Effect of Rates and Time of Nitrogen Fertilizer Application on Yield and Yield Components of Sorghum [sorghum bicolor (L.) Moench] at Raya Valley, Northern Ethiopia

Effect of Rates and Time of Nitrogen Fertilizer Application on Yield and Yield Components of Sorghum [sorghum bicolor (L.) Moench] at Raya Valley, Northern Ethiopia
Effect of Rates and Time of Nitrogen Fertilizer Application on
Yield and Yield Components of Sorghum [sorghum bicolor (L.)
Moench] at Raya Valley, Northern Ethiopia
*Kasaye Abera1, Tamado Tana2 and Abuhay Takele3
1Department of Agronomy, Ethiopian Institute of Agricultural Research, Mehoni Agricultural Research Center, Mehoni,
Ethiopia
2Department of Crop Production, Faculty of Agriculture, University of Eswatini, Eswatini
3Department of Agronomy, Ethiopian Institute of Agricultural Research, Debrzeyet Agricultural Research Center,
Debrzeyet, Ethiopia
A field experiment was conducted to assess the effect of rates and time of nitrogen fertilizer
application on yield and yield components of sorghum in northern Ethiopia. The treatments
consisted of four rates of nitrogen (23, 46, 69 and 92 kg N ha-1
) and three time of N application (1/2
dose at sowing and 1/2 dose at mid-vegetative, 1/2 dose at mid-vegetative and 1/2 dose at booting
stage, 1/3 dose at sowing, 1/3 dose at mid vegetative and 1/3 dose at booting stage). The main
effect of rate of N application showed signficantly the highest days to flowering, days to
physiological maturity, plant height, panicle length and biomass yield (10716 kg ha-1
) at 92 kg N
ha-1
. Similarly, the highest days to flowering, leaf area index (2.86) and panicle weight were
obtained from three split application and the maximum biomass yield (10142 kg ha-1
) was
recorded from two split application of N (1/2 dose each at mid-vegetative and at booting stage).
The interaction of rates and time of application of nitrogen had significantly the highest 1000
kernels weight (44.67 g), grain yield (4635 kg ha-1
) and harvest index from 69 kg N ha-1
in three
split application. Economic analysis showed that maximum net benefit of 33053.23 ETB ha-1
from
69kg N ha-1
in three split application. Based on the results, it can be concluded that application of
69 kg N ha-1
in three splits to be appropriate to increase the productivity of sorghum in the study
area.
Keywords: Sorghum, rate of nitrogen fertilizer, time of nitrogen application, Yield
INTRODUCTION
Sorghum [Sorghum bicolor (L.) Moench] is an important
cereal crop belonging to the grass family Poaceae
(Poehlman and Sleper, 1995). It is the world’s fifth most
important cereal crop after wheat, rice, maize and barley
in terms of production (Kumara et al., 2011). It is a staple
food for more than half a billion people in the world, 60
percent of whom are in Africa. It is a highly versatile crop
with many uses including human food and animal feed, for
brewing and bio-fuels.
In Africa, sorghum represents a large portion of the total
calorie intake in many countries and it is the most widely
spread staple food crop. It is the second most important
cereal (after maize) in Sub-Saharan Africa in terms of
production. Sorghum is among the most important grain
crops in the world including Ethiopia. Because of its
multiple purposes and its ability to cope up with
unfavourable growing conditions, sorghum will continue to
feed the world’s expanding populations. Moreover, it will
be the crop of the future due to the changing global climatic
trends and increase in use of marginal lands for agriculture
(Paterson et al., 2008). Sorghum is widely grown in the
high lands, low lands and semi-arid regions of Ethiopia;
especially in moisture stressed parts where other crops
can least survive (Tesfaye et al., 2008).
*Corresponding Author: Kasaye Abera; Department of
Agronomy, Ethiopian Institute of Agricultural Research,
Mehoni Agricultural Research Center, Mehoni, Ethiopia.
Email: kasayeab123@gmail.com;
Co-Author Email: 2
tamado63@yahoo.com;
3
kidumet94@gmail.com
Research Article
Vol. 7(1), pp. 598-612, January, 2020. © www.premierpublishers.org, ISSN: 2167-0449
International Journal of Plant Breeding and Crop Science

Abera et al. 599
In Ethiopia, during 2016/17 cropping season
(1,881,970.73 hectares) of land area was covered by
sorghum with the average yield productivity of 2.5 ton ha-1
(CSA, 2017). It is known for its versatility and diversity, and
is produced over a wide range of agro-ecological zones.
Main sorghum producing regions are Oromia, Amhara,
Southern Nations and Nationalities and Peoples
(S.N.N.P.) and Tigray. The leading sorghum producing
zones are East and West Hararge Zone in Oromia, North
Gondar and North Shoa Zone in Amhara (Demeke and Di
Marcantonio, 2013). In Tigray region, sorghum was
produced on 253757.11 hectares of land with average
yield productivity of 2.8 tons ha-1and in Southern Zone of
Tigray sorghum was produced on 48947.55 hectares of
land in the year 2016/17 cropping season with with
average yield of 2.1 ton ha-1 (CSA, 2017).
In the study zone, the average yield of sorghum is even
below the national yield average. The low productivity of
sorghum in developing countries including Ethiopia can be
attributed to many biotic and abiotic factors, like erratic rain
full, disease and pest and low soil fertility (CSA, 2017). Low
soil moisture or drought can reduce nutrient uptake by
roots and induce nutrient deficiency by decreasing the
diffusion rate of nutrients from soil to root, creating
restricted transpiration rates and impairing active transport
and membrane permeability (Yared et al., 2010). This
indicates that considering soil moisture or rainfall
distribution of an area is very important to limit the amount
of fertilizer to be applied.
Low soil fertility, particularly N and P deficiencies are
among the major biophysical constraints affecting
agriculture in Sub-Saharan Africa. According to Sanchez
et al., (1997), soil fertility depletion in smallholder farmers'
holdings is the fundamental biophysical root cause of
declining per capita food production. Nitrogen (N) is
commonly the most limiting nutrient factor for crop
production in the majority of the world's agricultural areas
and therefore adoption of good N management strategies
often results in large economic benefits to farmers.
Fertilizer N has contributed more than any other fertilizer
towards increasing yield of grain crops, including sorghum.
Consequently, N has become the foremost input in relation
to cost and energy requirement in advanced agricultural
production systems (Yousf, 1993).
Nitrogen is a major input in sorghum production, affecting
both yield and quality through influencing those
components which have great contribution in increasing
grain yield of sorghum (Wondimu, 2004). But in Ethiopia,
throughout the country, farmers use this fertilizer
(nitrogen/urea) as a blanket recommendation 46 kg N ha-1
which is the same rate of fertilizer application without
considering the soil moisture condition and the fertility
status of the soil of an area even though soil moisture
content and soil fertility status vary from place to place.
This problem is also common in the Southern Tigray area
which is one of the most sorghum producing areas of the
country.
Proper timing of application is the most important factor for
N fertilizer management. Plant use efficiency of N depends
on several factors including application time, rate of N
applied, cultivar and climatic conditions (Kidist, 2013). The
management of N application time is essential to ensure
sustained nutrition at the end of vegetative growth.
Therefore, the total amount of N should be divided into
suitable fractions to be applied to best satisfy the
requirement of the growing sorghum crop. The aim is to
avoid increasing early vegetative growth and to encourage
the development of the upper most green parts directly
involved in grain formation. Too late application, may lead
to N starvation where as too early supply may also
increase tillering and vegetative growth.
However, farmers in Ethiopian low land area apply N
fertilizer in the form of urea at sub-optimal blanket rate of
46 kg ha-1 of N in the form of urea mostly only once or
twice at the time of sowing, and this limits the potential
productivity of cereal crops (Bekele et al., 2000). Farmers
in Raya Valley district also apply low amounts of N in the
form of urea only one time at sowing or at a vegetative
growth stage for sorghum production (Personal
observation). Thus, there is lack of information on the
response of sorghum to rate and time of N fertilizer
application in South Tigray Zone of Northern Ethiopia. In
general, blanket recommendations, regardless of
considering the physical and chemical properties of the
soil, the soil moisture status; varieties grown etc as well as
application of maximum dose of fertilizer at one time do not
lead to increased yield of the crop. This may lead to low N
uptake efficiency of crops due to erratic rain fall
distribution. Therefore, the objectives of the study were:
➢ to assess the effects of rates and time of N fertilizer
application on yield components and yield of
sorghum;
➢ to estimate the most economic rate and time of N
fertilizer application for increased yield of sorghum in
the study area.
MATERIALS AND METHODS
Description of the Study Area
The experiment was conducted at Mehoni Agricultural
Research Center (Fachagama) located in Northern
Ethiopia, Tigray regional state, Southern zone under Raya
Valley in main season from July to October 2017 under
supplementary irrigation. The geographical location of the
site is at 12º 41' N latitude and 39º 42' E longitudes and at
an altitude of 1578 metere above sea level (m.a.s.l) and
about 678 km north from Addis Ababa and 120 km south
of Tigray regional capital, Mekele. The area has minimum
and maximum average annual temperatures of 13.19ºC
and 23.95ºC, respectively. The average annual rainfall is
539 mm (MhARC, 2017).

