Nativa, Sinop, v. 9, n. 5, p. 500-507, 2021.
Pesquisas Agrárias e Ambientais
DOI: https://doi.org/10.31413/nativa.v9i5.12777 ISSN: 2318-7670
Substrate mixing formulations for
Citrus
nursery management
Érica Maria Sauer LIBERATO1, Sarita LEONEL1*, Jackson Mirellys Azevedo SOUZA2,
Gabriel Maluf NAPOLEÃO1
1Department of Horticulture, São Paulo State University (UNESP), School of Agriculture, Botucatu, São Paulo, Brazil.
2Agricultural Sciences Center, University of Viçosa, Viçosa, MG, Brazil.
*E-mail: sarita.leonel@unesp.br
(ORCID: 0000-0001-7882-0365; 0000-0003-2258-1355; 0000-0003-2350-7114; 0000-0003-1938-5281)
Recebido em 20/07/2021; Aceito em 09/11/2021; Publicado em 17/12/2021.
ABSTRACT: The citrus seedling development is determined by several factors, including the physical and
chemical qualities of the substrate, which affect the quality of field seedlings. The purpose of this study was to
evaluate how the ‘Swingle’ citrumelo rootstock developed with different substrate formulations. The
experiment was carried out in a seedling nursery from seeding to grafting, and six treatments were carried out:
60% peat moss, 30% fine grade horticultural vermiculite, 10% rice hulls; 60% peat moss, 30% super fine grade
horticultural vermiculite, 10% rice hulls ; 50% peat moss, 30% fine grade horticultural vermiculite, 20% rice
hulls ; 50% peat moss, 30% super fine grade horticultural vermiculite, 20% rice hulls ; 50% peat moss, 20%
fine grade horticultural vermiculite, 30% rice hulls ; 50% peat moss, 20% super fine grade
horticultural vermiculite, 30% rice hulls. When container transplanting was performed, the emergence
percentage of seedlings was determined. Stem height, stem diameter, leaf number, area meter, root dry matter,
leaf and stem dry matter, and quality index were measured on seedlings. All substrate formulations improved
seedling development until grafting, except for the formulations with 30% rice hulls, which hampered seedling
development in ‘Swingle' citrumelo.
Keywords: [Citrus paradisi Macfad. Duncan grapefruit × Poncirus trifoliata (L.) Raf.]; peat moss; rice hulls;
vermiculite.
Manejo de viveiro de citros com mistura de formulações de substrato
RESUMO: Muitos fatores influenciam na formação das mudas cítricas, sendo que as propriedades físicas e
químicas dos substratos afetam a qualidade da muda levada a campo. O trabalho teve como objetivo avaliar o
desenvolvimento do porta-enxerto citrumeleiro ‘Swingle’ em diferentes formulações de mistura de substratos.
O experimento foi realizado em viveiro sendo as plantas conduzidas da semeadura até o ponto de enxertia. Os
tratamentos utilizados foram: Substrato 60% Turfa Sphagnum, 30% vermiculita fina, 10% casca de arroz;
Substrato 60% Turfa Sphagnum, 30% vermiculita super fina, 10% casca de arroz; Substrato 50% Turfa
Sphagnum, 30% vermiculita fina, 20% casca de arroz; Substrato 50% Turfa Sphagnum, 30% vermiculita super
fina, 20% casca de arroz; Substrato 50% Turfa Sphagnum, 20% vermiculita fina, 30% casca de arroz; Substrato
50% Turfa Sphagnum, 20% vermiculita super fina, 30% casca de arroz. No tranplantio, foi avaliada a
porcentagem de emergência das plântulas. Foram avaliadas altura das plantas, diâmetro do caule, número de
folhas, área foliar, massa seca das raízes e parte aérea e índice de qualidade. Todas as formulações de mistura
de substratos proporcionam desenvolvimento semelhante das mudas até a enxertia, exceto as formulações com
30% de casca de arroz que não promoveram o desenvolvimento adequado das plântulas de citrumeleiro
‘Swingle’.
Palavras-chave: [Citrus paradisi Macfad. Duncan grapefruit × Poncirus trifoliata (L.) Raf.]; casca de arroz
vermiculita; turfa de Sphagnum.
