Acta agriculturae Slovenica, 119/3, 1–10, Ljubljana 2023
doi:10.14720/aas.2023.119.3.2556 Original research article / izvirni znanstveni članek
Pinched sunflowers (Helianthus annuus ‘Teddy Bear’) produce high-
quality flowers under high nitrogen fertilizer
Y ahya SELAHV ARZI
 1, 2
, Maryam KAMALI
 1
, Sajede KARIMPOUR
 3
, Mahdiyeh KHARRAZI
 4
, Moham-
mad KARIMI
 1
Received February 13 2022; accepted July 27, 2023.
Delo je prispelo 13. februarja 2022, sprejeto 27. julija 2023
1 Department of Horticultural Science and Landscape Engineering, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran
2 Corresponding author, e-mail: selahvarzi@um.ac.ir
3 Department of Horticultural Science and Landscape Engineering, Shirvan Faculty of Agriculture, University of Bojnord, Bojnord, Iran
4 Ornamental Plants Biotechnology Research Department, Research Institute for Industrial Biotechnology, Iranian Academic Centre for Education, Culture and Re-
search (ACECR), Mashhad, Iran
Pinched sunflowers (Helianthus annuus ‘Teddy Bear’) pro-
duce high-quality flowers under high nitrogen fertilizer
Abstract: This study was investigated the effect of remov-
ing the central bud (pinching) and different levels of nitrogen 
fertilizer urea on some morphological and physiological traits 
of ornamental sunflower. This study was conducted as a factori-
al experiment in a randomized complete block design with four 
replications on ornamental sunflower (Helianthus annuus ‘ Te d-
dy Bear’) at Horticulture Farm, Department of Horticulture, 
Ferdowsi University of Mashhad, Iran, in 2020-2021. The first 
factor was pinching in two levels (pinching and non-pinching) 
and the second factor was using urea at four levels (0, 200, 300, 
and 400 kg ha
-1
) in the form of water-soluble fertilizer. Results 
showed that the highest flower dry mass (59.25 g) was observed 
in pinched plants fertilized by 400 kg ha
-1
 of urea. Besides, the 
application of a high level of urea fertilizer and pinching treat-
ment increased the amount of total chlorophyll and chlorophyll 
b. By removing the central bud, the amount of N, P , K, Ca, Zn, 
and Fe elements in the leaf increased by 1.5, 1.6, 1.3, 1.9, 1.4, 
and 1.5 times, respectively. Therefore, pinching and the adding 
of urea fertilizer at 400 kg ha
-1
is recommended for the produc-
tion of high-quality sunflower plant ‘Teddy Bear’ .
Key words: flowering period, head diameter, nutrient ele-
ments, photosynthesis, plant height
Pincirane sončnice (Helianthus annuus ‘Teddy Bear’) dajejo 
visoko kakovostna socvetja pri gnojenju z velimi količinami 
dušikovih gnojil
Izvleček: V raziskavi je bil preučevan učinek odstranje-
vanja (pinciranja) osrednjega socvetja in različnih odmerkov 
gnojenja z ureo na nekatere morfološke in fiziološke lastnosti 
okrasnih sončnic. Raziskava je bila izvedena kot popolni fak-
torski bločni poskus s štirimi ponovitvami na okrasnih sonč-
nicah (Helianthus annuus ‘Teddy Bear’) na Horticulture Farm, 
Department of Horticulture, Ferdowsi University of Mashhad, 
Iran, v rastni sezoni 2020-2021. Prvi dejavnik je obsegal dve 
ravni pinciranja (pincirano in ne pincirano), drugi dejavnik 
pa štiri različne odmerke uree (0, 200, 300, and 400 kg ha
-1
) 
v obliki vodotopnega gnojila. Rezultati so pokazali, da je bila 
dosežena največja suha masa socvetij (59,25 g) pri pinciranih 
rastlinah in uporabi 400 kg ha
-1
 of uree. Večji odmerek uree je 
pri pinciranih socvetjih povečal vsebnost celokupnega klorofila 
in klorofila b. Pri odstranitvi osrednega socvetja se je vsebnost 
N, P , K, Ca, Zn in Fe v listih povečala za 1,5; 1,6; 1,3; 1,9; 1,4 in 
1,5 krat. Zaradi naštetega priporočamo pinciranje in gnojenje 
s 400 kg ha
-1 
uree za vzgojo kakovostnih sončnic ‘Teddy Bear’ .
