THE FEASIBILITY OF A PEANUT/SORGHUM INTERCROPPING

SYSTEM UNDER RAIN-FED CONDITIONS

by

ALI MOHAMED ABDI, B.S

A THESIS

IN

CROP SCIENCE

Submitted to the Graduate Faculty of Texas Tech University in

Partial Fulfillment of the Requirements for

the Degree of

MASTER OF SCIENCE

Approved

( ^hairpers-on oY the Committee

v/̂ A-v-r-/ ^. !AA^:^^Z:^^Z^

kA ^y^yyxa*^^ c::;^4»3^<--^

Accepted

Dean djf the Graduate School

December, 1986

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ACKNOWLEDGEMENTS

I owe a deep debt to Allah who gave me the ability to do this

research study. I am also deeply indebted to Dr. Jack Gipson, my major

professor, for his assistance and guidance during this work; for

spending untold hours reviewing my thesis to ascertain accuracy and to

improve readability, and for his guidance in matters of emphasis and

balance in correcting wrong or misleading statements. I also want to

thank Drs. Howard Taylor, Norman Hopper, Dave Wester, and Raymond

Brigham, for serving as graduate committee members. I want to express

sincere appreciation to Dr. Taylor for his loan of the Giddings

hydraulic soil coring machine and continued guidance during the soil

sampling. Special thanks go to Dr. Wester who helped me with the

experimental design and statistical analysis. I gratefully acknowledge

as well, Dr. Hopper's generosity in allowing me the use of his seed

physiology lab facilities, and for his continual guidance during lab

analyses. I also appreciate Dr. Brigham's recommendations concerning

the manuscript. Special recognition goes to all the students and

colleagues who provided me with help when it was most needed,

especially A. A. Afrah, KH. A. Farah, Paul Georgen, Phillip Brown, and

Thomas Griggs. I also extend thanks to the staff and faculty members

in the Department of Plant and Soil Science at Texas Tech University

for advice and assistance during the course of my studies.

Finally, a special note of acknowledgement is due the Somali

government and USAID for providing the financial support needed for

this study.

ii

TABLE OF CONTENTS

ACKNOWLEDGEMENTS ii

LIST OF TABLES v

LIST OF FIGURES vi

I. INTRODUCTION 1

II. MATERIALS AND METHODS 4

III. LITERATURE REVIEW 8

Competition and Complementarity 8

Competition 8

Root competition 9

Types of root systems 10

Complementarity 11

Complementarity of root system 12

Temporal complementarity 13

Spatial complementarity 14

Row Arrangements for Maximization of

Intercropping Benefits 20

Effects of Moisture Stress on the

Growth of Peanuts and Sorghum 21

Peanuts 21

Sorghum 23

Data Analysis 23

111

IV. RESULTS AND DISCUSSION 27

Water Extraction Patterns 27

Grain and Nut Yields 40

Harvest Index 43

Water Use Efficiency 43

Chemical Composition of Peanuts and Sorghum 44

V. SUMMARY AND CONCLUSIONS 46

REFERENCES 48

APPENDICES 55

A. CARBOHYDRATE ANALYSIS 56

B. OIL EXTRACTION FROM PEANUTS 60

C. TABLES 7, 8, and 9:

VOLUMETRIC SOIL WATER CONTENT FROM EACH DEPTH

OVER THE GROWING SEASON 61

IV

LIST OF TABLES

1. Rainfall during the summer of 1985 at the Texas Tech Farm (north of 4th Street, Lubbock, Texas) 30

2. Soil water content (mean values expressed as percent of monocropped and intercropped peanuts and sorghum at the second and third gravimetric soil water sampling dates . . . . 39

3. Mean yield (kg/ha) of sorghum plants grown in monoculture and alternate-row intercrop culture 40

4. Harvest indices (%) of monocropped and intercropped peanuts and sorghum 43

5. Comparisons of water use efficiency (kg biomass/kg water) between monocropped and intercropped peanuts and sorghum . . . 44

6. Chemical composition of monocropped and intercropped peanuts and sorghum (expressed in percentage) 45

7. Water content from each depth of peanut and sorghum plants after emergence, after anthesis of sorghum plants, and at physiological maturity of sorghum plants (expressed in percentage) 60

8. Water content of monocropped sorghum and intercropped sorghum from each depth shortly after anthesis and at physiological maturity of sorghum plants (expressed in percentage) 61

9. Water content of monocropped peanuts and intercropped peanuts from each depth shortly after anthesis and at physiological maturity of sorghum plants (expressed in percentage) 62

LIST OF FIGURES

1. Volumetric soil water content versus depth for monocropped peanuts shortly after emergence (PI), anthesis (P2), and at physiological maturity (P3) 28

2. Volumetric soil water content versus depth for monocropped sorghum shortly after emergence (SI), anthesis (S2), and at physiological maturity 31

3. Volumetric soil water content versus depth for sorghum-peanut intercropping system shortly after emergence (II), anthesis (12), and at physiological maturity (13) 32

4. Volumetric soil water content versus depth for monocropped peanuts (P2) and intercropped peanuts (IP2) shortly after anthesis 34

5. Volumetric soil water content versus depth for monocropped sorghum (S2) and intercropped sorghum (152) shortly after anthesis 35

6. Volumetric soil water versus depth for monocropped peanuts (P3) and intercropped peanuts (IP3) at physiological maturity 36

7. Volumetric soil water content versus depth for monocropped sorghum (S3) and intercropped sorghum (153) at physiological maturity 38

V1

CHAPTER I

INTRODUCTION

The need to increase food production is the major problem facing

African nations today where population growth continues to exceed the

increase in food production. Although historically an agrarian

continent, Africa has lost the capacity to feed itself. Grain from

abroad now feeds in excess of one-fourth the continent's population

which amounts to about 520 million. Until the severe drought of 1983,

grain production increased in Africa by 2% per year between 1970 and

1982. The tragedy, however, is that per capita grain production, which

peaked in 1970, has been falling at about 1% per year since that time

(Brown and Wolf, 1984). Three factors are responsible for this decline

in per capita production: 1) the fastest population growth in history,

2) widespread environmental deterioration of the land, including soil

erosion, nutrient depletion, and desertification, and 3) chronic under­

investment in agriculture.

The population growth rate in Africa is 3% per year, which

translates to an additional 15 million people per year that Africa's

farmers must attempt to feed. This tremendous increase in population

is due to a significant decline in mortality rates without a

corresponding decline in birth rates.

Somalia, located in East Africa and bounded by the Indian Ocean on

the east, by the Red Sea on the north, Ethiopia on the west, and Kenya

to the south, is probably typical of the nations in the semi-arid

regions of East Africa. Most of the farms in Somalia are small family

1

units consisting of only 1-3 hectares, which provide at best only a

subsistence type existence for those who till these plots for their

livelihood. Lack of adequate soil moisture to produce satisfactory

yields is the single most important factor in this semi-arid and

frequently droughty region. This sparse rainfall is further aggravated

by the primitive and ineffective farming techniques employed. Seeds

are planted in an unprepared soil utilizing a zig-zag hill planting

pattern which results in very low plant population density. The native

recurved peduncle type sorghums are used and no fertilizers are

employed. As a consequence of lack of fertilizers, soil nutrients are

depleted and yields suffer even more. Frequently fuelwood for cooking

is scarce and animal dung is utilized in its place, which in turn

removes the one source of organic nutrients that could be used to

replenish the soils.

Somalia and some other African nations have set long-range goals

of becoming self-sufficient in grain sorghum production. Selected

students are being sent abroad for agricultural education, and

agricultural research is being conducted at a number of research

stations. The research conducted for preparation of this thesis falls

within the framework of the program for becoming self-sufficient.

In this context, intercropping has become increasingly more

important for many of the small Somali farmers. Intercropping, or

interplanting of different crops on the same plot of land, is typically

associated with high risk and low rainfall situations. Farmers who

employ this system usually aspire to produce a "full" yield from the

major crop, usually grain sorghum, plus some additional yield from the

second crop, usually peanuts or cowpeas.

