Effect of differential soil moisture and nutrient regimes on postharvest attributes of onion (Allium cepa L.) Satyendra Kumar a, * , M. Imtiyaz b , Ashwani Kumar c a Central Institute of Postharvest Engineering and Technology, Abohar 152116, Punjab, India b College of Agricultural Engineering, Allahabad Agricultural Institute (Deemed University), Allahabad 211007, India c Water Technology Center for ER, Bhubneshwar 751023, India Received 9 April 2006; received in revised form 3 November 2006; accepted 5 December 2006 Abstract Studies were conducted to observe the effect of different soil moisture and nutrient regimes on postharvest attributes of onion irrigated with microsprinkler irrigation system under semi-arid climate for 3 consecutive years (2002–2004). Soil moisture regime consisted of four irrigation treatments based on pan evaporation replenishment (0.60, 0.80, 1.00 and 1.20 Ep). Similarly, three fertigation treatments were tried with nutrient application rates of 100 (50:25:25), 150 (75, 37.5, 37.5) and 200 (100:50:50) kg/ha of NPK. Irrigation and fertigation had marked effect on yield, postharvest attributes and storability of onion. Irrigation at 1.20 Ep and fertigation at 200 kg/ha produced higher bulb and dry matter yield, mean bulb size and weight, which decreased with the decrease in amount of irrigation and fertigation. The percentage of B-grade bulbs, which is considered commercially important, had been considerably higher at 1.20 Ep of irrigation and 200 kg/ha of fertigation. TSS increased up to 1.00 Ep and then declined slightly, whereas it varied with fertigation significantly. A decreasing trend for protein content was recorded with the increase in irrigation from 0.60 to 1.20 Ep, however, protein content increased with increase in fertigation. Irrigation at 0.80 Ep and fertigation @ 200 kg/ha resulted into minimum physiological loss in weight (%) for onion during 60 days of storage. But for extended storage period, increasing fertigation and decreasing irrigation had adverse effect on storability of bulbs. Theoretically, 416 mm irrigation water was found optimum for maximizing the dry matter yield of onion. Studies indicated that onion crop should be irrigated at 1.0 Ep under microsprinkler irrigation regime for better postharvest attributes. Similarly, fertigation @ 150 kg/ha is most desirable for micro sprinkler irrigated onion crop under semi-arid climate of India. # 2006 Elsevier B.V. All rights reserved. Keywords: Irrigation scheduling; Fertigation; Onion; Postharvest quality; Storability 1. Introduction Onion (Allium cepa L.) is one of the most important vegetable crops grown in the world. India is the second largest producer (5.5 MT) of onions in the world after China. It is valued for its distinctive pungent flavour and is an essential ingredient of the cuisine in many regions of the world. It can be eaten raw or cooked in to different delicacies, and for salad purpose, usually mild flavoured or colorful bulbs are chosen. Onions are generally dehydrated and pickled as processed product. The ratio of raw material to finished processed product depends on the solid content of raw material, maturity at harvest, size and shape of the bulbs and deterioration of the produce during storage (Shalunkhe and Kadam, 1998). Onions with high solid content (dry matter) are preferred for dehydration. Both, water and nutrient management for onion production have a significant effect on postharvest behaviour of the produce. These pre-harvest inputs influence the storage behaviour of onion bulbs directly or indirectly (Komochi, 1990). For example, bulbs grown under low soil moisture regimes are usually smaller and tend to loose more moisture and dry earlier during storage (Narang and Dastane, 1972). Similarly, small-sized bulbs with higher surface area loose more moisture because water vapour losses occur lengthwise from the side of onion, thus dry earlier than large-sized bulbs. Further, nitrogen has an adverse effect on storability of onions. The crop grown with higher doses of N tend to rot and sprout earlier during storage. Despite the fact that amount and frequency of irrigation influence yield and quality of onions, www.elsevier.com/locate/scihorti Scientia Horticulturae 112 (2007) 121–129 * Corresponding author. Tel.: +91 9417 479391; fax: +91 1634 225313. E-mail address: [email protected](S. Kumar). 0304-4238/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2006.12.024
Transcript
www.elsevier.com/locate/scihorti
Scientia Horticulturae 112 (2007) 121–129
Effect of differential soil moisture and nutrient regimes on
postharvest attributes of onion (Allium cepa L.)
