Agricultural Science Research Journal Vol. 2(1), pp. 1 - 12, January 2012
Available online at http://www.resjournals.com/ARJ
ISSN-L: 2026-6073 ©2012 International Research Journals
Full length Research paper
Sweet Potato Growth Parameters as Affected by
Farmyard Manure and Phosphorus Application at
Adami Tulu, Central Rift Valley of Ethiopia
Teshome Abdissa1, Nigussie Dechassa2 and Yibekal Alemayehu2
1
Adami Tulu Agricultural research centre P.O. Box 35
Haramaya University College of Agriculture and Environmental Science
2
Corresponding author email: degituabdissa@gmail.com
ABSTRACT
Sweet potato is among the most important root crops produced in the central rift valley of Ethiopia.
However, the yield obtained in the area is far below its genetic potential. The major cause of the low
yield is the use of poor agronomic practices. Specifically, scarcity of information on the appropriate
rates of fertilizers to be applied for growing the crop is one of the problems limiting yield. Therefore, a
field experiment was conducted to investigate the effect of farmyard manure and phosphorus on the
yield and yield components of the crop at Adami Tulu, central rift valley of Ethiopia during the 2010
-1
main cropping season. The treatments consisted of five levels of FYM (0, 5, 10, 15, 20 t ha ) and three
-1
levels of P (0, 90,180 kg P2O5 ha ).The experiment was laid out as a Randomized Complete Block
Design in a factorial arrangement, and replicated three times. A sweet potato cultivar known as Belela
was used for the study Analysis of the results showed that the main effect of FYM significantly (P <
0.05) affected tuberous root length and shoot fresh weight, However, the main effect of P had no any
significant influence on all parameters studied except days to budding and maturity. Moreover, the
interaction effects of FYM and P significantly (P<0.05) affected tuberous root diameter, vine length and
shoot dry weight. Among those growth parameters studied, branch number/plant and number of
tuber/plant is not significantly affected by either of the fertilizer. Even though it was in statistically
parity at the other levels of farmyard manure, average tuberous root length increased by 17.07% when
-1
the rate of FYM increased from 5 to 20 t ha .In response to increased supply of the fertilizer towards 15t
-1
-1
ha and 20t ha shoot fresh weight increased significantly (P<0.05) by 33.03% and 54.96%, respectively.
The earliest maturity was attained by plants grown under the treatment of combined application of 20 t
-1
-1
ha FYM and 180 kg ha P2O5 (95), which was in statistical parity with the maturity days of plants that
-1
-1
received 15t ha FYM and 180 kg ha P2O5 (96 days).Therefore, it could be concluded the tuberous root
yield components of sweet potato was significantly enhanced in response to the application of
farmyard manure, indicating that enriching the soil of the area with organic matter through the use of
organic fertilizers holds the key for maximizing the yield of the sweet potato crop in the study area.
Key words: Sweet potato, Belela, Yield component, fertilization
INTRODUCTIONS
Sweet potato (Ipomoea batatas L.) is an herbaceous
dicotyledonous plant with creeping, perennial vines and
adventitious roots, and belongs to the family
Convolvulaceae (morning glory).
Globally it is among the important food crops in the
world, after wheat, rice, maize, Irish potato, and barley
and it ranks second following Irish potato in the world’s
root and tuber crops production and third after Irish
potato and cassava in consumption in several parts of
tropical Africa (Linne 1991)
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Agric. Sci. Res. J.
In Ethiopia, sweet potato has been cultivated for many
years and is important in diet where population growth is
highest, land holding is least and threat of large-scale
starvation is ever present (Habtu 1995). Over 95 percent
of the crop is produced in the South West, Eastern and
Southern parts where it has remained for centuries as
one of the major subsistence crops especially in the
periods of drought [Adhanom et al.1985]
Adhanom (1985) reported that sweet potato currently
covers about 75,000 hectares of land in Ethiopia with an
-1
average national yield of about 8 t ha which is low
compared to the world’s average production of about
-1
14.8 t ha . Production is mainly for food and it is also
cultivated to feed animals as well (Tesfaye et al.2008)
Tenaw et al (2001) Reported that the potential yield of
-1
sweet potato reached up to 50 t ha on research station
-1
and 17.5-30.50 t ha
on farms with improved
management practices. In addition, (Bwembya and
Yerokun, 2001) reported that sweet potato yield under
-1
research field ranged from 30-35 t ha with improved
cultivars. According to (Teshome and Amenti2010),
-1
average yield of 37.1 t ha was obtained for the Belela
variety at Adami Tulu area without application of fertilizer.
However, because of poor management practices, the
actual yield obtained under farmers’ condition has been
very low. A number of experiments were conducted in
Ethiopia to determine the response of sweet potato to NP
fertilizers. So far, the results of the experiments have
showed that the plant does not respond to NP fertilizer
application significantly as expected (Ambacha 2001)
Farmers in the study area are aware of the response of
sweet potato and other related crops to applied nutrients
and raise the crop in homesteads using farmyard
manure, household wastes etc. However, they do not
know the rate of farmyard manure and its combined
effect with inorganic fertilizers for high production of the
crop
In view of this fact, a systematic investigation into the
effect of using commercial fertilizers like phosphorus and
locally available, accessible and affordable farmyard
manure is of paramount importance for increasing yield
components of sweet potato that is a good estimator of
yield. To address those problems, the study was initiated
with the objective of investigating the effect of
phosphorus and farmyard manure yield components of
sweet potato.
