will include: depreciation and capital costs, labor, plant costs, water quality maintenance, utility costs, and value of product. Marketing and transportation costs are not considered. Evaluation of system design will consider the ability to mitigate insect damage, e.g., from aphids and thrips.Objective 5 (year 2; done after the harvest of crops). Identify growing methods that can enhance product quality in terms of nutrition, taste or shelf life. Shelf life of aquaponic vs. conventionally grown lettuce will be done. Plants will be collected at harvest, placed into clam-shell containers (commonly used form of presentation), and wilting and turbo pressures monitored over time and any differences noted. Berries will be analyzed for elemental profiles, dry weight percentages, and Brix ratings (Degrees Brix, symbol °Bx, is the sugar content of an aqueous solution; one degree Brix is 1 gram of sucrose in 100 grams of solution and represents the strength of the solution as percentage by mass). Strawberry yield will be recorded and taste characteristics will be evaluated using taste panels. Manipulations of electroconductivity will be used to evaluate effects of taste. As mentioned, Brix ratings will be determined as a measure of sweetness. Salt stress is known to affect taste in strawberries and will be evaluated as a correlate with the Brix ratings. Note that aquaponic systems will only be supplemented with chelated iron, which still allows the berries to be labelled as organically grown. JH Biotech Inc. (Ventura CA; 800-428-3493) has one such product, Biomin Iron, which is OMRI listed (Organic Materials Review Institute, www.omri.org).

Progress 10/01/17 to 09/30/18

Outputs
Target Audience:We have targeted the small farm families of NY State and the northeast. We also target New York State (NYS) greenhouse producers. The NYS greenhouse industry is broadly categorized into floriculture and vegetable producers. As of 2012 (the most recent year with comprehensive data) this segment in NYS was comprised of 1,124 operations with 550 acres of greenhouse area producing $211 million in wholesale value (USDA, 2014). We also directly addresses the needs of high tunnel/greenhouse producers of vegetables including strawberries. The production of vegetables in greenhouses is expanding in NYS, adding to the diversity of the industry. In 2012, NYS had 435 operations with 114 acres covered area producing an annual wholesale value of $27 million - this represents a 54% increase in production in 5 years (USDA, 2009/2014). Additional audiences include field vegetable producers that grow their own transplants in seasonal greenhouses, Master Gardener Volunteers, and urban agriculture practitioners. Changes/Problems:During this year, we are experiencing less problems with our aquaponic growing techniques for strawberries. Based upon mass balances established, we found that we can use conventional drip to drain methods (not recycle the nutrient solution), since there is adequate nutrients in the aquaponic waters which allows the nutrient flow (the drain part of the drip to drain) to be used as a single pass. By not returning the flow after the drip to drain step, we have had much less problems with emitter plugging. What opportunities for training and professional development has the project provided?We utilize several undergraduate students to assist in the daily care of the fish and strawberry systems. As a result, they are gaining hands-on experience and seeing the challenges of aquaponic production. Some of the students are going onto graduate school where they are continuing their interest in this field of study. How have the results been disseminated to communities of interest?We will be submitting a paper to a referred publication on our results. Paper is ready for submission. What do you plan to do during the next reporting period to accomplish the goals?We are refining our choice of strawberry cultivars and have eliminated use of the NFT as a viable technique for strawberries. We are conducting research on lettuce aquaponic production under 3 management techniques that focus on the frequency of adding aquaponic nutrient rich water to the deep water culture system. We will continue to establish nutrient mass balances between the fish system and the crops. This will lead to establishing management protocols that will maximize nutrient retention and maximum sustainability. We are also developing low cost monitoring and control systems to maintain target nutrient levels and pH values.

