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© 2020 by the authors; licensee Asian Online Journal Publishing Group 
 

Agriculture and Food Sciences Research 
Vol. 7, No. 1, 69-78, 2020 

ISSN(E) 2411-6653/ ISSN(P) 2518-0193 
DOI: 10.20448/journal.512.2020.71.69.78 

© 2020 by the authors; licensee Asian Online Journal Publishing Group 

    
 

 
 
 
Determination of NP Fertilizer Rates and Plant Population Density on Yield and 
Yield Related Parameters of Quality Protein Maize (Zea mays L.) in Southwestern 
Ethiopia 

 
Sisay Gurmu   

 

 
 
Jimma Agricultural Research Center, Jimma, Ethiopia. 

 

 
Abstract 

Field studies were conducted in 2015 and 2016 under rain fed conditions in south western 
Ethiopia, Jimma zone to determine optimum plant population density and NP fertilizer on Maize.  
The experiment had four NP fertilizer rates; 69/52, 92/69, 115/86, and 138/104 N/P2O5 kg ha-1 
and four plant population density; 44,444(75cm*30cm), 53,333(75cm*25cm), 66,666(75cm*20cm) 
and 88,888(75cm*15cm) plants per hectare. Each treatment was assigned to each plot in split plot 
design. Grain yield and above ground biomass significantly increased as plant populations and NP 
fertilizer rates increased. The number of ears per plant was significantly decreased as plant 
population density increased and increased with the increased rate of NP fertilizer. The greater 
lodging was recorded in 2015 cropping season when compared with that of 2016 cropping season. 
The highest grain yield 8752 kg ha-1 and above ground biomass 18.33 ton ha-1 were recorded from 
138/104 N/P2O5 fertilizer. Regarding plant population density the highest grain yield 9401 kg 
ha-1 and above ground biomass 19.90 ton ha-1 were recorded from 88,888 plants ha-1 (75cm*15cm). 
The highest net benefit 30,669ETB ha-1 with highest MRR 164% was recorded from 115/86 
N/P2O5 kg ha-1. Concerning plant population density the highest net benefit 36,705 ETB ha-1 with 
acceptable MRR 585% was obtained from 88,888 plants ha-1 (75*15cm). Therefore, plant 
population density 88,888 plants ha-1 (75*15cm a plant hill-1 or 75 x 30 cm two plants hill-1) with 
N/P2O5 fertilizer rate of 115/86 kg ha-1 can be advisable for farmers in the study area and 
adjacent woredas’ with similar agro-ecologies. 

 
Keywords: Grain yield, Plant population density, Quality protein maize and fertilizer. 

 
Citation | Sisay Gurmu (2020). Determination of NP Fertilizer 
Rates and Plant Population Density on Yield and Yield Related 
Parameters of Quality Protein Maize (Zea mays L.) in Southwestern 
Ethiopia. Agriculture and Food Sciences Research, 7(1): 69-78. 
History:  
Received: 5 February 2020 
Revised: 10 March 2020 
Accepted: 13 April 2020 
Published: 15 May 2020 
Licensed: This work is licensed under a Creative Commons 

Attribution 3.0 License  
Publisher:  Asian Online Journal Publishing Group 
 

Funding: The research was funded by Ethiopia Institute of Agricultural 
Research 
Competing Interests: The author declares that there are no conflicts of 
interests regarding the publication of this paper. 
Transparency: The author confirms that the manuscript is an honest, 
accurate, and transparent account of the study was reported; that no vital 
features of the study have been omitted; and that any discrepancies from the 
study as planned have been explained. 
Ethical: This study follows all ethical practices during writing.   

 

 

Contents 
1. Introduction ...................................................................................................................................................................................... 70 
2. Materials and Methods ................................................................................................................................................................... 70 
3. Results and Discussion ................................................................................................................................................................... 72 
4. Conclusion and Recommendation ................................................................................................................................................ 77 
References .............................................................................................................................................................................................. 77 
 

 

 

 

 

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Contribution of this paper to the literature 
This research study can find answers to things that are unknown around maize planting, filling 
gaps in knowledge and changing the way that maize agronomist works in general. 

 
1. Introduction 

Globally, maize (Zea mays L.) is among the leading cereals in production along with rice and wheat. In Africa, 
Ethiopia is the third largest maize producer next to Nigeria and Egypt [1]. Maize ranks second after teff in area 
coverage and first in total production in Ethiopia [2]. In 2016/17 the maize crop area and grain production in 
Ethiopia was 2,135,572 ha and 7, 8471,175 ton, respectively with productivity of 3675 kg ha-1 [2]. Normal maize 
grain has greater nutritional value as it contains 72% carbohydrate, 8.8% protein, 2.15% fiber and 2.33% ash [3]. It 
is a good source of carbohydrates, fat, protein and some important vitamins (B6, A and E) and minerals 
(magnesium, potassium and phosphorus), but deficient in essential amino acids viz., lysine and tryptophan that 
reduces its biological value [4]. The amount of these deficient amino acids has been increased by incorporating 
opaque-2 gene in quality protein maize (QPM) [5]. It produces 70-100% more of lysine and tryptophan than the 
most modern varieties of tropical maize [6].  

