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View Full Version : NFT vs constant flow grow bed



Roger L.
06-28-2013, 01:12 PM
I'm a little confused. What is the difference between NFT and a constant flow grow bed? They both have a constant flow of water, both use some form of media. The only difference I see is air gaps between the netty pots and it makes for a thinner grow area. Can somebody educate me why use one over the other. I plan on adding a NFT off the side of my system and make a strawberry row out of it. I'm using NFT just for space saving in my basement. Okay oh wise ones, time to teach the newbie. :?:

Oliver
06-29-2013, 11:53 AM
Roger,

There are three basic types of growing containers, NFT, DWC and Media filled beds.

NFT, or Nutrient Film Technology (Technique), generally utilizes a shallow (about 2 inches) and narrow (about 4 inches) trough or gully that has a thin film of water flowing through it and has no media in it. The plants are suspended from the top in some manner and their roots are exposed to this water as it flows by. The roots must reach the bottom of the trough in order for this thin film of water to wet and nourish them. NFT troughs require a slope from end to end that is great enough to insure the water flows around the flow restrictive roots of each plant for the length of the trough.

NFT has the advantage of using about one liter of water per minute flow through the trough and works well for near vertical positioning angle, as long as the water remains in the bottom of the trough. The disadvantage of NFT is that due to the large surface area to water ratio, the water can become heated during the transition from one end to the other. Long NFT troughs suffer from this as well as loss of nutrients, oxygen and sometimes a change in pH, as well as requiring considerable change in height from one end to the other in order to maintain rapid transition of the water from end to end. The slope of NFT is usually about 30 to 1. Another disadvantage to NFT is that if the water flow is interrupted for a period of time the roots are no longer in water and the plants can suffer. NFT is usually limited to leafy green plants but flowering plants like tomatoes have been successfully grown in them.

DWC, or Deep Water Culture, utilizes deeper troughs that are about 6 or 7 inches deep and have no media in them. Plants are suspended from a floating raft or a platform that is slightly above the top of the water. If properly designed, water flows through the trough at a rate that insures fairly consistent water quality from end to end. If the trough is long, say 100 feet, then the rate of flow has to be high. Depending on the trough width per planting row ratio, the restriction to flow can vary as the plants grow and requires a slope to compensate for the friction created by the trough and the plant roots. By making the trough considerably wider than the plant root, the water can flow through the trough with little plant root interference. Due to this low restriction, the slop of DWC is usually about 100 to 1. Wide DWC troughs can contain multiple rows of plants.

The advantage of DWC is that the mass of water in the system and the volume per plant generally provides a more consistent water chemistry throughout the trough. But that can be defeated by an excessive trough length and limited flow rate. Last year I visited a commercial aquaponics farm where they were using multiple side by side DWC troughs some 30 feet in length that were connected in series so that the water entered the first trough and exited from the last trough. They were seeing a considerable difference in growth rate from one end of the system to the other and were rotating the plants regularly while complaining about labor costs. They also found they needed to add aeration throughout the troughs as they found it beneficial but were also complaining about electricity cost.

The disadvantage to DWC is the amount of water that needs to be pushed through the system, especially if the grow beds are long, in order to maintain consistent water chemistry from end to end and the pumping and electricity required to do that. Most of the water going through the DWC trough never comes in contact with the plant. If the DWC grow bed is elevated, then its weight becomes a factor. DWC grow beds are generally limited to leafy green plants whose roots can tolerate continuous water submersion.

Media filled beds can include pots and other forms of containers that plants are grown in and water flows through, either continuously or in cycles. Properly designed deep media filled grow beds are usually 12 inches deep and are flood and drain. They generally employ either an auto siphon or have some type of a timed fill in order to achieve the flood and drain action. The media supports the plants and allows for deep rooting, and due to the flood and drain aeration of those roots, different types of plants can be grown. They also serve as a place for the beneficial bacteria to reside that convert the fish waste to plants nutrients thereby serving as a bio-filter.

Deep media grow beds are not a good place to grow leafy greens for commercial purposes. This is due to the fact that when they are harvested the plant roots usually bring with them large amounts of media that needs to be removed. In a backyard system this is no big deal; but in a commercial system, this is labor intensive costing extra money on an already limited profit margin. Deep Media beds are also large, heavy and if elevated for easy access then they need strong support.

Oliver

JCO
06-29-2013, 09:49 PM
Oliver 101....Sockit to him Oliver :mrgreen:

Roger L.
06-30-2013, 08:52 AM
So in a NFT system the plants must be rooted before putting into the system?

keith_r
07-01-2013, 05:52 AM
no.. many people will put a "wick" from the pot to the film (like a string from a mop), the humidity in the pipe will also keep the roots moist until they reach the water
nft will heat up if in direct sun, and could heat your ft water up quite a bit

Roger L.
07-01-2013, 06:32 AM
Okay, thanks Keith. So now to start building again. My system is in my basement so heat won't be to big of a factor.