Satyendra Kumar a,*, M. Imtiyaz b, Ashwani Kumar c
a Central Institute of Postharvest Engineering and Technology, Abohar 152116, Punjab, Indiab College of Agricultural Engineering, Allahabad Agricultural Institute (Deemed University), Allahabad 211007, India
c Water Technology Center for ER, Bhubneshwar 751023, India
Received 9 April 2006; received in revised form 3 November 2006; accepted 5 December 2006
Abstract
Studies were conducted to observe the effect of different soil moisture and nutrient regimes on postharvest attributes of onion irrigated with
microsprinkler irrigation system under semi-arid climate for 3 consecutive years (2002–2004). Soil moisture regime consisted of four irrigation
treatments based on pan evaporation replenishment (0.60, 0.80, 1.00 and 1.20 Ep). Similarly, three fertigation treatments were tried with nutrient
application rates of 100 (50:25:25), 150 (75, 37.5, 37.5) and 200 (100:50:50) kg/ha of NPK. Irrigation and fertigation had marked effect on yield,
postharvest attributes and storability of onion. Irrigation at 1.20 Ep and fertigation at 200 kg/ha produced higher bulb and dry matter yield, mean
bulb size and weight, which decreased with the decrease in amount of irrigation and fertigation. The percentage of B-grade bulbs, which is
considered commercially important, had been considerably higher at 1.20 Ep of irrigation and 200 kg/ha of fertigation. TSS increased up to
1.00 Ep and then declined slightly, whereas it varied with fertigation significantly. A decreasing trend for protein content was recorded with the
increase in irrigation from 0.60 to 1.20 Ep, however, protein content increased with increase in fertigation. Irrigation at 0.80 Ep and fertigation @
200 kg/ha resulted into minimum physiological loss in weight (%) for onion during 60 days of storage. But for extended storage period, increasing
fertigation and decreasing irrigation had adverse effect on storability of bulbs. Theoretically, 416 mm irrigation water was found optimum for
maximizing the dry matter yield of onion. Studies indicated that onion crop should be irrigated at 1.0 Ep under microsprinkler irrigation regime for
better postharvest attributes. Similarly, fertigation @ 150 kg/ha is most desirable for micro sprinkler irrigated onion crop under semi-arid climate of
S. Kumar et al. / Scientia Horticulturae 112 (2007) 121–129122
Indian farmers apply water to the crop without regard to
whether the plant actually needs it or not (Patil and Karale,
1985). The reasons behind improper use of water and fertilizers
in onion is that sufficient information is not available in India on
the simultaneous application of water and fertilizer in general
and microsprinkler irrigation in particular in relation to
postharvest attributes. Thus, there has been a great need for
investigating proper irrigation and fertigation schedule for
microsprinkler irrigated onion to get quality produce with better
postharvest life. Hence, the present studies were undertaken
with the objective to evaluate the differential water and nutrient
regimes for quality onion production and better shelf life.
2. Materials and methods
2.1. Experimental site description
The studies were carried out during crop growing season
(January–May, 2002–2004) at the research farm of Central
Institute of Postharvest Engineering & Technology, Abohar,
Punjab, India (308090N, 748130E, 185.6 m above MSL). The
soil type of experimental field was sandy loam. The physio-
chemical properties of soil and irrigation water of the
experimental site are given in Table 1. Available nutrients in
soil were determined by using the standard procedures (Tandon,
1993).
2.2. Weather conditions
The minimum and maximum temperature, humidity and
wind speed during crop growing period varied from 5 to
48 8C, from 19 to 96% and from 1.0 to 3.6 m/s, respectively.
The pan evaporation (Ep) rate varied from 0.5 to 12.0 mm/
Table 1
Physical and chemical properties of soil and water at the experimental site
Soil physical properties
Sand (%) 76.50
Silt (%) 15.4
Clay (%) 8.10
Field capacity (0–30 cm) (% (dry weight basis)) 11.49
Wilting point (0–30 cm) (% (dry weight basis)) 3.94
Bulk density (0–30 cm) (g cc�1) 1.56 g
Available water (cm m�1) 11.70
Soil chemical properties
pH (1:2.5) 8.48
EC (dsm�1) (1:2.5) 0.39
Organic carbon (%) 0.34
N (kg/ha) 51.10
P2O5 (kg/ha) 12.50
K2O (kg/ha) 300.00
Water properties
pH 7.70
EC (dSm�1) 0.51
RSC (meq/l) 1.70
Ca + Mg (meq/l) 4.10
Na (meq/l) 3.05
HCO3 (meq/l) 4.50
SAR ((meq/l)1/2) 2.13
day. Air temperature, relative humidity and wind speed were
monitored at 07:30 and 14:30 h. The greater fluctuation in
weather conditions was observed in latter part of growing
period, i.e., during the months of April and May. In general,
the higher air temperature and lower humidity resulted in
greater demand of water for the onion crop. During storage
period (June–September), average room temperature and
relative humidity varied from 24 to 36 8C and from 34 to 86%,
respectively.