Insufficient application of nutrients and poor soil management, along with harsh climatic conditions and other 
factors, have contributed to the degradation of soils including soil fertility depletion in developing countries, 
especially in SSA [7]. Poor soil fertility is one of the principal factors that limit maize productivity in maize 
growing areas of Ethiopia [8]. Degradation of soil physico-chemical properties, soil acidity with high P sorption 
and soil nutrient depletion due to low chemical fertilizer use by most small-holder farmers who cannot afford the 
expensive fertilizers leads to declining in maize production in SSA [9]. 

Among plant nutrients nitrogen is a vitally important, a major yield determining nutrient and its availability in 
sufficient quantity throughout the growing season is essential for optimum maize growth [10]. It is a component 
of protein, nucleic acids and other compounds essential for plant growth process [11]. Whereas phosphorus is the 
second most important nutrient element (after nitrogen) limiting agricultural production [10]. It is used for 
growth, utilization of sugar and starch, photosynthesis, metabolic process which leads to higher yield of the crop 
[12]. 

Maize is commonly planted in rows of varying spaces; less effort has been made to plant at optimum densities 
to maximize its productivity in different agro-ecologies of Ethiopia. Summaries of earlier results from different 
studies on maize plant population densities indicate that better yields were obtained at planting density in range of 
6-7.5 plants m-2 [13]. It is being observed that medium and early maize varieties in humid lowlands and low 
moisture stress area found to be varied in structure and leaf arrangements from known normal maize varieties. 
These variations in morphology may lead to different planting density to reach at their at maximum yield 
potentials.  

Plant population density has a significant impact on growth and yield of crops, including maize, a popular C4 
cereal crop. Therefore, understanding how plants regulate their growth in response to plant population densities 
has problems, such as determination of optimal sowing density. Increased plant populations could lead to increased 
yields under optimal climatic and management conditions due to greater number of smaller cobs per unit area 
[14]. 

Hence, for further dissemination and adoption of QPM hybrid there is a need to understand its performance 
with various agronomic management practices, of which nutrient management and plant stand are vital in 
influencing the growth and yield of the crop. Hence, this study was initiated with the objective to study the effect of 
plant population density and NP fertilizer on the growth and yield of maize.  
 

2. Materials and Methods 
2.1. Description of the Study Area 

The research activity was performed on farmers’ field in Omonadawareda (Nada-SadechaKebele) of Jimma 
Zone, South western Ethiopia in main cropping seasons (mid May up to early November) of 2015 and 2016 Figure 
1. This location is foundon latitude 7º36' N and longitude 37º 15' E and laid at an altitude of 1764 m.a.s.l. Ten years 
average minimum and maximum temperature is 8ºC and 28ºC respectively and reliably receives annual average 
rainfall of 1200 mm with agro-ecology characterized by humid mid altitude. The farming system of the study site is 
cereal crops dominated with maize, teff and sorghum also has warm and cold climate, also convenient topography 
which is very suitable for all agricultural practices. The soil type of the experimental area was Eutric-nitisols 
(reddish brown). 
 

 
Figure-1. Decadal time scale (2007-2016) of Precipitation, ETo, 1/2 ETo, maximum and minimum temperature at Jimma, Omonadaworeda. 
 



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2.2. Soil Physico-Chemical Properties  
The soil of the experimental field was characterized for selected physico-chemical properties before the 

application of the treatments Table 1.The average soil pH of the trial site was 5.13, which was strongly acidic [15] 
and ideal for the production of most field crops. The pH of the soil affects maize growth by suppressing the root 
development and reducing availability of macronutrients to plants especially phosphorus [16]. The soil total N 
was 0.19%.These was found to be a medium rate for crop growth and development [17]. The OC content of 
experimental area was 2.08% and it was found medium rate for crop growth [18]. The Bray II extractable 
available P was 6.17 mg kg-1 which is below the critical level (8 mg kg-1) for most crop plants as described by 
Tekalign and Haque [19]Table 1. 
 

Table-1.Selected physico-chemical properties of  the soil of  the experimental sites before planting. 

Soil characters Values Rating Reference Method of analysis 

pH(1:2.5) 5.13 Strongly  acidic  Batjes [15] 1:2.5 ratio water method  

Av P(mg kg-1) 6.17 Low  Tekalign and Haque 
[19] 

Bray II method [20] 

TN (%) 0.19 Medium Berhanu [17] Kjeldahl method [21] 

OC (%) 2.08 medium Tekalign [18] Walkley and Black method 
[22] 

C:N ratio 11.05 Medium Brady and Weil [23]  
OM (%) 3.58 High Berhanu [17]  

Note: Where pH= Hydrogen ion concentration, OC=Organic Carbon, TN=Total Nitrogen, Av. P=Available Phosphorous, OM=Organic Matter. 
Values are the means of duplicated samples. 

