Agriculture Reference
In-Depth Information
the nutrient cycles. The management condi-
tions (leaching percentage, characteristics
of the nutrient solution) of the soilless crop
(open system) will determine its environ-
mental impact, which will be similar to that
of crops grown in soil if the leachates are
similar.
If leachates are recirculated (closed sys-
tem) the salinity and pathology problems
must be considered and the nutrient con-
centrations must be well monitored and
controlled.
contains the acid. In this case, tank A has
most of the acid to correct the pH (usually,
nitric or phosphoric, and rarely sulfuric),
the phosphates and the sulfates, as well as
the microelements, except for iron. In this
tank A, part of the potassium nitrate can be
incorporated, but no calcium salts must be
added, to avoid precipitates. Tank B con-
tains the calcium nitrate and the potassium
nitrate (all or only a part), as well as some
nitric acid to regulate the pH and the iron
chelates. The magnesium nitrate is usually
added in tank B, but neither sulfates nor
phosphates must ever be added, to avoid
precipitates.
When three tanks are available, one of
them is destined only for the acid that is
usually nitrous acid, although sulfuric or
phosphoric acids can be used. In sophisti-
cated facilities, managed by means of a
computer, several tanks are usually avail-
able, containing solutions of individual
fertilizers.
The injection systems of concentrated
solutions in the irrigation water flux are of
such complexity or simplicity in agreement
with the type of tanks used.
In mixing the fertilizers their solubility
and compatibility must be taken into
account, not forgetting that it depends on
temperature (Tables 11.7 and 11.8). The lit-
erature on the preparation of simple solu-
tions is extensive (e.g. Cadahía, 1998).
Preparation of the nutrient solution
In an ideal soilless growing system there are
no mineral inputs from the substrate, and
therefore, all nutrients must be supplied
together with the water, in the nutrient
solution.
The preparation of the nutrient solu-
tion requires prior analysis of the irrigation
water, to allow for the formulation of the
best nutrient solution depending on the
crop to be grown. The preparation of this
nutrient solution will also depend on the
technical characteristics of the available
fertigation
hardware
(and,
possibly,
software).
In the simplest case, one concentrated
solution tank is available and another tank
for the acid. Most facilities have two tanks
for solutions (A and B), one of which already
Table 11.7.
Solid fertilizers most commonly used in fertigation: analysis and solubility at 20°C.
(Source: Cadahía, 1998.)
Fertilizer
Analysis of N-P
2
O
5
-K
2
O-others
a
(%)
Solubility (g l
−1
)
Calcium nitrate 4H
2
O
15.5-0-0-26.6 (CaO)
1200
Ammonium nitrate
33.5-0-0
1700
b
Ammonium sulfate
21-0-0-22 (S)
500
Urea
46-0-0
500
Potassium nitrate
13-0-46
100-150
Potassium sulfate
0-0-50-18 (S)
110
Mono potassium phosphate
0-52-33
200
Mono ammonium phosphate
12-60-0
200
Magnesium sulfate 7H
2
O
16 (MgO)-13 (S)
700
Urea phosphate
17-44-0
150
Magnesium nitrate 6H
2
O
11-0-0-9.5 (Mg)
500
a
The first three values in each entry refer to N-P
2
O
5
-K
2
O. Where there is a fourth entry this refers to other compounds.
The exception is the entry for magnesium sulfate which has no N-P
2
O
5
-K
2
O and contains16 (MgO)-13 (S) as indicated.
b
Steep water temperature decrease for concentrations above 250 g l
−1
.