Int. J. Plant Breed. Crop Sci. 600
Experimental Materials
The sorghum variety used in this experiment was Meko
which was released by Melkassa Agricultural Research
Center. The variety is adapted to lowland altitudes < 1600
masl, early maturing type, its productivity under research
field ranged from 2.2-3.3 tons ha-1 and in farmer field
condition 1.7 tons ha-1. Urea (46% N) and triple super
phosphate (TSP) with 46% P2O5 were used as source of
nitrogen and phosphorus respectively (MARC, 1997).
Soil Sampling and Analysis
Soil samples at a depth of 0-30 cm were taken from five
random spots diagonally across the experimental field
using auger before planting. The collected soil samples
were composited to one sample. The bulked soil samples
were air dried in shade house to reduce contamination,
thoroughly mixed and ground to pass 2 mm sieve size
before laboratory analysis. Then the samples were
properly labeled, packed and transported to Mekele soil
laboratory. After that, soil organic carbon, total N, soil pH,
available P, cation exchangeable capacity (CEC),
electrical conductivity (EC) and texture were analyzed at
Mekelle Soil Laboratory Research Center.
The soil pH was measured in the supernatant suspension
of a 1: 2.5 soil to water ratio using a standard glass
electrode pH meter (Rhoades, 1982). The Walkley and
Black (1934) method was used to determine the organic
carbon (%). Total N was determined using Kjeldhal
method as described by Bremner and Mulvaney (1982).
Available P (mg kg-1) was determined by employing the
Olsen et al. (1954) method using ascorbic acid as the
reducing agent. The cation exchange capacity (CEC) in
cmol (+) kg-1 was measured using 1M-neutral ammonium
acetate method (Jackson, 1973). Electrical conductivity
(EC) was determined in the soil to water suspension of 1:5
(Jackson, 1973). The soil particle size distribution was
determined using the Bouyoucos hydrometer method
(Bouyoucos, 1962).
Treatments and Experimental Design
The experiment was laid out in randomized complete block
design (RCBD) with three replications. Improved, early
matured sorghum variety (Meko-I) was used for the trial.
Factorial combination of four rate of nitrogen (23, 46, 69
and 92 kg ha-1) and three time of N application were
adjusted according to Zadoks et al., (1974) decimal growth
stage for sorghum. Timings of N application were adjusted
as follows: T1 (1/2 dose at sowing + 1/2 dose at mid-
vegetative); T2 (1/2 dose at mid-vegetative + 1/2 dose at
booting stage) and T3 (1/3 dose at sowing + 1/3 dose at
mid-vegetative + 1/3 dose at booting stage) were applied
as treatments.
The gross size of experimental plot was 3.75 m ×3.6 m
(13.5 m2) accommodating five rows of sorghum planted at
a spacing of 75 cm between rows and 20 cm between
plants. The net sampling plot size was 2.25 m × 3.2 m (7.2
m2) in all the cases, in which the two outer most rows and
one plant at both ends of the row considered as borders
leaving three middle rows for sorghum with the length of
3.2 m for data collection and measurement.
Experimental Procedure and Field Management
Land preparation was done at the beginning of June with
tractor, harrowed and leveled before planting. The seeds
were planted at row spacing of 75 cm and plant spacing of
20 cm recommended for sorghum and done by hand in the
rows as uniformly as possible and covered with soil
manually at rate of two seeds per hill then, after
emergence it was thinned to one seedling per hill.
Sorghum was planted on half of July, 2017. Nitrogen
fertilizer in the form of urea (46% N) was applied as per
treatment 5 cm away from the sorghum. The in-situ soil
moisture conservation practice (tied ridging) was made to
harvest water. The full dose of P (46 kg P2O5 ha-1) was
applied uniformly in band application in the form of triple
super phosphate (TSP) at planting time of sorghum for all
experimental units.
All other necessary agronomic management practices like
weeding and crop protection measures were carried out
uniformly are recommende for sorghum. Supplementary
irrigation was used when there was shortage of rainfall
during the execution of the experiment. When rain was
stop at critical time sorghum was irrigate three times in one
week interval up to maturity. The supplementary irrigation
was made using ground water resource through furrows.
Data Collection and Measurement
Crop phenology
Days to 50% flowering: was recorded as the number of
days from planting to the date at which 50% of the plants
in a plot produced flower.
Days to 90% maturity: It was also recorded on the date
at which 90% of the panicles per plot reached physiological
maturity. The development of black layer on the kernels,
which appears immediately above the point of kernel
attachment base, is an indication of maturity.
Growth parameters
Leaf area (LA): Five plants per net plot were randomly
taken to measure leaf area per plant (cm2) at 50% heading
using the method described by Sticker et al., (1961) as:
leaf area = length of the leaves × maximum width of leaf
×0.75 where, 0.75 is the correction factor for sorghum and
leaf area index (LAI): the leaf area index was calculated as
the ratio of unit leaf area per plant to the ground area
covered by the plant (Radford, 1967). .