 

2.3. Experimental Treatments and Procedures 
The experimental field was ploughed and prepared following the conventional tillage practice before planting. 

The land was leveled using manual power before the field layout was made. The maize was planted during mid 
May and harvested early November of each year. Two maize seeds were planted per hill and then thinned to one 
plant per hill after good establishment of seedlings so as to maintain a single healthy plant per hill. There were four 
NP fertilizer rates; 69/52, 92/69, 115/86, and 138/104 kg/ha N/P2O5 and four plant population density; 44,444, 
53,333, 66,666, and 88,888 plants per hectare. The experimental plot size was 22.95m2 (4.5 m x 5.1 m) for each 
treatment. The split plot design with three replications was used that plant population densities in main plot and 
fertilizer rates in subplots.  

Nitrogen and phosphorus fertilizers were calculated as per rates given above and applied per area base. To 
increase the nitrogen use efficiency, it was split in three equal rates and applied at planting time, knee height and 
flag leaf initiation stages. All other agronomic practices were applied uniformly to all experimental plots in the 
study area.  
 
2.4. Description of the Experimental Materials 

Medium maturing maize variety BHQPY545 was used in the present study. It was released by Bako 
Agricultural Research Centre through the National Maize Research Program in 2008. It performs well in agro-
ecology of 1000-2000 m.a.s.l with rainfall of 1000-1200 mm. It can give 8.0-9.5 and 5.5-6.5 t ha-1 grain yields under 
on-station and on-farm experiments, respectively. It was moderately tolerant to rust, blight and gray leaf spot with 
maturity date of 138.  
 

2.5. Data Collected  
2.5.1. Plant Height (cm) 

It was measured at ground level to terminal stem using measuring stick at the point where the tassel starts 
branching from six randomly selected plants. 
 

2.5.2. Number of  Ear per Plant 
It was obtained by counting total number of  ears in each plot and divided to total number of  plant stand 

harvested. 

2.5.3.Grain Yield (kg ha-1) 
Grain yield per plot was recorded using electronic balance and then adjusted to 12.5% moisture and converted 

to hectare basis. 
 

2.5.4.Above Ground Biomass (kg ha-1) 
All above ground biomass was harvested from net plot and weighted, ears were removed and weighted 

separately, six plants were selected, chopped and oven dried till get uniform weight.  
 

2.5.5. Lodging Percent 
It was obtained by counting the total number of stalk and root lodging in each plot and divided to the total 

number of plant stand at harvesting.  
 

2.5.6. Harvest Index 
Was calculated as the ratio of grain yield to above ground biomass yield on dry weight basis [24]. HI(%) =

Economic yield (kg/ha)

Total biological yield (kg/ha)
x100 

 
 
 



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2.6. Data Analysis 
Analysis of variance (ANOVA) for all collected data was computed using SAS version 9.3 statistical software. 

Whenever the ANOVA results showed the significant differences between sources of variation, the means were 
compared using least significant difference.  
 

2.7. Partial Budget Analysis 
Partial budget analysis was performed to investigate the economic feasibility of the treatments 

and assess the costs and benefits associated with different treatments of chemical fertilizers and 
plant population density of the seed rates. The partial budget technique as described by CIMMYT [25] was 
applied. The partial budget analysis was done using the prevailing market prices for inputs at planting and for 
outputs at the time the crop was harvested. All costs and benefits were calculated on a per hectare basis in 
Ethiopian Birr (ETB). The inputs and/or concepts used in the partial budget analysis were the mean grain yield of 
each treatment, the gross field benefit (GFB) ha-1 (i.e., the product of field price and the mean yield for each 
treatment), the field price of chemical fertilizers and urea kg-1 (the nutrient cost plus the cost of transportation from 
the point of sale to the farm), cost of labor spent on seed purchase and planting, the total costs that varied (TVC) 
which included the sum of field costs of fertilizers and their application, and seed purchase and planting. 

The net benefit (NB) was calculated as the difference between the GFB and the TVC. The 
marginal rate of return (MRR %) were also calculated. To obtain an estimate of these returns, 
the MRR (%) was calculated as changes in NB divided by changes in cost. Thus, a minimum 
acceptable MRR of 100% was used; indicating for every one ETB expended there is a return of 
one ETB for a given variable input [25] which is suggested to be realistic. This 
enables the farmer to make recommendations from marginal analysis. The dominance analysis 
procedure as detailed in CIMMYT [25] was used to select potentially profitable treatments 
from the range that was tested. Sensitivity analysis for different interventions was also carried out to test the 
recommendation made for its ability to withstand price changes. Sensitivity analysis simply implied redoing 
marginal analysis with the alternative prices. Through sensitivity analysis, maximum acceptable field price of an 
input was calculated with the minimum rate of return as described by Shah, et al. [26]. 

