Intercropping Cropping Systems 1. Monoculture (one crop) 2

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Intercropping
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Cropping Systems

• 1. Monoculture (one crop)
• 2. Polyculture (many crops)
• Separated in time crop rotation
• Same time intercropping (mixed cropping)

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Types of Intercropping

• Mixed
• Multiple crops, no rows
• Row
• Strip
• Relay cropping
• seeding a second crop in before the first crop is
  harvested.
• Agroforestry
• May be mixtures of intercropping types
• Ex strip, relay crop

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Intercropping
Row
Mixed
Strip
Smith et al., 2001
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Mixed- vanilla, cardamom, coffee, pepper under
areca and coconut palm
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Row- corn and beans
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Strip- wheat and soybean, corn and soybean
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Relay- wheat and cotton
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Intercropping-history

• The Three Sisters
• Maize, beans, squash
• Archaeological evidence going back 5,000 years.
• Common in U.S. before 1940s
• Synthetics made monoculture more economical.

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Intercropping-history and current use

• Common in Tropics
• New World Old World
• Africa
• 98 of cowpeas in Africa (Arnon 1972).
• 94 of ag land in Malawi (Edje 1979).
• South America
• 90 beans in Columbia (Gutierrez et. al. 1975).
• India
• 17 of ag land in India.
• China
• One third of land is intercropped.
• 50 of grain yield is intercropped (Tong 1994).

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Intercropping-history and current use

• Uncommon in modern U.S. agriculture.
• Large-scale and intensive.
• Mechanization.
• Agronomic recommendations dont exist.

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Benefits of Intercropping

• Increased yield per ha.
• Less competition.
• Better partitioning of resources by plants.
• Yield stability, greater variety of food crops in
  small farm plots.
• Protection against risk and environmental
  extremes (crop diversity, mutual shading, etc.).
• More efficient use of resources (land, vertical
  space, sunlight, etc.).
• Improved pest management.
• Other (improved soil quality, physical support
  for vine crops, maintain genetic diversity, etc.
  ).

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Competition or - ?

• Plant competition
• No advantage if both plant species aggressively
  pursue resources in same niche.
• Intercropping is then a hindrance instead of a
  benefit.
• Competition varies with situation.
• Crop species or cultivars.
• Density of each species.
• Arrangement (in rows, strips, etc.).
• Timing of planting of each crop (e.g., corn and
  vining beans).

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Competitive Production

• Growing two crops together can be advantageous.
• If interspecific competition lt intraspecific
  competition.
• Interspecific- between different species
• Intraspecific- between members of the same species

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Calculating Intercrop Advantage

• Land Equivalent Ratio (LER)-
• Amount of monoculture land needed to produce same
  yield as intercrop.

Photo Thomas Wright Photo P. E.
Hildebrand
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Land Equivalent Ratio (LER)

• Amount of monoculture land needed to produce same
  yield as intercrop.

Yield of crop 2 grown as intercrop Yield of crop
2 grown as monoculture
I1 I2 ---- ---- M1 M2
LER RY1 RY2
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Land Equivalent Ratio (LER)

• Amount of monoculture land needed to produce same
  yield as intercrop.
• If LER gt 1 intercrop is more efficient
• If LER lt 1 monoculture is more efficient

Yield of crop 2 grown as intercrop Yield of crop
2 grown as monoculture
I1 I2 ---- ---- M1 M2
LER RY1 RY2
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Land Equivalent Ratio (LER)
(kg/ha)
(kg/ha)
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Land Equivalent Ratio (LER)
Yield of crop 2 grown as intercrop Yield of crop
2 grown as monoculture
I1 I2 ---- ---- M1 M2
LER RY1 RY2
3000 750 ------- ----
4000 1000
Corn
Soybean
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Land Equivalent Ratio (LER)
1.5 ha of land needed to produce same amount
through monoculture
0.5 0.5 is expected just based on land area
LER 3000/4000 750/1000 0.75 0.75 1.50
Corn Soybean

• If LER gt 1 intercrop is more efficient
• If LER lt 1 monoculture is more efficient

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Mechanism of Intercrop AdvantageCompetitive
Production

• Competitive Production-
• Plants grow in same area but niches and resource
  partitioning are somewhat different.
• Together, both plants use available resources
  more efficiently.

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Competitive Production

• Partitioning light
• C4 plant in canopy, C3 plant in understory.
• Partitioning soil resources (water, N, minerals).
• Plants with different rooting patterns.
• Long tap root, shallow feeder roots.
• Example Intercropping legumes and non-legumes.
• legume using N2 source, non-legume using NO3-
  source.

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Mechanisms of Intercrop AdvantageFacilitation

• Facilitation
• One plant modifies environment for benefit of 2nd
  species.
• Soil resources and nutrients
• Example legume transfers more N into soil
  system, to the benefit of both plant species).
• Pest management
• Many examples of reduced pest incidence in
  intercrops.

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Facilitation

• Pepper in Perennial Peanut Living Mulch
• Legume facilitatesnon-legume.

