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EFFECT OF INTERCROPPING OF HOT PEPPER (Capsicum annuumL .) AND BLACK CUMIN (Nigella sativaL.) ON PERFORMANCE OF

COMPONENT CROPS AND PRODUCTIVITY OF THE SYSTEM INAWI ZONE, AMHARA NATIONAL REGIONAL STATE

M. Sc. Thesis

ACHENIF ABE HAILU

June 2006Alemaya University

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EFFECT OF INTERCROPPING OF HOT PEPPER (Capsicum annuum

L .) AND BLACK CUMIN (Nigella sativaL.) ON PERFORMANCE OF

COMPONENT CROPS AND PRODUCTIVITY OF THE SYSTEM IN

AWI ZONE, AMHARA NATIONAL REGIONAL STATE

A Thesis Submitted to the Department of Plant Sciences, School of

Graduate StudiesALEMAYA UNIVERSITY

In Partial Fulfillment of the Requirements for the Degree of

MASTER OF SCIENCE IN AGRICULTURE(HORTICULTURE)

By

Achenif Abe Hailu

June 2006

Alemaya University

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School of Graduate StudiesAlemaya University

As Thesis Research advisor, I here by certify that I have read and evaluated this thesis

prepared, under my guidance, by Achenif Abe , entitled Effect of Intercropping of Hot

Pepper (Capsicum annuum L.) and Black Cumin (Nigell a sativaL.) on Performance of

Component Crops and Productivity of the System in Awi Zone, Amhara National

Regional State.I recommend that it be submitted as fulfilling the Thesisrequirement.

Kebede W/Tsadic (PhD) ____________ ____________

Major advisor Signature Date

Tamado Tana (PhD) ____________ ____________Co-advisor Signature Date

As member of the Board of Examinersof the M. Sc Thesis Open Defense Examination, We

certify that we have read, evaluated the Thesisprepared byAchenif Abe and examined the

candidate. We recommended that the Thesisbe accepted as fulfilling the Thesis requirement

for the Degree ofMaster of Sciencein Agriculture (Horticulture).

_____________________ ____________ ____________Chairman person Signature Date

____________________ ____________ ____________Internal Examiner Signature Date

____________________ ____________ ____________

External Examiner Signature Date

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D E D I C A T I O N

This piece of work manuscript is dedicated to my father Ato Abe Hailuwho was eager to seemy success but passed at the beginning of my journey to it. O! My God would keep his soul

in the abode.

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STATEMENT OF THE AUTHOR

First, I declare that this thesis is my bonafide work and that all sources of materials used for

this thesis have been dully acknowledged. This thesis has been submitted in partial fulfillment

of the requirements for M. Sc. degree at the Alemaya University and is deposited at the

university Library. I solemnly declare that this thesis is not submitted to any other institutions

any where for award of any academic degree, diploma, or certificate.

Brief quotations from this thesis are allowable without special permission provided that

accurate acknowledgment of the source is made. Requests for permission for extended

quotation from or reproduction of this manuscript in whole or part may be granted by the

Head of Plant Sciences Department or the Dean of Graduate Studies when in his judgment the

proposed use of the material is in the interest of scholarship. In all other instances, however,

permission must be obtained from the author.

Name:Achenif Abe Signature_____________

Place: Alemaya University, Alemaya

Date of submission: ______________________

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BIOGRAPHICAL SKETCH

Achenif Abe Hailu, the author, was born in Woldahoyta, rural village in Guangua district,

Amhara National Regional State on 26 Sept. 1970. He attended his elementary school at

Hibach Elementary School and his junior and secondary school at Chagni Junior and Senior

Secondary Schools, respectively. He joined the then Alemaya University of Agriculture

(AUA) now Alemaya University (AU) in September 1989 and graduated with B. Sc degree in

Plant Sciences in Aug. 1993.

After his graduation, he was employed by the German Agro-action Family Development

Project (FADP) in Metekel area as an agronomist and served for more than one year. After

leaving the project in March 1995, he was employed by the then Amhara National Regional

State Bureau of Agriculture, now Amhara National Regional State Bureau of Agriculture and

Rural Development as an irrigation agronomist. Since then he has worked in different

positions as expert and team leader.

In September 2004 he joined Alemaya University to pursue his M. Sc. degree in Plant

Sciences majoring in Horticulture.

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ACKNOWLEDGMENT

First of all I am thankful to almighty God for every thing.

I express heartfelt gratitude to my thesis advisors Dr. Kebede W/Tsadik and Dr.Tamado Tana

for their diligent guidance, supervision and encouragement from proposal preparation to final

write up of this manuscript.

Special thanks goes to Dr. Zeleke Mekuriaw, Prof. U.R. Pal, Ato Workneh Kassa, Dr.

Tekalign Tsegaw and Ato Fikryohannes Gedamu for their encouragement and constructive

criticism to my thesis proposal and manuscript write up.

I am grateful to Amhara National Regional State Bureau of Agriculture and Rural

Development and Regional Agricultural Research Institute for their cooperation in partial

financial support.

My sincere acknowledgment is also extended to all staff members of Guangua District

Agricultural and Rural Development Office for their facility provision and valuable advice

and GuanguaDistrict Administration Office for giving me opportunity to study my M. Sc. I

also thank Bahir Dar Regional soil testing laboratory for helping me in soil analysis and

interpretation of the results.

I would like to extend my grateful acknowledgment to my parents W/ro Atalelech Belay and

Ato Abe Hailu who taught me with their love and supported me financially to complete my

thesis research work under limited budget from sponsor.

Last, by no means least, is special thanks reserved to my wife, Yeshiasab Endalamew, and my

kid son Henok Achenif for their continuous and lovely encouragement and support.

Achenif Abe Hailu

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TABLE OF CONTENTS

STATEMENT OF THE AUTHOR ivBIOGRAPHICAL SKETCH v

ACKNOWLEDGMENT vi

TABLE OF CONTENTS vii

LIST OF TABLES ix

LIST OF TABLES IN THE APPENDIXES x

ABSTRACT xi

1. INTRODUCTION 1

2. LITERATURE REVIEW 5

2.1. Multiple Cropping 5

2.2. Some of Agronomic Management Practices in Intercropping 6

2.2.1. Plant population in intercropping 6

2.2.2. Spatial arrangements of component crops 9

2.3. Assessment of Intercropping Advantage 11

2.3.1. Analysis of competition relations 12

2.3.2. Competition function 14

2.3.3. Indices of evaluating intercropping productivity and efficiency 14

2.4. Biological Basis to be benefited from Intercropping 16

2.5. The Intercropping Species 17

2.5.1. Pepper 17

2.5.2. Black cumin 22

3. MATERIALS AND METHODS 24

3.1. Description of the Experimental Site 24

3.2. Planting Materials 24

3.3. Treatments and Experimental Design 24

3.4. Data Collected for the Component crops 27

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TABLE OF CONTENTS (continued)

3.5. Evaluation of Productivity of the System. 29

3.6. Data Analysis 294. RESULTS AND DISCUSSION 30

4.1 Pepper Component 30

4.1.1. Yield and yield Components 30

4.1.1 1.Total and relative dry fruit yield 30

4.1.1.2. Marketable and unmarketable air dried fruit yield 34

4.1.1.3. Total fresh fruit yield 38

4.1.2 Yield related components 39

4.1.2.1. Fruit number per plant 39

4.1.2.2. Fruit length 41

4.1.2.3. Number of seeds per fruit 42

4.1.2.4. Fresh and dry fruit yields per plant 43

4.1.3. Phenology and growth parameters 45

4.1.3.1. Phenological parameters 45

4.1.3.2. Plant height and canopy width 48

4.2. Black Cumin Component 50

4.2.1. Yield and yield components 50

4.2.1.1. Total and relative seed yield 50

4.2.1.2. Seed yield per plant 52

4.2.2. Phenological and growth parameters 53

4.2.2.1. Number of days for flowering 53

4.2.2.2. Plant height and number of main branches 53

4.3. Total LER and GMV Pepper/Black Cumin Intercropping System 555. SUMMARY AND CONCLUSION 59

6. REFERENCES 62

7. APPENDIXES 73

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LIST OF TABLES

Table 1. Details of treatments showing spatial arrangement and component population

.......................................................................................................................................... 25

Table 2. Effects of spatial arrangement and component population on total dry fruit

yield (kg/ha) and relative yields of associated pepper................................................. 31

Table 3. Effects of spatial arrangement and component population on per cent

marketable and unmarketable yields of the associated pepper................................. 35

Table 4. Effects of spatial arrangement and component population on total fresh fruityield (kg/ha) of associated pepper................................................................................. 39