1. INTRODUCTION
Most seedlings are housed in containers with substrate in
greenhouses, but new technologies are allowing for greater
plant development. Therefore, new requirements are based
on a variety of studies, such as substrate, irrigation,
containers, and fertilizers (SCHÄFER et al., 2008;
FERRAREZI et al., 2019). Furthermore, several citrus
development plants have failed because of the type of
seedlings that were picked. Although some citrus is regarded
to be healthy, it is susceptible to viral infections and citrus
greening. Citrus seedlings require several years to come into
production, thus both growth (from seedlings to adulthood)
and disease development are gradual. (DORJI; LAKEY,
2015).
‘Swingle’ citrumelo is a hybrid [Citrus paradisi Macfad.
Duncan grapefruit × Poncirus trifoliata (L.) Raf.]. This hybrid
is also one of the most significant rootstocks for being
resistant to a variety of diseases that impact citriculture
around the world (LIBERATO et al., 2013), besides having
moderate drought tolerance, a long lifespan, and can be used
in place of Rangpur lime rootstock (Citrus limonia L. Osbeck)
(OLIVEIRA; SCIVITARO, 2007; PRADO et al., 2008).
Seedling production is crucial when it comes to growing an
orchard. All citrus nurseries (i.e. large or small) have obstacles
during the production stage in a protected environment
(MERLIN et al., 2012). Thus, selecting the appropriate
substrate can be a difficult task that requires consideration of
Liberato et al.
Nativa, Sinop, v. 9, n. 5, p. 500-507, 2021.
501
both physical and chemical features (ARCE; RIVERA,
2018). There are various substrate possibilities on the market,
all of which are made from diverse material combinations;
these substrates also have formulations and characteristics
that are either known or unknown to the producers
(FRANCO et al., 2007; ALMEIDA et al., 2018).
The physicochemical features of substrates will be a
determining influence on the quality of seedlings as the root
system develops, affecting plant growth and yield
(MAGGIONI et al., 2014).
Pine bark, rice hulls, peat moss, fine vermiculite, perlite,
pulverized coal, and coconut fiber are some of the raw
materials commonly utilized in citrus seedling combinations
in Brazil. Material, combinations, and formulations are also
primarily determined by the cost and availability of raw
materials (COSTA et al., 2005). Nonetheless, mixing more
than three components in the same combination is
impractical, because it results in higher expenses and poorer
profit margins, according to Guerrini; Trigueiro (2004).
Similar information was reported by ARCE; RIVERA,
(2018) and FERRAREZI (2019).
Peat is a type of plant material that is used to create an
anaerobic environment. It is widely utilized in temperate
climates. These adaptable plants have a low density and an
acidic pH. They are appropriate for use in the production of
substrate materials because of their capacity to hold water.
Sphagnum peat is a form of dry peat with a density of around
110 g/L-1 and a water retention capacity of 15 to 30 times its
weight. It usually originates from Canada, Ireland, and
Germany (BRITO et al., 2012).
Aluminium, magnesium, and iron are all found in
vermiculite, which is a hydrated silicate. Moreover, this
mineral absorbs up to five times its volume in water; its
presence in substrate composition boosts water retention
capacity (REZENDE et al., 2010; ARCE; RIVERA, 2018).
It also has a high capacity for cation exchange, making it a
great candidate (REZENDE et al., 2010).
After going through a roasting process, rice hulls are a
residue produced by the rice industry and has been used as a
component of substrates. Also, rice hulls have a low density,
they allow the substrate to have a higher overall porosity,
which aids in the drainage and aeration process of the
seedlings' root systems. Rice hulls have high macro porosity,
they work best when paired with microporous materials like
vermiculite (KRATZ et al., 2013).
Substrates and rootstocks are the most expensive
agronomic materials, accounting for 20.7 percent of total
production expenses, according to the ViveCitrus
Association and Conplant Consulting Company
(BATAGLIA et al., 2008). Furthermore, studies demonstrate
that lowering the use of discarded rootstocks and other
agronomic supplies, as well as making optimal use of
substrate and fertilizers, can increase the profitability of
commercial nursery plants (BREMER NETO et al., 2015).
