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Pak. J. Bot., 42(3): 1695-1702, 2010.
EFFECT OF POTASH APPLICATION ON YIELD AND QUALITY
OF TOMATO (LYCOPERSICON ESCULENTUM MILL.)
M. EHSAN AKHTAR1, M. ZAMEER KHAN1, M. TAHIR RASHID1,
ZAHIR AHSAN2 AND SAGHEER AHMAD3
1Land Resources Research Institute, National Agricultural Research Centre, Islamabad-45500, Pakistan
2Oilseed Research Lab, National Agricultural Research Centre, Islamabad-45500, Pakistan
3Sugarcrops Research Program, National Agricultural Research Centre, Islamabad-45500, Pakistan.
Abstract
A field experiment was conducted to evaluate comparative effects of sulphate and muriate of
potash (SOP and MOP) application on yield, chemical composition and quality of tomato
(Lycopersicon esculentum, M. cultivar Roma) at National Agricultural Research Centre Islamabad,
Pakistan. Potassium from two sources i.e., MOP and SOP was applied @ 0, 100 and 200 kg K ha-1
with constant dose of 200 kg N ha-1 and 65 kg P ha-1. A significant increase in tomato yield with K
application was observed. Potassium applied @ 100 kg K ha-1 as MOP produced significantly
higher marketable tomatoes as compared to SOP and control. Levels and sources of potassium
showed no effect on acidity of tomato fruits. Potash application decreased sugar content of tomato
fruits as compared to control. This effect of K on reducing sugar content was more pronounced in
K treated fruits as SOP than those of MOP. Vitamin C contents in tomato fruits increased with K
application in the form of MOP. The K use as MOP significantly reduced incidence of leaf blight
disease and insect pest attack in tomato plant as compared to SOP and control treatments.
Introduction
In Pakistan, tomatoes are grown over about 53.1 thousand hectares with an average
yield of about 10.1 tons ha-1 (Anon., 2008). However, much higher tomato yield has been
reported in other countries of the world e.g., 73.87 t ha-1 in USA, 63.55 t ha-1 in Spain,
88.91 t ha-1 in California and 146 t ha-1 in the Netherlands (Tomato News 2004). Higher
production of tomato depends upon adoption of high yielding varieties, appropriate crop
management techniques including precise and balanced fertilization, timely irrigation,
control of diseases and insect pests. In Pakistan, the tomato yields are far below than
average yield being achieved in many other countries of the world. One of the reasons of
low yield in Pakistan is imbalanced fertilizer use; nitrogen 250 kg N and phosphorus 125
kg P2O5 ha-1 are being used commonly (Anon., 2008), while the use of potash and
micronutrient are negligible. Potash use in Pakistan is only about 2 kg ha-1 (Anon., 2009).
Tomato is a heavy feeder of nutrients, especially potash as compared to cereals (Ehsan et
al., 2003a). On an average, a tomato crop producing 30 t ha-1 would require
approximately 280 kg N, 55 kg P2O5 and 540 kg K2O ha-1, (Anon., 1992; Ehsan et al.,
2003b). Traditionally SOP and MOP are being used as source of potash all over the
world, however MOP is considered a relatively cheaper source of K. Both the K sources
have similar effects on a number of crops tested (Akhtar et al., 1998). Thus the study was
planned to evaluate the sources of K2O for tomato, not only for their effects on yield, but
also on the quality of tomato, resistance against disease incidence and insect pest attack.
Material and Methods
The study was conducted at NARC experimental area and tomato variety Roma was
used as the test crop. Nursery was raised and 15 days old plants were transplanted on
M. EHSAN AKHTAR ET AL.,
1696
beds. Nitrogen and P @ 200 and P @ 65 kg ha-1 was applied. Three levels of K viz. 0,
100 and 200 kg ha-1 were applied from two sources i.e., MOP and SOP. All P and one
third of N and K fertilizers were applied at the time of transplanting as side dressing and
the remaining N and K fertilizers were applied at flower initiation and fruit setting stages.
