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Intuition Journals
Intuition Journal of Agricultural Research
Vol 1(1) pp. 001-009 April, 2015
http://www.intuitionjournals.org/ijar
Copyright © 2015 Intuition Journals
Research Paper
Effects of NPK Fertilizer and Irrigation intervals on Tuber Composition of Potato
(Solanum tuberosum L.) in Sudan savannah of Nigeria
A Muhammad1*, EB Amans2, BA Babaji2, NC Kuchinda2 and BA Gambo3
1
Department of Crop Science, Kebbi State University of Science and Technology, Aliero, Nigeria
2
3
Department of Agronomy, Ahmadu Bello University, Zaria, Nigeria
Department of Crop Production, University of Maiduguri, Borno State, Nigeria
Accepted 6th March, 2015
Field trials were conducted during the 2009/10, 2010/11 and 2011/12 dry seasons at the Teaching and Research Farm of
Kebbi State University of Science and Technology, Aliero, located at Jega in the Sudan savanna zone of Nigeria. The aim
was to study the effects of irrigation interval and NPK fertilizer rates on tuber dry matter, carbohydrates and crude
protein (CP) of three varieties of potato (Solanum tuberosum L). Treatments consisted of three irrigation intervals (3, 6
and 9 days), four rates of NPK [20:10:10] fertilizer (0, 300, 600 and 900kgNPK/ha) and three varieties of potato (Bertita,
Diamant and Nicola). Factorial combinations of irrigation intervals and fertilizer rates were allocated to the main-plots,
while varieties were assigned to the sub-plots in a split plot design, replicated three times. The size of each sub-plot was
4.5 x 3m (13.5m). Results revealed that the CP was not affected by irrigation interval. But with fertilizer, 600kg NPK/ha
gave the highest CP, above which there was no further response. Diamant and Bertita had significantly higher tuber dry
matter content than Nicola. Higher tuber carbohydrate content was recorded by Nicola and Bertita than Diamant; while
crude protein was higher in Bertita than both Nicola and Diamant. From the result of this study, variety Bertita proved to
be superior in terms of tuber crude protein; and was comparable to Diamant in terms of tuber dry matter; and Nicola in
terms of tuber carbohydrates. The use of 600kgNPK/ha was optimum for good tuber quality.
Keywords: Potato variety, NPK fertilizer, tuber composition, Sudan savanna.
Introduction
Irish Potato (Solanum tuberosum L.) originated in the high
plains of the Andes Cordillera where it is largely cultivated for
food. The Spanish, who conquered Peru, discovered the crop
and introduced it to Spain and the west of Europe in the mid16th century (Fergeria et al., 1991; Rolot, 2001). In Africa, it
was not until the end of the 19th century that potato was
imported from Europe by missionaries and the colonial
administration (Rolot, 2001).
Corresponding Author: [email protected]
Potato is one of the word's prime sources of human
nutrition. The protein/carbohydrate ratio is higher than for most
cereals and even higher than those of the other tuber and root
crops (Okonkwo et al., 1995). In terms of composition, potato
tuber contains 70 – 82% water, 17 – 29% dry matter, 11 – 23%
carbohydrate, 0.8 – 3% protein, 0.1% fat and 1.1% minerals.
Production per hectare of important vitamins, such as thiamine,
riboflavin, niacin and vitamin C is higher in potato than in other
major crops, such as rice, maize and wheat (Rolot, 2001;
Muhammad et al
Int. J. Agri Res.
Okonkwo et al., 1995; Beukema and Zaag, 1990; Harris,
1992). According to Okonkwo et al. (1995), daily consumption
of 1 kg of potato tuber provides all the essential amino acids
needed by the body, except cystine and methionine. Apart
from more conventional ways of using potato as food stuff,
industrial processes have become increasingly prominent in
industrialized countries, and have considerably widened the
range of possible uses of the crop. In the food sector, potatoes
are processed into deep-frogmen chips and mashed potato.
By-products such as potato starch, glucose and dextrose are
used in the brewing industry, confectionery and in the
distillation of alcohol. In the non-food sector, by- products such
as potato starch, starch proper and dextrin are used in
processes for the manufacture of cardboard, glues, textiles
and paints, and in the laundry business as ironing sprays
(Harris, 1992; Rolot, 2001).
High tuber dry matter content is particularly to be desired
in potatoes for processing. However, according to IPI (1993), N
and K application reduced tuber dry matter, content, with the
effect being less in K than N. But P was reported to slightly
increase tuber dry matter content. Protein content usually
expressed as a percentage of dry matter is favorably
influenced by increase in N and K, but reduced by the
increasing application of P (Singh, 2004). To achieve high
tuber quality, it is recommended to fertilize using NPK fertilizer
with less N than P and K (Vos, 1999).
