Scientia Horticulturae 122 (2009) 244–250
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Scientia Horticulturae
journal homepage: www.elsevier.com/locate/scihorti
Evaluation and correction of nutrient availability to Gerbera jamesonii H. Bolus in
various compost-based growing media
Raymundo Caballero, Purificación Pajuelo, José Ordovás, Eusebio Carmona, Antonio Delgado *
Dpto. de Ciencias Agroforestales, Universidad de Sevilla, Ctra. Utrera Km 1, 41013 Sevilla, Spain
A R T I C L E I N F O
A B S T R A C T
Article history:
Received 26 May 2008
Received in revised form 8 May 2009
Accepted 11 May 2009
Nutrient deficiencies usually constrain the use of some composted materials as peat-substitute growing
media even if some fertilizer is applied to the media. In this work, we assessed the suitability of various
composted materials as such or mixed with peat for potted plant production, with special emphasis on
their effects on nutrient availability to plants. Further, we examined the effect of vivianite
[Fe3(PO4)28H2O] as a fertilizer and its mixture with humic substances (HS) on these growing media
(particularly their effectiveness in preventing Fe deficiency chlorosis in alkaline substrates). A
completely randomized experiment design was developed involving the growth of gerber (Gerbera
jamesonii H. Bolus) and two factors, namely (i) the growing medium, specifically composted cork residue
(C), compost obtained from a mixture of olive husk and cotton gin trash mixed with rice hulls and peat in
a 1:1:1 volume proportion (OH), composted grape marc (GM), Sphagnum peat mixed with spent
mushroom compost (M), coconut fibre (CF), and Sphagnum peat; and (ii) the Fe source (control without
Fe, Fe-EDDHA, vivianite and vivianite + HS in a weight ratio of 10:1).
The highest chlorophyll meter readings were provided by the two media with the lowest pH (peat and
CF), and the lowest readings were provided by the medium exhibiting the highest pH (C). Composted
grape marc (GM) and M provided the largest amounts of dry matter (DM), whereas peat and M gave the
highest flower yields. Flower and DM yield were lower in CF and C than those in other substrates; the low
production in the former can be ascribed to Ca deficiency; in fact, the medium was poor in this nutrient;
therefore, plants grown on it exhibited low Ca concentration in leaves. On the other hand, the low
chlorophyll meter readings and DM yield in C can be largely ascribed to Fe deficiency chlorosis since the
application of Fe improved both the parameters, the best results being obtained with the vivianite + HS
mixture. Vivianite-based treatments increased P concentrations in leaves, but only in more acidic
medium (CF and peat), where the pH of the media facilitated the dissolution of the product. The adverse
effects of Fe sources on the Mn and Zn concentrations in leaves were as a result of the antagonistic effect
of the Fe supply, which varied with the particular growing medium: Fe-chelate depressed Mn in plants
grown on C, whereas vivianite + HS decreased the Mn concentration in plants grown on GM. The results
obtained with the different compost-based materials studied and the ability to overcome Fe deficiency in
C by using a vivianite + HS mixture are interesting with a view to reduce the use of peat in the potted
plant industry.
ß 2009 Elsevier B.V. All rights reserved.
Keywords:
Substrates
Fe chlorosis
Vivianite
Fe-chelates
Humic substances
1. Introduction
Peat is the most widely used substrate for potted plant
production in the nurseries and accounts for a significant portion
Abbreviations: C, composted cork residue; CF, coconut fibre; DM, total dry matter in
shoots; DTPA, diethylenetriaminepentaacetic acid; EDDHA, ethylenediaminedihydroxyphenylacetic acid; EDTA, ethylenediaminetetraacetic acid; GM, grape marc;
HS, humic substances; M, spent mushroom compost mixed with peat in a 1:1
volume ratio; OH, olive husk mixed with rice hulls and peat in a 1:1:1 volume
proportion; SPAD, soil plant analysis development.
* Corresponding author. Tel.: +34 954 486452; fax: +34 954 486436.
E-mail address: adelgado@us.es (A. Delgado).
0304-4238/$ – see front matter ß 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.scienta.2009.05.010
of the materials used to grow potted plants (Marfà et al., 2002;
Ribeiro et al., 2007). However, sustainable horticultural production
cannot rely on expensive, non-renewable natural resources such as
peat (Marianthi, 2006). There has been an intensive search for
peat-substitute growing media over the last few decades
(Robertson, 1993; Abad et al., 2001; Benito et al., 2005). Most of
these growing media have been obtained by recycling or
transforming (composting) organic residues of different origin
(agriculture, forestry, livestock farming, and urban) (Ingelmo et al.,
1998; Sánchez-Monedero et al., 2004; Girgatti et al., 2007).