Ključne besede: cvetenje, premer koška, hranila, fotosin-
teza, višina rastlin

Acta agriculturae Slovenica, 119/3 – 2023 2
Y. SELAHV ARZI et al.
1 INTRODUCTION
Sunflower (Helianthus annuus L.) is an annual plant 
belonging to the Asteraceae family. This plant is native to 
North America and has medicinal, nutritional, and or-
namental uses (Sehrawat et al., 2003) beside of its usage 
as a biodegradable source in biodiesel fuels (Saba et al., 
2016). According to the specialized institute of cut flow-
ers, in some sunflower cultivars, such as ‘Pro-Cut Gold’ 
and ‘Sunrich Lemon’ , the stems are so long. In contrast, 
other sunflower cultivars produce lateral shoots and have 
short stems and uniform flowers (Dole, 2002). Removing 
the central bud (pinching) is considered one way to stim-
ulate the plant to produce lateral branches and increase 
the number of stems per plant (Wien, 2015; Cheema, 
2018). Depending on the stage of plant growth, pinching 
can be beneficial or harmful for plants (Smakel, 2006), as 
pinching of the different sunflower cultivars at the right 
time enhanced flower production three to four times 
(Wien, 2012a). However, pinching delays flowering and 
reduces flower size (Cheema, 2018) and the formation of 
flowers for 7-10 days (Wajid et al., 2007). Wien (2016b) 
reported that pinching the ‘Sunrich Orange’ cultivar, led 
to the production of smaller flowers but appropriate stem 
length. The smaller size of the flower, but with the mar -
ketable stem length, allows the florists to use them in ar-
ranging the flower bouquets properly. The study results 
of  Badge and Panchbhai (2018) revealed that pinching 
the African marigold (Tagetes erecta L.) plants (15 days 
after transplanting) lead to the production of maximum 
flower yield in comparison to other treatments. The 
maximum nitrogen, phosphorus, and potassium content 
and uptake, as well as yield parameters, were obtained by 
pinching the plants 15 days after transplanting and foliar 
application of gibberellic acid at 300 mg l
-1
 (Badge et al., 
2015). Prakash et al. (2016) reported that pinching the 
African marigold (Tagetes erecta) affects the plant height, 
number of lateral branches, number of flowers, and num-
ber of days to 50 % of flowering.
Adequate nutrition with essential elements, espe-
cially with nitrogen, is very important for the successful 
development of plants. Nitrogen is an essential nutrient 
that plays a role in the structure of various proteins, en-
zymes, coenzymes, nucleic acids, and cytochromes (Has-
segawa et al., 2008), as well as, involving in the cell divi-
sion and expansion, thereby increasing leaf length and 
width (Kumari, 2011, Lehri et al., 2011). Besides, this ele-
ment plays a crucial role in the formation of chlorophyll 
and has a vital function in supplying carbohydrates and 
photosynthesis (Wajid et al., 2007). The effect of nitrogen 
on plant growth and development has often been linked 
to increased photosynthesis because the appropriate 
amount of nitrogen determines plant yield (Mekonnen 
et al., 2002). Studies indicated that the increase in growth 
and yield of the sunflower plant is dependent upon the 
adequate supply of nitrogen (Ali et al., 2004; Ali, 2015). 
The results of Oad et al. (2018) study indicated that sun-
flower plants treated with foliar application of urea (1 %) 
after 35 days of sowing in addition to recommended soil 
applied urea (130 kg ha
-1
) led to the highest plant height, 
head diameter, grains per head, seed index, and grain 
yield. Ali et al. (2014) reported that the application of 80 
kg ha
-1
 nitrogen fertilizer resulted in an increased plant 
height and head diameter of the sunflower plants. In an-
other study, a significant increment in crop growth, bio-
mass, dry matter production, and biological yield result-
ed in 100 kg ha
-1
 of N rate application (Saifullah, 1996), 
but Handayati and Sihombing (2019) recommended the 
application of 150 kg ha
-1
 nitrogen for the cultivation of 
this plant.
Considering the effect of pinching and nitrogen on 
the reproductive and vegetative traits of the sunflower 
plant, the present experiment was aimed to investigate 
the effect of removing the central bud (pinching) and 
different levels of nitrogen fertilizer (urea) on flowering, 
flower size, plant height, and other morphological and 
physiological traits of ornamental sunflower (Helianthus 
annuus ‘Teddy Bear’).