New substrate formulations, when compared to those on
the market, include low-cost and greater availability materials
that can positively impact the final cost of the seedling. The
seedlings' quality is directly connected to the substrate on
which they are grown. The purpose of this study was to
evaluate how the ‘Swingle’ citrumelo rootstock developed
with different substrate formulations until grafting, to then
develop innovative formulations for citrus nurseries that are
possibly cheaper, more available and mainly, that promote
better seedling development.
2. MATERIALS AND METHODS
The experiment was carried out in a nursery at the School
of Agriculture, Sao Paulo State University (FCA/UNESP) in
Botucatu, State of Sao Paulo, Brazil. The seeds of ‘Swingle’
citrumelo were collected at the Horticulture Department and
sieved under running water before being dried for 48 hours
without the tegument. The experiment was then divided into
two stages: a seedling nursery in tubes (stage 1) and a planting
phase in bags (stage 2).
This study used six mixtures of substrate formulations
that were prepared and supplied by the Carolina Soil®
Company, as follows: 60% peat moss, 30% fine grade
horticultural vermiculite, 10% rice (Oriza sativa) hulls (1); 60%
peat moss (Sphagnum spp), 30% super fine grade
horticultural vermiculite, 10% rice hulls (2); 50% peat moss,
30% fine grade horticultural vermiculite, 20% rice hulls (3);
50% peat moss, 30% super fine grade
horticultural vermiculite, 20% rice hulls (4); 50% peat moss,
20% fine grade horticultural vermiculite, 30% rice hulls (5);
50% peat moss, 20% super fine grade
horticultural vermiculite, 30% rice hulls (6).
Table 1 summarizes the physical parameters of each
moisture-sensitive substrate (Kämpf, 2001): moisture
substrate (Comité Europeén de Normalisation - CEN, 1999);
volumetric density, water retention capacity, porosity and
granulometry (Ministério da Agricultura, Pecuária e
Abastecimento - MAPA, 2008).
Table 1. Total porosity (TP), macroporosity (MA), microporosity (MI), water retention capacity (WRC), volumetric density (VD) and
moisture (M) of various substrate formulations.
Tabela 1. Porosidade total (TP), macroporosidade (MA), microporosidade (MI), capacidade de retenção de água (WRC), densidade
volumétrica (VD) e umidade (MO) das diferentes formulações de substrato.
Substrates1 TP MA MI WRC VD MO
(%) (%) (%) (55 mL cm-3) (Kg m-3) (%)
1 85.4 21.6 63.7 33.1 433.3 68.6
2 72.5 20.1 52.4 27.2 283.3 52.9
3 77.5 33.1 44.3 23.0 253.3 47.9
4 79.9 29.2 50.6 26.3 293.3 51.9
5 80.7 40.1 40.6 21.2 243.3 49.5
6 78.2 35.5 42.7 22.3 240.0 43.5
1: 60% peat moss, 30% vermiculite fine, 10% rice hulls; 2: 60% peat moss, 30% vermiculite super fine, 10% rice hulls; 3: 50% peat moss, 30% vermiculite
fine, 20% rice hulls; 4: 50% peat moss, 30% vermiculite super fine, 20% rice hulls; 5: 50% peat moss, 20% vermiculite fine, 30% rice hulls; 6: 50% peat moss,
20% vermiculite super fine, 30% rice hulls.
Substrate mixing formulations for Citrus nursery management
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502
2.1. Stage 1
Stage 1 began with the filling of 50 cm3 conical plastic
tubes with substrates, followed by planting one seed per tube.
These were placed in polypropylene trays (176 cells) 1 m
above the ground, on concrete benches in a greenhouse with
automated irrigation (i.e. a timer set for 10 minutes twice a
day and a medium irrigation plate of 6 mm). The shading
screen (sombrite) used was 0.87 x 0.30 mm, respectively on
the covering and on the sides.
The experiment was conducted in a completely
randomized design with six treatments consisting of
substrate mixtures, four replicates, with 51 seedlings per
replicate, totalizing 204 seedlings per treatment, utilizing a
split plot layout. The plots consisted of substrate mixtures,
with the subplots representing the evaluation time.