The experiment was laid out in a randomized complete design with four replications.
Data regarding growth, yield and yield components i.e. weight and number of fruits and
incidence of disease (leaf blight; Septoria) and (white fly; Bemisia tabbacci) and fruit
borer (Heliothus armigrah) attack were recorded on the basis of number per plant and
fruits damaged. Then Diethene M-45 was sprayed twice after 10 day intervals at
flowering stage to control the disease and Nogas and Melathian at fruiting stage to
control insect pest attack. Number and weight of healthy and damaged tomato fruits were
counted and weighed separately.
Initial soil physical and chemical characteristics of experimental field like soil
texture, pH, ECe, N, P and K were determined using proper analytical techniques
(Richards, 1954; Soltanpour, 1977). Sugar, acidity and vitamin C in tomato fruits were
determined by methods given by AOAC (Anon., 1990). Plant available NO3-N, P and K
was determined by the standard procedures given by Winkleman et al., (1990). The data
collected from the experiment regarding different parameters were subjected to analysis
of variance to test the significance of treatments and treatment means were compared
using least significant difference (LSD) (Steel et al., 1997). Further, statistical analysis
was also done to compare different treatment combination using orthogonal contrasts and
their coefficients (Peterson, 1977).
Results and Discussion
Soil analysis: Soil was loam in texture and belonged to Nabipur soil series (coarse-loamy,
mixed, hyperthermic, Udic Utocrept). The soil was normal having pH 7.73, ECe, 0.59 dS m-1,
AB-DTPA extractable NO3-N 30, P 9.7 and K was 214 mg kg-1 soil (Table 1). The surface
soil contained relatively larger amounts of nutrients as compared to the lower layers because
soil was under vegetable production and there had been regular addition of farm yard manure
and fertilizers.
Tomato yield: The yield of tomatoes increased significantly with K application (Table 2).
Maximum yield of 24.9 t ha-1 was obtained with application of 100 kg K ha-1 as MOP and it
was significantly higher than control (12.6 t ha-1) and the same level of K from SOP
produced 15.4 t ha-1. The yield increase was more pronounced with K applied as MOP
compared to SOP (Table 3). The orthogonal contrast analysis clearly indicated that tomato
yield harvested from control plot significantly differed from the yield obtained from K
treated plots on overall basis. The difference between K sources also differed significantly.
The response of tomato in terms of increase in tomato yield with applied K at 100 kg ha-1 as
MOP was higher than that of applied K at 200 kg ha-1. Whereas in case of K application as
SOP, tomato yield gradually increased with increasing K rates. This indicates the
preference of the tomato variety for K source (Table 2). The results of the study are in line
with those reported by Kaviani et al., (2004). They reported that MOP treated tomato plants
gave higher yield than that of SOP under field conditions. The findings of the study are in
contrary to the work reported by Loch & Petho, (1992). They compared the response of
tomato to SOP and MOP and reported a higher response of tomato to SOP than that of
MOP. The difference regarding preferential response of tomato to K sources could be due
to nature of tomato variety tested, soil and climatic condition etc. The experimental site in
the present study is situated in high rainfall area and low levels of soluble salts. It appears
that variety had preference for relatively higher levels of chloride.
EFFECT OF POTASH ON YIELD AND QUALITY OF TOMATO
1697
Table 1. Chemical characteristics of soil of the experimental site.
OM Sand Silt Clay ECe NO3-N P K S Depth
(cm) (%) pH (dS m –1) ----------- (mg kg-1) -------------- Cl
me L-1
0-15 0.85 20 29 51 7.73 0.59 30.57 9.70 214 18.4 3.02
15-30 0.63 22 31 47 7.81 0.44 21.30 9.80 198 8.0 1.98
30-60 0.56 25 32 43 7.80 0.40 19.00 8.00 112 8.8 2.01
Table 2. Effects of potash on yield and damage by fruit borer infestation of tomato.