2 MATERIALS AND METHODS
The field experiment was conducted at Research 
Farm, Department of Horticulture, Ferdowsi University 
of Mashhad, Iran, in 2020-2021. Before planting, chem-
ical analysis of the soil was done at an upper 0-30 cm 
zone, the results of which are shown in Table 1. 
This experiment was conducted as a factorial ex-
periment in a randomized complete block design with 
four replications on ornamental sunflower (Helianthus 
annuus ‘Teddy Bear’). The first factor was removing or 
not removing the central bud (pinching); and the second 
factor was applied in four levels of adding urea fertilizer 
(CO (NH
2
)
2
): 0, 200, 300, and 400 kg ha
-1
 in the form 
of water-soluble fertilizer. The sunflower seeds were 
purchased from the Dutch Hemogenetic Company and 
sown in April 2020. Four weeks later, the seedlings with 
four true leaves were planted at spacing 50 × 20 cm. Ten 
days after transplanting, urea fertilizer was applied three 
times (weekly) with irrigation water according to the 
mentioned levels. Then, one month after transplanting, 
the pinching treatment was applied.
During the experiment, the number of days to 
flowering (vegetative period), and the duration of the 
flowering period (flowering period) were recorded. The 
number of flowers per plant was counted, and the head 

Acta agriculturae Slovenica, 119/3 – 2023 3
Pinched sunflowers (Helianthus annuus ‘Teddy Bear’) produce high-quality flowers under high nitrogen fertilizer
diameter and the stem diameter of each treatment were 
measured with a digital caliper. In 50 % of the flowering 
stage, the number of leaves per plant and the plant height 
were calculated. At this stage, the rates of photosynthesis 
and transpiration were also measured using a portable 
photosynthesis system (Li-6400) from 9:00 to 11:00 AM 
under natural conditions.
Fresh leaf tissue was used for the measurement of 
chlorophyll contents. 0.2 g fresh leaf was crushed in 10 
ml of methanol 96 %. The resulted solution was filtered 
through Whatman filter paper and then centrifuged at 
2500 rpm for 10 minutes. The supernatant optical ab-
sorption was then read at 653, and 666 nm using a spec-
trophotometer (model CE2502, BioQuest, UK) method 
(Sukran et al., 1998). Finally, the chlorophyll pigments 
were obtained using the following equations:
Chl
a
 (µg.ml
-1
) = 15.65 A
666
 - 7.340 A
653
Chl
b
 (µg.ml
-1
) = 27.05 A
653
 - 11.21 A
666
Chl
Total
 = Chl
a
 + Chl
b
After applying the treatments, at the beginning of 
the reproductive phase, N, P , K, Zn, Fe, and Ca elements 
in the sunflower leaf were measured. The amount of 
nitrogen in the plant was measured using the Kjeldahl 
method (Bremmer and Mulvaney, 1982). Concentrations 
of P, K, Ca, Zn, and Fe were analyzed by an inductively 
coupled plasma optical emission spectrometer (ICP-
OES, Perkin-Elmer Optima 5300 DV) in plant samples 
(Van de Wiel, 2003).
The flowers were collected and dried during the 
flowering period to record the flower dry mass. After 
flowering, the leaf area was measured using the leaf area 
meter (Model Li-Cor-1300, USA). The specific leaf area 
(SLA = leaf area leaf dry mass
-1
) and the leaf area ratio 
(LAR = leaf area total dry mass
-1
) were also calculated. T o 
measure the dry mass of plant components (stems, roots, 
leaves, and flowers) and the total dry mass, the plant sam-
ples were dried at 70 °C until the sample mass was held 
constant. Then the dry mass of different plant parts was 
recorded.
2.1 DATA ANALYSIS
Data were analyzed with One Way ANOVA us-
ing JMP
®
 (v.8) software (SAS institute, 1989-2021), and 
means were compared based on the LSD test at the 5 % 
of probability level. 
3 RESULTS
The results of ANOVA revealed that urea applica-
tion and pinching have significant effects on different 
traits of the sunflower plant including mineral uptake, 
vegetative and generative traits, photosynthesis and tran-
spiration rate, chlorophyll contents, and dry mass of dif-
ferent parts of sunflower (data not shown).
