Articles
ENVIRONMENTAL CONTROL IN THE ROOT ZONE: NUTRIENT FILM CULTURE
Nutrient film culture is a technique for growing plants in a thin film of circulating nutrient solution.
Plants are grown in long plastic gullies (up to 30 metres) laid on sloping ground (1 in 75–100) or on an adjustable support system.
Nutrient solution flows continuously down the gullies and into a collecting tank from which it is recirculated.
The thin film of nutrient ensures adequate aeration of the roots, and plants grow at nutrient levels far below those required in static hydroponic culture.
Tomatoes and cucumbers, for example, show no difference in yield over the range of 10–320 ppm nitrate-N.
Uptake of nutrients is highly correlated with water uptake, which is itself in turn correlated with the level of solar radiation.
Nutrient supply is monitored and controlled on the basis of conductivity, and pH must also be controlled between pH 6.0–6.5 to ensure that phosphates and trace elements remain in solution.
Inclusion of a small proportion of ammonium-N in the solution helps to control pH between these levels.
High concentrations of ammonium-N are, however, phytotoxic to tomatoes.
The high efficiency of uptake of nutrients from the circulating solution means also that particular care has to be taken to avoid accumulation of potentially toxic micro-nutrients such as zinc and manganese.
Precise control of temperature can be achieved by heating the circulating nutrient and insulating the gullies.
Preliminary results indicate that yields can be doubled by raising the temperature of the solution from 14°C to 28°C.
Physiological and pathological problems of root death are being investigated, and the prospects for the application of the technique to field crops in arid zones is discussed.