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Characteristics of Inga Edulis

CHARACTERISTICS OF INGA EDULIS AS AN AGROFORESTRY TREE SUITABLE FOR ALLEY CROPPING

Inga edulis was selected after considerable research with many different trees, particularly other trees in the genus Inga.  The other good tree for the alley cropping was a related species, Inga oerstediana, but Inga edulis is used more and is more available.

Why is Inga edulis fit for the purpose?

  • It is a legume, which means it has root nodules with bacteria that fix nitrogen and mycorrhizae to recycle phosphorus (and other nutrients).

    Root nodules of an Inga edulis seedling, and a pruned plot showing the Inga re-growing, ground covered by Inga leaf mulch and so largely free of weeds and some of the firewood from the bigger prunings. Cameroon. Photos Gaston Bityo

  • It withstands annual severe pruning (chest height, too low can kill it).

  • Inga trees close their canopies across the alleys so well that lack of light kills the weeds.

    Dark alleys under Inga edulis trees that have closed their canopies. Cameroon. Photo Gaston Bityo

  • It grows in acidic tropical soil.
  • It tolerates some drought and flooding.
  • It grows within a not too narrow altitude range.

  • It germinates quickly, with a high rate of germination (when the seeds are planted soon after they are harvested).

    Inga nursery with good germination. Cameroon. Photo Linus Arong.

  • It survives on and re-fertilizes severely degraded soil.

  • It grows fast enough to be pruned annually, once it is established.

  • The time to reach the pruning stage is usually 18 months to 3 years, which is not excessively long.

  • It withstands repeated annual pruning for many years and keeps on and on producing a good amount of mulch, so long as it is not pruned too low (chest height is about right).

    Inga alley about 10 years old, showing line of repeated prunings. Honduras. Photo Tiiu Miller.

  • It has large thick leaves that don’t rot down too fast so that they form a permanent mulch to protect the soil so it is never left bare.  The mulch builds up year after year and retains moisture so that the crops can tolerate some drought.

    Mulch from tough Inga leaves covers the ground. Cameroon. Photo Gaston Bityo.

  • It has good resistance to pests and diseases. Nectaries on the leaf nodes feed ants that are thought to protect it from other damaging insects.

    Inga rows on steep slope planted along the contours to resist erosion. Honduras. Photo by Marco.

  • It is not poisonous.

  • It provides good firewood. Having some such valuable by-product besides being of intrinsic value makes it more acceptable to the farmers.

    Firewood from a small Inga plot (200 trees). Cameroon. Photo Gaston Bityo.

  • It has edible pulp round the seeds, another characteristics that may not be essential, but will make it more acceptable to the farmers.

  • It does not have a bad reputation as an invasive plant, particularly when used outside its original native range.

Inga edulis is a native of Western Amazon, but has been exported to many other tropical countries, mainly as a shade tree for coffee and cocoa, as it provides both shade and increased fertility, and therefore increased yields. A collaboration of Kew Gardens and the Inga Foundation failed to find a native African tree that was as good for the alley cropping, though there may be some other Asian trees that might be good.