The correct flow rate of closed hydroponic systems is critical for optimal growth of plants. The flow rates are important for all types of closed hydroponic systems such as pure NFT systems, gravel cultures and ebb-and-flow systems. Inadequate flow rate will result in:
- Reduced oxygen levels at root surfaces
- Increased susceptibility of disease
- Plants are under stress
Higher flow rates can be achieved by either increasing the slope of the NFT gullies, which is in most cases, impossible, or to increase the size of the gravel particles. Larger gravel particles provide greater air volume for root growth and reduces the risk of sediment buildup. Larger gravel pieces will reduce the occurrence of anaerobic conditions forming between roots, especially during the end of the growing season when root volume is at maximum.
Anaerobic conditions diminish root respiration, reduces nutrient uptake, increases N losses via de-nitrification, and makes roots susceptible to infection. The ideal flow rate should be between 1.25 and 1.5 L.min-1 as measured at the end of the gullies which should be a maximum of 1 m wide.