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Horticulture Thesis and Dissertations
2019-12-24
EFFECT OF INTRA-ROW SPACING
AND NITROGEN FERTILIZER RATE
ON GROWTH AND YIELD OF ONION
(Allium cepa L.) UNDER IRRIGATION
CONDITION IN MECHA DISTRICT OF
AMHARA REGION
Dasash, Atalay
http://hdl.handle.net/123456789/10084
Downloaded from DSpace Repository, DSpace Institution's institutional repository
BAHIR DAR UNIVERSITY
COLLEGE OF AGRICULTURE AND ENVIRONMENTAL SCIENCE
DEPARTMENT OF PLANT SCIENCE
M.Sc. PROGRAM IN HORTICULTURE
EFFECT OF INTRA-ROW SPACING AND NITROGEN FERTILIZER RATE ON
GROWTH AND YIELD OF ONION (Allium cepa L.) UNDER IRRIGATION
CONDITION IN MECHA DISTRICT OF AMHARA REGION
M.Sc. Thesis
By
Dasash Atalay Mitiku
October 2019
Bahir Dar, Ethiopia
i
BAHIRDAR UNIVERSITY
COLLEGE OF AGRICULTURE AND ENVIRONMENTAL SCIENCE
DEPARTMENT OF PLANT SCIENCE
M.Sc. PROGRAM IN HORTICULTURE
EFFECT OF INTRA-ROW SPACING AND NITROGEN FERTILIZER RATE ON
GROWTH AND YIELD OF ONION (Allium cepa L.) UNDER IRRIGATION
CONDITION IN MECHA DISTRICT OF AMHARA REGION
M.Sc. Thesis
BY
Dasash Atalay Mitiku
Submitted in Partial Fulfillment of the Requirements for the Degree of Master
of Sciences (MSc.) in HORTICULTURE
Major Advisor: Dr. Melkamu Alemayehu
Co-Advisor: Dr. Semagn Asredie
October 2019
Bahir Dar, Ethiopia
ii
THESIS APPPROVAL SHEET
As member of the board of Examiners of the Master of Science (M.Sc.) open defense exami-
nation, we have read and evaluated this thesis prepared by Dasash Atalay Mitiku “Effect of
Intra-Row Spacing and Nitrogen Fertilizer Rate on Growth and Yield of Onion (Allium
Cepa L.) Under Irrigation Condition in Mecha District of Amhara Region”. We here by
certify that, the thesis is accepted for the fulfilling the requirements for the awarded of the
Degree of Master of Science (M.Sc.) in Horticulture.
Boarder of Examiners
________________________ _______________ ____________
Name of External Examiner Signature Date
________________________ _______________ ___________
Name of Internal Examiner Signature Date
________________________ ______________ ____________
Name of chair Person Signature Date
________________________ ______________ __________
iii
DECLARATION
This is to certify that, this thesis entitled “Effect of Intra-Row Spacing and Nitrogen Ferti-
lizer Rate on Growth and Yield of Onion (Allium Cepa L.) Under Irrigation Condition in
Mecha District of Amhara Region” submitted in partial fulfillments for the award of the
degree of Master of sciences (M.Sc.) in Horticulture to the graduate program of College of
Agriculture and Environmental Sciences, Bahir Dar University by Ms. Dasash Atalay is an
authentic work carried out by her under our guidance. This thesis has not been submitted to
any other institution earlier for the award of any academic degree, diploma to the best of our
knowledge.
Name of the Student
Dasash Atalay Signature ____________ Date ________________
Name of Major Advisor
Dr. Melkamu Alemayehu Signature_____________ Date ________________
Name of Co- Advisor
Dr. Semagn Asredie Signature _____________ Date ______________
iv
ACKNOWLEDGEMENTS
First, I would like to offer lots of thanks to God and his mother Saint Virgin Mary for their
compassionate help in all aspects of my life. It is my pleasure to express my heartfelt appreci-
ation and deepest gratitude to my major advisor, Dr. Melkamu Alemayehu and my co-advisor
Dr. Semagn Asredie for their useful comments, as well as for guiding and supervising my
work during the entire period of the research and for shaping the final write-up of the thesis.
Further, I also extend my gratitude towards the Assosa University for granting me a scholar-
ship for my graduate study and to Bahir Dar University for hosting me.
My sincere acknowledgment is also extended to Adet Agricultural Research Center for
providing me tools and equipment’s that were required to accomplish the research work. Last-
ly and most importantly, my heartfelt thanks go to my classmates Mequannet Tilahun and
Eden Melaku and my beloved for their support and encouragement throughout the entire peri-
od of my study.
v
DEDICATION
I dedicate this thesis work to my mother, my beloved and respected families for their affection
and consistent care in the success of my life.
vi
ABBREVIATIONS AND ACRONOMY
AARC Adet Agricultural Research center
ANOVA Analysis of variance
CIMMYT International Maize and Wheat Improvement center
CSSE Crop Science Society of Ethiopia
CSA Central Statistical agency
EARO Ethiopian agricultural research Organization
EIAR Ethiopian Institute of agricultural research
FAO Food and Agricultural Organization
FAOSTAT Food and Agricultural Organization Statics
LSD Least Significance difference
MoARD Ministry of Agriculture and rural development
RCBD Random complete Block design
SAS Statistical application of science
SNNPRS Southern Nation, Nationalities and Peoples Regional state
EARO Ethiopian agricultural research Organization
vii
EFFECT OF INTRA-ROW SPACING AND NITROGEN FERTILIZER RATE ON
GROWTH AND YIELD OF ONION (Allium cepa L.) UNDER IRRIGATION CONDI-
TION IN MECHA DISTRICT OF AMHARA REGION
By
Dasash Atalay Mitiku
Major Advisor: Dr. Melkamu Alemayehu
Co-Advisor: Dr. Semagn Asredie
ABSTRACT
Onion is an important cash crop produced by smallholder farmers in Amhara Region. The
productivity of the crop is however low which is among others associated with Poor soil fertility management practice coupled with under optimum plant population. Moreover, farm-
ers are complaining where the present recommended 10 cm intra row spacing produces large sized bulbs, which are not preferred by consumers for home consumptions. Therefore, the present study was initiated with the objective of investigating the effects of intra row- spacing
and nitrogen fertilizer rates on growth and yield of onion. The treatments consisted of four levels of Nitrogen fertilizer rate (0, 41, 82, 123 kg ha-1 N) and three-intra row spacing (4, 7.
10 cm). The experiment was down in Randomized Complete Block Design (RCBD) in factori-al arrangement with three replications. Date on Growth, yield and yield components of onion were collected and subjected to ANOVA using SAS (version 9.0) software. Both the main ef-
fect as well as the interaction effect of intra row spacing and rates of nitrogen fertilizer signif-icantly influenced almost all the tested growth and yield components of onion. The highest
significant plant height (60.53cm), leaves number per plant (14.10cm), leaves length (60.90cm), day to maturity (115 days) and bulb weight (96.05 g) were recorded from onion plants supplied with 82kg ha-1 N and 123 kg ha-1 N both combined with 10 cm of intra row
spacing. The highest marketable bulb yield (43.80 t/ha) was recorded from treatment combi-nation of 82 kg ha-1 N and 4 cm of intra row spacing. Onion plants without nitrogen fertilizer
application and narrow intra row spacing were inferior in almost all growth and yield com-ponents. Based on the results of the present study, the combination of 82 kg ha-1 N and 4 cm of intra row spacing can be recommended for economical production of onion in the study
area since it recorded the highest net benefit with acceptable marginal rate of return. Since the results are limited to one season and location, it is advised to repeat the experiment in
different area and season for forceful recommendations.
Keywords: Bombay Red Variety, Koga Irrigation Scheme, Marketable and Total Bulb
Yield
viii
Table of contents
Contents Pages
THESIS APPPROVAL SHEET.......................................................................................................ii
DECLARATION ............................................................................................................................ iii
ACKNOWLEDGEMENTS ............................................................................................................iv
DEDICATION ................................................................................................................................ v
ABBREVIATIONS AND ACRONOMY.......................................................................................vi
ABSTRACT ..................................................................................................................................... vii
Table of contents .................................................................................................................. viii
Lists of Tables .................................................................................................................................xi
List of Figures ................................................................................................................................ xii
List of Appendices ........................................................................................................................ xiii
Chapter 1. INTRODUCTION ......................................................................................................... 1
1.1. Background and Justification ............................................................................................... 1
1.2. Statement of the Problem ..................................................................................................... 3
1.3. Objectives of the Study’s ..................................................................................................... 5
1.3.1. General objective........................................................................................................... 5
1.3.2. Specific objectives......................................................................................................... 5
Chapter 2. LITERATURE REVIEW ............................................................................................. 6
2.1. Origin and Distribution of Onion ......................................................................................... 6
2.2. Ecological Requirement of Onion........................................................................................ 7
2.3. Importance and Production of Onion in Ethiopia ................................................................ 7
2.4. Potentials and Constraints of Onion Production in Ethiopia ............................................... 8
2.5. Effects of Nitrogen on Growth and Yield of Onion............................................................. 9
ix
2.6. Effect of Plant Spacing on Onion Growth and Yield of Onion ......................................... 11
2.7. Interaction Effect of Nitrogen and Plant Spacing on Growth and Yield of Onion ............ 11
Chapter 3: MATERIAL AND METHODS ................................................................................. 13
3.1. Description of Study Area.................................................................................................. 13
3.2. Experimental Materials, Treatments and Design ............................................................... 14
3.3. Experimental Procedure ..................................................................................................... 15
3.4. Methods of Data Collection ............................................................................................... 18
3.4.1. Growth parameters of onion........................................................................................ 18
3.4.2. Yield related parameters of onion ............................................................................... 19
3.5. Methods of Data Analysis .................................................................................................. 19
3.6. Soil sampling of experimental plots................................................................................... 20
Chapter 4. RESULTS AND DISCUSION .................................................................................... 22
4.1. Effects of Nitrogen Fertilizer and Intra-row Spacing on Growth of Onion ....................... 22
4.1.1. Days to maturity .......................................................................................................... 22
4.1.2. Plant height.................................................................................................................. 23
4.1.3. Leaf number per plants................................................................................................ 24
4.1.4. Leaf Length ................................................................................................................. 25
4.2. Effects of Nitrogen Fertilizer and Intra-row Spacing on Yield Component of Onion....... 27
4.2.1. Bulb diameter .............................................................................................................. 27
4.2.2. Bulb weight ................................................................................................................. 28
4.2.3. Bulb size distribution of onion .................................................................................... 31
4.2.4. Marketable bulb yield.................................................................................................. 36
4.2.5. Unmarketable bulb yield ............................................................................................. 37
4.2.6. Total Bulb Yield.......................................................................................................... 38
4.3. Correlation Analysis of Growth and Yield Parameters as Influenced by Intra row
Spacing and Nitrogen Fertilizer ................................................................................................ 42
4.4. Economic Analysis............................................................................................................. 44
x
Chapter 5: CONCLUSION AND RECOMMENDATIONS ........................................................ 49
5.1. Conclusions ........................................................................................................................ 49
5.2. Recommendations .............................................................................................................. 50
REFFERENCES............................................................................................................................ 51
APPENDICES............................................................................................................................... 62
BIOGRAPHY.................................................................................Error! Bookmark not defined.