Depending on the mineral fertilizer forms, rates and
nutrient ratios; the contents of dry matter, starch, protein and
other substances may either increase or decrease. Excessive
nitrogen fertilization reduces starch, dry matter and sugar
contents in tubers and potatoes deteriorate more rapidly during
storage (Shock et al., 1999). This results from the fact that
nitrogen promotes growth of potato vines, and when lasting
drought occurs, the vines that have grown so large are most
dramatically affected and the growing season is extended. The
tubers, if harvested under such conditions, may not have been
able to mature completely and reach maximum dry matter
content. The starch also accumulates less rapidly, and part of it
is used for respiration (Eiasu et al., 2007). Dry matter content
is affected by various factors, among which the most significant
are tuber maturity, character growth, plant nutrient and water
uptake (Harris, 1992). This study was carried out to determine
some tuber quality attributes of selected potato varieties, in
response to irrigation intervals and NPK fertilizer rates.
2.0 Materials and Methods
The experiments were conducted during 2009/10, 2010/11 and
2011/12 dry seasons at the Teaching and Research Farm of
the Kebbi State University of Science and Technology at Jega
(lat. 120 11' N; long. 40 16' E) in the Sudan savanna
ecological zone of Nigeria. The climate of the area is semi-arid
with an average rainfall of about 550mm - 650mm per annum.
The relative humidity ranges from 21 - 47% and 51 - 79%
during the dry and rainy seasons, respectively. The
temperature ranges between 14 - 30oC during the dry season
and 27 – 41oC during the rainy season (Anonymous, 2012).
The treatments consisted of three irrigation intervals (3, 6,
and 9 days), four rates of NPK (20: 10: 10) fertilizer (0, 300,
600 and 900kg/ha) and three potato varieties (Nicola, Bertita,
and Diamant). The treatments were laid out in a split - plot
design with three replications. Irrigation intervals and fertilizer
rates were combined and allocated to the main plots while
variety was assigned to the subplots. The planting material
(seed tubers) for the three varieties was sourced from the
| 002
Potato Program Unit of the National Root Crop Research
Institute (NRCRI) sub-station Vom, Jos, Plateau State. The
seed tubers were pre-sprouted for six weeks before planting.
The seed tubers were dressed with fungicide (Muncozeb
powder) a day prior to planting. Planting was done manually
with whole or cut tubers of approximately 30g weight per hill at
intra-row spacing of 30cm and a depth of 8 – 10cm. Plots of
3.0 x 4.5m (13.5m2) were marked out, leaving a 1m space
between main plots. Each subplot was made into six ridges,
75cm apart. Water channels were constructed for effective
supply of water to each furrow during irrigation. The net plot
area consisted of the two middle rows (3.0 x 1.5m) (4.5m2).
The source of water was a tube well. Water pump
machine was used to draw water from the source to the field
through the constructed water channels. Irrigation was
scheduled according to the treatments, at 3, 6 and 9 days
interval. The whole field, irrespective of the irrigation treatment,
was watered 3 days before and after planting. The irrigation
treatment was imposed after the crop has fully emerged [within
3 weeks after planting (WAP)]. Compound fertilizer (NPK 20:
10: 10) was used at the variable treatment rates of 0, 300, 600
and 900kg NPK/ha. These rates were applied according to the
treatments in two split doses; the first and second doses were
applied at planting and at 4WAP, respectively. The fertilizer
was applied at about 10cm away from plant stand and 5cm
deep and covered. Weeds were controlled manually using
hand-hoe at 4 and 7 WAP. Karate (lambdacyhalothrin) was
sprayed at 4mlL-1 of water against insect pests. The crop was
harvested on 16th February, 2010; 12th February, 2011; and
11th February, 2012; for the 2009/10, 2010/11 and 2011/12
trials, respectively. A light irrigation was given to all plots a
day for harvesting irrespective of the irrigation treatment to
facilitate easy lifting of tubers.
Harvested tubers were sampled from each net plot,
sliced to very small pieces and oven-dried at 700C to a
constant weight in a paper bag. The tuber dry matter (DM) was
estimated as: DM= (Wd / Wf) x100, where Wd and Wf are
tuber dry and fresh weights, respectively. The oven-dried tuber
samples from each net plot were grounded, sieved and
analyzed for N contents in the laboratory using one gram each
of the samples by Micro Kjeldhal procedure. The crude protein
content of tubers was estimated by multiplying the total
nitrogen (N) content of the tuber by 6.25 as described by Yusuf
et al. (1999) Tuber carbohydrate content was estimated as
Nitrogen Free Extract (NFE) and was calculated as: NFE = 100
– (crude protein + moisture + crude fiber). Data generated
were subjected to analysis of variance (ANOVA) in accordance
with Gomez and Gomez (1984). The treatment means were
separated using the Duncan's Multiple Range Test (DMRT)
(Duncan, 1955).