Abera et al. 601
Plant height: was measured at physiological maturity
from the ground level to the tip of panicle from five
randomly taken plants and was averaged on per plant
basis.
Panicle length: It is the length of the panicle from the node
where the first panicle branches emerge to the tip of the
panicle which was determined from an average of five
randomly taken panicles per net plot.
Yield components and yield
Initial stand count: It was recorded by counting the
number of plant after thinning from the net plot area.
Stand count at harvest: It was determined by counting
the number of plants from the net plot area at the time of
harvesting.
Number of productive tillers: It was recorded by
counting those tillers which bear panicle with grains from
the net plot area.
Panicles numbers: It was determined counting the total
number of sorghum panicles found in the net plot area
including panicles from the tillers.
Panicle weight (g): Samples of five panicles were
weighed after harvesting and sun drying to determine
weight per panicle.
Thousand kernels weight (g): was determined by
counting 250 grains in duplicates and weighting them on
an electronic balance. The weights obtained were
multiplied by two to get the 1000 kernels weight. The
weight was adjusted to 12.5% moisture level.
Above ground dry biomass (kg): It was measured after
the plants from the net plot area were harvested and sun
dried till constant weight.
Grain yield (kg): It was obtained from all plants of net plot
area. It was determined using sensitive balance after the
panicles were threshed, cleaned and sun dried and the
yield was adjusted to 12.5% moisture level. Then, it was
converted to kg ha-1 basis.
Harvest index (HI): It was computed as ratio of grain yield
to the bio mass yield per plot as:
HI = Grain yield per plot (kg) x100
Aboveground dry biomass per plot (kg)
Agronomic efficiency (AE)
Agronomic efficiency is defined as the economic
production obtained per unit of nitrogen applied and was
calculated as: AE (kg kg-1) =
𝐺𝑓 (𝑘𝑔)−𝐺𝑢(𝑘𝑔)
𝑁(𝑘𝑔)
where, AE
stands for agronomic efficiency, Gf and Gu for grain yield
in fertilized and unfertilized plots, respectively, and N for
quantity of fertilizer applied.
Data Analysis
Data collected were subjected to analysis of variance
(ANOVA) using the Genstat 15 edition, (GenStat, 2012)
and interpretations were made following the procedure
described by Gomez and Gomez (1984). When ever the
effects of the treatments were found significant, the means
were compared using least significance difference (LSD)
test at 5% level of significance.
Partial Budget Analysis
The economic analysis was carried out by using the
methodology described in CIMMYT (1988) in which
prevailing market prices for inputs at planting and for
outputs at harvesting were used. All costs and benefits
were calculated on ha basis in Birr. The concepts used in
the partial budget analysis were the mean grain yield and
stalk yield of each treatment, the gross benefit (GB) ha-1
(the mean yield for each treatment) and the field price of
fertilizers (Urea and the time of application costs). The
benefit of biomass yield was included in the calculation of
the benefit since the farmers in the area use it.
Marginal rate of return, which refers to net income obtained
by incurring a unit cost of fertilizer and its application, was
calculated by dividing the net increase in yield of sorghum
due to the application of each fertilizers rate.
Unadjusted grain yield (UGY) (kg ha-1): is an average yield
of each treatment.
Adjusted grain yield (AGY) (kg ha-1): is the average yield
adjusted down ward by a 10% to reflect the difference
between the experimental yield and yield of farmers.
Unadjusted stalk yield (USY) kg ha-1): is an average stalk
yield of each treatment.
Adjusted stalk yield (ASY) kg ha-1): is the average stalk
yield adjusted down ward by a 10% to reflect the difference
between the experimental yield and yield of farmers.
Gross field benefit (GFB) (ETB ha-1): was computed by
multiplying field/farm gate price that farmers receive for the
crop when they sell it as adjusted yield. GFB = AGY ×
field/farm gate price for the crop.
Total variable cost (TVC) (ETB ha-1): was calculated by
summing up the costs that vary, including the cost of urea
fertilizer (988.55 Birr ha-1 ) and for each time of application
cost (5 person 50 birr / day) and the average open price of
sorghum price at Mehoni market was Birr 8 kg-1 in January
2017 during harvesting time.
The net benefit (NB) was calculated as the difference
between the gross benefit and the total cost that vary
(TCV) using the formula, NB= (GY × P) – TCV
Where GY x P = Gross Field Benefit (GFB), GY = Adjusted
Grain yield per hectare and P = Field price per unit of the
crop.

Actual grain and stalk were adjusted downward by 10% to
reflect the difference between the experimental yield and
the yield farmers could expect from the same treatment.
The dominance analysis procedure as described in
CIMMYT (1988) was used to select potentially profitable
treatments from the range that was tested. The discarded
and selected treatments using this technique were referred
to as dominated and undominated treatments,
respectively. For each pair of ranked treatments, %
marginal rate of return (MRR) was calculated using the
formula MRR (%) =
Change in NB (NBb−NBa)
Change in TCV (TCVb−TCVa)
× 100
Where, NBa = the immediate lower NB, NBb = the next
higher NB, TCVa = the immediate lower TCV and TCVb =
the next highest TCV. The treatment with highest net benfit
and MRR > 100 was considered for recommendation.
RESULTS AND DISCUSSION
Soil Physico-Chemical Properties of the Experimental
Site
Selected physico-chemical properties were analyzed for
composite soil (0-30 cm depth) from the samples collected
diagonally from five spots in every replication before
planting. The results indicated that texture of the soil in the
experimental site was dominated by the clay fraction. On
the basis of particle size distribution, the soil contained
sand (30%), silt (26%) and clay (44%) Table 1. According
to the soil textural class determination triangle, soil of the
experimental site was clay. The texture indicates the
degree of weathering, nutrient, and water holding capacity
of the soil. High clay content might indicate better water
and nutrient holding capacity of the soil in the experimental
site. The composite soil sample had 2.51% soil organic
matter which is rated as low according to EthioSIS (2014)
when soils having organic matter value in the range of 2-
3% are considered low.The organic matter content of the
soil is taken as a basic measure of fertility status, improve
water-holding capacity, nutrient release and soil structure.
[It is estimated indirectly from the organic carbon
determination by OM% = 1.72 x % OC (Walkley and Black,
1934]. The low amount of organic matter in the soil might
be due to low addition of crop residues to the soil.
Therefore, regular application of organic manure such as
crop residue, compost etc is important.
The soil reaction (pH) of the experimental site was 7.3
which rated as neutral according to Tekalign (1991) who
rated in the range of 6.73 to 7.3 as neutral soils. FAO
(2000) reported that the preferable pH ranges for most
crops and productive soils to be from 4 to 8. Thus, the pH
of the experimental soil was with in the range for
productive soils. Tekalign (1991) has classified soil total N
content of <0.05% as very low, 0.05-0.12% as poor, 0.12-
0.25% as moderate and >0.25% as high. According to this
classification, the soil samples were found to have poor
level of total N (0.12%) (Table 1), indicating that the
nutrient is a limiting factor for optimum crop growth. As
sorghum is highly exhaustive crop for nitrogen, the
production potential of it is highly affected by N deficiency
(Onwueme and Sinha, 1991). Therefore, there is a need to
apply nitrogen to the crop.
The analysis revealed that the available P of the soil was
16.42 mg kg-1 (Table 1). Indicative ranges of available
phosphorus have been established by Cottenie (1980), as
<5 mg kg-1 (very low), 5-9 mg kg-1 (low), 10-17 mg kg-1
(medium), 18-25 mg kg-1 (high) and >25 mg kg-1 of soil
(very high). Thus, the soils of the experimental site were
considered as medium in available P content which is
satisfactory for optimum sorghum growth and yield.
Table 1. Selected physico-chemical properties of the experimental soil before planting
Physical properties Chemical Properties
Particle size Distribution (%) OM % pH TN % Av.P (mg kg-1) CEC cmol (+) kg-1 EC (ms m-1)
Sand Silt Clay Textural Class
30 26 44 Clay 2.51 7.3 0.12 16.42 40.0 0.34
Cation exchange capacity (CEC) is an important
parameter of soil as it indicates the type of clay mineral
present in the soil and its capacity to retain nutrients
against leaching. According to Hazelton and Murphy
(2007), top soils having CEC greater than 40 cmol (+) kg-1
are rated as very high and 25-40 cmol (+) kg-1 as high.
Thus, according to this classification, the soil of the
experimental site had high CEC (40 cmol (+) kg-1 soil)
(Table 1). Cation exchange capacity (CEC) describes the
potential fertility of soils and indicates the soil texture,
organic matter content and the dominant types of clay
minerals present. In general, soils high in CEC contents
are considered as agriculturally fertile. The EC of the
experimental site was 0.34 (ms m-1) and this is rated as
non-saline according to Hazelton and Murphy (2007) who
rated soils having the EC values less than 4 ms m-1 is
considered as non-saline and suitable for cereal
production.
Phenological and Growth Parameters of Sorghum
Days to flowering (DF)
Analysis of variance showed that the main effect of the N
rate and timing of N application significantly (P≤0.01)
influenced days to flowering. However, the interaction
effect was not significant (Table 2).
The days to flowering of the plants was hastened under
lower rates compared to the higher N rates. Thus,

