Nutrient film technique (NFT) involves the recirculation of nutrient solution past the roots of the crops as a shallow stream of water in a watertight channel. This hydroponics system addresses many legislative challenges among which the reduced leaching of nutrients and pesticides. In addition, it offers several advantages related to cultivation on the one hand, i.e. ideal water, nutrient and O2 availability, and cost saving on inputs on the other hand, such as space, labour, water and fertilizers. Three key aspects make up for a successful adoption of NFT:
1) Channel length: Should not exceed 10-15 m
2) Channel slope: Ideally 1:100
3) Flow rate: ± 1 L/min
To eventually close the system, first of all, it is required to have a physical and (micro)biological treatment of the drain water (see relevant PA). Once it passed the filtration, fresh water (usually rain or ground water) in combination with nutrients is supplied to the drain water to attain again the ideal nutrient solution, which depends on the crop and seasons if present. This can be checked and regulated with a fertilizer unit.
The profitability is generally higher, e.g. the yield of soil-grown greenhouse lettuce is estimated at 65-100 heads/m²/year while that of the hydroponically-grown variant could reach 175-450 heads/m²/year. Overall though, the installation cost can be high (100-230 EUR/m²) for professional installations whereby the desired degree of automation makes up the price, however, low-cost setups do also exist. Different systems are already commercialized.
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