What is Inga Alley Cropping?
Alley cropping is the growing of crops in the spaces between rows of trees. The spaces are the alleys. Inga alley cropping is the growing of crops in the spaces between rows of Inga trees.
For Inga alley cropping the trees are planted in rows (hedges) close together, with a gap, the alley, of say 4m between the rows and 50cm to a maximum of 1 metre between plants.
If trees within the alley die, they are replaced to ensure the alley stays without gaps.
The preferred species of Inga to use for this purpose is Inga edulis. Inga oerstediana is also good.
If the land is on a gradient the alleys are grown on the contours to prevent soil erosion.
Rows of Inga planted along the contours to reduce erosion.
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.
After the crops are harvested the Inga regrows and the cycle of pruning, sowing and harvest is repeated year after year.
This system increases yields and maintains the plot’s fertility long term, thus eliminating the need for the continual burning of the rainforest to get new fertile plots (slash and burn or shifting cultivation).
Rainforest Saver is at present supporting Inga projects in, Cameroon, Honduras, Ecuador and Kenya.
The Inga tree is native to many parts of Central and South America, but has been found to grow well in other parts of the world in the tropical rainforest belt. It makes a good shade tree for coffee and cocoa and has therefore been taken to many tropical countries.
The Inga is suitable because (use the + symbols to find out more):
Branches create a thick canopy cutting off light from the weeds below
Grows well on the acid soils of the tropical rainforest and on degraded land
Inga is a leguminous tree that fixes nitrogen (converts nitrogen into a form usable by plants)
Inga withstands careful pruning year after year
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 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)
Valuable cash crop of vanilla on living supports growing within an Inga alley. (Photo Copyright © FUPNAPIB, Honduras 2006)
Young maize growing in an Inga alley. Note the weed free ground. Photo by Gaston Bityo.