Effect of Humic Acid on Growth and Productivity of Tomato Plants Under Heat Stress

Abstract

The purpose of this study was to evaluate the effect of humic acid (HA) applied at 4.8, 9.6 and 14.4 kg·ha⁻¹ on the growth and productivity of two tomato hybrids Nema 1400 and Platinium 5043 under hot continental climate. HA was applied twice to soil: the first one – three weeks from transplanting and the second one, after one week from the first application, in both seasons. Application of HA during the summer season targeted a great results on tomato plant growth and productivity. HA at 14.4 kg·ha⁻¹ in-creased the vegetative growth of tomatoes (plant height and fresh weight) and flowering parameters (number of flower clusters and flowers per plant) as well as yield characters (fruit number per plant and fruit weight, which resulted in higher early and total yield) in both seasons. HA application had the least impact on fruit number per plant, and on vitamin C and total soluble solids (TSS) concentration as compared with control.

Full text

Journal of Horticultural Research 2017, vol. 25(2): 59-66
DOI: 10.1515/johr-2017-0022
_______________________________________________________________________________________________________
*Corresponding author:
e-mail: islam_abdellatif@mu.edu.eg
EFFECT OF HUMIC ACID ON GROWTH
AND PRODUCTIVITY OF TOMATO PLANTS UNDER HEAT STRESS
Islam Mohamed Yassin ABDELLATIF*, Youssef Youssef ABDEL-ATI,
Yousry Tammam ABDEL-MAGEED, Mohamed Abdel-moneim Mohamed HASSAN
Horticulture Department, Faculty of Agriculture, Minia University
61111 El-Minia, Egypt
Received: June 2017; Accepted: December 2017
ABSTRACT
The purpose of this study was to evaluate the effect of humic acid (HA) applied at 4.8, 9.6 and
14.4 kg·ha-1 on the growth and productivity of two tomato hybrids Nema 1400 and Platinium 5043 under
hot continental climate. HA was applied twice to soil: the first one – three weeks from transplanting and
the second one, after one week from the first application, in both seasons. Application of HA during the
summer season targeted a great results on tomato plant growth and productivity. HA at 14.4 kg·ha-1 in-
creased the vegetative growth of tomatoes (plant height and fresh weight) and flowering parameters (num-
ber of flower clusters and flowers per plant) as well as yield characters (fruit number per plant and fruit weight,
which resulted in higher early and total yield) in both seasons. HA application had the least impact on fruit
number per plant, and on vitamin C and total soluble solids (TSS) concentration as compared with control.
Key words: tomato, humic acid, heat stress, abiotic stress
INTRODUCTION
Today, the world faces dangerous problems
which affected on human life headed by agriculture
and food security. One of these problems is environ-
mental changes and abiotic stresses that affects
plant growth, development, and productivity.
Tomato (Solanum lycopersicum L.) is one of
the major crops grown all over the world. According
to FAO (2016), tomato occupies the first rank
among the cultivated area of all vegetable crops in
Egypt.
The major challenge in tomato cultivation is
heat stress responses (Abdul-Baki 1991). The opti-
mum temperature for tomato growing ranges from
21 to 24 ºC, and temperature above 24 ºC will grad-
ually decrease the productivity with the death level
at 35 ºC. According to Srinivasa Rao et al. (2016),
high temperature is an important factor for growing
tomato because of its effects on all stages of tomato
plant from vegetative to reproductive phases.
Humic acid (HA) is a heterogeneous mixture
of many compounds, a mixture of weak aliphatic
and aromatic organic acids, which are not soluble in
water under acid conditions but are soluble in water
under alkaline conditions (Cacco & Dell’Agnolla
1984; Pettit 2004) that influences variously plant
growth and soil traits (Tan 2003). HA is produced
commercially and intended for organic fertilization.
Its components improve soil fertility and increase
nutrients availability, enhance plant growth, yield,
and decrease the harmful effect of stresses through
various mechanisms inside plants and soil (Rajaei
2010; Unlu et al. 2011; Moraditochaee 2012). In this
study, we evaluated the effect of HA on solving to-
mato challenges to high temperature during summer
season.
MATERIALS AND METHODS
This investigation was carried out during the
two successive summer seasons of 2014 and 2015
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60 I.M.Y. Abdellatif et al.
