By: Laura Tiu, PhD, Director of Ohio Aquaculture Extension and Brad Bergefurd, Horticulture Specialist
Introduction
Aquaponics is a growing area of interest for Ohio citizens in both urban and rural areas driven by the demand for locally grown food. The OSU Aquaculture and Horticulture Programs have received multiple requests for information each week. Seventy-five percent of current Aquaculture Boot Camp participants, new and beginning farmers, expressed interest in aquaponics. Additionally, multiple internal requests for information have been received from the College of Agriculture Engineering, the OSU College of Medicine, Ohio Sea Grant, and the College of Food, Agricultural, and Environmental Sciences. Unfortunately, unbiased Ohio research-based data to share with the interested clients has been limited. To address this, an OSU Extension Innovation grant was received to develop and construct a research/demonstration-scale aquaponics system at the OSU South Centers. The system, in operation since October 2013, was used for training and available for touring to the over 300 visitors that visited the OSU South Centers in 2014.
Methodology
In June 2013, a demonstration-scale system was constructed in a glass greenhouse at the OSU South Centers. The system consisted of a 500-gallon tank for rearing the fish, a biofilter for solids removal and nitrification, and three shallow water rafts, 3’ x 5’ x 6", for supporting floating raft culture (Figure 1). Rafts were made from 1 inch Styrofoam board. Holes were drilled in the Styrofoam to support small net pots for germination and growth of various plant species. Water flowed from the fish tank, through the biofilter and rafts, and was collected in a sump where a small pump returned the water to the fish tank. One small air pump also provided oxygen to the fish tank. A small amount of water (approximately 10 gallons) was added daily to accommodate for evaporation, leaks and plant uptake.
Water parameters were measured throughout the trials. Dissolved oxygen, temperature and pH were measured daily, while ammonia, nitrate, hardness and alkalinity were measured weekly. The system was operational on July 13, 2013 and a three week break-in period was initiated. Twelve 4-5 inch tilapia and one bluegill were stocked into the system on July 13, 2013. Fish are fed to satiation daily, approximately 1 oz. of fish food (approximately 1% bw). Three fish jumped out of the tank before seeds were planted.
Results
Phase I – Fall 2013
Phase one was designed to compare the effect of three commonly used growing media (Figure 2), expanded clay pellets, expanded shale, and potting soil, on production of two leafy greens, mizuna and red leaf lettuce, in a six-week growing trial. Nine tilapia and one bluegill were stocked into a 500 gallon tank and fed to satiation on a daily basis.
Seeds were placed directly on the media in net pots on August 22, 2013. The majority of the seeds germinated on day two. By week three, plant growth had slowed (Figure 3). It was hypothesized that this may be due to not enough nitrates being generated by the small number of fish in the system, given the nitrate level remained at zero. Because of the lack of nutrients, the plants were small and discolored.
Water quality tests showed a system pH of around 8. While this is fine for fish, plants prefer a pH under 7 and had difficulty synthesizing what nutrients were there. Plants were harvested on October 3, 2013 after 6 weeks of growth.
Additionally, weaknesses in the system were identified. Water levels need to be constantly maintained so that gravity could move the water. There were several locations where this could break down. The system design needed to be upgraded to reduce the chance of overflow, back-up, etc. The Styrofoam rafts also needed modifying with smaller holes so that the net pots stop dropping through and the plants are at a more appropriate water level.
Phase II – Winter 2013/2014
With a system redesign complete, the same experiment was repeated for phase two. On October 12, 2013, approximately twenty-five pounds of small yellow perch (2-3 inch) were stocked into the 500-gallon tank and fed to satiation. Net pots were seeded with red leaf lettuce and mizuna on November 1, 2013. Hydrochloric Acid (Muriatic acid) was added as needed to the water to control pH. Plants germinated and were
growing slowly, when a fish kill occurred on November 22, 2013. It was determined that high ammonia levels were the cause of the fish kill. Plants continued to grow in the system and were harvested December 12, 2013.
Phase III – Spring 2014
The experiment was repeated for a third time in the spring. The system was restocked with approximately forty pounds of yellow perch (3-6 inch) on March 25, 2014. On April 3, 2014 float trays with the three media were seeded with mizuna and red leaf lettuce. Plants were harvested May 1st. In this trial, the plants failed to germinate or grow well due to the salt and mineral build-up on the media.
Production Results (combined from all phases)
Media Species Production (ounces/sq.ft.)
Styrofoam float tray Mizuna 19.11
Styrofoam float tray Red leaf lettuce 11.44
Expanded Shale Mizuna 1.15
Expanded Shale Red leaf lettuce 8.15
Hydrocorn Mizuna 1.21
Hydrocorn Red leaf lettuce 7.44
Discussion
In this demonstration-scale system, the Styrofoam float trays filled with soilless potting mix performed the best in all the trials. The expanded shale and Hydrocorn both accumulated minerals and salts that inhibited the germination of seed and slowed growth. Red leaf lettuce performed most consistently in the system with mizuna performing well only in the Styrofoam float trays. The Styrofoam float trays with soilless potting mix are a good option for these small hobby-scale systems as they are inexpensive and readily available.
There were quite a few steep learning curves associated with this system, including system design, construction, operation and water quality balance. A lot was learned and shared with numerous clientele. The interest in aquaponics continues to grow and The Ohio State University should be prepared to offer research-based information to the public. Continued investment into the industry is warranted.
Future Plans
Two new varieties of mini-head lettuce, Dragoon and Rhazes, will be produced on a rotational basis with one float bed being harvested every two to three weeks. Data will continue to be collected from the system and educational tours will continue. For future trials, we will no longer utilize the rock media because of salt mineral buildup but continue to use the Styrofoam float trays with soilless potting mix. We are considering getting some backup power as a recent power outage resulted in a fish kill. Options for water treatment, such as a reverse osmosis system, are being explored.