2.3. Treatments
2.3.1. Irrigation treatments
The irrigation treatments consisted of four levels of
irrigation to create wide range of soil moisture regime, which
were scheduled on the basis of pan evaporation data, and were
computed as a sum of daily evaporation USWB class-A open
pan. Irrigation was applied at 0.60, 0.80, 1.00 and 1.20 of pan
evaporation (Ep) and the crop was irrigated when the sum of
previous day’s pan evaporation value reached approximately a
predetermined value of 10.50 mm. Total rainfall during the 1st,
2nd and 3rd crop growing season was 27, 36 and 11 mm,
respectively. Irrigation treatment started after 2 weeks of
transplanting of seedlings.
2.3.2. Fertigation treatments
Crop was subjected to three nutrient regimes by varying the
fertigation rate. The three fertigation treatments were as
follows:
(i) N
utrient @ 100 kg/ha with 50 kg N; 25 kg P2O5 and 25 kg,
K2O (F3).
(ii) N
utrient @ 150 kg/ha with 75 kg N; 37.5 kg P2O5 and
37.5 kg K2O (F2).
(iii) N
utrient @ 200 kg/ha with 100 kg N; 50 kg P2O5 and
50 kg K2O (F1).
F1 was recommended dose for onion as per package of
practices of nearest agricultural university for traditional
fertilization.
A water-soluble fertilizer (19:19:19, NPK grade) was
applied to the crop through microsprinkler irrigation system.
Additional nitrogen requirement was met through urea
fertigation. Fertigation was scheduled at 10-day interval and
was stopped at 90 days after transplanting.
2.4. Agronomic practices
Onion seedlings cv. Agrifound Light Red were transplanted
on 18th January every year with plant and row spacing of
0.1 m � 0.15 m. The crop was irrigated by microsprinkler
irrigation system. Microsprinklers were placed at 3 m apart and
the average discharge of microsprinkler was 64.80 lph at
1.20 kg/cm2 operating pressure. The area of each experimental
plot was 36 m2 (6 m � 6 m). A buffer zone spacing of 1.0 m
was provided between the plots. The crop was harvested in
second and/or third week of May every year.
Tab
le2
Su
mm
ary
of
AN
OV
Afo
ry
ield
and
po
sth
arves
tch
arac
teri
stic
ssi
gn
ifica
nce
of
sou
rce
of
var
iati
on
So
urc
ed
.f.
On
ion
yie
ldD
rym
atte
ry
ield
Mea
nbu
lbsi
zeM
ean
bu
lbw
eig
ht
Sp
ecifi
cg
rav
ity
To
tal
solu
ble
soli
ds
Mo
istu
reco
nte
nt
Pro
tein
con
ten
t
Mea
n
squ
are
F-v
alu
eM
ean
squ
are
F-v
alu
eM
ean
squ
are
F-v
alu
eM
ean
squ
are
F-v
alu
eM
ean
squ
are
F-v
alu
eM
ean
squ
are
F-v
alu
eM
ean
squ
are
F-v
alu
eM
ean
squ
are
F-v
alu
e
A2
76
.52
12
.66
*4
.41
35
.74
*0
.11
4.9
1*
17
8.8
62
6.2
2*
0.0
03
6.9
6*
12
.12
35
.47
*3
.45
9.7
8*
0.0
05
2.5
5ns
B3
10
24.8
01
69
.52
*1
5.4
61
25
.18
*4
.24
18
9.2
0*
28
75.3
24
21
.48
*0
.006
13
.98
*0
.99
2.9
2*
11
.69
33
.11
*0
.02
9.8
6*
A�
B6
9.7
11
.61
ns
0.8
36
.71
0.0
42
.00
ns
16
.35
2.4
0*
0.0
02
4.7
1*
1.5
64
.55
*1
.77
5.0
0*
0.0
02
1.2
4ns
C2
13
5.3
62
2.3
9*
3.9
43
1.8
8*
0.8
93
9.7
9*
27
7.9
54
0.7
4*
0.0
01
2.9
7ns
2.1
06
.14
*1
.09
3.1
0ns
0.0
63
0.1
0*
A�
C4
3.7
50
.62
ns
0.0
60
.45
ns
0.0
10
.03
ns
7.3
21
.07
ns
0.0
01
3.2
6*
0.5
71
.68
ns
1.0
02
.84
*0
.00
10
.53
ns
B�
C6
11
.68
1.9
3ns
0.1
81
.43
ns
0.0
52
.02
ns
12
.23
1.7
9ns
0.0
01
0.2
2ns
0.0
20
.05
ns
0.8
82
.48
*0
.01
15
.80
*
A�
B�
C1
21
.78
0.2
9ns
0.0
70
.54
ns
0.0
31
.25
ns
6.9
61
.02
ns
0.0
02
0.5
9ns
0.4
51
.32
ns
0.7
62
.14
*0
.00
31
.54
ns
Err
or
70
6.0
50
.12
0.0
26
.82
0.0
00
40
.34
0.3
50
.00
2
(A)
Yea
r;(B
)ir
rigat
ion
trea
tmen
ts;
(C)
fert
igat
ion
trea
tmen
ts;
*an
dn
sar
esi
gn
ifica
nt
and
no
n-s
ignifi
can
t,re
spec
tivel
y,at
p�
0.0
5.
