“FLOAT, RAFT, AND POND systems are
methods of solution culture where plants are
supported by a sheet of lightweight material,
typically polystyrene, that floats on the surface
of a large pond of nutrient solution.”
THE PRINCIPLES OF FLOAT SYSTEMS AND DFT
While float or DFT systems may seem like simple methods of
growing a wide range of crops, solution culture has several
principles growers must adhere to. Firstly, plants can easily
suffocate if there is insufficient oxygen in the root zone. Roots
require oxygen, which they either take up as oxygen gas (O 2 )
directly from the air or as dissolved oxygen from moisture
surrounding the root surface. Without it, water and nutrient
uptake is restricted, roots die off, and opportunist pathogens
such as pythium rapidly attack. While the air-filled pores in a
growing substrate contain atmospheric oxygen at high levels
(air is 21 per cent oxygen), nutrient solution can only maintain
six to 13 parts per million (ppm) of O 2 at saturation, depend-
ing on temperature. Thus, growers need to keep their solu-
tion culture systems adequately oxygenated for plant growth.
Oxygenation in float or DFT systems can be provided via air
pumps, injector systems, or nutrient circulation. In the latter,
air bubbles produced when the solution cascades back into
the pond or reservoir replenish the dissolved oxygen levels. In
small, basic raft systems built where electricity is unreliable
or not available to continually power pumps and timers, hand
aeration by agitation or whisking of the nutrient solution can
be used to increase dissolved oxygen levels.
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Maximum Yield