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AGRICULTURE AND BIOLOGY JOURNAL OF NORTH AMERICA
ISSN Print: 2151-7517, ISSN Online: 2151-7525, doi:10.5251/abjna.2010.1.5.1098.1105
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Sustainable horticultural crop production through intercropping:
The case of fruits and vegetable crops: A review
*George Ouma and Jeruto,P
Department of Botany and Horticulture, Maseno University
P. O. BOX 333 – 40105, Maseno
*Corresponding author :[email protected]
ABSTRACT
Sustainable agriculture seeks to at least use nature as the model for designing agricultural
systems. Since nature integrates her plants and animals into diverse landscape, a major tenet of
sustainable agriculture is efficiency and lack of waste products in nature. When domestication of
crops replaced hunting and gathering of food, landscape changed accordingly. By producing a
limited selection of crop plants and animals, human kind has substantially reduced the level of
biological diversity over much of the earth. There is more cooperation in nature than competition.
Cooperation is exemplified by mutually beneficial relationships that occur between species within
communities. If left undistributed and unplanted an abandoned crop field will first be colonized by
just a few species of organisms but after several years a complex community made up of many
wild species develops. Stability is reached by a community when it has reached a high level of
diversity. Diverse communities have fewer fluctuations in numbers of a given species and are
stable. The practices which promote diversity and stability on the farm are enterprise
diversification, crop rotation, use of wind breaks, provision of more habitats for microorganisms,
intercropping and integration of crop farming with livestock production. Intercropping is the
cultivation of two or more crops at the same time in the same field. Its advantages are risk
minimization, increased income and food security, reduction of soil erosion and pest and disease
control. This paper discusses the practice of intercropping in horticultural crop production to
promote sustainability. Many crop systems are discussed.
Keywords: Sustainable, horticultural, diversity, stability and crop.
INTRODUCTION:
Intercropping is the cultivation of two or more crops at
the same time in the same field. Sustainable
agriculture seeks to at least use nature as the model
for designing agricultural systems. Due to the fact
that nature integrates her plants and animals into
diverse landscape, a major tenet of sustainable
agriculture is efficiency and there are no waste
products in nature. When hunting and gathering were
replaced by domestication of crops landscape also
changed. The level of biological diversity over much
of the earth has been substantially reduced when
human kind produces a limited selection of crop
plants and animals. There is more cooperation in
nature than competition. Cooperation is exemplified
by mutually beneficial relationships that occur
between species within communities. If left
undisturbed and unplanted on abandoned crop field
will first be colonized by just a few species of
organisms but after several years a complex
community made up of many wild species develops.
Stability is reached by a community when it has
reached a high level of diversity. Diverse
communities have fewer fluctuations in numbers of a
given species and are stable. The practices which
promote diversity and stability on the farm are
enterprise diversification, crop rotation, use of wind
breaks,
provision
of
more
habitats
for
microorganisms, intercropping and integration of crop
farming with livestock production (Reddy and
Willey,1981;Reddy et al 1992). When two or more
crops are growing together, each should have
adequate space to maximize cooperation and reduce
competition between them. This is accomplished by
the following factors namely: spatial arrangement,
plant density, maturity dates of the crops grown, plant
architecture. The spatial arrangements are:
•
•
Row intercropping – Growing two or
more crops together at the same time
with at least one crop planted in rows.
Strip intercropping – Growing two or
more crops together in strips wide
Agric. Biol. J. N. Am., 2010, 1(5): 1098-1105
enough to separate crop production
using machines, but close enough to
interact.
•
Mixed cropping – Growing two or more
crops together in no distinct row
arrangement.
•
Relay intercropping – Plant a second
crop into a standing crop at a time when
the standing crop is at its reproductive
stage but before harvesting (Okigbo,
1979).
To optimize plant density, the seedling rate of each
crop on the mixture is adjusted below the full rate to
reduce competition from overcrowding. The crops will
yield well in the mixture (Hiesbick, 1980, Magaguda
et al, 1979, Prabhakar et al, 1983). Planning intercrop
with staggered maturity dates or developmental
periods utilize variations in peak resource demands
for nutrients, water and sunlight. This facilitates
harvesting and separation of grain and reduce
competition Akyempong et al 1999, Mead and Willey,
1980).
Plant architecture allows one intercrop to capture
sunlight that would not otherwise be available to
others. This is important to growth and yield of cereal
and legume crops (Reddy and Willey, 1981, Gardiner
and Craker, 1981).