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at the Farm of Minia University, under hot continen-
tal climate (Table 1). Two tomato hybrids Nema
1400 and Platinium 5043 were selected for this
study and grown in a clay loam soil. CANADA
HUMEX, commercial product containing 68% HA,
15% fulvic acids, 10% potassium, 5% nitrogen, 1%
iron, 0.5% manganese, and 0.5% zinc was used at
four concentrations (0, 4.8, 9.6 and 14.4 kg·ha-1). It
was melted in water and added to soil by pouring
the solution immediately after irrigation. The treat-
ment was repeated twice, the first one – after three
weeks from transplanting and the second one, after
one week from the first application, in both seasons.
In addition, a typical fertilization contained
60 m3·ha-1 organic fertilizer and 960 kg·ha-1 super
phosphate calcium, 240 kg·ha-1 potassium sulfate,
480 kg·ha-1 ammonium sulfate, 240 kg·ha-1 sulfur,
60 kg·ha-1 iron sulfate, 60 kg·ha-1 magnesium sul-
fate, 60 kg·ha-1 zinc sulfate, and 60 kg·ha-1 manga-
nese sulfate was applied.
Records for medium temperature and relative
humidity percentage obtained from Malawy Mete-
orological Station, about 52 km away from the ex-
periment location, are presented in Table 1. Data ob-
tained as daily records and summarized as average
of 15-day intervals.
Complete Randomized Blocks design in
a split-plot arrangement with three replicates was
used in each season. Main plots were assigned to
genotypes, while the subplots were allocated to the
HA levels. Each plot area was 14.40 m2 with three
rows; each one was 4-m long and 120 cm in width.
Transplanting was done on one side of each strip
with 40-cm intra-rows spacing between two hill-
ocks with one plant/hillock.
Studied characteristics
Plant height (cm), fresh weight of plant without
roots and fruits (g), and number of flower clusters
and flowers per plant were recorded at the full
blooming stage (after 55 days from transplanting)
by randomly taking three plants from each treat-
ment, while, early and total yield per hectare (ton)
as well as average number of fruits per plant were
determined during the harvest periods. Fruits were
picked six times, the first three were considered as
an early yield. On the third picking, 10 ripe fruits
were randomly taken from each plot to record the
average fruit weight (g) as well as vitamin C con-
centration (mg·100 g-1), which was determined by
using 2,4-dichlorophenol-indophenol dye according
to A.O.A.C. (2000), and total soluble solids (TSS)
percentage in the juice of fruits which was deter-
mined by using hand refractometer on the juice of
ten ripe fruits after blending for 1–2 minutes.
Data were statistically analyzed with the help
of MSTAT-C program to find out the statistical sig-
nificance of the experimental results separately for
each year of the experiment. The mean values of all
parameters were separated by Duncan's multiple
range test at 5% probability.
Table 1. Records for medium temperature and relative humidity percentage obtained from Malawy Meteorological
Station, far about 52 Km from the experiment location. Data obtained as daily records and summarized as average of
15 day intervals
Months
Days
Seasons
2014
2015
medium
temp. (°C)
humidity
(%)
medium
temp. (°C)
humidity
(%)
April
1-15
24.56
53.20
21.69
61.93
16-30
24.88
46.80
23.23
55.60
May
1-15
27.02
43.93
26.70
55.87
16-30
27.30
43.0
30.63
46.93
June
1-15
29.17
45.73
30.61
75.33
16-30
29.42
53.93
31.19
46.20
July
1-15
28.87
57.07
31.71
57.20
16-30
29.06
59.67
32.96
53.93
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Influence of humic acid on tomato plants 61
____________________________________________________________________________________________________________________
0
5
10
15
20
25
30
35
40
45
0 4.8 9.6 14.4
0
20
40
60
80
100
120
140
160
180
200
0 4.8 9.6 14.4
Fig. 1. The effect of humic acid (zero, 4.8, 9.6 and 14.4 kg ha-1) on plant height (cm) and fresh weight of aerial plant parts (g) of
two tomato hybrids Nema 1400 and Platinium 5043 during the summer seasons of 2014 and 2015
Fig. 2. The effect of four levels of humic acid preparation (control, 4.8, 9.6, and 14.4 kg·ha-1) on number of flower clusters and
flowers/plant of two tomato hybrids (Nema 1400 and Platinium 5043) during the summer seasons of 2014 and 2015
Plant height (cm)
F.W. of aerial parts of
plant (g)
season (2014)
st
1
season (2014)
nd
2
0
10
20
30
40
50
60
70
80
90
0 4.8 9.6 14.4
B
a
d
cd
b-d
ab
a-d
a-d
a-c
0
10
20
30
40
50
60
70
80
90
0 4.8 9.6 14.4
A
cd
cd
d
cd
a
a-c
ab
bc
0
200
400
600
800
1000
0 4.8 9.6 14.4
a
C
b
bc
d
d
d
d
cd
0
200
400
600
800
1000
0 4.8 9.6 14.4
D
a
b
b
d
d
c
cd
c
1-
Humic acid kg ha
1-
Humic acid kg ha
Hybrid Nema 1400
Hybrid Platinium 5043
season (2014)
st
1
season (2014)
nd
2
0
5
10
15
20
25
30
35
40
45
0 4.8 9.6 14.4
0
20
40
60
80
100
120
140
160
180
200
0 4.8 9.6 14.4
B
d
d
b
cd
bc
ab
bc
a
ab
cd
a
bc
a
ab
d
d
No. of flower clusters
D
a
b
a
C
b-d
ab
c
c
c
a-c
e
e
de
cd
d
c
No. of flowers
d
1-
Humic acid kg ha
1-
Humic acid kg ha
Hybrid Nema 1400
Hybrid Platinium 5043
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62 I.M.Y. Abdellatif et al.