Impacts
What was accomplished under these goals? This project led to improved understanding around the particular conditions required to successfully cultivate healthy and productive strawberry plants in soilless crop production systems. Within the nascent CEA strawberry industry, drip to drain irrigation methodology is almost exclusively utilized, which, due to our experience, is commensurate with the methodologies ease of production, resilience and performance. We tested 3 systems types: Drip to drain (pots that are irrigated and then allowed to drain); nutrient film technique (gutters), and Deep water culture (DWC) or floating rafts. The drip to drain methodology was the only system of the three that was able to produce results for both hydroponic and aquaponic conditions. However, the Drip to drain systems were not without flaw. We regularly encountered clogged drip emitters across all systems, which accounted for a majority of the plant loss over the course of the experiment, and added significantly to the day-to-day maintenance of the systems. This coupled with the use of synthesized substrates called to question the sustainability of such a practice. From our initial planting, implementations of the bare-root Deep Water Culture methodology seemed prone to root and crown rot, to which strawberry plants are particularly susceptible. The hydroponic DWC system succumbed to rot and failed before data collection even began while simultaneously the aquaponic plantings were also experiencing significant decline. In an effort to reverse the adverse conditions, we elevated the floating rafts populated with strawberry plants from direct contact with the aquaponic effluent by floating the rafts on strips of 1" thick insulation foam. After elevating the rafts (and associated plants) out of direct contact with the solution we noted the propagation of fresh, healthy, white roots, improved vigor and prolific vegetative growth. The plants were maintained in the aquaponic system for the remainder of the trial period and did produce viable and marketable fruit; offering promise for future commercial application. More research will be conducted on this in the immediate future. Similarly, both the hydroponic and aquaponic bare-root Nutrient Film Technique systems were particularly sensitive to overwatering (and rot) and under watering (and drought) depending on whether the plants were placed on the drain end or the fill end of the NFT trough. We suspect that the lack of media, to provide a consistent root zone environment across all plant sites contributed significantly to this effect.

Publications

  • Type: Books Status: Published Year Published: 2018 Citation: Timmons, M.B., Guerdat, T., Vinci, B.J. Recirculating Aquaculture, 4th edition. Ithaca Publishing Company LLC, Ithaca, NY 14850
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Chun, Chanwoo, Vinci, B.J., Timmons, M.B., 2018. Computation fluid dynamics characterization of a novel mixed cell raceway. Aquac. Eng. 81, 19-32.


Progress 10/01/16 to 09/30/17

Outputs
Target Audience:Working directly with commercial growers, hydroponic growers, and aquaponic growers. Interacting with other scientists in terms of interpreting results and developing testing procedures to evaluate fruit productivity and quality. Changes/Problems:We were not expecting the poor performance of the deep water culture (DWC) conventional design. We are also documenting the problems associated with the drip to drain (DTD) and nutrient film technique (NTF). Our proposed new design for the DWC will retain the advantage of DWC (large reservoir, no lack of nutrient solution on plant roots at all times, large thermal mass) will minimizing crown rot due to excessive moisture. What opportunities for training and professional development has the project provided?We make a strong effort to integrate our undergraduate and graduate students into the project. Students gain first hand experience with research protocols and with daily management procedures for both fish culture and hydroponic culture. How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals?We have a strong start in terms of evaluating berry performance and quality and quantity of berry being produced. Continue working on the modified DWC design system. Other goals on the project will be addressed in the next year of the project.

