Bangladesh Agron. J. 2017, 20 (1): 37-43 

 PRODUCTIVITY OF SUMMER ONION TO DIFFERENT SOURCES AND 
LEVELS OF POTASH 

 
M.S. Naher*, S. Brahma, M.A. Islam, M.B. Sarkar, M.M. Hasan and A.H.F. Fahim 

Spices Research Centre, Shibganj, Bogra, Bangladesh Agricultural Research Institute, Bangladesh 
*Corresponding Author: mahmud.nahar@yahoo.com 

Key words: Summer Onion; Potassium; Level; Source; Bulb Yield 

 

Abstract 
 

A field experiment was conducted at the research field of the Spices Research Centre, 
Shibganj, Bogra, Bangladesh in the summer season of 2013-2014 to find out the 
response of summer onion (var. BARI Peaj-3) to different levels and sources of 
potassium application. The experiment was laid out in a randomized complete block 
design with three replications.  Potassium fertilizer combinations were comprised of 
four levels (0, 60, 120 and 180kg ha -1) and two potassium sources viz. Potassium 
Chloride (KCl) and Potassium Sulphate (K2SO4). A significant improvement in different 
growth and yield parameters of onion was observed in response to different sources 
and levels of potassium. The results indicated that the maximum plant height, leaves 
plant-1, length of leaf, length of bulb, diameter of bulb, average bulb weight, number of 
bulb per m2  and yield of bulbs were obtained  from the onion crop which was treated 
with 120 kg K ha-1 from the Sulphate of Potash (SOP) fertilizer. Among the treatments 
the highest bulb yield (14.33 t ha-1) was obtained with 120 kg K ha-1 and the lowest 
(6.92t ha-1) from the control. The highest disease incidents (65.67%) were recorded 
from the control followed by the plots which were treated with 60 kg K ha-1  (62.28%). 
The lowest disease incidence (49.22%) was recorded from 180 kgha-1 SOP treated 
plot. Application of 120 kg K ha-1 from K2SO4 along with a blanket dose of 
N100P50S20B1.5Zn4 kgha-1 and 5 ton cowdung ha-1 appeared to be the optimum dose   
for maximizing the bulb yield of summer onion.  

 
 

Introduction 
 
Onion (Allium cepa L.) is one of the important commercial vegetable and spice crops of 
Bangladesh. It produces 17.04 lakh mt of onion from 4.19 lakh acres area (BBS, 2015). The 
average yield of onion in Bangladesh is far below 11 t ha-1 (BBS, 2015) as compared to the 
world average of 19.32 t ha-1. Onion is mainly produced in the winter season.but cultivation in 
summer season is constrained due to adverse weather and proper cultural practices (Islam et al, 
2008). By introducing drought tolerant onion varieties along with good cultural management, 
this may help increase onion production in Bangladesh. BARI has released three summer onion 
varieties for cultivating in the summer season. There is a significant response of onion to both 
inorganic and organic fertilizer (Nasreen et al., 2000 and Ullah, 2003). Potassium plays an 
important role in onion production and   responsive to potash application like other tuber and 
root crops. Among the various nutrients required to produce high yield of onion, potassium is 
considered to be very important element due to its influence on translocation of 
photosynthates, storage quality, bulb size, bulb numbers and yield per plant (Sangakara et al., 
1993). Potassium is one of the three major nutrients taken up by the plant in large quantities 
and an adequate level of potassium increases crop resistance to various diseases, stalk and stem 
breakage during stress conditions (Razzaque et al., 1990). Chloride in KCl may cause burning 

mailto:mahmud.nahar@yahoo.com


38 

Naher et al. 

of the leaves and deteriorate the onion bulbs; on the other hand sulphur in K2SO4 improves 
the quality of the onion bulbs. Among different sources of potassium, Sulphate of potash (SOP) 
contains sulfur that may lead to more growth and development as compared to Muriate of 
potash (MOP) for onion production (Nabi et al, 2010). Therefore, the experiment was 
undertaken to determine the response of summer onion (var. BARI Peaj-3) to different levels 
and sources of Potassium application. 
 