Material and Methods
Description of the Study Area
The experiment was conducted at the Research farm of
Adami Tulu Agricultural Research Centre during the main
cropping season of 2010. Adami Tulu Agricultural
Research Centre (ATARC) is located in the central Rift
Valley of Ethiopia at a distance of about 167 km South of
Addis Ababa on the road to the town of Hawassa. It lies
0
0
at a latitude of 7 9’N and a longitude of 38 7’E. It has an
altitude of 1650 meters above sea level with a bimodal
and unevenly distributed average annual rainfall of 760
mm. Rainfall extends from February to September with a
dry period from May to June, which separates the
preceding ‘’short’’ rains from the following ``long’’ rains.
The pH of the soil is 7.88. The soil is fine sandy loam in
texture with sand, clay and silt in proportions of 34, 48
and 18%, respectively (ATARC 1998)
Planting material
A standard variety of sweet potato called Belela was
used for the experiment by collecting vine cuttings from
ATARC. The cultivar was selected because of its
adaptability, high yield potential, diseases resistance and
early maturity (90-120 days of planting the vine).
Treatment and experimental design
The treatments consisted of five levels of farmyard
-1
manure (0, 5, 10, 15, 20 t ha ) and three levels of
-1
phosphorus (0, 90, 180 kg P2O5 ha ). The experiment
was laid out as a Randomized Complete Block Design
(RCBD) in a factorial arrangement with three replications
per treatment. Thus, there were 5 x 3=15 treatment
combinations, replicated three times numbering a total of
45 experimental units.
Data Collection and analysis
Data were collected on; days to bud sprouting, average
length of tuberous roots shoot fresh weight, average
number of branches per plant, average root number per
plant, average tuberous root diameter, average vine
length, and day to maturity. All data were subjected to
analysis of variance using SAS statistical software (SAS,
2000) version 8.1. To evaluate the degree of association
among dependent variables, correlation matrix was done
using Gen-stat software whenever it was applicable. For
dependent discrete variables whose data were
heterogeneous, log transformation were done to ensure
homogeneity. For treatments that were significant, mean
separation was done using the Least Significant
Difference (LSD) test at both 1% and 5% probability level.
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Abdissa et al.
3
Table 1. General characteristics of the planting material
1
2
3
4
5
Characteristics
Maturity
Root colour
Taste
Market preference
Root growth habit
6
Vine development
7
Preference of
Farmers’
Variety (Belela)
Early (90-120) days in the study area
Light white while raw and yellow when boiled
Milder
Moderate to high
Vertically downward(carrot type growth root system)
- Easy for farmers while they harvest root for consumption and
market display
-Vertical up ward and free of soil born disease and insect pest that
will be aggravated by rainfall splash.
- Easy to conduct different cultural practice because of the
manageable vine.
Highly preferred because of easy to operate management practice,
high yield and early maturity
Source: - Abdissa et al, 2011
Table 2. Pre-planting soil test result of the study area
Particle size (%)
Sand
silt
Clay
44
34
22
Textural
class
OC
(%)
TN
(%)
AP
ppm
loam
2.38
0.389
37.41ppm
Exchangeable Cation (cmol(+)/kg soil)
Mg
Ca
K
Na
CEC(meq/100gsoil)
3.06
22.95
1.8
4.42
15.70
Key: - OC: organic carbon; TN: Total nitrogen; AP: Available Phosphorous; CEC: Cation Exchange Capacity
RESULTS and DISCUSSION
Days to bud sprouting
Selected Physico-chemical Properties of the Soil of
the Experimental Site
The main effects of phosphorus and FYM significantly (P
< 0.01) and (P < 0.05) influenced the days to bud
sprouting of sweet potato, respectively (Table 10).
Similarly, this trait was significantly (P < 0.05) influenced
by the interaction effect of FYM and phosphorus.
-1
Combined application of 20 t FYM ha and 180 kg P2O5
-1
ha gave bud sprouting of 23.29% earlier than control
treatment (Table 3). This result indicated that even
though most of the yield and yield component parameters
were not responsive to combined application of the two
fertilizers, the crop benefited much from integrated
application of P and FYM to produce buds at earlier time.
As the combined application of the two levels increased,
the crop required fewer weeks to sprout.
The results of the soil analysis before planting showed
that the soil was sandy in texture (44 % sand) but it falls
under loam in soil textural classification (Table 2). Even
though the current pH result seems to be neutral (pH
7.32), the previous land history and analysis indicated
that the soil was strongly basic and calcareous
(ATARC1998).
The soil test results before planting showed that the
Exchangeable Cation (Mg, Ca, K, and Na) was in the
range of high availability to plants. The available
phosphorus of the soil fell under the range of high
availability (42.29 ppm) according to Landon (1991)
(Table 2). However; the results showed that total nitrogen
and organic carbon contents of the soil were low. This
finding further signifies that the soil requires external
application of nutrients for high growth and yield of the
crop.
Average length of tuberous roots
The current finding revealed that farmyard manure did
not interact with phosphorus to influence the length of
sweet potato tuberous roots. However, the main effect of
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Agric. Sci. Res. J.
