ABSTRACT Consequently, the application of 1.5-3 mgL -1 humic acid is recommended in hydroponic culturing of strawberry

Abdolhossein Aboutalebi

Farima Yosefi

Mehdi Dastyaran

Mehdi Hosseini Farahi

Saeid Eshghi

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AGRICULTURAL COMMUNICATIONS, 2013, 1(1): 13-16. 
 
   
 
 
Foliar Application of Humic Acid on Quantitative and Qualitative 
Characteristics of Aromas Strawberry in Soilless Culture. 
 
MEHDI HOSSEINI FARAHI1*, ABDOLHOSSEIN ABOUTALEBI2, SAEID ESHGHI3, MEHDI DASTYARAN4 and 
FARIMA YOSEFI1 
1Department of Agriculture, Yasouj Branch, Islamic Azad University, Yasouj, Iran. 
2Department of Horticulture, Jahroom Branch, Islamic Azad University, Jahroom, Iran. 
3Departments of Horticulture, College of Agriculture, Shiraz University, Shiraz, Iran. 
4Young Researchers Club, Yasooj Branch, Islamic Azad University, Yasooj, Iran. 
*Corresponding Author.                  (Accepted: 20 August 2013) 
 
 
ABSTRACT 
In order to evaluate the effect of humic acid on quantitative and qualitative characteristics of 
strawberry (Fragaria ananasa c.v Aromas), an experiment was conducted as factorial arrangement in 
randomized complete block design with three replications in a commercial hydroponic greenhouse. 
The rooted daughter plants of Aromas strawberry were planted in pots containing perlite and coco-
peat (1:1). Humic acid were sprayed on the plants when they were completely established. The 
treatments consisted of different concentrations of humic acid (Greenhum containing 13% humic 
acid) (0, 1.5, 3.0 and 4.5 mgL-1). Certain traits were measured including leaf chlorophyll index; the 
weight, length, width and length/width ratio of the fruits; number of fruit in plant; yield of single plant 
in a 2months period; malformed fruit percent; total soluble solid percent and fruit firmness. Results 
indicated that the application of humic acid had positive influence on fruit number, total yield of plant, 
TSS, fruit firmness and chlorophyll content. Generally, foliar application of humic acid led to the 
improvement of quantitative and qualitative characteristics of this cultivar of strawberry. 
Consequently, the application of 1.5-3 mgL-1 humic acid is recommended in hydroponic culturing of 
strawberry. 
 
Keywords: chlorophyll content, Fragaria ananasa, fruit quality, nutrition, single plant yield. 
 
Abbreviations:  
TSS: Total soluble solid. 
 
INTRODUCTION 
Today, greenhouse cultivation of strawberry as 
hydroponic is strongly increasing; nevertheless, in 
the course of its producing some problems loom up 
such as low yield, low quality, unsuitable fruit 
formation as well as susceptibility to unfavorable 
environmental conditions. Strawberry has various 
compositions, which has high nutritional value. 
Due to the high nutritional value and progress in 
greenhouse cultivation of strawberry in Iran, it 
seems mandatory on the part of the researches to 
improve its quality and quantity.  
Humic compounds are the most abundant of the 
complex ligands, which are found in nature. In this 
regard, it is well known that the humic compounds 
improve soil structure, increase soil microbial 
population, increase soil cation exchange capacity 
and providing some specific materials for plant 
root indirectly by providing macro and micro 
minerals, leading to the increase of soil fertility. 
The humic compounds are divided into three 
categories: humic acids, fulvic acids and humans 
(Tan, 2003).  
Humic acid effectively improves soil fertility 
and crop production especially in poor soils and 
alkaline-calcareous soils (Rajpar et al., 2011). The 
humic acid based on fertilizers causes yield 
increase (Mohamed et al., 2009), simulation of 
plant enzymes and hormones and soil fertility 
(Sarir et al., 2005; Mart, 2007). Several research 
works have been prominently shown the positive 
benefits of application of humic acid on higher 
plants (Ashraf et al., 2005; Susilawati et al., 2009; 
Mackowiak et al., 2001). In a study, application of 
compost and humic acid caused to increase total 
yield of strawberry significantly in comparison 
with the mineral fertilizers (Shehata et al., 2011). 
Zaki et al. (2006) observed the enhancement of 
shoot number in the plants, leaf area, total yield, 
fresh weight and phosphorus amount by 
application of 1 gL-1 humic acid as foliar 
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AGRICULTURAL COMMUNICATIONS.   
14 
 
