organic hydroponics
Organics and soil
Organic greenhouse horticulture is
defined by the International Society
of Horticultural Science (ISHS) as
the production of organic horticultural crops—vegetables, ornamentals
and fruits—using inputs derived only
from natural, non-chemical sources in
climate-controllable greenhouses and
tunnels. There is no mention of soilbased systems in this definition. Much
of the organic philosophy appears to
be based on the UK Soil Association
and the writings of Rudolph Steiner.
Both organizations have their origins
well before anyone considered growing crops commercially using hydroponic systems, so hydroponics did not
get considered.
But what is magical about soil? Soil
is normally comprised of inorganic
particles derived from rock (such as
clay or silt or sand), organic matter
(humus), a range of microorganisms,
water, air and some nutrients
dissolved in the water. In some
“soils,” the inorganic particles
might be partially or totally
replaced by semi-decomposed organic
matter (peat).
"It was not until
the ’60s that
researchers
began to consider
alternatives
to soil for the
production of other
greenhouse crops."
156
Maximum Yield USA | September 2012
Well, a recirculating organic hydroponic system can comprise all of these,
with the exception of the solid inorganic particles (although pedantically
it would not be too difficult to add
a few pieces of rock to the system to
fulfill all of a normal soil’s characteristics). In fact, a recirculating organic
hydroponic system is also much more
sustainable than a soil-based system.
One of the major claims of organic
vegetable growers is environmentally
friendliness, but from a sustainable
viewpoint, a recirculation system is
much better in nutrient and water
efficiency. This is because considerable
quantities of nutrients leach through
the soil profile into the water table
and aquifers in an intensive traditional
greenhouse situation in order to obtain acceptable levels of production.
This does not occur with organic
hydroponic systems.
Organic hydroponics
In the early 1950s, virtually all
greenhouse crops were grown in
soil. It was not until the '60s that
researchers began to consider alternatives to soil for the production
of other greenhouse crops, such as
tomatoes, cucumbers, and lettuce.
What started as straw bales, peat base
beds, etc. resulted inevitably in the
establishment of commercial hydroponic systems like nutrient film
technique (NFT) and rockwool. This
had a huge influence on productivity
and a marked increase in yield, as the
complex balance of aeration and adequate moisture at the roots became
much easier to obtain (the control
of soil-borne pathogens also became
easier due to isolation).
Then, in 2001, a number of greenhouse studies were conducted at
Massey University by Kim Atkin to
compare conventional and organic hydroponic systems. He found
that, in a comparison between an