3.0 Results
3.1 Percent Tuber Dry Matter Content
The proportion/percentage dry matter content (DM) as
influenced by irrigation interval, fertilizer rate and variety in the
three dry seasons and the combined is presented in Table 1.
Except in 2009/10, irrigation intervals of 3 days consistently
increased tuber dry matter contents in all the seasons and the
combined data. In 2009/10, 3 and 6 days intervals gave, the
more tuber dry matter than 9 days intervals. In 2009/10,
application of 900kg NPK/ha produced significantly higher DM
than only 300kgNPK/ha, which was in turn higher than the
untreated control. In 2010/11, 2011/12 and the combined data,
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Muhammad et al
Int. J. Agri Res.
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fertilizer rates of 600 and 900kgNPK/ha gave higher DM than
300kgNPK/ha and the lowest was in the untreated control.
Varieties Bertita and Diamant produced statistically similar
DM, with Bertita being significantly higher than Nicola in
2009/10 dry season. In 2010/11 dry season, variety Diamant
gave significantly higher DM than Bertita, which in turn was
superior to Nicola. Both Bertita and Diamant were at par in
terms of DM and each produced significantly higher percent
tuber dry matter than Nicola in 2011/2 and the combined
seasons. Interactions of irrigation intervals, NPK rates and
variety of percent tuber dry matter were not significant in all
trials and the combined data.
significant effect of irrigation interval on tuber nitrogen content
in all the seasons and in the combined data. Application of 600
and 900kgNPK/ha gave more tuber nitrogen content than 300
and 0kg NPK/ha in 2010/11, 2010/11 and the combined data.
But in 2011/12 season, tuber nitrogen content was not affected
by NPK rates. Varieties Bertita and Diamant produced
statistically the same tuber nitrogen content in 2009/10 and
2010/11 and each was superior to Nicola. In 2011/12 and the
combined data, Bertita was superior to Nicola, and Diamant
was at par with both Bertita and Nicola. Interactions of
irrigation intervals, NPK rates and variety of tuber nitrogen
content were not significant in all trials and the combined data.
3.2 Percent Tuber Carbohydrate Content
3.4 Percent Tuber Crude Protein Content
Irrigation interval and fertilizer rates did not have any significant
effect on percent tuber carbohydrate content throughout the
seasons and in the combined data as shown in Table 2. In
2009/10 and 2010/11, Nicola had the highest tuber
carbohydrate content followed by Diamant, and the lowest was
in Bertita. In 2011/12 the combined data, Nicola and Bertita
were at par, each of which had significantly higher percent
carbohydrate content than Bertita. Interactions of irrigation
intervals, NPK rates and variety of percent tuber carbohydrate
content were not significant in all trials and the combined data.
The effects of irrigation interval, fertilizer rate and variety of
tuber crude protein (CP) content are presented in Table 4.
Irrigation interval did not show any significant effect on tuber
crude protein content in all the three dry seasons, and the
combined mean. Fertilization at 600 and 900kgNPK/ha
produced similar and significantly higher percent tuber crude
protein than the two other rates in 2009/10, 2010/11 and the
combined means, except in 2010/11 when 0 and 399kgNPK/ha
was at par with 600kgNPK/ha. Variety Bertita consistently gave
higher percent tuber crude protein than Diamant and Nicola in
the three trials and the combined data. In the combined data,
Diamant in turn gave more protein content than Nicola.
Interactions of irrigation intervals, NPK rates and variety of
tuber crude protein content were not significant in all trials and
the combined data.
carbohydrate content in varieties Nicola and Bertita over
Diamant, and crude protein in Bertita over Nicola and Diamant
further indicated the genetic variation among the three varieties
tested in this study (Babaji et al., 2008; Manrique and
Barthlomew, 1991).
