Effects of organo mineral glass matrix b

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Effects of organo-mineral glass-matrix based
fertilizers on citrus Fe chlorosis
Article in European Journal of Agronomy · January 2013
DOI: 10.1016/j.eja.2012.07.007

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Europ. J. Agronomy 44 (2013) 32–37

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European Journal of Agronomy

journal homepage: www.elsevier.com/locate/eja

Effects of organo-mineral glass-matrix based fertilizers on citrus Fe chlorosis
Biagio Torrisi a,∗ , Alessandra Trinchera b , Elvira Rea b , Maria Allegra a ,
Giancarlo Roccuzzo a , Francesco Intrigliolo a
a
b

Consiglio per la Ricerca e la sperimentazione in Agricoltura – Centro di ricerca per l’Agrumicoltura e le Colture Mediterranee (CRA-ACM), C.so Savoia 190, 95024 Acireale, Italy
Consiglio per la Ricerca e la sperimentazione in Agricoltura – Centro di ricerca per lo studio delle Relazioni tra Pianta e Suolo (CRA-RPS), Via della Navicella 2-4, 00184 Roma, Italy

a r t i c l e

i n f o

Article history:
Received 9 March 2012
Received in revised form 6 July 2012
Accepted 17 July 2012
Keywords:

Fe chlorosis
Orange
Glass-matrix based fertilizer
Dried vine vinasse

a b s t r a c t
Several citrus orchards develop symptoms of Fe deficiency when cultivated in calcareous and alkaline
soils. In a field trial a new type of fertilizer, the glass-matrix based fertilizer (GMF, a by-product from
ceramic industries) was applied. GMF is able to release nutrients, particularly Fe, on the basis of plantdemand, being nutrients not soluble in water, but only in acidic or metal complexing solutions. In our
experiment, the effectiveness of GMF was tested on “Tarocco” orange trees of twenty years, severely
suffering from Fe chlorosis, also by mixing GMF with meat meal (MM) or digested vine vinasse (DVV),
thus comparing these treatments to the conventional Fe-chelate fertilization and the Fe-unfertilized
control.
The GMF + DVV mixture showed to be able to supply adequately micronutrients (particularly Fe) on long
term, reducing the chlorosis symptoms, increasing the leaf SPAD index, Fe concentration and decreasing
Fe index. No significant effect on yield and fruit quality was noticed. Our results indicated that these
innovative formulates, and in particular glass-matrix based fertilizer mixed with digested vine vinasse,
could be used as an “environmental friendly” fertilizer, allowing not only to reduce the use of chemicals
(such as Fe-chelate), but also to re-use industrial wastes and organic residues which gave an “adding
value” to these novel organo-mineral formulates.

© 2012 Elsevier B.V. All rights reserved.

1. Introduction
Fe chlorosis is the most complex phenomenon in citrus orchard
and one of major abiotic stresses affecting fruit tree crops in the
Mediterranean area (Abadía et al., 2011; Pestana et al., 2003). One
of the most common symptoms is the leaf blade yellowing, starting from apical leaves, which may progress and turn into necrosis
(Tagliavini and Rombolà, 2001). It exhibits a temporal and spatial
variability, requiring an efficient diagnosis system. Fe chlorosis is
mainly caused by low Fe availability in soil, due to the presence of
high amount of active lime and high soil pH (Lindsay and Schwab,
1982).
In general, tolerant genotypes of citrus rootstocks display an
enhanced ability to reduce Fe(III) at root level (by the FCR enzyme),
releasing protons into the rhizosphere under low external Fe availability (Bienfait, 1988; Mantey et al., 1994; Pestana et al., 2011),
reducing and/or chelating substances such as phenols and flavins
(Welkie and Miller, 1993; Susìn et al., 1994). Strategy I also includes
morphological changes, such as the development of root hairs

∗ Corresponding author. Tel.: +39 095 7653132; fax: +39 095 7653113.

