Intercropping

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Intercropping
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Cropping Systems

• 1. Monoculture (one crop)
• 2. Polyculture (many crops)
• a) crops separated in time crop rotation, cover
  crops
• b) crops at same time intercropping
• c) combinations relay cropping

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Intercropping

• Uncommon in modern US agriculture
• Common in Tropics (Carroll, 1990 98 of cowpeas
  grown in Africa are intercropped)

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Intercropping

• Uncommon in modern US agriculture
• Common in Tropics
• Also called Mixed Cropping more than one crop
  at same time
• Intercropping vs monoculture --- problems with
  mechanized systems

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Types of Intercropping

• Mixtures of crops (no rows)
• Alternate rows or strips
• Relay cropping 2nd crop planted during life
  cycle of first crop

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Intercropping
Row Mixed
Smith et al., 2001
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Types of Intercropping

• Mixtures of crops (no rows)
• Alternate rows or strips
• Relay cropping 2nd crop planted during life
  cycle of first crop
• May have various combinations of these !!

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Types of Intercropping

• Mixtures of crops (no rows)
• Alternate rows or strips
• Relay cropping 2nd crop planted during life
  cycle of first crop
• Agroforestry

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Agroforestry Effects of Trees

• Shield smaller shade-tolerant crops, vines
• Stabilize temperatures
• Permanent reservoirs for parasitoids predators
• Slow decomposition of organic matter
• Supply nutrients mulch via leaf litter, etc.

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Cacao Intercrop

• Cacao main cash crop, but takes 4-5 yrs to
  produce.
• This farmer is maximizing the efficiency of his
  land by growing short duration, fast growing food
  crops that provide income and food for the
  family, as well as shade, leaf litter, and
  erosion control in cacao grove.

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Cacao Intercrop

• Plantain Bananas, Cocoyam, Papaya, Sugar cane
  (coconut and oil palms, rubber, etc.)
• Microclimate for Cacao Shade, humidity, leaf
  litter (nutrients, OM, soil moisture, weed
  control), windbreak.
• Economically important crops food for farmer

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Leucaena
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Erosion Control
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Advantages of Intercropping

• Increased yield per ha
• Less competition
• Better partitioning of resources

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Advantages of Intercropping

• Increased yield per ha
• Yield stability, greater variety of food crops in
  small farm plots
• Protection against risk and environmental
  extremes (crop diversity, mutual shading, etc.)

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Advantages of Intercropping cont.

• 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 a hindrance instead of a
  benefit.

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Potential competition or compatibility can vary
with situation, depends on

• 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

• Advantage
• If interspecific competition lt intraspecific
  competition

Interspecific between different
species Intraspecific between members of the
same species
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Determining Intercrop Advantage Land Equivalent
Ratio

• amount of monocultured land needed to produce
  same yield as intercrop

Photo Thomas Wright Photo P. E.
Hildebrand
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Land Equivalent Ratio

• amount of monocultured 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

• amount of monocultured 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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LER example
(kg/ha)
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Land Equivalent Ratio
Yield of crop 2 grown as intercrop Yield of crop
2 grown as monoculture
I1 I2 ---- ---- M1 M2
LER RY1 RY2
Corn I/M 3000/4000 Soybean
I/M 750/1000
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Land Equivalent Ratio
I1 I2 ---- ---- M1 M2
LER RY1 RY2
LER 3000/4000 750/1000 0.75 0.75 1.50
Corn Soybean
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Land Equivalent Ratio
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
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Mechanisms of Intercrop AdvantageCompetitive
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 (canopy differences in
  intercrop vs monocrop, C3 vs C4 plants)
• Partitioning soil resources (water, N, minerals,
  etc.)
• Example legume using N2 source, non-legume using
  NO3- source)

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Mechanisms of Intercrop AdvantageFacilitation

• 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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Pepper in Perennial Peanut Living Mulch
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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 - Several Hypotheses
to Explain Trend

• 1. Disruptive Crop Hypothesis 2nd plant species
  disrupts ability of pest to attack host crop
  efficiently (interferes with insect host finding
  volatiles, visual, etc.)
• 2. Natural Enemies Hypothesis more predators
  and parasites in intercrop
• 3. Trap Crop Hypothesis 2nd plant species
  attracts pest, keeping it away from the more
  vulnerable crop

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Reduced Pests in Polyculture - Several Hypotheses
to Explain Trend

• 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 - Several Hypotheses
to Explain Trend

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

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White Dill (Queen Anne Lace) Weedy Intercrop
Good Source of Natural Enemies
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Weedy Hedgerow
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Sunflower hedgerow intercropped with peppers
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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3. Trap Crop Hypothesis

• Pest 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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Trap Crop
Altieri, 1994
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Trap Crop

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

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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
• specific biologies of insects involved

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Assessment Intercropping Successful or Not?
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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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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.
• Vandermeer, 1990. Ch. 18 in Agroecology (Carroll,
  Vandermeer, and Rosset, eds.). McGraw-Hill, New
  York.