 
3. Results and Discussion 

The effect of different rates of NP fertilizer and plant population density on yield and yield related parameters 
of QPM maize variety and cost benefit analysis were presented and discussed as follows.It has been observed that 
medium maturing maize variety like BHQPY545 vary in structure and leaf arrangements from other late maturing 
maize varieties. These variations in morphology may lead to different planting density to reach the maximum yield 
potentials.  
 
Table-2. Mean square from combined analysis of the effects of NP fertilizer rates and plant population density on growth, yield attributes 
and yield of QPM maize during 2015 and 2016 cropping seasons at Omonadaworeda, Jimma zone southwestern Ethiopia. 

Mean square for source of variation 

Parameter 
 

Year (1) Intra row 
(3) 

Year*Intra 
row (3) 

Year x 
NP (3) 

NP (3) Intra row 
x NP (9) 

Year x 
Intra row 
x NP (9) 

Error a 
(6) 

Error 
b 
(24) 

Plant 
height(cm) 

41242.7** 823.5972* 88.39583ns 52.6875ns 2132.5** 119.44ns 209.340ns 238.079 88.396 

Ears per plant 1.3085** 0.98015** 0.02850ns 0.02554ns 0.23307** 0.02496ns 0.03228ns 0.0522 0.0285 
Lodging % 4773.8** 431.436ns 457.346ns 544.517ns 93.628ns 56.884ns 94.989ns 82.85 89.85 
Grain yield 
(kg ha-1) 

112165917** 48126018** 1241199ns 1692656ns 17101704** 1535100ns 1459915ns 2916763 12411
98 

AGB (t ha-1) 402.058** 219.1591** 0.5320ns 7.3594ns 54.8910** 6.2721ns 5.2058ns 8.539 0.532 
Harvest index 0.0011ns 0.000973ns 0.0051ns 0.00011ns 0.001581ns 0.002343n

s 
0.0017ns 0.0026 0.0051 

Note: *Numbers in parenthesis = Degrees of freedom; *= Significant (P < 0.05); ** = highly significant (p<0.01) difference; AGB= Aboveground biomass; ha = Hectare. 

 
The homogeneity test of the error variances for years indicated that the error variance was homogenous and 

hence combined analysis of variance was conducted. Over year combined analysis effects of NP fertilizer rates and 
plant population density didn’t show significant (P >0.05) interaction effect on plant height, ears per plant, lodging 
percent, grain yield, aboveground biomass and HI. Plant height was significantly (P <0.05) influenced by plant 
population density and highly significantly (P <0.01) influenced by NP fertilizer and year. Whereas ears per plant, 
grain yield and above ground biomass were highly significantly (P <0.01) influenced by NP fertilizer rates, plant 
population density and year. However, lodging percent and harvest index were not significantly (P >0.05) affected 
by both NP fertilizer rates and plant population density, but lodging percent was highly significantly (P <0.01) 
affected by the year difference Table 2. 
 

3.1. Effect of  NP Fertilizer and Plant Population Density on Growth Parameters 
3.1.1. Plant Height 

At Omonada woreda Jimma zone, medium maturing maize hybrid (HBQPY545) had exhibited vigorous growth 
performances and resulted in good response to both NP fertilizer and plant population density. The mean 
significant higher plant height was recorded in 2016 main cropping season. Numerically, the longer plant height 
(247.0cm) was recorded by plant population density of 88,888 plants ha-1 (75*15cm) but its effect was not 
statistically significant different from plant population density of 53,333 and 66,666 plants ha-1. While the shorter 
plant height (237.1cm) was recorded by 44,444 plants ha-1 (75*30cm) Table 3. These results indicated as plant 
population increased the plant height also increased and vice versa. The plant height was increased by 4.2% at the 
highest plant population density as compared to the lowest plant population density.Highest plant height in closer 
intra row spacing might be due to the presence of higher competition for sun light, crowding effect of the plant and 



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other resources that decrease in the stem diameter and number of green leaves. Earlier results explained that the 
number of plants increased in a given area, the competition among the plants for nutrients uptake and sunlight 
interception also increased [27]. These finding is in agreement with Hassan [28] who revealed that plant height 
increased with increasing plant density from 47600 to 71400 plants ha-1. 

Regarding the effect of NP fertilizer rates the longer plant height (250.5cm) was recorded by 138/104 kg ha-1 
N/P2O5 fertilizer. But its effect was statistically at par with 115/86 kg ha-1 N/P2O5 fertilizer,while the shorter plant 

height (0.90) was recorded from 69/52 kg ha-1 N/P2O5 fertilizer Table 3. The results indicated that as NP fertilizer 
increased the plant height was also increased and vice versa. Application of 138/104 kg ha-1 N/P2O5 fertilizer 
increased plant height by 6.7% over 69/52 kg ha-1 N/P2O5 fertilizer. The increase in plant height with increasing 
rate of NP fertilizer could be due to their major effect in crop growth and development. Nitrogen is considered as 
one of the major limiting nutrients in plant growth and adequate supply of it promotes the formation of chlorophyll 
which in turn resulted in higher photosynthetic activity, vigorous vegetative growth and taller plants. Whereas 
phosphorous is required for shoot and root development where metabolism is high and cell division is rapid [29]. 
These results were in line with the findings of Adekayode and Ogunkoya [30]who explained that there was very 
high significant difference in maize plant height in plots treated with higher fertilizer compared with nil 
application. Also Kumar, et al. [31] reported that growth and yield of maize plants in terms of plant height varied 
significantly due to various fertility levels. He reported the highest plant height was recorded from application of 
100% NPK (120N:26.2P:33.2K) with 10 ton FYM ha-1 over control.  
 