xi
Lists of Tables
Table 3.1: Treatment combinations used in the study.............................................................. 15
Table 3.2: Major physic-chemical properties of the experimental soil before planting .......... 21
Table 4.1: Main effect of nitrogen rates and intra-row spacing on growth of onion at Koga
Irrigation Scheme during the (2018) irrigation season............................................................. 26
Table 4.2: Interaction effects of intra-row spacing and nitrogen fertilizer levels on Growth of
onion plants .............................................................................................................................. 27
Table 4.3: Main effects of intra-row spacing and nitrogen on diameter and weight of onion
bulbs ......................................................................................................................................... 30
Table 4.4: Interaction effect of intra-row spacing and nitrogen fertilizer levels on diameter and
Weight of onion bulb................................................................................................................ 31
Table 4.5: Main effect of intra-row spacing and nitrogen fertilizer rates on bulb-size
distribution of onion ................................................................................................................. 35
Table 4.6: Interaction effect of intra-row spacing and nitrogen fertilizer levels on Bulb-size
Distribution of onion ................................................................................................................ 36
Table 4.7: Main effects of intra-row spacing and nitrogen fertilizer on bulb yield of onion at
Koga Irrigation Scheme during the (2018) irrigation season ................................................... 40
Table 4.8: Interaction effect of intra-row spacing and levels of nitrogen fertilizer on yield of
onion at Koga Irrigation Scheme during the (2018) irrigation season ..................................... 41
Table 4.9: Simple correlation between growth and yield components of onion as influenced
by intra row spacing and rate of nitrogen................................................................................. 44
Table 4.10: Economical analysis for marketable yield of onion as affected by nitrogen
fertilizer rate and intra-row spacing ......................................................................................... 46
Table 4.11: Dominance analysis for marketable yield of onion as affected by nitrogen
fertilizer and intra-row spacing ................................................................................................ 47
Table 4.12: Marginal rate of return (MRR) of marketable onion yield as affected by nitrogen
fertilizer and intra-row spacing ................................................................................................ 48
xii
List of Figures
Figure 3. 1: Map of the study area Mecha district ........................................................................ 13
xiii
List of Appendices
Appendix 1: Mean squares of analysis of variance for plant height (PH), leaf length (LL), leaf
number per plant (LN), day to maturity (DM) ......................................................................... 62
Appendix 2: Mean squares of analysis of variance for yield and yield related traits of onion 63
Appendix 4: Mean squares of analysis of variance for marketable and unmarketable size
distribution of onion ................................................................................................................. 63
Appendix 5: Mean squares of analysis of variance for marketable bulb yield, unmarketable
bulb yield and total yield of onion ........................................................................................... 64
1
Chapter 1. INTRODUCTION
1.1. Background and Justification
Onion (Allium cepa L.) belongs to the family Alliaceae is an important vegetable bulb crop
cultivated in tropical and subtropical parts of the world, which ranks second next to tomato
(FAO, 2012). The crop is grown in at least 261 countries of the world (FAOSTAT, 2017). In
Ethiopia, onion is one of the most cool season bulb vegetables produced by smallholder farm-
ers mainly as as a source of cash income (Lemma Dessalegn and Shimeles Aklilu, 2003).
Onion contributes a significant nutritional value to the human diet and has medicinal proper-
ties. The crop primarily consumed for its unique flavor or ability to enhance the flavor of oth-
er foods (Randle and Ketter, 1998). All the plant parts are edible, but the bulbs and the lower
stem sections are the most popular as seasoning or as vegetables in stews (MoARD, 2009). It
is one of the richest sources of flavonoids in the human diet and flavonoid where its consump-
tion has been associated with a reduced risk of cancer, heart disease and diabetes. Flavonoids
are not only anti-cancer, but also known to be anti-bacterial, antiviral, anti-allergenic and anti-
inflammatory. Quality parameters of onion bulb have become important to meet demands of
both processing and fresh market buyers (Brewster, 1990 and Pelter et al., 2004).
According to FAOSTAT (2017), 97,862,928 tons of onion yields were produced on 5201591
hectares across the world. China and India are the leading onion producing countries contrib-
uted 26.3% and 22.6% of the total world onion production respectively (FAOSTAT, 2014). In
terms of productivity however, USA is the first country in the world with 54.6 t/ha followed
by Netherland (49.7 t/ha), Egypt (33.7 t/ha) and Iran (31.8 t/ha) (FAOSTAT, 2014). The pro-
duction of onion in Africa is very low as compared to the world. As statistics showed,
12,174,553 tons of onion yields were produced in area coverage of 1114907 hectares with av-
erage productivity of 11.4 t/ha (FAOSTAT, 2017).
Onion was introduced to the agricultural community of Ethiopia in the early 1970’s when for-
eigners brought it in (Tadesse Adgo, 2008). Though shallots are traditional crop in Ethiopia,
Onion is becoming more widely grown in recent years.
2
Currently, the crop is producing in different parts of the country for local consumption (Lem-
ma Dessalegn and Shimeles Aklilu, 2003). It is considerably important in the daily Ethiopian
diet.
Vegetables including onion are producing in many home-gardens and in some extent com-
mercially in different parts of Ethiopia. The major producers are however, the small-scale
farmers using mainly rainfall although some produced using irrigation (CSA, 2016). The av-
erage productivity of onion in Ethiopia is about 10.06 t/ha (FAOSTAT, 2017) which is very
low compared to world`s average of 18.81 t/ha (FAOSTAT, 2017). Amhara region contrib-
utes for production of onion in the country by constituting the estimated area coverage of
12,262.79 hectare with average productivity of of 11.6 t/ha (CSA, 2016).
The production and productivity of vegetables in particular onion is very low in Ethiopia alt-
hough the country has huge potentials to the crop production and utilization. Several factors
contribute to this low level of production and productivity. Among these, lack of appropriate
agronomic packages, shortage of seeds of improved varieties, diseases, insect pests and poor
extension services, high costs of chemical fertilizers and sometimes their unavailability to
small-scale farmers (Currah and Proctor, 1990, Melkamu Alemayehu et al., 2015).
The use of appropriate agronomic and management practices play a key role in increasing
crop yields including onion. Optimum agronomic and management practices for a crop varies
with plant population, planting, and harvesting dates and fertilizers used, with the prevailing
environmental conditions (soil fertility, rainfall, etc), purpose of production of the crop and
even within cultivar.
Maintaining adequate level of soil fertility is recognized as one of management practices that
affect growth, development and yield of plants including onion (Tisdale Sintayehu et al.,
1995). One of the options to maintain soil fertility as well as to obtain higher yield is the ap-
plication of inorganic fertilizers. According to Shaheen et al. (2007), onion is a heavy feeder
of mineral elements. A crop of 35 t/ha removes approximately 120 kg N, 50-kg P2O5 and 160-
kg K2O per hectare (Mohanty et al., 2015). Hence the greater its ability to utilize nutrients for
crop production, the greater is the yield potential.
3
Because of their shallow and unbranched root system, onions are the most susceptible crop
plants in extracting nutrients. Hence, they require and often respond well to addition of ferti-
lizers (Brewster, 1994; Rizk et al., 2012). Therefore, optimum fertilizer application and culti-
vation of suitable varieties with appropriate agronomic practices in specific environment are
necessary for obtaining good yield of onion.
In addition to nutrients, plant spacing is an important factor determining onion yield and qual-
ity. An essential aspect of any crop production system is the development of a crop canopy
that optimizes the interception of light, photosynthesis, and the allocation of dry matter to
harvestable parts. Manipulating row spacing and plant population influences crop canopy. As
plant density increases, yield per unit area up to certain level increases. Further increasing of
plant density, yield per unit area declines since yield per plant tends to decrease because of
competition for growth factors between adjacent plants (Silvertooth, 2001). Planting density
greatly influence texture, quality, taste and yield of onion even within a particular variety
(Saud et al., 2013).Thus, spacing is an important factor for the production of onion since it
affects both bulb yield and quality.
1.2. Statement of the Problem
Onion is one of the most important vegetable crops cultivated mostly under irrigated condi-
tion in Mecha district in West Gojam Zone of Amhara Region. However, the crop productivi-
ty is remained very low compared to the world average (Yemane Kahsay et al., 2016). The
low level of vegetable production in general and that of onion in particular is associated with
poor agronomic practices, shortage of seeds of improved varieties, diseases and insect pests,
poor extension services, high costs of agricultural chemicals including fungicides, insecticides
and fertilizers ( Melkamu Alemayehu et al., 2015; Nigatu Muluneh, 2016). Moreover, quality
and yield of particular onion variety are greatly affecting planting density even if grown in the
same environment (Fahad et al., 2013).
Mineral fertilizers are one of the principle factors that materially set up onion growth and pro-
duction. However, due to ever increasing prices, smallholder farmers may not apply full dose
of inorganic fertilizers which are required to sustain and increase yields (Takashi and Ayumi,
2010; Negasi Tekeste et al., 2013).
4
At present, onion growers in the study area produce onion with the application of nitrogen
fertilizer rates and intra-raw spacing which they feel as best for obtaining higher yields of on-
ion crop (Personal communication). However, the blanket recommended rates of fertilizers
are 200 kg ha-1 of DAP and 100 kg ha-1 Urea (Nikus Olani and Mulugeta Fikre, 2010).
Plant density is another important appropriate management area for onion production. Opti-
mum plant spacing enables the farmer to keep optimum plant population, avoid over and less
population in a given plot of land, which has negative effect on growth, yield and quality
(EARO, 2004). To avoid nutrient competition sufficient spacing between plants and rows is
vital to get maximum yield of onion in a given land. The optimum use of spacing or plant
population has dual advantages. It avoids strong competition between plants for growth fac-
tors such as water, nutrient and light. In addition, optimum plant population enables efficient
use of available cropland without wastage (Geremew Awas et al., 2010).
The recommended spacing for production of onion is however 40 cm x 20 cm x 10 cm in
Ethiopia (Lemma Dessalegn and Shimeles Aklilu, 2003). However, wider plant spacing pro-
duced the large size of bulbs; the large size of bulb contains highest water and has more sur-
face area per unit of bulb there by highest rate of transpiration and then highest weight loss.
Sing and Sing (2003) reported that, large size of bulb exhibited the highest weight loss com-
pared to smaller size of bulbs.
Recently research results confirmed that spacing of 10 cm between plants produced large bulb
size. Hence, individual consumers do not prefer these large sized bulbs for home consumption
(EHDA, 2011; Habtamu Tegen et al., 2016). For example, Geremew Awas et al. (2010) rec-
ommended intra row spacing of 4 cm for ‘Adama’ Red varieties, and 6 cm for ‘Bombay’ Red
variety, in central rift valley areas of Ethiopia. According to Yemane Kahsay et al. (2013), at
wider intra row spacing (10 cm) produces big size bulb which are liable to highest rotting per-
centage compared those produced with intra-row spacing (5 and 7.5 cm). Bosekeng (2012)
also observed that large plants grown at wider spacing are associated with split bulbs and sen-
sitive to a cold stimulus causing bolting. Optimization of Plant population is thus important
and needs to be optimized. Therefore, the present study was proposed to evaluate the effects
of spacing and nitrogen fertilizer on growth and yield of onion.
5
1.3. Objectives of the Study’s
1.3.1. General objective
The general objective of the present study was contributing towards the improvement of pro-
duction and productivity of onion in the study area through optimizing plant spacing and ni-
trogen fertilizer rate.
1.3.2. Specific objectives
The specific objectives of the study were to asses:
Effect of intra -row spacing and nitrogen fertilizer rate on growth and yield of onion;
and
Determine the optimum intra- row spacing and nitrogen fertilizer rate for economical
production of onion at Koga irrigation Scheme.