application. In a research, all morphological traits 
such as plant height, number of leaf and stem in 
plant, fresh weight of leaf, yield and yield 
components of cucumber showed effective 
influences in response to high concentration of 
humic acid (3 gL-1) and Ecormon (0.45 cmL-1) in 
comparison with other treatments.  
Foliar application of humic acid and bio-
stimulators led to positive effects on plant growth, 
fruit set and improvement of cucumber production 
(El-Nemr et al., 2012).In the same line, this study 
aimed to investigate the effects of humic acid on 
quantitative and qualitative characteristics of 
strawberry.  
 
MATERIALS AND METHODS 
Plant Material: 
This experiment was carried out in a 
commercial greenhouse for strawberry growing 
with soilless culturing system (hydroponic) located 
in Yasouj, Nargah village in 2012. The rooted 
daughter plants of strawberry c.v Aromas were 
purchased from a commercial grower and cultured 
in the pots containing Perlite and Coco-peat (1:1).  
Treatment: 
The treatments were sprayed on the plants 
when they were completely established. The 
treatments consisted of humic acid 0, 1.5, 3.0 and 
4.5 gL-1 (Greenhum containing 13% humic acid). 
Before spraying, all flowers and fruits were 
eliminated from plants until the treatments effect 
was well known. In order to increase contact, a few 
drops Tween20 were added to the area of solution 
and leaves. For maximum absorption, foliar 
spraying was done in the morning when air was 
cooler. Program of plant nutrition was separately 
performed in vegetative and generative stages. 
Irrigation and nutrition of the plants were daily 
conducted once a day. For preparation of nutritive 
solutions the ozone water was used an hour-
worked and preserved for 12 hours. Also 150 ml 
nitric acid was added to nutritive solutions.  
Quantitative and Qualitative Characteristics: 
Chlorophyll index of leaf was measured by 
SPAD-502 (Minolta, Japan). Fruit weight was 
measured by digital scales and fruit length and 
wide by using digital caliper. Total weight of the 
produced fruits from each plant (2 months period) 
was calculated. Total soluble solid (TSS) was 
measured by manual refractometer (Atago, Japan) 
and fruit firmness by using Texture analyzer 
device.  
Data Analysis: 
Data was analyzed by using SAS software and 
the means were compared by Duncans multiple 
range test (DMRT) and the charts were drawn by 
Excel software.  
 
 
 
RESULTS 
Effect of Humic Acid on Fruit Number: 
The obtained results indicated that application 
of humic acid increased fruit number of Strawberry 
c.v Aromas. The results in Fig. 1 show that 
application of 3 gL-1 humic acid led to the increase 
in fruit number in comparison with the untreated 
plants.    
 
 
Fig 1. Effect of humic acid on fruit number. 
 
Effect of Humic Acid on Plant Yield: 
Due to the findings, the sprayed plants with 
different levels of humic acid produced more yield 
in comparison with the untreated plants. The 
presented results in Fig. 2 showed that application 
of 3 gL-1 humic acid increased single plant yield 
(126.5 g) in a two-month period. Also the results 
revealed that the concentrations more than 3 gL-1 
humic acids decreases single plant yield.    
 
 
Fig 2. Effect of humic acid on single plant yield. 
 
Effect of Humic Acid on Leaf Chlorophyll Index: 
Results demonstrated that chlorophyll index in 
the leaves of the sprayed strawberry plants by 
different concentrations of humic acid was more 
than the untreated plants. The presented results in 
Fig. 3 showed that the highest and the lowest 
amount of leaf chlorophyll index were observed in 
the sprayed plants by 4.5 gL-1 humic acid and 
control treatments respectively.  
 