3.1 ELEMENT UPTAKE
The element content of sunflower shoots was af-
fected by urea application and pinching, and not by their 
interaction. The use of urea led to an increase in N con-
tent in shoots as well as P , K, Ca, Zn, and Fe contents. As 
the amount of urea fertilizer increased, the accumulation 
of these elements in the shoots also increased. Using urea 
fertilizer at 400 kg ha
-1
 induced mineral accumulation 
2.4, 2.6, 1.7, 2.3, 4.1, and 4.2 times more than the control 
for N, P , K, Ca, Zn, and Fe, respectively (Table 2). Contra-
riwise, these element contents decreased when pinching 
was applied. Pinched plants had 1.5, 1.6, 1.3, 1.9, 1.4, and 
1.5 times less amount of N, P , K, Ca, Zn, and Fe than non-
pinched sunflower plants, respectively (Table 2).
3.2 VEGETATIVE TRAITS
The interaction of pinching × urea fertilizer had 
a significant effect on vegetative traits including plant 
height, stem diameter, leaf number, leaf area, SLA, and 
LAR. Sunflower plants had the biggest height (153 cm) 
when grown using 400 kg ha
-1 
of urea fertilizer and not 
pinched, while pinched plants without urea fertilizing 
showed the lowest height (129 cm). The same results 
were obtained for stem diameter growth with 28.98 and 
20.90 mm, respectively. The leaf number increased by 
urea application and pinching (27.5-30.0), whereas, the 
lowest number of leaf production (13.0) was recorded in 
non-pinched plants without urea. The biggest leaf area 
(16130.25 cm
2
) showed in 400 kg ha
-1
 of urea applica-
Table 1: The physical and chemical properties of the soil
Ca Zn Fe K P N EC pH Loam Clay Sand Soil Texture Depth
                               (mg kg
-1
) (dS m
-1
)                       (%) (cm)
29371 52 24716 6251 606 610 1.3 7.5 27 33 40 Sandy loam 0-30

Acta agriculturae Slovenica, 119/3 – 2023 4
Y. SELAHV ARZI et al.
tion and pinching treatment, while non-pinched plants 
grown without urea fertilizer expanded their leaf to the 
minimum amount (8953.65 cm
2
). SLA was the highest 
when 400 kg ha
-1
 of urea fertilizer with pinching (302.46 
cm
2
 g
-1
) and 300 kg ha
-1
 of urea fertilizer without pinch-
ing (301.37 cm
2
 g
-1
) was applied and the lowest amount of 
SLA was shown in the 300 kg ha
-1
 of urea application with 
pinching (266.60 cm
2
 g
-1
) treatment (Table 3). The high-
est amount of the LAR was obtained in two treatments 
include 400 and 300 kg.ha
-1
 of urea fertilizer + pinching 
(73.64 and 72.97 cm
2
.g
-1
, respectively), and the lowest 
amount was recorded for plants with no urea fertilizing 
with (62.11 cm
2
.g
-1
) or without (62.36 cm
2
 g
-1
) pinching 
(Table 3).
3.3 GENERATIVE TRAITS
We obtained the highest number of flowers (77.75) 
in pinched plants fertilized by 400 kg ha
-1
 of urea ferti-
lizer, and non-pinched plants produced the less flower 
number (21.25-26.00) in all levels of urea fertilizer (Ta-
ble 4, A). The head diameter had the highest amount 
(146.68-15.1.59 mm) when pinching was not applied in 
plants of urea fertilizer in 0, 200, and 300 kg ha
-1
, and the 
lowest amount (97.42 mm) was recorded in the pinched 
plants with no urea using. The number of days to first 
flower appearance and the duration of the flowering stage 
were affected by urea fertilizer, that is, the increase in 
urea levels led to prolongation of the vegetative and gen-
erative period and low levels of urea stimulate the enter-
ing to and shortening of the generative stage. Duration of 
the flowering stage also was increased by pinching up to 
6 days compared to the non-pinched plants (Table 4, B).
