Agri Kultuur January / January 2018 - Page 13

DWC Grow Canals: Canals can be of variable lengths, from one to tens of meters, enabling an adequate nutrient supply due to the large volume of water used in this system. As far as the width is concerned, it is generally recommended to be the standard width of a sheet of polystyrene, but it can be multiples of this. However, narrower and longer canals enable a higher water speed that can beneficially hit the roots with larger flows of nutrients. The choice of width should also consider accessibility by the operator. The recommended depth is 30 cm to allow for adequate plant root space and to allow for sufficient water flow. Like fish tanks, canals can be made from any strong inert material that can hold water. For small–scale units, popular materials include fabricated IBC plastic containers or fiberglass. AgriKultuur |AgriCulture Much larger canals can be constructed using wood lengths or concrete blocks lined with food–grade waterproof sheeting. If using concrete, make sure it is sealed with non– toxic, waterproof sealer to avoid potential toxic minerals leaching from the concrete into the system water. The retention time for each canal in a unit is 1–4 hours, regardless of the actual canal size. This allows for adequate replenishment of nutrients in each canal. Plant growth will benefit from faster flow rates and turbulent water because roots can then be exposed by many more ions, whereas slower flows and almost stagnant water would have a negative impact on plant growth. Aeration for DWC units is vital. In a densely planted canal, the oxygen demand by the plants can cause dissolved oxygen (DO) 13