Breaking the Slash-and-Burn Cycle
How the Inga Model Is Helping Farmers Grow Food without Destroying Rainforest
For centuries, traditional slash-and-burn agriculture has locked tropical smallholders into a destructive cycle of forest clearing and rapid soil exhaustion. But when tropical ecologist Mike Hands set out to uncover why rainforest soils fail so quickly after burning, his 1980s research at Cambridge University laid the foundation for unlocking a permanent, regenerative alternative.
Teaming up with farmers in Honduras, Hands founded the award-winning Inga Foundation to champion Inga alley cropping—a transformative agroforestry model that uses nitrogen-fixing, phosphorus-unlocking Inga trees to restore vital nutrients, choke out weeds, and deliver consistent annual crop yields on the exact same plot of land, breaking the relentless march of deforestation.
The results have been so rewarding that the method is being adopted in larger numbers in Central America and explored in African countries.
The Futility of ‘Slash and Burn’
Slash-and-burn is an agricultural practice that involves felling parts of a forest before the dry season to take advantage of the rich woodland soil for staple crops like rice, maize, cassava, and beans.
The original vegetation is dried and burned before the next planting season, the ashes refertilizing the soil. But the crops and the tropical weather quickly exhaust vital nutrients, and by the second or third year of cultivation, yields plummet. Farmers are then forced to clear fresh sections of forest in a never-ending cycle of ecological destruction.
“The process is not sustainable and is actually keeping people in poverty and food insecurity,” Hands said in an interview with The Earth & I.
Through his Cambridge investigation in 1985, Hands found that while his colleagues agreed slash-and-burn was a dead-end agricultural process, the reasons for its failure were a mystery.
“I found to my dismay—and disgust, in a sense—that science could not explain why the fertility of soil in rainforests fails so quickly after a slash-and-burn operation,” Hands recalled.
Another slash-and-burn drawback is that when the cut biomass is burned, subsistence farm families’ health and the local environment are damaged. Weakening local ecosystems through deforestation can even change the regional climate, which makes the farming process yet more difficult. This is especially true when industrial agricultural practices enter the picture—cattle ranching, palm oil production, avocado farms, and the like.
Tropical deforestation in general accounts for 13%–21% of greenhouse gas emissions because of the CO2 released by rotting and burning trees.
Tropical rainforests cover less than 2% of the world’s surface yet are home to more than 50% of terrestrial biodiversity. But due to human activities, tropical deforestation in general accounts for 13%–21% of greenhouse gas emissions because of the CO2 released by rotting and burning trees.
Back to the 1980s
During his 1980s work as a topological surveyor and senior research assistant at Cambridge, Hands traveled to Costa Rica and worked with smallholder farmers there to investigate the cause of slash-and-burn’s sustainability failure. Analyzing soil samples from various before-and-after stages of the agricultural cycle, he found that the slashed-and-burned plots were severely deficient in phosphorus.
“Until we could explain and understand the problem, we could not think of developing a solution,” he told The Earth & I.
“The loss of phosphorus that I discovered on the sites over the seven years since the burning operation was so huge that, on its own, it would probably explain what is driving slash-and-burn agriculture and why people have to keep moving on into fresh forest, cut some more, and then move on again,” Hands said. “[It explained] why it is such a destructive, consumptive process.”
Putting Phosphorus Back in the Soil
Industrial agricultural practices would suggest that the solution is simply to buy synthetic fertilizers to make up for the loss of the essential macronutrients (nitrogen, phosphorus, and potassium).
Hands, however, wanted to find a more sustainable and long-term solution that would replenish the soil and even improve the yield. He understood that while fertilizers boost yields in the short term, they don’t truly revitalize the soil. Additionally, crops that rely on synthetic fertilizers tend to be less nutritious and sturdy compared to ones grown in naturally enriched soil. Not only that, the cost of fertilizers could be out of reach for most subsistence farmers.
“It’s never that simple to whack on the fertilizers and get lots and lots more [production],” Hands said. “It’s never that stupidly simple—and how could it be when you’re dealing with nature?”
Armed with his phosphorus discovery, his research led him to explore “alley cropping” (also known as intercropping) to improve soil fertility and crop yield. Alley cropping involves planting single parallel rows of trees or shrubs to form alleyways. Between the tree rows, cash crops are grown. This allows farmers to grow multiple plant types on the same plot, and if strategically done, the two or more species can benefit by providing each other with different necessary nutrients, improve the microclimate (like adding a bit of shade for the cash crop), and help protect one another from pests and weeds.
In fact, Hands and his colleagues would later determine that Inga trees can recapture land from invasive grass species in about 24 months.
Trees in the genus Inga were a popular choice to help shade the cash crop and deliver nutrients back to the soil at the same time.
Hands observed coffee bean alley crops in the highlands of Costa Rica and noticed that trees in the genus Inga were a popular choice to help shade the cash crop and deliver nutrients back to the soil at the same time. They are fast-growing, low-maintenance trees, and there are hundreds of tropical species within the Inga genus, all native to Central and South America.