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Fig. 3. The effect of four levels of humic acid preparation (control, 4.8, 9.6, and 14.4 kg·ha-1) on early and total yield·ha-1 (ton) of
two tomato hybrids (Nema 1400 and Platinium 5043) during the summer seasons of 2014 and 2015
Fig. 4. The effect of four levels of humic acid preparation (control, 4.8, 9.6, and 14.4 kg·ha-1) on average fruits number/plant and
average fruit weight (g) of two tomato hybrids (Nema 1400 and Platinium 5043) during the summer seasons of 2014 and 2015
0
5
10
15
20
25
30
a
c
b
d
c
e
ff
0 4.8 9.6 14.4
0
5
10
15
20
25
30
a
b
cd
bc
d
d
a
b
0
5
10
15
20
25
c
bc
b
a
d
e
f
f
0
5
10
15
20
25
dd
a
b
b
b
c
e
0 4.8 9.6 14.4
season (2014)
st
1
season (2015)
nd
2
B
D
Early yield/ha (ton)
C
1-
Humic acid kg ha
1-
Humic acid kg ha
Hybrid Nema 1400
Hybrid Platinium 5043
Total yield/ha (ton)
A
0 4.8 9.6 14.4
0 4.8 9.6 14.4
0
20
40
60
80
100
120
140
ab
d
a
d
b
e
e
c
0
20
40
60
80
100
120
140
a
ab
d
d
b
d
c
d
0
10
20
30
40
50
60
b
a
b
a
b
a
b
a
0
10
20
30
40
50
60
b
c
c
a
c
ab
c
b
B
Average fruits No./plant
C
D
Average fruit weight
1-
Humic acid kg ha
Hybrid Nema 1400
Hybrid Platinium 5043
A
)season (2014
st
1
season (2015)
nd
2
0 4.8 9.6 14.4
0 4.8 9.6 14.4
0 4.8 9.6 14.4
0 4.8 9.6 14.4
1-
Humic acid kg ha
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Influence of humic acid on tomato plants 63
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Fig. 5. The effect of four levels of humic acid preparation (control, 4.8, 9.6, and 14.4 kg·ha-1) on vitamin C (mg·100 g-1) and
TSS (%) of two tomato hybrids (Nema 1400 and Platinium 5043) during the summer seasons of 2014 and 2015
RESULTS
Plant height (cm) and fresh weight of plants (g)
In the both hybrids, the highest plants were obtained
when HA was applied at 14.4 kg·ha-1 and they sig-
nificantly differed from control in both seasons (Fig.
1A, B).
The application of HA at 9.6 and 14.4 kg·ha-1
significantly increased the fresh weight of plants as
compared with control in both seasons. The highest
fresh weight was recorded when 14.4 kg·ha-1 of HA
was applied in both hybrids and seasons (Fig. 1C, D).
Number of flower clusters and flowers per plant
Both tomato hybrids reacted for all levels of HA
with increasing number of flowers per cluster and
general number of flowers per plant as compared
with control in both the seasons (Fig. 2A, B, C, D),
with the highest values for levels 9.6 and 14.4 kg·ha-1.
Early and total yield per hectare (ton)
Early yield in hybrid Nemo 1400, higher in compar-
ison with control, was obtained with HA at 9.6 and
14.4 kg·ha-1, respectively, in the first year and at the
three levels in the second year of experiment (Fig.