 
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  HOSSEINI FARAHI ET AL. 
15 
 
Effect of Humic Acid on Fruit Firmness: 
Application of 1.5 gL-1 humic acid produced 
firmer fruits than other treatments. Fruit firmness 
decreased by increasing humic acid concentration. 
The revealed results in Fig. 4 indicated that the 
highest and the lowest fruit firmness obtained from 
the sprayed plants by 1.5 and 4.5 gL-1 humic acid 
treatments respectively.  
 
 
Fig 3. Effect of humic acid on Chlorophyll index. 
 
 
Fig 4. Effect of humic acid on fruit firmness. 
 
Effect of Humic Acid on TSS: 
Application of humic acid increased TSS amount 
in strawberry fruits. The highest TSS was observed 
in 1.5 and 3.0 gL-1 humic acid treatments. TSS 
decreased by increasing humic acid concentration 
to 4.5 gL-1 (Fig 5).   
 
 
Fig5. Effect of humic acid on TSS. 
 
 
 
Discussion 
The results of this study showed that 
application of humic acid has increased 
quantitative and qualitative characteristics of 
strawberry in hydroponic system. Increasing leaf 
area, weight of first and second fruits, achenes 
number, fruit length, shoot fresh and dry weight, 
root fresh and dry weight and yield of strawberry 
c.v Selva by using humic acid has been reported by 
Zare (2011), which is in accordance tour findings. 
Increasing quantitative and qualitative 
characteristics by using humic acid have been 
reported by some researchers such as: Kamari-
Shahmaleki et al. (2012), Ferrara and Brunetti 
(2010) and Pouzeshi et al. (2011). Formation of 
complex between humic acid and mineral ions, 
catalysis of humic acid by the enzymes in plant, 
influence of humic acid on respiration and 
photosynthesis, stimulation of nucleic acid 
metabolism and hormonal activity of humic acid 
are amongst effective assumptions that has been 
expressed to describe the effect of humic acid on 
plants growth parameters (Turkmen et al., 2004). 
Some researchers (Atiyeh et al., 2002) reported 
that the reason behind the effectiveness of humic 
acid on plant growth and development is the 
existence of plant growth regulators such as IAA, 
GAs and CKs. Moreover, some investigators 
attributed the positive effects of humic acid due to 
its influence on plants root (Adani et al., 1998; 
Atiyeh et al., 2002; Turkmen et al., 2004; Yildrim, 
2007 and Ozdamarullu et al., 2011). High 
concentrations of humic acid simulate growth of 
the root in hydroponic systems and cause to 
increase root volume, which may be due to easier 
absorption and more efficient nutrients. It is likely 
that increasing nutrient uptake by plants can 
particularly be associated with an increase in root 
growth. Also root development can be due to 
hormone-like activity of humic acid (David et al., 
1994). Cangi et al. (2006) indicated that foliar 
spraying of humic acid and amino acids on 
Asparagus plants increase uptake of macro and 
micro elements in shoot and rhizome has increased 
carbohydrates production, chlorophyll and 
carotenoids in edible stems. Enhancing the 
quantitative and qualitative characteristics as a 
result of increased respiration, photosynthesis and 
total protein in the plants, due to humic acid and 
folic acid application has also been reported by 
Nardi et al. (2002).    
 
CONCLUSION 
Generally speaking, the results of this 
experiment show that the application of humic acid 
as foliar spray will improve quantitative and 
qualitative properties of strawberry fruits. For that 
reason, application of 1.5 to 3.0 gL-1 humic acid in 
hydroponic system is recommended. 
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AGRICULTURAL COMMUNICATIONS.   
16 
 
ACKNOWLEDGEMENT 
Authors wish to thank Dr. Reza Amiri and 
Dr. Bijan Kavoosi for their useful help in plant 
material preparation and statistical analysis. 
Mrs. Hamedih Marzban assistance in English 
editing of the paper is also appreciated. 
 
 
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Foliar Application of Humic Acid on Quantitative and Qualitative Characteristics of Aromas Strawberry in Soilless Culture

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Foliar Application of Humic Acid on Quantitative and Qualitative Characteristics of Aromas Strawberry in Soilless Culture

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