To evaluate the performance of intercrop
components, the concept of Land Equivalent Ratio
(L. E. R.) is used. It measures the advantages of
using intercropping systems on combined yields of
both crops (Okigbo, 1979). It provides a standardized
basis for comparing systems under different
situations and crop combinations (Mead and
Willey,1981).
The distinct aspects of intercropping are:
•
•
•
Detailed planning
Timely planting of each crop
Adequate fertilization at optimal rate and
times
•
Effective weed, pest and disease control
•
Efficient harvesting
Planning should involve selection of crop species,
appropriate cultivars, water availability, plant
populations, spacing and labour requirements
throughout the season, tillage requirements and
predicted profitability of inter crops, timely planting,
proper fertilization, pest and disease control
(Prabhakar et al,1983,Reddy and Willey,1981).
Advantages of intercropping: There has been an
increase in grower interest in using intercropping
since it could reduce management inputs that result
in sustainable systems more efficiently using an even
potentially replenishing natural resources used during
crop production for long term management of
farmland. Intercropping has been practiced in the
developing countries of Central America, Asia and
Africa (Allen and Obura, 1983, Altier and
Liebman1994, Bekunda and Woomer, 1996 1999,
Grossman and Qualles1993, Henzel andVallis1977,
Jodha, 1979, Prabhakar et al, 1983). The advantages
of intercropping are risk minimization, effective use of
available resources, efficient use of labour, increased
crop productivity, erosion control and food security
(Bekunda and Woomer, 1996, 1999, Jodha1979,
Owuor et al,2002). There is reduction of insect/mite
pest populations due to the diversity of crops grown
and reduction of plant diseases because the distance
between plants of the same species is increased due
to the planting of other crops between them,
alteration of more beneficial insects especially when
flowering crops are included in the cropping system,
increase of total farm production and profitability and
reduction of weed population through allelopathy and
efficient crop production (Maguguda et al,1979).
Further, when the intercrop provides a good soil
cover, soil temperature will stay relatively low. This
prevents burning of the organic matter in the soil and
loss of nutrients. It also provides a microclimate that
can be favourable for associated crops. Last but not
least, in a maize-bean intercrop, for example climbing
beans can use the maize stalks for support
(Maguguda et al,1979).
Potential problems of Intercropping:
Depending on the crops intercropped, competition for
water, light and nutrients may result in lower yields.
Changes in the spatial arrangement of the crops will
reduce competition (Reddy and Willey,1981, Roger
and Dennis,1993). A larger distance between plants
reduce competition for water. Other problems are
difficulties in mechanization and increased labour
requirements
(Reddy and Willey, 1981, Roger and Dennis, 1993).
Crop rotation and Intercropping: Weed population
density and biomass production may be markedly
reduced using crop rotation (temporal diversification)
strategies. Crop rotation resulted in emerged weed
densities in test crops that were lower in comparison
to monocrop systems. In a good number of cases
seed density of weeds in crop rotation was lower
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compared to monocultures of component crops. In
intercropping systems where a main crop was
intersown with a “smother” crop species, weeds
biomass in the intercrop was lower in many cases
(Jodha,1979). When intercrops were composed of
two or more main crops, weed biomass in the
intercrop was lower than in all of the component sole
crops ( Jodha,1979).
The success of rotation systems for weed
suppression appears to be based on the use of crop
sequences that create varying patterns of resource
competition, allelopathic interference, soil disturbance
and mechanical damage to provide a stable and
frequently inhospitable environment that prevents the
proliferation of a particular weed species. Intercrops
may demonstrate weed control advantages over sole
crops in two ways. First, greater crop yield and less
weed growth may be achieved if intercrops are more
effective than sole crops in usurping resources from
weeds or suppressing weed growth through
allelopathy. Alternatively, intercrops may provide
yield advantages without suppressing weed growth
below levels observed in component sole crops if
intercrops use resources that are not exploitable by
weed or convert resources to harvestable material
more efficiently than sole crops (Jodha, 1979).
For weed suppression to occur in crop rotation and
intercropping three areas need to be researched on
namely:
1.
2.
3.
There must be continued attention to the
study of weed population dynamics and
crop-weed interference in crop rotation
and
intercropping
systems.
More
information is required on the effects of
diversification of cropping systems on
weed
longevity,
weed
seedling
emergence, weed seed production and
dormancy, agents of weed mortality,
differential resource consumption by
crops and weeds and allelopathic
interactions.
There
needs
to
be
systematic
manipulation of specific components of
rotation and intercropping systems to
isolate and improve those elements (e.g.
inter row cultivation, choice of crop
genotype) or combinations of elements
that may be especially important for
weed control (Magaguda et al,1979).