3.2. Effect of  NP Fertilizer and Plant Population Density on Yield and Yield Related Parameters 
3.2.1. Number of Ears per Plant 

Number of ear per plant was determined by prolific ability of the BHQPY545 maize variety as described by 
Adefris, et al. [32] and the growth behavior of the crop which is dependent upon management practices and 
edaphic and climatic factors. The number of ears per plant was higher (1.43) during 2016 main cropping season as 
compared with 2015 cropping season. The maximum number of ear per plant (1.50) was recorded from 44,444 
plants ha-1 (75*30cm) which was statistically at par with 53,333 plants ha-1 (75*25cm) while the minimum number 
of ears per plant (1.17) was recorded from 88,888 plants ha-1 (75*15cm) Figure 2. These results indicated as plant 
population density increased number of ears per plant linearly decreased and vice versa. The number of ears per 
plant was increased by 28.2% at the lowest plant population density (44,444 plants ha-1) as compared to the highest 
plant population density (88,888 plants ha-1). This might be due to in the closest spacing there is high inter stem 
competition to nutrients and sun light so, it caused lack of nutrient for each plant and consequently compelling the 
plants to undergo less reproductive growth. These finding are in agreement with Hashemi-Dezfouli and Herbert 
[33] who reported a significantly higher number of ear per plant at lower plant density as compared to higher 
plant density.  

Concerning the response of number of ears per plant to NP fertilizer rates the maximum number of ears per 
plant (1.41) was recorded from 138/104 kg ha-1 N/P2O5 fertilizer. But its effect was statistically at par with 92/69 
and 115/86 kg ha-1 N/P2O5 fertilizer, while the minimum number of ears per plant (1.26) was recorded from 69/52 
kg ha-1 N/P2O5 fertilizer Figure 2. These result indicated as NP fertilizer rate increased to 138/104 kg ha-1 N/P2O5 
fertilizer, the number of ears per plant was increased and vice versa. Application of 138/104 kg ha-1 N/P2O5 
fertilizer increased number of ears per plant by 11.9% over application of 69/52 kg ha-1 N/P2O5 fertilizer. The 
improvement of the soil conditions or enrichment with nutrients due to soil-added materials might be responsible 
for better cob production under plots treated with higher NP fertilizer. Nitrogen can trigger vegetative growth 
and development and it is an integral part of chlorophyll, which is the primary absorber of light energy needed for 
photosynthesis. These results were in line with the result of Singh and Nepalia [34] who reported the application 
of higher dose of chemical fertilizer improved the number of cobs plant-1 in QPM hybrid significantly over the 
lower nutrient application.  
 

  



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Figure-2.Effect of  NP fertilizer and plant population density on number of  ear per plant at Jimma, Omonadaworeda in 2015 and 2016 
cropping seasons. 

 
3.2.2. Lodging Percent 

During 2015 main cropping season the lodging percent of QPM maize variety was higher than during 2016 
cropping season. It was not significantly (P>0.05) affected by both NP fertilizer rates and plant population density 
Table 2. 
 

3.2.3. Grain Yield 
Hybrid QPM maize BHQPY545 had exhibited vigorous growth performances and resulted in good response to 

NP fertilizers and plant population density in season 2015 and significant increase in grain yield was recorded 
Table 3. Over season mean indicated, the higher plant population density (88,888 plant ha-1) gave higher grain 
yield (9401.2 kg ha-1) while the lower grain yield (7046.0 kg ha-1) was recorded from 44,444 plants ha-1 
(75*30cm)Table 3. The result indicated as the plant population density increased the grain yield of QPM maize 
variety linearly increased and vice versa. The grain yield of the crop was increased by 33.4% at the highest plant 
population density (88,888 plants ha-1) as compared to lowest plant population density (44,444 plants ha-1) and this 
is due to low plant population harvested ha-1 in wider spacing intra row spacing.  Thus, balanced growth and 
development of plants need optimum plant density because optimum density enables plants efficient utilization of 
available nutrients, soil water and better light interception coupled with other growth influencing factors. 
Therefore, results of this contradicted the previous recommendation 75x30cm inter and intra row spacing resulted 
in the production of grain yield. These results were supported by Emam [35] who verified that kernels ear-1 and 
kernels row ear-1 were the most important yield adjustment components in response to plant population density in 
maize. These finding was in agreement with Farnham [36] who reported that maize grain yield increased as plant 
density increased from 59,000 to 89,000 plant ha-1.  