Table 5. Effects of spatial arrangement and component population on yield relatedparameters of associated pepper................................................................................... 40

Table 6. Effects of spatial arrangement and component population on fresh and dryfruit yields per plant of associated pepper................................................................... 44

Table 7. Effects of spatial arrangement and component population on some of the

phenological parameters of associated pepper............................................................ 47

Table 8. Effects of spatial arrangement and component population on plant height and

canopy width of associated pepper............................................................................... 49

Table 9. Effects of spatial arrangement and component population on seed yield per

plant (g), per hectare (kg) and relative yield of associated black cumin................... 51

Table 10. Effects of spatial arrangement and component population on days to

flowering, plant height and numbers of main branches of associated black cumin 55

Table 11. Effects of spatial arrangement and component population on total LER and

GMV................................................................................................................................ 58

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LIST OF TABLES IN THE APPENDIXES

Appendix 1. Monthly rainfall, monthly maximum, minimum and mean

temperature of experimental site in 2005............................................................ 74

Appendix 2. Some physical and chemical properties of the soil of experimental site................................................................................................................................. 74

Appendix 3. Analysis of variance tables...................................................................... 75Appendix 3.1. Analyses of variance for total dried fruit and relative yields of the

associated pepper............................................................................................................ 75

Appendix 3. 2. Analysis of variance for marketable and unmarketable dried fruit

yields of the associated pepper............................................................................. 75

Appendix 3. 3. Analysis of variance for fruit related parameters of associatedpepper..................................................................................................................... 76

Appendix 3. 4. Analysis of variance for mean fresh and dry fruit yields per plant of

associated pepper................................................................................................... 76

Appendix 3. 5. Analysis of variance for some of phenological parameters ofassociated pepper................................................................................................... 77

Appendix 3. 6. Analysis of variance for plant height and canopy width of associated

pepper..................................................................................................................... 77

Appendix 3. 7. Analysis of variance for yield per hectare, relative yield and seed

yield per plant of associated black cumin ........................................................... 78

Appendix 3. 8. Analysis of variance for date of flowering, plant height and

numbers of main branches per plant of associated black cumin...................... 78

Appendix 3. 9. Analysis of variance for total LER and GMV .................................. 79

Appendix 3. 10. Analysis of variance for yield and yield related traits of theassociated pepper as affected by cropping system............................................. 80

Appendix 3. 11. Analysis of variance for phenological and some growthparameters of pepper as affected by cropping system....................................... 81

Appendix 3. 12. Analysis of variance for yield and yield components and somegrowth parameters of black cumin as affected by cropping system................ 81

Appendix 3. 13. Analysis of variance for Total LER and GMV............................... 82

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EFFECT OF INTERCROPPING OF PEPPER (Capsicum annuum L.) AND BLACKCUMIN (Nigell a sativaL.) ON PERFORMANCE OF COMPONENT CROPS AND

PRODUCTIVITY OF THE SYSTEM IN AWI ZONE, AMHARA NATIONAL

REGIONAL STATE

ABSTRACT

Field experiment was carried out under farmers field during 2005 crop season in Guangua

district, Awi zone, Amhara National Regional State to determine effect of spatial arrangement

and component population of hot pepper (Capsicum annuum L.) and black cumin (Nigella

sativa) on yield and yield related attributes of associated crops and productivity of the

intercrop system. Hot pepper, Bako local cultivar and black cumin local cultivar were used

for the experiment. Two spatial arrangements (1:1 and 2:2) assigned as main plots and six

component populations (100% pepper with 75%, 50% and 25% and 75% pepper with 75%,

50% and 25% black cumin populations) and two sole crops assigned as sub plots were laid in

split plot design with three replication. Significant variations were observed among

component populations in days required to fruit setting and to fruit maturity, canopy width,

fruit number per plant, fruit length, fruit yield, seed number per fruit, per cent marketable and

unmarketable fruit yield, total and relative yields of pepper. Variations in days to 50%

flowering, number of main branches, total and relative yields of black cumin was also

significant. None of parameters studied were influenced by spatial arrangements, but total

fresh and dry fruit yields (kg/ha) and relative yield of pepper were significantly influenced by

interaction of spatial arrangement and component population. The highest values of dry fruit

yield (52.3g/plant, 2396.8kg/ha), relative yield (1.07), per cent marketable yield (91%), fruit

number (24 fruits/plant), canopy width (40.5cm), fresh fruit yield (158.3g/plant, 6198.4 kg/ha)

of pepper and least yield of seed (170.6kg/ha), relative yield (0.317) of black cumin were

obtained in component population of 100% pepper and 25% black cumin. The least values for

total dry fruit yield (1051.6kg/ha), relative yield (0.47), time for fruit setting (116.7days) ofpepper and the highest seed yield (447.1kg/ha) and relative yield (0.83) of black cumin were

obtained in component population of 75% of pepper and 75% black cumin. The longest time

elapsed to fruit setting (126 days) and maturity (157.2 days), least seed number (104.3

seeds/fruit) of pepper and least number of main branches (7 branches/plant) of black cumin

were recorded in component population of 100% pepper and 75% black cumin. 75% pepper

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and 50% black cumin component population gave the shortest time to fruit setting

(116.7days) and maturity (134.8days), longest fruit length (10.8 cm) of pepper and highest

main branches (9.7 branches/plant) of black cumin. The least values in fruit number (17.3

fruits/plant), fruit length (8.45cm), canopy width (26.4 cm), fresh fruit yield (102.8g/plant,

3492.1kg/ha) and dry fruit yield (31.8g/plant) and per cent marketable(83.3) of pepper were

obtained in component population of 75% pepper and 25% of black cumin. The highest total

LER (1.47) was obtained in component population of 100% pepper and 50% black cumin

while the highest GMV (18928.6) was in 100% pepper and 25% black cumin but both the

least total LER (0.86) and GMV (10444.4) were in component population of 75% pepper and

25% black cumin. Hence based on the results of this study , it can be concluded that among

component populations, 100% pepper and 50% black cumin populations arranged in 1:1

arrangement was best to get maximum total LER, but to get maximum gross monetary value

at current price component population of 100% pepper and 25% black cumin can be

considered as the best intercropping mixture for the study area.

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1. INTRODUCTION

In most of developing countries of the tropics, the bulk of food consumed is derived from the

small scale agriculture. The cropping systems of these countries are characterized by land

holding of few hectares, limited mechanization, low levels of purchased inputs, intensive

labor and multiple cropping that include intercropping as its mainstay (FAO, 1983; Francis,

1986).

Intercropping can be defined as growing of two or more species simultaneously on the same

field during a growing season. The crops may not necessarily be sown exactly at the same

time and their harvesting times may also be quite different, but they stay together for aconsiderable time to interact (Willey, 1979a).

Intercropping is a practice that has been in use by the peasant farmers in the tropical regions

of the world since time immemorial. But it has been regarded as a primitive system inherently

unworthy for agricultural development, which eventually gave way to sole cropping with

agricultural development (Jodha, 1979:Willey, 1979a). Intercropping has been used to avert

poor adoption of the system of sole cropping by subsistence farmers and risks of growing

genetically uniform crops on a large area at time of disease or insect pests out break and

during abrupt fluctuations in weather variables (Kranth et al., 1976).

Although risk minimization is the major objective of intercropping in developing countries,

small farmers also view intercropping as a potential system for diversification and

intensification of production on their smallholdings. Diversification by growing different sole

crops on separate plots is limited due to the existing acute shortage of land. Their capacity to

intensify production through purchase of inputs is also restricted due to their poor financial

position (Francis, 1986; Chatterjee et al.,1989). In addition, intercropping helps for efficient

use of growth resources (Aggarwal et al., 1992); supply balanced nutritional diet (Jodha,

1979); is an option to weed control (Baumann, et al., 2002); improves soil fertility

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(Bandyopadhay and De, 1986) and minimizes peak labor demand (Okigbo and Greenland,

1976).

Depending on the local agro-climatic variations, 50 to 80 % of rainfed crops in developing

countries are grown as intercrops (Norman, 1974). Notwithstanding its vast coverage and

strong rationale behind, intercropping received little attention from the standpoint of research,

policy and planning. Thus, in the past, researchers engaged in technology generation for

agriculture have, for the most part, shown indifference to intercropping and as a result all high

yielding varieties were developed largely as sole crops. It was since the 1950s that

intercropping was considered as a potent ially beneficial system of crop production (Willey,

1979a).