There are scientific merits associated with such a system. It

provides more efficient use of both land and labor, and since no two

crops have identical environmental requirements, unfavorable conditions

for one crop may not be as unfavorable for another. Thus the

combination of two crops may provide a buffering mechanism against

total crop failure in some instances.

With this thought in mind, the overall objective of this thesis

study was to determine the feasibility of a peanut-sorghum

intercropping system under rain-fed conditions, similar to those

encountered in Somalia. The specific objectives were as follows:

1) To determine whether or not differences exist in the water

extraction patterns among monoculture peanuts, monoculture sorghum, and

peanut-sorghum intercropping system.

2) To compare yields under these planting arrangements where:

a) Half of the field was planted to sorghum and half to

peanuts.

b) Alternate rows were planted in a peanut-sorghum

intercropping system

3) To compare the effects of monoculture versus intercropping on

total carbohydrates of sorghum, and total protein and oil of peanuts.

CHAPTER II

MATERIALS AND METHODS

A one year field study involving a peanut-sorghum intercropping

system was conducted during the 1985 growing season on the Texas Tech

University Farm located between Fourth Street and Erskine Avenue in

Lubbock, Texas.

The soil type was an Amarillo fine sandy loam (Aridic Palenstalfs,

fine-loamy, mixed, thermic) overlying caliche at a depth of 60 to 90

centimeters. The preceeding crop was wheat, thus the land had been

fallow for 11 months at the time of planting of the intercropping

study. Land preparations consisted of descing the fallow ground,

followed by listing to one m. rows in March and then prewatering in

April to fill the soil profile and permit timely planting. No

fertilizers or herbicides were used, and weeds were controlled by

hoeing.

Treatments were sorghum monoculture, peanut monoculture, and

peanut-sorghum alternate row intercropping. A randomized complete

block design with four blocks was employed. Plot size was eight rows,

twelve meters long. Thus, each monocrop consisted of eight rows, while

each intercropped plot had four alternate rows of each crop.

An early maturing Valencia type peanut (Arachis hypogaea L.) and a

non-senescent sorghum (Sorghum bicolor Moench) hybrid developed by

DeKalb (DK 4446) were used as the cropping species.

All plots were planted with a tractor-mounted two-row planter on

June 10, 1985. Shortly after emergence, both crops in all plots were

hand thinned to approximately 7 plants per m.

4

Soil moisture determinations were made at three dates, each

corresponding to a specific stage in the development of the sorghum

plants. These stages were shortly after emergence, shortly after

anthesis, and at physiological maturity. Soil samples were collected

at 30 cm intervals to a depth of 180 cm, with the aid of a Giddings

hydraulic sampling machine, and soil moisture determined

gravimetrically. At the first sampling date, four soil cores were

taken from each plot regardless of whether it was monocrop or intercrop

to simply establish the amount of moisture in the soil profile under

each plot. At the other two sampling dates, however, four sets of soil

cores were again taken from the monoculture plots, but eight sets were

taken from the intercrop plots. The cores were always taken either in

or very near the planted rows.

Soil from each core was cut into 30 cm segments, a representative

sample taken from each segment, placed in a pre-weighed can, and then

carried to the lab where wet weights were obtained.

The soil samples were oven-dried for 48 hours at 110 C, and then

weighed. Soil moisture was calculated as follows:

wet weight - dry weight ^ -.p.̂ % soil moisture = ^ ^— x 100

dry weight - can weight

The dates for soil moisture sam.pling were June 27 and 28 for the

first sampling, July 7 and 8 for the second sampling, and September 24

for the third sampling.

Due to the proximity of the research plots to the city of Lubbock,

sparrows began to feed on the sorghum heads in the milk stage. This

necessitated covering the heads with paper hags to avoid bird damage.

Even so, considerable bird damage occurred following a violent rain and

hail storm which blew off many of the paper bags. The bags were

replaced, but sufficient damage occurred to necessitate calculations

for percent damage.

Harvests for gain and peanut yields and for calculating the

harvest indices were made on October 3 and 4, 1985. Harvested plots

consisted of three rows, four m. long from the middle of each plot for

yield purposes.

Both the sorghum and peanuts were then threshed and weighed for

yield. Calculations to compensate for bird damage to the sorghum were

made as follows: 1) from each plot, between 24 and 34 undamaged heads

were harvested, dried, and threshed together; 2) seed weights were

taken and weight/head determined for these undamaged heads; 3) seed

weight/head was then determined on the damaged heads from the harvested

area being used for yield; and 4) seed weight/head of the undamaged

heads was then subtracted from the seed weight/head of the damaged

heads, and the difference expressed as percent bird damage.

Sorghum was analyzed for total carbohydrates using acid extraction

with 0.2 N HCL as described by Murphy (1958) and Smith (1964),

(Appendix A).

Peanuts were analyzed for oil content by the petroleum ether

extraction method, using a macro soxhlet apparatus (Appendix B), and

protein content was determined by a commercial lab (A&L Labs, Lubbock),

using the standard macro-Kjeldahl method.

The data were tested using the analysis of variance package of the

Statistical Analysis System (SAS). Protected LSD was used as the mean

separation technique unless specified otherwise.

CHAPTER III

LITERATURE REVIEW

Competition and Complementarity

The two most important principles in a mixture of crops are

competition and complementarity. Very little effort has been extended,

however, towards producing any meaningful measure of these two factors

between component crops.

Competition

Competition has been defined as the difference in the ability of

different species to get from the environment the factors necessary for

their growth and reproduction when these factors are in limited supply

(Bunting, 1960). Competition occurs during that period in which the

supply of a single necessary factor falls below the combined demands of

the plant (Clements, et al., 1929). Mather (1961), indicated that

competition occurs when the combined need of the individuals exceeds

the supply of whatever commodity is needed. According to Donald

(1958), competition enables the successful species to achieve better

utilization of the resources than the suppressed species. For example,

when more available water is taken by a dominant species, the

suppressed species may wilt due to a shortage of water. Wilting, in

turn, may decrease the photosynthetic products available for plant

maintenance and root and shoot growth. In the final analyses, the less

competitive crop will be reduced in growth and will not be able to make

use of the environment available to it.

8

Root competition

Roots are the principal organs responsible for the absorption of

water and nutrients from the soil, and are very important in competing

for these resources. Clements et al., (1929) state that the larger,

deeper and more active the root system a crop has, the more competitive

it is in securing the larger proportion of the total water available

for growth. Weaver and Clements (1938), indicated that both the extent

and the distribution of roots determine the competitive ability of the

root system. Pavlychenko and Harrington (1934), stated that a root

system with a larger mass of fibrous roots near the surface but with

its main roots penetrating deeply determine the degree of success of

competition. Taylor (1983) stated that, in field crops, all the

available water is absorbed from between crop rows if the soil

conditions are favorable. Further, he states that the rate of lateral

root growth is unimportant since the roots from one row of plants will

reach those of the adjacent rows early in the season. Pavlychenko

(1937), states that root length per plant decreased by increasing crop

density or weed population. After testing several species of weeds and

crops, Pavlychenko (1942) indicated that weeds occupy the soil with

their roots earlier because they germinate earlier, and grow more

rapidly than the cereals. Indeed, weeds that do the most damage to

crop plants d^re those which have similar growth habits, and especially

root systems. In fact, the extent of root systems determines both the

competitive efficiency and the natural distribution of the roots.

Crops with different types of root growth make the best intercropping

companions.

10

Types of root systems

Many studies have been conducted to determine plant root systems.

Weaver (1926) indicated that the root system of sorghum has 90 to 180

cm of lateral spread, and a maximum depth of 140 to 180 cm. According

to Heatherly (1975), more than 80% of the root mass of sorghum is at

the top 30 cm of the soil except under extremely dry conditions.