6
Chapter 2. LITERATURE REVIEW
2.1. Origin and Distribution of Onion
The primary origin of onion is Central Asia with secondary center in Middle East and Medi-
terranean Region (Zohary and Hopf, 2000, Grubben and Denton, 2004). Onion is a herba-
ceous monocot plant, which is cultivated as an annual crop for the purpose of bulb production.
However, it is cultivated as biennial crop for seed production. During the first season, bulbs
are formed while flower stalks and seeds are developed in the second season (Corgan et al.,
2000. Onion belongs to the genus Allium of the family Alliaceae (Hanelt, 1990). It is a cross-
pollinated crop having diploid chromosomes number (2=16 (Bassett, 1986). Recent estima-
tions accept about 750 species in the genus Allium, among which onion, Japanese bunching
onion, leek and garlic are the most important edible Allium crops (Rabinowitch and Currah,
2002).
Jones and Mann (1963) gave simple classification of the genus where Allium cepa L. is cate-
gorized into common onion group, aggregatum group or shallots and ever-ready onion. From
horticulture, point of view common onion group is the most important and widely produced
group worldwide. The onion bulb is composed of fleshy enlarged leaf base or scale (Shanmu-
gasundaram and Kalib, 2001). Onion roots are short lived, being continuously produced, rare-
ly have branches and root hairs, and rarely increase in diameter. The terminal inflorescences
develops from the ring like apical meristem scapes and several, generally elongate well above
the leaves and ranges in height from 30 to more than 100 cm (Brewster, 1994;
Shanmgasundaram and Kalib, 2001).
Onion has its own distinctive flavor, pungency, is eaten as fried, boiled, roasted or raw in sal-
ad as vegetable, and is widely used as a condiment in preparation of soups, savory dish,
canned food product, salads and sandwiches. Moreover, it is also processed as pickle, chut-
ney, and sauces and consumed in dehydrated form (Muhammad S. J, 2004).
7
2.2. Ecological Requirement of Onion
Onion can grow between 500 and 2400 meter above sea level. Nevertheless, according to
Lemma Dessalegn and Herath (1994), the best growing altitude in Ethiopia is between 700
and 1800 m above sea level.
Onion crop can be successfully produced on most fertile soils. The onion crop requires alluvi-
al or sandy loam soli with high levels of organic matter for optimum vegetative growth. The
onion crop is gross feeder since they require high fertile soil to maintain maximum yields
(Brewster, 1999). The favorable pH for onion production ranges from of 6.2 to 6.8. However,
onion crop may also grow on relatively acidic soils (Karim and Ibrahim, 2013). According to
Karim and Ibrahim (2013), onion yields however severely reduced in soil salinity.
Temperatures around 20 –22oC are favorable for vegetative growth while temperatures around
12oC favor seed stalk formation (Sukprakarn et al., 2005). According to CSSE (2006), the di-
verse agro-climatic conditions that prevailed in Ethiopia generally provide the opportunity to
produce bulbs and seeds of onion for local use and export market.
2.3. Importance and Production of Onion in Ethiopia
The production of vegetables including onion is an important sector of horticulture. Its pro-
duction is in increasing trend, which is associated with the expansion of irrigated agriculture.
The sector is an important source of income, row material for industry, employment oppor-
tunity and improvement of food security as indicated by (Lemma Dessalegn et al., 2006). On-
ion contributes substantially to the national economy, apart from overcoming local demands.
It is used almost daily as a spice and vegetable in the local dish regardless of religion, ethnici-
ty, and culture (CSSE, 2006). It has distinctive flavor, pungency, is eaten as fried, boiled,
roasted or raw in salad as vegetable, and is widely used as a condiment in preparation of
soups, savory dish, canned food product, salads and sandwiches. Moreover, it is also pro-
cessed as pickle, chutney, and sauces and consumed in dehydrated form (Muhammad S. J,
2004).
Onion is producing on small and large scale in Ethiopia. It occupies an economically im-
portant place among vegetables in the country. The crop is produced commonly under rain-
8
fed season and under irrigation in the offseason. However, the offseason crop (under irriga-
tion) constitutes much of the area under onion production. In Ethiopia, onion production area
is growing from time to time which is associated with its high productive and cost-effective
per unit area, ease of production and the increases in small-scale irrigation areas (Lemma
Dessalegn and Shimeles Aklilu, 2003). The main onion producing regions are Amhara, Tig-
ray, Oromia, Benishngule-Gumuz, Gambella and South Nation Nationalities and Peoples Re-
gions (CSA, 2016).
2.4. Potentials and Constraints of Onion Production in Ethiopia
Ethiopia including Amhara Region has diverse agro-ecologies that enable the country to pro-
duce tropical, subtropical and temperate vegetables including onion throughout the year
(Kubsa A. et al., 2006). The country has a great potential to produce onion throughout the
year both for local consumption and for export because of presence of underground and sur-
face water potential, which can be used, for the production of horticultural crops including
onion (Selesh Bekele, 2010). Moreover, the Ethiopian Agricultural Research Institute has
made efforts towards improvement of varieties and released different improved varieties in-
cluding Adama Red, Bombay Red, Red Creole, Melkam, Mermiru Brown, Nasik Red and
Nafis (Lemma Dessalegn and Shimelis Aklilu, 2003; MoARD, 2010). Onion is therefore pop-
ular over the local shallot, which is low in its productivity (Lemma Dessalegn, 2004).
The production and efficiency of horticultural crops including onion is significant poorer than
other African countries. Generally, in Ethiopia, as well as in Amhara Region the production of
onion is very low due to insufficient availability of quality seeds, technologies used and inap-
propriate cultural practices (Nikus Olani and Fikre Mulugeta, 2010). In addition to this, since
most of the time onion is produced by smallholder farmers, appropriate agronomic practices
employed agricultural inputs such as fertilizers, improved varieties and pesticides are not suf-
ficiently used, and inappropriate postharvest handling practices are done. Generally, farmers
produce horticultural crops with traditional farming system that leads to low production and
productivity (Melkamu Alemayehu et al., 2015).
Moreover, the production of horticultural crops is dependent on natural rainfall and therefore
their production is totally influenced by rainfall fluctuation, Like to other horticultural crops,
9
onion is produced by traditional farming practices where the farmers lack improved onion
production technologies. Improved onion seeds are inadequate because of lack of seed pro-
duction system in the region. Fertilizers are mostly available for main season crops while for
irrigated vegetable crops like onion, fertilizers are not available in sufficient quantity
(Melkamu Alemayehu et al., 2015).
Furthermore, due to favorable tropical conditions in Ethiopia, which favor the development of
pests, onion is suffering from various diseases and insect pests throughout the country includ-
ing in Amhara Region. The most common diseases occurred in Ethiopian onion farms are
purple blotch, onion neck rot and powdery mildew, which are caused by the fungi Alternari-
aporri, Botrytis cineraria and Peronospora destructor, respectively (Lemma Dessalegn and
Shimelis Aklilu, 2003). Among insect pests, thrips, mites and cutworms are the most im-
portant once in farmer`s onion farms (Lemma Dessalegn, 2004). The damages caused by pests
are further interested because most onion-growing farmers do not use the exact pesticides and
the recommended rates for the control of pests. Some traders mix pesticides with other sub-
stances (adulteration) which may either reduces their effectiveness or damage the crop plants
and sosustain economic losses for onion growing farmers (Edossa Etissa, 2013).
Poor infrastructures such as rural roads and communication for efficient flow of goods and
market information are limited, where most onion production sites are not accessible for
transportation. As onions are perishable by nature, they cannot be stored for long period with-
out quality decline unless properly handled. Moreover, there is a serious problem in the mar-
keting of horticultural crops including onion in Ethiopia in general and in Amhara region in
particular which affect not only the incomes negatively but also the interests of farmers to par-
ticipate in the onion production in the following years (Melkamu Alemayehu et al., 2015).
2.5. Effects of Nitrogen on Growth and Yield of Onion
Nitrogen often refers as primary macronutrients because of the probability of plants being de-
ficient in this nutrient and the large quantities taken up from the soil relative to other essential
nutrients (Marschner, 1995). Nitrogen comprises 7% of total dry matter of plants and is a con-
stituent of many fundamental cell components (Bungard et al., 1999). The amount of nitrogen
needed is usually based on soil organic matter content, crop uptake and yield levels. Nitrogen
10
uptake levels by onion crops may vary from less than 50 kg to more than 300 kg per hectare,
depending on cultivar, climate, plant density, fertilization, irrigation efficincy and yield levels
(Sorensen, 1996; Suojala et al., 1998).
Nitrogen plays an important role in the growth and development of plants including onion. A
good supply of nitrogen stimulates root growth and development as well as the uptake of oth-
er nutrients (Brady and Weil, 2002). Under sub-optimal supply of nitrogen, onions could be
severely stunted, with small bulb size then reduced marketable yields. By contrast, too much
nitrogen could result in excessive vegetative growth, delayed maturity, increased susceptibil-
ity to diseases, reduced dry matter contents and storability and, thus, result in reduced yield
and quality of marketable bulbs (Brewster, 1994; Sørensen & Grevsen, 2001).
Nitrogen significantly affected plant height, number of leaves, fresh weight, diameter, length
and weight of bulb as well as bulb yield of onion (Nasreen et al., 2007; Al-Fraihat, 2009 and
EI-hamady, 2017). Moreover, fertilization of onion plants with nitrogen fertilizer extended the
number of days required for onion crop to attain its physiological maturity. In this regard, Ab-
dissa Yadeta et al. (2011) reported that nitrogen fertilization extended physiological maturity
by about 6 days over the unfertilized plants regard less of its rate. Morsy et al. (2012) also re-
ported that maturity of onion plants was delayed in response to increasing nitrogen applica-
tion.
Morsy et al. (2012) reported that onion plant height was significantly increased as increased
nitrogen fertilizer rates. The increase in plant height with the addition of higher nitrogen ferti-
lizer level could be attributed to more availability of the nutrient, which enhances protein syn-
thesis that lead to increased accumulation of carbohydrates, which in turn, may result in in-
creased plant growth such as leaf number and leaf length (Rizk, 2012; Marschner, 1995). Sim-
ilarly, various researchers reported that higher nitrogen fertilization increased leaf length and
marketable yield of onion (Balemi et al., 2007; Soleymani and shahrajabian, 2012; Rao et al.,
2013). However, the yield of any crop including onion depends on the optimum level of plant
nutrients in the soil (Tisdale Sintayehu et al., 1995).
11
2.6. Effect of Plant Spacing on Onion Growth and Yield of Onion
Plant population refers to number of plants per unit area. It is important in onion production
since it influence growth, yield and quality of onion bulbs (Brewster, 1994). Plant population
affects interplant competition towards the growth factors like water, nutrient and light, which
influences growth and development of plant. According to Khan et al. (2002), wider intra row
spacing significantly recorded taller plant height as compared to narrow intra-row spacing.
Similarly, Demes Rahel (2018) reported that Leaf length increased as intra-row spacing ex-
panded from 7 to 13 cm.
Similarly, Kantona et al. (2003); Aliyu U. et al. (2008) and Jilani et al. (2009) also reported
that taller onion plants were recorded at wider spacing than narrower spacing where narrower
spacing leads to stiffer competition among plants for growth factors.