Nutrient availability is one of the major factors influencing the
suitability of organic substrates for growing plants (Carmona et al.,
2002; Caballero et al., 2007), which may depend not only on their
R. Caballero et al. / Scientia Horticulturae 122 (2009) 244–250
245
evidences (Carmona et al., 2002; Caballero et al., 2007). All
composts were obtained by using the method of open windrows,
which involves composting in trapezoidal section piles (1.7–2 m
high, 2.5–3.5 m wide, 40 m3 volume) that were aerated by
mechanical turnover each 2–3 weeks (Carmona et al., 2002,
2004).
elemental composition, but also on other factors affecting nutrient
forms and dynamics such as adsorption capacity, pH, biological
stability of the growing medium, and presence of dissolved organic
compounds (Caballero et al., 2007). In general, micronutrient
deficiencies, particularly Fe chlorosis, have frequently been
described as nutritional imbalance in growing media (Fisher
et al., 2003; Smith et al., 2004; Wik et al., 2006). However, Fe
chlorosis is not always related to the limited Fe content in these
materials; in fact, pH, the specific Fe forms present and their
content, and nutrient competition may also influence the Fe
availability to plants (Velázquez et al., 2004; de Santiago and
Delgado, 2006). Caballero et al. (2007) found iron chlorosis in
gerber to be more closely related to a high pH than to low Fe
content in various growing media. The effect of an alkaline pH on
Fe availability can be ascribed not only to the low solubility of this
metal, which is essentially present as ferric oxide (Miller et al.,
1984; Mengel, 1994), but also to reduced Fe uptake from the
apoplast into the symplast restricting Fe availability to plant cells
(Yu et al., 2000; Lucena, 2000).
Growing media capable of inducing Fe chlorosis could be
extensively used for the potted plant production of plants sensitive
to Fe deficiency if a cost-effective method that overcomes
nutritional imbalance was available. In soils that induce Fe
deficiency, the most effective and widely used method is the
application of Fe-chelates (Godsey et al., 2003; Lucena, 2003).
However, this type of Fe-containing fertilizers are very expensive;
moreover, they have a short-lasting re-greening effect and high
risk of leaching in growing media owing to their high solubility
(Rombolà et al., 2003; Álvarez-Fernández et al., 2004). Vivianite
[Fe3(PO4)28H2O] has been proven effective in preventing Fe
chlorosis over several growing seasons in various crops (Rosado
et al., 2002; Rombolà et al., 2003). Vivianite is long-term effective
and can be readily prepared from low-cost products (ferrous
sulfate and bi- or mono-ammonium phosphate); moreover, its
high P content makes it a useful P fertilizer. The effectiveness of
vivianite in preventing Fe chlorosis is enhanced by mixing with
humic substances (HS) (de Santiago et al., 2008).
The main purpose of this work is as follows: (i) assessing the
potential of various composted materials, whether alone or mixed
with peat, for potted plant production with special emphasis on
their impact on nutrient availability to plants; and (ii) studying the
effect of vivianite and its mixture with HS on nutrient supply to
plants (particularly its effectiveness in preventing Fe deficiency
chlorosis in alkaline substrates). To this end, we used gerber
(Gerbera jamesonii H. Bolus) on the grounds of its sensitivity to Fe
chlorosis and its importance as an ornamental potted plant
(Caballero et al., 2007).
Electrical conductivity and pH were determined in an extract
with substrate:water ratio of 1:2 after shaking the suspension at
2.5 Hz in an end-over-end shaker for 2 h. NO3-N and NH4-N in
this extract were determined according to Mulvaney (1996), and
P according to Murphy and Riley (1962). The amounts of Ca, Mg,
K, and Na extracted by 1 M ammonium acetate buffered at pH
4.65 (substrate:extractant ratio of 1:5) according to the
Australian Standard (1993) for the determination of nutrient
levels were used as availability indices for these nutrients.
Extraction at a substrate:extractant ratio of 1:2 with 2 mM DTPA
buffered at pH 7.3 according to Lindsay and Norwell (1978) was
used to determine Fe, Zn, Cu, and Mn availability indices. Both
extractions were performed by shaking in an end-over-end
shaker at 2.5 Hz for 2 h. After extraction, the suspensions were
filtered through Whatman 42 paper and centrifuged at 4150 g
for 1 h. K and Na in the supernatants were determined by atomic
emission spectrometry; and Ca, Mg, Fe, Zn, Cu, and Mn by atomic
absorption spectrometry. All extractions were performed in 1 L
polyethylene flasks at 25 8C. Air at water holding capacity and the
water holding capacity of the growing media were determined
according to the method proposed by Ordovás et al. (1997), and
bulk and particle density, and total porosity according to Ordovás
et al. (1996).