Table 3. Interaction effect of applied farmyard manure and phosphorus on days to bud sprouting of sweet potato at Adami Tulu
during the 2010 main cropping season
Sweet potato days to bud sprouting
-1
kg ha P2O5
90
19.3cde
19.33cde
19 00def
18.66efg
19 00ef
Treatments
-1
t ha FYM
0
5
10
15
20
F-test
0
21.33a
20.66ab
21.00ab
20.33abc
20.00bcd
**
LSD (P*FYM)
3.6
CV (%)
180
19 00efg
18.30efgh
17.66gh
18.00gh
17.33h
1.165
Where **= Significant at P<0.01 probability level;.means within and between a column for a factor sharing common letter(s) are not significantly
different at 5% level of significance
Table 4. Main effect of phosphorus and farm yard manure on average tuberous root length
and shoot fresh weight of sweet potato at Adami Tulu during the 2010 main cropping season
Treatment
0
5
10
15
20
F-test
LSD (0.05)
-1
Kg ha of P2O5
0
90
180
F-test
LSD(0.05)
CV (%)
-1
Root length (cm)
12.88ab
11.42b
12.17ab
11.91ab
13.37a
*
1.607
Shoot fresh weight (t ha )
82.41b
87.60 b
92.08 b
109.63ab
127.70a
*
35.10
12.33
12.22
12.48
Ns
1.245
1 3.6
87.65
99.44
112.55
Ns
27.19
18.59
Where *=significant at p<0.05 probability level; Ns= non-significant; CV = coefficient of variation; means
within a column for a factor sharing common letter(s) are not significantly different at 5% level of significance
farmyard manure significantly (P < 0.05) affected average
length of tuberous roots whereas phosphorus did not
have significant main effect on this parameter of the plant
(Table 10).
Even though it was in statistically parity at the other
levels of farmyard manure, average tuberous root length
increased by 17.07% when the rate of FYM increased
-1
from 5 to 20 t ha (Table 4). This indicates that on top of
providing a wide range of nutrients, farmyard manure
enhances the bulking of tuberous roots through improving
the bulk density of the soil. This result is corroborated by
those of Abdissa et al.(2010), who reported that different
media like farmyard manure, termite tomb, coarse sand
and red ash were used to make ideal soil conditions,
which best supported tomato seedlings and other crops
like root and tubers by providing good aeration and better
water holding capacity at Adami Tulu areas.
These results are also in conformity with the findings of
Ojeniyi et al., (2009) who reported increment in cassava
root length in response to the increased application of
-1
-1
organic manure of palm bush ash from 0 t ha to 5 t ha .
This indicates that crops grown for their roots and tubers
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Abdissa et al.
5
Table 5. Interaction effect of farmyard manure and phosphorus on shoot dry weight of sweet potato at Adami Tulu
during the 2010 main cropping season
-1
Shoot dry weight t ha
-1
Treatments
-1
FYM t ha
P2O5 kg ha
0
90
180
0
13.38b
10.51b
25.58 a
5
10.60b
14.20b
11.10b
10
11.41b
12.51b
10.92b
15
9.61b
11.79b
9.83b
20
8.10b
12.92 b
8.47b
F-test
**
LSD (P*FYM)
CV (%)
6.182
16.30
Where **=significant at p<0.01 probability level; CV = coefficient of variation ;means within and between a column for a factor sharing
common letter(s) are not significantly different at 1% level of significance
Table 6. Main effects of phosphorus and manure on the number of branch/plant and root number/plant of
sweet potato at Adami Tulu during the 2010 main cropping season
Treatment
0
5
10
15
20
F-test
LSD (0.05)
-1
Kg of P2O5 ha
0
90
180
F-test
LSD (0.05)
CV (%)
Number of branch per plant
8.04 (0.897)
7.44 (0.8472)
8.79 (0.9200)
8.47 (0.8894)
8.29 (0.9020)
Ns
1.794 (0.953)
Root number/plant
3.49 (0.2527)
5.74 (0.3721)
4.75 (0.2965)
5.65 (0.3367)
6.44 (0.3941)
Ns
2.958 (0.100)
8.39 (0.913)
7.68 (0.855)
8.55 (0.9044)
Ns
1.38 (0.0738)
22.87 (11.18)
5.98 (0.3227)
4.89 (0.3141)
4.77 (0.354)
Ns
1.82 (0.0775)
47.30 (31.66)
Where NS= non-significant; CV= Coefficient of variation; Means in parentheses represent log-transformed values.
benefit from organic manures not only as a source of
nutrients but also as a room for good root extension and
tuber bulking. Worldwide, manure has been used as a
source of organic matter to improve soil bulk density
creating a conducive environment for crops like sweet
potato (Arriaga and Lowery, 2003), water-stable soil
aggregation (Estevez et al.,1996; Whalen et al., 2003),
microbial biomass and activity (Gunapala and Scow,
1998), and crop yield (Arriaga and Lowery, 2003;
Nyiraneza and Snapp, 2007). Manure can also increase
soil C and N reserve by increasing protected SOM within
aggregates (Aoyama et al., 1999). Even though it was not
significant at alpha level of P < 0.05, average tuberous
root length development was negatively correlated with
shoot fresh weight (r = -0.198), Shoot dry weight (r = 0.210), vine length (r =-0.11) and average branch per
plant (r = -0.10). This result indicated any treatments that
favoured the aforementioned parameters negatively
affected average tuberous root length that is a good yield
estimator of sweet potato.
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Agric. Sci. Res. J.