S. Kumar et al. / Scientia Horticulturae 112 (2007) 121–129 123
2.5. Storage study
The field cured onion bulbs with a sample size of 20 kg
were stored on cemented floor in loose at room temperature.
The observation on physiological loss in weight (PLW)
was recorded at 15-day interval till 120 days of storage.
PLW included loss in weight of onion due to drying effect
of atmosphere and due to rotting. Sprouted bulbs were
also considered unsuitable for consumption and were
taken for PLW count. PLW (%) was estimated on weight
basis.
2.6. Observations
Soil samples were collected with soil auger from three
points in a plot and prepared a representative samples. The
points were selected randomly in such a way to take care the
nearest and farthest point from microsprinklers. Gravimetric
method was used to monitor the soil moisture at weekly
interval. Soil moisture was determined for 200 kg/ha fertiga-
tion treatment which was commenced after 6 weeks of
transplanting of seedling to 15 weeks after transplanting, i.e.,
critical period for bulb formation and maturity. Onion bulbs
were divided into pieces, dried at 60 8C for 48 h to determine
their dry matter content. For estimation of bulb weight,
1 m � 1 m area was earmarked from the center of the field.
With the help of total weight and number of harvested bulbs,
mean bulb weight was determined. Similarly, 5 kg sample of
onion bulbs was taken randomly from a heap of each treatment
combination and polar and equatorial diameter was measured
by using vernier caliper. Mean size of bulb was presented as
square root of polar and equatorial diameter. For grading,
onion bulbs from earmarked area of each treatment were
classified into four categories: (A) with mean size > 60 mm;
(B) with size between 60 and 41 mm; (C) with mean size
between 30 and 40 mm and (D) with mean size < 30 mm. Total
soluble solids (TSS) were estimated with hand refractometer
(0–50, ERMA, Japan). Specific gravity of onion bulb was
estimated by water displacement method (Mohsenin, 1970).
Percentage protein in the bulbs was estimated by using
spectrophotometer (Spectron 20) by following standard
procedures (AOAC, 2000).
2.7. Statistical analysis
The experiment was laid out in randomized block design
(RBD) with two factors, viz., irrigation scheduling (4) and
fertigation (3), i.e., 12 treatment combinations. The data
obtained from the experimentation of 3 years were pooled
because irrigation � fertigation � years interaction was not
significant (Table 2). Data in percentage units (physiological
loss in weight) underwent square root transformation before
analysis. Statistical analysis was done by standard analysis of
variance (ANOVA). Least significant difference (LSD) method
was used to determine whether differences existed between
certain comparisons. The probability level for determination of
significance was 0.05.
S. Kumar et al. / Scientia Horticulturae 112 (2007) 121–129124
3. Results
3.1. Soil moisture
Fig. 1 shows the dynamics of soil moisture at 0.15 and
0.30 m from 23 March to 7 May. The trend of soil moisture
depletion at 0.15 m was similar to that at 0.30 depth. The
fluctuation in soil moisture level under irrigation treatment
0.60 Ep was maximum due to greater irrigation intervals,
whereas irrigation at 1.20 Ep provided the highest irrigation
frequency, which resulted in the soil moisture very near to field
capacity. Soil moisture depletion in 1.0 Ep was often found
with in 30% of available soil moisture.
3.2. Onion bulb and dry matter yield
A significant increase in onion bulb yield was recorded with
the increase in irrigation from 0.60 to 1.20 Ep, but the trend was
found to be non-linear (Table 3). Onion bulb yield also
increased significantly with the increase in fertigation from 100
Fig. 1. Soil moisture content during bulb formation period under different
irrigation treatments in onions. (A) Soil moisture content at 15 cm and (B) soil
moisture content at 30 cm; values determined for 200 kg/ha fertigation treat-
ment in year 2004.
to 200 kg/ha. However, increase in yield with 200 kg/ha from
150 kg/ha was insignificant. Interactive effect of irrigation and
fertigation with these treatments was non-significant. Further,
dry matter yield followed the same trend as that of bulb yield
except that dry matter yields of 1.00 and 1.20 Ep of irrigation
were not statistically significant.