The studied growing media differed widely in terms of chemical
properties and nutrient content (Table 1). Thus, pH of the
substrates ranged from 5.5 (peat) to 7.62 (composted cork residue,
C); and their electrical conductivity in 1:2 substrate extracts
ranged from 0.31 (peat) to 3.06 dS m 1 (M). Porosity and water
holding capacity of compost-based materials were lower than
those in CF and peat (Table 2), which was in agreement with the
previous results of Hernández-Apaolaza et al. (2005) and Ribeiro
et al. (2007). Overall, the physical properties of studied substrates
were within the recommended ranges for ornamental plant
production in containers, and there were no significant restrictions
to gerber growth from them (Hernández-Apaolaza et al., 2005),
particularly with regard to the anoxic conditions due to slow
drainage or air content at water holding capacity (Table 2), which
could affect nutrient availability to plants.
2. Materials and methods
2.3. Experimental design
2.1. Growing media
A complete randomized experiment with six replications and
two factors was conducted over a period of 147 days. The factors
examined were as follows:
Six different plant-growing media were used to study the
effect of various Fe-containing fertilizers on nutrient availability
to gerber (G. jamesonii H. Bolus) grown in them. The specific
substrates studied were as follows: (i) composted cork residue
(C); (ii) compost obtained from a mixture of olive husk and cotton
gin trash mixed with rice hulls and peat in a volume proportion of
1:1:1 (OH); (iii) composted grape marc (GM); (iv) Sphagnum peat
mixed with spent mushroom compost in a volume ratio of 1:1
(M); (v) coconut fibre (CF); and (vi) Sphagnum peat amended with
CaCO3 to raise pH (3 g L 1 peat). The composted materials were
selected in such a way as to encompass the typical agricultural
and agroindustrial residues from South Europe, and included CF
and peat as controls. Mixtures of the different materials were also
used so as to ensure good growing conditions based on previous
2.2. Substrate characterization
(i) Growing medium with six treatments levels as described
above.
(ii) Fe-containing fertilizer: control without Fe, Fe-chelate (FeEDDHA) applied daily as an irrigating solution with a
concentration of 10 mM; vivianite applied at 0.32 g Fe L 1
growing medium (equivalent to 1 g vivianite per L of
substrate); and a mixture of vivianite with humic substances
(HS) in a weight ratio of 10:1 applied at a rate of 1.1 g mixture
per L of growing medium, as recommended by de Santiago et al.
(2008). Vivianite and the vivianite + HS mixture were applied
as suspensions in deionized water, which was mixed with the
growing medium before gerber was planted.
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R. Caballero et al. / Scientia Horticulturae 122 (2009) 244–250
Table 1
Chemical properties of the studied growing media.
Growing mediuma
EC
dS m
OH
C
M
CF
GM
Peat
NO3-N + NH4+-N
pH
1
0.57
1.20
3.06
0.92
2.42
0.31
mg L
7.30
7.62
7.14
5.87
6.92
5.48
P
1
K
gL
23.8
18.3
56.3
23.5
5.5
5.4
4.3
0.9
6.0
0.05
2.9
0.04
Mg
Ca
Na
1
0.21
0.29
0.72
0.42
0.96
0.01
Fe
mg L
0.08
0.21
0.34
0.48
0.38
0.11
1.57
1.95
15.13
0.17
3.42
1.05
0.4
0.09
0.02
0.15
0.04
0.02
17.0
12.3
34.6
2.5
10.5
46.9
Zn
Cu
Mn
3.0
5.6
8.2
1
4.0
0.9
0.8
0.3
0.9
n.d.
0.4
0.3
6.9
5.0
4.1
2.5
7.2
2.8
1
Electrolytic conductivity (EC), pH, NO3-N + NH4+-N, and P concentration in the 1:2 growing medium:water extract; K, Mg, Ca, and Na expressed in g L 1 growing medium as
determined in 1:5 (v/v) growing medium: 1 M ammonium acetate (pH 4.65) extract; Fe, Zn, Cu, and Mn expressed in mg L 1 growing medium as determined in 1:2 (v/v)
substrate: 2 mM DTPA (pH 7.3) extract; n.d., not detectable.
a
C, composted cork residue; OH, olive husk mixed with rice hulls and peat in a 1:1:1 volume proportion; GM, grape marc; M, spent mushroom compost mixed with peat in
a 1:1 volume ratio; CF, coconut fibre.
Table 2
Physical properties of the studied growing media.