Abera et al. 603
increasing the rate of nitrogen from 23 to 46, 69, and 92 kg
N ha-1 prolonged the days to flowering by about 5.66%,
11.32%, 14.47% and 17.83% respectively. This showed
that the most prolonged duration to flowering was recorded
under plant grown at the rate of 92 kg N ha-1 (68.78 days)
whereas the shortest duration to flowering (62.33 days)
was recorded for plants grown at at the rate of 23 kg N ha-
1 (Table 2). Moreover, delay in days to 50% flowering with
application of higher level of N might be due to that
nitrogen increased vegetative period and it delays
reproductive period. This could be related to the vigorous
growth that resulted in higher number of days for flowering
compared with days to flowering obtained for the rate of 23
kg N ha-1. Generally, the number of days to flowering
recorded over all the fertilized plots significantly higher
than the rate of 23 kg N ha-1 (Table 2). This result was
complimentary with Moges (2015) who reported that
nitrogen fertilizer increasing N from 23 kg N ha-1 to 128 kg
N ha-1 that increased duration of tasseling time of maize.
Similarly, Abdulatif (2002) in chat/ maize intercropping also
reported delayance of days to tasselling and silking of
maize with increased rate of applied N up to 92 kg N ha-1.
Sorghum accumulates more thermal time up to booting,
heading and flowering with increasing N rates (Amanullah
et al., 2009). In contrast with this result, Buah and
Mwinkaara (2009) reported that maximum N fertilized
plants flowered earlier than those that were minimum
amount fertilized plants. This result was in line with that of
Imran et al., (2015) who stated that delay in days to
tasseling was observed with increase in N rate (210 kg ha-
1) by 5 days. The results also agreed with Kawsar et al.,
(2012); and Akmal et al., (2010) who observed that maize
took higher number of days to tasseling with the
application of high amount of nitrogen fertilizer.
Timing of nitrogen application showed significant effect on
days to flowering (Table 2). The maximum days to
flowering (66.33 days) was for three split application,
i.e.1/3rd at sowing, 1/3rd dose at mid-vegetative and 1/3rd
dose at booting compared to the other time of application
(Table 2). The prolonged duration to flowering with three
split application of nitrogen might be that the fertilizer is
used efficiently to promote active vegetative growth and
plants use nutrients efficiently. This result is in line with the
finding of Ma and Dwyer (2000) who reported that
application of N before heading and silk development
prolonged the flowering of sorghum and maize crops,
respectively.
Days to physiological maturity (DPM)
Days to 90% physiological maturity was significantly
(P≤0.01) affected due to nitrogen rate and time of N
application, but not due to interaction (Table 2).
The rates of 46, 69 and 92 kg N ha-1 significantly delayed
maturity as compared to 23 kg N ha-1. The maximum days
to 90% maturity (113.00 days) was recorded from 92 kg N
ha-1 and the minimum (103.4 days) was recorded at rate of
23 kg N ha-1 (Table 2). Delay in days to maturity could be
due to application of higher level of nitrogen increased
vegetative growth and delayed reproductive period as
nitrogen boosts vegetative growth of the plants and make
them stay green for long period of time. This result was
complimentary with Kidist (2013) who report that maturity
was more prolonged at the rate of 174 kg N ha-1. Similarly,
Dawadi and Sah (2012) reported that nitrogen rate
significantly delayed days to maturity of maize with the
application of maximum nitrogen dose of 200 kg N ha-1
with average of 151.3 days as compared to other
treatments.
The time of N application had significant (P≤0.01) effect on
days to 90% maturity of sorghum (Table 2). Even though
it was statically significant, the days to maturity ranged
from 108.4 days to 109.9 days which was only 1.5 days
difference (Table 2). The delay in maturity of sorghum
plants in response to the split applications of N, 1/2 at mid-
vegetative and 1/2 at booting stage might be because of
the fact that two-time applications in critical time promoted
vigorous vegetative growth and development of the plants
possibly due to synchrony of the time of need of the plant
for uptake of the nutrient and availability of the nutrient in
the soil. In agreement with this result, Ma and Dwyer
(2000) reported that application of N before silk
development prolonged the maturity of maize crop when
nitrogen application was in two split (at mid-vegetative and
booting stage).
Table 2. Days to flowering,days to physiological maturity
and leaf area of sorghum as affected by N rate and time
of N applications
Treatments Days to 50%
flowering
Days to 90%
physiological
maturity
Leaf area
(cm2)
Nitrogen rate (kg
N ha-1)
23 62.33d 103.4d 3401d
46 65.33c 108.8c 3944c
69 67.00b 111.1b 4481a
92 68.78a 113.0a 4230b
LSD (0.05) 0.84 1.05 250.0
N application
time (NT)
T1 65.17b 108.4b 3848b
T2 66.08a 109.9a 3894b
T3 66.33a 108.9b 4300a
LSD (0.05) 0.72 0.91 216.5
CV (%) 1.3 1.0 6.4
Where, LSD= Least significant difference; CV= coefficient
of variation and T1= N application of 1/2 at sowing and 1/2
at mid-vegetative; T2= N application of 1/2 at mid-
vegetative and 1/2 at booting and T3= N application of
1/3rd at sowing, 1/3rd at mid-vegetative and 1/3rd at
booting. Variable means followed by the same letters are
not significantly different according to LSD Test.