According to Sikder et al. (2010), higher leaf numbers per plant of onion was recorded in re-
sponse to wider plant spacing. Intra row spacing also influenced the yield of onion. He also
reported that wider intra row spacing gave higher total dry biomass of onion recorded as com-
pared to narrower spacing. Additionally, Mahadeen (2008) reported that maximum marketa-
ble bulb yields were recorded at lower intra-row spacing compared to wider spacing. Similar-
ly, Coleo et al. (1996) reported the highest commercial bulb yield at higher planting density,
while the highest proportion of large sized bulbs were recorded at lower planting density.
2.7. Interaction Effect of Nitrogen and Plant Spacing on Growth and Yield of Onion
The amount of nitrogen to apply depends on the various factors including the fertility of the
soil, environmental conditions and the type and density of crops planted. Reports of research-
ers indicated that the interaction effect of intra-row spacing with the amount of nitrogen ferti-
lizer applied where highest spacing in association with higher nitrogen level increased number
leaves per plant and spitted bulbs (Islam et al., 1999; Pervez et al., 2004). Application of
higher rate of nitrogen at wider spaced plants increased number of leaves per plants of onion
(Shojaei et al., 2011).
According to Naik and Hosamani (2003), maximum bulb yield of onion was recorded at nar-
row spacing while wider intra row spacing decreased bulb yield.
12
The combination of closer intra row spacing and higher levels of nitrogen recorded the high-
est bulb yield. On the other hand, onion plants spaced at wider intra row spacing recorded
highest bulb diameter of onion plants compared to narrow spaced once. Similarly, increased
in nitrogen levels increased diameter and average weight of onion bulbs (Naik and Hosamani,
2003). Shojaei et al. (2011) also reported that plants, supplied with higher rate of nitrogen and
planted at lower population density, produced highest mean bulb weight. Based on
Weldemariam Seifu et al. (2015) reports, the longest leaf number per plan was obtained with
the application of N at the rate of 138 kg ha-1 while the shortest plant leaf was observed in the
control plots.
13
Chapter 3: MATERIAL AND METHODS
3.1. Description of Study Area
The study was conducted at Koga Irrigation Scheme during the irrigation season of 2018 in
Mecha district of Amhara Region, Northwester Ethiopia. The district is located in West
Gojam zone of the Amhara Region. Koga irrigation scheme is found about 35 km far to
Southwest of Bahir Dar, Capital city of Amhara Regional State. It is located at 11O 10′N to
11O 25′N latitude and 37O 02′E to 37O 17′E longitude with and with an elevation of 1960
m.a.s.l. According to Bahir Dar Meteorology station (unpublished), the study area received an
annual mean rain fall of 1395.23 mm. The mean maximum and minimum temperature of the
study area 270C and 12.80C respectively. Major crops grown in Koga Irrigation Scheme in-
cludes, maize, finger millet, bread wheat and teff during the main cropping season while;
bread wheat, potato, onion, tomato and cabbage during the irrigation season (Melkamu Ale-
mayehu et al., 2015).
Figure 3. 1: Map of the study area Mecha District
14
3.2. Experimental Materials, Treatments and Design
Bombay Red variety of onion was used as a test crop, which was collected from Adet Agri-
cultural Research Center (AARC). The variety is released by Melkasa Agricultural Research
Center (EARO, 2004), for its high yielding and promising agronomic performances. It is an
early maturing variety, takes less than 120 days to maturity (EARO, 2004). The cultivar is
well adapted to the experimental areas and preferred by smallholder farmers in the locality as
well as by commercial farmers throughout the country. The variety can be grown in the areas,
which have an altitude of 700-1800 m.a.s.l.
A field experiment was conducted on 3x4 factorial arrangement of different intra row spacing
(4cm, 7cm, 10cm) and nitrogen fertilizer rates (0kg, 41kg, 82kg, 123kg/ha) totally 12 treat-
ments with three replications. The experiment was laid out in Randomized Complete Block
Design (RCBD) with three replications and there could be 36 plots. The size of each plot was
2mx1.8m, which accommodates different net plot areas. The distance between furrow, blocks
and plots was 40 cm, 1.5 m and 1 m respectively. All other agronomic management activities
except intra row spacing and nitrogen fertilizer such as cultivation; weeding, plant protection
and ridging were practiced uniformly in all plot of the experiment as per the recommendation
(Lemma Dessalegn and Shimeles Aklilu 2003).
15
Table 3.1: Treatment combinations used in the study
Treatments number Intra row-spacing (cm) Nitrogen rate (kg) Treatment combinations
1
2
3
4
4
0
41
82
123
T1= 4cm x 0kg ha-1
T2= 4cm x 41kg ha-1
T3= 4cm x 82kg ha-1
T4= 4cm x 123kg ha-1
5
6
7
8
7
0
41
82
123
T5= 7cm x 0kg ha-1
T6= 7cm x 41kg ha-1
T7= 7cm x 82kg ha-1
T8= 7cm x 123kg ha-1
9
10
11
12
10
0
41
82
123
T9= 10cm x 0kg ha-1
T10= 10cm x 41kg ha-1
T11= 10cm x 82kg ha-1
T12= 10cm x 123kg ha-1
3.3. Experimental Procedure
Good quality seeds of Bombay Red variety of onion was sown in rows on 1m x 5m well pre-
pared seedbed at seeding rate of 3-4 kg/ha to raise seedlings (EIAR, 2012). The management
of seedlings such as watering, cultivation, fertilization, control of diseases and insect pests
were done as per the recommendation as described by EARO (2004).The experimental site
was prepared well by broken down large clods in order to make the fine tilth of the experi-
mental plots. The whole field was divided in to three blocks containing twelve (12) plots. The
plots were leveled and prepared with a distance of 1 m between plots, 1.5 m between blocks
and 40 cm between furrows. Each of the twelve-treatment combination was assigned to the
experimental plots with three replications.
After 55 days of sowing, seedlings which have 3 to 4 true leaf stage with 12-15 cm height,
healthy and vigorous seeding were transplanted on well prepared experimental plots where
they were plowed and harrowed using oxen. Replanting of dead seedlings in the field was
done one week after transplanting on the place where the first first seedlings were planted.
18
Urea and Diammonium Phosphate (DAP) and Triple Super Phosphate in the form of (P2O5)
for (control) were supplied as a source of nitrogen and phosphorus respectively. However,
Diammonium Phosphate (DAP) was applied uniformily for all plots except (control) at the
time of transplanting. The recommended rate of urea (46%N) was applied to onion plants in
two equal splits where one half was applied at 25 days after transplanting and the remaining
one half after 45days of transplanting as recommended by (EARO, 2004).
Experimental units were irrigated using furrow irrigation method in each plot and row in plots
received water from the source without passing any of the experimental plots to prevent mix-
ing of fertilizer rates agreed to different plots. Transplanted seedlings were irrigated using fur-
row irrigation at 4-5 days interval until their establishment and at 5-7 days intervals until ma-
turity. Fifteen days before harvesting however, irrigation of plants was stopped for curing
purpose as recommended by Nigus Olani and Mulugeta Fikrie (2010).
3.4. Methods of Data Collection
3.4.1. Growth parameters of onion
Days to 80% maturity ( days):- The number of days elapsed from the time of transplanting
up to the date when 80% of plants became dry and collapsed at the neck was counted and the
mean values were computed and used for further analysis as indicated by Guesh Tekle, (2015)
and Nigatu Muluneh, (2016).
Plant height (cm):- Plant heights from the soil surface to the longest leaf of ten randomly se-
lected plants grown in the net plot area were measured using a ruler at physiological maturity
and the mean values were computed and used for further analysis.
Number of leaves/plant (count):- The numbers of leaves of ten randomly selected plants
grown in the net plot area were counted at physiological maturity and the mean values were
computed and used for further analysis.
Leaf length (cm):- The longest leaf of ten randomly selected plants grown in the net plot area
were measured from the attachment of stem up to the tip using ruler at physiological maturity
and the mean values were computed and used for further analysis.
19
3.4.2. Yield related parameters of onion
Bulb diameter (cm):- The widths of ten randomly selected bulbs, which were harvested from
the net plot area, was measured at the middle of the bulb-using caliper (Guesh Tekle, 2015;
Nigatu Muluneh, 2016) and the mean values were computed and used for further analysis.
Bulb weight (g):- The weights of ten randomly selected bulbs which were harvested from the
net plot area were measured using sensitive balance and the mean bulb weight was computed
and used for further analysis (Guesh Tekle, 2015; Nigatu Muluneh, 2016)..
Bulb size distribution: Onion bulbs are categorized based on the weight as undersized bulb
(<20g), small (20 - 50 g), medium (50 – 100 g), large (100 -160 g), and oversized (> 160 g) as
described by Lemma Dessalegn and Shimeles Aklilu, (2003) and Guesh Tekle, (2015). The
weights of such bulbs, which were harvested from the net plot area, were weighed using sen-
sitive balance and expressed in tone per hectare.
Marketable bulb yield (t/ha):- Bulbs harvested from the net plot area which were free from
damages and greater than or equal to 20g in weight were considered as marketable (Morsy et
al., 2012; Guesh Tekle, 2015). The weight of such bulbs was weighed using sensitive balance
and expressed in tone per hectare.
Unmarketable bulb yield (t/ha):- Bulbs harvested from the net plot area which were thick
necked, physiological disorder, splitted, rotten, damaged, and discolored diseased and insect
attacked and under sized (<20g), were considered as unmarketable (Guesh Tekle, 2015, Dera-
jew Asres et al., 2017). ). The weight of such bulbs was weighed using sensitive balance and
expressed in tone per hectare.
Total bulb yield (t/ha):- It was obtained by summation of Marketable and unmarketable bulb
yield.
3.5. Methods of Data Analysis
The collected data were subjected to Analysis of Variance (ANOVA) using the Statistical
Analysis System (SAS) Software version (9.0). Mean separation between treatments was done
20
using Least Significance Difference at 5% and 1% probability base on the ANOVA results as
indicated by Gomez and Gomez (1984). .
3.6. Soil sampling of experimental plots
To evaluate some of the physical and chemical properties, soil samples were collected from
the experimental sites before planting using an auger at the depth of 0-20 cm. The samples
were taken randomly in a zigzag pattern from the plots and bulked. The collected soil samples
were composited and analyzed Amhara Design and Supervision Works Enterprise Soil Labor-
atory.
The laboratory analysis of the physical and chemical properties of the composite experimental
soil results revealed that the texture of the composite soil sample was clay, in its textural clas-
sification. According to Karim and Ibrahim, (2013), suitable soil range for onion is 6.2-6.8.
However, the soil pH at Koga is moderately acidic with a pH value of 5.32. Moreover, the
experimental soil also has organic matter content of 1.926%, 5.251 ppm available phospho-
rous, 18.18cmol/kg and 0.156% total nitrogen contents (Table 3.2).
According to the rating of Tekalign Tadesse (1991), the soil of the study area is low in organ-
ic carbon as well as total nitrogen. These results indicate that there is not sufficient mineral-
ized nitrogen in the native soil for uptake of the plant during growth (Murage et al., 2000).
Therefore, there was a need to apply mineral nitrogen fertilizer to grow the crop.