 

Materials and Methods 
 
The experiment was conducted at the experimental fields of Spices Research Centre in 
Bogra,Bangladesh. The experimental site represents Agro-Ecological Zone (AEZ)-26   as “Level 
Barind Tract” and situated at 24°51′ North latitude and 89°22 East longitude (FAO, 1988).The 

soil of the experimental field belongs to Grey Terrace Soil. It was developed from Madupur 
Clay and silty loam in texture. Organic matter content of the soil was low (1.02%). The soil was 
acidic in nature (pH 5.7). Total N and the exchangeable K status of the soil were also low. The 
available phosphorus, sulphur, boron and zinc contents were found to be either at par or below 
the critical level (Table 1).  Summer onion var. BARIPiaz 3 was used as a test crop.  
 
Table 1. Physical and chemical characteristics of the initial soil 

Texture 
 

pH 
 

OM 

E
x
ch

a
n
g
e
a
b
le

 M
g
 

E
x
ch

a
n
g
e
a
b
le

 K
 

E
x
ch

a
n
g
e
a
b
le

 C
a
 

T
o
ta

l 
N

 

A
va

ila
b
le

 P
 

A
va

ila
b
le

 S
 

A
va

ila
b
le

 B
 

A
va

ila
b
le

 Z
n
 

A
va

ila
b
le

 C
u
 

% (c mol kg-1)  (mg kg-1 soil) 

Silt loam 5.7 1.02 1.06 0.10 3.03 0.071 11.2 8.6 0.14 0.56 0.07 

Critical 
level 

- - 0.8 0.20 2.0 - 14 14 0.2 2.0 0.2 

 
There were Seven treatment combinations viz. T1: 0 kg K ha-1 (Control), T2: 60 kg K ha-1 from 
KCl, T3: 120 kg K ha-1 from KCl, T4: 180 kg K ha-1 from KCl, T5: 60 kg K ha-1 from K2SO4, 
T6: 120 kg K ha-1 from K2SO4 and T7: 180 kg K ha-1 from K2SO4. The experiment was laid 
out in Randomized Complete Block design (RCBD) with three replications. Fertilizer with a 
blanket dose of N100P50S20B1.5 Zn4 kg ha-1 and cowdung (5tha-1) was used. The experimental 
plots were prepared uniformly and mixed with well-decomposed cow dung. Apart from 
potassium, all other fertilizers were applied to the soil during final land preparation. Urea 
fertilizer was applied with three equal splits at basal, 20 DAT and 40 DAT, respectively. The 
size of seedbed was 3 m × 1 m with 20 cm height. The onion seeds were directly sown in the 
raised seedbed followed by irrigation. About 40 days old seedlings were uprooted from the 
seedbed and transplanted in the morning to the main field with the spacing of 10 cm × 15 cm 
followed by irrigation. Intercultural operations like gap fillings, weeding and mulching were 
done whenever required. Second and third irrigation was given at 20 and 30 DAT, 
respectively. Insect and diseases were also controlled with appropriate control measures. Data 



39 

Productivity of Summer Onion to Different Sources and Levels of Potash 

of plant height (cm), length of leaf (cm) and number of leaves per plant were recorded from the 
selected five plants in each plot at 30, 50, 70 and 90 days after transplanting (DAT). The plant 
height (cm) was taken from the neck of the onion bulb to the tip of the longest leaf. The leaf 
length (cm) was measured from the pseudo stem to the tip of the leaf and the number of leaves 
from each plant. Onions were harvested when more than 40% of leaves tops were bent down 
(Khan and Khan, 1990 and Khokhar and Jilani, 2000). The bulbs were placed for five days 
under partial shade in the open for curing.  Yield components data (length of bulb per plant 
(cm), diameter of bulb per plant (cm), single weight of bulb (g), number of bulbs per plot and 
yield of bulb (t ha-1) were collected  and statistically analyzed using MSTAT-C computer 
package program (Russel, 1994). The significance of the differences among the pairs of 
treatment means was evaluated by the Duncan Multiple Range Test (DMRT) at 5% level of 
probability (Gomez, et al, 1984). 
 
 

Results and Discussion 
 
Plant height  

The plant height was significantly influenced by different sources and levels of potash (Table2). 
At 70 DAT, the highest plant height (50.78cm) was recorded from 120 kg K ha-1 from K2SO4 
source and the lowest plant height (39.85cm) from the control.. Similar effect was also 
recorded at 30, 50 and 90 DAT. The rate 120 kg K ha-1 from K2SO4 showed the best 
performance which might be due to the availability of optimum source and level of potassium 
than other treatment. Hassanpouraghdam etal., (2008) also reported that different 
concentrations of N and K influenced height of the plants, the greatest height being observed in 
N and K with 200 mg L-1each  and  concluded that different concentrations of N and K have 
remarkable effects on the growth. Sulphate of potash produced significantly taller plants (60.58 
cm) as compared to Muriate of potash (59.04 cm). This may be due to the availability of more 
readily available forms of potassium and sulfur than other sources.  
 