Leaf area (LA)
Leaf area influences interception and utilization of solar
radiation of sorghum crop canopies and, consequently,
sorghum dry matter accumulation and grain yield (Boote et
al., 1996). As indicated in the table 2, the main effect of N
rate and time of N application had highly significant
(P≤0.01) effect on the leaf area; however, no significant
interaction effect between rate and time of N application.
The highest leaf area (4481 cm2) was obtained from 69 kg
N ha-1; while the lowest leaf area (3401 cm2) was obtained
from rate of 23 kg N ha-1 the fertilizer application (Table
2). The increase in the leaf area with application of N
increase is attributed to the more vegetative growth due to
nitrogen application, as it is a general truth that N
enhances vegetative growth in sorghum. The result was
also supported by Debebe (2010) who reported that
maximum application of 105 kg N ha-1 resulted in higher
leaf area. In conformity with this result, Uhart and Andrade
(1995) reported that N deprivation reduced leaf area index,
leaf area duration and radiation interception of sorghum.
Imran et al., (2015) also stated that increasing N
application from 0 - 210 kg ha-1 increased leaf area from
1973 cm2 to 2757 cm2 in maize linearly and significantly.
These results indicated that sorghum with higher leaf area
can produce more food through photosynthesis as leaf is
responsible part for preparation of food and may have
higher biomass or grain yield. Similarly, Berhane et al.,
(2015) reported that application of high N fertilizer at 61.5
kg N ha-1 increased leaf area of sorghum.
Time of N application also had high significant effect on the
leaf area. Application of N in three split, i.e. 1/3rd dose of N
at sowing, 1/3rd dose at mid-vegetative and 1/3rd dose at
booting stage had the maximum leaf area (4300 cm2) than
other application time. However, there was no significant
difference among the other application time (Table 2). The
highest leaf area with three split application of N may lead
to efficient recovery of the nutrient by roots and there by
enhanced leaf area of the plant. This result is in line with
the finding of; Ma and Dwyer (2000) who reported that
application of N before heading and silk lead to plants use
nutrients efficiently this increases leaf area of sorghum and
maize crops, respectively.
Leaf area index (LAI)
Leaf area index is major factor determining photosynthesis
and dry matter accumulation (Moosavi et al., 2012). The
main effect of rate and time of nitrogen fertilizer application
had highly significant (P≤0.01) influence on leaf area
index. However, the interaction effect of rate and time of N
application had no significant effect on leaf area index.
The highest leaf area index (2.98) was recorded from 69
kg N ha-1; while the lowest (2.26) was recorded from rate
of 23 kg N ha-1 (Table 3). Thus, 69 kg N ha-1 application
resulted in 23.02% more leaf area index than lower rate of
fertilizerd plot. Generally, an increasing trend in LAI was
observed with increased N application rates which might
be due to improved leaf expansion in plants due to
optimum nitrogenous fertilizers. In line with the result
Moges (2015) reported that increase in leaf area with the
increase of nitrogen level from 0-128 kg N ha-1 and
attributed to the more vegetative growth due to nitrogen
application, as it is a general truth that N enhances
vegetative growth in maize. Nitrogen deficiency
accelerates senescence as revealed by strong decrease
in chlorophyll concentration under low N as compared to
non-stressed conditions. In line with this result, Kidist
(2013) reported as that increasing the rate of N from 0 to
130.5 kg N ha-1 linearly increased leaf area index of maize.
In line with this result, Gebrelibanos and Dereje (2015)
reported that application of high fertilizer dose increased
the leaf area index of sorghum. Similarly, Haghighi et al.
(2010) and Asim et al., (2012) reported an increasing trend
in LAI on maize due to an increase in N fertilizer application
rates. Jasemi et al., (2013) also reported higher LAI of
maize associated with nitrogen treated plants have been
probably due to increased leaf production and leaf area
duration.
Time of N application also high significant (P≤0.01) effect
on the leaf area index wherethe application of nitrogen in
three splits, i.e. application of 1/3rd dose at sowing, 1/3rd
dose at mid-vegetative; and 1/3rd dose at booting stage of
growth led to the highest leaf area index (2.86) than the
other time of application. However, there was no
significant difference among the other time of application
(Table 3).
Plant height (PH)
The main effect of nitrogen application rate had high
significant (P≤0.01) effect on plant height. However, main
effect of time of N application and interaction effect of rate
and time of N application did not significantly affect this
parameter.
When the rate of nitrogen application increased plant
heights was also increased (Table 3). The result showed
that with increase in rate of nitrogen from 23 to 92 kg N ha-
1, plant height increased by 6.49%. The tallest plant (167.7
cm) was recorded from 92 kg N ha-1 and the shortest plant
(155.10 cm) was recorded from rate of 23 kg N ha-1 (Table
3). The increase in plant height with respect to increased
N application rate indicates maximum vegetative growth of
the plants under higher N availability due to the increase
in cell elongation as nitrogen is essential for plant growth
process including chlorophyll which is responsible for dark
green color of stem and leaves which enhance vigorous
vegetative growth. In agreement with this result, Maral et
al., (2012) obtained significant increase in plant height of
sorghum when supplied with higher rates of N. Similarly,
Adeniyan (2014) reported significant increase in various
growth parameters of maize when supplied with higher
rates of N fertilizer. Likewise, Kidist (2013) reported that
increasing the rate of N from 0 to 174 kg N ha-1 linearly
increases plant height from 250.1 cm to 265 cm of maize.

Abera et al. 605
Table 3. Leaf area index, plant height and panicle length
of sorghum as influenced by N rate and time of N
applications
Treatments Leaf area
index
Plant
height (cm)
Panicle
length (cm)
Nitrogen rate
(kg N ha-1)
23 2.26c 155.10d 23.06d
46 2.62b 160.20c 24.16c
69 2.98a 163.60b 25.03b
92 2.82ab 167.70a 25.95a
LSD (0.05) 0.1678 1.895 0.706
Time of N application
(NT)
T1 2.56b 162.02 24.38
T2 2.59b 161.77 24.54
T3 2.86a 161.12 24.72
LSD (0.05) 0.14 NS NS
CV(%) 6.4 1.2 2.9
Panicle length (PL)
Panicle length of sorghum was significantly affected
(P≤0.01) by the main effect of rate of N application. But
main effect of time of N application and interaction of two
factors were not significant.
The highest panicle length (25.95 cm) was recorded for 92
kg N ha-1 and the minimum panicle length (23.06 cm) was
recorded from rate of 23 kg N ha-1 (Table 3). An increasing
the rate of nitrogen from 23 to 46, 69 and 92 kg N ha-1
markedly increased the panicle length by about 1.38%,
2.03%, 2.54% and 3.09%, respectively. The increase in
panicle length with respect to increased N application rate
indicates maximum vegetative growth of the plants under
higher N availability due to the increase in cell elongation
as nitrogen is essential for plant growth process. In
conformity with this result, Haftom et al., (2009) reported
that panicle length increased significantly in response to
increasing rate of nitrogen application with the maximum
panicle length being obtained at the highest rate of 200 kg
N ha-1. Similarly, Kidist (2013) reported that the length of
ears per plant was significantly affected by N application
rate in which the maximum length of ear 21.43 cm was
produced in response to applying 130.5 kg N ha-1.
Generally, the trend showed that decrease in ear length
occurred with decrease in nitrogen rate (Kidist, 2013).
Yield Components and Yield of Sorghum
Panicle number
The analysis of variation showed that panicle number per
net plot was not significantly affected either the main effect
of rate and time of N application nor interaction of the two
effects (Table 4).
However, the maximum panicle number (52.5) was
recored from 46 kg N ha-1 and the minimum value 50.56
was obtained from rate of 23 kg N ha-1, though most study
showed that the rate of N application and panicle number
showed a positive relationship, the result of this study
showed that this parameter was no affected by any of the
factors (Table 4).
Table 4. Panicle number per net plot and panicle weight
of sorghum as influenced by N rate and time of N
applications
Treatments Panicle
number
Panicle weight
panicle-1 (g)
Nitrogen rate (kg N ha-1)
23 50.56 72.08d
46 52.50 77.09c
69 50.67 94.84a
92 50.89 84.71b
LSD (0.05) NS 2.17
N application time (NT)
T1 50.25 82.3ab
T2 50.83 80.79b
T3 51.67 83.44a
LSD (0.05) NS 1.881
CV (%) 2.9 2.70
not significantly different according to LSD Test
Panicle weight (PW)
The analysis of variance showed that the main effect of
rate of N application had highly significant (P≤0.01) and
time of N application had significant (P≤0.05) effect on
panicle weight, while the two interaction effect was not
significant.
The maximum panicle weight per panicle (94.84 g) was
obtained from application of 69 kg N ha-1, where as the
minimum panicle weight (72.08 g) was recorded from the
rate of 23 kg N ha-1. When nitrogen increases from 23 up
to 69 kg N ha-1, the panicle weight also increased but no
further increase with rate of 69 kg N ha-1 (Table 4). This is