The weed-related impacts of combining
crop rotation and intercropping strategies
should be assessed through careful
study of complex farming systems and
the design and testing of new integrated
approaches.(Magaguda et al,1979)
Intercropping and soil fertility: One important
reason for intercropping is the improvement and
maintenance of fertility. An example of this is when a
cereal crop or tuber crop is intercropped with
legumes (beans, peas, ground nuts. After the
intercrop is harvested, decaying roots and fallen
leaves provide nitrogen and other nutrients for the
next crop, legumes also fix nitrogen. The crop
residues of the legumes can also be used as fodder,
by cutting and carrying them to the animals, or by
letting the animals graze the residues in the field. The
nutrients in the crop residues can then be recycled
when manure is used to fertilize crops. Legumes in
an intercrop system also provide humus in the soil,
due to decaying crop remains resulting in improved
soil structure, reducing the need for soil tillage. Water
losses, soil erosion and leaching of nutrients are also
reduced in intercropping systems due to the
improved structure and better soil cover. In
intercropping, nitrogen fixation by the legume is not
sufficient to maintain soil fertility. If chemical fertilizers
are applied, it is not necessary to use nitrogen
fertilizer on the cereal crop. Fertilizers are more
efficiently used in an intercropping system, due to the
increased amount of humus and the different rooting
systems of the crops as well as differences in the
amount of nutrients taken up (Rehman et al
2006,Rukazambuga et al 2001,Sakala et al,
2000,Trenbath,1976,Trenbath,1979,
Willey
and
Osiru,1972,1979).
DIFFERENT INTERCROPPING SYSTEMS:
Intercropping of fruit crops: In East Africa fruit
crops are usually intercropped with annual crops. For
example, banana is intercropped with food and / or
fodder crops to increase and use efficiency for small
holder farms (Clark and Francis,1985). In one study
banana was intercropped with three densities of
Grevilla robusta of 208, 313 and 0.25 trees per
hectare and it was reported that after 31/2 years the
wood volume of Grevilla robusta was highest while
banana and bean yields in the intercrop system were
unaffected Reddy et a,1992, Roger and Dennis,1993;
). Intercropping banana with sweet potato and beans
has been reported to reduce the incidence of weevils
and nematodes. (Lima and Lopez1979, Reddy et
al1992, Roger and Dennis,1993).In Kenya, an
intercrop between Maize,desmodium,alegume and
Napier grass has reduced the incidence of Striga
hermontheca( Striga) and Maize stemborer(Chilo
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partellu) (Ahmed et al,2008). In India bananas are
intercropped with potato which has led to good
returns (Okigbo,1979). Mustard has also been
intercropped with bananas in India. Other fruit trees
have also been intercropped. For example, in an
intercrop between citrus mandarin seedlings and
cucumber there was a high yield of cucumber fruit
and minimal interference in the growth of citrus
seedlings possibly due to the low growing nature of
the latter (Nataraja and Nairk,1992). In Kenya fruit
trees are intercropped with all types of short term
crops such as beans, peas, potatoes, maize, millet,
exotic and indigenous vegetables when they are still
young as a way of attaining food security and income
before the trees mature.
Vegetable crops: In an intercrop system between
cereals, beans and peas, there has been increased
yield presumably by the transfer of biologically fixed
nitrogen from the roots of legume to the root zone of
the companion crop (Akyempong et al, 1999, Gold et
al, 1999, Ndungu et al, 2003, Reddy and Willey,
1981;Nanecke et al,1989).
This biologically fixed nitrogen can reduce the need
for N from commercial fertilizers (Lima and
Lopez1979, Hiesbick, 1980). Vegetables such as
cabbage, cucumber, radish, snap bean, and broccoli
are intercropped into double rows of field maize
planted on raised soil beds. Intercropping two
vegetables with different architecture and nutritional
value such as beet and okra, pepper and onion has
been practised in tropical Asia (Okigbo, 1979). In
some areas of Africa, vegetable cropping systems
such as maize and cowpea often are practiced (Mead
and Willey, 1980). Some factors that will influence or
not whether two crops can be successfully
intercropped include plant height (Spiejer et al 2006),
the size of the leaves and the orientation and
distribution of these leaves in the plant canopy
(Sogbedji et al 2006). These variables affect the
amount of sunlight that passes through the canopies
(Grossman and Quales, 1993), which could influence
the photosynthetic rates of the leaves within the
canopy. In intercropping systems with different
canopy heights the crop in the under story needs to
be shade tolerant for the plant to be productive
(Sogbedji et al, 2006).