3.3. Irrigation production efficiency
The number of irrigation and total water applied during crop
growing season varied with irrigation treatments (Table 3). The
highest number of irrigation and depth of water was applied at
1.20 Ep of irrigation, while the minimum number and depth of
irrigation was recorded at 0.60 Ep. The highest irrigation
production efficiency for dry matter of onion was determined at
0.80 Ep of irrigation and the least at 1.20 Ep of irrigation.
3.4. Mean bulb size
An increase in bulb size was observed with the increase in
irrigation from 0.60 to 1.20 (Table 4). The size of bulb was 4.28
and 3.39 cm at 1.20 and 0.60 Ep of irrigation, respectively.
Fertigation treatments had also shown a marked effect on bulb
size. Fertigation @ 200 kg/ha produced bigger sized bulb
(4.05), followed by 150 and 100 kg/ha. However, difference
between bulb size at 150 and 200 kg/ha of fertigation was not
statistically significant (Table 4).
3.5. Mean bulb weight
A significant increase in bulb weight with the increase in
irrigation from 0.60 (28.80 g) to 1.20 Ep (51.84 g) was
observed (Table 4). Bulb weight also responded positively to
nutrient application rates with fertigation from 100 to 150 kg/
ha. Further increase in nutrients from 150 to 200 kg/ha, did not
improve the bulb weight statistically (Table 4).
3.6. Specific gravity
Specific gravity of bulbs increased progressively with the
increase in irrigation level from 0.60 to 1.20 Ep (Table 4), but
the difference at 1.00 and 1.20 Ep of irrigation was non-
significant. However, there was significant reduction in specific
gravity from 1.00 to 0.60 Ep of irrigation. The maximum
specific gravity (0.97) was recorded at 1.20 Ep of irrigation and
the minimum was recorded at 0.60 Ep (0.94). Although,
irrigation influenced the specific gravity of onion bulbs
significantly, but the effect of fertigation was statistically
non-significant (Table 4).
3.7. Total soluble solids
Total soluble solids of onion increased with the increase in
irrigation from 0.60 to 1.00 Ep, and then declined at 1.20 Ep of
irrigation (Table 4). Although, TSS at 0.80 and 1.00 Ep of
irrigation was statistically not significant, but at 1.00 Ep was
significantly higher than the others. Fertigation also had
Table 3
Number of irrigation, amount of irrigation, onion bulb yield, dry matter yield and irrigation production efficiency of dry matter of onion at different irrigation and
fertigation treatments
Treatment No. of
irrigation
Amount of
irrigation (mm)
Onion bulb
yield (t/ha)
Dry matter
yield (t/ha)
Irrigation production
efficiency (kg/m3)
Irrigation (I) at
0.60 Ep 20 289 18.50 2.85 1.00
0.80 Ep 27 358 26.69 3.96 1.13
1.00 Ep 34 436 30.44 4.37 1.02
1.20 Ep 41 506 32.45 4.51 0.91
LSD ( p = 0.05) – – 1.34 0.19 0.05
Fertigation (F) @
100 kg/ha – – 24.86 3.55 –
150 kg/ha – – 27.58 4.04 –
200 kg/ha – – 28.62 4.18 –
LSD ( p = 0.05) – – 1.16 0.17 –
Interaction
I � F – – ns ns –
Table 4
Postharvest attributes of onion bulb at different irrigation and fertigation treatments
Treatment Mean bulb
size (cm)
Mean bulb
weight (g)
Specific
gravity
TSS
(8B)
Protein
(g/100 g)
Moisture
content (%)
Irrigation (I) at
0.60 Ep 3.39 28.80 0.94 13.38 1.04 84.55
0.80 Ep 3.91 41.68 0.95 13.57 1.01 85.16
1.00 Ep 4.17 49.17 0.96 13.75 1.00 85.69
1.20 Ep 4.28 51.84 0.97 13.34 0.98 86.07
LSD ( p = 0.05) 0.08 1.42 0.01 0.32 0.02 0.32
Fertigation (F) @
100 kg/ha 3.76 39.74 0.95 13.25 0.96 85.33
150 kg/ha 4.00 43.84 0.96 13.54 1.02 85.56
200 kg/ha 4.05 45.04 0.96 13.73 1.04 85.20
LSD ( p = 0.05) 0.07 1.22 ns 0.28 0.02 ns
Interaction
I � F ns ns ns ns 0.04 0.55
S. Kumar et al. / Scientia Horticulturae 112 (2007) 121–129 125
significant effect on TSS of onion bulbs as fertigation @
200 kg/ha recorded the maximum TSS (13.73 8B) and 100 kg/
ha of fertigation had lowest TSS (13.25 8B).
3.8. Protein content
Protein content of onion bulb increased consistently with the
decrease in irrigation from 1.20 to 0.60 Ep (Table 4). Unlike
irrigation, protein content increased with the increase in
fertigation from 100 to 200 kg/ha. Interactive effect of
irrigation and fertigation was also found significant.