K2O applied
(kg ha-1) Total yield
(t. ha-1) Marketable
(t. ha-1) Damaged
(kg ha-1)
Control 12.6 c 11.6 c 943 a
100 MOP 24.9 a 24.0 a 847 ab
100 SOP 15.4 bc 14.6 bc 783 ab
200 MOP 19.2 ab 18.4 ab 951 ab
200 SOP 16.5 bc 15.8 bc 624 b
LSD 6.25 6.28 238
Note: Means followed by the similar letter(s) do not differ significantly at p≤0.05.
Table 3. Orthogonal contrast comparison of yield and fruit borer infestation infestation of tomato.
Total yield Marketable Damaged
Orthogonal contrast F. Value Prob. F. Value Prob. F. Value Prob.
Control vs K 7.95 0.05* 8.367 0.014* 4.889 0.047*
SOP vs MOP 8.819 0.012* 8.481 0.013* 1.501 0.244 NS
SOP (K100 vs K200) 0.128 0.089 NS 0.170 0.240 NS 2.101 0.173 NS
MOP (K100 vs K200) 3.86 0.073 NS 3.702 0.078 NS 54.75 0.768 NS
Note: * Significant at alpha 5%; NS = Non-significant
Tomato is a high K requiring crop and K application increased the yield though soil
had relatively high plant available K. This indicates that despite being adequate K levels
in soil, the crop K requirements for attaining higher yield could not be met from native
source, thus addition of K through fertilizers was required (Ehsan et al., 2003b).
Hariprakasa & Subramanian (1991) studied the effect of different sources and levels of K
on vegetables and reported that the higher yield of tomato was obtained with 100 kg K2O
ha-1 application under field conditions. They also reported non-significant difference
between the K sources in terms of yield. However, Nandel et al., (1993) reported that the
maximum tomato yield was obtained with 80 kg K2O ha-1. Potassium application also
affected the marketable yield as higher marketable tomato yield was obtained from K
treatments compared to control. Effect of K on increased marketable yield of tomato is in
conformity with the findings of Usherwood, (1985). Khan et al., (2005) conducted an
experiment to study the effect of NPK on yield of sugar at NIA Tando Jam, Pakistan and
reported a significant increase in sugar with K application at 150 kg ha-1.
Pattern of tomato production: Though there is a significant response of tomato to K
application, however the pattern of production remained unaffected with K treatments
i.e., K sources and their levels (Fig. 1). The figure shows that the production of fruits
started from 56 day after transplanting (DAT) and last till 110 DAT. Maximum fruit
production was obtained from 79 to 94 DAT. The difference between different treatments
became more pronounced at this growth stage.
M. EHSAN AKHTAR ET AL.,
1698
0
1000
2000
3000
4000
5000
6000
7000
56 61 69 76 79 87 94 98
Days after transplanting
Tomato yield (kg h-1)
NP
NPK 1 MOP
NPK 1 SOP
NPK 2 MOP
NPK 2 SOP
Fig. 1. Comparative effect of sources and levels of K application on tomato production.
Table 4. Comparative effects of potash on chemical composition of tomato fruit.