Gutierrez (1972), demonstrated an inverse proportionality between root

growth of sorghum and the available water remaining in the soil. In

addition, he showed three phases of root growth in the soil and a

distinct difference in the relations of root growth and soil water

utilization in each phase. First, roots grow slowly and little water

is used; second, roots grow faster, and maximum root growth is

attained, resulting in maximum water depletion. In the third phase,

growth of roots is slow and little water is used. Blum and Ritchie

(1984) found that the number of crown roots in sorghum decreased when

the water content of the surface soil was low. With reduction of the

crown roots, deeper growth of the existing root resulted and the total

root length per plant was approximately the same. Blum and Ritchie

(1984) concluded the major factors controlling sorghum root

distribution are topsoil water content, strength of crown root

establishment, and growth response of the existing roots. Leach (1978)

found legumes to be least efficient in water use of a range of crop and

pasture plants. He found alfalfa to have a high water loss due to poor

stomatal control. Peanuts are characterized by a relatively deep tap

root system and a well developed lateral root system. From the results

11

of a Pearl millet - Peanut intercropping study, Gregory and Reddy

(1982), concluded that peanuts had greater total root length in the

upper 30 cm of the soil profile than Pearl millet, while root length

density of Pearl millet in the upper 10 cm of the soil was greater than

for peanuts.

Complementarity

Complementarity is the opposite of competition and is most

pronounced in intercropping. Three types of complementary mechanisms

have been reported. First some crops emit substances that protect or

nourish others (al lelochemical or allelopathic effects). Wahua and

Miller (1978) found that when soybeans were intercropped with dwarf

sorghum (BR-44), total nodule activity (TNA) of the intercropped

soybeans increased, and they suggested that sorghum excreted some

biologically active substance which enhanced soybean N^-fixation, thus

making more nitrogen available to the intercropped sorghum. Secondly,

one crop may suppress the harmful effects of some pests (insects,

diseases and weeds) thus benefiting the other crop (Auckland, 1970;

Finlay, 1974). Thirdly, some species may even benefit from reduced

levels of certain resources. This was suggested by Chen (1961) as one

of the possible reasons why TNA increased in soybeans intercropped with

dwarf sorghum (BR-44). He stated that sorghum roots may have reduced

the concentration of nitrates around the soybean roots, which in turn

depressed nodulation with N^-fixation. This allowed greater N^-

fixation in intercropped soybeans compared with N^-fixation in

12

monocropped soybeans. Reddy and Willey (1981) found that greater

amounts of nutrients were absorbed by a Pearl millet/peanut

intercropping system than the average of the monocrops. Gupta and

Mather (1964), found that in general when the two crops have almost

equal amounts of mineral and other nutrient necessities, their mixtures

seem to be more profitable.

Complementarity of root systems

Root complementarity is believed to be one of the most important

factors that gives a yield advantage to intercropping over

monocropping. Willey (1979) indicated that complementarity of root

systems coupled with better control of weeds, pests, or diseases can

explain the yield advantage in intercropping compared to monocropping.

He showed that combined crops have differences in resource use and this

determines the overall better usage of the resource. Clements et al.,

(1929) indicated that the greater the differences between the

intercropped species, the lower the competition between them, and Dalai

(1974) showed that by selecting species of different growth habits,

decreases in yield as a result of the use of legume and non-legume

crops can be reduced. Weaver (1926) found that yield increases in

mixed cultures may be partially explained by lessened competition.

Whittington and O'Brien (1968) found that when crops of different

growth habit were mixed, competition between them was lowered. Hurd

and Spratt (1975) proposed that productivity per unit area can be

increased by combining cultivars with different root growth patterns,

Wiw"-

i.e., one with extensive lateral root growth and the other with a

deeper penetrating root system. According to Snaydon and Harris (1979)

production may be increased when species with different resource needs

are mixed. In addition, they showed that when the most competitive

crop is the most productive, it is possible to obtain more yield in

intercropping systems than in monocropping systems. Willey (1979)

showed that three things may happen in an intercropping situation. The

first is inhibition, which can either be competition between

intercropped species or allelopathic effects; the second is

cooperation, referring to sharing of resources (complementation); and

the third is compensation. This last case may take place when, for

instance, the elongation of certain parts of the root system is

exhausted after a certain depth, and the photosynthate that had been

moving to this part of the root is transported to another part of the

root system, resulting in increased growth and greater competitive

ability at that depth. Aiyer (1949) indicated that resources in both

the upper and lower layers will be utilized more effectively when crops

of varying root depth and absorption capacities are mixed.

Temporal complementarity

Temporal complementarity refers to that complementarity which is

reduced for only a period of time.

Harris and Lazenby (1974) stated that mixing grasses of different

growth habits can increase yield. As Trenbath (1976) suggested in crop

mixtures, the earlier a crop absorbs the mobile nutrients and water.

13

14

the better competition it retains. Baker and Norman (1975) indicated

that the yield advantage of intercropping is due to better usage of the

media, light, and to the different growth patterns of the intercropped

species, i.e., competition is reduced due to the temporal growth cycle.

Willey et al., (1982) suggest that where the peak of the growing

periods do not coincide, there can be sharing of the resource between

sorghum and other crops in an intercropping situation. Willey et al.,

(1982) conclude that it is this sharing of the resource use and the

subsequent efficient overall use of the resource that gives the yield

advantage to intercropping over monocropping. In general, legumes

absorb less amounts of nutrients in the early stages of growth and more

from full bloom to maturity. Thus Dalai (1974) found that corn with

pigeon-pea makes a desirable intercropping system because the greatest

nutrient demand by the pigeon-pea occurs after the corn has completed

its growth cycle.

Spatial complementarity

Difference in the rooting system among plants is one of the major

factors that contributes to yield advantages of intercropping over

monocropping (Tothill, 1948). Martin and Snaydon (1982) suggested that

both the differences in the rooting depths and the uses of resources at

different times could increase the water use efficiency in

intercropping situations. According to ICRISAT (Annual Report 1977-

1978), a com.plementary rooting habit is the most probable factor for

better water use efficiency of intercropping versus monocropping.

15

Willey et al., (1982) suggested that overall morphological and

physiological differences between the intercropped species were

responsible for yield advantages of intercropping systems over

monocropping systems. When crops with different root distributions are

intercropped, both upper and lower layers of the soil will be better

exploited and this will lead to better absorption of the soil moisture

(Gupta and Mather, 1964). Lingegouda et al., (1972) stated that when

crops of different growth habits are grown together, the total

environment will be exploited more effectively and greater yields will

be achieved than with monocropping. In fact, shallow rooting crops

cannot extract the soil nutrients in the deeper soil layers. Thus,

Berendse (1982) suggested that a combination of a deep rooting crop

with a shallow rooting crop leads to a better nutrient utilization in

deep soil layers. With a shallow rooted crop alone, these nutrients

would either leach or remain unused.

In spite of the great increase in intercropping studies during

recent years, there have been inconsistent results as to whether

intercropping: a) induces deeper rooting, b) increases water use

efficiency, and/or, c) provides maximum advantage under water stress.

Moreover, the question may be raised as to whether it is the below

ground or the above ground plant interaction that gives the yield

advantage frequently associated with intercropping,

Willey (1979) showed the possibility that a deeper rooting crop

could be forced even deeper when grown in combination with a shallow

rooting crop in an intercropping situation. In a millet/sorghum

16

intercropping system, Andrews (1972) showed that each crop produced

larger root systems than in a monoculture system with the component

crops. Whittington and O'Brien (1968) observed more phosphorous

absorption from the deeper layers of the soil in a crop mixture than in

monoculture. Pearson (1966) stated that the deepest root penetration

occurs under the lowest moisture treatments. Crocioni (1951) showed

that potato and sunflower could make a beneficial mixture due to the

diverse depths of the two root systems. He indicated that potato

encouraged the sunflower to root more deeply. Apples and grapes

produced deeper root systems when mixed with other crops (Baldy, 1964).