Table 7. Interaction effect of applied farmyard manure and phosphorus on average sweet potato root
diameter at Adami Tulu during the 2010 main cropping season
Average sweet potato tuberous root diameter (cm)
-1
Treatments
-1
FYM t ha
0
5
10
15
20
F-test
0
5.87bcd
5.13bcd
4.84d
5.59bcd
5.97bcd
*
LSD (P*FYM)
18.69
P2O5 kg ha
90
5.93bcd
8.52a
4.96cd
5.91bcd
6.79abc
180
4.71d
5.55bcd
6.22bcd
5.34bcd
6.96ab
1.84
CV (%)
Where * = Significant at P<0.05 probability level; CV= Coefficient of variation; Means within and between a column for a
factor sharing common letter(s) are not significantly different at 5% level of significance
Table 8. Interaction effect of applied farmyard manure and phosphorus on average sweet potato vine length at Adami Tulu during
the 2010 main cropping season
Treatments
-1
FYM (t ha )
0
5
10
15
20
F-test
CV (%)
Average sweet potato vine length (cm)
-1
P2O5 kg ha
0
90
98.33e
136.33abcd
118.87cde
124.57bcd
137.00abc
136.00abcd
153.00ab
149.33abc
168.67a
137.87abcd
*
LSD (P*FYM)
33.76
15.08
180
110.33cd
133.77abcd
139.10abc
129.70abcd
134.67abcd
Where * = significant at P < 0.05 probability level; CV: Coefficient of variations; means within and between a column for a factor sharing common
letter(s) are not significantly different at 5% level of significance
Shoot fresh weight
Similar to the other most growth parameters of sweet
potato, shoot fresh weight was not affected statistically by
the combined application of farmyard and phosphorus
(Table 10). However, the main effect of FYM was
significant, while the main effect of P was not at P < 0.05.
-1
Increasing the rate of P from 0 to 180 kg ha P2O5 did not
affect shoot fresh weight significantly (Table 4).
But, the result of the current finding indicated that
sweet potato fresh weight is highly responsive to
increased levels of farmyard manure. This is because, as
-1
-1
the rate of FYM increased from 0 t ha to 20 t ha , the
green top yield increased significantly and linearly.
Even though it was statistically insignificant, as the rate
-1
-1,
of farmyard manure increased from 0 t ha to 10 t ha
shoot fresh weight increased by 11.61%. But in response
-1
to increased supply of the fertilizer towards 15t ha and
-1
20t ha shoot fresh weight increased significantly (P <
0.05) by 33.03% and 54.96%, respectively. From this
result, it can be deduced that, as the rate of farmyard
manure increased, the development of green top at the
expense of production of tuberous root yields was
promoted. This might be attributed to the fact that
farmyard manure constitutes important mineral nutrients
such N, P, K, as well as micronutrients, and provides
decomposable organic matter thereby increasing soil
aggregations which in turn improves physico-chemical
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Abdissa et al.
7
Table 9. Interaction effect of applied farmyard manure and phosphorus on days to maturity of sweet potato at Adami Tulu during
the 2010 main cropping season
Treatments
-1
FYM t ha
0
5
10
15
20
F-test
CV (%)
Sweet potato total days to maturity
-1
P2O5 kg ha
0
90
121.6ab
123.6a
120b
123.3a
124.3a
116c
115c
115c
122.3ab
121.6ab
**
LSD (P*FYM)
2.682
1.39
180
115c
115c
100d
96e
95e
** = significant at P<0.01 probability level; CV= Coefficient of variation; means within and between a column for a factor sharing
common letter(s) are not significantly different at 1% level of significance
conditions of the soil such as water holding capacity. In
addition, the carbon content in the manure is utilized as
food by soil micro-organism, which increases microbial
activity to convert unavailable plant nutrients to available
forms through biological transformation (mineralization)
(Gupta, 2000 and Balesh, 2005). This property of manure
may have promoted sweet potato leaf and vine growth
and expansion in this experiment.
It is evident that, although the green top and tuberous
root fresh weights correlated positively, the correlation
coefficient was low (r = 0.057) indicating minimum linear
relationship. This result also indicates that applying
farmyard manure beyond the optimum need of the crop
becomes uneconomical when the crop is grown for its
tuberous roots, which holds true for sweet potato. But, if
the crop is produced for livestock feed (Tesfaye et
al.,2008), application of the maximum farmyard manure
helps for better fresh foliage production since increasing
farmyard manure application and foliage development
are positively correlated (Table 3).
Shoot dry weight
The analysis of variance indicated the main effect of
farmyard manure resulted in significant (P < 0.05)
variation in shoot dry weight while P did not. Shoot dry
weight of sweet potato was also highly responsive and
was significantly (P < 0.01) affected by the combined
application of farmyard manure and phosphorus
(Table10).
-1
-1
As the rate of FYM decreased from 20 t ha to 0 t ha
and concurrently as the rate of P increased from 0 kg
-1
-1
P2O5 ha to 180 kg P2O5 ha , shoot dry weight increased
by 215.8% and was statistically significant at P < 0.01,
but it was in statistically parity with the shoot dry weight
obtained at the other treatment combinations. This
indicates that even though shoot fresh weight is benefited
at the highest level of farmyard manure, shoot dry weight
was increased as the proportion of farmyard manure to
phosphorus decreased. (Table 5) This result is consistent
with that of Naidu et al (2000) and Singh and Singh
(2000) who disclosed that increased supply of
phosphorus increased shoot dry weight.
The correlation values showed there were negative and
significant (P < 0.05) association of this parameters with
root dry weight (r =-0.32*), root fresh weight(r =-0.241)
and marketable root weight (r = 0.326*) indicating any
fertilizer inputs that favoured shoot dry weight was
negatively affecting the economically important part of
this crop and vice- versa.