Medium
Air at water
holding
capacity
Water
holding
capacity
% (v/v)
OH
C
M
CF
GM
Peat
19.9
13.1
14.3
17.5
21.4
18.6
Bulk
density
kg L
64.3
68.8
68.6
77.6
56.7
74.5
0.33
0.37
0.35
0.09
0.38
0.11
Particle
density
1
Total
porosity
%
2.07
2.02
2.02
1.56
1.75
1.54
84.2
81.8
82.9
95.1
78.1
93.0
C, composted cork residue; OH, olive husk mixed with rice hulls and peat in a 1:1:1
volume proportion; GM, grape marc; M, spent mushroom compost mixed with peat
in a 1:1 volume ratio; CF, coconut fibre.
Vivianite was prepared according to Rosado et al. (2002), by
mixing 25 g (NH4)2HPO4 and 75 g FeSO47H2O in 1 L of water to
produce a suspension containing 5 g of vivianite. The resulting
suspension, which was highly saline (32 dS m 1), was washed
several times with deionized water until the electrical conductivity
was lower than 0.5 dS m 1. The contribution of the suspension to N
supply to plants after washing was deemed negligible.
Humic substances (HS) were prepared as described by de
Santiago and Delgado (2007) from a commercial liquid mixture of
humic and fulvic acids (Solfer húmicos1, Valencia, Spain), which
was dialyzed into 15-kDa cut-off Visking tubing (Sigma, Barcelona,
Spain) against deionized water until the electrical conductivity of
the solution was <1 dS m 1. Then, the pH was lowered to 8 with
HCl. A detailed description of the main properties of these dialyzed
HS can be found elsewhere (de Santiago and Delgado, 2007; de
Santiago et al., 2008).
2.4. Growing conditions
The experiment was conducted in a greenhouse in the
Agriculture School of the University of Seville, Spain (378210 N,
58560 W) from 24 June to 18 November 2004. Plants were grown in
3-L pots (one pot per replication); each of the pots was filled with
one growing medium at its bulk density. In order to avoid Cu
deficiency owing to the low content of this nutrient in the studied
media (Caballero et al., 2007), 40 mg of CuSO45H2O per L of
growing medium was added prior to transplantation. Plants were
transplanted at four true leaves stage (one plant per pot). After
planting, the growing media were irrigated to saturation. Before
planting, the media were fertilized to ensure a similar initially
available nutrient level in all by applying Peters1 M-77 (27% N, 15%
P2O5, 12% K2O, 0.125% Fe, 0.25% B, 0.001% Mo, and 0.63% Cu, Mn,
and Zn) at 1 g L 1 substrate and Osmocote1 (12–14 month release
period; 18% N, 9% P2O5, 10% K2O, 2% MgO, 0.009% B, 0.024% Cu,
0.03% Mn, 0.008% Mo, 0.008% Zn, and 0.20% Fe) at 4 g L 1 substrate.
Both fertilizers were supplied by Scotts España, S.A. (Tarragona,
Spain) and iron was present as Fe-EDTA. The fertilizer rates were in
the usual range for commercial pot production. Overall, no
restrictions in nutrient supply to plants were expected based on
the available nutrient data (Table 1), additional Cu supply, and
fertilizer applied to the growing media before planting (Caballero
et al., 2007). Plants were irrigated daily with 125–250 mL
deionized water (or 10-mM Fe-EDDHA solution in chelate
treatment) in order to facilitate slight drainage. Based on the
use of this irrigation regime and the water holding capacity of the
media (Table 2), no differences arising from low water availability
to plants in the media were to be expected. During the last 7 weeks
of growth, plants were irrigated once a week with 250 mL of water
(or Fe-EDDHA solution in the chelate treatment) containing 1 g L 1
ammonium nitrate so as to avoid N deficiency (1.75 g of this
fertilizer applied per plant during the stated period). pH of the
drainage water was determined at 30-day intervals (i.e., five times
during the growing period); for this purpose, pots were irrigated
with 0.5 L of deionized water to promote drainage and obtain an
adequate volume of water sample.
2.5. Plant analysis
The chlorophyll content in each plant during cropping was
measured on a weekly basis at the same time each day (early in the
morning) from 26 June by using a Minolta SPAD 502 chlorophyll
meter (Minolta, Osaka, Japan). Twenty SPAD were taken during the
growing season. Measurements were made on the five youngest
completely expanded leaves. An accurate relation between
chlorophyll content and SPAD readings was previously reported
for gerber: chlorophyll [mg g 1 fresh weight] = 0.0209
SPAD + 0.0002 SPAD2, R2 = 0.98, P < 0.001 (Caballero et al., 2007).