The number of seeds that emerged once a week until 102
days after sowing (DAS) was counted to determine the
emergence percentage of each treatment (MAGUIRE, 1962).
When the plants were about 20 cm tall, (BATAGLIA et
al., 2008), eight plants were randomly selected from each
treatment to assess the following: stem height (cm) that was
measured from the base to the apices of the stem; stem
diameter (mm) that was measured at a height of around 1 cm
above the substrate (mm); leaf number, root and aerial dry
matter were calculated using a traditional drying method
(LACERDA et al., 2009).
2.2. Stage 2
Two months after sowing, the most robust seedlings
from stage 1 were transplanted into polyethylene bags (4 L)
containing the same mixtures of substrates used in the
previous stage. The rootstocks were grown in benches at a
height of about 1 m above ground in a greenhouse and the
fertilizations started with a solution of calcium nitrate (0.8 g
L-1 equivalent to 0.11 g L-1 N + 0,13 g L-1 Ca) + magnesium
sulphate (0.4 g L-1 equivalent to 0,036 g L-1 Mg + 0,044 g L-1
S) + mono ammonium phosphate (0.4 g L-1 equivalent to
0,24 g L-1 P2O5 + 0,05 g L-1 N), potassium chloride (0.4 g L-
1 equivalent to 0,24 g L-1 K) + urea (0.3 g L-1 equivalent to
0,14 g L-1 N) + micronutrients solution was applied (1 g L-1),
according with the recommendations of Bataglia et al., (2008)
and Bremmer Neto et al., (2015) adapted. Once a week, 200
ml of the solution was administered to each bag, for all the
treatments evaluated and according to the recommendations
of Bremmer Neto et al., (2015) adapted. Drainage of
substrate mixtures was minimal.
A solution portion was tested for electrical conductivity
and pH value by using a DIGIMED brand conductivity and
pH meter. Values ranged from CE: 0.52 to 0.63 dS m-1and
pH: 6.02 to 6.71.
Stage 2 was undertaken in a completely randomized
design with four replicates of twenty plants per parcel, using
a split plot design. The plots contained six substrate mixtures,
whereas the subplots represented the evaluation period.
Three plants per replication of each treatment were randomly
gathered every 28 days to obtain a growth curve and examine
the effect of varied mixing amounts on ‘Swingle' citrumelo
development. Thus, measuring stem height and diameter,
number of leaves, root, and aerial dry matter, as well as leaf
area meter - derived using the LI-Cor model LI-3100C in
cm2; and Dickson Quality Index (DQI) (DICKSON et al.,
1960).
Data were subjected to analysis of variance, the mean
between substrates was compared using the Tukey test
(p<0.05) and regression analysis was used to determine the
mean emergence and seedling growth over time. The model
was chosen according to the determination coefficient (R2).
The emergence percentage data was converted according to
equation 1.
arcsin √x/100 (01)
3. RESULTS
3.1. Stage 1
The interaction between substrate mixtures and days after
sowing for seedling emergence was not significant
throughout the emerging stage and early seedling growth,
although there was an isolated influence of the variables.
Substrate 1 stimulated higher seedling emergence than
substrate 2, but not substantially different from 3, 4, 5, and 6
(Figure 1A). At 28 DAS, the seedlings started to emerge. The
seedling emergence rate had a quadratic growth from this
point on, reaching 105 DAS (Figure 1B).
The error bars represent the Tukey test least significant difference (LSD) at a probability
of 5%.
Figure 1. Seedling emergence (%) of ‘Swingle’ citrumelo rootstock
as a function of substrates (A) and days after sowing (DAS) (B).
FCA/UNESP. Botucatu, 2017.
Figura 1: Porcentagem de emergência do porta-enxerto citrumeleiro
‘Swingle’ em função das formulações dos substratos (A) e dias
depois da semeadura (DAS) (B). FCA/UNESP. Botucatu, 2017.
When plants were examined till the transplanting period
(stage 1), the only variation between the substrate
combinations was the aerial and root dry matter (Table 2).