Average number of branches per plant
The analysis of variance for average number of branch
per pant showed that this trait was not influenced
statistically by the interaction effect of FYM and P.
Similarly, the main effects due to farmyard manure and
phosphorus were not significant (Table 10).
Although average number of branch per plant is one of
the most important yield components of root and tuber in
general and sweet potato in particular, the result of the
current study showed that the main effect of both
fertilizers did not result in statistically significant (P <
0.05) differences for this parameter (Table 6). Consistent
with the current findings, Zelalem et al. (2009) and
Mukhtar et al. (2010) found non-significant increase in
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Agric. Sci. Res. J.
Table 10. Means square for yield component of sweet potato
Source of variation
DF
Block
Farmyard manure
Phosphorus
Farmyard manure X
Phosphorus
Error
CV (%)
2
4
2
8
28
Days to
budding
0.2Ns
1.64*
25.8**
4.34**
0.485
3.6
Means squares
Days to
maturity
Vine length
Shoot fresh
weight
4.3Ns
201.6**
1276.6**
291.7**
1932.8*
1600.8*
220.3Ns
862.7*
10252.7**
3118.8 *
2326.9Ns
1886.7Ns
2.56
1.39
407.49
15.08
Shoot dry
weight
45.41Ns
61.95*
25.7Ns
50.81**
Branch
number
13.6
16.3
1401.9
18.59
91.7**
2.2Ns
3.2Ns
4.52Ns
Root
number
13.2Ns
11.6Ns
6.5Ns
8.53 Ns
Root
diameter
0.66Ns
2.83Ns
3.50Ns
2.87*
2.82
11.18
5.69
31.66
1.21
Root
length
2.6Ns
5.4*
0.25Ns
3.9Ns
2.47
13.6
Where Ns = non-significant (P < 0.05); * and ** =Significant at P < 0.05and P < 0.01 probability levels, respectively
stem number per plant of potato in response to
fertilization. This could be because this trait is
much more influenced by the inherent
characteristics of the crop than application of
fertilizers. In agreement with the result of the
current study, different scholars reported that
stem number is determined very early in the
ontogeny of plant (De la Morena et al., 1994;
Lynch and Rowberry, 1997).
According to Susnoschi (1982) and Peter et al.
(1988), among the three major yield determining
factor of potato (number of stem per plant,
number of tuber per stem and average tuber
weight), average number of stem per plant
depends more on the intrinsic potential of the
cultivar than on addition of inputs such as
fertilizers. Thus, stem number may be influenced
by other factors such as storage condition of
tubers, genetic potential of the cultivar, number of
viable sprouts at planting, sprout damage at the
time of planting and growing conditions (Zelalem
et al., 2009).
Average root number per plant
The interaction effect of P and FYM was
statistically non-significant (P < 0.05) on average
tuberous root number of sweet potato per plant.
Similarly, the main effect of FYM and P resulted in
statistically non-significant effect on this
parameter (Table10).
Even though there were non-consistent and
statistically non-significant differences in the
values obtained at the other levels, increasing
-1
FYM from 0 to 20 t ha tended to increase
average tuberous root number per plant by 84.5
% (Table 6). Among all levels of FYM, treatments
that received zero FYM resulted in the lowest root
number per plant. Similar to average number of
vine per plant, tuberous root number developed
from a plant is highly dependent to the genetic
makeup of a given plant than fertilization. The
result is in conformity with the finding of Parwada
et al. (2011) who found insignificant root counts
per plant of sweet potato in response to chicken
manure applied at planting. But similar to the
current farmyard manure, according to this
authors’ non-significant and slight yield variation
observed was chicken manuring supplemented
with ridging helped as a room having ample space
for free root proliferation compared to planting
without ridging. The beneficial effect of organic
manure on yield may be due to an increase in
organic matter rate caused by the generation of
carbon dioxide during compost decomposition and
improvement of the soil structure conditions,
which encouraged the plant to have a good root
development by improving the aeration of the soil
(Arisha et al., 2003).
8
Abdissa et al.
9
In contrast to the application of FYM, as the level of P
-1
increased from 0 to 180 kg P2O5 ha average root
number per plant decreased by 20.3%, indicating the
contribution of FYM to creating conducive environment by
reducing soil bulk density for the emerging root till the
final harvesting than that of the application of inorganic
fertilizer.
beds, mounds (where bulk density is low) than on the flat.
This was attributed to chicken manuring which may have
enhanced soil aeration, resulting from both a greater soil
surface to soil volume ratio and a lower bulk density.
These attributes would have enhanced root growth and
nutrient uptake, hence better root growth and tuber yield
like that of the current farmyard manure.
Average tuberous root diameter
Average vine length
The analysis of variance for tuberous root diameter
showed that the main effects due to farmyard manure
and phosphorus were non-significant (P < 0.05) on
tuberous root diameter. However, this parameter was
significantly (P < 0.05) affected by the interaction effects
of FYM and P (Table 10).
The highest tuberous root diameter was obtained when
-1
-1
5 t ha FYM and 90 kg P2O5 ha were applied in
combination. Even though this value is in statistically
-1
parity with the combined applications of 5t FYM ha and
-1
180kg P2O5 ha
it resulted in 18.31% root diameter
advantage (Table 7).This indicates that minerals supplied
from both P and FYM had the most profound effect on
increasing this parameter of the plant. Evidently, the
lowest tuberous root diameter was recorded from the
treatment that received no farmyard manure at all.