Flower harvesting began on 19 August 2004 (i.e., 56 days after
transplantation) and was completed at the end of the experiment.
Flower diameter and stem length were measured. Dry matter (DM)
in vegetative shoots per pot was measured at the end of the
growing season.
The five youngest completely expanded leaves in each plant
were collected, dried in a forced air oven at 65 8C for 48 h and
milled to pass though a 1-mm sieve. An aliquot of the milled plant
material (0.5 g) was mineralized by ashing at 550 8C for 8 h and the
obtained ash was dissolved in 1 M HCl. The resulting solution was
used to determine P and B colorimetrically by using the blue
Molybdophosphate method (882 nm) and azomethine-H method
(410 nm), respectively; Ca, Mg, Fe, Cu, Mn, and Zn by atomic
absorption spectrometry; and K by atomic emission spectrometry.
Total nitrogen in the plant samples was determined by using the
Kjeldahl method.
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R. Caballero et al. / Scientia Horticulturae 122 (2009) 244–250
Table 3
Analysis of variance of chlorophyll meter readings at 5, 10 and 20 weeks (SPAD 5, SPAD 10, and SPAD 20, respectively), average chlorophyll meter reading for the last 10 weeks
(SPAD mean), shoot matter in plants (DM), number of flowers per plant, length of flower stem, flower diameter, and pH of drainage water.
Source of variation
Growing media (A)
Fe treatment (B)
AB
d.f.
P value
5
3
15
SPAD 5
SPAD 10
SPAD 20
SPAD mean
DM
Flowers per plant
Flower stem length
Flower diameter
pHa
0.0000
0.9044
0.7241
0.0000
0.4728
0.2527
0.0000
0.2868
0.0337
0.0000
0.0854
0.0003
0.0000
0.0159
0.0157
0.0000
0.3596
0.3898
0.1060
0.7726
0.8932
0.8274
0.8611
0.6648
0.0000
0.0435
0.0029
P values lower than 0.05 indicate a significant effect of the source.
a
Measured 17 weeks after transplanting.
2.6. Statistical analyses
Analysis of variance was performed in order to asses the
significance of the effect of the substrates and application of Fecontaining fertilizer on plant variables and pH in drainage water.
Analysis of variance, regressions, and comparison of means
(Tukey’s test) were all done using Statgraphics Plus 5.1 (StatPoint,
2000).
3. Results
The growing media under study were found to have a
significant effect on shoot dry matter (DM) and flower production
and also on the chlorophyll content as determined by using the
SPAD meter on gerber plants (Table 3). However, no significant
differences were observed in flower quality (diameter and stem
length) between the substrates (Table 3). Chlorophyll meter
readings in plants grown on peat and CF were higher than those
grown in other substrates (Table 4 shows the mean SPAD for the
last 10 weeks of growth). Grape marc compost (GM) and M
exhibited the highest amount of DM (Table 5), whereas peat and M
gave the highest number of flowers per plants (results not shown).
Coconut fibre (CF) and C exhibited the lowest amount of DM
(Table 5) and lowest flower yield (results not shown).
Table 4
Effect of the different growing media and iron sources on the average chlorophyll
meter readings for the last 10 weeks of growth.
Fe-EDDHA
Control without Fe
Vivianite + HS
Vivianite
55
40
54
60
53
64
54
53
54
57
54
64
55
45
54
60
55
63
The effect of Fe sources on chlorophyll readings and DM
production was only significant in C (Tables 4 and 5), which
accounts for the significant interaction observed between both
factors (Table 3). In this substrate, vivianite + HS was found to be
more effective in increasing both plant parameters than Fe-EDDHA
and vivianite without HS.
The iron sources had a varying effect on pH in drainage water
depending on the type of growing medium (Table 3). Thus,
vivianite + HS decreased the pH in comparison to the other Fe
sources in C and CF, but increased the pH in GM (Table 6).
Significant differences were observed in the P, Fe, Mn, and Zn
concentrations in plants grown on media with varying Fe sources
(Table 7). However, the effect of Fe sources differed across growing
media, as revealed by the significant interaction observed between
the growing medium and Fe treatment (Table 7). Vivianite and its
mixture with humic substances were effective in increasing the P
concentration in plants grown on peat and CF (Table 8). However,
both vivianite-based treatments increased Fe concentration in
comparison to the control containing no Fe only for the former
substrate (Table 9). It was also found that the effect of Fe sources on
the Mn and Zn concentration in plants varied with the growing
medium. Thus, in C, the application of Fe-chelate decreased the Mn
concentration in comparison to the control without Fe; in GM,
however, the Mn concentration was only reduced by vivianite + HS
(Table 10). Overall, Fe supply (especially as Fe-EDDHA) tended to
decrease the Zn concentration in C, OH, M, and GM. In peat,
however, vivianite + HS increased the concentration of this
nutrient in comparison to the control without Fe (Table 11).