It must also be appreciated that there can be some disadvantages of intercropping. More

serious disadvantage is often thought to be the difficulty in the practical management

especially where the re is a high degree of mechanization and when the component crops have

different requirements for fertilizers, herbicides, pesticides, etc. However, these problems are

typically associated with more developed agriculture; the poorly developed farmers are well

able to handle intercropping and have strong inherent preference for it. Thus, any break-

through in intercropping technology will benefit the less endowed farmers than relatively

better ones (FAO, 1983).

Pepper (Capsicum spp)is a new world crop that belongs to the Solanaceae family. The genus

Capsicum is the second most important vegetable crop of the family after tomato (Rubatzky

and Yamaguchi, 1997). Pepper is a dicotyledonous woody perennial small shrub in suitable

climatic conditions, living for a decade or more in the tropics. It is with erect sometimes-

prostrate growth habit that may vary in certain characteristics depending on type of species

(Bosland and Votava, 1999).

Cultivated peppers are, and will remain difficult to be classified as species or by common

names. Species are extremely variable, particularly in fruit characteristics, and many of the

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so-called species are locally adapted strains or cultivars (Bosland and Votava, 1999). Pepper

species are diploid and have the same chromosome number of n=12, 2n=24. But recent

studies indicated that chromosome number for non pungent species is n=13 (Bosland and

Votava, 1999).

Pepper is grown in many countries of the world and its production for culinary and vegetable

uses has been increased from time to time. According to FAO (2002) report, world production

of pepper was 21,719,000 metric tons on 1.59 million hectare of land, of which Africa

contributed 2,027,000 (9.3%) metric tons on 0.264 million hectare of land. According to the

Ethiopian Agricultural Sample Enumeration (EASE, 2002), private peasants produced

41716.5 metric tones of green pepper and 77962.4 metric tones of red pepper on 4,672 and

56,202 ha of land, respectively.

Pepper is a national spice of Ethiopia. Eventhough no documented information is available, it

was introduced to Ethiopia probably by the Portuguese in the 17 century (Hafnagel, 1961). He

also reported that Ethiopia was one of a few developing countries that have been producing

paprika and capsicum oleoresins for export markets. It is usually grown in pure stands, but

peasant farmers also commonly intercrop it with black cumin (Nigella sativa), cumin

(Cuminium cumin), and cress seed (Lepidium sativa). Some of the reasons given by

smallholder farmers for their preference of intercropping compared, to sole cropping are,

minimizing risk, income diversification and solving the acute land problems (Weiss, 2003).

Black cumin is native to the Mediterranean region and it has been used for thousands of years

by various cultures and civilizations around the world as a traditional medicine (natural

healing aid) and as a supplement to maintain good health and well being. The constituents of

the black seed give it the importance of being an immune system booster. The seeds contain

the components nigellone, thymoquinone and essential oils. It also contains numerous esters

of unsaturated fatty acids with terpene alcohols (Jansen, 1981; Toncer and Kizil, 2004;

Tuncturk et al.,2005).

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In Ethiopia, black cumin is sometimes found as an escape, although possibly, it could belong

to the indigenous flora. It is cultivated as rainfed crop at boundary of cereal crops field and

intercropped with some vegetables and spices (Jansen, 1981).

Black cumin is grown under a wide range of environments but flourishes with temperature

range of 5-250C, with the optimum being 12-140C. Plants are sensitive to frost at any stage.

Prolonged higher temperature reduces number of flowers or causes flower drop after

pollination (Weiss, 2003). Thus, growing black cumin in intercropping with pepper is

assumed that it will benefit from shade provided by pepper and produce better yield.

In many parts of Ethiopia, pepper intercropping with black cumin is a common practice.

Although, pepper and black cumin intercropping is a long and still common practice there is

no documented evaluation of the productivity of intercropping versus sole cropping of these

crops. Moreover, there has been no clear pattern of arrangement of the two crops in

intercropping. Therefore, the objective of this study was to determine effect of spatial

arrangement and component population of hot pepper (Capsicum annuum L.) and black cumin

(Nigella sativa L.) on yield and yield related attributes of associated crops and productivity of

the intercrop system.

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2. LITERATURE REVIEW

2.1. Multiple Cropping

Although multiple cropping has been practiced by farmers from time immemorial, there is

still lack of uniformity in terminologies used. For example, on one hand one may cite

terminologies such as monoculture, single cropping, and sole cropping to indicate growing of

only one crop. On the other hand, ployculture, multiple cropping, companion cropping,

multistorey as well as sequential cropping, intercropping and row cropping are used to

indicate growing of two or more crops (FAO, 1983). Based on the existing terminology in

various countries a successful attempt to propose a uniform terminology has been made by

Andrews and Kassam (1976) who suggested general definitions of main multiple cropping

patterns together with other related terms currently in use.

According to Andrews and Kassam, (1976) multiple cropping is a general term, which is

defined as growing of two or more crops on the same field in a year. It is classified as

sequential cropping and intercropping. Sequential cropping is time dependent type of multiple

cropping where two or more crops are grown in a sequence on the same field in a year. So,

crop intensification is only in time dimension and there is no interspecies competition.

Farmers manage only one crop at a time in the same field. On the other hand, intercropping is

space dependent form of multiple cropping where two or more crops are grown

simultaneously on the same field. Here crop intensification is both in time and space

dimension and there is interspecies competition during all or part of a growing period.

Farmers manage two or more crops at a time in the same field (Vandermeer, 1989; Sullivan,

2003).

Combination of crops in mixtures have been devised by researchers, and most certainly

beforehand by the farmers, to optimize use of natural growth resources, to capitalize on

generated (cereals using N fixed by legumes) or converted resources (release of P by legume

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roots) and to reduce external inputs (Midmore, 1993). To achieve these objectives plants need

to be arranged properly in intercropping (Sullivan, 2003).

In intercropping, as proposed by Vandermeer (1989), there are at least four basic types of

spatial arrangements most commonly used. These include: mixed intercropping, which is

growing of two or more crops simultaneously with out any distinct row arrangement. This is

frequently used in indigenous slash and burn or fallow agriculture. Row intercropping is the

other intercropping involving growing of two or more crops simultaneously where one or both

crops are planted in rows. This is the pattern usually encountered in intensive agriculture. The

other type that is more common in highly modernized system, especially where the intensive

use of machinery is desired, is strip intercropping. It is growing of two or more crops

simultaneously in different strips, which are wide enough to permit independent cultivation

but narrow enough for the crops to interact agronomically. Relay intercropping is also a type

of intercropping which involves growing of two or more crops simultaneously during part of

the life cycle of each batch. This form of intercropping may actually include the other three as

subsets, since its primary categorization variable is time.

2.2. Some of Agronomic Management Practices in Intercropping

2.2.1. Plant population in intercropping

Plant population/density refers to the number of plants per unit area, and/or the size of area

available to an individual plant (Willey, 1979b; Natarajan, 1990). Plant population can have

pronounced influence on plant growth, development and marketable yield of many vegetable

crops. Sundstorm et al. (1984) reported an increase in harvested Tabasco pepper (Capsicum

frutescens L.) yield as population increased from 8200 to 65000 plants/ha. A significant

marketable yield difference because of population variation was reported by Stoffella and

Bryan (1988). They reported that marketable bell pepper fruit number and weight per plant

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generally decreased but per hectare yield increased as plant population increased. Batal and

Smittle (1981) reported significant marketable yield increment as pepper population were

increased from 27,000 to 40,000 but subsequent increment from 40,000, to 60,000 was non-

significant in yield increment.

In intercropping system optimum population should be maintained to optimize yield and

quality of the produce. Tilahun (2002) reported yield increment as total population of maize

and faba bean were increased from 75% and 25% to 100% and 75% of maize and faba bean

recommended sole population, respectively. But when 100% maize and 100% faba bean were

sown yield reduction of 606 kg/ha of maize and 32 kg/ha of faba bean was recorded which

was 7362kg/ha of maize and 524kg/ha of fababean as compared to 7968 of maize and

556kg/ha in 100% maize and 75 % of fababean sole population.

In intercropping system two populations namely: total population (sum of population of the

component crops) and component populations (population of component crops) have to be

distinguished. The proportion of component population and total populations of intercrops in

relation to the sole crops should be expressed in relative terms. For example, if they are taken

as 100 each, a simple intercropping system having half of the sole crop optimum of each

component are considered to have 50:50 component population and total population pressure

as 100 (Willey, 1979b; Natarajan, 1990).