Generally, good tuberous root diameter was obtained in
treatments that received more FYM than the rest even
though the values were not consistent across the all
-1
rates. Thus, the tuberous root diameter attained at 5t ha
-1
FYM integrated with 90 kg P2O5 ha was superior to the
-1
one recorded at 0t ha FYM integrated with 180 kg P2O5
-1
ha by 80.8%. In general, a close look at Table 7
indicates that as the proportion of FYM to P increased,
root diameter also increased progressively. This may be
attributed to enhanced availability of micronutrients as
well as organic carbon as food for soil biota. This may
have enhanced release of nutrients from the soil thereby
promoting root growth and nutrient uptake, hence better
root growth and tuber yield. This result is also in
agreement with the suggestion of Palm et al. (1997) that
one of the beneficial effects of combined organic and
mineral fertilizer application is that organic materials
influence nutrient availability through addition of nutrients,
mineral immobilization patterns, as an energy source for
microbial activities, as well as precursors to soil organic
matter (SOM), and by reducing P absorption of the soil.
In addition, manure may also improve the synchrony of
release of nutrients with the time that the plant needs the
nutrients for uptake since the release of nutrients is slow
(Kramer et al., 2002).
Howeler et al., (1993) also reported the superiority of
planting sweet potato on chicken manure, ridges, raised
The analysis of variance for average vine length showed
that the main effect due to farmyard manure was
statistically significant (P < 0.05). The main effect of
phosphorus was not significant on this parameter.
However, vine length was highly influenced by the
interaction effect of FYM with P (Table 10).
-1
-1
As application of 0t FYM ha +0 P2O5 ha increased to
-1
15t FYM+90kg P2O5 ha , average vine length increased
by about 51.86% and it was statistically significant at P <
0.05. In response to keeping the level of P constant (90
-1
kg P2O5 ha ) and continuously increasing the supply of
-1
FYM to 20t ha , average vine length increased by
71.53% even though it was statistically insignificant
-1
compared to the vine length obtained at 15t FYM ha +
-1
90 kg P2O5 ha (Table 8).The current finding is consistent
with that of Najm et al. (2010) who found a highly
significant vine development of potato in response to
application of cattle manure. The increase in vine length
in response to increased rate of FYM may be ascribed to
increased availability of nutrients in the soil for uptake by
plant roots that may have enhanced vegetative growth
through increasing cell division and elongation (Halvin et
al., 2003).
For this particular result, better vine development was
obtained where the proportion of farmyard manure to that
of P was high indicating that sweet potato benefited little
from P to increase its canopy compared to the benefit
that it derived from farmyard. Similar to the current
finding, Gonzalez et al. (2001) reported that organic
manure and inorganic fertilizer supplied all the essential
nutrients at seedling stage resulting in increased
measured variables like plant height. Corroborating this
result, Bwembya and Yerokun (2001) also reported that
plants treated with both inorganic fertilizer and manure
were significantly taller than those that received either of
the treatments indicating positive interaction effect of the
two fertilizers on this trait.
Similarly an experiment conducted on potato in Kenya,
Powon et al (2005) reported that combined application of
-1
-1
100 kg P ha and 20 t FYM ha gave the highest plant
height compared to control treatment which resulted in
the lowest height. But for vegetable crops like onion,
9
10
Agric. Sci. Res. J.
Islam et al. (2007) found the highest plant height for
plants treated with phosphorus at the rates ranging
-1
from130 to 260 kg P2O5 ha .
Days to maturity
The main effect of FYM and P were statistically (P < 0.01)
significant on days to maturity of sweet potato as well it
was affected by the interaction effect of the two fertilizers
(Table 10).
Days to maturity decreased by 23.57% and were
statistically significant (P < 0.01) at the combined
-1
-1
application of 10t FYM ha + 0kg P2O5 ha . The result on
days to maturity obtained at this combined level of
phosphorus and farmyard manure is in statistically parity
-1
with the result obtained at 15t FYM ha +180 kg P2O5 ha
1
, at which the crop mature 22.76 % earlier than the one
-1
obtained at combined application of 10t FYM ha + kg
-1
FYM ha (Table 9)
The results clearly indicated that days to maturity were
prolonged in response to increased levels of farmyard
manure with respect to reduced rate of phosphorus. This
may be attributed to the role that manure (which contains
high amount of nitrogen) plays in promoting vegetative
growth before the start of tuberous root development.
This is in line with the suggestion of Marschner (1995);
Gupta and Sharma (2000) that nitrogen promotes
vegetative and lush growth thereby delaying plant
maturity. This indicates the nutrients taken up by plant
roots from the soil will be used for increased cell division
and synthesis of carbohydrate, which will predominantly
be partitioned to the vegetative sink of the plants,
resulting in plants with luxurious foliage growth
(Marschner, 1995).
Significantly delayed time of maturity of tuberous roots
was observed at the peak application of phosphorus
combined at any level of FYM. The result on days to
maturity obtained in this experiment is in line with that of
Ajay et al., (2000) who reported that medium levels of
phosphorus reduced the days required to mature by
crops, compared to small doses. Similarly, Gustafson
(2010) also reported that increased application of
phosphorus fertilizer facilitated early maturity. Consistent
with this result, Halvin et al., (2003) also stated that if
nitrogen is used properly in conjunction with other
nutrient sources, it can speed up maturity of the crop
nutrient management. Thus, information on soil fertility
status and crop response to different soil fertility
management practices is very important to come up with
profitable and sustainable crop production.