3.3 Percent Tuber Nitrogen Content
Tuber nitrogen content as influenced by irrigation interval,
fertilizer rate and variety is presented in Table 3. There was no
4.0 Discussion
The tuber content of N, P, K, crude protein and carbohydrate
was generally not affected by irrigation interval. This is in line
with Pereira and Shock (2006) who opined that although water
is the main medium through which soil nutrients are made
available to plants, the mobilization of the individual nutrient to
other plant parts like tubers depends on the amount of
nutrients present, the crop’s physiological demand for the
nutrients and genotype. The tuber contents of N and CP were
maximized with the application of 600kgNPK/ha above which
there was no further significant positive response. The high
content of the applied fertilizer, particularly the 600 and
900kgNPK/ha rates, in addition to the inherent high soil fertility
might have resulted in ample uptake and translocation of N,
which is a factor in protein synthesis; to the plant system and
its subsequent mobilization to other plant parts, including the
tubers. According to Adhikari and Sharma (2004), N and K
application reduced tuber dry matter, content, with the effect
being less in K than N, but P was reported to slightly increase
tuber dry matter content. Protein content usually expressed as
a percentage of dry matter was enhanced by increase in N and
K but reduced by increasing P application (Shukla and Singh,
1976; Ezzat et al., 2011). The significantly high tuber
5.0 Conclusion
From the result of this study, it could be concluded that
application of 600kgNPK/ha is optimal for good potato tuber
quality. Also variety Bertita proved to be superior in terms of
crude protein and relatively comparable in terms of dry matter
and carbohydrate contents, to the other two varieties.
6.0 Acknowledgements
The authors wish to express their gratitude to the Kebbi State
University of Science and Technology, Aliero, for providing the
enabling environment for the successful conduct of this
research. We also acknowledge the effort of the Coordinator of
the Potato Program Unit of the National Root Crop Research
Institute (NRCRI) sub-station Vom, Jos, Plateau State, in
person of Dr. Amadi Charles who provided the potato varieties
used in this study.
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Table 1: Effect of irrigation interval and NPK rates on tuber dry matter of three potato
varieties in 2009-12 dry seasons and the combined data at Jega
Treatments
Dry Seasons
2009/10
2010/11
2011/12
Combined
Bertita
23.75a
22.20b
22.92a
22.96a
Diamant
22.48ab
23.40a
23.38a
23.09a
Nicola
21.82b
20.47c
21.95b
21.41b
SE±
0.510
0.37
0.33
0.24
3
24.40a
23.81a
23.84a
24.01a
6
23.36a
22.20b
22.85b
22.45b
9
21.19b
19.06c
20.56c
22.33c
SE±
0.523
0.379
0.384
0.271
0
20.13c
20.56c
18.45c
19.71c
300
22.89b
21.15b
22.44b
22.16b
600
23.23ab
22.82a
23.83a
23.29a
900
23.47a
22.96a
24.09a
23.51a
SE±
0.603
0.438
0.443
0.313
IxF
NS
NS
NS
NS
IxV
NS
NS
NS
NS
FxV
NS
NS
NS
NS
IxFxV
NS
NS
NS
NS
Variety
Irrigation interval (days)
NPK rates (kg ha-1)
Interactions
Means followed by the same letter(s) within a treatment group are not significantly different
using DMRT at 5%. Ns= not significant.
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Table 2: Effect of irrigation interval and NPK rates on tuber carbohydrate content (%) of three
potato varieties in 2009-12 dry seasons and the combined years at Jega
Treatments
Dry Seasons
2009/10
2010/11
2011/12
Combined
Bertita
71.59c
74.14c
72.28b
72.67b
Diamant
83.04b
82.29b
83.42a
83.42a
Nicola
83.66a
83.57a
83.64a
83.62a
SE±
0.260
0.270
0.270
0.130
3
80.81
80.61
80.69
80.70
6
79.96
79.95
80.25
80.05
9
80.54
80.43
80.40
80.46
SE±
0.536
0.509
0.532
0.213
0
80.91
80.72
80.73
80.79
300
80.63
80.43
80.72
80.59
600
79.61
79.96
79.54
79.99
900
80.58
80.63
80.81
80.67
SE±
0.618
0.588
0.614
0.246
IxF
NS
NS
NS
NS
IxV
NS
NS
NS
NS
FxV
NS
NS
NS
NS
IxFxV
NS
NS
NS
NS
Variety
Irrigation interval (days)
NPK rates (kg ha-1)
Interactions
Means followed by the same letter(s) within a column in each treatment are not significantly
different at 5% using DMRT. NS= not significant.