3.9. Moisture content
Table 4 depicts the estimated moisture content of onion bulb
before storage. Moisture content of onion bulb increased with
increase in irrigation from 0.60 to 1.20 Ep, but fertigation
treatments had no significant effect. However, interactive effect
of irrigation and fertigation was found significant.
3.10. Grades of onion bulb
The irrigation levels influenced the production of different
grades of onion bulbs considerably (Table 5). Irrigation at 1.00
and 1.20 Ep produced considerably higher percentage of A-
grade bulbs (>60 mm). Similarly, irrigation at 1.20 and 1.00 Ep
produced higher percentage of B-grade bulbs also, which are
most preferred by the consumers, but its percentage decreased
with the decrease in irrigation (Table 5). At lower irrigation
frequency, the percentage of smaller sized bulbs (C and D
grade) was higher. At 1.20 Ep of irrigation, the percentage of A-
, B-, C-, and D-grade onion bulbs was 7.50, 55.04, 32.83 and
4.63, respectively, whereas at 0.60 Ep, it was 0, 10.60, 50.59
and 38.78%, respectively.
Like irrigation, fertigation also influenced the production of
different grades of onion considerably (Table 5). Amongst all
fertigation treatments, fertigation @ 200 kg/ha produced
highest percentage of A and B grades of onion. However, a
small difference was observed between 200 and 150 kg/ha.
Table 5
Percentage of different grade onion bulbs under different irrigation and
fertigation treatments
Treatment Grade (%)
A
(>60 mm)
B
(40–60 mm)
C
(30–39 mm)
D
(<30 mm)
Irrigation (I) at
0.60 Ep 0.00 10.60 50.59 38.78
0.80 Ep 0.38 32.01 53.74 13.88
1.00 Ep 4.15 50.07 39.39 6.48
1.20 Ep 7.50 55.04 32.83 4.63
Fertigation (F) @
100 kg/ha 2.60 28.18 48.61 22.65
150 kg/ha 3.86 39.98 39.17 15.14
200 kg/ha 4.95 45.63 42.26 8.12
Fig. 3. Effect of fertigation treatment on physiological loss in weight during
storage; values averaged over 3 years.
S. Kumar et al. / Scientia Horticulturae 112 (2007) 121–129126
Similarly, significant reduction in percentage of A- and B-grade
bulbs was recorded in fertigation @ 100 kg/ha. At 200 kg/ha,
percentage of A-, B-, C- and D-grade bulbs was 4.95, 45.63,
42.26 and 8.12, respectively, while at 100 kg/ha, it was 2.60,
28.18, 48.61, 22 .65, respectively.
3.11. Storability
Physiological loss in weight measured during the storage
period of 120 days indicated that it increased with the increase
in irrigation from 0.60 to 1.20 Ep up to 45 days of storage
(Fig. 2). Thereafter, PLW increased at faster rate in 0.60 Ep
irrigation and recorded higher loss during storage than 0.80
and 1.0 Ep, while in latter part of storage, i.e., 90 days
onward, higher PLW was recorded in 0.60 Ep of irrigation and
minimum at 1.20 Ep. At 45 days of storage, PLW was
recorded 8.42 and 9.51% in 0.60 and 1.20 Ep of irrigation,
respectively, which increased to 42.80 and 29.03% after 120
days of storage for same irrigation treatments. However, PLW
at 1.00 and 1.20 Ep was not statistically significant. Similarly,
Fig. 2. Effect of irrigation treatment on physiological loss in weight during
storage; values averaged over 3 years.
up to 75 days of storage, PLW decreased with the increase in
fertigation from 100 to 200 kg/ha and thereafter, a reverse trend
was observed. Fertigation @ 200 kg/ha resulted in the highest
PLW at the end of 120 days of storage period (Fig. 3).
3.12. Production function
Water production function of dry matter yield of onion
sought through regression analysis. The production function
was found to be second-degree quadratic (Fig. 4). Mathematical
relationship indicated increase in dry matter yield with the
increase in water applied up to 417 mm, thereafter it tended to
decline. It clearly indicated that further increase in seasonal
water beyond above mentioned value is not desirable for
enhancing the dry matter yield.
Fig. 4. Relationship between dry matter yield of onion and seasonal water
applied.
S. Kumar et al. / Scientia Horticulturae 112 (2007) 121–129 127
4. Discussion
4.1. Soil moisture
In our experiments, fluctuation in available soil moisture
increased with decrease in Ep for irrigation. The greater
fluctuation in available soil moisture at 0.60 Ep of irrigation
was observed, which may be due to insufficient frequency of
irrigation. At 1.20 Ep of irrigation, soil moisture content
remained closer to field capacity as compared to other
treatments because of the highest irrigation frequency.