Substrates 4 and 5, which differed only from substrate 6,
yielded the highest root dry matter. Substrate 5 had the
highest aerial dry matter, while substrates 3 and 6 had lower
values (Table 2).
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503
Table 2. Height (H), diameter (D), leaf number (LN), root dry matter (RM) and aerial dry matter (AM) of ‘Swingle’ citrumelo rootstocks
with substrates in proportions till transplanting time. FCA/UNESP. Botucatu, 2017.
Tabela 2: Altura (H), diâmetro (D), número de folhas (LN), matéria seca de raízes (RM) e matéria seca da parte aérea (AM) do porta-enxerto
citrumeleiro ‘Swingle’ em função das formulações de substrato até o período de transplantio.
Substrates1 H D LN RM AM
(cm) (mm) (mg/cm3) (mg/cm3)
1 21.83a 1.90a 15.00a 0.11ab 0.37ab
2 21.46a 1.91a 11.38a 0.12ab 0.36ab
3 20.61a 1.94a 10.38a 0.10ab 0.31b
4 22.08a 2.14a 12.75a 0.13a 0.39ab
5 22.36a 2.28a 15.38a 0.15a 0.47a
6 20.93a 1.96a 12.50a 0.08b 0.27b
CV (%) 5.02 9.07 20.30 20.93 22.62
DMS 2.43 0.41 5.88 0.05 0.18
Tukey test results show that means preceded by the same letter do not differ by 5% probability.
The error bars represent the Tukey test least significant difference (LSD) at a probability
of 5%.
Figure 2. Stem diameter (A) and seedling height (B) of ‘Swingle’
citrumelo in various mixes of subtracts, as a function of days after
transplanting. Botucatu-SP, 2017.
Figura 2: Diâmetro de caule (A) e altura de muda (B) do porta-
enxerto citrumeleiro ‘Swingle’ em diferentes formulações de
substratos em função dos dias após o transplantio. Botucatu-SP,
2017.
The error bars represent the Tukey test's least significant difference (LSD) at a probability
of 5%.
Figure 3. Leaves per seedling (A) and leaf area (B) of ‘Swingle’
citrumelo rootstock in various mixes of subtracts, as a function of
days after transplanting. Botucatu-SP, 2017.
Figura 3: Folhas por mudas (A) e área foliar (B) do porta-enxerto
citrumeleiro ‘Swingle’ em diferentes formulações de substratos. Em
função dos dias após o transplantio.
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3.1. Stage 2
The relationship between substrates and days after
transplanting was significant for all variables in the second
stage of rootstock development. Until 112 days after
transplanting (DAT), the substrates did not induce variations
in stem diameter, leaf number, or root dry matter across
plants (Figures 2A, 3A and 4A). Only 84 DAT had a substrate
influence on height, aerial dry matter, and leaf area (Figures
2B, 3B and 4B).
Larger stem diameters were encouraged by substrates 1,
2, 3, and 4, which increased linearly up to 168 DAT (Figure
2A). Stem diameter is a critical variable since it determines
the optimal time for grafting (i.e. 8 mm in diameter) and, as
a result, seedling precocity. At 168 DAT, that criterion was
not attained in treatments 5 and 6. At 168 DAT, the
substrates with 30% rice hulls produced plants with a 26.98%
lower stem diameter than the others. Therefore, the seedlings
grown on these substrates (5 and 6) could not be grafted at
this time. After 112 DAT, the increase in stem diameter
halted on these substrates (Figure 2A).
Error bars correspond to the least significant difference (LSD) obtained by Tukey test at
5% probability.
Figure 4. Root (A) and aerial (B) dry matter of ‘Swingle’ citrumelo
rootstock in various mixes of subtracts, as a function of days after
transplanting. Botucatu-SP, 2017.
Figura 4: Massa seca da raiz (A) e aérea (B) do porta-enxerto
citrumeleiro ‘Swingle’ em diferentes formulações de substratos em
função dos dias após o transplante. Botucatu, 2017.
Moreover, height, leaf number, leaf area, root and aerial
dry matter, and Dickson Quality Index (DQI) showed a
quadratic increase as a function of DAT on the substrates.