due to optimum nutrient providing crop to grow to full
maturity, rather than taking long maturity time. This could
be due to the role of the essential nutrients in enhancing
the seed holding capacity of the panicle. This result is in
line with the finding of Berhane et al., (2015) who reported
that panicle weight of sorghum was significantly increased
with the application of high amount of nitrogen.
The time of N application had significant effect on panicle
weight (Table 4). The maximum panicle weight (84.44 g)
was obtained from three split application of 1/3rd dose at
sowing, 1/3rd dose at mid-vegetative and 1/3rd dose at
booting and it was statistically at par with combination of
69 two split application of 1/2 at sowing and 1/2 at mid
vegetative growth stage (82.3 g) while the minimum
panicle weight (80.79 g) was recorded in two split
application at 1/2 at mid-vegetative and 1/2 at booting.
Maximum panicle weight was recorded from three split
application due to efficient use of nutrients in each stage
of sorghum. In line with this result, Limaux et al., (1999)
reported that supplying N in two or three applications are
a good recommendation to increase N use efficiency in
sorghum.
Thousand kernels weight (TKW)
The result indicated that thousand kernel weight was
significantly (P≤0.01) affected by the main effect of N
fertilizer rate and time of N application and the interaction
effect of the two factors (Table 5).
The highest thousand kernels weight of (44.67 g) was
recorded from 69 kg N ha-1 applied at three times of split
application (1/3rd at sowing, 1/3rd at mid-vegetative and
1/3rd at booting stage) and it was statistically at par with the
combination of 69 kg N ha-1 at two time of split application
(1/2 at mid-vegetative and 1/2 dose at booting growth
stage (44.33 g). In contrast, the lowest thousand kernels
weight of (26.33 g) was recorded from 23 kg N ha-1 at two
time of split application ((1/2 dose at sowing + 1/2 dose at
mid-vegetative) (Table 5). Increased kernel weight with
increasing nitrogen up to optimum levels might be due to
efficient use of nutrients and this led to the formation of
more leaf area which might have intercepted more light
and produced more carbohydrates in the source which
was probably translocated into the sink (the grain) and
resulted in more increased kernel weight.
Increasing N rates increased the enzyme activity in
sorghum which may result in maximum thousand kernels
weight. In line with this result, Limaux et al., (1999)
reported that supplying N in two or three applications are
a good recommendation to increase N use efficiency in
sorghum. Similarly, Cassman et al., (2002) described that
greater synchrony between crop demand and nutrient
supply is necessary to improve nutrient use efficiency, and
split applications of N during the growing season, rather
than a single, more application, are known to be effective
in increasing N use efficiency. Iqtidar et al., (2006) also
reported that the application of the highest rate of N
fertilizer gave highest thousand kernels weight. Likewise,
Miao et al., (2006) and Raja (2003) indicated that higher
rate of N level increased kernel weight in maize.
Table 5. Thousand kernels weight (g) as influenced by the
interaction of N rate and time of N application
Time of N application (NT)
Nitrogen rate (kg
ha-1)
T1 T2 T3
23 26.33g 29.00g 32.67f
46 34.67ef 37.33cde 39.67bc
69 41.00b 44.33a 44.67a
92 36.67cd 37.67cd 37.67cd
LSD (0.05) 2.748
CV (%) 4.4
not significantly different accordingto LSD Test
Grain yield (GY)
The analysis of variance showed that the main effect of
rate of N application and time of N application and their
interaction was significant (P≤0.01) on grain yield of
sorghum.
The highest grain yield (4635 kg ha-1) was recorded for
application of 69 kg N ha-1 in three split of 1/3rd dose at
sowing, 1/3rd dose at mid-vegetative and 1/3rd dose at
booting stage followed by the combination of 69 kg N ha-1
at two split application of 1/2 at sowing and 1/2 at mid-
vegetative growth stage (4363 kg ha-1). On the other hand,
the lowest grain yield (2638 kg ha-1) was obtained from 23
kg N ha-1 at two time of split application (1/2 at mid-
vegetative and 1/2 dose at booting growth stage (Table 6).
Grain yield increased with the increase in the rate of
nitrogen across the increased number of split application
(Table 6). The highest grain yield at the higher N rates
might have resulted from improved root growth and
increased uptake of nutrients and better growth that
enhanced yield components and yield.
Sorghum yield increase with increase in the rate of
nitrogen application, but no further increase when the rate
of N application was beyond optimum which could be
excess supply of nitrogen favoured more growth of the
plant parts which increased the biomass yield rather than
grain yield.
Likewise increasing the number of split application from
two to three equal doses at sowing, mid vegetative and
booting stage significantly increased grain yield at 46 and
69 kg N ha-1 (Table 6). This may be because the plants
may have been able to take up balanced amounts of

Abera et al. 607
nitrogen throughout the major growth stages due to better
synchrony of the demand of the nutrient for uptake by the
plant and its availability in the root zone in sufficient
amounts. In line with this result, Limaux et al., (1999)
reported that supplying N in two or three applications is a
good recommendation to increase N use efficiency in
sorghum. Cassman et al., (2002) also reported that greater
synchrony between crop demand and nutrient supply is
necessary to improve nutrient use efficiency, and split
applications of N during the growing season, rather than a
single, more application, are known to be effective in
increasing N use efficiency. Kidist (2013) reported that
increasing the rate of nitrogen from 130.5 to 174 kg N ha-1
decreased the grain yield by 5.4%. Thus, the optimum
grain yield was obtained at 130.5 kg N ha-1.
Table 6. Grain yield of sorghum (kg ha-1) as influenced by
the interaction of N rate and time of N application
Nitrogen rate (kg ha-1) T1 T2 T3
23 2792h 2638h 3143g
46 3517f 3848d 4109c
69 4363b 4301bc 4635a
92 3775de 3585ef 3572ef
LSD (0.05) 241.9
CV (%) 3.9
not significantly different according to LSD Test
Above ground dry biomass yield (AGBY)
The above ground dry biomass yield of sorghum was
highly significant (P≤0.01) for the main effects of N fertilizer
rate and time of N application. But there was no significant
interaction effect of nitrogen rate and time of N application
on this parameter.
The highest above ground biomass yield (10716 kg ha-1)
was obtained from 92 kg N ha-1 while the lowest biomass
yield (8361 kg ha-1) was recorded from 23 kg N ha-1. In
general, as the nitrogen rate increased, the biomass yield
was increased (Table 7).
The increase in biomass yield with increased N rate might
be attributed to the enhanced availability of N for
vegetative growth of the plants and LAI and accumulation
of photo assimilate due to maximum days to maturity by
the crop, this higher photosynthetic rate also results in
higher accumulation of dry matter. In conformity with this
result, Ali et al., (2005) and Iqtidar et al., (2006) reported
the highest biomass yield was recorded in the highest rate
of nitrogen application. Biomass in larger amounts of
nitrogen, investment of assimilates to leaves and stems
increased and finally increased dry matter yield.
Complimentary with Zerihun (2015) application of 92 kg
ha-1 gave the highest biomass yield. Similarly, Buah and
Mwinkara (2009) and Hugar et al., (2010) reported positive
effect of nitrogen on grain yield and yield attributes of
sweet sorghum. In line with this result Amanullah et al.,
(2009) reported the highest biological yields of 14.70 t ha-
1 were attained in maize in response to the N application
at the rate of 180 kg ha-1. In consistent with this result,
Habtamu (2015) reported the highest biomass yield of
maize at 90 kg N ha-1. Similarly, Yohanes (2014) reported
that increasing the rate of nitrogen from 0 to 138 kg N ha-1
significantly increased above ground dry biomass of
wheat.
Biomass yield was significantly influenced by the main
effect of time of N application. Significantly the highest
biomass yield (10142 kg ha-1) was obtained from two split
application of 1/2 mid-vegetative and 1/2 dose at booting
stage (Table 7). From this result, it is evident that N
availability must be adequate at the vegetative stage of
growth to ensure the maximum biomass yield. This resultis
in agreement with Settimi et al., (1998) who reported that
maize starts to take up N rapidly at the middle vegetative
growth period and maximum rate of N uptake occurs near
silking stage. Hence, application of N at mid-vegetative
and silking stage should be one of the best ways of
supplying the nutrient N to meet this high demand and the
crop never experienced with N stress in the later growth
stage to maintain prolific dry matter production.
Table 7. Biomass yieldof sorghum as influenced by N rate
and time of N application
Treatments Biomass yield (kg ha-1)
Nitrogen rate (kg N ha-1)
23 8361c
46 10124b
69 10070b
92 10716a
LSD (0.05) 373.7
N application time (NT)
T1 9540b
T2 10142a
T3 9771b
LSD (0.05) 323.7
CV (%) 3.90
at mid-vegetative; T2= N application 1/2 at mid-vegetative
and 1/2 at booting and T3= N application of 1/3rd at
sowing, 1/3rd at mid-vegetative and 1/3rd at booting.
Variable means followed by the same letters are not
significantly different according to LSD Test.
Harvest index (HI)
The physiological efficiency and ability of a crop for
converting the total dry matter into economic yield is known
as harvest index. Here, the analysis of variance showed
that harvest index was highly significant (P ≤ 0.01) affected