However, irrigation frequency at 1.00 Ep also seems to be
sufficient as soil moisture depletion was often found in the
range of 30% of available soil moisture. Yuan et al. (2003)
observed optimum soil moisture availability at 1.00 and
1.25 Ep of irrigation under drip irrigation in potato.
4.2. Bulb and dry matter yield
Our results indicated that onion bulb yield increased with
the increase in irrigation from 0.60 to 1.20 Ep. Higher yield in
irrigation treatment 1.20 Ep was recorded due to higher bulb
size and weight than the others. Frequent irrigation in 1.20 Ep
perhaps created more favorable microclimate (Fig. 1) as
available soil moisture in 30 cm top soil remained close to
field capacity than the other treatments. Chung (1989) has
also observed better onion bulb size and weight under
sufficient irrigation. Shock et al. (1998) have also observed
that onion yield is affected significantly when the available
soil moisture in the top soil surface dropped below 80%. Dry
matter yield followed the same trend as that of onion yield
because it was obtained by drying the onion bulbs. However,
our results indicated that dry matter yields of 1.0 and 1.20 Ep
of irrigation did not differ significantly. This was probably
due to the fact that moisture content contributed significantly
towards the enhancement of onion yield at 1.20 Ep from
1.00 Ep (Table 4).
Significant reduction in bulb yield when fertigation was
reduced from 150 to 100 kg/ha may be because of reduction in
size and weight of onion bulb. Subsequently, dry matter yield
reduced considerably with the reduction in fertigation. Patel
et al. (1992) have also observed higher crop yield of onion with
higher dose of fertilization. Rizk (1997) also has similar
observations on onion yield with variation in fertigation. A
further increase in nutrient application rate from 150 to 200 kg/
ha did not influence the dry matter yield significantly, perhaps
due to better utilization of nutrient applied in fertigation.
Rumple (2003) has observed that reduction of nitrogen from
200 to 125 kg in fertigation does not reduce yield of onion crop.
4.3. Irrigation production efficiency
The irrigation production efficiency (IPE) was significantly
minimum when crop was irrigated at 1.20 Ep despite the
production of highest dry matter yield, which may be due to the
fact that percentage increase in yield was lesser as compared to
increase in seasonal water applied. This corresponds to earlier
finding of Imtiyaz et al. (2000) who reported highest IPE of
onion at 80% replenishment of pan evaporation.
4.4. Bulb size and weight
Bulb size and weight was highest at 1.20 Ep of irrigation,
i.e., as and when amount and frequency of irrigation was
adequate, which is in agreement with the findings of
Woldetsadik et al. (2003). In general, mean bulb size and
weight reduced significantly with the decrease in irrigation,
which may be due to water shortage. Onion plant experienced
water stress during latter part of growing period, i.e., bulb
development under irrigation regimes of 0.60–0.80 Ep and
produced smaller sized bulbs. Begum et al. (1990) observed
that transpiration, photosynthesis and growth rates are lowered
by mild water stress and water stressed plant produced smaller
sized bulbs. Thus our results confirm the findings of Doorenbos
and Kassam (1979) and Olalla et al. (2004).
A significant increase in size and weight of bulb was
recorded with optimum dose of nutrient (Table 4). The
significantly higher size and weight of bulb with 150–200 kg/ha
of fertigation might be due to better vegetative growth with this
nutrient application, which accelerated photosynthesis and
translocation of photosynthates (dry matter) into storage organ,
resulting in an increased diameter and weight of bulb (Talha
et al., 1978; Yadav et al., 2003). Non-significant difference in
150 and 200 kg/ha of fertigation might be due to the fact that
bulb size and weight did not response linearly with fertigation
rate.
4.5. Postharvest attributes
Specific gravity of onion bulb increased progressively with
the increase in irrigation level from 0.60 to 1.20 Ep. Similarly,
specific gravity of onion bulb increased with increase in
fertigation, but it was found statistically non-significant. To our
knowledge, information regarding the effect of irrigation and
fertigation is not available in the literature. However, literature
available for other vegetable crops shows that the specific
gravity of potato tubers seems to increase with the increase in
soil water (Shock et al., 1998), although Phene and Sanders
(1976) have reported that specific gravity of potato tubers
tended to increase as water applied decrease. Under such
condition, our results need further confirmation.
Total soluble solids of onion bulb increased with the increase
in irrigation from 0.60 to 1.00 Ep and then declined. On the
other hand, TSS increased with the increasing fertigation.
Highest TSS at 1.00 Ep of irrigation and 200 kg/ha fertigation
may probably be due to fulfillment of optimum demand of crop
for moisture and nutrients and their proper utilization. This
corresponds to earlier findings of Chopade et al. (1998), who
reported higher TSS in onion with optimum water and fertilizer
application. However, in contradiction, Orta and Ener (2001)
had reported non-significant effect of irrigation on TSS of
onion.