E-mail address: biagiofrancesco.torrisi@entecra.it (B. Torrisi).
1161-0301/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.eja.2012.07.007

and transfer cells and increased rates of protons excretion (LòpezMillan et al., 2001).
Low Fe availability induces morphological changes in root epidermal cells that are similar to those induced by P deficiency. When
Fe is limiting, root-hair formation and elongation increases. The
extra root hairs that result from limited Fe availability are often
located in positions that are occupied by non-hair cells under normal conditions (Lòpez-Bucio et al., 2003; Römheld and Marschener,
1981).
The prevention and cure of Fe chlorosis in fruit trees have been
traditionally approached through the use of synthetic Fe chelates
(Lucena, 2003). Soil application of Fe chelates aims to enhancing
Fe availability for the following uptake at root level and represents an efficient prevention tool, due to the mechanism by
which it is absorbed by the roots, transported and utilized by the
leaves.
It should be remarked that Fe chelates generally applied to soil
are water-soluble and thus easily leached out from the rhizosphere
if excessive irrigation regimes are applied, or during the rainy
season (Rombolà and Tagliavini, 2006). Moreover, a likely underestimated problem related to synthetic chelates is their potential

to bind also undesired heavy metals (Grˇcman et al., 2001). In
addition, the cost for treating or preventing Fe chlorosis in citrus
orchards with the use of synthetic Fe chelates is very high, as to be

B. Torrisi et al. / Europ. J. Agronomy 44 (2013) 32–37
Table 1
Main physical and chemical parameters of 0–30 cm soil (mean values).
Parameter

Value

Clay (g kg−1 )
Silt (g kg−1 )
Sand (g kg−1 )
pH
Available Fe (g kg−1 )
EC1:2 (dS m−1 )
Active lime (g kg−1 )
Total CaCO3 (g kg−1 )
Organic matter (g kg−1 )

240
180
580
8.7
5.2
0.26
165
530
20

applicable only to high value crops, corresponding to more than
400D ha−1 (Rombolà and Tagliavini, 2006).
Glass-matrix based fertilizer (GMF), obtained by altering the
crystalline structure of a mineral natural substance through a physical process by mixing different salts and oxides, represents a
new typology of fertilizer, characterized by the specific attitude to
release nutrients on the basis of plant-demand, being nutrients not
soluble in water, but only in acidic or in metal complexing solutions
(∼99%), similar to those exuded by plant roots (Pinton et al., 2007;
Trinchera et al., 2009).

The GMF ability to release large amounts of macro and microelements, in particular Fe, when applied alone or in combination
with small amounts of organic amendments, was already tested
in laboratory under different extractive conditions (0.2% and
2% citric acid; 0.1% and 1% HCl) (Trinchera et al., 2009, 2011),
confirming its attitude to solubilize nutrients in presence of
complexing acidic solutions. On the basis of such previous laboratory results, in this field trial these fertilizers were tested in
field as a suitable alternative to synthetic Fe chelates to cure Fe
chlorosis.
The aim of our work was to evaluate if glass-matrix based
fertilizer, alone or in combination with two alternative organic
materials, could act on the prevention and treatment of nutrient
deficiency and, in particular, of Fe chlorosis in field conditions, in
comparison with the use of a common synthetic Fe-chelate fertilizer.
2. Materials and methods
2.1. Orchard description
The research was realized in a farm located in the Eastern
Sicily (Italy), where twenty years old “Tarocco” orange trees [Citrus
sinensis (L.) Osbeck] grafted on sour orange rootstock [C. aurantium (L.)] were cultivated with a planting distance of 6 m × 4 m
(416 trees ha−1 ). The area is characterized by high summer and
low winter temperatures. The rainfalls are concentrated in the

autumn–winter season. During the experimental period total rainfall had typical values of this Mediterranean region. The irrigation
was carried out with two micro-sprinklers per plant with an average annual water supply of 3360 m3 ha−1 . Soil of citrus orchard was
a sandy-loamy soil, with a low content of organic matter, high contents of active lime and total calcium carbonate, low content of
available Fe (Suppl. Ord. G.U. No. 248, 21.10.1999, Method IX.3).
Main chemical–physical soil parameters are reported in Table 1
(soil sampled at 0–30 cm of depth, layer most explored by citrus
roots).
Before treatments (early spring season, 2008), plant leaves
showed typical symptoms of Fe deficiency by green discoloring, in
particular the intervenial leaf yellowing, starting from apical leaves.
Trees canopy showed symptoms of Fe chlorosis throughout the
year, but they were more evident in spring, when shoot growth is
faster and the bicarbonate concentration in the soil solution buffers