In terms of total population pressure, two broad classes of intercropping systems can be

distinguished. One is substitutive or replacement series of intercropping in which

proportional populations are related to sole crop of the series and whatever the population is

added the two proportions must always add up to 100. The second is additive or super

imposed intercropping in which one component crop is added to the other so that the final

plant population is generally more than either crops sown sole (Natarajan, 1990).

Substitutive intercropping generally consists of crops from the same phenological group and

the yield gain in such mixture is from a simple response to reduced population because of

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complementary in space and to some extent to time or both. The challenge comes in knowing

how much to be substituted to optimize the yield (Sullivan, 2003).

Additive refers to a situation where the component crops are plastic enough to take advantage

of their lower plant population in intercrop and when specific objectives of the farmers is a

particular proportion of the product which consists of crops from different phenological

groups (Cannell, 1983).

Combination of components may be influenced by farmers objectives. In terms of farmers

yield considerations; density and relative proportion of component crops within intercrops are

tied to their expectations in terms of relative crop yields and profitability. Generally, if

farmers wish to maintain yield of the dominant component at close to sole crop yield levels

while reaping yield from an associated crop; failures will be minimized if mixtures include a

crop that is harvested for its vegetative yield. Vegetative yield adopts an asymptotic

relationship with plant population. Hence, compared with many crops cultured for

reproductive yield, these crops have less critical optimum population densities and maximum

vegetable yield is achieved at minimum density stress (Cannell, 1983; Forshy and Elfving,

1989).

While combinations of some crops are grown in association at full stands it could be

impractical to plant them together. So, staggering by delaying early planting and growth of

the dominant crop in mixture or by synchronizing harvest of the dominant crop at critical

development stage of dominated (understorey) will permit planting of full crop stand of

component crops. Both systems are subjected to confounding effects of environmental and

genetic factors that influence the onset or release of competition, particularly for the light

(Midmore et al.,1988), but this does not inevitably lead to yield advantage over simultaneous

sowing (Ofori and Stem, 1987).

The other option is reduction of component population. Pal et al. (1993) in sorghum or maize

and soybean intercropping for maximum productivity and land use efficiency recommended

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sorghum or maize to be planted at optimum population of sorghum or maize and the soybean

to be planted at 1/3 of its optimum population. Tarfder et al.(2003) found the highest yield

and highest LER of 1.37 from 100% pepper and 20% onion intercropping than 100% of

pepper and 60% of onion.

In Awi zone hot pepper (Capsicum annuum L.) and black cumin ( Nigella sativa L.)

intercropping is a common practice in which peasants sow black cumin during the first

weeding of pepper in direct sown fields or during transplanting of seedlings for transplanted

fields. Farmers need to plant pepper as its sole cropping and add black cumin as additive but

in some cases they reduce pepper population to favor the black cumin (personal observation).

These farmers objectives were considered in planning of the current study using populations

of both additive and substitutive types.

2.2.2. Spatial arrangements of component crops

Increased productivity of intercropping over sole cropping has been attributed to better use of

solar radiation, nutrients and water and less incidence of insect pest and disease (Okigbo,

1990; Willey, 1990; Keating and Carbearry, 1993; Morris and Garrity, 1993). Spatial

arrangement of intercrops is an important management practice that can improve better use of

these resources and opportunities (Reddy et al., 1989).

Spatial arrangement defines the pattern of distribution of plants over the ground, which

determines the shape of the area available to the individual plants (Willey, 1979b). In

spatial arrangement of intercrops different aspects should be considered. The first is

proportional area allocated to each crop at the time of sowing. Often the proportional

areas are related to component population. Thus, if 50:50 component populations were

achieved by having equidistance alternate rows, proportional area would be 50:50.

However, the allocation of space can be altered without changing component population

by manipulation of inter-row and intra-row spacing (Nataranjan and Willey, 1985).

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The second aspect is how intimately the crops are associated. Intimacy refers to how the

proportional crops are arranged with respect to each other. Even when the space allocated

to the component crop is directly related to component population, the intimacy of the

arrangement could still vary. For example, an intercrop with 50:50 population areas could

be arranged as i) alternate plants within the rows; ii) alternate rows; iii) alternate double

rows and so on, but intimacy of an arrangement vary (Willey 1979b). It has been often

suggested that to get maximum benefits from any complementary effects, crops should be

as intimately associated as possible (IRRI, 1973).

Another aspect of plant arrangement that may be important is the direction of rows (North-

South or East-West). According to Donald (1963) yields are generally greater with N-S

rows than with E-W rows. This is likely due to difference in the light regimes with superior

lighting in N-S rows as compared with the poor lighting in E-W rows. But according to

Tsubo and Walker (2004) different row directions of maize and bean in both sole and in

intercropping gave statistically non-significant difference in yield between row

orientations.

Availability of growth resources can greatly alter the competitive relationships between

component crops. Thus, a row pattern, which is most ideal in terms of physiological

efficiency of the system in a given environment may not necessarily be the best in other

situations. It becomes necessary to alter the arrangement to take care of such differences in

the availability of growth resources (Trenbath, 1986; Natarajan, 1990).

The planting pattern which produces the highest physiological advantage can not always be

the one used by the farmers because the choice is likely to be influenced by several other

considerations such as preference for specific components, convenience in sowing, weeding

and harvesting. Moreover, the planting which produce the highest physiological efficiency

need not necessarily give the required proportion of the produce and the highest monetary

return (Natarajan, 1990; Amare, 1992).

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Crops mixtures in which component crops vary in plant height are amenable to manipulation

of some spatial arrangements principally to provide more space for the shorter (understorey)

crop(s) through reduction of space from taller crop. Reducing the space from dominant crop

besides limiting their access to solar radiation will reduce the size of their soil moisture and

nutrient pool as a result reducing competition over that of understorey crops. Thus, alteration

of spatial arrangement often leads to over yielding (Dayal and Reddy, 1991). Maintaining sole

crop population for tall (dominant) crop but altering the spatial arrangement by changing

within rows and between rows to increase space for understorey crops yields above those

achieved when less space was available to them (Chui and Shibles, 1984). Of the agronomic

options open to resource poor farmers, perhaps the selection of spatial arrangements i.e.

positioning of one component plants relative to that of the other component plant(s) offers the

greatest scope to maximize interspecies complementary.

2.3. Assessment of Intercropping Advantage

In literature advantages of intercropping were highlighted as early as 1949 (FAO, 1983). The

suggested advantages are greater stability of yield over different seasons; better use of growth

resources; better control of weeds, pests and diseases; one crop provides physical support for

the other; one crop provides shelter to the other; erosion control by providing continuous leaf

cover, etc. There are also some disadvantages of intercropping as well, yield decrease because

of adverse competition effect; allelopathic effect; creates obstruction in free use of machines

for intercultural operations (FAO, 1983).

But for evaluation of the advantages of intercropping three different situations can be

distinguished. Recognition of these different requirements ensures that advantages are validly

assessed as well as research aimed at improving the intercropping situation is based on sound

objectives. These three different situations are: situation where intercropping must give full

yield of a main crop and some yield of the second crop. It is often applicable where the

primary requirement is for a full yield of staple food crop and some yield of second crop. This

has been well recognized in India, where the primary objectives of many intercropping

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combinations are to produce a full yield of staple cereal. The other is situation where the

combined intercrop yields must exceed the higher sole crop yield. This is criterion, which has

traditionally been used for assessing yield advantages in grassland mixtures. It is based on the

assumption that unit yield of each component crop is equally acceptable and, therefore, the

requirement is simply for maximum yield regardless of the crop from which it comes. This

criterion assumes that growing only higher yielding crops is a valid alternative to growing

both. The third situation is where the combined intercrop yields must exceed a combined sole

crop yield with equal area. This is the commonest criterion, which is based on the assumption

that farmers usually need to grow more than one crop. For example, to satisfy dietary

requirements, to spread labor peaks, to guard against market risks, etc. In this case, the

combined intercrop yield does not have to out yield the higher yielding sole crop, since by

definition growing only one crop is not an acceptable alternative to growing both crops

(Donald, 1963; Willey 1979a; Reddy and Chetty, 1984).

2.3.1. Analysis of competition relations

Competition and complementary are not totally exclusive to each other; they may go hand in

hand. Sharing of light amongst species with contrasting adaptation to irradiance level may go

hand in hand with competition for nutrients within the soil. Additionally, complementary and

sharing of resources early in the intercrop cycle may gradually evolve in to competition at

later stage with an indistinct period separating the two. So, complementary in intercrops

implies minimizing competition (Midmore, 1993).