Regarding the effect of NP fertilizer rates 138/110 kg ha-1 N/P2O5 fertilizergave significantly higher grain 
yield of 8751.6 kg ha-1 which was statically at par with 115/86 kg ha-1 N/P2O5 fertilizerrate while, the lowest grain 
yield 7442.2 kg ha-1 was recorded from 69/52 kg ha-1 N/P2O5 fertilizerrateTable 3. The grain yield advantage of 
15.2% was obtained from 115/86 kg ha-1 N/P2O5 when compared to 69/52 kg ha-1 N/P2O5 fertilizerrate. The 
responses of  maize grain yield to increased NP fertilizer application rates were simulated via a linear regression 
model, at four densities over two years Figure 3. The result indicated as NP fertilizer rate increased the grain yield 
was increased and vice versa. Reduction of grain yield might be due to nutritional imbalance and deficiency of 
certain important plant growth elements at various important growth stages and also due to reduced leaf area 
development resulting in lesser radiation interception and, consequently, low efficiency in the conversion of solar 
radiation. The higher doses of chemical fertilizers increased grain yield as nutrients are the main driving force to 
produce high yield of maize [37].It is clear from the result that grain yield increased in response to increasing rate 
of NP fertilizer application possibly due to higher number of ears per plant.These increase the nutrients in the soil 
and modification of soil environments that resulted in better vegetative growth which in turn enabled the crop to 
produce greater photo-assimilate. The N has synergistic effects on growth and yield attributes resulting in greater 
translocation of photosynthates from source to sink, beneficial effect on physiological process, plant metabolism, 
growth and it is the major ingredient of proteins, enzymes, amino acids, amides and nucleic acids [38] and there by 
leading to higher grain yield. The P supply is particularly important for stimulating early root formation and 
growth, functions in plant macromolecular structures as a component of nucleic acids and phospholipids, with 
crucial roles in energy metabolism, participation in signal transduction path ways via phosphorylation and 
controlling key enzyme reactions [39]. 
 



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Figure-3. Maize grain yields as a function of NP application rate for four plant population densities over the year 
study. Planting densities were 44,444 (75x30cm), 53,333 (75x25cm), 66,667 (75x20cm) and 88,888 (75x15cm) in 
panels A–D respectively. 

 

3.3. Aboveground Biomass Yield 
The significant higher above ground biomass was recorded during the 2015 main cropping season than 2016 

cropping season. The maximum above ground biomass 19.90 ton ha-1 was recorded from plant population density 
of 88,888 plants ha-1 (75x15cm) while, the minimum above ground biomass yield was obtained from plant 

population density of 44,444 plants ha-1 (75x30cm) Table 3. The result indicates that as plant population density 
increased up 88,888 plants ha-1 the above ground biomass linearly increased and vice versa. It was increased by 
33.3% by planting the highest plant population rate than 44,444 plants ha-1. The result showed that biological yield 
was increased by increasing plant density due to high grain yield, number of ears per plant and plant height in the 
treatment of high plant population density of 88,888 plants ha-1 (75x15cm) and low biomass yield was obtained in 
the treatment of lower plant population density 44,444 plants ha-1 (75x30cm). The aboveground biomass yield was 
decreased in wider spacing due to minimum plant height and decreased ability of plants for capturing resources 
which was reflected as evident in their decreased biomass production. These results were in agreement with 
Bullock, et al. [40] who reported that narrow row spacing made more efficient use of available light and shaded the 
surface soil more completely during the early part of the growing season while the soil is still moist and therefore, 
narrow row spacing are more effective in producing biomass.  
 

3.4. Harvest Index 
The harvest index was not significantly (P>0.05) affected by cropping season, plant population density and NP 

fertilizer rate. But, the gained data was in the acceptable range of 0.4 - 0.6 for maize [41]. 

 
3.5. Economic Analysis 

The official prices of chemical fertilizer (NPS=13.5 birr kg-1) and urea (10 birr kg-1) were calculated based on 
stock sale prices of OmonadaFarmers Cooperative in May, 2015 and 2016. The sale of grain maize at Omonada 
open market average price was 4.6 ETB kg-1 in January, 2016 and 2017.The cost of labor spent on chemical 
fertilizer application and transport, seed planting and purchase were also used for partial budget analysis. The cost 
of application and transport of fertilizer was taken to be 15 birr 100 kg-1. Grain yield was adjusted by 10% for 
management difference to reflect the difference between the experimental yield and the yield that farmers could 
expect from the same treatment [25, 42]. 