by the main effect of rate and time of N application and
significantly (P≤ 0.05) influenced by the interaction effect
of two factors (Table 8).
The highest harvest index (0.45) was recorded from 69 kg
N ha-1 at the three split application of 1/3rd N each at
sowing, mid-vegetative and booting stage and it was
statistically at par with the combination of 69 kg N ha-1 at
two split applications. In contrast, the lowest harvest index
(0.29) was obtained from 23 kg N ha-1 in combination with
two split application of 1/2 N (at mid-vegetative and at
booting stage) (Table 8).
The highest harvest index at 69 kg N ha-1 might be that
greater improvement in grain yield compared to the
corresponding increase in biomass yield, while the highest
N rate (92 kg N ha-1) gave more biomass than the grain
yield. In consistent with this result, Cassman et al., (2002)
reported that greater synchrony between crop demand
and nutrient supply is necessary to improve nutrient use
efficiency, and three split applications of N during the
growing season, rather than single, more application are
known to be effective in increasing N use efficiency and
plants uses nutrients effectively. In line with this result,
Lawrence (2008) reported that harvest index in maize
increased when nitrogen rates increased. Similalry,
Merkebu and Ketema (2013) reported that harvest index
of maize was significantly increased when the application
of N increased from 0 to 60 kg ha-1. Similarly, Orkaido
(2004) reported that increasing N level from 0 to 120 kg N
ha-1 increased harvest index of maize. In contrast, Abdo
(2009) reported highest harvest index from treatments with
the lowest rate of nitrogen application in wheat.
Table 8. Harvest index of sorghum as influenced by the
interaction of N rate and time of N application
23 0.34def 0.29g 0.38bc
46 0.36bcd 0.36cde 0.39b
69 0.43a 0.42a 0.45a
92 0.35cde 0.31g 0.33ef
LSD (0.05) 0.0319
CV (%) 5.10
Agronomic use efficiency (AUE)
The analysis of variance showed that agronomic efficiency
was highly significantly (P ≤0.01) affected by the main
effect of rate and time of N application or thier interaction
effect of the two factors (Table 9).
The highest agronomic efficiency (40.68 kg grain yield kg-
1 N) was obtained from 46 kg N ha-1 in combination with
three split application of 1/3rd N each at sowing, mid
vegetative and booting stage and it was statistically at par
with the combination of 23 kg N ha-1 with three split
application (39.34 kg grain yield kg-1 N applied). On the
other hand, the lowest agronomic efficiency (14.49 kg
grain yield kg-1 N) was recorded at 92 kg N ha-1 in three
split application of nitrogen (Table 9).
Decline in agronomic efficiency at higher level of N may be
attributed to nutrient imbalance and decline in indigenous
soil N supply. In agreement with this result, Craswell and
Godwin (1984) asserted that high agronomic efficiency is
obtained if the yield increment per unit N applied is high
because of reduced losses and increased uptake of N.
Similarly, Karim and Ramasamy (2000) obtained higher
fertilizer use efficiency which is always associated with low
fertilizer rate, cultural practices meant for promoting
integrated nutrient management will help to save the
amount of fertilizer applied to the crops and to improve
fertilizer use efficiency.
Thus, the goal of N-fertilizer research has to maintain high
levels of crop productivity with minimum nitrogen input, i.e.
to improve the agronomic efficiency of N. Agronomic
efficiency of N can be increased by increasing plant uptake
and use of N and by decreasing N losses from the soil-
plant system. Agronomic approaches, such as fertilizer
placement, proper level of fertilizer application in optimum
plant density, time of fertilizer application and use of
nitrogen efficient varieties are some of the practices that
can be used to improve nitrogen use efficiency. The result
of the study is in conform with Settimi et al., (1998) who
reported that maize starts to take up N rapidly at the middle
vegetative growth period and maximum rate of N uptake
occurs near silking stage. Fageria and Baligar (2005) also
asserted that high agronomic efficiency is obtained if the
yield increment per unit N applied is high because of
reduced losses and plants enhanced use of nutrients
effectively.
Table 9. Agronomic efficiency (kg grain kg-1 N) as
influenced by the interaction of N rate and time of N
application
23 24.07cd 17.40de 39.34a
46 27.79c 34.99ab 40.68a
69 30.80bc 29.89bc 27.41c
92 16.70e 14.63e 14.49e
LSD (0.05) 7.18
CV (%) 16.00