According to Vandermeer (1989) competition is a term, which might be applied differently in

different schools of thoughts. One school of thought (American school) considers competition

as simply the negative effect of an individual or population on another individual or

population. In this thinking frequently competition is subdivided into exploitation competition

(in which both populations or individuals are attempting to exploit the same or similar

resources) and interference competition (in which one or the other population or individuals

interferes in some way with well being of the other). For example through shading or

production of allelochemicals. Another school of thought (British school) reserves the word

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competition for those situations in which the populations or individuals are in competition for

something (such a critical resources). This school uses the word interference as the general

term for negative interaction. Thus what is competition for Americans school of thought is

interference for British and what is exploitation competition for Americans is interference for

British.

But in one way or the other, competition or interference is an individual or population

influence to its neighbor individual or population by changing its/their environment. The

changes may be by addition or subtraction and there may also be indirect effects; not acting

through resources or toxins but affecting conditions such as temperature, wind velocity,

encouraging or discouraging pest disease etc(Vandermeer, 1989).

Most of the analyses of competition relationships are derived from works of double cropping

grown in substitutive or replacement series. When two crops are intercropped they may be

related in one of the following three broad categories (Willey, 1979a). The first is non

competitive that occurs when different plants share a growth factor that is present in sufficient

amounts, so that it is not limiting. In this case output of one crop may be increased with out

any influence on the output of the other. This situation usually arises when the maturity of two

component crops or their duration differs widely. The second is competition, which occurs

when one or more factors are limiting and it can take one of the two forms- mutual inhibition

or compensation. Mutual inhibition is the case when the actual yield of each species is less

than expected yield (yield that would be obtained if each species experienced the same degree

of competition as sole crop, i.e., inter-species competition was equal to intra-species

competition). But this may be unlikely in practice, while compensation occurs when one

species yields less than expected and the other yields better than expected. In such cases the

species better equipped to utilize growth factors increases its yield at the expense of the other

species. The species that yield more than expected is believed to have greater competitive

ability and is called dominant species. The third is complementary that occur when one plant

species helps another. In this case, the yield of each species is greater than expected. Willey

(1979a) also called this situation as mutual cooperation.

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2.3.2. Competition function

Competition function is proposed as a measure of intercrop competition to indicate the

number of times by which one component crop is more competitive than the other (Willey

and Rao, 1980). These competition functions could be useful to compare the competitive

ability of different crops, to measure competitive changes within a given combination, to

identify which plant character is associated with competitive ability and to determine what

competitive balance between component crops is most likely to give yield advantage

(Chatterjee et al., 1989).

2.3.3. Indices of evaluating intercropping productivity and efficiency

Before the productivity of a cropping system can be assessed the basis upon which the yield

will be measured must be decided. For sole crop the most usual expression is some measure

of weight per unit of land. In intercropping system, however, because yields of different crops

cannot be compared directly with each other and therefore not simply added together, special

methods have to be used. So in intercropping, the measurement of crop yield and the size of

area allocated to individual associated crops require techniques that are distinct from those

which are used in dealing with monocropping systems (Ndiage, 1996).

Different indices have been suggested for evaluating productivity and efficiency per unit area

of intercrop systems. These include comparison of absolute yields, protein yields and caloric

equivalent and, in economic terms, gross returns from intercrop and sole crop (Willey,

1979a). But price of crop yield tends to fluctuate, composition and quality of crop products

will vary and energy contents and growth duration of component crops differ depending on

the environment. So, absolute yield comparison and economic evaluations are of little value.

Therefore, many workers suggested relative yields for comparing performance of crops in

intercropping (Ofori and Stern, 1987).

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Some of indices used to evaluate intercropping productivity and efficiency are Relative Yie ld

Total, RYT (De Wit and Vanderbergh, 1965); Land Equivalent Ratio, LER (Willey and Osiru,

1972); Staple Land Equivalency Ratio, SLER (Reddy and Chetty, 1984); Area Time

Equivalency Ratio, ATER (Hiebsch and McCollum, 1980) and Area Harvest Equivalency

Ratio, AHER (Balasubramanian and Sekayange, 1990).

All these possibilities have their advantages and disadvantages. There is no single

straightforward universally appropriate method and the method used depends on specific

objectives. The value RYT and LER are similar but RYT is based on the replacement series.

Besides the RYT, ATER, AHER and SLER are restricted to specific intercropping situations.

ATER is only appropriate in a system with component crops contrasting maturities such as

110-day maize and 170 days pigeon pea. When component crops have similar growth

durations, ATER values are similar to RYT and LER. AHER is applicable in multi season

intercropping system in which one crop or more of the component crops occupy the land for

more than one season. In situation where there is single season association, AHER is equal to

LER. Staple Land Equivalent Ratio is only applicable when it is desired to attain specific

yield of staple crop and yield from the other as a bonus. Therefore, SLER cannot be used to

evaluate intercropping efficiency in situations where it is desired to produce yield from

equally acceptable component crops. Among various indices, LER is considered to be the

most appropriate general function to determine the efficiency and productivity of

intercropping system (Mead and Willey, 1980; Reddy, 1990).

However, when the difference between the growth durations of component crops is

substantial, time becomes an important element and ATER is considered to be a more

applicable index (Ofori and Stern, 1987). It must also be noted that, when presenting

intercropping results, the calculation of LER values should not exclude the need for some

presentation of absolute yield and economic evaluations, since the practical significance of

LER can only be fully assessed when related to the actual yield levels (Adetiloye and

Adekunle, 1989).

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In a comparative study, Willey (1979a) concluded that of all possible ways the land

equivalent ratio (LER) is probably the most useful single index for expressing yield advantage

when comparing intercropping with monocropping. It is also most frequently used measure of

determining the advantages of intercropping (Ndiage, 1996).

LER is defined as ratio of the area needed under sole cropping to one of intercropping at the

same management level to give an equal amount of yield. The sole crop population should be

at optimum population and spacing (Beets, 1982). Total LER is the sum of fraction of yields

of intercrops relative to their sole crop yields (Willey, 1979a) and mathematically total LER is

presented as:

=yii

yiLERTotal

Where =yi the yield of component from a unit of intercrop

=yii the yield of component crop grown as sole crop over the same area

When a ratio is greater than one, it indicates yield advantage and a ratio less than one

indicates yield disadvantage. For example, LER 1.2 indicates a yield advantage of intercrop

over the sole crops by 20%, i.e., sole crops would require 20% more land to achieve the yieldobtained by intercropping, but this does not reflect absolute yield. In practice, however, the

intercropping combination with the highest LER is not always the best one as far as farmers

need is not concerned. In most situations component crops are not equally acceptable and one

crop may be preferred more to the other (Reddy, 1990).

2.4. Biological Basis to be benefited from Intercropping

Evidences indicate that intercropping gives better yield as compared to monocropping. The

major way in which higher yields can be obtained in intercropping in a given season is better

and complete use of growth resources like light, water and nutrients (Willey, 1990) as well as

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less risk of insect pest and diseases (Okigbo, 1990). This is because component crops differ in

their use of growth resources in such a away when they are grown in combination they have

differed in space or time of growth. As a result, they are able to complement each other and so

make better overall use of resources than grown separately. Eventhough in some way there is

competition, the component crops are not competing equally in interacrop and in intercrop

competitions. Therefore, maximizing the degree of complementary between components and

minimizing the intercrop competition maximizes the intercropping advantages (Beets, 1982;

Reddy and Willey, 1981).

Complementary in an intercropping system can occur when the growth pattern of component

crops differ in time, so that the crops make their major demand on resources at different times

of the season, thus giving better temporal use of resources. Complementary between

component crops can occur also when they are better in spatial use of resources because of

variation in space. Here there is the need for ideal spatial arrangement to enhance

complementary between the component crops. Although it can be useful in theory to

distinguish between temporal and spatial effects, in practice they are often inseparable

(Willey, 1990).

Similarly, difficulty exists in trying to distinguish the relative importance of the different

growth factors that are closely inter-related (Willey, 1990). Environmental factors including

light, temperature and water can produce variation in plant growth and these variations could

be greater than genetic differences (Bowes et al., 1972). Therefore, better understanding of

these resources use and their effect is essential if intercropping is to be more productive.

2.5. The Intercropping Species

2.5.1. Pepper

Temperature controls plant development including, morphogenesis, yield and quality. These

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processes make it a major growth factor. The productivity of capsicum is constrained by

adverse effect of high and low temperatures. Capsicum flourishs in warm, sunny conditions

and requires 3-5 months with a temperature range of 18-30C; below 5C frost kills plants at

any growth stage (Wein, 1997).