The dominance analysis procedure as detailed in CIMMYT [25] was used to select potentially profitable 
treatments. Dominance analysis led to the selection of treatments ranked in increasing order of total variable costs 
Table 5. For each pair of ranked treatments, the percent marginal rate of return (MRR) was calculated. The MRR 
(%) between any pair of un-dominated treatments were the return per unit of investment in chemical fertilizer and 
plant population density. It was calculated by dividing the change in net benefit to the change in variable costs. 
100% MRR means for every 1 birr invested in different cost of fertilizer and maize seed, farmers can expect to 
recover 1 birr and obtain an additional1 birr [25]. 
 
 
 
 



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Table-3. Main effects of intra row spacing, NP fertilizer rates and year on growth and yield component of BHQPY-545 at Jimma zone, 
Omonadaworeda over 2015 and 2016 cropping season. 

Treatment Plant height (cm) lodging % Grain yield (t ha-1) AGB (t ha-1) HI 

Year 
2015 228b 28.4a 8950a 18.75a 0.48 
2016 257a 18.4b 7421b 15.85b 0.47 
LSD (0.05) 4.398 4.159 486.830 0.833 0.015 
F-test ** ** ** ** NS 

Plant population density (plantha-1) 
88,888 (75x15cm) 247a 21.0 9401a 19.90a 0.47 
66,667 (75x20cm) 243a 20.6 8485b 18.00b 0.47 
53,333 (75x25cm) 243a 26.6 7809b 16.37c 0.48 
44,444 (75x30cm) 237b 25.3 7046c 14.93d 0.47 
LSD (0.05) 6.11 13.86 727.7 0.474 0.046 
CV (%) 6.36 38.9 20.87 16.89 10.81 
F-test * NS ** ** NS 

N/P2O5 Fertilizer rates(kg ha-1) 

69/52  235c 22.0 7442c 15.91c 0.47 
92/69  241b 22.4 7974bc 17.05bc 0.47 
115/86  245ab 24.2 8574ab 17.91ab 0.48 
138/104  251a 25.0 8752a 18.33a 0.48 
LSD (0.05) 6.22 5.88 688.5 1.178 0.021 

CV (%) 3.87 40.5 13.61 4.22 15.19 
F-test ** NS ** ** NS 

Note: LSD= Least Significant Difference; CV=Coefficient of Variation; NS=Non significant; HI= Harvest Index; AGB=Above Ground Biomass; Values 
followed by the same letter within a column are not significantly different at P< 0.05. 

 
The highest net benefit 36,705.0 ETB ha-1 was obtained from plant population density of 88,888 plants ha-1 

(75*15cm) with acceptable MRR 584.5%. Whereas, the lowest net benefit 28,062 ETB ha-1 was obtained from the 
lower plant population density 44,444 plants ha-1Table 4. Due to planting of 88,888 plants ha-1 (75*15cm), there 
was a net benefit increase by 30.8% (8,643 ETB ha-1) when compared with that of lower plant population density 
44,444 plants ha-1 (75*30cm). 
 
Table-4. Partial budget analyses of NP fertilizer rates and plant population density on grain yield of medium maturing maize variety QPYBH545 at Jimma 
zone during 2015-2016. 

N/P2O5 
(Kg ha-1) 

GY 
(kg ha-1) 

Adj.GY 
(kg ha-1) 

GFB 
(ETB ha-1) 

TVC 
(ETB ha-1) 

NB 
 (ETB ha-1) 

69/52  7442.2 6698.0 30810.71 2933.6 27877.11 
92/69  7973.6 7176.2 33010.7 3885.3 29125.4 
115/86  8574.1 7716.7 35496.77 4827.5 30669.27 

138/104  8751.6 7876.4 36231.62 5807.3 30424.32 

Plant population density 
88888(75*15cm)  9401.2 8461.1 38920.97 2216 36705.0 
66666(75*20cm) 8485.2 7636.7 35128.73 1662 33466.7 
53333(75*25cm) 7809.2 7028.3 32330.09 1317.6 31012.5 
44444 (75*30cm)  7046 6341.4 29170.44 1108 28062.4 

Note: *GY= Grain yield; GFB = Gross field benefit; TCV = Total cost that varied; NB = Net benefit; 
ETB = Ethiopian Birr; Price of chemical fertilizer = 13.5birr kg-1; Price of Urea = 10 birr kg-1; Wage rate = 30 Birr man-day-1; Retail price of grain = 4.6 birr 
kg-1. 

 
Table-5. Partial budget with dominance analysis and MRR (%) of NP fertilizer and plant population density of medium maturing maize 
variety QPYBH545 at Jimma zone in 2015-2016. 