Abera et al. 609
Partial Budget Analysis of N Fertilizer Rate and Time
of Application
The interest of producers in applying fertilizer is not limited
to increasing yield alone, but also to make profit out of it.
Towards maximizing profit, the amount and time of
fertilizer application as well as costs of fertilizer are
determining factors. In the study area the demand and
market price of sorghum is important. Due to this fact
increasing both grain yield and biomass yield can increase
farmers’ income.
As indicated in the Table 10, the partial budget analysis
showed that the highest net benefit of 33053.23 Birr ha-1
was obtained in the treatment that received 69 kg N ha-1 in
to three split application of 1/3rd at sowing +1/3rd at mid
vegetative and 1/3rd at booting stage. However, the lowest
net benefit 21122.90Birr ha-1 was obtained from rate of 23
kg Nha-1. The highest marginal rate of return (2144.74%)
was obtained from the plot treated with 46 kg N ha-1 in two
split application (1/2 dose at mid-vegetative and 1/2 dose
and booting stage). However, the dominated treatment
was rejected from further economic analysis to distinguish
treatments with optimum return to farmer’s practice;
marginal analysis was performed on non-dominated
treatment. For treatment to be considered as advisable to
farmers, between 50% and 100% marginal rate of return
(MRR) was the minimum acceptable rate of return
(CIMMYT, 1988). Therefore, 843.36% was recorded from
application of 69 kg N ha-1 in three split (1/3rd dose at
sowing, 1/3rd dose at mid- vegetative and 1/3rd dose at
booting stage) with highest net benefit and MRR is
profitable and recommended for farmers in Mehoni district
area and others similar agro-ecological condition.
Table 10. Partial budget analysis of sorghum yield as influenced by N fertilizer rates and time of application at Mehoni
Treatment AGY
(kg ha-1)
ASY
(kg ha-1)
GFB
(ETB ha-1)
TVC
(ETB ha-1)
NB
(ETB ha-1)
MRR
(%)
NR NT
23 T1 2512.8 4698.9 22216.9 1094 21122.90 260.09
23 T2 2374.2 5679.0 21549.15 1120 20429.15 D
23 T3 2828.7 4482.9 24646.90 1258 23388.90 2144.74
46 T1 3165.3 5394.6 27749.97 1762 25987.97 515.68
46 T2 3463.2 6031.8 30419.91 1782 28637.91 D
46 T3 3698.1 5581.8 32096.61 1998 30098.61 676.25
69 T1 3926.7 5134.5 33724.12 2261 31463.12 518.82
69 T2 3870.9 5146.2 33282.99 2296 30986.99 D
69 T3 4171.5 4938.3 35594.23 2541 33053.23 843.36
92 T1 3397.5 6115.5 29931.97 2720 27211.97 D
92 T2 3226.5 6717.6 28834.92 2770 26064.92 D
92 T3 2314.8 7159.5 21740.17 3125 18615.17 D
Where, NR= Rate of nitrogen, NT= Time of N application, AGY= Adjusted grain yield, ASY= Adjusted stalk yield, GFB=
Gross field benefit, TVC = total variable cost, NB= Net benefit, MRR= Marginal rate of return, D= Dominated treatments.
Market price of sorghum 8 ETB kg-1, Cost of Urea = 988.55 ETB ha-1; Labour cost for application of nitrogen = 5 persons
ha-1,each 50 ETB day-1, Price of stalk =0.45 cents kg-1, ETB= Ethiopian birr, T1= N application of 1/2 at (sowing and mid-
vegetative); T2= N application of 1/2 at (mid-vegetative and at booting) and T3= N application of 1/3rd at (sowing, mid-
vegetative and at booting).
CONCLUSION
Sorghum is one of the major staple crops in Ethiopia in
terms of both production and consumption. Even though it
is such an important cereal crops in Ethiopia, it is giving
low yield due to many production constraints such as
minimum use of improved varieties, diseases, weeds, and
low soil fertility and lack of location specific fertilizer
recommendation in Ethiopia in general and in Southern
Tigiray Zone in particular.
In Northern Ethiopia, farmers in Raya valley district of low
land area apply N fertilizer in the form of urea at sub-
optimal blanket rates and use low amounts of nitrogen in
the form of urea only one time at sowing or at a vegetative
growth stage for sorghum production.
Therefore, field experiment was conducted during the
2017 main cropping season at Mehoni Agricultural
Research Center to assess the effect of nitrogen fertilizer
rates and time of application on yield and yield
components of sorghum; and to determine economically
appropriate rates of nitrogen and time of application for
sorghum production. The experiment was laid out as a
Randomized Complete Block Design (RCBD) with three
replications using a sorghum variety ‘Meko’ as a test crop.
The treatments consisted of four levels of N (23, 46, 69
and 92 kg ha-1) and three time of nitrogen fertilizer
application (1/2 dose at sowing and 1/2 dose at mid-
vegetative, 1/2 dose at mid-vegetative and 1/2 dose at
booting, 1/3rd dose at sowing, 1/3rd dose at mid vegetative
and 1/3rd dose at booting stage).

Analysis of the results revealed that days to flowering,
days to 90% maturity, leaf area, leaf area index, panicle
weight and above ground biomass were significantly
affected by main effect of rates of nitrogen as well as main
effect of time of nitrogen application; while plant height and
panicle length were affected by main effect of nitrogen
rates. The maximum days to flowering (68.78 days), days
to maturity (113 days), plant height (167.7 cm), panicle
length (25.95 cm) and above ground dry biomass (10716
kg ) were recorded at N rate of 92 kg N ha-1; where as leaf
area (4481 cm2), leaf area index (2.98) and panicle weight
(94.84 g) were recorded at N rate of 69 kg N ha-1.
Similarly, the maximum days to flowering (66.33 days),
leaf area, leaf area index (2.86), panicle weight (83.44 g),
days to 90% maturity (109 days) and above ground
biomass (10142 kg ha-1) were obtained from three time of
nitrogen application (1/3rd dose at sowing, 1/3rd dose at mid
vegetative and 1/3rd dose at booting stage) and two time
of nitrogen application (1/2 dose at mid-vegetative and 1/2
dos at booting).
The interaction of N rates and time of N application also
significantly affected thousand kernels weight, grain yield,
harvest index and agronomic efficacy. The maximum
thousand kernel weight (44.67 g), grain yield (4635 kg ha-
1) and harvest index (0.45) were recorded at combination
of 69 kg N ha-1 in to three split application (1/3rd dose at
sowing, 1/3rd dose at mid vegetative and 1/3rd dose at
booting stage). On the other hand, the highest agronomic
efficiency (40.68 kg grain yield kg-1 N) was recorded at
combination of (46 kg N ha-1) rates and three split
application of (1/3rd dose at sowing, 1/3rd dose at mid
vegetative and 1/3rd dose at booting stage).
The partial budget analysis revealed that combined
applications of 69 kg N ha-1in three split to 1/3rd dose at
sowing, 1/3rd dose at mid vegetative and 1/3rd dose at
booting stage gave the best economic benefit (33053.23
Birr ha-1) with MRR of 843.36%. Therefore, it can be
concluded that use of 69 kg N ha-1 in three split application
(1/3rd dose at sowing, 1/3rd dose at mid vegetative and
1/3rd dose at booting stage) can be tentatively
recommended for farmers for production of sorghum in the
study area and other areas with similar agro-ecological
conditions. However, since the experiment was conducted
for one season at one location, it is suggested that the
experiment has to be repeated over seasons and locations
using this and other improved sorghum varieties.
ACKNOWLEDGEMENT
The Ethiopian Institute of Agricultural Research (EIAR) is
gratefully acknowledged for the financial support during
this study. Haramaya University and Mehoni Agricultral
research Center and the staff members deserve thanks for
provision and preparation of necessary research materials
and cooperation in this work. Similarly, Mekelle Soil
Research Center soil laboratory is appreciated for their
cooperation during soil analysis.
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Accepted 18 December 2019
Citation: Abera K, Tana T,Takele A (2020). Effect of Rates
and Time of Nitrogen Fertilizer Application on Yield and
Yield Components of Sorghum [sorghum bicolor (L.)
Moench] at Raya Valley, Northern Ethiopia. International
Journal of Plant Breeding and Crop Science, 7(1): 598-
612.
Copyright: © 2020: Abera et al. This is an open-access
article distributed under the terms of the Creative
Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium,
provided the original author and source are cited.

Effect of Rates and Time of Nitrogen Fertilizer Application on Yield and Yield Components of Sorghum [sorghum bicolor (L.) Moench] at Raya Valley, Northern Ethiopia

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Effect of Rates and Time of Nitrogen Fertilizer Application on Yield and Yield Components of Sorghum [sorghum bicolor (L.) Moench] at Raya Valley, Northern Ethiopia