Aero-Hydroponics
The Method of the Future by Lawrence L. Brooke
A Brief History
The aero-hydroponic method was developed in Israel
in the early 1980's. Dr. Hillel Soffer, senior researcher
at the Volcani Institute at Ein Gedi developed the aero-hydroponic
method to overcome the challenges presented by the hot,
arid conditions at Ein Gedi. The discoveries that followed
the development of aero-hydroponics
offer great benefits to all hydroponic
growers.
During a two-year period from 1986 to 1988, Dr. Soffer
performed extensive research using the
aero-hydroponic method at the University of California
at Davis, where he had received his Ph.D. in the early
1970s. The specific area of research was in quantifying
the effect of various levels of dissolved oxygen on
root growth, especially in the propagation of plants
from cuttings.
The findings of his research were published in the
Journal of the American Society for Horticultural Science,
and HortScience. Both studies were co-authored with
David Burger at UCD. In addition, Dr. Soffer presented
his findings at the annual conference of the Hydroponic
Society of America in 1988.
Except for the papers mentioned above, very little
has been printed up to now on the aerohydroponic method.
The method was patented internationally, though few
licenses for the production of equipment have been granted.
Without aggressive commercial support, the aero-hydroponic
method has remained largely a research tool, known mostly
to university researchers.In the meantime, the rockwool
method was becoming available internationally following
12 years of exhaustive research and a strong marketing
program with lots of investment in advertising, production
and distribution, first in Europe and later in Japan.
Following nearly a decade of rockwool use, the Dutch
contacted Dr. Soffer to request permission to develop
and use the aero-hydroponic
method. The reason for the sudden interest of the Dutch
in the aero-hydroponic method has implications for the
development of hydroponic
cultivation worldwide. For rockwool cultivation
to work efficiently in most commercial operations it
is preferred to a use a non-recirculating nutrient solution.
Nutrient solution is sent on a one-way trip through
the rockwool and is then discarded. The real cost advantage
of rockwool cultivation over other hydroponic methods
was that the nutrient did not have to be recaptured
and recirculated, reducing the system complexity of
reservoirs, plumbing, pumps and pH and conductivity
controllers. The once-through nutrient system also reduces
the problem of nutrient solution becoming imbalanced
due to erratic uptake of minerals by rapidly growing
plants; plus the build up of dissolved minerals from
slowly dissolving rockwool.
The discharge of enormous amounts of spent nutrient
solution has become a major problem in Holland, contaminating
surface and ground waters. Consequently, the Dutch government
has prohibited the dumping of nutrients resulting in
renewed interest in recirculating systems such as aero-hydroponics.
As leaders in both horticulture and commercial hydroponics,
the Dutch have recognized the value of a method, which
enables rapid and trouble-free cultivation and eliminates
the problems of disposing of spent nutrients and exhausted
media.
The Aero-hydroponic Method
Aero-hydroponics
is not a simple method to understand. The equipment
required is somewhat more complicated than other hydroponic
methods, but there is a great advantage in that once
an aero-hydroponic system is set up, it will run almost
indefinitely without additional investment in such disposable
components as growing media and non-recirculating nutrients.
What is most surprising about aero-hydroponics is
not how it works, but why plants grow better. The key
is dissolved oxygen at the root boundary zone. The essence
of Dr. Soffer's work at UCD was in quantifying root
growth in proportion to dissolved oxygen. Only the green
parts of the plant can form oxygen from carbon dioxide
- roots require a supply of oxygen for metabolism and
growth. Plant growth in oxygen deficient conditions,
such as those found in many soils, is limited. Dr. Soffer
found the enhanced oxygen at the root zone produced
enhanced growth. In aero-hydroponics, the nutrient solution
is sprayed through the air in order to infuse the nutrient
with dissolved oxygen. The method differs from classic
aeroponics in that most of the plant's roots are not
suspended in air and fed by a spray of nutrient solution;
rather, the majority of the roots are submerged in oxygen-infused
nutrient which is in constant motion in order t maintain
high levels of dissolved oxygen at the root boundary
zone where oxygen and nutrients are taken in by the
plant.
The result is a propagating tool of unsurpassed performance.
Dr. Soffer was successful in propagating plant varieties
at UCD that had never been propagated before. He took
particular delight in propagating varieties of conifers
and even pistachio trees (pistachio cuttings required
90 days to generate roots). Moreover, he found that
cuttings could be rooted aerohydroponically in purified
water without using rooting hormones such as IBA or
NAA. This is because plant tissue already contains the
natural rooting hormone IAA (Indole Acetic Acid).
Aero-hydroponic Systems
Aero-hydroponic systems can be built using quite a
variety of materials and in numerous design configurations.
The Ein Gedi "Mini Unit" which was used at
UCD for dissolved oxygen studies is a stand-alone module
which supports four plants in 10 liters of nutrient
solution. An electric motor mounted on the top of the
unit spins a nutrient sprayer, which lifts nutrient
solution and sprays it onto the "aerial roots."
Additionally, the rotation causes the nutrient within
the unit to stir, moving it constantly over the submerged
roots.
Large-scale aero-hydroponic systems follow the design
of the commercial installation at Ein Gedi. These commercial
systems consist of "canals" or growing chambers
with plant sites on top. A pump provides the pressure
to drive a system of sprayers to supply the aerial roots,
while the submerged roots hang into the flowing nutrient
in the canal. Both of these systems share fundamental
characteristics, which define the aero-hydroponic method.
The plants are supported above the flowing nutrient.
The roots hang down through an air gap in which nutrient
is sprayed, then into the moving nutrient solution below
the air gap.
The nutrient sprayed through the air gap is not so
much intended to feed the plant, but rather to infuse
oxygen into the nutrient solution wherein the feeder
roots remain constantly submerged. It is these submerged
roots in oxygen rich nutrient that provides most of
the nutrition and oxygen for the plant.
Home Installation
The AeroFlo
system is designed and built by
General Hydroponics following the Aerohydroponic
method. It consists of a reservoir placed below the
growing chambers, which support the plants. The nutrient
in this system is changed every two weeks and the pH
is adjusted to 5.5 to 6.5 and nutrient conductivity
is maintained at about 800 to 1200 ppm. Since there
is no growing medium except a handful of "GROROX"
at each plant site, pH remains very stable and only
requires an initial adjustment when mixing fresh nutrient,
if the water supply is of good quality.
The AERO-HYDROPONIC METHOD is without doubt the most
advanced hydroponic method that has been developed to
date. The cost of constructing and installing systems,
plus the complications of obtaining licensing, have
been deterrents to widespread commercial application.
This is changing as commercial growers, researchers,
serious hydroponic gardeners and manufacturers become
aware of the capabilities and value of aero-hydroponics.
Lawrence L. Brooke is the owner and founder of General
Hydroponics in Sebastopol, California
Originally published in The Growing Edge, Vol 2, No
1, Fall 1990