N/P2O5 
(Kg ha-1) 

GY 
(kg ha-1) 

Adj.GY 
(kg ha-1) 

GFB 
(ETB ha-1) 

TVC 
(ETB ha-1) 

NB 
(ETB ha-1) 

Domi 
nance 

MRR 
(%) 

69/52  7442.2 6698.0 30810.71 2933.6 27877.11 --- --- 
92/69  7973.6 7176.2 33010.7 3885.3 29125.4 UD 131.2 
115/86  8574.1 7716.7 35496.77 4827.5 30669.27 UD 163.9 
138/104  8751.6 7876.4 36231.62 5807.3 30424.32 D --- 
Population Density 
44444 (75*30cm) 7046.0 6341.4 29170.44 1108.0 28062.4 --- --- 
53333(75*25cm)  7809.2 7028.3 32330.09 1317.6 31012.5 UD 1407.5 
66666(75*20cm) 8485.2 7636.7 35128.73 1662.0 33466.7 UD 712.6 
88888(75*15cm ) 9401.2 8461.1 38920.97 2216.0 36705.0 UD 584.5 

Note: *GY= Grain yield; GFB = Gross field benefit; TCV = Total cost that varied; NB = Net benefit; 
ETB = Ethiopian Birr; Price of chemical fertilizer = 13.5birr kg-1; Price of Urea = 10 birr kg-1; Wage rate = 30 Birr man-day-1; Retail price of grain = 4.6 birr 
kg-1. 

 
Regarding the effect of NP fertilizer rates the highest net benefit 30,669ETB ha-1 was obtained from 115/86 kg 

ha-1 N/P2O5 fertilizer with acceptable MRR 163.9%. Whereas, the lowest net benefit (27,877 ETB ha-1) was 
obtained from the lower NP fertilizer rate 69/52 kg ha-1 N/P2O5Table 5 and Figure4. Due to application of 115/86 
kg ha-1 N/P2O5 fertilizer, there was net benefit increase by 10% (2792 ETB) when compared with 69/52 kg ha-1 
N/P2O5 fertilizer. 
 
 



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Figure-4. Total variable cost, net benefit and MRR % of NP fertilizer rate and plant population density rate of QPYBH545 maize variety at 
Jimma zone in 2016 and 2017 cropping season. 

 
Market prices are ever changing and as such a recalculation of the partial budget using a set of 

likely future prices (i.e., sensitivity analysis) was essential to identify treatments which may 
likely remain stable and sustain satisfactory returns for farmers despite price fluctuations. The 
sensitivity analysis study indicates an increase in the field price of the total variable costs, and a fall in the price of 
maize grain, which represented a price variation of 15%. 

The price changes are realistic under market conditions prevailing at Jimma area which were 
above the minimum acceptable MRR of 100% for application of 115/86 NP2O5 fertilizer.  

Concerning plant population density 88,888 plants ha-1 (75*15cm), 66,666 plants ha-1 (75*20cm) and 53,333 
plants ha-1 (75*25cm) are realistic which were above the minimum acceptable MRR of 100% Table 6. 
 

Table-6. Sensitivity analysis of maize production based on a 15% rise in total cost and maizeprice of gross field benefit fall. 

N/P2O5 Fertilizer TVC (ETB ha-1) NB (ETB ha-1) Raised cost Raised benefit MRR (%) 

69/52 3373.64 23695.54 ---- ---- ---- 
92/69  4468.095 24756.59 1094.46 1061.05 96.95 
115/86  5551.625 26068.88 1083.53 1312.29 121.11 

Population density 
     

44444 (75*30cm) 1274.2 23853.1 ---- ---- ---- 
53333(75*25cm)  1515.24 26360.6 241.04 2507.54 1040.30 
66666(75*20cm) 1911.3 28446.7 396.06 2086.10 526.71 

88888(75*15cm ) 2548.4 31199.2 637.10 2752.50 432.04 
Note: *TCV = Total cost that varied; NB = Net benefit; ETB = Ethiopian Birr; MRR= Marginal rate of 
return; Price of chemical fertilizer = 13.5 birr kg-1; Price of Urea = 10 birr kg-1, Wage rate = 30 Birr man-day-1; Retail price of grain = 6 birr kg-1. 

 

4. Conclusion and Recommendation 
Lately innovated maize varieties such as quality protein maize (QPM) versions vary in stature and leaf 

arrangements from known normal maize varieties. These variations in morphology may lead to different planting 
density to reach at their at maximum yield potentials. In view of this, plant population density study on QPM 
hybrid (BHQPY 545) was proposed with two objectives to maximize yield potential and to help small holder 
farmers to feed their families with high protein diet. Accordingly, rigorous research efforts were made on research 
station fields of JimmaJimma Research Center (Melko and Mettu) and on farmers field in vicinity of the center for 
three cropping seasons. Summary of results from across seasons and sites indicated that at highest plant population 
density, grain and biomass yields were significantly increased. Similarly, the higher fertilizer doses produced 
significantly higher biomass and grain yields. To increase certainty and further use of optimum plant density 
evaluation criteria was set by farmers and subjected to choose or reject any density not technically appropriate. 
Thus, for the future production of maize hybrid, BHQPY545 in Omonadawareda and adjacent waredas with similar 
agro-ecologies, a plant population density of 88,888 plant ha-1 (75 x 15cm a plant hill-1 or 75 x 30 cm two plants 
hill-1) in complement with NP fertilizer rate of 115/86 kg ha-1 can be recommended.  
 

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