Updated: Mar 13, 2020
The best way to operate an NFT microgreens system is to be position on the floor and make sure you can walk along the channels planting and harvesting close to the floor with your upper body curved forward. This will help keep the output per man-hour low. This approach has been the best over the last 15 yrs of working with NFT.
Nutrient film technique (commonly known as NFT) is a method of growing in which the microgreens have their roots in a depth-less stream of recirculating nutrient enriched water, in which are dissolved all the ingredients required. There is no solid rooting medium. A root mat is not fully in the depth-less stream of recirculating water and partly over it. The stream is very shallow and the upper surface of the root mat which develops above the water, it is slightly damp, is in the air. Around the roots which are in the air, there is a film of nutrients - hence the name nutrient film technique.
Measurement of pH:
The easiest method of measuring pH is to use pH test strips which changes color according to pH of the nutrient water which it is dipped. The color of the damp strip is then compared with a pH color chart. When using this method to measure the pH of nutrient water, it's not the most sufficiently accurate way for the purpose.
The best method is to use a Bluelab pH pen, It's a small, battery operated device with a probe that is placed in a reservoir of nutrient water. An acidic solution has more positively charge hydrogen ions in it than an base one, its like a battery that can produce a higher voltage. A pH meter takes advantage of this and works just like a voltmeter, it measures the voltage produced by the nutrient water.
Adjustment of pH:
The pH of the nutrient water for most microgreen crops should not rise over 6.5 or drop under 5.8. If the pH of the nutrient water being fine tuned manually, it should be measured twice daily. If your local water source is acidic, the pH will drop (usually this is not the case, most local water comes out neutral); if it is base the pH will rise. If the pH rises, pH down should be added to the nutrient water to lower the pH to 5.8, whenever the pH value has risen to 6.5 or higher.
One Part Nutrient Versus On-Site Mixing:
One part nutrient, specially developed for microgreens, can be purchased. This has been made workable by the broad range of leniency to nutrient supply that is exhibited by microgreens crops. One part nutrient will give satisfactory growth of most varieties at the vegetation stage. The leverage of using one part nutrient are several. The most important leverage is that it reduces output per man-hour. The quality control of mixing is in the factory. Errors in measuring that can occur on an NFT indoor farm are reduced because less measuring is required.
The drawback of one part nutrient is that they're much more expensive. Before deciding that it is cheaper to buy the component chemicals and mix the formulation on site, an evaluation should be made of all the costs. There is the very difficult assessment of the managerial cost of ensuring quality control in the formula. A further consideration is the difficulty of obtaining all the components locally and sustainable. If it is decided to use one part nutrient, it is preferred to have available on site a supply of chelated iron, If the pH of the nutrient water unknowingly allowed to rise too high, the iron in the nutrient water will be converted into a form in which it is not available to the microgreens crop. Should this arise, it can be easily fixed, after correcting the pH, by adding chelated iron to the nutrient water.
The first step of starting a microgreens system, is to fill up the reservoir with water. Water is continually being lost from the system, generally through the leaves of the crop by a process called transpiration. The mass of water in the system is, maintained constant by the automatic replacement of that water that is lost. This is done by a float valve in the reservoir, it allows water to flow into the NFT system from an external source as required. This make up water will need to run thru a filtration system before entering the reservoir. It helps keep dissolved substances out of it. The nature and quality of the substances in tap water will vary with locality. If the substances are not removed from the water by the microgreens crop at a faster rate than they are supplied by the make up water , then the toxicity level will increase, until a concentration of one ion will be reached at which growth will be affected, and eventually a toxic level will occur. The number one substances which commonly causes trouble in this way is salt (sodium chloride, NaCI). Most microgreens require a little sodium and very little chloride for growth. When presented with a detailed analysis of your local water supply it is very difficult with present science to express an opinion as to whether the water supply is suitable for NFT microgreens system.
Temperature of Recirculating Nutrient Water:
One of the main advantages of NFT system, is that it provides the facility in large scale microgreens production, to control the root zone more accurately than has been possible in the past in conventional farming. One of the factors is the ability to control root temperature. In conventional farming, the soil temperature established has to be accepted, it is impossible to influence it. In NFT system, the root zone temperature can be controlled because the temperature of the recirculating nutrient water can be control. The best way to achieve this is with a water chiller or water heater.