Gregory and Reddy (1982) in a pearl millet/peanut intercropping system,

found that the distribution and the total length of roots in an

intercrop system was intermediate between the two monocrop situations,

even though there was a slight increase (10-15%) in root length beneath

the intercrop, compared to the monocrop. Natarajan and Willey (1980a)

in a sorghum/pigeon-pea study showed that sorghum root concentration

dominated the top soil (15 cm) while pigeon-pea root concentration was

the greatest in the lower soil layers (15-30 cm). They concluded that

there was no evidence that intercropping could change the root

distribution in any significant way that might result in a better use

of the soil moisture.

Scientists are also divided on whether intercropping increases or

decreases water use efficiency. Kurtz et al., (1952) stated that under

intercropping conditions, changes in soil moisture were more rapid,

partly because of the increased moisture utilization by the

17

intercropped species than the component crops. Aiyer (1949) suggested

that the combination of intercropping cover (short and spreading) and

taller (upright growth) reduced soil evaporation and increased the

water use efficiency. He also stated that the cover crop could

decrease soil evaporation while the taller crop provides shade

protection from dessication and breaks the wind velocity. Others

(Ferguson et al., 1970; Baker and Norman, 1975; Hedge and Saraf, 1979)

reported that intercropping increases water use efficiency. Willey

(1982) was dubious as to whether increased water uptake in an intercrop

is the cause or effect of increased yield. Nararajan and Willey (1982)

found no difference in the total water use efficiency between

sorghum/pigeon-pea intercropping system, and the monocultures of

sorghum and pigeon-pea. Under dryland conditions, De and Singh (1979)

predicted intercropping to have greater total consumptive use and water

use efficiency than monoculture, but water use efficiency could

decrease due to shading and the subsequent decrease in yield of the

shorter legume. Baker and Norman (1975) could not get reliable

information on water use efficiency in intercropping.

Arguments also exist about the possibilities that intercropping

may maximize advantages under stress. Kass (1978) in his literature

review, concluded that a crop mixture performs better in the dry

season. Baker and Norman (1975) showed that the farther north one

proceeds in Nigeria, the drier it gets, and the more intercropping

becomes dominant. Evans (1960) and Paner (1975) found that when water

availability and precipitation were favorable, intercropping showed no

18

yield advantage over the monocrops; in fact, the monocrops out-yielded

the intercropped crops. Willey (1982) and ICRISAT's Annual Report for

1981 stated that an intercropping advantage is greater under low

fertility (nitrogen deficiency) and water stress. As was indicated by

Mather (1961) as the supply of a resource goes down, the interaction

between plants in an intercropping situation goes from cooperation to

competition. With competition, better root distribution (length and

density) is achieved which can result in improved utilization of the

potential resources in the soil. According to ICRISAT (Annual Report

1977-1978), intercropping produces no yield advantage when moisture and

other resources are adequate. Snaydon (1971) stated that intercropping

becomes more effective as the supply of a resource goes down. Snaydon

and Harris (1979) found the greater the availability of a resource

supply, the less the advantage of intercropping over monocropping. In

an intercropping system of sorghum and corn with phaseolus bean and

cowpea, Marfe et al., (1979) found greater advantages associated with

intercropping when water was limiting. In general, all these studies

report that intercropping has a yield advantage under stress.

Resources in the soil are commonly limiting in the semi-arid

tropics where intercropping is most commonly practiced. Perhaps this

is why many researchers have concluded that the below ground plant

interaction is more important than the above ground interaction in

achieving the yield advantage in intercropping. Litav and Isti (1974)

suggested that it is almost entirely the below ground and not the above

ground interaction that determines the competition effect in

19

intercropping. Martin and Snaydon (1982) showed a greater effect of

the below ground than of the above ground interaction in an

intercropping study. It should be noted that roots are dependent on

shoots for carbohydrates, growth regulators, and organic substances.

On the other hand, shoots depend on roots for their water, minerals,

and growth regulators. Even though roots absorb water and minerals

from the soil, it is mainly due to the transpirational pull exerted by

the transpiring leaves. Therefore, maintenance of balance in growth

and function between roots and shoots is indispensable for the

successful growth of the plant. Willey and Reddy (1981) indicated that

intercropping benefits are due mainly to the light interaction (shoot

competition or above ground plant interactions), but states that below

ground interactions are more important than the above ground when below

ground sources are limiting. Snaydon and Harris (1979) gave more

importance to the below ground than the above ground competition that

permits the yield advantage in intercropping. Remison and Snaydon

(1980) working with Dactyl is glomerata and Holcus lanatus showed the

supremacy of the root competition over shoot competition. From the

analysis of competition between plants of Trifolium repens L., Snaydon

(1971) indicated that root competition begins before shoot competition

and has a greater effect than the shoot growth. Seshardi et al.,

(1956) compared bunch to spreading peanuts and indicated that the bunch

type grew taller and had more shading than the spreading type. In

conclusion, he preferred the spreading type as being more suitable for

intercropping. According to the report from ICRISAT (Annual Report,

1979-1980) water loss from peanuts decreased by the shading effect

20

produced by millet when these two crops were grown together

(intercropped). Natarajan and Willey (1980b) showed that when pigeon-

peas were intercropped with sorghum, pigeon-peas produced a higher

harvest index than either crop alone. They also found that leaf area

indices of the pigeon-peas were reduced due to the shading effect of

sorghum while leaf area indices in sorghum showed no differences.

Radke and Hagstrom (1976) found that when a short and a taller crop

were intercropped, the shorter crop would grow taller and produce more

dry matter with greater leaf area and yield due to the taller crop

acting as a wind protector and altering the microclimate for the

shorter crop. Reddy and Willey (1979) were unable to show any real

evidence that would indicate that root systems in intercrop systems are

more efficient than root systems in monocrop systems.

Row Arrangements for Maximization of Intercropping Benefits

It is difficult to determine optimum planting arrangements and

plant populations for intercropped species because these factors vary

from one environment to another. Kass (1978) indicated, however, that

planting in alternating rows will provide greater returns than the

other intercropping patterns, i.e., random, strip, relay, and mixed

intercropping systems. Dalai (1974) also showed a greater advantage

* Mixed intercropping (random): Growing two or more crops simultaneously with no distinct row arrangement. Stripped intercropping: Growing two or more crops simultaneously in different strips wide enough to permit independent cultivation but narrow enough for the crops to interact agronomically. Relay intercropping: Growing two or more crops simultaneously during part of the life cycle of each. A second crop is planted after the first crop has reached its reproductive stage of growth but before it is ready for harvest (Andrews and Kassam, 1976).

21

of alternate rows in a corn/pigeon-pea intercropping system, wherein he

obtained maximum protein and achieved maximum absorption of potassium,

calcium, and magnesium. ICRISAT (Annual Report, 1979-1980), showed a

higher LER value from a 1:2 row arrangements of a peanut/sorghum

intercropping system under severe stress. As Chetty and Rao (1979)

found, resourse sharing in intercropping is only possible when the

mixed crops are adjacent to each other, and Kass (1978) stated that the

farther the intercropped species are separated, the more the

intercropping advantages decrease.

Effects of Moisture Stress on the Growth of Peanuts and Sorghum

Peanuts

Nageswara et al., (1985) examined the effect of moisture stress

imposed at different growth phases on peanuts (Cultivar Robust 33-1).

They found that the lowest pod yields resulted from the most severe

stress (in the continuous water stress). In addition, as the water

deficit increased, the ratio of kernel to pod weight was hardly

affected by the water deficit, suggesting that peanuts only initiated

pods that it could subsequently fill. This prolonged the water deficit

effect on the establishment of pods. Others (Stansell et al., 1976;

Vivekanandan and Gunasena, 1976; Pallas et al., 1979) have shown that

continuous water deficit reduces dry matter production. Slatyer (1955)

and Allen et al., (1976) stated that water deficits inhibit leaf and

stem expansions as turgidity is reduced.