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Reduced Pests in Polyculture

• Several Hypotheses to Explain Trend
• Disruptive Crop Hypothesis
• Natural Enemies Hypothesis
• Trap Crop Hypothesis

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Reduced Pests in Polyculture

• 1. Disruptive Crop Hypothesis 2nd plant
  species disrupts ability of pest to attack host
  crop efficiently (interferes with insect host
  finding volatiles, visual, etc.)

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Reduced Pests in Polyculture -

• 2. Natural Enemies Hypothesis more predators
  and parasites in intercrop.

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White Dill (Queen Anne Lace)

• A weedy intercrop is a good source of natural
  enemies.

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Weedy Hedgerow
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Sunflowers and peppers

• Intercropping enhances biological control.
• Attracts Orius spp. (minute pirate bug) and other
  beneficial insects.
• Food resources and refuge for parasitoids
  predators.
• Provide a perch for birds who also prey on
  insects.

Photo G. A. Jones
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Reduced Pests in Polyculture

• 3. Trap Crop HypothesisPest diverted away from
  cash crop to less important but more attractive
  trap crop.
• a) Density and timing of trap crop is critical
• Too low ? pest not attracted away.
• Too high ? build up pests or attract more pests
  into area.
• b) Examples
• Lygus bugs attracted from cotton to strips of
  alfalfa in California (Altieri, 1994).
• Flea beetles from collard to cruciferous weeds
  with stronger chemical attractants (Cromartie,
  1991).
• Others (Altieri, 1994, p. 33).

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Altieri, 1994
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Trap Crop

• Could increase pests and cause more trouble in
  some cases !!

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Maize and Sorghum with Molasses Grass

• Khan et. al. 1997- Nature.
• Kenya
• Intercrop with Molasses grass
• Decreased damage stem borers
• 39 mono, 4.6 inter.
• Increased parasitism of stem borers
• 5.4 mono, 20.7 inter.
• Molasses grass produces volatile that
• Repels female stem borers.
• Attracts parasitoid wasps.

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Assessment Pests and Natural Enemies in
Polyculture vs. Monoculture

• Andow (1991) summarized large number of
  polyculture vs. monoculture studies.
• Figure shows usual trends, but note exceptions.
• Results vary, depend on
• relative densities and ages of plants involved.
• biology of specific insects involved.

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Assessment Intercropping Successful or Not?
32
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Andow, 1991
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Polyculture vs. Conventional Monoculture

• Magnitude of pest reduction in polyculture may be
  small compared to insecticide treatment.
• Yields are usually more in polyculture than in
  monoculture (unsprayed).
• Yields are usually more in monoculture sprayed
  with insecticides than in polyculture.
• Difficult to design experiments that compare
  polyculture or monoculture methods often biased
  toward one method or other.

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Agroforestry

• Type of intercropping
• Cultivate trees with annual or perennial crops.
• Shares the benefits of other types of crop
  intercroppingand some additional ones.
• Drawbacks-
• Economics of long term crop
• Land ownership
• In general, adaptable to every situation.

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Agroforestry Benefits

• Shield smaller shade-tolerant crops, vines
• Stabilize temperature, slow decomposition of
  organic matter
• Permanent above and below ground structure
• Moderates extremes- wind, water
• Canopy- shades
• Root system- reduce erosion, reach deeper
  resources.
• Permanent reservoirs for parasitoids predators
• Supply nutrients mulch via leaf litter, etc.

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Mixed- banana and cacao
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Intercropping Cacao

• Cacao
• main cash crop.
• 4-5 yrs. to mature.
• Intercropping
• Maximizes land use by growing fast-growing food
  crops.
• Income
• Food
• Good microclimate for cacao.

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Intercropping Cacao

• Grown with economically important crops and food
  for farmer.
• Plantain bananas, cocoyam, papaya, sugarcane,
  coconut and oil palms, rubber, etc.
• Microclimate for Cacao Shade, humidity, leaf
  litter (nutrients, OM, soil moisture, weed
  control), windbreak.

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Leucaena

• Legume
• Tropical / subtropical
• Fast growing
• Forage
• Firewood, Fence

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Alley cropping of Leucaena
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Leucana for erosion control
Erosion Control
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References

• Text, Ch. 13, pp. 266-276.
• Altieri, 1987. Ch. 9.
• Altieri, 1994. Biodiversity and Pest Management
  in Agroecosystems. Food Products Press, New
  York.
• Andow, 1991. Pp. 257-284 in CRC Handbook of Pest
  Management in Agriculture (Pimentel, ed.). CRC
  Press, Boca Raton, FL.
• Cromartie, 1991. Pp. 183-216 in CRC Handbook of
  Pest Management in Agriculture.
• Smith et al., 2001 Environ. Entomol. 3089-100.
• Tivy, 1992. Ch. 6, pp. 111-114.
• Tong, 1994. Cropping System and cultivation
  technology 77 1-5.
• Vandermeer, 1990. Ch. 18 in Agroecology (Carroll,
  Vandermeer, and Rosset, eds.). McGraw-Hill, New
  York.
• Vandermeer, 1989. The Ecology of Intercropping.
  Cambridge University Press.