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Table 3: Effect of irrigation interval and NPK rates on tuber nitrogen content (%) of three potato
varieties in 2009/12 dry seasons and the combined years at Jega
Treatments
Dry Seasons
2009/10
2010/11
2011/12
Combined
Bertita
1.48a
1.47a
1.47a
1.47a
Diamant
1.38a
1.36a
1.35ab
1.36ab
Nicola
1.27b
1.30b
1.32b
1.30b
SE±
0.04
0.05
0.04
0.02
3
1.30
1.34
1.32
1.32
6
1.36
1.40
1.42
1.39
9
1.31
1.37
1.39
1.36
SE±
0.075
0.083
0.081
0.032
0
1.25b
1.33b
1.37
1.32b
300
1.27b
1.33b
1.36
1.32b
600
1.44a
1.43a
1.47
1.45a
900
1.45a
1.45a
1.46
1.45a
SE±
0.087
0.096
0.094
0.037
NS
NS
NS
NS
NS
NS
NS
NS
FxV
NS
NS
NS
NS
IxFxV
NS
NS
NS
NS
Variety
Irrigation interval (days)
NPK rates (kg ha-1)
Interactions
IxF
IxV
Means followed by the same letter(s) within a column in each treatment are not significantly
different at 5% using DMRT. NS= not significant.
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Table 4: Effect of irrigation interval and NPK rates on tuber crude protein (%) of three potato
varieties in 2009-12 dry seasons and the combined data at Jega
Treatments
Dry Seasons
2009/10
2010/11
2011/12
Combined
Bertita
9.25a
9.19a
9.19a
9.19a
Diamant
8.63ab
8.50ab
8.44b
8.50b
Nicola
7.94b
8.13b
8.25b
8.13c
SE±
0.24
0.28
0.26
0.12
3
8.12
8.37
8.25
8.12
6
8.49
8.75
8.87
8.53
9
8.18
8.56
8.68
8.37
SE±
0.472
0.520
0.508
0.212
0
7.81b
8.31b
8.56
8.23b
300
7.92b
8.31b
8.49
8.24b
600
8.99a
8.96ab
9.20
9.05a
900
9.10a
9.10a
9.13
9.10a
SE±
0.545
0.600
0.586
0.245
IxF
NS
NS
NS
NS
IxV
NS
NS
NS
NS
FxV
NS
NS
NS
NS
IxFxV
NS
NS
NS
NS
Variety
Irrigation interval (days)
Fertilizer NPK (20:10:10) kg/ha
Interactions
Means followed by the same letter(s) within a column in each treatment are not significantly
different at 5% using DMRT. NS= not significant.
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Appendix I: Physical and chemical properties of the soil of the experimental site in 200912 dry seasons
2009
2010
2011
Sand (g kg-1)
800
624
687
Silt (g kg-1)
157
254
250
Clay (g kg-1)
43
122
103
Soil Textural Class
Sandy loam
Sandy loam
Sandy loam
pH (Water)
5.6
5.9
6.1
pH (CaCl2)
5.5
5.7
5.6
Organic carbon (%)
0.4
0.8
1.0
N (g kg-1)
0.32
0.37
0.52
P (mg kg-1)
1.38
1.21
1.29
K (Cmol kg-1)
0.54
0.99
0.97
Na (Cmol kg-1)
0.39
0.44
0.52
Ca (Cmol kg-1)
0.45
0.33
0.30
Mg (Cmol kg-1)
0.50
0.70
0.85
CEC (C mol kg-1)
1.88
2.46
2.64
Physical properties
Chemical properties
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Appendix II: Mean monthly temperatures, relative humidity and solar radiation at the experimental site during the period
of the experiments (2009, 2010, 2011 and 2012)
Month
Temperature (OC)
2009
201
Relative Humidity
Solar Radiation
(%)
(kcalcm-2)
2011
2012
2009
2010
2011
2012
2009
2010
2011
2012
0
January
-
23.8
25.8
23.4
-
27
25
24
-
14.5
15.7
14.8
February
-
26.0
27.3
25.8
-
23
22
20
-
18.3
17.4
17.6
March
-
30.8
30.7
31.7
-
22
22
20
-
18.3
17.5
17.2
April
-
35.0
35.6
34.9
-
33
38
30
-
18.0
17.7
17.5
May
-
33.2
33.9
34.2
-
39
35
38
-
18.7
18.6
18.3
June
-
28.2
30.4
31.4
-
52
55
60
-
17.3
17.5
17.6
July
-
27.2
26.8
-
-
70
68
-
-
15.2
15.4
-
August
-
27.2
26.7
-
-
79
80
-
-
14.7
14.9
-
September
-
26.8
25.2
-
-
78
81
-
-
17.2
17.5
-
October
29.2
26.7
28.6
-
47
62
69
-
17.8
16.4
16.8
-
November
29.4
28.4
29.6
-
29
30
27
-
17.3
17.6
17.8
-
December
26.9
25.3
25.8
-
27
26
25
-
16.7
16.5
16.9
-
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