Length of leaf 

Length of leaf of summer onion was significantly influenced by different sources and levels of 
potash (Table 2). At 70 DAT, the highest leaf length (44.09cm) was recorded from 120 kg K 
ha-1 from K2SO4 source and the lowest plant height (34.10cm) from control (0 kgK ha-1  ). 
Similar effects were also observed at 30, 50 and 90 DAT. The rate 120 kg K ha-1 from K2SO4 

showed the best performance which might be due to the availability of the optimum source and 
level of potassium than other treatments. Pettigrew (2008) reported that potassium deficiency 
can lead to a reduction in the size of individual leaves. 
 
Number of leaves plant-1  

Table 2 shows significant differences among the different treatments. At 70 DAT, the 
maximum number of leaves per plant (7.58) was recorded from 120 kg K ha-1 from K2SO4 
source and the lowest (5.52) from control. Similar effect was also recorded at 30, 50 and 90 
DAT. The rate 120 kg K ha-1 from K2SO4 showed the best performance compare to MOP 
application. Similarly Pettigrew (2008) reported that potassium deficiency can lead to a 
reduction in both the number of leaves and the size of individual leaves. 
 



40 

Naher et al. 

Table 2. Effect of different sources and levels of potash on yield components of summer onion 

Treatment 

30 DAT* 50 DAT 70 DAT 90 DAT 

Plant 
height 
(cm) 

Length 
of leaf 
(cm) 

Number 
of leaves 

per 
plant 

Plant 
height 
(cm) 

Length 
of leaf 
(cm) 

Number 
of leaves 
per plant 

Plant 
height 
(cm) 

Length 
of leaf 
(cm) 

Number 
of leaves 
per plant 

Plant 
height 
(cm) 

Length 
of leaf 
(cm) 

Number 
of leaves 

per 
plant 

T1: 0 kg 
K ha-1  

21.32f 16.11f 3.02g 28.62f 22.52g 4.11e 39.85g 34.10f 5.52g 35.66e 30.65g 4.31f 

T2: 60 kg 
Kha-1 
from KCl 

23.88e 18.38e 3.28f 30.75e 24.44f 4.66de 42.56f 37.45e 6.05f 38.45d 33.29f 4.55e 

T3: 120 
kg Kha-1 
from KCl 

33.52b 27.88c 4.38d 35.87d 29.71d 5.55cd 45.52d 41.22d 6.55d 41.44c 36.07d 5.22c 

T4: 180 
kg Kha-1 
from KCl 

32.44c 26.96c 4.48c 36.96c 30.88c 5.65c 46.78c 42.35c 6.78c 42.51c 37.11c 5.29b 

T5: 60 kg 
Kha-1 
from 
K2SO4 

25.88d 21.67d 3.88e 32.25e 26.67e 5.18d 44.29e 39.38de 6.41e 39.28d 35.35e 4.80d 

T6: 120 
kg Kha-1 
from 
K2SO4 

36.35a 31.01a 5.71a 39.85a 35.88a 6.68a 50.78a 44.09a 7.58a 47.01a 39.89a 5.88a 

T7: 180 
kg Kha-1 
from 
K2SO4 

36.24a 29.87b 5.30b 37.12b 33.66b 6.39b 48.11b 41.88b 7.08b 45.15b 36.01b 5.37b 

CV (%) 5.6 4.8 3.6 4.72 4.8 5.02 3.8 3.6 4.65 3.88 3.96 4.56 

Means having common letters are not significantly different at 5% level of significance as per DMRT 
* DAT= Days After Planting



41 

Productivity of Summer Onion to Different Sources and Levels of Potash 

Plant disease incidence (%)  
There were significant differences  among the different potash sources and various levels of 
potash treatment combinations. The Fig. 1 shows that the maximum disease incidence 
(65.67%) was recorded in the control  followed by 60 kg K ha-1  from KCl (62.28%)., while the 
minimum  (49.22.17%)  in 180 kg K ha-1 from K2SO4 source followed by 52.88 and 51.55 % 
in 60 and 120 kg K ha-1 from K2SO4 source, respectively. Mandal et al. (2008) reported that 
application of 40 kg K ha-1 reduced percent disease index (PDI) by more than 10% compared 
with 0 kgKha-1. Muriate of potash treated plot comparatively produced significantly higher 
disease incidence as compared to Sulpfate of Potash. The presence of the sulfur element in the 
Potassium Sulphate, may have increased the disease tolerance characters in the plants.  