At 168 DAT, the rootstocks in substrate 4 had grown to
a height of 102.68 cm. When compared to the others,
substrates 1 and 2 promoted intermediate vegetative growth,
with no difference between them. Substrates 5 and 6
exhibited lower height from 84 to 168 DAT (Figure 2B).
In all substrates, the number of leaves per seedling
increased more between 140 and 168 DAT. Seedlings from
substrate 5 had more leaves at the ending of the evaluation
period, whereas those from substrate 4 had the lowest
average (Figure 3A). Meanwhile, rootstocks grown in
substrate 1 had a greater leaf area at 168 DAT, indicating that
their leaves were larger (Figure 3B). This might be due to the
substrate's increased moisture holding capability (Table 1).
The leaves of the seedlings from substrates 5 and 6 are
already smaller, despite their abundance, because of their
reduced leaf area (Figure 3B).
Plants grown in substrates 1, 2, 3, and 4 performed better
than those grown in the other treatments, accumulating more
dry roots matter at 140 and 168 DAT, respectively (Figure
4A). Their physical differences can explain this finding.
Higher aerial dry matter was also promoted by these
substrates. When the first seedlings reached grafting stage
(168 DAT), it was discovered that substrate 4 outperformed
the others in terms of aerial dry matter, weighing 18.92 g,
while substrates 5 and 6 weighed 9.61 g and 9.42 g,
respectively (Figure 4B).
Higher DQI was possible with substrates 1, 2, 3, and 4
that showed high averages at 168 DAT (Figure 5). The DQI
enables for accurate selection since it combines important
parameters (such as bud and root dry matter, stem height and
diameter) into one marker (DIAS et al., 2012). In the same
time frame, the DQI of seedlings from substrates 5 and 6 was
28.49 percent lower (Figure 5). Figure 6 depicts the growth
of seedlings derived from each of the substrates.
The error bars represent the Tukey test least significant difference (LSD) at a probability
of 5%.
Figure 5. Dickson Quality Index (DQI) of ‘Swingle’ citrumelo
rootstock in various mixes of subtracts, as a function of days after
transplanting. Botucatu-SP, 2017.
Figura 5. Índice de Qualidade Dickson (DQI) do porta-enxerto
citrumeleiro ‘Swingle’ em diferentes formulações de substratos em
função dos dias após o transplante. Botucatu-SP, 2017.
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505
1: 60% peat moss, 30% vermiculite fine, 10% rice hulls; 2: 60% peat moss,
30% vermiculite super fine, 10% rice hulls; 3: 50% peat moss, 30%
vermiculite fine, 20% rice hulls; 4: 50% peat moss, 30% vermiculite super
fine, 20% rice hulls; 5: 50% peat moss, 20% vermiculite fine, 30% rice hulls;
6: 50% peat moss, 20% vermiculite super fine, 30% rice hulls.
Figure 6: ‘Swingle’ citrumelo seedlings grown on various substrates.
Figura 6. Mudas de citrumeleiro ‘Swingle’ produzidas em diferentes
substratos.
4. DISCUSSION
The substrate mixtures evaluated only presented effects
after 84 DAT. This can be explained by roots acclimating to
new plastic bags as well as increased substrate volume
exposing roots.
The increased density, porosity, and water retention of
substrate 1 (Table 1) encouraged an acceptable balance
between water and O2, allowing for improved seedling
emergence throughout the initial stage of seedling
production. On the other hand, substrate 2 had the lowest
overall porosity and water retention among the examined
substrates. Higher micro porosity in substrates is reported to
hinder seed germination and root aeration by Fernandes et al.
(2006); however, this was not found in our study. Therefore,
we should bear in mind that the percentage of different
component groups and the combination type must be
created with the adequacy of the physical characteristics,
according to Kratz et al. (2013). Chemistries may be modified
with fertilization and irrigation management methods.