21
Table 3.2: Major physic-chemical properties of the experimental soil before planting
Soil parameters Values Ranks References
PH of Soil 5.32 (%) Acidic Morphy, (2007)
Organic Carbon 1.926 (%) Weakly Tekalign, (1991)
Total Nitrogen 0.156 (%) Very low Tekalign, (1991)
Available Phosphorus 5.251 (ppm) Low Olsen et al., (1965)
Exchangeable Potassium 0.89 (cmol/kg) Low Hazelton and Morphy, (2007)
Cation Exchange Capacity
(CEC) 18.18(Meq/100g soil
Moderate Hazelton and Morphy, (2007)
Soil texture
Sand 16 (%)
Clay
Hazelton and Morphy, (2007) Clay 69 (%)
Silt 15(%)
Clay+Silt 84 (%)
3.7. Economic Analysis
To determine the economic feasibility of the treatments, economic analysis in the form of par-
tial budget analysis and marginal rate of return were calculated based on the procedures de-
veloped by CIMMYT (1988). The costs of nitrogen fertilizer, seeds as well as labor for ap-
plication of fertilizer were considered as variable costs. On the otherhand, costs that were sim-
ilar for all treatments were considered as fixed costs and were not considered in the analysis
of Marginal Rate of Return as described by CIMMYT (1988).
22
Chapter 4. RESULTS AND DISCUSION
4.1. Effects of Nitrogen Fertilizer and Intra-row Spacing on Growth of Onion
4.1.1. Days to maturity
The analysis of variance revealed that the main effects of intra-row spacing and nitrogen ferti-
lizer rates as well as their interaction highly significantly (P < 0.01) influenced leaf number
per plant of onion (Appendix Table 1).
Increasing intra row spacing as well as rate of nitrogen markedly prolonged the days to ma-
turity of the onion crop (Table 4.1). In the interaction effect, the highest days to maturity (115
days) were recorded by application of highest rates of nitrogen on plant spaced at wider intra-
row spacing. On the other hand, the shortest days to maturity was recorded when onion plants
were planted at narrower intra row spacing without nitrogen application (Table 4.2).
The relatively long maturity day due to higher nitrogen rate could be associated to prolonged
canopy growth and thereby continuing photosynthesis. This indicates that the nitrogen taken
up by plant roots may be used for cell division and synthesis of carbohydrate and thus, pre-
dominantly partitioned to the vegetative sink of the plants that resulting with a luxurious foli-
age growth of plants (Marschner, 1995).
The results are consistent with the findings of Guesh Tekle, (2015) who reported that plants
grown with higher nitrogen fertilizer (123 kg ha-1 N) at higher intra row spacing (10cm) took
longer time for maturity. On the other hand, plants supplied with low rate of nitrogen and
planted at narrower intra row spacing matured earlier.
The results of the present study are also in agreement with the findings of Weldemariam Seifu
(2015) and Wondye Mengistu, (2017) who noted that application of higher nitrogen fertilizer
rate was prolonged maturity of onion plant. Similarly, In agreement with the present study,
Dargie Miretie, (2015) reported that increasing the rate of nitrogen from nil to 32 kg N ha-1
significantly extended the number of days required to reach maturity by onion plants.
23
Similar findings also reported that plants grown at widest intra row spacing took longer time
to reach maturity while those at lowest intra row spacing matured earlier (Habtamu Tegen et
al. 2016; Weldemariam Seifu et al. 2015).
4.1.2. Plant height
The analysis of variance revealed that main effects of intra-row spacing and nitrogen fertilizer
rates and their interaction effect highly significantly (P < 0.01) influenced plant height of on-
ion (Appendix Table 1).
Increasing intra row spacing as well as nitrogen generally increased height of onion plant
(Table 4.1). In the interaction effect, application of highest rate of nitrogen on plant spaced at
wider intra row spacing recorded highest plant height (60.53cm). On the other hand, plants
planted at narrower intra row spacing without nitrogen fertilizer recorded the lowest plant
height (49.4 cm) as indicated in Table (4.2). This might be due to the application of nitrogen
mainly related to the production of new shoots and improvement of vegetative growth, which
is directly related to the increase in plant height. Additionally, there is less competition for
nutrients, moisture and light among the plants to achieve the required food for their growth
due to the wider intra-row spacing.
The results are in conformity with the findings of Fikadu Negesse (2015) who stated that the
interaction effect of 150 kg ha-1 N and 20 cm spacing recorded highly significant plant height
(30.33 cm). Similar findings were reported by Aliyu U. et al. (2008) who reported that higher
plant height of onion was recorded from the interactions effect of 100 kg ha-1 combined with
20 and 25 cm intra row spacing while lower plant height of onion was recorded from the in-
teraction effect of control plants without nitrogen and narrow intra-row spacing.
The result are also concordant with the findings of Weldemariam Seifu et al. (2015) who re-
ported longest plant height of onion when onion plants supplied with the rate of 138 kg ha-1
nitrogen at wider spaced plants while shortest plant height were recorded in the control plot
at narrower intra row spacing. Consistent with the results of the present study, Demisie Rahel,
(2018) reported that as intra-row spacing increased from 7 to 13 cm, the plant height also in-
creased from 58.79 cm to 64 cm.
24
Habtamu Tegen et al. (2016) also reported that onion plants grown at the highest intra row
spacing of 10 cm recorded the highest value of (51.42 cm). On the other hand, onion plants
grown with the lowest intra row spacing of 4 cm recorded the lowest plant height with the
value of (45.35 cm).
4.1.3. Leaf number per plants
The main effect of nitrogen and intra-row plant spacing as well as their interaction effect
highly significantly (P < 0.01) influenced the onion bulb diameter (Appendix Table 1).
Increasing intra row spacing significantly increased onion leaf number per plant across the
increasing rate of the nitrogen fertilizer (Table 4.1). The maximum number of leaves per plant
(14.1 cm) was recorded with combination of wider (10cm) intra-row spacing and higher ni-
trogen fertilization (123 kg N ha-1). On the other hand, the smallest number of leaves per/
plant (4.1 cm) was recorded in response to the interaction effects of narrowest intra-row spac-
ing (4cm) as well as nil rate of nitrogen fertilizer (Table 4.2).
The application of nitrogen is may related to production of new shoots and improvement of
vegetative growth of plants, which is directly related to the increase in leaf number (Rizk,
2012 and Kokobe et al., 2013). Similarly, less competition of plants for nutrients, moisture
and light due to wider intra-row spacing may improve growth of plants.
The results of the present study are in agreement with the results of Guesh Tekle et al. (2015)
who reported highest leaf number in interaction of (123 kg ha-1 N) and widest intra-row spac-
ing (12.5 cm). According to him, the interaction of narrowest intra-row spacing (2.5 cm and 5
cm) with nil rates of the nitrogen fertilizer rates resulted lowest number of leaves per plant,
which is in conformity to the present results.
Consistent with the results of the present study, Weldemariam Seifu et al. (2015) also indicat-
ed that highest leaf number obtained from the combination of 138 kg ha-1 N and 15 cm intra-
row spacing. Rao et al. (2013) also reported that onion plants grown at higher intra row spac-
ing of (12.5 cm) interact with 75 kg ha-1 N recorded the highest leaf number per plant of on-
ion.
25
The results are in conformity with the findings of Sikder et al. (2010) and Wondye Mengistu,
(2017) who reported that wider plant spacing and application of higher rate of nitrogen rec-
orded higher number of leaves per plant.
4.1.4. Leaf Length
The analysis of variance showed that onion leaf length was highly significantly (P < 0.01) in-
fluenced by both the main and interaction effect of intra row spacing and nitrogen rate (Ap-
pendix Table 1).
Generally, widening of the intra-row spacing and increasing rate of nitrogen increased leaf
length of onion plants (Table 4.1). In the interaction effect, plants treated with nitrogen at
rates 123 kg N ha-1 and spaced at 10 cm produced longest leaves (60.9 cm). On the other
hand, plants with the lowest leaf length (49.13 cm) produced in response to the interaction
effect of narrowest intra row spacing (4 cm) and nil nitrogen rates (Table 4.2). This could be
due to the fact that, nitrogen is a constituent of many fundamental cell components and plays
a vital role in cell division and elongation in plants. Moreover, nitrogen improves the vegeta-
tive growth which lead to increasing of leaf length through the increased photosynthetic area
and thus enhanced assimilates production and partitioning to the plants.
The results are in concordant with the findings of Muluneh Bekele, (2012) and Rao et al.
(2013), who reported that higher nitrogen fertilization increased leaf length of onion. Guesh
Tekle et al. (2015) also reported that wider intra-row spacing with application of highest rate
of nitrogen significantly increased length of onion. According to Kahsay Yemane et al.
(2013), onion plants grown at 10 cm intra-row spacing recorded the highest leaf length than
plants grown at 7.5 and 5 cm intra-row spacing which also in agreement with the results of the
present study.
26
Table 4.1: Main effect of nitrogen rates and intra-row spacing on growth of onion at Koga Ir-
rigation Scheme during the (2018) irrigation season
N-rate Day to maturity Plant height Number of Leaf length
(kg/ha) (days) (cm) leaves (cm) (cm)
0 108.0b 53.03c 7.92d 53.10b
41 108.2a 54.05bc 8.64c 54.59ab
82 109.4ab 55.59ab 9.40b 55.71a
123 110.2a 56.37a 10.64a 56.10a
P-value ** ** ** **
Intra row spacing (cm)
4 107.8b 53.5b 8.23c 54.04b
7 109.0ab 54.96ab 9.15b 54.44ab
10 110.2a 55.83a 10.08a 56.13a
P-value ** ** ** **
CV (%) 1.13 2.64 5.54 2.88
SE ± 1.24 1.44 0.51 1.58
Means followed by the same letters within a column are not significantly different at (P<
0.01); ** denotes Highly Significance Difference at (P<0.01); CV = Coefficient of Variation;
SE= Standard error
27
Table 4.2: Interaction effects of intra-row spacing and nitrogen fertilizer levels on Growth of
onion plants
Intra row N- rate Day to maturity Plant height Number of Leaf length
spacing (cm) (kg/ha) (days) (cm) leaves (cm) (cm)
4 0 105.0g 49.4f 4.10i 49.1f
41 106.7efg 53.57cde 7.07g 52.4ddef
82 108.3def 54.57cde 9.67de 55.0cde
123 111.0cd 56.03c 11.80bc 57.5abc
7 0 106.0fg 51.53ef 5.0hi 50.2f
41 107.0efg 53.67cde 7.86fg 52.7def
82 109.0de 55.0cd 10.77cd 55.9bcd
123 112.0bc 56.47bc 12.10b 59.9a
10 0 106.0fg 52.57def 5.57h 51.4ef
41 107.6efg 54.17cde 8.83ef 54.7cde
82 114.0ab 59.63ab 12.97ab 58.8ab
123 115.0a 60.53a 14.10a 60.9a
P-value ** ** ** **
CV (%)
1.13 2.64 5.54 2.87
SE ± 1.24 1.44 0..51 1.58
Means followed by the same letters within a column are not significantly different at
(P<0.01); ** denotes Highly Significance Difference at (P<0.01); CV = Coefficient of Varia-
tion; SE= Standard error
4.2. Effects of Nitrogen Fertilizer and Intra-row Spacing on Yield Component of Onion
4.2.1. Bulb diameter
The main effects of nitrogen and intra-row plant spacing as well as their interaction effect
highly significantly (P < 0.01) influenced the onion bulb diameter (Appendix Table 2).
Increasing the rate of nitrogen as well as widening of intra row spacing consistently increased
the bulb diameter of onion (Table 4.3). Application of highest rate of nitrogen (123 kg ha-1)
on plants spaced at widest intra row spacing (10 cm) recorded the highest bulb diameter as
28
indicated in Table 4.4. On the otherhand, combination of 4cm intra row spacing and nil rate of
nitrogen produced the narrowest bulb diameter (Table 4.4).