3A, B), whereas in hybrid Platinium 5043, all levels
of HA increased early yield. Also total yield of fruits
was significantly higher after applying HA and in-
creased with the increase in HA level (Fig. 3C, D).
Number of fruits per plant and fruit weight (g)
The average number of fruits in hybrid Nema 1400
was higher only with HA at 14.4 kg·ha-1 in the first
season, whereas in the second season and in hybrid
Platinium 5043, this trait was not affected by HA
(Fig. 4A, B). The average fruit weight of hybrid
Nema 1400 was not affected with HA application in
the first year, but in the second year, it was increased
at 9.6 and 14.4 kg·ha-1 HA. The hybrid Platinium
5043 increased fruit weight at each level of HA in
the both years (Fig. 4C, D).
Vitamin C and TSS
HA application did not affect the mean vitamin C
concentration in both hybrids as compared with
control in both seasons except for 9.6 kg·ha-1 in hy-
brid Platinium 5043 in the second year (Fig. 5A, B).
Also the TSS concentration did not change in the
season (2014)
st
1
season (2015)
nd
2
0
5
10
15
20
25
30
35
40
a
aa
a
a
a
a
a
0 4.8 9.6 14.4
0
5
10
15
20
25
30
35
40
a-c
a-c
ab
a
bc
a
a
c
0 4.8 9.6 14.4
)
1-
g 100·
Vit. C (mg
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
ab
abab
ab
a
a
b
ab
0 4.8 9.6 14.4
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
ab
b
ab
ab
ab
ab
ab
a
0 4.8 9.6 14.4
T.SS (%)
B
C
Hybrid Nema 1400
Hybrid Platinium 5043
A
1-
Humic acid kg ha
1-
Humic acid kg ha
D
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64 I.M.Y. Abdellatif et al.
_______________________________________________________________________________________________________
first year, and in the second year, it increased in hy-
brid Platinium 5043 when 4.8 kg·ha-1 of HA was ap-
plied (Fig. 5C, D).
DISCUSSION
According to several reports, HA significantly
increased the plant height of tomato (Kazemi 2013,
2014; Farnia & Moradi 2015), fresh weight of tomato
(Abdel-Monaim et al. 2012), and number of flowers
of tomato (Kazemi 2014), as well as early fruit yield
of tomato (Yildirim 2007) and pepper plants (Kara-
kurt et al. 2009) and total yield of tomato (Abdel-
Monaim et al. 2012; Aman & Rab 2013; Kazemi
2013, 2014; Asri et al. 2015; Farnia & Moradi 2015).
The reasons behind this increment are connected
with each other. Also, several studies have shown
that HA has the ability to decrease the harmful effect
of stressors on plants (Ozkutlu et al. 2006; Rajaei
2010; Unlu et al. 2011; Moraditochaee 2012) and in
soils (Baldotto et al. 2010). In our experiments, HA
similarly positively influenced the growth and yield
parameters of two tomato hybrid cultivars.
HA plays important roles on plants through
stimulation of root growth and increase of water and
nutrient uptake by vegetable crops (Cimrin & Yil-
maz 2005). It can also influence the cell division
(Chen et al. 2004) and enhance protein synthesis
(El-Ghamry et al. 2009; Patil 2010), which result in
enhancing total protein content in plants (Nardi et
al. 2002). HA also provides growth regulators to
regulate and control hormone levels in plants (Nardi
et al. 2002) and stimulates production of plant en-
zymes and hormones (Sarir et al. 2005; Mart 2007).
It also increases enzyme catalysis and enhances res-
piration and photosynthesis processes (Nardi et al.
2002; Nardi et al. 2002). These mechanisms refer to
the direct influence of HA on plants and its influ-
ence on soil fertility is also very important (Nardi et
al. 2002; Fahramand et al. 2014). It happens through
the improvement of soil physical (Varanini & Pin-
ton 1995; Nardi et al. 2002), chemical, and biologi-
cal properties (Keeling et al. 2003; Mikkelsen 2005)
that increase water holding capacity (McDonnell et
al. 2001). Furthermore, it is a good source of energy
for beneficial soil organisms (Chen et al. 2004; Pet-
tit 2004; Zimmer 2004) by stimulating the enzyme
activities (Burkowska & Donderski 2007). HA is
used for soil reclamation purposes (Baldotto et al.
2010; Mauromicale et al. 2011; Khaled & Fawy
2011; Ameri & Tehranifar 2012).
I it can be concluded that HA added to the soil
for growing tomatoes under hot continental climate
in the amount of 9.6 and 14.4 kg·ha-1 can increase
the yield, both early and total.
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