In line with this, research was undertaken to investigate
the response of Sweet Potato (Ipomoea batatas L.) to the
application of farmyard manure and phosphorus at Adami
Tulu, Central Rift Valley of Ethiopia that has average
rainfall of 750 mm per annum and characterized by sandy
loam soil with slightly alkaline and basic pH. High
yielding, adaptable, disease resistant/ tolerant variety of
sweet potato called Belela was used to evaluate its yield
and yield components by using five levels of FYM
-1
(0,5,10,15,20 t ha ) and three levels of P (0,90,180 kg
-1
P2O5 ha ) combined in factorial arrangement with three
replications.
Significantly highest mean value of average tuberous
-1
root length (13.37 cm) was recorded at 20 t FYM ha and
the smallest tuberous root length (11.42 cm) was
-1
obtained at 5 t ha FYM. Similarly the highest green top
-1
-1
(127.70 t ha ) was harvested from 20 t ha FYM followed
-1
by 15 t ha FYM that gave a green top yield of 109.63 t
-1
ha . Among all levels, the control treatment gave the
lowest (82.41 t) even thought it is in statistically parity
with above ground growth obtained at the remaining
treatments
This indicated that in arid and semi arid areas like
Adami Tulu and similar agro-ecologies where, rainfall is
marginal, unevenly distributed and where crop residues
are removed for fire wood and supplemental feedings,
application of farmyard manure not only supplies
nutrients but also improves physicochemical properties of
the soil thereby significantly enhancing the yield of the
crop.
ACKNOWLEDGMENT
I am grateful to the Oromia Agricultural Research Institute
(OARI) for granting me a scholarship for this study. I
would like to express my special thanks to Mr. Abebe
Temesgen, a technical assistant of horticulture search
team for assisting me in the preparation of the planting
materials, the experimental plots, as well as in data
collection. I appreciate the assistance received from all
staff of Horticultural research team and Adami Tulu
Agricultural Research Centre during all years of my study
REFERENCES
SUMMARY AND CONCLUSIONS
Sustaining soil and soil fertility in intensive cropping
systems for higher crop yields and better quality can be
achieved through integrated organic and inorganic
Adami Tulu Research Center (ATARC) (1998). ATARC profile.
Oromiya Agricultural
development Bureau, Addis Ababa,
Ethiopia.
Adhanom N, Tsedeke A, Emana G (1985). Research on insect
pests of roots and tuber crops: In: Tsedeke Abate (ed.)
10
Abdissa et al.
(1985). A Review of Crop Protection Research in Ethiopia:
Proceedings of the first Ethiopian Crop Protection
Symposium, 4-7 February, Institute of Agricultural Research,
Addis Ababa, Ethiopia.
Ajay K, Singh JV, Chetan Kumar SA,
Singh C (2000).
Influence of phosphorus on growth and yield of onion (Allium
cepa L.). Indian J. Agric. Res., 34(1): 51-54.
Ambecha, (2001). Influence of nitrogen and phosphorus on
yield and yield components and some quality traits of two
sweet potatoes [Ipomoea batatas (L) Lam.] cultivars. An MSc
Thesis presented to the school of graduate studies, Alemaya
University. 94p.
Aoyama, M., D. A. Angers, A. N'Dayegamiye, and N
Bissonnette, 1999. Protected organic matter in water-stable
aggregates as affected by fertilizer and manure applications.
Can. J. Soil Sci., 79:419–425.
Arisha, H.M.E., A.A. Gad and S.E. Younes, 2003. Response of
some pepper cultivars to organic and mineral nitrogen
fertilizer under sandy soil conditions. Zagazig J. Agric. Res.,
30: 1875–99
Arriaga JF, Lowery B (2003). Soil physical properties and crop
productivity of an eroded soil amended with cattle manure. J
Soil Sci., 168: 888–899.
Assefa T, Teshome A, Engida T, Tesfaye T (2007). Summary
of progress on orange-fleshed sweet potato research and
th
development in Ethiopia. Proceedings of the 13 ISTRC
Symposium, Arusha, Tanzania pp. 728 – 731,
Balesh T (2005). Integrated plant nutrient management in crop
production in the central Ethiopian highlands. Doctor of
Philosophy (Ph.D). Norwegian University of Life Science.
Bwembya S, Yerokun OA (2001). Effects of cassia spectabilis,
cowdung and their combination on growth and grain yield of
maize. Seventh Easter and Southern Africa Regional Maize
Conference, 11th-15th February 2001. pp.361-366.
CACC, (Central Agricultural Census Commission Part I), 2002:
Report on the preliminary results of area, production and yield
of temporary crops. Addis Ababa.
De la Morena IA, Guillen, Garcia del Morel LF (1994). Yield
development in potatoes as influenced by cultivar and the
timing and level of nitrogen fertilizer. Am. Potato J., 71: 165173.
Gunapala N, Scow K (1998). Dynamics of soil microbial and
activity in conventional and organic farming systems. Soil
Biol., 30:-805–816
Gupta RP, Sharma VP (2000). Effect of different spacing and
levels of nitrogen for production of export quality onion bulbs
planted on raised bed. News-Letter-National Horticultural
Research and Development Foundation, 20:-1-4.
Gustfson AA (2010). Hand book of fertilizers, their source,
makeup, effect and use Agrobios, India. 3:-.78-88.
th
Habtu A (1995). Proceeding of the 25 anniversary of Nazareth
agricultural research center: 25 years of experience in
lowland crops research, 20-23 September 1995. nazareth
agricultural research center, Nazareth. p.36.
