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Soilless Culture : Run to waste or Recirculating System
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Open or Closed Systems
Run - to-waste or Recirculation
The volume of nutrient solution applied to soilless cultures must be greater than the volume of water evaporated by the crop, to avoid accumulation of nutrients (salts) in the media. This is an essential characteristic of all soilless culture systems regardless of whether the media is rockwool, coir, bark, pumice, perlite, sawdust,gravel or whatever.
Run-to- waste growing system apply the nutrient solution and allow the excess to run to waste, such systems are sometimes called open systems. The waste pollutes the environment with un-used fertilisers and nutrients in the run-off solution.
The run-off can be collected and recirculated as part of the applied nutrient solution in subsequent irrigation, systems doing this are described as recirculating systems or closed nutrient systems.
Any grower using a run to waste system is short changing himself and needlessly polluting the environment for everyone.
A typical run-to waste system in New Zealand
This system uses rockwool slabs with recirculation of all run-off, but planter bags or horizontal bags work equally well in this system.
There are simple low cost cost systems for collecting clean run-off from soilles growing systems. The collected run-off does have to be pumped into a storage tank where it can be mixed with more fresh water. Nutrient stock solution can be added to the storage tank or added to the dilute nutrient solution as it is being pumped from the tank to the trickle irrigation system. Run-to-waste systems often have injectors adding nutrient stock solution to the waterat fixed dilution rates, but when recirculating these injectors need to be automatically controlled so that nutrient solutions of the proper conductivity are delivered tothe irrigation system regardless of the varying conductivity of the solution being drawn from the storage tank. This automatic control is the biggest cost item in making a conversion from run-to-waste to recirculating solution.