A Re-circulating Nutrient System for Aquaponics
Barb and James started their aquaponics gardening by studying the nutrient film technique hydroponics system of growing vegetables and herbs. This system requires a shallow film of water streaming dissolved nutrients past the bare roots of plants. Well, in a hydroponics system, the dissolved nutrients come from fertilized water. Barb and James want to use the same nutrient film technique in aquaponics. The dissolved nutrients will come from the fish waste in the tank below the growing bed.
The depth of the re-circulating stream should be very shallow, little more than a film of water. This ensures that the thick root mat, which develops in the bottom of the channeled grow bed, has an upper surface that is moist and in the air.
Subsequent to this, an abundant supply of oxygen is provided to the roots of the plants. A properly designed nutrient film hydroponic system (or aquaponic system) is based on using the right channel slope, the right flow rate, and the right channel length.
James and Barb know the main advantage of the nutrient film system is that the plant roots are exposed to abundant supplies of water, oxygen and nutrients. With the nutrient film technique, because of its design, provides a system wherein all three requirements for healthy plant growth can be met at the same time.
Barb and James see advantages in higher yields of high-quality produce obtained over an extended period of cropping. One downside of the nutrient film technique that James sees is there could be interruptions in the flow, e.g., power outages, but, overall, it is one of the more productive techniques.
As a general guide, Barb and James designed for flow rates for each grow bed to be 1/4 gallon per minute and an upper limit of 1/2 gallon per minute appears about the maximum. Flow rates beyond these extremes are often associated with nutritional problems.
Depressed growth rates of many crops have been observed when channels exceed 40 feet in length. Barb and James designed their aquaponics system with grow bed length not exceeding 30 feet. Care needs to be taken to maintain hygienic conditions and to avoid heavy metal contamination of nutrient film technique systems by using mainly plastic or stainless steel pumps and components.
The nutrient film technique is similar to the ebb and flow system in that it utilizes a pump to move nutrients in a continuous, constant flow. The difference with nutrient film technique is that the solution flows directly over the roots.
Pros of nutrient film technique
- The cost of building a NFT system is low.
- Constant water movement keeps water from going stagnant.
- You can have a lot of plant sites.
- You can use any grow media to hold the plant.
- You can reuse the water.
- Doesn’t have parts to clog.
- Great with organics.
- No timer to worry about breaking, because the water is always flowing.
- Grow media is not required.
Cons of nutrient film technique
- pH fluctuation/ monitoring required.
- If the pump breaks, your plants will die quickly. This is because there is no media to hold water.
- May need a chiller.
- Plants with short roots will need to be top fed or drip line incorporated, until roots grow to bottom of PVC.