3.4 CHLOROPHYLL CONTENTS, PHOTOSYN-
THESIS, AND TRANSPIRATION RATE 
The content of chlorophyll
b
 and total chlorophyll 
was affected by the interaction of urea fertilizer × pinch-
ing, while the chlorophyll content was not influenced by 
interaction but was affected by simple effect of them. The 
plants which were grown under 400 kg ha
-1
 of urea ferti-
lizer with (0.28 µg g
-1
 FM) or without pinching (0.24 µg 
Table 2: The simple effect of pinching and urea fertilizer treatments on element content in sunflower shoots
Fe Zn Ca K P N Treatments Factors
                                                            (mg kg
-1
)
93.000d 8.0000d 9167.0d 12346.0d 820.00d 940.00d
*
0 Urea fertilizer (kg ha
-1
)
108.500c 11.3750c 11939.3c 16934.0c 968.00c 1088.00c 100
333.875b 17.8750b 20584.0b 19746.0b 1094.00b 1212.50b 200
393.125a 32.8750a 20798.0a 20847.8a 2172.00a 2292.00a 400
277.000a 20.3750a 20623.1a 19499.4a 1539.50a 1659.50a - Pinching
187.250b 14.6875b 10621.1b 15437.4b 987.50b 1106.75b +
*
Means followed by similar letters in each trait and for each factor didn’t have any significant difference based on LSD test (p ≤ 0.01)
Table 3: The interaction effect of pinching × urea fertilizer on vegetative traits of the sunflower plant
Pinching
Urea fertilizer 
(kg ha
-1
)
Plant height 
(cm)
Stem diameter 
(mm) Leaf number
Leaf area 
(cm
2
)
SLA
** 
(cm
2
 g
-1
)
LAR
**
 
(cm
2
 g
-1
)
- 0 139.33abc
*
25.49abcd 13.00b 8953.65d 294.81bc 62.36c
- 200 143.66abc 26.25abc 22.00ab 9976.30cd 298.51ab 69.07ab
- 300 147.00ab 26.37abc 21.00ab 12407.76b 301.37a 72.97a
- 400 153.00a 28.98a 30.33a 9856.37cd 273.78cd 64.12bc
+ 0 129.00c 20.90d 22.33ab 11416.25bc 276.35c 62.11c
+ 200 133.00bc 21.45cd 27.50a 12969.25b 296.16ab 69.29ab
+ 300 138.00abc 23.02bcd 26.66a 12813.25b 266.60e 65.21b
+ 400 147.33ab 28.01ab 30.00a 16130.25a 302.46a 73.64a
*
Means followed by similar letters in each trait do not have any significant difference based on the LSD test (p ≤ 0.01)
**
SLA: The specific leaf area, LAR: The leaf area ratio

Acta agriculturae Slovenica, 119/3 – 2023 5
Pinched sunflowers (Helianthus annuus ‘Teddy Bear’) produce high-quality flowers under high nitrogen fertilizer
g
-1
 FM) had the highest amount of chlorophyll b and the 
lowest was related to not using urea fertilizer for pinched 
and non-pinched plants (0.11-0.13 µg g
-1
 FM). In the 
same manner, total chlorophyll content was the highest 
in non-pinched plants treated by 400 kg ha
-1
 of urea ferti-
lizer (0.45 µg g
-1
 FM), and the lowest amount was record-
ed in the pinched and non-pinched plants without urea 
fertilizing (0.25-0.26 µg g
-1
 FM)(Table 5, A). Unlike the 
chlorophyll
b
 and total chlorophyll, the amount of chlo-
rophyll only was affected by urea fertilizer and pinching. 
Urea fertilizer at 300 kg ha
-1 
(0.19 µg g
-1
 FM) and pinch-
ing (0.17 µg g
-1
 FM) provoked chlorophyll
a
 accumula-
tion. There was a trend for photosynthesis and transpira-
tion rate, increasing urea levels from zero to 400 kg ha
-1
 
enhanced the amounts of photosynthesis from 6.19 to 
11.39 µmol mol
-1
 CO
2
 and transpiration rate from 1.44 to 
2.65 mmol.mol
-1
 H
2
O, respectively. Pinching significantly 
led to a decrease in photosynthesis and transpiration rate 
(Table 5, B).