33

Table 2
Elemental composition (g kg−1 ) of fertilizers utilized in different treatments (a), and
amount of nutrients (g tree−1 ) distributed yearly during the trial (b).
N

(a) Treatment
GMF
GMF + DVV
GMF + MM
Fe chelate
(b) All

P as P2 O5

K as K2 O

Fe

–
8
14
30

295
238
265
–

198
161
158
150

83
66
88
60

370

200

300

15a

a
In all GMF treatments, the three years’ Fe amount (45 g) was distributed in the
first year; no Fe addition in the control.

the soil pH in the rhizosphere and root apoplast (Rombolà and
Tagliavini, 2006; Torrisi and Intrigliolo, 2009). Results reported in
this paper are related to three years of field trial (2008–2010).
2.2. Experimental design
The trial was realised by adopting a system with two randomized blocks; within each block 3 plants per treatment were
identified, for a total of 6 index plants per treatment. To evaluate
the effect of three GMF treatments, in comparison with a standard
treatment with a Fe-chelate fertilizer and a Fe-untreated control,
five treatments were applied: GMF (100% glass mineral fertilizer,
powdered at 0.1 mm), GMF + DVV (80% glass mineral fertilizer + 20%
digested vine vinasse, powdered at 0.1 mm), GMF + MM (80%
glass mineral fertilizer + 20% meat-meal, powdered at 0.1 mm), NK
fertilizer containing Fe-EDDHA [ethhylenediamine-di(o-hydroxyphenylacetic) acid], and the control Test (treatment without Fe
supply).
GMF composition was determined for P2 O5 (295.1 g kg−1 ),
K2 O (198.2 g kg−1 ), Fe2 O3 (118.5 g kg−1 ), CaO (100.2 g kg−1 ),
MgO (56.8 g kg−1 ), MnO (45.7 g kg−1 ), ZnO (45.3 g kg−1 ), B2 O3
(25.6 g kg−1 ), CuO (9.1 g kg−1 ), SiO2 (73.8 g kg−1 ) and Al2 O3
(28.8 g kg−1 ).
Besides, main parameters of DVV and MM were also determined: pH (8.4 and 6.4), Corg (155 g kg−1 and 415 g kg−1 ), Ntot
(41 g kg−1 and 81 g kg−1 ), P2 O5 (9 g kg−1 and 125 g kg−1 ), K2 O
(16 g kg−1 and 10 g kg−1 ), Fe2 O3 (no detectable content and
1.5 g kg−1 ), respectively. No detectable amount of heavy metals
were recorded in GMF, DVV and MM (Table 2). To prepare the fertilizing mixtures, GMF and organic matrices (DVV and MM) were
dried in a oven at 40 ◦ C for 18 h, weighted and then mixed at the
ratio GMF/organic matrix = 80/20 (w/w).
All the trees received the same NPK amount (370 g N, 200 g P2 O5
and 300 g K2 O per tree), applied each year on the 2nd decade of
March. In the control treatment and in all other treatments, to
complete the annual requirements of N, P and K, single nutrient
fertilizers were added as urea, simple superphosphate and sulphate of potash, respectively. The total Fe three years’ request (45 g
per tree) was applied in one rate at the beginning of the first year
(2nd decade of March) for all the GMF treatments, whereas the Fe
chelate one was fractionated in yearly applications (15 g per tree
per year), added on the 2nd decade of March. Treatments with the
addition of DVV or MM alone were not performed because of the
negligible Fe supply respect to that added with GMF fertilizer (see
Table 2).
The fertilizers were applied every year under canopy projection
on the soil, whereas glass-matrix based fertilizers, with or without addition of organic materials, were applied as powder the first
year, to add the overall Fe amount, inside two trenches dug at
soil depth of 20 cm at a distance of about 150 cm from the trunk
under the canopy projection and without any soil tillage. In particular, the depth at 20 cm for trenches was chosen in order to
draw up the GMF fertilizers with fine roots (particularly active in