A seedbed temperature of 20-28C is optimum for germination, which will slow down out of

these ranges and ceases at below 15and above 35C. In addition to slow seed germination

and seedling emergence rate, pepper has a relatively slower seedling growth rate than some

other vegetable crops. The slower growth rate was attributed to a reduced production of leaf

area (Wein, 1997).

The rate of plant growth is also strongly influenced by the air temperature, which affects both

the dry matter production and the partitioning of assimilate in to leaf tissue (Miller et al.,

1979). Pepper growth in vegetative stage has been found to be greatest at 25 - 27 C day and

18-20C night temperatures (Bakker and Uffelen, 1988). For high yields of good quality fruit,

they found that mean air temperatures of 21-23C were optimal during the fruit growth

period. Lower temperature during growth also reduces future productivity by increasing

specific leaf weight and decreasing the ratio of leaf area to total plant dry weight (Nilwick,

1981). Temperatures above 30C without adequate soil moisture will adversely affect growth

and when this occurs at the time of flowering it result in substantial flower drop (Bakker,

1989).

Fruit shape, size and regularity are major determinants of fruit quality in capsicum.

Commonly, at optimal growth conditions, pepper fruit are regular and blocky with an average

of 150-300 seeds per fruit. However, in cooler temperatures (particularly night temperatures)

and in short day lengths, high percentages of the fruit become flattened, small, and

parthenocarpic (Aloni and Karni,1999).

It is suggested that assimilate partitioning may be an important process in determining flower

morphology, pollination and subsequent fruit shape. This is because flower buds accumulate

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more carbohydrates during day following a low night temperature, because possibly less

carbohydrate was consumed by respiration under low night temperature thus leaving more

carbohydrate available for translocation to the developing flowers. Therefore, it increased

availability of carbohydrate that has an important role in causing low temperature related

flower swelling (Aloni et al., 1994).

Fruit set is related directly to flower development especially to those processes leading to

female and male gametogensis. Chilling induced pollen sterility is one of the main causes for

decreased seed set and fruit quality in chilling sensitive species. Sensitivity to low

temperature varies during the different stages of pollen development and pollen grain

maturation (Mercado et al., 1997). They indicated that low night temperatures decreased

pepper pollen fertility and affected the size and morphology of pollen grains. Reduced

viability induced by cold night temperatures were the results of defective meiosis and

inadequate young microspore development. But the subsequent phases of microspore

development and maturation of pollen grains were not altered in temperature ranges of the

pollen grain were altered.

The process of fruit growth begins with the formation of the ovary during the early stages of

flower differentiation. In the period before flower anthesis, the basic structure of the ovary,

including the number of carpals to be found in the mature fruit is determined. Cell division

dominates this stage, followed by cell enlargement after flowering (Barkker, 1989).

High day and night temperatures and small differences between them, typical to the tropics,

are the main factors in flower abscission and subsequently, the failure to obtain commercial

yields of pepper in different parts of the world (Bakker, 1989). Similarly, flower abscission

can be induced by shading stress conditions, since both extremely high temperatures and low

light intensity generate ethylene evolution in flowers, the primary factor for flower drop

(Wein et al.,1989).

Plants grown in the open field develop fruits early and develop their first fruits on the first two

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flowering nodes, and such plants will be short to medium in height. On the other hand, in

shaded plants fruit setting can be delayed, to the fourth to eighth nodes due to strong flower

abscission, resulting in very tall plants (Schoch, 1972). He showed that plants exposed to high

temperature and natural light during anthesis had flower abscission on the ir first to fourth

nodes only.

Light is a critical factor affecting crop production. The amount of light intercepted by

component crops in an intercrop system depends on the spatial arrangement of the crops and

plant architecture (Tsubo and Walker, 2004). Light is the least controllable factor by human

being, but can be manipulated through crop selection or sowing at different time of the year,

or mixing of the crops in different proportions or manipulate spatial arrangement that can

achieve greater utilization of solar energy and other resources. Intercropping is believed to

increase light interception by as much as 30-40 % (Chatterjee et al.,1989).

The influence of light on the productivity of peppers differs depending on whether one is

considering a glass house grown crop during the low light conditions or a field of pepper

growing in full sun out doors. Wein (1997) demonstrated that supplementing the reduced

irradiance during low light in green house significantly increased yield and fruit size. Dufault

and Wiggans (1981) indicated the importance of using mulch or reflector to increase light

reception in peppers. Midmore (1993) also highlighted the importance of maximizing light

interception either through increasing plant population or through intercropping pepper with

maize. Intercropping of chili pepper and onion with different population combinations has

been reported to result in higher equivalent yield and net monetary return per hectare than sole

(Tarafderet al., 2003).

In the field, Mercado et al. (1997), quoted, Rylski and Spiglman (1986) that as the irradiance

level averaged 28MJ/m2/day in Negev desert of Israel, the total fruit yield reduced by 19%,

while marketable yields were decreased by 50% compared to plants lightly shaded from

transplanting. The shading treatments sharply reduced sunscald injury of the fruit and

increased fruit size as a result of an increase in seed number per fruit was reported. The

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decrease of over all productivity of the plants grown in full sunlight was related to the lower

leaf area measured for the main fruit bearing nodes.

Naturally, pepper seedlings have thicker leaves. But it has been shown that it is possible to

reduce leaf thickness and increase the proportion of leaf area to total plant mass by reducing

light incidence (Nilwick, 1981). These changes occur at the expense of the plant growth rate

and thus may be counter productive. Nevertheless, use of light shade (25-50%) during

seedling growth has been advocated to increase yield of pepper in a tropical environment by

maximizing leaf area production (Schoch, 1972). The author reported production of pepper

will increase with increasing irradiance, only as long as temperatures remain in the optimal

range, and plants have access to sufficient water.

Estimation of canopy photosynthesis over the whole growing period is suggested for a better

understanding of canopy response to environmental conditions and agronomic practices

(Pattey et al.,1991). Canopy architecture is a function of internal and external factors of the

plant and differences in canopy form may affect not only the amount of photosynthetically

active radiation intercepted by leaves, but also the efficiency of conversion of incident solar

radiation (Alvino et al.,1994).

Extremely reduced incident light during high light periods with shade can significantly

increase reproductive structures abscission pepper. Application of 80% shade to which crop

stayed for 10 days in the field has been reported to increase abscission from 23% in unshaded

to 60% in shaded (Wein, 1997).

Pepper fruits exposed to high intensity of sunlight after they have reached the mature green

stage of growth are susceptible to tissue damage and bleaching. The injury is caused by a

combination of heat and light. When tissue temperature rose to 50C, only a 10 minutes

exposure to intense light was sufficient to cause the damage, but similar level required at least

12 hr exposure at 38-40C.

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Sunscald can be a serious determinant to production of pepper (Wein, 1997). Sunscald

damage is caused by a combination of direct injury of the tissue due to the heating effect and

the generation of super oxide anion radicals through the action of light on chlorophyll at high

temperature. Heating of chlorophyll in the dark causes the pericarp of the fruit to turn flaccid,

brown, and bleached. Pepper fruits are most susceptible to this disorder at mature green stage,

and when turning their color from green to red. The immature green fruits are less subjected

to the disorder and the fully ripe ones are not susceptible. Chlorophyll must be present in the

pericarp for sunscald to occur. Presence of enzyme super oxide dismutase in the chloroplast of

the fruit can lessen or prevent injury by catalyzing the formation on of hydrogen peroxide and

oxygen from the super oxide radicals. The increase in susceptibility of the mature green fruit

to sunscald was correlated with lower super oxide dismutase activity at that stage of growth

(Wein, 1997).

2.5.2. Black cumin

Black cumin (Nigella sativa L.) is native or endemic to the Mediterranean region but has also

been used extensively in the Middle East, Africa, and Asia, dating back literarily thousands of

years. It is an erect annual herb with a well developed taproot producing numerous secondary

and tertiary roots. The stem grows up to 70 cm; the leaves are alternate, and the petiole (1-6

cm) present only on basal leaves. The flowers are pale green when young, light blue when

mature, solitary and terminal. The fruit is a capsule, up to 16x12 mm in diameter, grayish

initially, yellow/brown when mature, containing numerous number of black seeds (Weiss,

2003).

Black cumin is grown under a wide range of environment, but flourishes in cooler regions

with a temperature ranges of 5-25C, the optimal being 12-14C. Plants are frost sensitive at

any growth stage and this limits its production in high land areas. In regions with wet and dry

seasons it is sown just after the first rains. A rainfall of 400-500 mm is indicated to produce

good crop and above this the soil must be free draining (Weiss, 2003).