3.5 DRY MASS OF PLANT ORGANS
Leaf, head, root, and total dry mass of sunflower 
was affected by the interaction of urea fertilizer × pinch-
ing, as the highest amount of them was recorded on 
pinched plants were fertilized by 400 kg ha
-1
 of urea ferti-
lizer, 53.33, 59.25, 39.99, and 219.04 g, respectively. Non-
Table 4: The interaction effect of pinching × urea fertilizer (A) and simple effect of them (B) on generative traits of the sunflower 
plant
(A) (B)
Pinching
Urea fertilizer 
(kg ha
-1
)
Flower 
number
Head 
diameter 
(mm)
Day to1st 
flowering 
(day)
Duration of 
flowering 
(day)
- 0 23.50d
*
146.68a Urea 
fertilizer 
(kg ha
-1
)
0 44.0000D 32.3750D
- 200 21.25d 151.59a 200 46.1250C 34.1250C
- 300 26.00d 148.68a 300 48.7500B 36.7500B
- 400 25.50d 119.27b 400 52.7500A 40.7500A
+ 0 45.50c 97.42c Pinching
+ 200 46.75c 106.84bc - 44.9375A 32.9375B
+ 300 63.50b 111.24bc + 50.8750A 39.0625A
+ 400 77.75a 110.04bc
*
Means followed by small (interaction effect) and capital (simple effect) letters in each trait does not have a significant difference based on the LSD 
test (p ≤ 0.01)
Table 5: The interaction effect of pinching × urea fertilizer on chlorophyll b and total chlorophyll content (A) and simple effect of 
them on photosynthesis, transpiration rate and Chlorophyll a content (B) in sunflower plant
(A) (B)
Pinching 
Urea 
fertilizer 
(kg ha
-1
)
Chlorophyll
b
 
content 
(µg g
-1
 FM)
Total chloro-
phyll content 
(µg g
-1
 FM)
Chlorophyll
a
 
content 
(µg g
-1
 FM)
Photosynthesis 
(µmol.mol
-1
 CO
2
)
Transpiration rate 
(mmol mol
-1
 H
2
O)
- 0 0.11c
*
0.25d Urea 
fertilizer 
(kg ha
-1
)
0 0.13C 6.19D 1.44D
- 200 0.15bc 0.30cd 200 0.15BC 7.67C 1.78C
- 300 0.11c 0.37b 300 0.19A 8.96B 2.08B
- 400 0.24a 0.45a 400 0.17AB 11.39A 2.65A
+ 0 0.13c 0.26d Pinching
+ 200 0.16bc 0.31c - 0.15B 9.07A 2.09A
+ 300 0.18b 0.31c + 0.17A 8.09B 1.88B
+ 400 0.28a 0.42ab
*
Means followed by small (interaction effect) and capital (simple effect) letters in each trait does not have a significant difference based on the LSD 
test (p ≤ 0.01)

Acta agriculturae Slovenica, 119/3 – 2023 6
Y. SELAHV ARZI et al.
pinched plants had the lowest amount of leaf (30.37 g), 
head (33.75 g), root (22.78 g), and total (143.57-153.70 
g) dry matter. Indeed, the total dry matter was not much 
significantly affected by urea fertilizer levels (Table 6, A).
Urea fertilizer and pinching had a significant ef-
fect on stem dry mass as a simple effect. The application 
of urea at 300 kg ha
-1
 induced the highest dry matter in 
the stem, while the lowest amount was detected when 
no urea fertilizer was used. Pinching increased stem dry 
mass to 1.2 times (62.03 g) in comparison with non-
pinching (Table 6, B).
The percentage of dry matter allocation in differ -
ent parts of the plant showed no distinctive difference 
between treatments. On average, the highest to the low-
est percentage of dry matter allocation were for stem 
(32.7 %), head (26.0 %), leaf (23.4 %), and root (17.9 %), 
respectively (Table 7).
4 DISCUSSION 
Besides the high cost of chemical fertilizer, the envi-
ronmental impacts of their application are the important 
reason for the need to determine the exact amount of 
fertilizers. In our experiment, the interaction of different 
amounts of urea fertilizer (CO (NH
2
)
2
) and the removal 
of apical bud (pinching) had distinctive results on sun-
flower ‘Teddy Bear’ growth and development. The nitro-
gen fertilizer that used in this experiment is quite soluble 
and converts to ammonia in several days. So, as expected, 
a rise in the urea levels caused an increase in the nitrogen 
uptake. Similarly, the uptake of nitrogen is enhanced in 
broccoli plants when nitrogen fertilizer amounts increase 
(Vagen, 2003). In addition, the amount of P, K, Zn, Fe, 
and Ca was enhanced in the sunflower shoots by increas-
ing the urea levels (Table 2). Confirmed results were re-
ported by Karitonas (2003) and Yildirim et al. (2007) on 
broccoli plant, that an increase in the uptake of P , K, Fe, 
and Ca were shown by adding nitrogen fertilizer. Similar-
ly, lettuce and tomato plants which were foliar sprayed by 
urea had higher amounts of N and K (Padem and Alan, 
1995), and N, K, and Fe (Alan and Padem, 1994), re-