34

B. Torrisi et al. / Europ. J. Agronomy 44 (2013) 32–37

water and nutrient uptake) without damaging them, to promote the
mechanism of “plant demand”. The chosen depth was that of an
ordinary soil tillage in the area.
2.3. Tree nutritional status
Every year, nutritional status was determined by foliar analysis performed on 20 leaves of the index trees collected in October
from non fruit bearing terminal shoots of the year’s spring flush
on 6 trees per treatment (Embleton et al., 1973), according to a
standard practice for determining citrus nutritional status in Sicily
(Intrigliolo et al., 1999).
Leaves were washed with distilled water, oven dried at 65 ◦ C for
24 h, until they reached constant weight. A representative subsample was mill-ground and nitrogen (N, in g kg−1 ) was determined
by micro-Kjeldahl digestion procedure. Leaf subsamples were also
analyzed for phosphorus (P, in g kg−1 ), potassium (K, in g kg−1 ),
calcium (Ca, in g kg−1 ), magnesium (Mg, in g kg−1 ) and Fe (Fe,
in mg kg−1 ) content by Inductively Coupled Plasma Spectrometry
(ICP-OES Optima 2000DV, Perkin Elmer, Italy), after dry-ashing of
samples in muffle furnace at 550 ◦ C for 12 h and dissolution in a
1% (v/v) solution of hyperpure HNO3 69% (Panreac Quimica SAU,
Barcelona, Spain).
2.4. Estimation of Fe deficiency and SPAD index
Every year, for the estimation of Fe deficiency, 20 leaves per tree
were sampled from non-fruit bearing shoots, in the 2nd decade of
May, when the leaves were well developed and the symptoms of
Fe chlorosis, if present, become easily analytically evaluable. The
leaves were treated as above and analyzed for Fe (mg kg−1 ) by ICPOES.
SPAD value was estimated using the portable instruments SPAD502 chlorophyll meter (Minolta, Osaka, Japan), using the same 20
leaves per tree already sampled for the estimation of iron deficiency, before they were oven dried. The SPAD readings, expressed
as SPAD units, were taken from the mid area of the fully expanded
spring leaves (Intrigliolo et al., 2000; Pestana et al., 2005).
2.5. Yield and fruit quality
Every year, total yield per tree was recorded at commercial harvest (February) and, on a sub-sample of 50 fruits collected from the
outer part of the canopy, the fruit mean weight and fruit physical
and chemical parameters were determined. Fruit weight, firmness,
width of the central axis and peel thickness were measured according to Wardowski et al. (1979). Furthermore, for each sub-sample
juice content, total acidity (TA) and total soluble solids (TSS) were
determined. Vitamin C was determined by high-performance
liquid chromatography (HPLC) (Rapisarda and Intelisano,
1996).
2.6. Statistical analysis
Data were evaluated for the analysis of variance (ANOVA) by
SPSS-10 package (SPSS, Chicago, USA); Duncan’s multiple range test
was used for mean separation.

Fig. 1. Leaves sampled after three years of the experiment: different levels of chlorosis are shown, as a result of the different fertilization treatments.

GMF + DVV showed an increased green colour in all the years of
testing, thus suggesting a positive action of this mixture on chlorosis even until three years after treatment (Fig. 1).
Results of leaf analyses and SPAD are shown in Table 3, as mean
values of three years’ experiment.
Plants treated with the mixture GMF + DVV and Fe chelate, compared to GMF, GMF + MM and the control, showed a significant
increase of SPAD index.
Moreover, a positive effect on Fe (Table 3) was found in
the different treatments. As expected, after three years of
experiment, fertilization with Fe-chelate gave the highest values of Fe contents, but it was comparable to what obtained
after addition of GMF + DVV. The other fertilization treatments gave results comparable to control treatment without Fe
supply.
It has been proposed to identify Fe deficiency, not only by Fe concentration in leaves, but also analysing the concentration of other
elements. In this context, P/Fe ratio (P and Fe ␮g g−1 d.w.) is considered to be an useful index to evaluate chlorosis due to Fe deficiency.
The ratio increases when the chlorosis becomes severe (ÁlvarezFernández et al., 2005; Chouliaras et al., 2004) due to the increase
of plant P uptake and/or the decrease of Fe uptake. K/Ca ratio (K and
Ca ␮g g−1 d.w.) gave similar information (Chouliaras et al., 2004;
Wang et al., 2008; El-Jendoubi et al., 2011), but related to the effect
of calcium excess in the soil cation exchange complex. The Fe index,
[(10P + K)50]/Fe (where P and K g 100 g−1 d.w., Fe ␮g g−1 d.w.), is