22

Water stress imposed from emergence until start of peg initiation

resulted in a more favorable distribution of dry matter into the

reproductive components. When the water stress occurred from the start

of flowering to the start of kernel growth, the total biomass and the

pod yield decreased. One important factor that influences yield when

drought occurs at this stage (pegging) is the moisture content of the

topsoil. According to Cox, (1962); Underwood et al., (1971); and Boote

et al., (1976) the greatest reduction in pod yield has been due to the

hard topsoil. The greatest reduction in pod and kernel yields occurred

from the stress of water at the start of kernel growth to maturity.

According to Matlock et al., (1961); Boote et al., (1976); Pallas

et al., (1979); Underwood et al., (1971) and Ono et al., (1974) soil

water available in the top 4 to 5 cms of the profile is of critical

importance for peg and pod development. They stated that fruit

initiation is continuous after the start of kernel growth, so the soil

water deficit during the pod filling stage reduces both the initiation

and development of pods.

Ono et al., (1974) found that because of the high soil

temperatures, pegging may not result in the development of pods. Allen

et al., (1976) and Boote et al., (1976) suggested that the growth of

pods in the soil may be affected by inadequate moisture in the root

zone, and Skelton and Shear (1971) stated that lack of calcium uptake

by developing pods may affect the growth of pods in the soil.

23

Sorghum

Chauduri and Kansemasu (1982) conducted a field study during the

1980 growing season to determine the effects of soil moisture gradient

on sorghum water relationships and the growth and yield of four

hybrids. From their investigation, they made the following

conclusions: a) dry matter production, LAI (Leaf Area Index) and plant

height increased as the watering level increased. As the water

supplied was increased, xylem water potential increased and leaf

diffusive resistance decreased, b) Increasing the watering levels

increased the water use efficiency for total dry matter and grain

yield. Magnitudes of water use efficiency were greater for total dry

matter production than for grain yield under different watering levels,

c) Increasing the supply of water increased grain sorghum yields.

Yields of sorghum hybrids correlated well with water use, average

canopy temperatures and canopy temperature minus air temperature.

Data Analysis

It is widely accepted that intercropping out-yields monocropping,

but problems exist in assessing the degree of yield advantages of

intercropping over monocropping. As Willey and Osiru (1972) showed,

there is a danger in comparing the combined yield of intercropped

species with yield from monocropped species, because competition in

intercropping usually results in a different proportion of final yields

than from monocropping. Oyejola and Mead (1982), and Huxley and Maingu

(1978) stated that it is important to compare the yield of

24

intercropping with that of monocropping at the optimum population and

spacing. Mead and Willey (1980) presented three reasons why it is

important to assess intercropping advantages. First, interpretation of

the yield advantage of an intercrop in a given situation or season may

be quite different from that of longer term effects. (It is impossible

to predict which single crop would be higher yielding in any given

season.) A second type of assessment is required where it is desired

that the intercropping system will provide a full yield of a main crop

(i.e., as much as in the monocrop), and some additional yield of a

second crop. For instance, this situation occurs where the main crop

is a highly valued source of cash which the farmer is not prepared to

sacrifice. The third and the most common situation is where

intercropping gives a yield advantage if two of the required crops

produce more yield as an intercrop combination than when grown

separately. This latter situation occurs where the farmer needs to

grow more than one crop, whether intercropped or not, to spread labor

peaks, reduce marketing risks, or to satisfy different requirements.

Assessment of this situation involves comparisons between the combined

intercrop yields and the yield of some combination of monocrops (i.e.,

the total from each monocrop).

According to Willey (1979) the most general useful single index

for expressing the yield advantage in intercropping is probably the

Land Equivalent Ratio (LER). LER is defined as the relative land area

required for monocrops to produce the same yields as intercropping. It

can be written as:

25

Where L. and Lg are the LERs for the individual crops.

Y. and Yg are the individual crop yields in intercropping.

S« and Sg are the yields of the monocrops.

Mead and Willey (1980) stated that LER has three advantages.

First, it provides a standardized basis so that crop yields can be

added to form "combined" yields, i.e., LER can be compared between

different situations and even between different crop combinations, but

they admit to some problems in this case. Secondly, comparison between

individual LERs (L« and Lg) can indicate competitive effects (Willey,

1979) and the third and the most important is that the total LER can be

taken as a measure of the relative yield advantage. For instance, a

LER of 1.2 indicates a yield advantage of 20%, or that 20% more land

would be required as a monocrop to produce the same yields as with

intercropping.

There are two unavoidable problems with the use of LER. First,

since LER is defined as a ratio, large values can be obtained because

of large yields in intercropping, but large values can also be obtained

because of small yields in the corresponding monocrops. The second

difficulty in using LERs as a measure of biological efficiency to

compare different situations is the implicit assumption that the

harvested proportion of the two crops are exactly those that are

required in each situation. Willey (1979) stated that LER application

does not estimate the need for the presentation of absolute yield in

intercropping experiments. Mead and Riley (1981) showed that LER can

26

be large either because intercropping yields are higher, or monocrop

yields are smaller, and encouraged the inclusion of absolute yields in

the analysis of intercropping research. Mead and Stern (1979) stated

that a variety of indices should be used for the determination of the

total yield and discouraged the use of any single measurement. Faris

et al., (1983) said that in assessing intercropping yield advantages,

it is important to consider both the LER and the absolute yield.

Pearce and Gil liver (1978) showed that the bivariate analysis of

variance is required when two variates must be dealt with in

conjunction. They showed that in order to use the bivariate method,

one must assume the same degree of competition for all treatments.

Mead and Riley (1981) suggested the use of bivariate method with LER

because, they said, the bivariate method assumes that the correlation

between yield for the two crops is constant for all treatments.

CHAPTER IV

RESULTS AND DISCUSSION

Water Extraction Patterns

The water extraction patterns of monocropped peanuts shortly after

emergence, anthesis, and at physiological maturity are shown in Figure

1. During the period from emergence to anthesis, the greatest decrease

in water content occurred at the more shallow depths of 15 to 75 cm.

The greater utilization of water from the surface depths would be

expected in the earlier phases of plant growth as the root system is

much more extensive at depths above 75 cm (Gregory and Reddy, 1982).

Between anthesis and physiological maturity, much more water was

extracted at depths below 75 cm as the water content at the more

shallow depths was depleted and root systems apparently proliferated at

the deeper depths. At 165 cm, the maximum depth sampled, water content

decreased from 19 to 15 percentage points (Figure 1). Obviously there

must have been differences in water content between the two sampling

dates below 165 cm.

These data indicate that peanuts grown in monoculture system

develop wery effective root systems deep into the caliche horizons.

The difference of 4 percentage points at the 165 cm depth indicates

that root systems were well developed beyond the deepest sampling

depth.

Above 75 cm, water content increased about 5 percentage points

between the sampling depths of 45 and 75 cm and held steady at even the

15 cm depth. This was due to 55 mm of rainfall between August 9 and

27

28

Volumetric soil water content (5)

0

E o

0 --

1 5 ••

30 ••

45 •-

6 0 ••

75 •-

90 •-

105 --

120 ••

135 •-

150 •-

165 -•

5 10 15 20 -+—

25 -i

••-

•o-

• • -

PI

P2

P3

Figure 1 Volumetric soil water content (%) versus depth (cm) for monocropped peanuts shortly after emergence (PI), anthesis (P2), and at physiological maturity (P3)

29

September 12 (the third sampling date was September 24). Thus, there

was sufficient rainfall in September to partially recharge the upper

profile to about 45 cm depth (Table 1).

The water extraction patterns for monocropped sorghum at the three

soil water sampling dates are shown in Figure 2. As with monocropped

peanuts, during the period from emergence to anthesis, change in soil

water content over time decreased with increasing depth. The greatest

decline in soil water content from the first to the second sampling

dates occurred at depths above 105 cm, amounting to 8 percentage points

at 15 and 45 cm, and about 5 percentage points at 105 cm and below.