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Plant height and number of branches per plant are strongly influenced by seeding rate as

indicated by Tuncturk et al.(2005) where the plant height increased with increasing seeding

rate while number of branches decreased. Toncer and Kizil (2004) reported seed yield

reduction as seed rate increased from 10 kg/ha to 20, 30, 40 and 50 kg/ha. They reported the

seed yield reduction from 0.83g/pl to 0.75, 0.67, 0.59 and 0.57 g/plant, and from 828 kg/ha to

769, 769, 740 and 594 kg/ha at 20, 30, 40 and 50 kg seed/ha, respectively.

The number of umbels per plant and number of seeds per capsule depends on the environment

under which the crop is grown, seeding rate and variety difference. The highest mean number

of branches (14.65) per plant was obtained at 5 kg/ha seed rate and the highest number of

seeds (71.12) per capsule was recorded at 10 kg/ha seed rate as compared to 9.48 branches per

plant and 66.45 seeds per capsule at rate of 20 kg/ha (Tuncturk, et al.,2005).

Eventhough black cumin can adapt to arid and semi arid climates , flowering of plants depends

on the average temperature. Optimal temperatures accelerate flowering, but high temperatures

generally cause flower drop after pollination (Weiss, 2003). The crop is sensitive to flower

abscission at high temperature and low night temperature (Weiss, 2003). Improving this

conditions using intercropping could improve its productivity.

In Ethiopia Black cumin is cultivated as rainfed crops in the highlands of 1500-2500 meters

above sea level. Farmers broadcast it after the first rains in a well prepared soil at rate of

20kg/ha. Its sowing date is variable and it varies with place. Sowing starts from the beginning

of July (Chercher highlands and Bale area) to September (in Gonder area) (Jansen, 1981)

It is common to get the seeds of black cumin in every markets of Ethiopia, indicating that it

grown in wide part of country and has great national demand. It has different local names in

different parts of the country, for example in Amharic it called as tukur azmut, tikur azmud,

asumt; in oromipha habasudu, abosuda, nugi guracha, gurati and in tigrian awosetta. It is used

as culinary and herbal medicine (Jansen, 1981). Its wide adaptation and high national and

international demand makes the crop one of promising crops to Ethiopia.

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3. MATERIALS AND METHODS

3.1. Description of the Experimental Site

The experiment was conducted in 2005 cropping season under rainfed condition in Addis

Zemen Peasants Association, GuanguaDistrict, Amhara National Regional State on farmers

field. The site is located at 10 45' N and 3625E about 215 km from Bahir Dar, at an altitude

of 1650 meters above sea level. The annual rainfall in the area during the cropping season was

1705 mm with maximum, minimum and annual mean temperatures of 28.57C, 13C, and

21.5C, respectively (Appendix 1). The top 30 cm depth soil sample analysis of the site

indicated the soil to be heavy clay textured with pH of 5.19, total N of 0.17%, available P of

6.6 ppm and CEC of 21mileq/100g (Appendix 2).

3.2. Planting Materials

Hot Pepper (Capsicum annuum L.) variety used for the experiment was Bako local, released

in 1987(Yosef and Yayeh, 1987). Black cumin material used in this study was a local type

that is widely grown in the area.

3.3. Treatments and Experimental Design

The experiment was conducted using split plot Design with three replications. Two spatial

arrangements were assigned to the main plots. Treatments assigned to the sub plots comprised

population densities of component crops at 100% pepper: 75% black cumin, 100 pepper: 50%

black cumin, 100% pepper: 25% black cumin, 75% pepper: 75% black cumin, 75% pepper:

50% black cumin, 75% pepper: 25% black cumin and sole cropping of the component crops

(Table 1).

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Table 1. Details of treatments showing spatial arrangement and component population

Treatments Spatial arrangement

Pepper: Black cumin rows

Component population

%Pepper: % Black cumin1 1:1 100:75

2 1:1 100:50

3 1:1 100:25

4 1:1 75:75

5 1:1 75:50

6 1:1 75:25

7 2:2 100:75

8 2:2 100:50

9 2:2 100:25

10 2:2 75:75

11 2:2 75:50

12 2:2 75:25

13 Sole pepper

14 Sole black cumin

The two spatial arrangements were arranged alternatively i.e. one row of pepper and one row

of black cumin (1:1 arrangement), in which pepper plants were planted with 70 cm between

rows and 30 cm within rows to get 100% population and 70 cm between rows and 40 cm

between plants to get 75% population. The black cumin was planted 35 cm apart from pepper

rows and 70 cm apart between two rows of black cumin. The required amount of black cumin

population was maintained by manipulating within rows spacing so that within rows spacings

were 10 cm, 15 cm and 30 cm to get 75%, 50% and 25% of black cumin sole populations.

The second spatial arrangement was alternate two rows of pepper and two rows of black

cumin (2:2 arrangement), in which pepper plants were planted with 70 cm between rows and

30 cm between plants to get 100% population and 70 cm between rows and 40 cm between

plants to get 75% population, while black cumin rows were planted at 20cm apart from

pepper rows and 30 cm apart between black cumin rows and 110 cm between double black

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cumin rows. The required amount of black cumin population was maintained by manipulating

within rows spacing so that within rows spacing was 10 cm, 15cm and 30cm to get 75%,

50%, and 25% of black cumin sole populations, respectively.

For sole crops spacings were 70 cm by 30 cm for pepper and 35 cm by 15 cm for black cumin

between rows and between plants, respectively. The sole populations were 47619 plants per

hectare for pepper and 190476 plants per hectare for black cumin.

Each plot has area of 12.6 m2(3.6 m length and 3.5 m width). The numbers of pepper plants

per row were 12 plants in 100% and 9 plants in 75% component populations. The number of

black cumin plants per row was 36 plants in 75%, 24 plants in 50% and 12 plants in 25% of

the sole black cumin component population. In the experimental field, 1m space between sub

plots and 1.5 m space between main plots and replications were maintained as foot path.

For establishment of pepper, seedlings were raised in nursery which was sown on 2nd, June

2005 on nursery bed. Seeds of pepper were sown in rows 15 cm wide on well prepared bed.

After sowing, the beds were covered with hay mulch until emergence. At 3-4 leaves stage, the

seedlings were thinned out in order to maintain optimum plant population and to keep

seedlings vigorous. In the nursery 10 kg/ha P20

5in the form of DAP (46% P

20

5and 18% N)

at sowing and 10 kg/ha N in the form of urea (46% N) after thinning were applied.

Pepper seedlings were planted in the field on 25th, July 2005. In the experimental field, 90

kg/ha P205 (113.4 g/plot) in the form of DAP and 90 kg/ha N (113.4 g/plot) in the form of urea

and DAP were applied. DAP was applied during final land preparation and urea was applied

in two splits at the time of transplanting and flowering stages to pepper rows only. The

fertilizer rates used in intercropping and sole pepper were recommended rates for Bako local

pepper (Yosef and Yayeh, 1987).

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The black cumin was sown directly in the field at the time of transplanting of pepper. The

seeds were soaked overnight before sowing to enhance quick and uniform germination. Three

seeds were sown per hill and thinned out to one plant per hill. Weeding and other agronomic

practices were carried out following local farmers' practices.

3.4. Data Collected for the Component crops

Data were collected for each component separately. For pepper the following parameters were

measured and recorded. The number of days from emergence until 50% of plants per plot

produced the first flower, number of days from emergence until 50% of the plants per plot had

green mature fruits, and number of days from emergence until 50% of the plants per plot had

physiologically mature red fruits.

The height from ground level to the highest point at 100% ripening was measured from five

randomly taken plants and averaged to get plant height per plot. To get average canopy width,

canopy widths of five randomly taken plants per plot were measured at the widest point

immediately after the first harvest and were averaged. From these randomly taken five plants

number of fruits per plant were counted and averaged. In addition to these, 10 fruits from

second and third nodes were taken and their lengths was measured and averaged to get fruit

length.

The fresh mature red ripe fruit yield of five randomly taken plants per plot were measured and

averaged at harvest and after air drying to get mean fresh fruit weight and dry yield per plant.

Harvesting was done in four rounds and the total yield from each plant was obtained using

their sum.

The fresh mature red ripe fruits of three harvestable rows from each plot before air drying and

after air drying were measured and recorded as fresh fruit weight and dry total yield per plot.

Number of seeds obtained from 10 fruits taken, from second and third nodes from 5 randomly

taken plants per plot were counted and averaged to get seed number per fruit.

