- The total yield per unit area can be higher than with monocultures, and soil fertility
is maintained for a longer period. - The soil is often protected more efficiently against erosion.
- Labour requirements are spread more evenly over the year.
- The food supply is also extended over a longer period, and is more varied.
Disadvantages of Mixed Cropping
Compared with monocultures:
- Mixed cropping is generally not appropriate for mechanised harvesting.
- The utilisation by plants of fertilisers and other agrochemicals is less efficient.
- The different plants can become tangled and grown together which may make
harvesting slow and tedious. - Immature crops (eg the sorghum in the example above) may be damaged during
harvest of the mature crops (the haricot beans in the example above). In this
example, the sesame and sorghum are harvested at the same time.
Maize is often grown together with cassava (manioc). Research has shown that in humid
areas the yield is often the same whether maize is grown with cassava or not. In other
words the few tonnes per hectare of cassava are a virtually free bonus.
In a study of one arid area conducted by ICRISAT (International Crops Research
Institute for the Semi Arid Tropics) near Hyderabad it was calculated that the
probability of total or nearly total crop failure of pigeon peas grown as a monoculture is
1 year in 5, and when sorghum is grown as a monoculture, 1 year in 8. When both crops
are grown, in separate fields, the chance of both crops failing falls to 1 year in 13. But
when the two crops are intercropped the failure rate falls to only 1 year in 36.
This farming technique has been developed at the IITA (International Institute for
Tropical Agriculture) in Nigeria since 1976 and has subsequently spread to most parts
of the world.
The basic system consists of various field crops growing between rows of trees,
particularly leguminous species such as Leucaena leucocephala and Sesbania
drummondii (Rattlebox, Poison Bean, Coffee Bean, Siene Bean, Rattle-bush etc).
Foliage from the trees improves the soil organic matter content, and the nitrogen
fixed in their roots—as well as other nutrients present in their foliage—increases soil
fertility. In addition, soil erosion by both wind and rain is reduced.
Alley cropping systems adapt the principles of ancient systems of bush-fallow, but
there are two major differences:
- the trees are planted and replanted at regular intervals, and not just allowed to
slowly re-grow - the trees are improved strains of fast growing legumes, and not just the local wild
species of trees, shrubs, etc.