The development of wider bulb diameter with increased intra-row spacing and rate of nitrogen
observed in the present study could be associated with the supply of enough nitrogen, which
promotes cell elongation, above ground vegetative growth and synthesis of chlorophyll due to
less competition within plants. This may be linked to more metabolic processes that increase
dry matter production and translocation to the bulbs (Guesh Tekle, 2015).
The results of the present study are in agreement with the findings of Guesh Tekle, (2015)
who reported that increasing the rate of nitrogen fertilizer consistently increased the bulb di-
ameter of onion across the increasing intra-row spacing. The author obtained widest bulb di-
ameter in response to the application of 123 kg ha-1 N on widest spaced onion plants 12.5 cm.
On the otherhand, the narrowest average bulb diameter was obtained from plants supplied
with lower rate of nitrogen and planted at narrower intra row spacing of 2.5 cm and 5cm.
Muluneh Nigatu et al. (2018) also reported that application of nitrogen fertilizer up to 136 kg
ha-1 significantly improved the weight of onion bulbs. Demisie Rahel, (2018) also recorded
highest bulb diameter (5.63 cm) when onion plants were spaced at 13 cm intra-row spacing
followed by 10 cm intra-row spacing (5.50 cm). Similar to the results of the present study,
Derajew Asres et al. (2017) also recorded the highest bulb diameter (6.69 cm) at 15 cm intra
row spacing followed by 12.5 while significantly minimum bulb diameter (5.26 cm) obtained
at closer spacing of 7.5 cm. The results are also consistent with the finding of Nigullie et al.
(2017) where wider intra row spacing recorded highest bulb diameter.
4.2.2. Bulb weight
The analysis of variance revealed that the main effects of intra-row spacing and nitrogen ferti-
lizer rates and their interaction highly significantly (P < 0.01) influenced bulb weight of onion
(Appendix Table 2).
Increasing the nitrogen rate and widening intra row spacing generally increased average bulb
weights of onion plants (Table 4.3).
29
The highest average bulb weights were recorded at treatment combination of highest rate of
nitrogen (123 kg ha-1 N and wider intra-row spacing (10cm) while the lowest average bulb
weight was recorded at treatment combination of nil rate of nitrogen rate and narrower intra-
row spacing (Table 4.4). This might be the fact that, wider spacing accommodates less num-
ber of plants, which received adequate nutrient, moisture, and light and thus helped to im-
prove the bulb weight of onion plants (Khan et al., 2002).
In agreement with the result of the present study, Guesh Tekle, (2015) reported that ample
nitrogen supply could with wider intra row spacing result higher bulb weights of onion. Ac-
cording to the finding of various researchers decreasing the intra row spacing results signifi-
cantly decrease in bulb weight of onion (Derajew Asres et al., 2017; Demisie Rahel, 2018).
The results are consistent with the finding of Gesesew Seifu et al. (2015) who reported that as
intra row spacing increased from 10 to 15 cm, the weight of onion plant increase from 41.97
to 92.2 g. Muluneh Bekele (2012) also reported that increasing the level of N from 0 to 150
kg ha-1 significantly increased bulb weight by about 17% as compared to the control treatment
(41.35 g). Similarly, increasing the rate of nitrogen increased the bulb weight of onion, which
is in line with the present study (Dorcas et al., 2012; Morsy et al., 2012).
30
Table 4.3: Main effects of intra-row spacing and nitrogen on diameter and weight of onion
bulbs
N-rate (kg/ha) Bulb diameter (cm) Bulb Weight (g)
0 5.36b 79.0c
41 5.47b 82.3bc
82 5.81ab 88.4ab
123 6.07a 88.2a
P-value ** **
Intra row spacing (cm)
4 5.31b 81.5b
7 5.74a 83.2ab
10 5.98a 87.2a
P-value ** **
CV (%) 6.43 4.15
SE ± 0.37 3.48
Means followed by the same letters within a column are not significantly different at (P<
0.01); ** denotes Highly Significance Difference at (P<0.01); CV = Coefficient of Variation;
SE= Standard error
31
Table 4.4: Interaction effect of intra-row spacing and nitrogen fertilizer levels on diameter and
Weight of onion bulb
intra row N-rate Bulb diameter Bulb Weight
(cm) (kg/ha) (cm) (g)
4 0 4.15g 63.52e
41 4.97efg 77.56d
82 5.69cde 90.51ab
123 6.44abc 92.37ab
7 0 4.49g 65.44e
41 5.34def 81.13ab
82 6.05ab 91.14ab
123 7.80a 95.28a
10 0 4.67fg 73.49d
41 5.48def 86.84bc
82 6.59ab 94.48ab
123 7.20a 96.05a
P-value ** ** **
CV (%)
6.43 4.15
SE ± 0.37 3.48
Means followed by the same letters within a column are not significantly different at
(P<0.01); ** denotes Highly Significance Difference at (P<0.01); CV = Coefficient of Varia-
tion; SE= Standard error
4.2.3. Bulb size distribution of onion
Under-sized bulb yield
Results from the analysis of variance revealed that the main effects of intra-row spacing and
nitrogen fertilizer rate as well as their interaction highly significantly (P < 0.01) influenced
under sized bulb yield of onion (Appendix Table .3).
Increasing the rate of nitrogen application with widening intra-row spacing markedly de-
creased the yield of under sized bulbs (Table 4.5). The maximum under sized bulb yield was
32
recorded when onion plants were fertilized with 0 kg ha-1 N followed by 41 kg ha-1 N at spac-
ing of 4 cm intra-row spacing which could be associated with stiffer competition among
plants for growth resources including nitrogen at closer plant spacing. Conversely, the treat-
ment combination of 123 kg ha-1 N with all intra-row spacing recorded minimum under-sized
bulb yield of onion (Table 4.6).
The results of the present study are in conformity with the findings of various researchers who
reported higher undersized bulb yield at highest planting density and control treatments where
no nitrogen fertilizer applied (Nasir et al., 2007; Jilani et al., 2009; Negash Aregay et al.,
(2009)
Small sized bulb yield
The main effects of intra-row spacing and nitrogen fertilizer rate and their interaction effect
highly significantly (P < 0.01) influenced the small sized bulb yield of onion bulbs (Appendix
Table 3).
The current result indicates generally small sized bulb yield decreased with increasing of both
intra row spacing and nitrogen fertilizer rates (Table 4.5). The highest small sized bulb yield
(12.79 t/ha) was recorded by the treatment combination of 0 kg ha-1 N and 4 cm intra row
spacing which was statistically similar with those yields recorded by treatment combination of
0 kg ha-1 N with 7 and 10 cm intra row spacing (Table 4.6). On the other hand, plants supplied
with higher nitrogen rate (82 kg ha-1 N and 123 kg ha-1 N) at intra-row spacing of 7 and 10 cm
were recorded lowest small sized bulb yield of onion.
The highest yield of small sized bulbs at control plants without nitrogen fertilizer could be
associated with the reduction of above growth biomasses, leaf area and leaf length, which re-
sulted small sized bulbs.
The results are concordant with the finding of Yemane Kahsay et al. (2013) who stated that as
intra row spacing increased from 5 to 10 cm, the production of small-sized bulbs was de-
creased 23.76% to 4.4%. Consistent with the result of the present study, Bosekeng (2012) re-
ported that plants that are highly populated tend to produce high yield of small bulbs, whereas
plants at low population produce larger bulbs but with low yield.
33
Similarly, Negash Aregay et al. (2009) reported that increment in rate of nitrogen application
from 0 kg ha-1 N to 138 kg ha-1 N significantly decreased the yield of small sized bulbs of on-
ion by 61.8%. Nasreen et al. (2007) also indicated that small size bulb yield reduction were in
response to increased N fertilization. The results of the present study are also supported by the
results of Dorcas et al. (2012) and Yemane Kahsay et al. (2013) who reported higher popula-
tion density increased the yield of small sized bulbs.
Medium- size bulb yield
The analysis of variance revealed that the main effects of intra-row spacing and nitrogen ferti-
lizer rates and their interaction highly significantly (P < 0.01) influenced medium-sized bulb
of onion (Appendix Table 3).
Increasing of rate of nitrogen up to 82 kg ha-1 N and intra-row spacing up to 7cm significantly
increased the production of medium sized bulb yield of onion. Moreover, medium sized bulb
yield decreased when onion plants without nitrogen at intra-row spacing of 4 cm (Table 4.5).
The treatment combination of 82 kg ha-1 N and 4 cm intra-row spacing recorded the highest
medium sized bulb yield. On the other hand, in response to nil nitrogen and plants spaced at
4cm intra-row spacing scored lowest medium sized bulb yield of onion plants (Table 4.6).
Increasing of medium sized bulb could be associated with the supply of optimum rate of ni-
trogen as well as intra-row spacing, which were optimum for growth and enhanced productiv-
ity of the crop.
The results are conformity with the the findings of Habtamu Tegen et al. (2016) who reported
that (49%) of medium sized bulbs were produced at 6 cm intra row spacing while only 32% of
medium sized bulbs were produced at 8 cm intra row spacing.
The results of the present study are in agreement with the findings of Negash Aregay et al.
(2009) and Nasreen et al. (2007) who reported that application of optimum nitrogen rate was
produced highest weights of medium sized bulb yield. Similar findings were reported by Na-
sir et al. (2007), Rumpel et al. (2000) and Stoffela, (1996) who reported that maximum
weights of medium sized bulbs were obtained at higher planting densities.
34
Large size bulb yield
The main effects of nitrogen and intra-row plant spacing as well as their interaction effect
highly significantly (P < 0.01) influenced large sized bulb yield of onion. (Appendix Table 3).
Increasing in rates of nitrogen with increasing intra row spacing significantly increased the
production of large sized bulb yield of onion. The maximum large sized bulb yield was rec-
orded in response to the application of 82 kg ha-1 N at intra-row spacing of 7 cm but the result
is statistically similar with the application of 123 kg ha-1 N intra row spacing of 4 cm. On the
other hand, onion plants without nitrogen fertilizer and 41 kg ha-1 N interact with all intra-row
spacing’s gave the minimum value of large bulb.
The development of large size bulb with increasing of both nitrogen and intra row spacing
could be associated to the availability of resource and assimilation and less stiff competition
among the onion plants (Khan et al., 2002). This may lead to increased weights of individual
bulbs shifting from small to medium and then to large bulb categories.
Similar to the present study, Negash Aregay et al. (2009) and Kokobe et al. (2013) reported
that onion bulb size increased with increasing nitrogen dose. Islam et al. (1999) also reported
large sized bulbs in response to higher rates of nitrogen at wider intra-row spacing. The re-
sults are consistent with findings of Dawar et al. (2007); Jilani et al. (2009); Yemane Kahsay
et al. (2013) and Mallor et al. (2011) where lower population densities recorded maximum
value of large size bulbs.
Over-sized bulb yield
Main effects of intra-row spacing and nitrogen fertilizer rate as well as their interaction highly
significantly (P < 0.01) influenced the over-sized distribution of onion bulbs (Appendix Table
3).
Ample availability of growth resources including wider intra row spacing may lead to high
bulb expantion and growth, leading to the production of markedly higher yield of over- sized
bulb yield of onion (Table 4.5). The highest oversized bulb yield of onion was recorded with
combinations of 123 kg ha-1 N at 10 cm intra-row spacing. On the other hand, onion plants
35
grown at rate of 41 kg ha-1 N and nil nitrogen and plants spaced at 4 cm intra-row spacing
recorded lowest oversized bulb yield.