Highest protein content in bulbs was found when crop was
irrigated at 0.60 Ep, while irrigation at 1.20 Ep produced bulbs
S. Kumar et al. / Scientia Horticulturae 112 (2007) 121–129128
with least protein content. El-Gizawy et al. (1993) have also
obtained similar results and reported that total protein content
increased significantly with the decreasing soil moisture.
Increase in fertigation from 100 to 200 kg/ha, increased protein
content of onion bulbs because of availability of higher N to the
plants and its subsequent uptake as N has been reported to
synthesize proteins in the plants.
Moisture content of onion bulb varied with variation in Ep
for irrigation due to variability in available soil moisture during
crop growing season. The highest moisture content in bulb
under 1.20 Ep may be due to prevailing higher soil moisture
during crop raising, while least moisture content in bulb under
the regimes of 0.60 Ep was probably due to the fact that crop
experienced water stress during bulb formation and maturity
period. Fig. 1 shows that 0.60 Ep of irrigation resulted in greater
fluctuation in available soil moisture, while in 1.20 Ep, soil
moisture remained closer to the field capacity than the other
treatments.
Grading of bulbs is an important parameter associated with
the postharvest quality (processing) of onion. In our experi-
ments, B-grade bulbs, which are considered important from
commercial point of view, had been considerably higher at
1.20 Ep of irrigation and fertigation @ 150–200 kg/ha, which
may be probably due to adequate availability of soil moisture
and nutrient to the plant at these irrigation and fertigation
treatments. Olalla et al. (2004) had also reported higher
percentage of large sized bulbs in the presence of optimum soil
moisture, whereas water shortage during crop growing period
led to higher percentage of smaller sized bulbs.
4.6. Storability
Our results have shown that PLW (%) increased with the
increase in irrigation from 0.60 to 1.20 Ep during the storage of
onion bulbs up to 45 days. This trend may be due to the fact that
initially bulbs had more moisture to loose when grown at
1.20 Ep, which declined with decrease in amount of irrigation.
Thereafter, it increased at a faster rate (0.60 Ep onwards) due to
spoilage of bulbs because of rotting. Our observations indicated
that crop grown under 0.60 Ep has experienced water stress and
hence it was forced to early maturity. Thus, it resulted into
development of either immature or partial matured bulbs, which
started rotting during storage at an early date in rainy season.
Ali and Shabrawy (1971) have observed increased incident of
neck rot disease in early harvested onion bulbs during storage,
which resulted in higher PLW loss. At 90 days of storage and
thereafter, higher PLW (%) in 0.60 Ep was recorded, which is
mainly due to higher sprouting of bulbs as sprouting was started
after 75 days of storage (visual observations), which verify the
findings of Narang and Dastane (1972) who have observed
marked increase in sprouting in onion bulbs grown under low
soil moisture regimes. In all, results of our study revealed that
although PLW (%) was maximum at 1.20 Ep and minimum in
0.60 Ep during 45 days of storage, but higher yield in 1.20 Ep
offset the higher storage loss. Thus, for storage of onion,
irrigation at 1.20 Ep was found to be the best irrigation
treatment for growing onion with microsprinkler.
During 45 days of storage, least PLW was recorded in the
bulbs grown under fertigation of 200 kg/ha because of lower
surface area in a constant sample weight (20 kg/ha) as
compared to smaller bulbs. It can be justified from the
observations of Thambizarsi and Narasimhan (1988) who
reported that moisture loss takes place largely from the side of
bulbs. In latter half of the storage, higher PLW was recorded in
fertigation @ 200 kg/ha, which primarily may be due to rotting
and sprouting of bulbs under higher nutrient application to the
crop. Rao and Srinivas (1990) and Batal (1991) have also
reported that higher dose of nitrogen had adverse effect on
storability of onion due as crops grown under high N dose tend
to rot early during storage than those grown under optimum
doses.
The relationship between dry matter yield and total water
applied during crop growing period was found to be polynomial
in nature due to the fact that onion bulb yield did not increase
linearly with the increase in irrigation water. According to
Imtiyaz et al. (2000), the polynomial relationship between dry
matter yield and total water applied may be due to poor soil
aeration and nutrient utilization caused by excessive water
application.
5. Conclusion
Our study indicated that onion crop should be irrigated at
1.20 Ep under microsprinkler irrigation regime for higher
percentage of A- and B-grade bulbs, onion yield and long-term
storage. However, irrigation at 1.00 Ep is most appropriate for
growing onion with better postharvest attributes. If water
becomes limiting factor, irrigation at 0.80 Ep would be most