K2O applied
(kg ha-1) Acidity Sugar
(%) Vit C
(mg 100-1 g)
Control 1.50 4.21 a 23.13 ab
100 MOP 1.30 3.18 ab 25.99 a
100 SOP 1.33 3.15 ab 18.81 b
200 MOP 1.35 3.47 ab 25.24 a
200 SOP 1.29 2.45 b 18.77 b
LSD NS 1.40* 6.13*
* = Statistically significant; NS = Statistically non-significant
Quality of tomato pulp: Acidity of tomato fruit tended to decrease with K application
and it remained unaffected amongst the applied K sources and levels (Table 4). Similar
trend was also observed for sugar content in tomato fruits. When K as MOP was applied
at 100 kg ha-1, the sugar contents decreased and at higher K levels a slight increase was
observed. While in case of SOP, a linear decrease in sugar content was observed with
increasing levels of applied K. The maximum value of sugar content (4.2%) was
observed in the control and the minimum in treatment where K was applied at 200 kg ha-1
as SOP. In general, a decreasing trend of sugar content in tomato fruit was observed with
K application as compared to control. This decreasing trend of sugar content may be due
to dilution effect, as the yield increased significantly by K application that might have
resulted in reduction of sugar contents in tomato fruits with K treatments. The results are
in contradiction with those reported by Wuzhong (2002) who reported that K fertilization
increased sugar contents in tomato.
EFFECT OF POTASH ON YIELD AND QUALITY OF TOMATO
1699
High vitamin C contents were observed where K as MOP was applied (Table 4). The
difference between K sources was also significant and between K treatments (on overall
basis) and control was non significant (Table 5). The effect of K sources on vitamin C
content of tomato differed significantly with respect to control on overall basis. These
results are in line with those reported by Kaviani et al., (2004). They reported a decreasing
trend of Vitamin C contents with K application. Anac & Colakogle (1993) in a study on
response of some major crops to K fertilization reported a positive effect of K supply on the
vitamin C content of tomato fruits. Ibrahim (1996) also reported that sugar and vitamin C
content increased with K application regardless of the sources. It was not clear why there
was higher content of vitamin C in the tomatoes fruits treated with K as MOP, however,
Serg et al., (1993) studied the salt tolerance of tomato varieties and reported that with
increasing levels of NaCl in solution culture, Cl contents, vitamin C and acidity of tomato
fruits increased non significantly. Zubeda et al., (2007) also reported similar range of
vitamin C content in tomato fruit. Application of K as MOP the Cl contents also increased
in tomato fruit (Table 6). Nandal et al., (1993) studied the effect of different levels of P and
K nutrition on growth, yield and quality of tomato and reported that P and K application
increased the acidity and sugar contents of tomato fruit. Hariprakasa & Subramanian (1991)
also reported that acidity in tomato increased with K application.
Mineral composition of tomato: Potassium application tended to increase K content in
the tomato pulp and effect of K application on K, Na, S and Cl contents in the tomato was
non-significant. Higher rates of K from both sources tended to increase K content in
tomato pulp but the difference was statistically non-significant (Table 6). Similarly, a
slight increase in Cl content of the tomato pulp was observed where MOP fertilizer was
applied compared to control and SOP but it was also non-significant (Table 7).
Phosphorus content in tomato pulp significantly increased with K application. Higher P
concentration was observed in tomato fruits harvested from plots supplied with higher K
level from both K sources. The levels of different elements in tomato fruits were found
within the normal range for human health (Anon., 1993). The results of the study showed
that applied K had positive interaction with other nutrients in the plant system. In a field
study Khan et al., (2006) also reported a synergistic effect of foliar application of K on N
and P concentration in wheat plant.
Diseases and insect pest damage: The incidence of leaf blight Septoria was also
affected with K application. Relatively lesser number of tomato plants were affected in K
treated plots as compared to plants grown without K application on overall basis. The
disease incidence was less on the plants treated with K as MOP as compared to control.
Plants treated with K as SOP showed less resistance against disease incidence as
compared to MOP ones (Table 8). In MOP treated plots, the effect of K on suppressing
the disease was more pronounced as compared to SOP treated plots. Muriate of potash
seemed to be more effective in suppressing the disease incidence as compared to SOP.
Kirali (1976) also reported that K application suppressed damage caused by Alternaria
solani to tomato.
Insect pest attack was also influenced with K treatments. A decreasing trend of fruit
borers (Heliothus armigrah) and white fly (Bemisia tabacci) attack was observed in K
treated plants as compared to control. Damage due to the insect pest attack was reduced
with K treatments and at the higher level of applied K, it was further decreased. However,
difference among the control and K levels was statistically non-significant. The
difference between the K sources was significant as plant treated with K as MOP showed
more resistance against pest attack as compared to SOP treated plants.