Ample availability of growth resources including wider intra row spacing may lead to high
bulb expansion and growth, leading to the production of markedly higher yields of over-sized
bulbs. (Rumpel et al., 2000). Consistent with the results of the present study, Khan et al.
(2002), Coleo et al. (1996) and Nasir et al. (2007) reported highest proportions of over large
bulbs at lower planting densities.
Table 4.5: Main effect of intra-row spacing and nitrogen fertilizer rates on bulb-size distribu-
tion of onion
N-rate) Undersized Small sized Medium sized Large size Oversized
(kg/ha bulb (t/ha) bulb (t/ha) bulb (t/ha) bulb (t/ha) bulb (t/ha)
0 8.00a 8.19a 10.09b 4.71c 1.11c
41 7.09ab 7.78ab 12.93a 7.54b 3.02b
82 5.74bc 6.59b 14.64a 9.50a 3.38b
123 4.68c 4.87c 13.66a 8.78ab 6.03a
P-value ** ** ** ** **
Intra row spacing (cm)
4 7.88a 8.22a 12.39b 6.12b 1.09c
7 6.12b 7.17a 14.88a 8.01a 2.76b
10 5.14b 5.19b 11.21b 8.73a 6.29a
P-value ** ** ** ** **
CV (%) 17.15 14.96 10.86 13.59 14.86
SE ± 1.10 1.03 1.39 1.04 0.50
Means followed by the same letters within a column are not significantly different at
(P<0.01); ** denotes Highly Significance Difference at (P<0.01); CV = Coefficient of Varia-
tion; SE= Standard error
36
Table 4.6: Interaction effect of intra-row spacing and nitrogen fertilizer levels on Bulb-size
Distribution of onion
Intra row N-rate Undersized Small sized Medium sized Large size Large size
spacing (cm) (kg/ha) bulb (t/ha) bulb (t/ha) (t/ha) bulb (t/ha) bulb (t/ha)
4 0 14.27a 12.79a 5.19h 0.00h 0.00e
41 10.27bc 9.84b 12.58de 2.67fg 0.31e
82 5.50ef 6.30cd 22.95a 13.02b 1.53cd
123 1.48gh 3.94e 18.84b 14.28a 2.53c
7 0 12.23ab 12.58a 7.52gh 0.98gh 0.12e
41 8.49cd 9.84bc 13.62cd 3.98ef 0.65de
82 3.77fg 4.78de 15.0bc 16.33a 2.11c
123 0.67h 2.75e 11.40de 12.69b 7.18b
10 0 11.70b 10.72ab 8.57fg 1.80fgh 0.42de
41 7.59de 6.82cd 14.61cd 0.67de 0.67de
82 1.27gh 3.22e 11.45def 10.15c 8.40b
123 0.00h 0.00f 10.209efg 7.38d 15.65b
P-value ** ** ** ** **
CV (%)
17.15 14.96 10.86 13.59 14.86
SE ± 1.10 1.03 1.39 1.04 0.50
Means followed by the same letters within a column are not significantly different at
(P<0.01); ** denotes Highly Significance Difference at (P<0.01); CV = Coefficient of Varia-
tion; SE= Standard error
4.2.4. Marketable bulb yield
The main effects of nitrogen highly significantly (P < 0.01) and that of the intra-row spacing
significantly (P < 0.05) influenced marketable bulb yield of onion. On the other hand, the in-
teraction effect (nitrogen and intra-row spacing highly significantly (P < 0.01) influenced the
marketable bulb yield of the onion (Appendix Table 4).
37
The highest marketable bulb yield of onion was recorded at treatment combination of 82 kg
ha-1 N and 4cm intra-row spacing. On the other hand, onion plants spaced at widest intra-row
spacing without nitrogen recorded lowest marketable bulb yield of onion (Table 4.8).
The closer intra row spacing and application of optimum rate of nitrogen leads to highest
number of bulbs with marketable size. Although plant height, number of leaves per plant and
leaf length increased with increasing spacing in the present study, higher number of plants per
unit area with enough supply of nitrogen increased marketable bulb yield.
The marketable bulb yield of onion per unit area does not completely depend up on the per-
formance of individual plants but also related with the total number of plants per unit area and
yield contributing parameters (Aliyu U et al., 2008 and Latif et al., 2010).
The results of present study are consistent to the findings of Islam et al. (1999) and Naik and
Hosamani, (2003) who reported maximum bulb yield of onion at treatment combination of
narrow intra-row spacing and optimum nitrogen fertilizer level. Hailu Dinka et al. (2015) re-
ported similar observations where highest marketable yield (34.49 t/ha) recorded from the
closest intra-row spacing (5 cm).
Generally, closer intra row spacing with optimum rates of nitrogen resulted higher marketable
bulb yield compared to widest intra row spacing as indicated by various researchers, which is
associated with the number of plants per unit area (Demise Rahel, 2018; Yemane Kahsay et
al., 2013). Soleymani and Shahrajabian (2012) and Balemi et al. (2007) also reported that
plants supplied with higher rate of nitrogen fertilization (120 kg ha-1) recorded higher value of
marketable yield.
4.2.5. Unmarketable bulb yield
The analysis of variance revealed that the main effects of intra row spacing and nitrogen rate
as well as their interaction highly significantly (P < 0.01) influenced the unmarketable bulb
yield of onion (Appendix Table 4).
With the increase in the intra-row spacing and nitrogen fertilizer rate, unmarketable bulb yield
of onion decreased significantly (Table 4.7). The highest value of unmarketable bulb yield
38
was recorded in control plots at 4cm intra-row spacing followed by rate of 41 kg ha-1 N. On
the other hand, onion plants fertilized with 82 kg N ha-1 and 123 kg ha-1 N at spacing of 7 and
10 cm recorded minimum unmarketable bulb yield (Table 4.8). This might be due to more
interplant competition for nutrient, water, light and air in narrowest plant spacing, which in-
fluences the growth of onion plants (Sikder et al., 2010).
The results of the present study in agreement with the findings of Habtamu Tegene et al.
(2016) who reported highest unmarketable bulb yield of 7 t/ha at lowest intra row spacing of 4
cm. On the other hand, onion plants spaced at wider intra row spacing (10 cm) produced the
lowest unmarketable bulb yield of 2 t/ha. Likewise, Negash Aregay et al. (2009) and Jilani et
al. (2004) also reported that nil nitrogen fertilizer rates resulted in more unmarketable bulb
yield.
The results are also concordant with the finding of Derajew Asres et al. (2017) and Demisie
Rahel, (2018) who reported highest unmarketable yield (39.52 t/ha) and lowest total marketa-
ble yield from closest and widest intra-row spacing, respectively.
Similarly, in line with the present study, Yemane Kahsay et al. (2013) reported as intra-row
spacing increased from 5 to 10 cm, unmarketable bulb yield decreased from 34.49 to 28.1
t/ha. Geremew Awas et al. (2010) also reported that plant density tested at intra-row spacing
of 4 cm scored the maximum unmarketable bulb yield.
4.2.6. Total Bulb Yield
The main effects of nitrogen and intra-row spacing as well as their interaction highly signifi-
cantly (P < 0.01) influenced the total bulb yield of onion (Appendix Table 4). Total bulb yield
increased significantly in response to increasing the rate of nitrogen fertilizer application (Ta-
ble 4.7). In the interaction effect, plants supplied with 82 kg ha-1 N and planted at 4cm intra
row spacing recorded the highest total bulb yield. On the other hand, the treatment combina-
tion of 10 cm intra row spacing and nil nitrogen recorded the lowest total bulb yields (Table
4.8).
39
The higher total bulb yield in response to the treatment combination of 4cm intra row spacing
and 82 kg ha-1 N in the present study might be due to application of optimum rate of nitrogen
fertilizer required for plants per unit area as described by Latif et al. (2010). Moreover, onion
plants planted at optimum density also helps for attaining their optimum bulb size (Rumpel et
al., 2000).
These results agree with the findings of Latif et al. (2010), and Yemane Khasay et al. (2013)
who reported that the highest onion bulb yields recorded at closest spacing. Similarly, Nig-
ullie and Biawas, (2017) found the highest total bulb yield from densely populated onion
plants than sparsely planted ones. Similar to the present study, Dereje Ademe et al. (2012)
also reported the decrease in total bulb yield with increasing intra-row spacing of shallot.
Jilani et al. (2004) showed that with increase in dose of nitrogen up to 120 kg ha-1, the total
bulb yield was increased, but below this rate, the total bulb yield began to decrease.
Soleymani and Balemi et al. (2007) also observed a significant increase in total bulb yield in
response to increased application of nitrogen.
40
Table 4.7: Main effects of intra-row spacing and nitrogen fertilizer on bulb yield of onion at
Koga Irrigation Scheme during the (2018) irrigation season
N-rate Marketable Unmarketable Total bulb
(kg/ha) Yield (t/ha) yield (t/ha) yield (t/ha)
0 26.00c 3.50a 29.50c
41 30.08b 2.81b 32.89b
82 34.11a 2.17c 34.55ab
123 32.60a 1.95c 36.28a
P-value ** ** **
Intra row spacing (cm)
4 32.20a 3.55a 35.75a
7 31.05a 2.29b 33.33b
10 28.84b 1.95c 30.83c
P-value * ** **
CV (%) 6.01 15.95 5.23
SE ± 1.85 0.42 1.74
Means followed by the same letters within a column are not significantly different at (P
<0.01); *= Significance difference at (p<0.05); ** denotes Highly Significance Difference at
(P<0.01); CV = Coefficient of Variation; SE= Standard error
41
Table 4.8: Interaction effect of intra-row spacing and levels of nitrogen fertilizer on yield of
onion at Koga Irrigation Scheme during the (2018) irrigation season
Intra row N- rate Marketable Unmarketable Total bulb
spacing (cm) (kg/ha) Yield (t/ha) yield(t/ha) yield (t/ha)
4 0 17.97g 7.27a 25.24e
41 25.41ef 3.75c 29.16e
82 43.80a 1.60ed 45.4a
123 41.63b 1.57ed 43.20ab
7 0 21.20fg 5.17b 26.37e
41 24.81e 1.70d 28.51e
82 36.17bc 1.57ed 37.74b
123 34.02d 0.71ef 34.73c
10 0 21.51fg 4.20c 25.71e
41 27.40e 1.69d 29.10e
82 33.22d 1.53ed 34.78d
123 33.23d 0.52f 33.75d
P-value ** ** **
CV (%)
6.01 15.95 5.23
SE ± 1.85 0.42 1.74
Means followed by the same letters within a column are not significantly different at (P
<0.01); ** denotes Highly Significance Difference at (P<0.01); CV = Coefficient of Varia-
tion; SE= Standard error
42
4.3. Correlation Analysis of Growth and Yield Parameters as Influenced by Intra row
Spacing and Nitrogen Fertilizer
Correlation coefficients were calculated to show the relationship of different parameters of
marketable bulb yield of onion as influenced intra row spacing and nitrogen rate. According-
ly, marketable bulb yield was highly significantly and positively correlated with most of the
tested growth parameters including plant height (r=0.65**), number of leaves (r=0.79**), leaf
length (r=0.70**), days to maturity (r=0.56**). Moreover, bulb diameter (r=0.72**), bulb
weight (r=0.87**), small sized bulbs (r=0.34*), medium sized bulb (r=0.90**), large bulb size
(r=0.88**), over-sized bulb (r= 0.33*) and total yields ((r=0.99**) were significantly and posi-
tively correlated with marketable bulb yield of onion as indicated in Table 4.9. However,
marketable yield was highly significantly and negatively correlated to under-sized bulbs (r=-
0.79**) and unmarketable bulb yields (r=-0.88**).
