Inga Alley Cropping 

Many Central American farmers still practice damaging slash-and-burn farming: slashing through rainforest and burning down patches in order to expose fertile soils to grow crops on. When the forest floor becomes exposed in this way, the nutrients are quickly stripped and fertility diminishes within a few years. Farmers have to keep moving and burning new areas of forest, damaging vast areas of land in the process. The ecosystem and habitat functions of rainforest are lost, carbon is emitted into the atmosphere through the burning (climate change!!), and increasing amounts of land lose precious fertility.

Inga Alley Cropping is a sustainable alternative, practiced here at Maya Mountain Research Farm. It’s a type of tree intercropping, which means that annual crops (corn, beans, things you’d find in a vegetable garden) are farmed amongst trees. Planting trees together with crops provides a variety of benefits that help maintain fertility and store atmospheric carbon in the soil. This practice has huge potential to combat climate change if implemented on a global scale – Tree Intercropping ranks #17 on Project Drawdown’s list of top 100 solutions to climate change (more info on this list in the ‘Book Club’ tab).

Delicate webbed leaves of an Inga Tree

Inga Alley Cropping has two components: 1) rows of Inga trees and 2) alleys between the trees for planting crops. The cycle begins with matured Inga trees shading out the alleys, preventing photosynthesis and killing off any weeds. Then, we cut back the Inga trees: larger branches can be hauled off and used for firewood, while smaller twigs and leaves are left in the alleys as mulch. The mulch helps build soil and add nutrients, like the leaf litter of a forest floor. With the trees cut back, the alleys are opened up to sunlight for photosynthesis, and we can plant seeds in the mulched alleys. This week Alfonso and I planted peanuts, okra and cucumber, but any other crop of choice would work.

Inga Trees planted in rows with newly seeded alleys between them

In a few months we’ll harvest our peanuts and maybe even plant a second crop while the Inga trees grow back again. Eventually the trees will shade out the alleys (and the weeds!) once more and we’ll restart the cycle by cutting back the trees, mulching the cuttings, and planting crop seeds. 

The same area can be used to plant the next crop because the trees helped maintain soil fertility. First, the process of mulching the tree cuttings builds soil and returns nutrients to the ground. In addition, the trees have deep roots that pull up nutrients to the surface. On top of that, Inga Trees are Nitrogen Fixers – which means they build Nitrogen in soil (important for plant growth!) through a special symbiotic relationship with bacteria around their roots. All that to say, the Inga Trees maintain soil fertility so that a farmer can continue to farm the same patch of land over and over, rather than having to slash and burn a new section of rainforest every few years. This can help protect virgin rainforest, especially as populations continue to rise.

Nodules in the Inga Tree roots harbor Nitrogen Fixing bacteria

MMRF holds workshops with local outreach groups like the Ya’axe Conservation Trust to help disseminate this technique to local subsistence farmers. From what I’ve heard, it’s been well received so far. Hopefully it gathers even more momentum moving forward!

The method was developed by Mike Hands in Costa Rica. For more info, check out:

You can also read more about tree intercropping as a solution to climate change from Project Drawdown:

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