During the period from anthesis to physiological maturity, water

content at the deeper depths continue to decline, with the lowest water

content observed at the 135 cm depth at physiological maturity. Above

135 cm, soil water content at the third sampling date steadily

increased from 10% volumetric soil water content found at the 135 cm to

21% at the 45 cm depth. This value was followed by a decline to 13% at

the 15 cm depth. Again, the reason for the greater water content at

the more shallow depths was because of rainfall received between

anthesis and physiological maturity.

The volumetric soil water content for the peanut-sorghum

intercropping system at the three sampling dates is shown in Figure 3.

The pattern is similar to that just discussed for monocropped sorghum

and the only difference observed between the two was at the second

(anthesis) sampling date. This difference will be discussed in

conjunction with Figure 5.

30

Table 1, Rainfall during the summer of 1985 at the Texas Tech Farm (North of Fourth Street).

Date Amount Total

May 7 35.5 May 8 3.O ^,^y 15 29;3 May total = 123.6 mm May 17 10.0 May 20 5.5 May 22 46.3 June 1 9.0 June 3 5.0 June 4 37.5 June 6 37.5 June 10 15.0 June total = 126.8 mm June 11 4.3 June 18 12.5 July 1 6.0 July 16 1.3 July 22 1.3 July total = 63.1 mm July 23 0.3 August 9 3.3 August 11 11.0 August 15 33.5 August total = 53.8 mm

August 23 6.0

September 12 0.3

September 13 10.5

September 14 16.0 September total = 95.3 mm

September 19 37.5

September 20 31.0 _ _ _ _ _ _ _ _

31

Volumetric soil water content (%)

0

E

Q.

CD

0 '-

15--

30--

45 •-

60 •'

75 •-

90 •'

105 •-

120 ••

135 ••

150 ••

165 --

5

Figure 2

10 — f —

15 -4—

20 —+—

25 — <

•• -

•o-

••-

SI

S2

S3

Volumetric soil water content (%) versus depth (cm) for monocropped sorghum shortly after emergence (SI), anthesis (S2), and at physiological maturity (S3)

32

Volumetric soil water content (%)

<_)

0

0

15

30

45 "•

60 •-

7 5 ••

90 •-

^ 105 +

^ 120--

135 ••

150 -•

165 ••

5 -+-

10 -4—

15 -+—

20 —+—

25 — I

Figure 3. Volumetric soil water content (%) versus depth (cm) for peanut-sorghum intercropping system shortly after emergence (II), anthesis (12), and at physiological maturity (13)

33

Figure 4 shows a comparison of jjhe water extraction patterns of

monocropped and intercropped peanuts shortly after anthesis. There

were no differences apparent at this stage, although there were

pronounced visual differences in plant size. Monocropped peanut plants

were much larger and more luxuriant than those in the intercrop plots.

Lack of any differences in extraction patterns at this stage is

difficult to reconcile, although 55 mm of precipitation occurred

between anthesis and physiological maturity.

A comparison of the soil water content in monocropped and

intercropped sorghum shortly after anthesis is shown in Figure 5. At

the more shallow depths, there were no differences but, at 135 cm,

monocropped sorghum plots showed almost 5 percentage points less water

than for intercropped sorghum. This implies, of course, that the

intercropped sorghum plants must have been extracting moisture from the

adjacent peanut rows. At the 165 cm depth, the difference in water

content was about 3 percentage points, thus the difference in the

extraction patterns continued to some depth below 165 cm.

Figure 6 compares the moisture extraction patterns of monocropped

and intercropped peanuts at the third sampling date, September 24,

which represented the physiological maturity stage for sorghum (not for

peanuts). Peanuts were approaching maturity at this stage, although

the plants were still green and probably consuming some moisture. At

the 15 cm depth, there was no difference in moisture content because of

recharge from September rainfall, but at the 45 cm depth the

intercropped peanuts showed a water content of 6 percentage points

34

u

0

0

15 --

30 ••

45 -•

60 ••

75 ••

90 ••

120 --

135 ••

150 --

165 •-

Volumetric soil water content (%)

5 10 -+-

15 —f—

20 —+—

•v o.

• v Q

• o

25 -H

••- P2

•o- 1P2

Figure 4. Volumetric soil water content (%) versus depth (cm) for monocropped peanuts (P2) and intercropped peanuts (IP2) shortly after anthesis

35

Volumetric soil water content {%)

E o

QJ

0 J— 0

15 -•

30 •-

45 •-

60 •-

7 5 ••

90 -•

105 ••

120 •-

135 •-

150 ••

165 ••

5 10

—H-

15

-f-

20

— f —

• o

• Q

2 5

—I

Figure 5. Volumetric soil water content (%) versus depth (cm) for monocropped sorghum (S2) and intercropped sorghum (IS2) shortly after anthesis

36

Volumetric soil water content (%)

0

E o

Q.

Q

0 •-

1 5 "

30 •-

45 -•

60 -•

75 -•

90 -•

105 -•

120 -•

135 ••

150 •-

165 -•

5 10 • H —

15 -4—

20 —h-

25 -H

O^^

o •

Figure 6. Volumetric soil water content (%) versus depth (cm) for monocropped peanuts (P3) and intercropped peanuts (IP3) at physiological maturity

37

greater than for monocropped peanuts. At 75 cm the difference in water

content was 4 percentage points. At the 105 cm and deeper depths the

differences were minimal. A possible explanation for the higher

moisture content of the intercropped peanuts at the 45 cm depth could

relate to plant size. The monocropped plants were much larger and were

probably utilizing considerably more moisture than the more stunted

plants in the intercrop system. Yield data also verify this

assessment.

Soil water extraction patterns for monocropped versus intercropped

sorghum are presented in Figure 7. At the shallow depths (15 and 45

cm), there was no difference in water content between the two systems,

but at 45 cm, the intercropped sorghum showed 6 percentage points less

soil water than the monocropped sorghum. Soil water then declined

under both system to essentially the same value (11 percentage points)

at the 105 cm depth. At the 165 cm depth, both systems showed a value

of about 12 percentage points. The much lower value at 45 cm in the

intercropped plots is probably due to water extraction by the

intercropped sorghum from the adjacent peanut rows. Obviously the

values obtained at 105 cm and below for both monocropped and

intercropped sorghum (and peanuts) reflected the extent to which water

has been utilized from the lower profile during the course of the

season. Moreover, at some point in time, water must have been depleted

to an equal or more likely to a greater extent at depths of 15 to 75

cm, where the bulk of both peanut and sorghum roots would be expected

to be located. From Figures 1 and 2, it is apparent that at the

38

Volumetric soil water content (%)

0

E (J

Q. (U

0 --

15 -•

30 ••

45 •-

60 ••

75 --

90 ••

105 ••

120 ••

135 ••

150 ••

165 ••

5

-+• 10 -4—

15 -f-

20 — » —

25 — «

o •

• o

Figure 7. Volumetric soil water content (%) versus depth (cm) for monocropped sorghum (S3) and intercropped sorghum (IS3) at physiological maturity

39

beginning of the season, water content between 75 and 165 cm depth

averaged about 22%. At the second sampling date (July 7 and 8 ) , this

value had dropped to about 19% in monocropped peanuts, 16% in

monocropped sorghum, and 16 to 20% in the intercropping system

(depending on depth). By the third sampling date (September 24),

monocropped sorghum and the peanut-sorghum intercropping system at

depths of 135 to 165 cm were showing values of only 12 to 13 percentage

points. Peanut monoculture was a little higher with values of 14 to

15% at 135 to 165 cm. Due to the recharging effect of rainfall in

August and September, we do not know how extensive water depletion was

in the upper profiles. However, there were no significant differences

(P<0.05) in the amount of soil water extracted to a depth of 180 cm by

either monocropped or intercropped peanuts or sorghum at the second and

third gravimetric soil sampling dates (Table 2). It seems likely that

the upper 45 cm were alternately depleted and recharged during the

growing season. The fact that extensive water extraction occurred from

the lower profiles under both monocropping and intercropping systems

indicates that water was not available in the upper profiles during

peak use periods (Figures 5 and 6).