Halvin JL,. James DB, Samuel LT, Warner LN (2003). Soil
fertility and fertilizers an introduction to nutrient management
th
(6 ed.). Peason Education Inc., New Delhi, India.
Howeler RH, Ezumah HC Midmore DJ (1993). Tillage systems
for root and tuber crops in the tropics. Soil Tillage Res. 27:
211-240.
Landon JR (1991). Booker tropical soil manual: A handbook for
11
soil survey and agricultural land evaluation in the tropics and
sub-tropics. Longman Scientific and Technical, Essex, New
York. p. 474.
Lenne JM (1991). Diseases and pests of sweet potato: South
East Asia, the pacific and east Africa. Natural Resources
Institutes. Bulletin 46(7):116
Lynch DR, Rowberry RG (1997). Population density studies
with Russet Burbank potatoes. II. The effect of fertilization
and plant density on growth, development, and yield. Am.
Potato J., 54: 57-71.
Marschner H (1995). Mineral nutrition of higher plants. Second
edition, Academic Press, London. pp. 285-299.
Mukhtar B, Tanimu UL, Arunah, Babaji BA (2010). Evaluation of
the agronomic characters of sweet potato varieties grown at
varying levels of organic and inorganic fertilizer. World J.
Agric. Sci., 6 (4): 370-373.
Naidu AK, Tiwari JP, Dwivedi SK, Saxena SK (2000). Effect of
various levels of N, P and K on physiological growth
determinants of productivity in Garlic (Allium sativum L.).
Vegetable Science, 27(2):165-167.
Najm, M. R. Haj Seyed Hadi, F. Fazeli , M. Taghi Darzi , R.
Shamorady, 2010.Effect of utilization of organic and inorganic
nitrogen source on the potato shoots dry matter, leaf area
index and plant height, during middle stage of growth.
International Journal of Agricultural and Biological Sciences,
1: 26-29.
Nyiraneza J, Snapp S (2007). Integrated management of
inorganic and organic nitrogen and efficiency in potato
systems. Soil Sci. Soc. Am. J., 71:1508–1515.
Ojeniyi SO, Ezekiel PO, Asawalam DO, Awo AO, Odedina SA,
Odedina JN (2009). Root growth and NPK status of cassava
as influenced by oil palm bunch ash. Afr. J. Biotechnol;,
8(18): 4407-4412.
Palm CA, Myers RJK, Nandwa SM (1997). Combined use of
organic and inorganic nutrient source for soil fertility
maintenance and replenishment. In: Buresh et al (Eds.).
Replenishing soil fertility in Africa. Special publication No. 51.
Wisconsin, USA. pp 193-217
Parwada C, Gadzirayi T, Sithole AB (2011). Effect of ridge
height and planting orientation on Ipomea batatas (sweet
potato) production; J. Agric. Biotechnol. Sustainable Dev.,
3(4): 72-76.
Peter V, Hruska CL (1988). Yield formation in potatoes. In:
Yield formation in main field crops. Elsevier Science
Publishers. B.V. Amsterdam, The Netherlands. Pp. 268-330.
Powon JN, Aguyoh Mwaja V (2005). Effects of inorganic
fertilizers and farmyard manure on growth and tuber yield of
potato. African Crop Science Conference Proceedings,
7:1089-1093.
Singh JV, Kumar A, Singh C (2000). Influence of phosphorus
on growth and yield of onion (Allium cepa L.). Indian J, Agric.
Res., 34:1
Tenaw W, Debelle T, Tesfa B, Wakene N, Minale L, Tewodros
M, Burtukan M, Waga M (2001). Sweet potato production
nd
constraints and research in Ethiopia. 2 National Root and
Tuber crops Workshop of Ethiopia.
Tesfaye K, Tesfaye L, Estifanos T, Mieso G (2008). Effect of
level of substitution of sweet potato (Ipomoea batatas. L)
Vines for concentrate on body weight gain and carcass
characteristics of browsing Arsi-Bale goats. J. Cell Anim.
Biol., 2 (2): 036-042.
11
12
Agric. Sci. Res. J.
Teshome A, Amenti C (2010). On farm participatory evaluation
and selection of sweet potato (Early, Medium and Late set)
varieties at Adami Tulu Jiddo Kombolcha District. Int. J.
Agric.,, 2(4): 1-5.
Teshome A, Amanti C, Geremew H, Taha (2010). Effect of
seedling management on yield and quality of tomato at Adami
Tulu Jiddo Kombolcha District, Central Rift Valley of Ethiopia.
Afr. J. Agric. Res., 5(22): 3056-3059.
Teshome A, Amenti C, Kassaye T, Fiseha T, Geremew A
(2011). Yield and yield components of sweet potato as
influenced by plant density: In Adami Tulu Jido Kombolcha
District, Central Rift Valley of Ethiopia, Am. J. Exper. Agric.,
1(2): 40-48.
Whalen JK, Hu Q, Liu A (2003). Compost applications increase
water stable aggregates in conventional and no-tillage
systems. Soil Sci. Soc. Am. J., 67: 1842–1847.
Zelalem A, Tekalign TNi, gussie D (2009).Response of potato
(Solanum tuberosum L.) to different rates of nitrogen and
phosphorus fertilization on vertisols at Debre Berhan, in the
central highlands of Ethiopia. Afr. J. Plant Sci., 3 (2): 16-24.
12