4. Discussion
Arbitrary units
OH
C
M
CF
GM
Peat
54
46
53
59
53
62
C, composted cork residue; OH, olive husk mixed with rice hulls and peat in a 1:1:1
volume proportion; GM, grape marc; M, spent mushroom compost mixed with peat
in a 1:1 volume ratio; CF, coconut fibre; HS, humic substances.
Table 5
Effect of the different growing media and iron sources on shoot dry matter (DM).
Fe-EDDHA
g plant
OH
C
M
CF
GM
Peat
29
26
36
22
37
30
Control without Fe
Vivianite + HS
Vivianite
30
14
33
22
34
28
32
31
34
18
32
25
30
21
32
17
31
25
The increased DM and flower yields obtained with the substrate
containing spent mushroom compost (M) in comparison to the
other media (Tables 4 and 5) are consistent with previous results of
Benito et al. (2005). Compost based on olive husk has been found to
induce Fe chlorosis in plants with a similar nutrient supply
(Caballero et al., 2007). However, it was found that its mixture with
peat lowered the pH of our growing media in comparison to the
previous results (Caballero et al., 2007), which may account for the
increased chlorophyll content, and DM and flower yields, possibly
Table 6
Effect of the different growing media and iron sources on the pH of drainage water
17 weeks after planting.
1
C, composted cork residue; OH, olive husk mixed with rice hulls and peat in a 1:1:1
volume proportion; GM, grape marc; M, spent mushroom compost mixed with peat
in a 1:1 volume ratio; CF, coconut fibre; HS, humic substances.
OH
C
M
CF
GM
Peat
Fe-EDDHA
Control without Fe
Vivianite + HS
Vivianite
6.95
7.48
6.90
5.99
6.74
6.2
6.90
7.58
7.03
6.21
6.73
5.91
6.90
7.17
6.80
5.5
7.02
5.94
6.83
7.70
6.90
5.65
6.80
6.03
C, composted cork residue; OH, olive husk mixed with rice hulls and peat in a 1:1:1
volume proportion; GM, grape marc; M, spent mushroom compost mixed with peat
in a 1:1 volume ratio; CF, coconut fibre; HS, humic substances.
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R. Caballero et al. / Scientia Horticulturae 122 (2009) 244–250
Table 7
Analysis of variance of nutrient contents in plant leaves after harvesting.
Source
d.f.
Growing medium (A)
Fe treatment (B)
AB
5
3
15
P value
N
P
K
Ca
Mg
Fe
Cu
Mn
Zn
B
Fe/Mn
0.0000
0.0538
0.0313
0.0000
0.0000
0.0000
0.0000
0.6903
0.6813
0.0000
0.2454
0.0995
0.0000
0.7579
0.3369
0.0000
0.0086
0.0038
0.0000
0.9515
0.3198
0.0000
0.0236
0.0029
0.0000
0.0000
0.0426
0.0000
0.6506
0.3412
0.0000
0.0000
0.2610
P values lower than 0.05 indicate a significant effect of the source.
Table 8
Effect of the different growing media and iron sources on the phosphorus
concentration of gerber leaves.
Fe-EDDHA
g kg
OH
C
M
CF
GM
Peat
1
Control without Fe
Vivianite + HS
Vivianite
0.18
0.24
0.14
0.19
0.20
0.19
0.16
0.18
0.17
0.38
0.20
0.35
0.17
0.24
0.14
0.40
0.22
0.35
DM
0.15
0.24
0.15
0.20
0.20
0.16
C, composted cork residue; OH, olive husk mixed with rice hulls and peat in a 1:1:1
volume proportion; GM, grape marc; M, spent mushroom compost mixed with peat
in a 1:1 volume ratio; CF, coconut fibre; HS, humic substances; DM, dry matter.
due to the effect of increased micronutrient availability to plants.
The benefits on plant development from the usage of mixtures of
composted residues with peat as a result of lowering of pH in the
growing media have been previously demonstrated (Benito et al.,
2005). Moreover, GM has been reported to induce Fe chlorosis
(Caballero et al., 2007). In contrast, our results revealed an
interesting potential of GM as a peat-substitute growing medium
in combination with commercial Fe-enriched fertilizers.