Table 2. Soil water content (mean values expressed as percent) of monocropped and intercropped peanuts and sorghum at the second and third gravimetric soil water sampling dates.

Sampling Peanuts Sorghum

Time Monocrop Intercrop Monocrop Intercrop

Second 10.40 a 10.65 a 9.80 a 11.02 a

Third 8.56 a 8.73 a 9.09 a 8.04 a Means with the same letters within each crop are not significantly different at the 5% probability level.

40

Grain and Nut Yields

Mean yields of both peanuts and sorghum grown in the two cropping

systems are shown in Table 3. Peanut yield was significantly greater

in monoculture while sorghum yield was significantly greater in the

alternate row intercrop system.

Table 3. Mean yield (kg/ha) of peanuts and sorghum grown in monoculture and alternate-row intercrop culture.

Peanuts Sorghum Monocrop Intercrop Monocrop Intercrop

541 a 176 b 3632 a 4744 b

Means with the same letters within each crop are not significantly different at 5% probability level.

Although water extraction patterns associated with the two systems were

not significantly different (Figure 7 ) , peanuts grown in alternate rows

with sorghum were obviously stressed for water at periodic intervals

between the sporadic rainfall that fell during July and August. More

frequent soil-water determinations on a regular basis (10 to 14 days)

would have probably revealed water stress in intercropped peanuts,

particularly at depths above 75 cm that is not revealed in Figures 1

and 7. A consideration of the extraction pattern for the third soil

water sampling date in Figures 2 and 7 provide adequate grounds for

speculation. It is readily apparent that soil water declines from the

165 cm depth up to the 105 cm depth (Figure 7) for both the monocropped

and intercropped peanuts, then suddenly begins increasing due to

41

recharging from rains. What is not revealed by these figures is the

extent to which soil water was extracted from the upper profile prior

to recharge. A comparison of water content at the deeper depths

(Figure 1) at the first and third sampling dates, however, reveals a

considerable decline in water content at these depths, thus it would

appear that the upper profile suffered an even greater decline than the

lower depths during this same period. Unfortunately, however, the

infrequent soil water sampling dates employed in this research neither

defined the extent of the extraction from the upper depths nor the

difference that must have been manifested between monocropped and

intercropped peanut soil moisture levels.

The significant increase in sorghum yield obtained from

intercropping over that obtained from monocropping can be accounted for

by assuming that sorghum roots extracted water from under the adjacent

peanut rows. Sorghum, a C. plant, is much more photosynthetically

efficient than the C^ peanut plants. One reason for this is because of

their ability to effectively utilize soil moisture reserves. Sorghum

plants produced deep and extensive root systems, and as a consequence

were much more competitive (12 percentage points) for soil water uptake

from emergence to physiological maturity at the 165 cm depth. Figure 7

shows the relative differences in water content between monocropped and

intercropped sorghum at physiological maturity. There are no

differences at the lower depths, and the values at the upper depths do

not explain the declines in sorghum yield between monocropping and

intercropping because of the rains which recharged the upper profile.

42

Nevertheless, it would appear that the increase in yield of

intercropped sorghum over monocropped sorghum had to result from

additional moisture extraction from under peanut rows.

It is generally accepted that intercropping will out-yield

monocropping, but there are problems in comparing the combined yield of

the intercropped species with yield of a single crop because

competition in intercropping frequently results in a different

proportion of final yields over that of a monocrop (Willey and Osiru,

1972).

According to Willey (1979), the use of the Land Equivalent Ratio

(LER) is probably the best single index for expressing the yield

advantage in an intercropping system. The LER is defined as the land

area required as a monocrop to produce the same total yield as produced

by intercropping.

The LER calculated for the present study is shown below.

LER = Y^/S^ + Yg/Sg where;

Y. and Y^ are the individual crop yields in intercropping. A D

S. and So are the yields of monocrops. A D

176/541+3632/4744

0.3254+7656 = 1.09 = LER

These calculations indicated a yield advantage of 9% for the

peanut-sorghum intercropping system over the monoculture combinations

of peanuts and sorghum.

43

Harvest Index

The harvest index defined as the ratio of the economic yield to

the biological yield (total dry weight) is shown in Table 4.

Table 4, Harvest indices (%) of monocropped and intercropped peanuts and sorghum.

Peanuts Sorghum Monocrop Intercrop Monocrop Intercrop

20 a 17 a 39 a 38 a

Means with the same letters within each crop are not significantly different at 5% probability level.

There were no significant differences in the harvest index between

monocropping and intercropping for either peanuts or sorghum. Davis

(1984) obtained similar results with cowpeas and sorghum in an

intercropping system.

Water Use Efficiency

Water use efficiency, defined as the ratio of kg of dry matter

produced per kg of water consumed, or as the ratio of dry matter

production (Y) to the amount of water transpired by a crop (T), is

shown in Table 5. Water use efficiency was calculated as the total

above ground dry matter production divided by total change in

volumetric soil water content for sorghum, and as total dry matter

production divided by total change in volumetric soil water content for

44

peanuts. Biomass from the middle three rows of crops in each plot were

used to determine the water use efficiency values. No differences were

found between monocropping or intercropping of either peanuts or

sorghum. It was not possible to make valid calculations for the water

use efficiency values under the peanut-sorghum intercropping system

because of the extraction of water by the sorghum plants from under

peanut rows. Therefore, the values presented for intercropping in

Table 5 should not be considered as absolute.

Table 5. Comparisons of water use efficiency (kg/biomass/kg water) between monocropped and intercropped peanuts and sorghum.

Peanuts Sorghum Monocrop Intercrop Monocrop Intercrop

0.0020 a 0.0022 a 0.0040 a 0.0040 a

Means with the same letters within each crop are not significantly different at 5% probability level.

Chemical Composition of Peanuts and Sorghum

Kass (1978) states that when cereal grains are intercropped with

legumes, percent carbohydrates (calories) increases in the cereals,

while protein content of legumes decreases. Results of chemical

analyses of monocropped and intercropped peanuts and sorghum are shown

in Table 6.

Table 6. Chemical composition of monocropped and intercropped peanuts and sorghum (%).

45

Peanut Monocrop Intercrop

Sorghum Monocrop Intercrop

Oil

Total proteins

48.4 a

36.4 a

2 Total carbohydrates n.a.

47.1 a

36.0 a

2 n.a.

n.a.

n.a.

79.0 a

n.a.

n.a.

76.1 a

Means with the same letters within each crop &re not significantly different at 5% probability level.

1 At approximately 3 to 4 percent moisture level.

Not analyzed

There were no significant differences in either oil or protein content

of peanuts or carbohydrate content of sorghum grown in either monocrop

or intercrop culture.

CHAPTER V

SUMMARY AND CONCLUSIONS

1. There were no significant differences (P<0.05) detected in the

amount of soil water extracted to a depth of 180 cm by either

monocropped or intercropped peanuts or sorghum.

2. There were pronounced visual differences in plant size between

monocropped and intercropped peanuts, with monocropped peanut plants

being much larger and more luxuriant than intercropped plants.

3. Nut yield of monocropped peanuts was significantly greater

(P<0.05) than nut yield of intercropped peanuts.

4. Grain yield of intercropped sorghum was greater (P<0.05) than

grain yield of monocropped sorghum.

5. The failure to detect significant differences in the soil water

extraction patterns between monocropped and intercropped peanuts and

sorghum may be accounted for by the infrequent soil water sampling

dates, and by the 55 mm of rainfall which occurred between August 9 and

September 12. The patterns associated with this rainfall would have

provided partial recharge of the upper profile on at least three

different occasions (Table 1).

