Determining accurate nitrate level requirements in an aquaponic system.

View the project final report

Commodities

• Vegetables: greens (lettuces)

Practices

• Production Systems: aquaponics

1. Statement of Problem: Aquaponics is gaining increasing popularity in Texas, as documented by the volume of calls from interested parties to Texas A&M. Actual census data of the number of existing aquaponics farm is not available as most operations are new or don’t report to USDA. Most growers are beginners with less than 2-years’ experience. Large commercial aquaponics operations are non-existent.

Extensive research is available for hydroponic system on the level of nitrate necessary for a successful production system, usually at 200-300 ppm. However, little or no research data is available for aquaponics systems. With lack of research data available, growers are relying on ‘gut feeling’ for their nitrate levels in the water. Of course, each grower is convinced that his level is the correct one. Discussion with growers on their current nitrate concentrations has shown a range from 2 to 120 ppm.

2. Statement of Proposed Solution: A MS student is currently researching the conversion rate from fish feed of various protein concentrations to nitrate. Additional research is needed to evaluate productivity of lettuce and other greens at various levels of nitrate to maximize production and increase profitability. Dr. Masabni is building an aquaponics system to become operational by June 2015. However, on-farm facilities are currently available to initiate research until that system is built. I propose conducting research at Sand Creek Farm in Cameron, TX to determine yield and production of lettuce grown at various nitrate levels. Sand Creek Farm has 3 systems in operation. An experiment can be conducted to evaluate 5, 25, and 50 ppm nitrate on the production and profitability of lettuce at those rates. In other words, the requested funds are to cover a 3-pronged proposal: evaluation of 3 nitrate rates, determine the cost of feed necessary to maintain these 3 rates, and determine the economic profitability of lettuce production. A cost analysis of lettuce production from seeding to harvest will be calculated to determine which nitrate rate is most profitable.

1. Approach and Methods:
   An experiment will be conducted at Sand Creek Farm to evaluate 3 nitrate concentrations in the water on lettuce production. A complete system housed in one tunnel will be used for each rate. Each tunnel is 30 ft x 96 ft and contains two 8-ft wide troughs where lettuce and other greens are currently grown.

Nitrate level at Sand Creek Farm is about 5 ppm and one tunnel will be used as treatment 1. Tunnels 2 and 3 will have ammonia added to the water to increase nitrate level to the desired concentrations, namely 25 and 50 ppm. Daily monitoring of nitrate concentration in the water will be conducted and levels will be adjusted accordingly to maintain the rates as near 25 and 50 ppm as possible.

Normal production practices will be followed in terms of seeding, transplanting, fish feeding, and daily recording of pH, dissolved O₂, electrical conductivity, and nitrite levels. These are common practices in an aquaponic operation. We will record these data in all tunnels to monitor the effect of higher nitrate levels on those other parameters.

In addition, fish health and survivability will also be monitored and the number of dead fish recorded for all treatments on a weekly basis. Weekly visual ratings of the crop stand will be recorded for all 3 treatments.

At 8-12 weeks after transplanting, the crop will be harvested and fresh weight recorded. A sample from each treatment will be sent for tissue analysis to determine the nitrate level in the plants at harvest.