Table 3
Leaf macronutrient (g kg−1 ), Fe (mg kg−1 ) content and SPAD index. Leaf macronutrient are referred to leaves sampled in October, Fe and SPAD to leaves sampled in
May. Mean values of three years ± standard error in parenthesis; n = 18.
Treatment

N

P

K

Ca

Mg

Fe

SPAD

GMF

26.4b
(±0.4)
25.1a
(±0.4)
25.5ab
(±0.5)
25.6ab
(±0.4)
26.2ab
(±0.5)

1.29
(±0.01)
1.32
(±0.02)
1.31
(±0.03)
1.33
(±0.03)
1.32
(±0.02)

11.7c
(±0.5)
9.3b
(±0.4)
10.2b
(±0.6)
7.3a
(±0.5)
9.1b
(±0.7)

43.6ab
(±1.1)
46.7bc
(±1.5)
42.1a
(±1.9)
48.1c
(±2.1)
44.2abc
(±1.7)

1.75ab
(±0.04)
1.84b
(±0.06)
1.67a
(±0.03)
1.86b
(±0.06)
1.65a
(±0.05)

64a
(±8.2)
73ab
(±7.7)
63a
(±6.7)
80b
(±8.9)
64a
(±6.0)

47.6a
(±3.5)
67.0b
(±1.9)
52.6a
(±2.9)
73.4b
(±1.6)
50.6a
(±2.6)

GMF + DVV

3. Results
Visual symptoms of the citrus leaves, sampled after three years
of experiment, showed clearly the effects of different treatments
on Fe chlorosis. Leaf greenness in the Fe chelate fertilizer treatment
showed the overcoming of the Fe chlorosis, as predictable, whereas
in the other treatments leaves maintained the typical intervenial
leaf yellowing. Only the leaves sampled from trees treated with

GMF + MM
Fe chelate
Test

Mean separation at p < 0.05 with Duncan’s multiple-range test. Means in a column
followed by the same letter are not significantly different.

B. Torrisi et al. / Europ. J. Agronomy 44 (2013) 32–37

P/Fe rao

35,00

35

90,0

25,00

B

70,0

c

c

bc

B

60,0

SPAD

ab
a

20,00

B

C

80,0

30,00

15,00

50,0

ab

b

AB
ab

40,0

ab

a

A

A

A

A

A

30,0
20,0

10,00

10,0

5,00

0,0

0,00
GMF

GMF+DVV

Fe chelate

Test

K/Ca rao

0,35
0,30

GMF+MM

2008

2009

2010

Fig. 3. SPAD index (mean values, calculated for each year of experiment). Mean
separation at p < 0.05 (small letters) and p < 0.001 (capital letters) by Duncan’s
multiple-range test. Means with the same letter are not significantly different.

c
c

0,25
b
b

0,20
a

4. Discussion

0,15
0,10
0,05
0,00
GMF

GMF+DVV

GMF+MM

Fe chelate

Test

Fe index

3,00
d

cd

2,50
bc
ab

2,00

a

1,50
1,00
0,50
0,00
GMF

GMF+DVV

GMF+MM

Fe chelate

Test

Fig. 2. Leaf P/Fe ratio, K/Ca ratio and Fe index (mean values of three years). Mean
separation at p < 0.05 by Duncan’s multiple-range test. Means with the same letter
are not significantly different.