The correlation analysis indicates that any improvement in positively correlated parameter of
onion such as leaf number, plant height, diameter and bulb weight of bulbs and medium and
large sized bulbs contribute to increment in marketable bulb yield of onion. Similarly, reduc-
ing negatively correlated parameters including under-sized bulbs and unmarketable bulb
yields increase marketable bulb yield of onion.
44
Table 4.9: Simple correlation between growth and yield components of onion as influenced by intra row spacing and rate of
nitrogen
PH LN LL DM BD BW UN SM MD LG VL MY UY TY
PH 1
LN 0.87** 1
LL 0.84** 0.92** 1
DM 0.85** 0.89** 0.887** 1
BD 0.85** 0.93** 0.87** 0.90** 1
BW 0.80** 0.92** 0.89** 0.79** 0.87** 1
UN -0.85** -0.96** -0.89** -0.88** -0.93** -0.90** 1
SM -0.62** -0.71** -0.70** -0.76** -0.72** -0.57** 0.72** 1
MD 0.36* 0.52** 0.43** 0.23 0.44** 0.66** -0.51** -0.07 1
LG 0.58** 0.76** 0.68** 0.58** 0.70** 0.81** -0.80** -0.58** 0.74** 1
VL 0.79** 0.78** 0.75** 0.85** 0.77** 0.60** -0.74** -0.77** -0.02 0.31 1
MY 0.65** 0.79** 0.70** 0.56** 0.72** 0.87** -0.79** 0.34* 0.90** 0.88** 0.33* 1
UY -0.80** -0.87** -0.79** -0.72** -0.82** -0.89** 0.86** 0.39** -0.70** -0.71** -0.57** -0.88** 1
TY 0.59** 0.75** 0.66** 0.50** 0.66** 0.83** -0.74** 0.31 0.92** 0.89** 0.26** 0.99** -0.82* 1
Where PH= Plant height, LN= Leaf number per plants LL=Leaf lengths, DM= Day to maturity, BD= Bulb diameter, BW=Bulb weight,
UN=Undersized bulb, SM=Small sized bulb , MD=Medium sized bulb, LG= Large sized bulb, VL= Oversized bulb, UY= Unmarketable
bulb yield, MY= Marketable bulb yield, TY=Total bulb yield, *= Significant at (P<5%), **= Highly significant at (P<1%)
45
4.4. Economic Analysis
According to CIMMYT (1988), the partial budget analysis includes the total variable cost and
net benefits of each treatment. To calculate the gross incomes, the marketable yields obtained
from each treatment of onion plants were downscaled by 10%. In the present study the field
price of onion bulb and nitrogen fertilizer cost were taken as 8.00 ETB birr kg-1 and 13.60
ETB birr kg-1 respectively. The results of partial budget analysis of the study are presented in
Table 4.10. Accordingly, the highest net benefit (310933.7 ETB Birr ha-1) was recorded from
plants treated with the treatment combination of 82 kg ha-1 N and 4cm intra row spacing fol-
lowed by the treatment combination of 123 kg ha-1 N and 4cm intra row spacing.
To calculate the marginal rate of return, the dominance analysis was carried out by listing the
treatments by total variable costs in increasing order. According to CIMMYT (1988), any
treatments that have net benefits less or equal to the previous treatment is dominated which
should be removed from further analysis (Table 4.11). Accordingly, all treatment combina-
tions resulted acceptable marginal rate of return (>100%), plants, which were planted at 4 cm
intra row spacing and supplied with 82kg ha-1 nitrogen recorded the highest marginal rate of
return (8469.65%) as indicated by Table 4.12.
46
Table 4.10: Economical analysis for marketable yield of onion as affected by nitrogen fertilizer rate and intra-row spacing
Treatment
combinations
Un-adj
MY (t/ha)
Adjusted
MY (t/ha)
Gross- bene-
fit(birr/ha)
Seed cost
(birr/ha)
Labor cost
(birr/ha)
Urea- cost
(birr/ha)
TV cost
(birr/ha)
Net- bene-
fit(birr/ha) Rank
4X0 17.97 16.17 129360 1500 0 0 1500 127860 12
4X41 25.41 22.87 182960 1500 249.2 1213.96 2963.16 179996.84 8
4X82 43.8 39.42 315360 1500 498.4 2427.92 4426.32 310933.68 1
4X123 41.63 37.47 299760 1500 747.6 3641.88 5889.48 293870.52 2
7X0 21.2 19.08 152640 856.8 0 0 856.8 151783.2 11
7X41 24.81 22.33 178640 856.8 249.2 1213.96 2319.96 176320.04 9
7X82 36.17 32.53 260240 856.8 498.4 2427.92 3783.12 256456.88 3
7X123 34.02 30.62 244960 856.8 747.6 3641.88 5246.28 239713.72 4
10X0 21.51 19.36 154880 600 0 0 600 154280 10
10X41 27.4 24.66 197280 600 249.2 1213.96 2063.16 195216.84 7
10X82 33.22 30.01 240080 600 498.4 2427.92 3526.32 236553.68 5
10X123 33.23 29.91 239280 600 747.6 3641.88 4989.48 234290.52 6
47
Table 4.11: Dominance analysis for marketable yield of onion as affected by nitrogen ferti-
lizer and intra-row spacing
Treatment
Combinations
Un-adj
MY (t/ha)
Adjusted
MY (t/ha)
Total variable
Cost (birr/ha)
Net –
benefit(birr/ha) Dominance
10X0 17.97 16.17 600 154280
7X0 25.41 22.87 856.8 151783.2 D
10X41 43.8 39.42 1500 127860 D
7X41 41.63 37.47 2063.16 195216.84
10X82 21.2 19.08 2319.96 176320.04 D
4X0 24.81 22.33 2963.16 179996.84 D
7X82 36.17 32.53 3526.32 236553.68
10X123 34.02 30.62 3783.12 256456.88
4X41 21.51 19.36 4426.32 310933.68
7X123 27.4 24.66 4989.48 234290.52 D
4X82 33.22 30.01 5246.28 239713.72 D
4X123 33.23 29.91 5889.48 293870.52 D
48
Table 4.12: Marginal rate of return (MRR) of marketable onion yield as affected by nitrogen
fertilizer and intra-row spacing
Intra row spacing (cm) x
rates of nitrogen (kg/ha)
Total variable cost
(birr/ha)
Net benefit
(birr/ha) MRR (%) Rank
10X0 600 154280
10X41 2063.16 195216.84 2797.838 4
10X82 3526.32 236553.68 2825.176 3
7X82 3783.12 256456.88 7750.467 2
4X82 4426.32 310933.68 8469.652 1
49
Chapter 5: CONCLUSION AND RECOMMENDATIONS
5.1. Conclusions
Determining profitable of optimum and profitable rate of nitrogen fertilizer and optimum in-
tra- row spacing of specific area are paramount important to improve the production and
productivity of vegetable crops including onion. Thus, the objective of the present study was
to identify optimum rate of nitrogen fertilizer and plant population for economical production
of onion in Mecha district of Amhara Region.
The results of the present study showed that application of nitrogen fertilizer and intra row
spacing significantly influenced almost all the growth and yield components of onion. The
interaction effect of intra row spacing and rates of nitrogen fertilizer influenced plant height,
leaf number per plant, leaf length, days to maturity, diameter and weight of onion bulbs and
their size distribution as well as marketable yield. The growth parameters as well as yield
components increased as intra row spacing extends from 4 to 10 cm. Nevertheless, the mar-
ketable and total bulb yield decreased with increased intra row spacing (10 cm).
The interaction of closest intra row spacing (4 cm) with optimum nitrogen fertilizer rate (82kg
ha-1 N) gave the highest marketable and total bulb yield with highest net benefit and marginal
rate of return (8469.652). Application of highest rate of nitrogen fertilizer (123 kg ha-1) to
plants spaced at wider intra row spacing of 10 cm recorded highest bulb weight. Likewise,
application of 82 kg ha-1 N to plants spaced at 4 cm and 7 cm intra row spacing recorded the
highest medium sized and large-sized bulb yield respectively. On the other hand, highest rate
of nitrogen fertilizer applied to plants spaced at increased intra row spacing significantly in-
creased the over- sized bulb yield.
50
5.2. Recommendations
Based on the results of the present study, application of site and plant density specific rate of
nitrogen is necessary for economic production of onion. Accordingly, application of 82kg ha-1
nitrogen fertilizer for onion plants, which were spaced at 4 cm intra row spacing is recom-
mended for economically and agronomical feasible production of onion in the study area and
similar agro-ecologies since it recorded the highest net benefit with acceptable marginal rate
of return. However, as the results are limited to one season and location, further study should
be done over multi-seasons and locations so as to improve the production and productivity of
onion in the study area.
51
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APPENDICES
Appendix 1: Mean squares of analysis of variance for plant height (PH), leaf length (LL), leaf
number per plant (LN), day to maturity (DM)
63
Mean square of growth parameters
Source of Degree of Plant Number of Leaf Day to
Variation Freedom Height Leaves length maturity
Intra-row 2 16.567** 10.175** 14.503** 17.528**
N-Fertilize 3 20.238** 12.177** 16.297** 8.880**
NxIntra-row 6 38.675** 50.184** 68.215** 49.046**
Replication 3 0.184 0.381 0.081 1.194
Error 22 2.087 0.257 2.49 1.528
CV 2.64 5.54 2.89 1.13
Appendix 2: Mean squares of analysis of variance for yield and yield related traits of onion
Mean square of bulb diameter and weight
Source of Degree of Bulb Bulb
Variation Freedom Diameter Weight
Intra-row 2 1.391** 101.365**
N-Fertilize 3 0.954** 155.742**
NxIntra-row 6 4.690** 627.489**
Replication 2 0.583 11.699
Error 22 0.133 12.124
CV 6.43 4.15
Appendix 3: Mean squares of analysis of variance for marketable and unmarketable size dis-tribution of onion
Mean square of bulb size distributions
Source of Degree of Under-sized Small-sized Medium-sized Large-sized Over-sized
64
Variation Freedom Bulb Bulb Bulb Bulb bulb
Intra-row 2 23.166** 28.327** 42.45** 21.139** 84.380**
N-Fertilize 3 19.434** 19.905** 34.46** 40.132** 36.909**
NxIntra-row 6 124.953** 73.080** 101.73** 174.116** 83.197**
Replication 2 0.335 11.534 0.72 0.551 0.44
Error 22 1.198 1.052 42.69 1.075 0.253
CV 17.15 14.96 10.86 13.59 14.86
Appendix 4: Mean squares of analysis of variance for marketable bulb yield, unmarketable
bulb yield and total yield of onion
Mean square of Marketable, Unmarketable and Total bulb yields
Source of Degree of Marketable Unmarketable Total
Variation Freedom bulb yield bulb yield bulb yield
Intra-row 2 35.034* 8.250** 72.801**
N-Fertilize 3 113.045** 4.399** 75.025**
NxIntra-row 6 334.863** 18.105** 213.212**
Replication 2 2.308 0.075 1.628
Error 22 3.414 0.173 3.017
CV 6.02 15.95 5.22