Agriculture Reference
In-Depth Information
1500
10
Air
Water
5
1
A
RAW
RW
NRAW
SM
0
60
0
10
20
30
40
50
70
80
90
100
Volume (%)
Fig. 10.2.
Water retention curves in an ideal substrate (adapted from Caldevilla and Lozano, 1993).
A, percentage of air (25%); RAW, percentage of readily available water; RW, percentage of reserve water;
NRAW, percentage of not readily available water; SM, percentage occupied by solid matter (15%).
the solution (e.g. rockwool) at the beginning
of the cultivation, which can be corrected
by accordingly adjusting the pH of the sup-
plied nutrient solution. The optimum pH
level of the nutrient solution, for horticul-
tural crops, ranges between 5.5 and 6.5
(Pardossi, 2003).
In general, a good substrate must be
chemically stable, which avoids any
release of elements that can generate
problems of salinity or phytotoxicity, or
induce undesired precipitations in the
solution.
The salinity of the substrate can be
altered by an imbalance between absorp-
tion (plus leaching) and supply, or by a
high CEC of the substrate, so monitoring
the EC of the solution is of paramount
importance.
In soilless cultivation, the availability
of mineral elements is essential. Therefore,
the substrate that does not interfere with this
availability will always be preferable.
Biological properties
Substrates of mineral origin are biologically
inert (at least at the beginning), which is
not the case with organic substrates, which
are biodegradable and able to release ammo-
nia, or phytotoxic substances or growth
regulating substances. The use of organic
substrates with high biodegradability must
be avoided as they contain a lot of plant
roots which eventually degrade and become
a problem.
The carbon/nitrogen (C/N) ratio has
been proposed as a biological stability index
for organic-based substrates. A C/N ratio
between 20 and 40 is considered appropri-
ate for substrate cultivation (Abad and
Noguera, 1998).