Inga tree roots also have a strong ability to form mycorrhizal (“fungus/root”) networks with the vast web of filamentous fungi that grow underground. These symbiotic networks recycle and help prevent phosphorus leaching in rainforest environments, and they produce an acid environment that aids in releasing phosphorus from rock in the soil.
“I was very impressed with what it did to the soil … how it performed,” Hands recalled. He was so enthralled by the promise of the alley-cropping model using Inga trees that he wrote a thesis on the topic and spent the next few years looking for funding to help farmers adopt this practice. Thus, the idea that would later become the Inga Foundation was born.
Starting a Movement
Once the organization was ready to start approaching farmers, a main funder at the time encouraged them to start operations in Honduras. So, the team began work with one of Honduras’ top universities, Universidad Nacional Autónoma de Honduras, to set up Inga alley-cropping plots to continue to conduct research and demonstrate the method to local nonprofit organizations and farm families. The people there were impressed by the high yield of maize and firewood per hectare and the minimal amount of weeding required.
“By 2002, the verdict was we’ve got a winner. It worked. People liked it. It ticks all the boxes,” Hands said. The local community saw the vision and grew interested. After 20 years of research, Hands and his team had enough financial and community backing to formally launch the Inga Foundation.
Flash forward and now the organization reports working with more than 700 Honduran farm families. Hands says practically every farmer they’ve worked with has maintained use of the method.
The foundation provides all the materials and technical assistance needed to help farmers get started and only asks for them to use at least a 10th of a hectare (a quarter of an acre). “Big enough to be significant, small enough not to be too much of a nuisance if it [fails] for them,” Hands explains.
Hands said the organization doesn’t pay people to adopt their method but rather relies on its merits and a farmer-to-farmer adoption process. The Inga Foundation hires workers in Honduras to help build community connections. In fact, the chief of field operations, Abraham Martínez, and the chief agronomist, Luís Miranda, are both Honduras farmers who fell in love with the foundation’s mission. Several farm families have increased the amount of crop they can grow on their land to the extent that they’ve been able to expand to new foods to either enjoy themselves or sell.
“They’ve got food,” Hands said. “They’re not worried by El Niño because … if it was planted before the drought, they’ve got a crop. The neighbor’s crop will fail, but their crop will succeed.”
The Method’s Success
The foundation recommends planting tight hedgerows of Inga trees, which are pruned to about 1.5 meters (5 feet) in height, and spreading the clippings over the ground as mulch to nourish the soil for the cash crops and mitigate weeds. Essentially, the method duplicates the rich organic supply that the forest provides.
“If you’re going to develop a sustainable system for human consumption, you’ve got to do what the forest does,” Hands explained. “You’ve got to imitate the forest. That’s the only model of sustainability I have that could be adapted for human use.”
He said the Inga alley-cropping method actually works faster than the natural forest because when the trees get heavily pruned once a year, the cuttings are still green and blanket the ground with about 6 inches of organic matter, which slowly decomposes and protects the soil from extreme weather conditions. That’s a bigger influx of nutrients at once compared with the continuous stream of mostly dead pieces that trees would drop in the forest.
Beyond that, the only supplement the Inga Foundation recommends for farmers to buy is rock phosphate—and not much is required to make a big impact.
The Inga Foundation boasts of being one of the few organizations to positively impact 11 of [the Sustainable Development Goals], including no poverty, zero hunger, decent work, and climate action.
The Inga alley-cropping method continues to yield success. A 2024 account of Inga tree agroforestry in Honduras, published by Tropenbos International, reported a 98% tree survival rate when it observed a plot with about 5,000 Inga trees per hectare (2.5 acres) planted 50 centimeters (20 inches) apart in contour rows about 4 meters (13 feet) apart. And that was without using synthetic chemicals and minimal rock phosphate. Additionally, the Inga Foundation states that Inga alleys can provide basic food security and firewood to farmers on only 1–2 hectares (2.5–5 acres) of land where it would take about 8 rotating hectares (20 acres) of slash-and-burn to get the same results.
The nonprofit has gained the support of United Nations organizations like the Food and Agriculture Organization for providing innovative support for several of the UN’s Sustainable Development Goals. In fact, the Inga Foundation boasts of being one of the few organizations to positively impact 11 of those goals, including no poverty, zero hunger, decent work, and climate action.
An Urge to Grow
The Inga Foundation plans to continue concentrating its efforts in Honduras because Hands believes it’s better to concentrate effort on doing things well in fewer places than spreading resources too thin. That being said, the nonprofit also has smaller projects in the Congo and Madagascar, where the team is working with local experts to investigate native plants that would function like Inga trees.
“The strategy of the Inga Foundation is we probe the system scientifically. We proved it socioeconomically with the trials [and] we proved it institutionally, so that there are NGOs and social institutions—the kind of people who will roll it out—who are convinced as well,” Hands summarized.
“Finally, we wanted proof of concept at landscape scale, and that is what we’ve now achieved.”
*Becky Hoag is a freelance environmental reporter. You can find her work on her site beckyhoag.com and through her YouTube channel https://youtube.com/beckisphere.
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