6. There were no significant differences (P<0.05) in the harvest

indices between monocropped and intercropped peanuts or sorghum.

7. There were no significant differences (P<0.05) in the chemical

composition (protein and oil content) between monocropped and

intercropped peanuts or total carbohydrate content between monocropped

and intercropped sorghum.

46

47

8. A Land Equivalent Ratio (LER) of 1.09 was obtained for the peanut-

sorghum intercropping system, which indicates a 9% advantage in the

total yield of this system compared to the combined yields of the

monocropped peanuts and sorghum.

9. Based on number 8 above, it would appear that the frequent use of

intercropping systems by small family farmers in Somalia, may in fact,

have some merit in certain circumstances. There is however, much to be

learned about the compatibility of sorghum and peanuts in an

intercropping system. Thus the results of this thesis research

suggests additional research on peanut-sorghum intercropping under

local Somalian conditions might be more useful in formulating more

productive agronomic practices.

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APPENDICES

55

APPENDIX A

CARBOHYDRATE ANALYSIS

Reagents

0.2 N HCl-16.67 ml of concentrated HCl made up to 1 liter with

distilied water.

Anthrone-Reagent -- to a cold water bath 340 ml of concentrated

H^SO^ were added to 140 ml of distilled water, and cooled to room

temperature. Then 5.0 grams of thiourea and 0.25 grams of anthrone

were added to the mixture.

Glucose stock solution -- in a 100 ml volumetric flask, 1 gram of

glucose was added to make 200 ml with distilled water. 1 ml of this

solution was diluted to 100 ml in a volumetric flask. This is

equivalent to 0.1 mg glucose/ml solution.

Standard -- 1 ml of glucose solution was added to 10 ml of

anthrone reagent, and was heated with samples in the heated block.

This had a reading of approximately 0.27 on the linear absorbance on

the spectrophotometer.

Blank -- 1 ml of distilled water was added to 10 ml of anthrone

reagent and heated with samples in the block. The spectrophotometer

was set at a zero reading. This blank and all the sample and the

standard were read against it (read at the end of run).

56

57

Equipment

Boiling flask - flat bottom - 300 ml

Reflux apparatus

Funnels

Whatman No. 2 filter paper

100 ml volumetric flasks

Test tubes - 20 * 150 mm and racks, or any size that could hold 11

ml of liquid.

Acid resistant dispenser

Heater block or hot water bath

Spectrophotometer and cuvets

Cold water bath

Procedure

1. Exactly 0.5 grams of plant material was weighed using an

analytical balance, and were placed in a 300 ml boiling flask or

flask appropriate to reflux apparatus.

2. Put 60 ml of N HCl in each flask and heated for 2 hours at a

gentle boil on a reflux apparatus. Swirl samples once or twice

during extraction to wash plant material down sides of boiling

flasks.

3. Cool samples to room temperature (Ice backer). Filter through

Whatman No. 2 filter paper into 100 ml volumetric flasks.

4. Add distilled water to bring filtrate up to 100 ml. Stopper and

invert several times to mix.

58

5. Pipette 1 ml aliquot from filtrate in (100 ml volumetric flask)

diluted with 4 ml distilled water in a test tube. Mix on vortex

mixer.

6. Repipette 1 ml aliquot from dilution into another test tube. Add

10 ml anthrone reagent by acid resistant repipette dispenser to

each test tube. Mix thoroughly using a vortex mixer.

7. Heat sample, glucose standard and blank for 15-20 minutes in a

heater block set at 97°C (temperature of heater block, not sample)

or a hot water bath using a hot plate and a large (1000 ml) beaker

filled with water. Bring water to boil and put test tubes in

water bath.

8. Remove test tubes from heat and place immediately in a cold water

bath until samples cool to room temperature.

9. Remove from bath. Zero spectrophotometer using the blank. Read

absorbance of each sample and standard. Spectrophotometer set at

612 nm and warmed up.

10. Compare readings to standard set of values developed using glucose

at known concentrations.

Glucose Test Standard

1 ml of each of the following was added to 10 ml of anthrone

reagent, mixed well in a test tube and heated for 15-20 minutes in

heater block at 97°C. Absorbance was then read at 612-620 nm on the

spectrophotometer.

59

1. 1 gram of glucose (dextrose/100 ml of distilled water out

range).

2. 10 ml of solution 1 + 90 ml of distilled water = 2.712.

3. 5 ml of solution 1 + 95 ml of distilled water = 1.390.

4. 1 ml of solution 1 + 99 ml distilled water = 0.306.

% carbohydrate = Sample absorbance

approximately 0.027

APPENDIX B

OIL EXTRACTION FROM PEANUTS

1. Shelled peanuts were oven-dried at approximately 60°C overnight.

2. 10 grams of peanuts were taken as a sample from each plot and were

ground using a 20 mesh screen (20 per cm).

3. 5 grams of ground peanuts v/ere put into an extraction tube.

4. 80 millimeters of petroleum ether were added to the pre-weighed

volumetric flasks containing the ground peanuts and the mixtures

were heated for 4 hours.

5. Petroleum ether was separated from the oil by heating.

6. After heating, the flasks containing oil were weighed. The

original flask weights were subtracted to determine the weight of

oil, and the percentage of oil was determined by dividing the

weight of the oil by the weight of the original material.

% oil = ^^^'9*^^ °^ °'^ X 100 weight of original material

60

APPENDIX C

VOLUMETRIC SOIL WATER CONTENT FROM EACH DEPTH OVER THE GROWING SEASON

Table 7. Water content from each depth of peanuts and sorghum plants after emergence, after anthesis of grain sorghum plants, and at physiological maturity of sorghum plants in percentage.

Time

1

2

3

Depth (cm)

15 45 75 105 135 165

Total cm of water in profile

15 45 75 105 135 165

Total cm of water in profile

15 45 75 105 135 165

Monocrop Peanuts

%

19.0 22.0 22.5 23.1 22.5 21.0

39.03

9.0 13.5 18.0 19.5 19.5 19.5

29.70

14.0 14.2 8.0 10.5 14.0 15.0

Monocrop Sorghum

%

17.0 23.4 22.0 21.5 21.0 24.0

38.67

9.3 15.0 15.0 16.5 15.6 18.3

26.91

13.5 21.0 15.0 12.0 10.5 12.5

Intercrop Sorghum/Peanuts

19.0 25.0 23.0 23.0 21.3 24.3

40.68

9.0 15.0 16.0 18.2 19.1 21.0

29.49

13.5 18.0 12.0 10.0 12.0 13.5

Total cm of water 22.71 25.35 23.70 in profile

61

62

Table 8. Water content of monocropped sorghum and intercropped sorghum from each depth shortly after anthesis and at physiological maturity of sorghum plants expressed in percentages.

Time Depth (cm)

15 45 75 105 135 165

Monocropped Sorghum

%

9.3 15.0 15.0 16.5 15.6 18.3

Intercropped Sorghum

%

9.0 16.0 16.0 18.0 20.1 21.3

Total cm of water in p r o f i l e

26.90 30.12

15 45 75

105 135 165

13.5 21.0 10.0 12.0 10.5 12.5

13.5 19.5 12.0 9.5

12.0 13.5

Total cm of water in p r o f i l e

25.35 24.00

63

Table 9. Water uptake of monocropped peanuts and intercropped peanuts from each depth shortly after anthesis and at physiological maturity of grain sorghum plants, expressed in percentages.

Time

2

3

Total cm in profi'

Depth (cm)

15 45 75 105 135 165

of water le

15 45 75 105 135 165

Monocropped Sorghum

%

9.0 13.0 17.0 18.3 18.5 18.5

28.30

14.3 13.5 10.5 11.0 14.0 15.0

Intercropped Sorghum

%

10.5 14.0 15.5 18.5 18.0 20.0

29.95

13.5 20.3 12.0 9.5 12.0 13.5

Total cm of water in profile

23.49 24.30

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