Land Equivalent Ratio (L. E. R.): This is a method
used to determine the effectiveness of intercropping
systems. It is the most widely used index for
measuring the advantages of intercropping systems
on combined yield of both crops. (Mandal and Roy,
1986). It is defined as the relative land area under
sole crops required to produce yields achieved in
intercropping (Trenbath, 1976). Monetary advantage
was calculated to find out the extent of monetary
advantage derived due to intercropping (Trenbath,
1979).
The L. E. R. emphasized land area without
consideration of the time the field is dedicated to
production. To correct the deficiency the L. E. R.
method was modified (Liebman and Elizabeth,.1993)
to include the duration of time the crop was on the
land from planting to harvest (ATER).
ATER = Area-Time Equivalent Ratio
ATER takes into consideration the time taken when
the crop was on the land and it is a means of
assessing yield advantages using LER as a means of
determining
productivity
(Liebman
and
Elizabeth,1993). In an intercropping between corn
with cow pea and Soya bean productivity was
increased on L. E. R. basis by 22 to 32%.
There was also an increase in productivity in an
intercropping system between wheat (T. cestirum L.)
and chick pea (cicer arientimum L). The increase was
29% ( Mandal and Roy,1986) Intercropping barley
with lentil with one irrigation and straw mulch
produced 28% more productivity, ( Ndungu,1987)
when monetary advantage was considered with one
irrigation and straw mulch ( Ndungu,1987)
For vegetable crops intercropping system to be
successful in a geographical location effective
cultural practices must be determined, with respect to
plant population. It has been reported that in an
intercropping between southern pea and sweet corn
there was no effect on the number of ears of sweet
corn per plant but yields were increased as plant
population density increased. This has also been
reported previously by other workers (Mashingaidze
et al, 2000; Trenbath, 1976, Reddy and Willey, 1981)
who observed that in a bean and maize mixture in
which the population density of maize was varied
increased maize yield was attributed to increasing
population of maize as in the study of sweet corn and
southern pea (Reddy and Willey, 1981).
Plant density and nitrogen fertilizer did not influence
the number of ears produced per plant (Reddy and
Willey, 1981)
Light interception previously has been implicated as a
major factor affecting plant growth and yield in a
cereal-legume intercrop (Grossman and Quales,
1993). In the intercropping system of southern pea
and sweet corn the reduction in component crop light
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intercepted by southern pea and sweet corn as
compared to light intercepted by the monocrop
system of those crops probably contributed to the
reduction in their respective yields (Reddy and Willey,
1981). Intercropped southern pea was more affected
by the reduction in light interception than
intercropped sweet corn hence had lower yield
(Reddy and Willey, 1981). In a previous study (Clark
and Francis, 1985), it was reported that growth of
maize and beans in an intercrop could be increased if
the planting dates of the individual crops were
staggered. In the southern pea and sweet corn
intercrop their yields were reduced when planting of
each was delayed (Reddy and Willey 1981).
Maize and legume intercropping has been done for
many years in Africa for house hold food security.
The yields in most farms have declined due to
nutrient depletion. (Clark and Francis,1985,
Grossman and Quales,1993, Hiesbick,1980). In such
an intercropping system maize gains from the N fixed
biologically by beans.
Intercropping with different legumes such as
groundnuts, cowpea in crop rotation systems has
improved yields and so is the staggering of the rows
of maize.
Combinations such as carrot-cabbage, lettucecabbage, carrot-garlic, tomato-beans, sweet potatopumpkin, maize-tomato, tomato-beans, sweet potatopumpkin and maize-sugarcane have been successful
in Kenya and elsewhere.
In some countries such as Kenya maize and pigeon
pea (cajanus cojan) are intercropped especially in
Machakos district. At the beginning of the rains,
maize and pigeon pea are planted in rows. After 5
months the maize is harvested at the time the pigeon
pea starts to flower and fruit. Pigeon pea being deep
rooted improves soil fertility through nitrogen fixation
and is also used for food security, shade and
firewood. In South Africa, Pigeon Pea is intercropped
with Maize and are planted at the same time but early
development of pigeon pea is slow and Maize is
harvested before the long duration pigeon pea begins
to form substantial biomass. After the Maize is
harvested pigeon pea grows for several more months
on residual soil moisture and produces a complete
canopy cover and produces good yields. Maize is
planted at the same spacing as the monocrop and
yields of Maize planted as an intecrop are similar to
those of sole Maize. Combining Maize and pigeon
pea reduces N and P fertilizer needs in subsequent
years( Spiejer et al,1993) Inputs of N through fallen
pigeon leaves contributes 75-90 kgNper ha which
immensely benefits a subsequent crop of Maize (
Sanchez et al,1996). Pigeon Pea is also able to
access scarce soluble P and can efficiently utilize
residual P remaining in the soil from fertilizer applied
to Maize( Bahl and Pasricha,1998).The use of pigeon
also causes significant pest and disease damage(
Allen and Obura,1983, Sogbedji et al, 2006). Other
countries practicing Maize-Pigeon pea intercropping
are South Malawi, Parts of Mozambique and
Tanzania, Benin and Southern Nigeria (Sileshi and
Mafongoya,2003)In Kenya sweet potato (ipomea
batatus) is intercropped with maize and bananas.