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After harvesting and air-drying marketable and unmarketable fruits were separated based on

visual observations of their physical appearance. Bleached, insect damaged, non-uniform

color and relatively smaller size fruits were considered to be unmarketable. Yield per plot was

calculated from the three harvestable rows (net plot) and converted to yield per ha and from

the total yield per hectare relative dry yield was calculated as:

pepperofyielddrycropSole

pepperofyielddryedIntercropp

For the black cumin component, days to 50% flowering were determined by counting the

number of days from emergence to 50% of total plants per plot produce the first flower.

Average height of plants per plot was recorded by measuring the height of ten randomly taken

plants from ground level to the highest point when most of the branches ripened. From these

ten randomly taken plants number of main branches were counted and averaged. Plants were

harvested by hand when most of the branches were mature but before shattering of the seeds.

Dry seed yield per plant was measured by taking the mean of 10 randomly taken plants yield

and per plot was recorded by measuring the yield obtained from the plants of three

harvestable rows. Threshing of hand-harvested plants was done after sun drying for a week.

Dried fruit yield per plant of pepper and seed yield per plant and per plot of black cumin were

determined using 200 g capacity sensitive balance. Fresh mean weight per plant and per plot

and total dried fruit yield per plot of pepper were determined using a 20 kg capacity balance

graduated in 100g. The relative yield of black cumin after conversion to yield per ha was

calculated as:

Intercropped dry seed of black cumin

Sole crop dry yield of black cumin

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3.5. Evaluation of Productivity of the System.

Productivity of intercropping system was evaluated by calculating Land Equivalent Ratio

(LER) and Gross Monetary Value (GMV). From yields of pepper and black cumin

components total land equivalent ratio (total LER) was calculated using the formula described

by Willey (1979a) as:

=yii

yiLER

Where

=yi The yield of component from a unit of intercrop

=yii The yield of component crop grown as sole crop over the same area

The intercrop yields of the component crops were expressed over the area occupied by both

pepper and black cumin.

Gross Monetary Value (GMV) was calculated based on the marketable yield (kg/ha) of

pepper and total attainable yield of black cumin and their local prices. It was calculated as a

product of yields of component crops (kg/ha) and their respective unit price (8 Birr for pepper

and 14 Birr for black cumin) at Chagni market, Western Amhara National Regional State.

3.6. Data Analysis

The component crops data, relative yield of each and total land equivalent ratio (total LER)

and GMV were subjected to analysis of variance using statistical procedures described by

Gomez and Gomez (1984).

All data recorded were analyzed using MSTAT C computer program (Freed et al., 1989).

Separate analyses were carried out for intercrop treatments, sole cropped pepper and sole

cropped black cumin. Wherever treatments were found significant, mean differences were

tested following LSD procedure of pair comparison for separation of treatment means.

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4. RESULTS AND DISCUSSION

4.1 Pepper Component

4.1.1. Yield and yield Components

4.1.1 1.Total and relative dry fruit yield

The analysis of variance for total dry fruit yield (kg/ha) of pepper in association with black

cumin showed non-significant variation between two spatial arrangements when averaged

over component populations. But there was a highly significant (p

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Table 2. Effects of spatial arrangement and component population on total dry fruit yield

(kg/ha) and relative yields of associated pepper

Component Total dry fruit yield (kg/ha) Relative yield

Population (P) Spatial arrangement (Sa) Spatial arrangement (Sa)

Pepper: Pepper: Black cumin Pepper: Black cumin

Black cumin 1:1 2:2 Mean 1:1 2:2 Mean

100:75 1435.2 1798.9 1617.1 0.64 0.81 0.725

100:50 2121.7 1886.2 2004.0 0.95 0.84 0.900

100:25 2396.8 2148.1 2272.5 1.07 0.96 1.013

75:75 1091.3 1051.6 1071.4 0.49 0.47 0.482

75:50 1232.8 1391.5 1312.2 0.55 0.62 0.587

75:25 1206.3 1121.7 1164.0 0.54 0.50 0.520

Mean(intercropping) 1580.7 1566.4 1573.5 0.71 0.70 0.70

Sole pepper 2238.1 1.0

CS P Sa P X Sa CS P Sa P X Sa

LSD (5%) 184.47 206.7 NS 292.3 0.05 0.09 NS 0.1319

CV (%) 2.75 10.91 1.73 10.57

NS = means are non-significant,CS =cropping system, comparing sole vs. intercropping

Batal and Smittle (1981), Sunstrom et al.(1984), and Stofella and Brayn (1988) similarly

reported that there was yield reduction as plant population of pepper (Capsicum spp)

decreased. This result was also in line with the report of Tarafder et al.(2003) which showed

yield reduction of pepper from 1025 kg/ha to 884 kg/ha as component population of onion

was increased from 100% pepper and 20% onion to 100% pepper and 60% onion population.

Similarly, Pal et al. (1993) showed reduction in maize and sorghum yield as component

population of soybean was increased.

The yield reduction was also observed in higher component populations i.e. in 100% pepper

with 75% and 50% black cumin. At higher component populations, plants were found to be

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thin and longer having diffused branches and large leaf size but few in number. This might

have been due to high competition for growth resources. As plant density increased number of

leaves exposed to full sunlight decreased steadily and to compete there might be excessive

enlargement of leaves. But this enlargement of leaves could be at the expense of assimilates

that could have been partitioned to yield. Forshy and Elfving (1989) reported that a practice,

which tends to induce vigorous shoot growth, could reduce flower production and fruit set of

apple fruits.

Light interception is a function of leaf area and the spatial distribution of leaves in the canopy.

The basis for maximum yield of pepper in component population of 100% pepper and 25%

black cumin might be due to better light interception, which was increased by black cumin

intercropping, but with less population and less interspecies competition. Midmore (1993)

highlighted the importance of intercropping pepper with maize to increase light interception at

early growth stage of maize so that yield can be increased. Dufault and Wiggans (1981) also

reported that use of green mulch in pepper initiated 2.5 times as many flowers as non-

mulched plants. They reported significant yield increment when mulching was used.

Spatial arrangement by component population interaction had a significant (p

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(0.482) was recorded in 75% pepper and 75% black cumin component population. The

highest relative yield indicated that pepper has benefited from association with black cumin

and the lowest performance indicated that black cumin has impeded it at this combination.

As indicated in Table 2, the mean relative dry yield values ranging from 0.482 to 1.013

indicated the reduced yield advantage of pepper by 51.8%, 48%, 41.3%, 27.5% and 10% in

component populations of 75% pepper and 75% black cumin, 75% pepper and 25% black

cumin, 75% pepper and 50% black cumin, 100% pepper and 75% black cumin and 100%

pepper and 50% black cumin populations, respectively. But it has increased yield by 1.3% in

component population of 100% pepper and 25% black cumin population as compared to the

sole cropping. The relative yield of pepper was significantly high at low population of black

cumin and high population of pepper and vise versa.Similar result was reported by Tarafder

et al. (2003) indicting relative yield value increase from 3 to 37% as total population

decreased from component population of 100% pepper and 60% onion to component

population of 100% pepper and 20% onion.

Alike total total dry fruit yield; the relative yield was also significantly (p

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deciding the type of arrangement to be chosen based on the type of field operation to be

practiced.

While comparing the performance of intercropping with sole cropping there was a highly

significant difference in total dry fruit yield of pepper planted as sole and intercropping. The

highest total dry fruit yield 2238.1 kg/ha was obtained in sole cropping as compared to mean

total dry fruit yield of 1573.5 kg/ha in intercropping (Table 2 and appendix 3.10). As

indicated by the relative yield in the Table 2, intercropping resulted in 30% (664.6 kg/ha)

yield reduction as compared to sole cropping.

Even though the mean total dry fruit yield of intercropping system was inferior to sole

cropping, the highest dry yield (2396.8 kg/ha) of 100% pepper and 25% black cumin arranged

in 1:1 was 7% (158.7 kg/ha) more than sole. Similarly Tilahun (2002) reported a yield

advantage of 12.8% in component population of 100% maize and 75% faba bean population

arranged in 1 row of maize with 2 rows of faba bean, even though the averaged yield of

component population of maize and faba bean combinations were inferior to sole planting.

4.1.1.2. Marketable and unmarketable air dried fruit yield

Per cent marketable air dried fruit yield (marketable air dry fruit divided by total fruit yield

multiplied by 100) was not affected by either spatial arrangement or the interaction of spatial

arrangement by component populations. However, highly significant (p

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Table 3. Effects of spatial arrangement and component population on per cent marketable and

unmarketable yields of the associated pepper

Treatment Marketable yield (%) Unmarketable yield (%)

Spatial arrangement

1:1 87.4 (1395.5) 12.6 (185)

2:2 88.0 (1390.0) 12.0 (176.4)