The lowest DM yield was obtained with CF (Table 5) despite the
high SPAD readings for plants grown on it (Table 4). This was
possibly as a result of restricted Ca supply to plants as revealed by
the low Ca concentration in leaves of gerber grown on this
substrate, which were approximately five times lower than in the
other media (results not shown). The restricted Ca availability to
plants can be ascribed to the low concentration of this nutrient in
the substrate (Table 1) since no Ca was applied with the fertilizer.
Composted cork (C) also exhibited lower DM and flower yields
than those for the other media; however, it differed insignificantly
from CF in this respect (Table 5, flower results not shown).
Chlorophyll meter readings (SPAD) and dry matter (DM) yields
were significantly related to pH in drainage water (Fig. 1), with
decreasing SPAD readings at increased pH, and decreasing DM
yields at extreme pH values. The low DM yield obtained at low pH
values can be ascribed to low Ca availability in CF, which exhibited
the lowest average pH in drainage water (Table 6 shows the means
for each Fe source). The low DM yield obtained at high pH values
Table 9
Effect of the different growing media and iron sources on the iron concentration of
gerber leaves.
Fe-EDDHA
mg kg
OH
C
M
CF
GM
Peat
52
43
49
87
74
141
1
Control without Fe
Vivianite + HS
can be ascribed to deficiencies in other nutrient. Composted cork
residue (C) was the substrate exhibiting the highest pH in drainage
water; this may explain the low chlorophyll content of plants
grown on it by effect of micronutrient deficiencies. The symptoms
observed were typical of Fe deficiency, namely, interveinal
chlorosis in the youngest leaves. The hypothesis of Fe availability
being the main limiting factor for plants grown on C was supported
by the efficiency of Fe sources in increasing chlorophyll and DM
yield in this substrate (Tables 4 and 5). Dry matter and flower yield
in C amended with vivianite + HS were not significantly different
from those observed in peat, GM, or OH (Table 5, flower results not
shown). Thus, Fe deficiency must be the main nutritional factor
limiting plant yield in C. Furthermore, the Mn, Cu or Zn
concentration in plants in C were not significantly lower than
those in other media, which exhibited a similar DM and flower
yields to those registered in peat (Tables 10 and 11 show the Mn
and Zn concentrations, respectively); therefore, these micronutrients cannot be considered as the limiting factors. Moreover, Fe
supply in the form of applied commercial fertilizers was not
sufficient to prevent this nutritional imbalance since the Fe-chelate
present in both products (Fe-EDTA) was not as effective as other Fe
sources in growing media with high pH values (Wik et al., 2006).
The effect of Fe sources on Fe nutrition status in gerber grown
on C was not related to the increased Fe concentration in plants
(Table 9), and this was consistent with the previous findings of de
Santiago et al. (2008). The Fe concentration in plants is not an
accurate measure of the Fe nutrition status of plants since Fe
Table 10
Effect of the different growing media and iron sources on the manganese
concentration of gerber leaves.
Fe-EDDHA
mg kg
OH
C
M
CF
GM
Peat
21
11
13
44
58
55
Vivianite
58
48
75
101
58
305
C, composted cork residue; OH, olive husk mixed with rice hulls and peat in a 1:1:1
volume proportion; GM, grape marc; M, spent mushroom compost mixed with peat
in a 1:1 volume ratio; CF, coconut fibre; HS, humic substances; DM, dry matter.
Vivianite + HS
Vivianite
20
24
15
66
45
52
17
18
13
41
29
61
16
16
13
49
41
39
Table 11
Effect of the different growing media and iron sources on the zinc concentration of
gerber leaves.
Fe-EDDHA
mg kg
58
62
66
115
60
382
Control without Fe
DM
C, composted cork residue; OH, olive husk mixed with rice hulls and peat in a 1:1:1
volume proportion; GM, grape marc; M, spent mushroom compost mixed with peat
in a 1:1 volume ratio; CF, coconut fibre; HS, humic substances; DM, dry matter.
DM
45
50
68
74
51
179
1
OH
C
M
CF
GM
Peat
3
13
2
29
9
31
1
Control without Fe
Vivianite + HS
Vivianite
6
20
4
29
13
37
3
12
3
29
13
50
4
19
3
33
11
39
DM
C, composted cork residue; OH, olive husk mixed with rice hulls and peat in a 1:1:1
volume proportion; GM, grape marc; M, spent mushroom compost mixed with peat
in a 1:1 volume ratio; CF, coconut fibre; HS, humic substances; DM, dry matter.
R. Caballero et al. / Scientia Horticulturae 122 (2009) 244–250
249
may also have resulted from the fast dissolution of vivianite at a
low pH.