another important index for evaluating Fe deficiency (Köseo˘glu,
1995; Wang et al., 2008).
Our data showed the increase of P/Fe ratio, K/Ca ratio and Fe
index (Fig. 2) in GMF, GMF + MM and control treatments, and the
decrease in GMF + DVV and Fe-chelate ones.
Of particular interest is the behavior of the SPAD during the three
years. Fig. 3 shows that, at the third year, the SPAD value obtained
for GMF + DVV treatment was quite similar to that of Fe-chelate one.
These differences were just evident in the second year, indicating
a sort of Fe slow release in the soil by GMF-DVV.
Concerning the yield and quality of fruits, only the mean values
of three years (Table 4) were reported, since the annual performances were similar during the three years of study.
No significant differences were noticed as far as yield and fruit
quality parameters were concerned (Table 4). An upward trend
of maturity index (TSS/TA) in GMF + DVV treatment was noticed,
mainly due to a lower value of total acidity (TA) in fruit juice.

Treatments GMF and GMF + MM showed a SPAD index rather
low when compared with the corresponding measured leaf Fe content. This may be due to a Fe inactivation effect, in particular in
the leaf apoplast (as an example, through a process of alkalinization): as a matter of fact, a high concentration of foliar Fe cannot
always be considered as a reliable indicator to diagnose Fe chlorosis
(Römheld, 2000).
In our experiment, visible symptoms of chlorosis due to high
content of soil active lime that strongly influenced not only Fe, but
also other nutrients uptake, were found in correspondence with
sub-optimal or optimal leaf Fe content. In the so-called “chlorosis
paradox” (Morales et al., 1998; Pestana et al., 2003), chlorotic leaves
with low SPAD index show total leaf Fe concentration similar to that
of Fe sufficient leaves. In our experiment this “paradox” was found,
since plants with lower SPAD index however showed a fairly good
Fe content in leaves (Table 3).
The beneficial effect of organic matter on Fe chlorosis prevention
depends on the direct Fe chelating ability of the humic and fulvic
acids and the biostimulation exerted by organic components on
both the soil microbial activities and the root growth (Shenker and
Chen, 2005). In particular, previous studies showed that plant roots
development was positively influenced by the presence of particles
of added organic materials, which have also the ability to attract
roots towards them, increasing mucigel excretion (Trinchera et al.,
2010) and acidic root exudates (Oburger et al., 2009), so to be able
to solubilize nutrients from GMF + DVV mixture.
Data from the literature (Intrigliolo et al., 2000) suggest that
SPAD index is correlated with leaf-N-concentration, but in our
study we did not found this indication. In fact, severely chlorotic
leaves, with low SPAD values, had higher N content. This correlation
is preferentially found in plants with a good nutritional status, without strong biotic or abiotic stresses, and the absence of association
could also be due to the fact that leaf N allocation is not exclusive
of pigment-protein reaction center complex and that growth environment plays a central role (Jifon et al., 2005). As also showed
in Table 3, the N content of the plants treated with GMF + DVV
and Fe chelate which showed greener leaves (that implies higher
SPAD index) was 25.1 and 25.6 g kg−1
, respectively, while for treatds
ment GMF, which gave chlorotic leaves (lower SPAD index), it was
. The GMF + MM treatment gave a N leaf concentration
26.4 g kg−1
ds
corresponding to 25.5 g kg−1
. However, recorded N contents were
ds
all into the optimal N concentration range; this tendency was also
showed by P, K and Ca foliar content.

36

B. Torrisi et al. / Europ. J. Agronomy 44 (2013) 32–37

Table 4
Yield and fruit quality characteristics (mean values of three years ± standard error, n = 18).
GMF
Yield (kg tree−1 )
Fruit weight (g)
Juice (g kg−1 )
Peel thickness (mm)
Central axis (mm)
Firmness (kg cm−2 )
Total soluble solids (g kg−1 )
Total acidity (g kg−1 )
TSS/TA
Vitamin C (mg l−1 )