M. EHSAN AKHTAR ET AL.,
1700
Table 5. Orthogonal contrast comparison of quality parameters of tomato fruit.
Acidity Sugar (%) Vitamin C
Orthogonal contrast F. Value Prob. F. Value Prob. F. Value Prob.
Control vs K 3.49 0.03* 5.77 0.03* 0.39 0.23 NS
SOP vs MOP 0.05 0.04* 1.71 0.22 NS 15.65 0.00*
SOP (K100 vs K200) 0.07 1.02 NS 10.89 0.00** 1.22 0.00*
MOP (K100 vs K200) 0.07 0.13 NS 0.22 0.00 NS 1.22 0.09 NS
Note: * = Statistically significant; NS = Statistically non-significant
Table 6. Effect of MOP and SOP on mineral composition of tomato fruit.
K Na P S Cl
K2O applied
(kg ha-1) --------------------------------------(mg kg-1)----------------------------------------
Control 1680 120 90 B 90 610
100 MOP 1980 140 130 b 110 840
100 SOP 1650 140 140 b 90 640
200 MOP 1930 150 160 a 100 880
200 SOP 1800 140 180 a 110 690
LSD NS NS 40 NS NS
* = Statistically significant; NS = Statistically non-significant
Table 7. Orthogonal comparison of different treatments on mineral composition of tomato pulp.
K (%) Na (%) P (%) S (%) Cl (%)
Orthogonal
contrasts F.
Value Prob. F.
Value Prob. F.
Value Prob. F.
Value Prob. F.
Value Prob.
Control vs K 1.23 0.29 NS 1.03 0.33 NS 8.43 0.01* 1.43 0.25 NS 0.09 0.00 NS
SOP vs MOP 2.88 0.11 NS 0.00 0.03* 0.00 0.20 NS 0.00 0.03 NS 1.81 0.20 NS
SOP (K100 vs K200) 0.64 0.00 NS 0.00 0.06 NS 0.46 0.02* 0.00 0.75 NS 0.05 0.00 NS
MOP (K100 vs K200) 0.01 0.07 NS 0.00 0.11 NS 1.28 0.28 NS 0.00 0.12 NS 0.49 0.00 NS
* = Statistically significant; NS = Statistically non-significant
Table 8. Effect of MOP and SOP on disease and insect pest incidence on tomato.
K2O applied (kg ha-1) Disease incidence Insect pest damage
Control 12.0 a 14.0
100 MOP 4.3 b 11.0
100 SOP 7.9 ab 11.0
200 MOP 5.3 b 9.0
200 SOP 8.7 ab 9.0
LSD 6.9 NS
* = Statistically significant; NS = Statistically non-significant
Table 9. Orthogonal comparison of different treatments on disease and insect pest incidence.
Insect pest damage Disease incidence
Treatments F Value Prob. F Value Prob.
Control vs K treatments 1.325 0.272 NS 5.835 0.033*
SOP vs MOP 0.167 0.044 * 2.440 0.144 NS
SOP (K100 vs K200) 2.813 0.097 NS 1.596 0.064 NS
MOP (K100 vs K200) 2.813 0.188 NS 1.596 0.089 NS
* = Statistically significant; NS = Statistically non-significant
EFFECT OF POTASH ON YIELD AND QUALITY OF TOMATO
1701
Conclusions
Application of K from both the sources of K increased tomato yield, however MOP
was more effective im improving yield and quality of tomato. Though, soil K level was in
the high range, it couldn’t meet the requirements for high yield crop of tomato. Hence,
the generalized adequacy range of K in soil needs to be refined for vegetable production,
especially for high yield agriculture.
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(Received for publication 15 November 2009)