Part – I
Many people want to have a small production system with which to grow fresh, leafy vegetables that they can enjoy year round. The nutrition of freshly harvested plants is superior to similar plants purchased at your local market. Plus, by growing your own, you have complete control over the treatment of any pest and disease that may occur. The control programme that you implement in your hobby greenhouse can be one with which you are comfortable. You will know exactly what has been used on your own crops, eliminating the concerns over what chemicals or other products might have been used on commercially purchased produce while it was grown at a foreign production location or during its transport to your market.
The NFT system is a good choice for this purpose, since its relatively easy to set up and operate. Using this fairly simple system to grow plants from seedling to harvest size, and then quickly planting them with new seedlings for future harvests, provides you with a continuous supply of produce. What will grow in a Nutrient Film Technique system? Small, relatively fast growing plants are the most suitable for an NFT system. They start in the channels a few weeks before they are harvested and are replaced or cut back and allowed to re-grow. Vegetative plants like various leaf, Bibb and Cos type (Romaine) lettuces can be grown along with mustard greens, kale and many oriental vegetables. Any of the fast growing herbs can also be grown in the same NFT system at the same time.
What is the Nutrient Film Technique System?
Nutrient Film Technique system involves a thin layer or film of nutrient solution flowing over the roots of the plants in the system. The only solid media used in the system is the small piece of media in which the seed was sown to start the plant, which is necessary to keep the seed from floating away during the early stages of plant growth. All the plants nutrient needs are met through the air and water solution washed through the plants root system. Soluble fertilizers are dissolved in the solution that re-circulates through the system to supply the minerals and other elements the plants need for optimal growth.
Components of the NFT System?
Plants in an NFT system will be grown in channels. Normally, these are flat-bottomed runways that are positioned on a slope so that the nutrient solution can be fed at one end and drained, collected in a return pipe and returned to the reservoir tank. The amount of slope should be between one and three per cent. Channels are often very slightly v-shaped so that the solution will run along the center of the channel. The length of the channels is dictated by the planned size of the system. Channels can be as short as two to three feet in a small-sized system or as long as 13 to 15 feet long in a large commercial-sized system.
It is usually better to position the length of the channel at right angles to the length of the greenhouse. This way, both the system and the rest of the greenhouse space will be more accessible. Special NFT Channels are available from several hydroponic equipment suppliers. The inconsistent environment in the pipe does not generate as vigorous a growth as the environment in a flat or almost flat bottomed NFT channel where the nutrient solution is evenly distributed along the bottom of the channel. This does not mean that the pipes will not work; many people use them. The issue is that production is not as consistently good in a pipe compared to an NFT channel.
NFT channels are usually extruded using a compound that includes an ultra violet light protectant. PVC material that is exposed to light for long periods of time will become brittle and will break more easily.
Additional disadvantages of using PVC pipe is the extra work involved in the drilling of holes in pipes, which may be quite extensive even in a larger hobby system. In addition, the table or bench supporting the system must be designed so that the pipes do not roll and displace the plants and the nutrient solution during the operation of the system. The base and cap construction of many of the extruded NFT channels make cleaning of the channels between crops much easier for the grower.
Since the NFT system is a recirculating system, a reservoir is needed to hold the nutrient solution. A plastic container is adequate. Some people use heavy duty plastic garbage containers, and plastic livestock watering troughs can be used for larger NFT systems. Galvanized steel or any metal container should not be used as a reservoir, since this material is reactive.
The fertilizer is very corrosive to the metal and can pick up components from the reservoir in quantities that can be harmful to the growth of the plants in the system. The size of the reservoir is determined by the number of plants to be grown in the system. A small system with a plant capacity of 40 – 50 should have a reservoir with a minimum five gallon capacity. An additional gallon of capacity should be added for each additional 20 to 25 lettuce sized plants in the system. It is always better to have a little more volume capacity than is needed rather than to be a little short. During warm days, the plants use more water.
The writer is affiliated with the Ohio Agricultural Research and Development Center, Ohio State, USA.