spectively. All studied nutrient elements (i.e., N, P , K, Ca, 
Zn, and Fe) play several important functions and criti-
cal roles within plants; metabolism, and catabolism pro-
cesses, so, increasing in their uptake by plants can explain 
the significant differences in the studied traits in this ex-
periment. The availability of nitrogen in the soil increase 
Table 6: The interaction effect of pinching × urea fertilizer (A) and simple effect of them (B) on the dry mass of different parts of 
the sunflower plant
(A) (B)
Pinching
Urea 
fertilizer 
(kg ha
-1
)
Leaf dry mass 
(g)
Head 
dry mass 
(g)
Root dry 
mass (g)
Total 
dry 
masst (g)
Stem 
dry mass 
(g)
- 0 30.37e
*
33.75e 22.78e 143.57c Urea 
fertilizer 
(kg ha
-1
)
0 53.83B
- 200 33.42de 37.14de 28.50cde 144.42c 200 55.60AB
- 300 41.17ab 45.75bcd 30.88bcd 170.03bc 300 60.87A
- 400 36.00cde 40.00cde 25.07de 153.70c 400 57.19AB
+ 0 41.31bcd 45.90bcd 32.84bc 183.78b
+ 200 43.79bc 48.66bc 36.04ab 187.16b Pinching - 51.71B
+ 300 48.06ab 53.40ab 35.70ab 196.48ab + 62.03A
+ 400 53.33a 59.25a 39.99a 219.04a
*
Means followed by small (interaction effect) and capital (simple effect) letters in each trait does not have any significant difference based on the LSD 
test (p ≤ 0.01)
Table 7: The percentage of dry matter allocation in differ -
ent parts of the sunflower plant under different levels of urea 
fertilizer and pinching
Pinching
Urea 
fertilizer 
(kg ha
-1
)
Dry mass (%)
Leaf Head Stem Root
- 0 20.5 27.0 33.2 19.2
- 200 20.6 28.2 32.2 19.0
- 300 25.6 23.1 35.7 15.6
- 400 25.6 24.0 34.1 16.2
+ 0 22.8 26.8 32.3 18.1
+ 200 22.8 27.8 30.7 18.8
+ 300 22.7 28.0 30.4 18.9
+ 400 26.5 22.8 33.0 17.7
Mean 23.4 26.0 32.7 17.9

Acta agriculturae Slovenica, 119/3 – 2023 7
Pinched sunflowers (Helianthus annuus ‘Teddy Bear’) produce high-quality flowers under high nitrogen fertilizer
RuBisCO contents in leaves, even though some climate 
and soil factors including light, air humidity, and soil pH 
showed considerable influences on the fraction of nitro-
gen allocated to RuBisCO regionally (Luo et al., 2021). 
Many scientists believe that the higher uptake of essential 
nutrients by plants as a result of the urea application is re-
lated to the positive influence of nitrogen on the chemi-
cal properties of the soil (Malhi et al., 2006; Haydon et 
al., 2007; Choudhury et al., 2011; Ai et al., 2017; Adekiya 
et al.,2018; Pasley et al., 2019). Ewulo et al. (2009) stated 
the possible reason for this is related to more microbial 
soil activity induced by urea application that causes more 
production and mineralization of organic matter in the 
soil. The reduction in the soil pH is another probable rea-
son for higher element uptake by urea application that 
is shown in the Adekiya et al. (2018) report. As the sun-
flower plants like the slightly acidic soils, this reduction 
in pH can improve elements uptake as the soil pH of the 
experiment site was close to neutral, 7.5 (Table 1). 
‘Teddy Bear’ cultivar of sunflower is a dwarf cultivar 
and mature plants grow up maximum 140 cm. Urea ap-
plication up to 400 kg ha
-1
 had a positive influence on 
plant height, and pinching reduced its effect. The sup-
pressive effect of pinching on the plant height has been 
previously reported for different cultivars of sunflow-
ers (Wien, 2016b; Cheema, 2018). Increasing the plant 
height and the stem diameter by using urea fertilizer is 
related to more leaf area production (Milford et al. 2000), 
while increasing the amount of chlorophyll in the sun-
flower leaves, followed by increasing photosynthesis and 
dry matter production, is closely related to higher uptake 
of various elements, including iron and zinc. It has been 
reported that iron is involved in the structure of chloro-
phylls, cytochrome, and nitrogenase enzymes, and zinc 
is involved in the activity of enzymes associated with 
chlorophyll formation and consequently increase photo-
synthesis, accelerating the formation of growth composi-
tions such as tryptophan as the raw material of auxins 
(Haydon et al., 2007). Enhanced dry matter production 
in non-pinched plants under more urea fertilizer, is 
probably due to increased water and mineral absorption 
by extended roots and rapid growth (Solangi et al., 2015). 