Impacts
What was accomplished under these goals? This year we initiated the project, which primarily consisted of building the experimental systems and initiating production. The research effort is conducted in the Ken Post Laboratory (KPL) greenhouses (190C) on the Cornell campus in Ithaca, NY. Utilizing known and common recirculating soilless culture methodologies. The three primary types of commercial production systems being evaluated are: Deep Water Culture (DWC) ponds, which are constructed of 3'x 6' rectangular 10" tubs filled with nutrient solution and covered with Styrofoam floats that are modified to accept bare-root plant stock and support the vegetation and fruit bearing trusses of the strawberry plant. Drip irrigated (i.e. drip to drain pots, or DTD) recirculating pots that are ~ 1.5 L individual 6" pots filled with a 50/50 blend of perlite vermiculite mix to support the strawberry plant root structure and are irrigated on a cyclical basis. Nutrient Film Technique (NTF) recirculating troughs, each fitted with lids that are modified to accept 15 bare root strawberry plants at 8" on center. In NFT systems the nutrient solution is pumped continuously and flows from the fill end to the drain end by gently pitching the trough back towards the reservoir. In all of these systems, water is conserved and near 100% recycled through catchment and return to a centralized reservoir, or containment, with the only water loss being from evapotranspiration and accidental loss. The DWC system was constructed in duplicate to accept up to 30 plants per condition (3 clusters of 10 plants each, placed in groups of 2 rows of 5). One system accepts conventional mineral based nutrient solution the second receives recirculating nutrient solution form the recirculating aquaculture system. The DTD system was constructed in triplicate for hydroponic plants and once for aquaponic conditions (plants with fish nutrients), so a total of 4 systems are constructed with accommodations for 30 plants per system (so that 3 cultivar strains, 10 plants of each, can be tested in each system concurrently for a total of 120 plants across the 4 systems). The NFT system, similarly, was constructed in triplicate for hydroponic production and once for aquaponic conditions, so a total of 4 systems are constructed with accommodations for 30 plants per system (so that 3 cultivar strains, 10 plants of each, can be tested in each system concurrently for a total of 120 plants across the 4 systems). All three systems are being maintained with Day-neutral varieties of strawberries of cultivars Albion, Monterey, and Sea Scape (all UC Davis cultivars). All system types are being assessed with hydroponic and aqua-culture nutrient laden water and are being conducted concurrently to avoid seasonality effects when evaluating performance across system design. The aquaculture system has only been supplemented with chelated iron, which depending on source, could enable organic certification. JH Biotech Inc. (Ventura CA; 800-428-3493) has one such product, Biomin Iron, which is OMRI (Organic Materials Review Institute, www.omri.org)) listed. We began harvesting berries in october 2017 by collecting yield and fruit quality data from the resulting berries. Berries are being counted for total yield and marketable yield, by number and by weight, as well as analyzed for acidity and Brix values. We will continue to harvest and analyze the resulting crop from this planting through april 2018. The initial planting stock was purchased from a disease indexing national supplier of field grown propagative strawberry rootstock material in May of 2017. The plants had received several weeks to several months of cold storage before they were received for the experiment. The crowns were graded by size (roughly choosing 1 plant from 6 available to maximize uniformity) and then maintained in a recirculating trough of nutrient solution until they were transplanted to their final production system in July 2017. From July 2017 - September 2017 the plants were fed a nitrogen rich fertilizer regiment to encourage vegetative growth and sizeable crown development. All the flower buds as well as the vegetative runners developed during that period were removed to encourage the plant to further develop its crown and vegetative canopy. Beginning October 1 2017 the plants received fertilizer with decreased N and increased P and K, to encourage fruit initiation and blooms were no longer removed from the plants. Beginning the 3rd week of October we began harvesting berries and have subsequently implemented protocols for collecting yield data, and fruit quality data. We have maintained twice a week harvests since mid October and will continue to do so through april 2018. Preliminary results indicate that the DWC and NFT methods are not well suited to strawberry production, primarily because of crown rot. We have developed an alternative DWC design that appears to correct the problem. New DWC systems are being designed and will be tested in parallel with the original research objectives.

Publications

  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Vandam, D.A.; Anderson, T.S.; de Villiers, D.; Timmons, M.B. Growth and Tissue Elemental Composition Response of Spinach (Spinacia oleracea) to Hydroponic and Aquaponic Water Quality Conditions. Horticulturae 2017, 3, 32. Anderson, T.S.; Martini, M.R.; de Villiers, D.; Timmons, M.B. Growth and Tissue Elemental Composition Response of Butterhead Lettuce (Lactuca sativa, cv. Flandria) to Hydroponic Conditions at Different pH and Alkalinity. Horticulturae 2017, 3, 41. Anderson, T.S.; de Villiers, D.; Timmons, M.B. Growth and Tissue Elemental Composition Response of Butterhead Lettuce (Lactuca sativa, cv. Flandria) to Hydroponic and Aquaponic Conditions. Horticulturae 2017, 3, 43. Wielgosz, Z.J., Anderson, T.S., Timmons, M.B. Microbial effects on the production of aquaponically grown lettuce. Horticulturae 2017, 3(3), 46.