Application of Fe to the growing media affected the accumulation
of Mn and Zn in plants, but the effect was different in each media
(Tables 10 and 11). The decreased Mn concentrations observed in
gerber plants grown on C treated with Fe-EDDHA (Table 10) were
consistent with previous results of Heitholt et al. (2003), who found
that Fe supplied as Fe-chelate to decrease the Mn concentration in
plant shoots to a greater extent than that for inorganic Fe sources
under conditions of restricted Fe availability in the growing media.
This can be explained in terms of the antagonistic effect of Fe on Mn
accumulation in plants, which is well documented (Ghasemi-Fasaei
et al., 2003; Izaguirre-Mayoral and Sinclair, 2005; Chatterjee et al.,
2006). The lower efficiency of Fe-chelate in increasing crop yield in C
as compared with vivianite + HS can be at least partially ascribed to
its enhancing antagonistic effects on Mn. This is supported by
previous evidence reported by Ronaghi and Ghasemi-Fasaei (2008),
who found that a favourable response to Fe-chelate treatments can
be only expected in alkaline growing media if the Fe:Mn ratio in
plants is low enough to prevent the antagonistic effect of Fe on Mn. In
GM, the antagonistic effect of Fe supply on Mn was observed with
vivianite + HS (Table 10), possibly as result of faster dissolution of
this Fe source because of the lower pH of this substrate than in C. The
adverse effect of Fe-EDDHA on Zn concentration in plants (Table 11)
was also consistent with the previous results (Heitholt et al., 2003)
and likely to be related to nutrient antagonism (Assimakopoulou,
2006). Furthermore, sorption of Zn on Fe compounds (oxides)
formed from applied Fe sources in the growing media can adversely
affect the Zn uptake by plants (Montilla et al., 2003).
5. Conclusions
Fig. 1. Average chlorophyll meter (SPAD) readings of the five youngest, completely
expanded leaves for the last 10 weeks of growth and dry matter production (DM) of
gerber (grown on various media amended or not with different Fe sources) as
related to the average pH of drainage water during the growing period.
chlorosis in sensitive plants has frequently been ascribed to an
adverse effect of a high pH on the uptake rate of this nutrient from
the apoplast into the symplast (Lucena, 2000; Brand et al., 2000; Yu
et al., 2000). The ability of HS to enhance the efficiency of vivianite
in increasing SPAD readings and plant development can be partly
due to their effects on plant metabolism (Muscolo et al., 1999;
Pinton et al., 1999; de Santiago and Delgado, 2007), root
development (Cañellas et al., 2002; Chen et al., 2004), and the
interaction of HS with Fe forms formed from vivianite applied to
the growing media (Fe complexation and inhibition of Fe oxide
precipitation, de Santiago et al., 2008), which accounted for more
available Fe forms in the growing media, thereby increasing the Fe
availability to plants. Vivianite + HS decreased the pH of drainage
water in comparison to the control without Fe in C (Table 6), which
could also have contributed to increasing Fe availability to plants.
The effect of vivianite on the P concentration in peat and CF
(Table 8) can be ascribed to the increased dissolution rate of this
compound under acidic conditions in comparison to media with a
neutral to alkaline pH (Eynard et al., 1992; Rosado et al., 2002).
Therefore, vivianite could be an effective P fertilizer in acid media.
Moreover, the increased Fe concentration in plants grown on peat
amended with vivianite and its combination with humic acids in
comparison to the other Fe sources studied in this media (Table 9)
Composted grape marc (GM), and mixtures of olive husk and
cotton gin trash compost (OH) or spent mushroom compost with
peat (M), were found to provide essentially similar flower yields as
that for peat typically used for potted gerber production. Dry
matter yield was even higher in GM and M than that in peat.
Restrictions in coconut fibre can be ascribed to deficiency in Ca
availability to plants, and those in composted cork (C) to the
incidence of Fe deficiency chlorosis. A mixture of vivianite with
humic substances with a weight ratio of 10:1 was applied at a rate
of 1.1 g per L of substrate; it was found to be more effective – and
inexpensive – in overcoming Fe chlorosis than Fe-chelate (FeEDDHA) in C. Dry matter and flower production in C amended with
vivianite + HS was not significantly different from that in peat. The
effectiveness of this Fe source in preventing Fe chlorosis in high pH
media and the results obtained with the different compost-based
growing media studied are interesting with a view of reducing peat
consumption in horticulture.
Acknowledgements
This work was funded by the Spain’s Ministry of Education and
Research and also by the Regional Development Funds of the
European Union through the National R & D Program (Plan
Nacional I + d + i) (Projects AGL2005-06691-CO2-02-02-AGR and
AGL2008-05053-CO2-01). The work of Mr. Raymundo Caballero at
the University of Seville was funded by a grant from the Mexican
Federal Government.
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