Background Research

The Cambridge Research Projects (1986-2002)

Inga Foundation projects are based on the findings of founder Mike Hands’ long-term studies into subsistence slash-and-burn farming for Cambridge University. Research was conducted in secondary rainforest, on two acid-soil sites, in the humid tropical lowlands of Costa Rica in the late 80s and early 90s, focusing on the ecology of both intact rainforest and slash-and-burn systems on acid soils.

This research was particularly important at the time because of the confusions and contradictions which dominated the scientific literature, especially regarding the fluxes and fates of plant nutrients during and after burning.

The overall objectives were firstly to determine the key ecological constraints causing slash-and-burn to fail, and secondly, to establish the minimal ecological requirements of an alternative sustainable system.


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Research Findings

In total, we ran a series of four research and development projects in Costa Rica and later in Honduras. These yielded vital and powerful insights into why slash-and-burn works in the short term but then fails so quickly, and how the soil of slash-and-burn sites degrades. The findings are applicable to a wide range of soil types across much of Latin America.

From the 6 years of trials, we only discovered one system capable of sustaining a harvest – the agroforestry technique known as alley cropping. It worked only when using the indigenous nitrogen-fixing trees of the genus Inga rather than conventional alley-cropping species.

The studies demonstrated that phosphorus (P) is the key limiting nutrient in slash and burn systems. Inga alley cropping works sustainably because it retains and recycles the phosphorus that it inherits from the original burned forest ecosystem. In addition to this, it also retrieves, retains and recycles the small supplementary quantities of rock-phosphate, the only nutrient a subsistence farmer can afford to apply. This rock-phosphate replaces the phosphorus lost with each crop harvest.

It is important to stress that this system of Inga Alley Cropping is radically different to the original notion of alley cropping developed in West Africa that is now widely regarded as a failed hope of the 1980s.

The Inga system provides soil protection, weed control and a nutrient regime that is far superior to those provided by the conventional alley cropping species (for example, Leucaena spp, Gliricidia sp and Calliandra spp) used in the original system.

Biological Weed Control

Another key benefit of alley cropping is that it reduces weed growth to virtually zero. This is of vital importance for the farmers as it transforms the amount of labour required to achieve a successful harvest.

The key difference between alley cropping with the Inga species and with almost all others cited in the literature (the trials in Costa Rica included Gliricidia sepium and Erythrina fusca, together with 9 Inga species) is that Inga produces tough, durable mulch, thus simulating the protected soil conditions of the rainforest floor and preventing the regrowth of weeds.