Steer et al. (1986), also reported an increscent in N up-
take and dry matter production by enhancing nitrogen 
fertilizer levels, as the application of low amounts of ni-
trogen fertilizer reduced leaf expansion and also the ac-
cumulation of dry matter in sunflower. We also obtained 
the higher dry matter of leaf, root, and head amounts in 
pinched plants in positive relation with urea levels, while 
there was an optimum level at 300 kg ha
-1
 in non-pinched 
plants (Table 6).
Leaf area, SLA, and LAR traits were the highest in 
400 kg ha
-1 
of urea fertilizer application with pinching 
(Table 3). Leaf area is a critical index for plant growth as 
it is associated with important criteria including light in-
terception, photosynthesis, transpiration, and evapotran-
spiration rates (Goudriaan and V an Laar, 1994; Zahoor et 
al., 2010). Leaf growth in earlier stages needs more nitro-
gen amounts (Evans, 1989; Johnson et al., 2010) and leaf 
area is limited when nitrogen is deficient by affecting cell 
division and enlargement (Roggatz et al., 1999). Pinching 
also had a positive effect on leaf area expansion in chry-
santhemum ‘Snowball’ (Ona et al., 2015). An increase in 
leaf number after pinching is reported by others on dif-
ferent herbaceous plants (Sehrawat et al., 2003; Tomar et 
al., 2004; Sudarshan, 2004; Salyh, 2013; and Ona et al., 
2015). It seems that it might be related to the fact that 
pinching alters the direction of growth from upward to 
lateral parts of the plant (Salyh, 2013).
The findings of this study indicated that pinching 
and urea application extended vegetative and flowering 
stages up to eight more days (Table 4. B). The number of 
days to flowering increased up to 70 days in pinched or-
namental sunflowers, while non-pinched plants started 
to flower after 63 days (Wien et al., 2016). The same re-
sults were reported by Ona et al. (2015) for chrysanthe-
mum ‘Snowball’ and other species (Ahmad et al., 2007; 
Ryagi et al., 2007; Salyh, 2013). The pinching effect on 
delayed flowering is due to delay in flower initiation and 
bud physiological maturity (Naresh and Singh, 2012) 
because the growth rate in axillary buds is slower than 
apical buds.
In pinched plants, flower number was affected by 
urea levels in a positive trend, while head diameter in-
dicated a negative trend. Flower diameter was indepen-
dently by cultivar decreased by pinching intensity (Bur-
nett, 2017; Cheema, 2018). Other studies also confirmed 
these results (Ryagi et al., 2007; Habiba, 2012; Salyh, 2013; 
Ona et al., 2015). The removal of the shoot apex leads to 
the activation of dormant axillary buds below it to form 
branches Naresh and Singh (2012). Flower disk diameter 
of sunflower (Wien, 2016b) and the flower size of chry-
santhemum (Ona et al. 2015) were reduced by pinching 
due the competition between branches and flowers. They 
have revealed that the number of the branches in a unit 
area has a negative linear relationship with head size in 
sunflower (Majid and Schneiter, 1987; Robinson et al., 
1980; Wien, 2016b).
5 CONCLUSION
This study demonstrated that adding urea in the 
soil and pinching improved photosynthetic traits by 
increasing leaf area and number, SLA, LAR, and total 
chlorophyll content. The findings also revealed that the 

Acta agriculturae Slovenica, 119/3 – 2023 8
Y. SELAHV ARZI et al.
interaction of pinching × urea application at 400 kg ha
-1
 
is the best combination of investigated variation sources 
for the cultivation of sunflower ‘Teddy Bear’ . The suitable 
amount of dry matter production (219.04 g), number 
of flowers (77.7), head diameter (110.04 cm), and plant 
height (147.3 cm) are the important reasons for this rec-
ommendation. 
6 AUTHOR CONTRIBUTION STATEMENT
All authors have participated in (a) conception and 
design, or analysis and interpretation of the data; (b) 
drafting the article or revising it critically for important 
intellectual content; and (c) approval of the final version.  
7 ACKNOWLEDGMENTS
We would like to thank Ferdowsi University of 
Mashhad, Mashhad, Iran for their support to perform 
this study.
8 CONFLICT OF INTEREST 
The authors certify the following:
- This manuscript has not been submitted to, nor 
is under review at, another journal or other publishing 
venue;
- The authors have no affiliation with any organi-
zation with a direct or indirect financial interest in the 
subject matter discussed in the manuscript.
9 DATA AV AILABILITY 
The data used to support the findings of this study 
are available from the corresponding author upon re-
quest.
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