describes those systems where the excess nutrient or “run-off” is not
re-circulated. Conventional ‘soil culture’ is a type of run-to-waste
with a high water holding capacity are used (e.g.
Rockwool). Feeds are small and infrequent.
The ‘run-off’ is either drained directly onto
the ground (Fig 1.5a) or is collected (Fig 1.5b & 1.4b).
Collecting the run-off allows feed volume and
frequency to be calculated more accurately. This helps prevent
under-dosing or over-dosing. It also allows the waste nutrient to be
disposed of more responsibly. Feed volume and frequency is calculated so
that the percentage run-off is typically 10-20% (Table
Irrespective of whether the nutrient is
collected or drained directly onto the ground, plain water flushes are
usually needed at frequent intervals through the same plumbing. This helps
minimize salt build-up in the root zone and also helps keep the feed
circuit free of blockages.
System design is similar to satellite systems. Plants are usually seated
in pots (Fig 1.4b & 1.5a) or leach trays (Fig 1.5b).
to run to waste systems
pH and EC of the nutrient feed solution is
- Plants receive fresh nutrient at each
- The use of media having high water
holding capacity minimizes the risk of plant death in the event of
nutrient pump failure.
- In the event of root disease
outbreak, there is less risk of cross contamination between pots or trays
because the nutrient is not recirculated.
- Can be an advantage for higher
salinity waters. Unlike recirculating systems, salinity does not build-up
in the nutrient solution.
Disadvantages to run to waste systems
- Intermittent feeding results in salt
build-up at the root zone and the
blockage of drippers. However, this can
be minimized by periodic flushing with water.
- Unlike recirculating systems, it can
be difficult to control the nutrient’s EC at the root zone.
- High water holding capacity media are
prone to water-logging and therefore waterings must be carefully
controlled. This can be especially difficult when
air temperatures fluctuate greatly. Over-dosing causes water-logging,
disease and wasted nutrient.
- Top-fed nutrient tends to channel
downward through the medium where root density is lowest (Fig
- In commercial systems this practice
is rapidly being outlawed because the discarding of ‘run-off’ causes
contamination of groundwater.