93
216
367
4.2
10.0
2.65
121.3
11.9
10.5
637.1

±
±
±
±
±
±
±
±
±
±

9.1
9.0
14.0
0.15
0.23
0.13
1.5
0.47
0.35
7.1

GMF + DVV

GMF + MM

Fe chelate

Test

103
226
385
4.5
10.8
2.82
123.1
10.9
11.2
674.3

102
202
442
4.2
9.6
3.33
125.5
11.5
10.9
681.5

99
198
372
4.4
9.4
3.22
125.2
12.1
10.3
672.3

96
200
380
4.1
9.8
2.48
118.9
12.9
9.4
663.3

±
±
±
±
±
±
±
±
±
±

5.3
10.8
18.7
0.04
0.18
0.16
1.0
0.22
0.20
5.4

The high K concentrations in GMF and GMF + MM leaves cannot
be explained by differences in K supplied with fertilization, since
it was equally distributed in all treatments. Probably, its increase
was due to an increase of ATPases activity of root plasma membrane, directly involved in protons excretion (Marschner, 1995).
The high K concentration may be also associated to the accumulation of organic acids that occurs under Fe deficiency (Belkhodja
et al., 1998; Welkie and Miller, 1993). On the contrary, with treatment Fe-chelate we found a reduction of K uptaken by plant.
Urrestarazu et al. (1994) also pointed out that plants take K much
more than Fe and excessive amounts of K could inhibit the Fe uptake
and translocation in plants, leading to Fe deficiency. Some recent
studies showed that, when the chlorosis symptoms occurred, corresponding high K contents in chlorotic leaves were found (C¸elik
and Katkat, 2007; Li et al., 2001). This relationship between potassium and Fe may be attributed to the normalization effect of K on
Fe absorption and translocation into the shoots (Li et al., 2001).
The lower values of P/Fe and K/Ca ratios and of Fe Index obtained
after addition of the organo-mineral fertilizer GMF + DVV confirmed the hypothesized mechanism of nutrient release based on
plant demand, already described by Trinchera et al. (2010), which
take place by increasing plant root exudation and favouring the
release of nutrients by the mixture. The dried vine vinasse, constituted mainly by humo-similar organic compounds, is particularly
able to complex mineral nutrients contained in GMF and making them available for the following root uptake; conversely, in
GMF + MM, this mechanism is not effective being MM constituted
mainly by simple proteins, not able to complex or chelate nutrients
from GMF.
The rationale for the decrease of fruit yield in Fe deficient trees
has to be found in the decreased assimilatory power caused by Fe
chlorosis (Álvarez-Fernández et al., 2006). In our case, in spite of the
evident chlorotic leafy symptoms, almost all the values of nutrient
in leaves were in the optimum range, with the only exception of
magnesium (Embleton et al., 1973). For this reason no clear effect
on yield and fruit quality was noticed.

5. Conclusions
Results obtained attested that the considered organo-mineral
fertilizers increased significantly the nutrient release from GMF,
favoring the following nutrient uptake by plants. In particular, foliar
K, Ca, Mg and Fe seemed to be positively affected by the organic
matter addition to GMF at different extent.
In relation to Fe chlorosis of citrus plants, all evidences allowed
to affirm that the mixture GMF + DVV is the most promising formulate able to front Fe deficiency of citrus in field conditions,
by increasing plant Fe uptake and related photosynthetic activity. The ability of the specific added organic components, mixed
to the alumino-silicate material, to complex main nutrient elements, makes them, and Fe in particular, more available to plants:
the mixtures of GMF and used organic matrices seems to be

±
±
±
±
±
±
±
±
±
±

10.9
10.5
17.9
0.14
0.28
0.11
0.6
0.30
0.33
6.2

±
±
±
±
±
±
±
±
±
±

10.3
12.5
20.1
0.04
0.36
0.20
1.1
0.08
0.13
4.8

±
±
±
±
±
±
±
±
±
±

8.2
9.1
5.7
0.18
0.23
0.18
2.6
0.36
0.36
13.8

particularly effective as “environmental friendly” fertilizers, since
they allow not only to reduce the use of chemicals, but also to
re-use agro-industrial wastes and organic residues which gave an
“adding value” to these novel organo-mineral formulates. At the
end, since the reported experience is related to a medium-term
period, it should be considered the potential “residual” Fe that the
proposed mixtures could supply to plant on long term: this aspect
needs to be further investigated.
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