Substrates 1, 2, 3, and 4 allowed the development of more
robust seedlings in stage 2. When opposed to 5 and 6, these
substrates stand out because of the reduced proportion of
rice hulls. The irrigation levels were the same for all
treatments and could explain the worst performance of
treatments 5 and 6. This hypothesis can be attributed to lower
water availability due to higher percentages of rice hulls. The
results allow us to suggest that there was a possible hydric
stress in treatments 5 and 6 and that if there had been a
greater frequency of irrigation on these substrates mixtures,
their performance could have been better. However,
according to per manufacture information in substrates
mixtures evaluated it was used roasted rice hull, in which the
material undergoes a high temperature process followed by
cooling for maintaining the structure of the particles. The
method used is a differential, as it maintains the
characteristics of the size of the rice hulls particles, which can
influence the drainage properties in the substrate, in addition
to reducing the tendency to break during the transport
process.
Schäfer et al. (2008) found that lower volumetric density
substrates increased macro porosity of mixtures and lowered
substrate water retention capacity and the need for
specialized fertilization and irrigation. The poorer
performance of seedlings in substrates 5 and 6 can be
explained by the fact that the rice hulls supplied more macro
porosity to these substrates and consequently, the lowest
humidity percentage and water retention (Table 1).
The presence of a higher percentage of rice hulls (material
with higher porosity) can be advantageous for the aeration of
the root development, but at the same time, worrying due to
the deficiency in retaining water, since the smaller pores are
responsible for the function.
The pores oversee gas exchange in the quest for a balance
between substrate and surrounding atmosphere, besides
determining water flow in the container (BRITO et al., 2012).
The presence of a larger proportion of rice hulls (a substance
with a higher porosity) might be beneficial for aeration of the
root environment, but it can also be concerning owing to a
lack of water retention, as the smaller pores are important for
this function.
When rice hulls are used in significant numbers, they can
cause water shortages in plants, especially if irrigation is done
infrequently (REZENDE et al., 2010). As a result, it is
recommended to combine it with high micro porosity
elements, such as vermiculite.
The size and arrangement of the particles determine the
physical properties of a substrate; high proportions of larger
fractions enhance aeration space, while smaller particles
minimize void spaces in rice hulls; thus, increasing micro
porosity and, consequently, decreasing macro porosity.
Seedlings on substrates 1, 2, 3, and 4 may have more leaf
area due to their better moisture retention ability, as water is
a vital component in cell growth. Leaf area is an excellent
indication of production, according to Taiz et al. (2017),
because leaf area and photosynthetic efficiency are closely
related. Plants can also influence variations in radiation
interception, resulting in increased gas exchange efficiency.
The substrates that supported larger accumulation of
shoot dry matter also offered root system growth, indicating
that the seedlings were growing in a balanced manner
(FONSECA et al., 2002). The differences in dry matter
accumulation in the aerial part and in the root system
observed between substrates can be explained as dry matter
accumulation is the best indicator of plant growth, since it is
less variable than fresh matter, which can vary throughout the
day due to a variety of factors, such as temperature and the
amount of water available to plants (MARTÍNEZ, 2002;
MERLIN et al., 2012). Plant photosynthesis has a significant
impact on dry matter development. Thus, greater
accumulation indicates improved physiological performance.
After 112 days, the differences arising from the usage of
different substrate mixtures were noticeable. The least
interference occurs at the start of this phase due to
transplanting to larger bags, when plants have most likely
experienced environmental changes and need time to restore
reserves for growth. The restricted capacity of container and
substrate fertility impact plant development in plastic bags
(MOURÃO FILHO et al., 1998). This fertility depends on
substrate components, and cover fertilizers are generally
required to boost fertility (DECARLOS NETO et al., 2002).
5. CONCLUSIONS
All substrates supported greater seedling emergence,
apart from the substrate comprising 60% peat moss, 30%
fine vermiculite, and 10% rice hulls. Most substrate
formulations allowed for the generation of superior quality
seedlings, except for substrates containing 30% rice hulls,
Substrate mixing formulations for Citrus nursery management
Nativa, Sinop, v. 9, n. 5, p. 500-507, 2021.
506
which produced seedlings with lower development and
cannot be recommended for ‘Swingle’ citrumelo rootstock
seedlings.
6. AKNOWLEDGEMENT
The Brazilian National Council for Scientific and
Technological Development funded this study (CNPq
#304455/2017-2).
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