In 8 to 36 months the canopies close over the alley. Lack of light kills the weeds. The trees are then pruned to about chest height, letting in the light. The bigger branches make valuable firewood whereas the leaves are left in the alleys to rot down to a fertile mulch.
The farmer then pokes holes into the mulch and plants his crops into the holes.
The crops grow, fed by the mulch. The crops feed on the lower layers while the latest prunings form a protective layer over the soil and roots, shielding them from both the hot sun and heavy rain. This makes it possible for the roots of both the crops and the trees to stay to a considerable extent in the top layer of soil and the mulch, thus benefiting from the food in the mulch, and escaping soil pests and toxic minerals lower down. Pruning the Inga also makes its roots die back, thus reducing competition with the crops.
Beans growing in Inga alley in Honduras on a slight slope, planted along the contours.
The Inga is suitable because (use the + symbols to find out more):
Thick Canopy
Branches create a thick canopy cutting off light from the weeds below
Soil
Grows well on the acid soils of the tropical rainforest and on degraded land
Nitrogen Fixer
Inga is a leguminous tree that fixes nitrogen (converts nitrogen into a form usable by plants)
Withstands Pruning
Inga withstands careful pruning year after year
Mycorrhizae
Inga has mycorrhizae (special fungi that grow with its roots) that take up phosphorus allowing it to be recycled instead of being washed out
Grows Fast
Grows fast enough to close the canopies across the alley in 8 – 36 months. Often ready for first pruning within 2 years
Protects Soil and Roots
Inga has thick leaves. When left on the ground after pruning, they form a thick cover that protects both soil and roots from the sun and heavy rain
Inga alley showing ground free of weeds and covered in mulch after pruning the trees. (Photo Copyright © Tiiu Miller, Honduras 2009)
Freshly pruned Inga plots. Photo from Ecuador
Pruned Inga plot rotted down to a mulch, with the Inga beginning to regrow. Note the pile of good firewood from the bigger branches. Photo by Gaston Bityo
Research has found that a major reason for the soil losing its fertility with slash and burn farming was loss of phosphorus. The special fungi (mycorrhizae) that grow with the Inga roots take up phosphorus, which then goes to the roots and into the tree. When the tree is pruned the leaves fall on the ground and rot down and phosphorus is released for the crops. Then the fungi again take up spare phosphorus. Thus the cycle is repeated time and again. The only input that has sometimes been needed is rock phosphate. An initial application of this has kept the system going for many years but to date none of the projects supported by Rainforest Saver have used or needed to use this.
Not only do the farmers grow their basic crops of maize and beans, but also they now grow cash crops with this system. Previously this was difficult because when the plot was a good distance from the farmer’s home he would not have been able to guard it, or give the crops all the attention they might need. But with the same plot being used continuously it can be near his home, thus allowing his family to help to tend and guard it, even when there are young children.
Pablo, a farmer, in his tall maize crop within his Inga alley. (Photo Copyright © Antony Melville 2007)