The leaves and stems of sweet potato are used as
cattle feed while its tubers are eaten. After a single
weeding and fertilization, sweet potato are planted in
between maize. The advantages of the sweet potatomaize-banana intercrop are a diversification of crops
and more efficient use of land. The permanent soil
cover by the sweet potato reduces weed costs and
soil erosion.
Innovations in Maize-Legume intercropping allow
farmers to grow a wide range of food legumes as
understory intercrops with Maize. Maize can be
planted at its recommended population, but every
other row is shifted to provide a wider alternate
inter_row to the legume or strip-cropped by lowering
Maize population but maintaining similar yields. This
approach permits more advantageous intercropping
with high value food legumes such as groundnuts,
green gram, soybean, etc, which are not usually
intercropped with Maize because of excessive
shedding( Woomer et al, 2004). This Intercropping
system is called MBILI( Better Interactions For
Legume Intecrops) has been reported( Sileshi and
Mafongoya,2003).This system also involves the
application of Rock Phosphate( Buresh et al,1997)
and application of fortified manure compost( Ndungu
et al,2003) to the Maize legume intercrop, it is aimed
at increasing legume productivity but the Maize
yields have also increased. In Western Kenya the
widespread recommendation is to plant seed of
Maize at a spacing of 75cm between and 30cm
within, rows resulting in a plant population of about
44000 plants per hectare from 75kg of seed. Beans
are then planted between the 75cm Maize rows. With
MBILI, the row arrangement is changed. Maize rows
are spaced as 50cm pairs that are 100cm apart (the
gap).Two rows of legumes are planted within the gap,
33cm row spacing. By staggering the rows of Maize
into a two –by-two arrangement, the same plant
populations as conventional intercrops is maintained
but the legumes are better able to compete with the
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Maize.The rows should be run on an East-West
direction on a level land. The results have been high
returns to benefits cost ratio.Similar results have
been observed with Sorghum –Legume intercropping
in Uganda.( Owuor et al,2002)
Sorghum and Millet have also been intercropped with
Cowpea in West Africa where Cowpea is used for
human food and fodder and the breeding work at
IITA( International Institute for Tropical Agriculture) is
aimed at increasing Cowpea biomass to produce
reasonable quantities of both grain and fodder with
minimal application of pesticides.(Sileshi and
Mafongoya,2003) Finally, Maize and Pumpkin have
been intercropped in Zimbabwe and reported to
reduce the number of weedings as compared to
Maize sole cropping( Mashingaidze et al,2000).High
levels of intercropping population reduced Pumpkin
vine length and harvestable leaf area per plant. This
agrees with ( Olaniyan et al, 2006)who indicated that
spacing should be increased in Pumpkin for the best
vining habit.Naturally,Pumpkin has a prostrate growth
habit and requires a lot of free space which was
lacking in the intercropping between it and Maize
resulting in reduced vine length as reported
(Mashingaidze et al,2000) However, leaf yields and
partial Leaf Area Index increased with high levels of
Pumpkin intercropping populations signifying the
importance
of
intercropping
populations
in
determining yields. Similarly, intercropping groundnut
with Pumpkin populations of 0.5,1 and 2 percent of
the groundnut population reduced groundnut yield
significantly.All the pumpkin intercropping populations
had a yield a weed suppression advantage over sole
cropping of groundnut (Mashingaidze et al,2000)
CONCLUSION:
Due to ever increasing human population especially
in Africa leading diminishing land sizes, intercropping,
with its advantages of risk minimization, reduction of
soil erosion, increased food security should be
practiced. Most crops can now be intercropped
including fruit trees. and therefore farmers with small
pieces of land should no longer worry. However
research still need to be carried particularly with
respect to row orientations and light interception and
the economic benefits as more horticultural crops are
intercropped.
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