 
Fig. 1 Effect of different sources and levels of potash on disease incidence (%) in Summer onion 
 
Bulb Characters 

The number of harvested bulbs per square meter, bulb diameter and average bulb weight of 
summer onion were statistically significant (Table 3). The highest length of bulb (4.21 cm) was 
observed from 120 kg K ha-1 of K2SO4 and the lowest length of bulb (2.36 cm) by 0 kg K ha-1. 
The highest diameter of bulb (4.25 cm) was recorded from 120 kg K ha-1 of K2SO4 and the 
lowest (2.78 cm) from the control. The maximum bulb weight (52.14 g) was recorded from the 
treatment combination with 120 kg ha-1 potassium from K2SO4 and the lowest bulb weight 
(14.01 g) from basal application of 0 kg Kha-1. The highest number of bulbs m-2  (50.00) was 
recorded from 120 kg ha-1 potassium from K2SO4 and the lower number (41.00) from 
potassium control treated plot. 
 
Yield of bulbs  

There were significant differences  among the different potash sources and various levels of 
potash. The maximum  bulbs yield (14.33 t ha-1) was recorded with potash  at 120 kg ha-1of  
K2SO4 followed by 13.95 t ha-1  with 180 kg Kha-1 from K2SO4 (Figure 2). The bulb yield 
increase with the increasing level of K upto 120 Kg ha-1.  It indicates that application of 120 kg 
K ha-1 from K2SO4 at vegetative as well as bulb formation stage was much better than the 
other levels of K. The minimum bulb yield (6.92 tha-1) was recorded in control plot, followed by 
10.44 t ha-1  with 60 kg K ha-1 from KCl. According to Nabi et al., (2010) Sulphate of potash 
treated crop produced higher yield as compared to MOP.  
 

0 

10 

20 

30 

40 

50 

60 

70 

0 kg K/ha 60 kg K/ha 120kg 
K/ha 

180kg 
K/ha 

D
is

e
a
se

 in
ci

d
e
n
ce

 (
%

) 

Levels of potash 

MOP Source 

K2SO4 Source 



42 

Naher et al. 

Table 3. Effect of different sources and levels of potash on yield contributing characters of 
summer onion 

Treatment 
Length of 
bulb (cm) 

Diameter 
of bulb 
(cm) 

Wt. of 
single 

bulb (g) 

No. of 
bulb m-2 

Bulb 
yield 

(t ha-1) 

T1: 0 kg K ha-1  2.36e 2.78e 14.01g 41d 6.92f 
T2: 60 kg K ha-1 from KCl 3.51d 3.55d 26.06f 44c 10.44e 
T3: 120 kg K ha-1 from KCl 4.07ab 4.11a 47.88b 47b 13.68ab 
T4: 180 kg K ha-1 from KCl 4.01b 4.06b 44.56d 45c 12.98c 
T5: 60 kg K ha-1 from K2SO4 3.54c 3.60c 29.78e 46b 11.41d 
T6: 120 kg K ha-1 from K2SO4 4.21a 4.25a 52.14a 50a 14.33a 

T7: 180 kg K ha-1 from K2SO4 3.98b 4.02b 45.22c 49ab 13.95b 

CV (%) 3.75 4.32 3.66 5.32 4.88 

Means having common letters are not significantly different at 5% level of significance 

 
Conclusion 

 
On the basis of results, it was clearly showed that application of 120 kg K ha-1 from K2SO4 
along with a blanket dose of N100P50S20B1.5Zn4 kg ha-1 and 5 ton cowdung ha-1 appeared as 
optimum dose for maximizing the bulb yield of summer onion of var. BARIPiaz-3 in AEZ-25 of 
Level Barind Tract, Bangladesh.   
 

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Productivity of Summer Onion to Different Sources and Levels of Potash 

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