The smell of wet earth is unmistakable and evokes something in all humans. But why do we like that smell so much? Probably because it’s more than just a scent—it’s the aroma of “active” soils, rich in organic matter, fertile, and full of life. This smell, characteristic of a biologically healthy soil, results from geosmin, a compound produced by certain bacteria. Even with our limited sense of smell, we could detect its aroma if just one spoonful of geosmin were dissolved in 200 Olympic-sized swimming pools.
Although we often imagine soil as mere handfuls of inert dirt, healthy soils are home to millions of organisms. Just a few grams of soil can contain vast biodiversity, including fungi, bacteria, animals, plants, and more. In fact, soils harbor more than half of all species on the planet. The interaction between these organisms, their waste, and the minerals in the soil results in organic matter—the material that sustains the many benefits soil provides to people.
Organic matter allows plants to grow and provide us with food, while also giving soil its structure and regulating water flow by facilitating rain infiltration and preventing rivers from drying up during dry seasons. Additionally, organic matter contains more carbon than both the atmosphere and all the world’s vegetation combined. Therefore, creating new organic matter is a key strategy in combating climate change. The carbon from the atmosphere that organic matter incorporates into the soil can remain trapped there for hundreds or even thousands of years, helping to mitigate climate change. However, if organic matter is lost, its carbon is released into the air, contributing to climate change.
Since the origins of agriculture around 12,000 years ago, human activity has often negatively impacted soils and their organic matter. Today, soil organic matter has decreased in nearly every part of the world due to deforestation, the expansion of farmland, agricultural practices, and urban development. These transformations have led to the loss of approximately 116 billion tons of carbon from the soil on a global scale—an amount equivalent to the world’s total carbon dioxide emissions over ten years.
Latin America is no exception to this pattern. The region has experienced organic matter losses averaging between 5% and 15%. However, areas that have been converted for intensive agriculture or livestock production have seen even more dramatic losses—between 40% and 75%. This is the case, for example, in the Atlantic Forest and certain parts of the Cerrado and Amazon in Brazil, the Chaco and Pampas regions of Argentina (as well as Paraguay and Uruguay), and the Andean and Orinoco regions of Colombia.
But how can we restore lost organic matter? To answer this question, we must first understand how it forms. Until a few years ago, we believed that organic matter was primarily composed of highly complex substances. Today, we know that it consists of both simple substances that decompose quickly (such as soft leaves and fine roots) and complex substances that decompose slowly (such as tough leaves, wood, and thick roots). Simple substances can decompose and release their nutrients within months, but some of them can also bind to small soil minerals, becoming trapped for millennia. Thus, simple substances provide nutrients and stability in both the short and long term. Meanwhile, complex substances, since they are not bound to soil minerals, decompose over years or decades, supplying nutrients and soil structure in the medium term.
To recover lost organic matter and maintain healthy, fertile soils, we need to incorporate diverse materials into the soil—both slow- and fast-decomposing ones. This requires a shift in certain agricultural management paradigms, particularly rethinking the widespread reliance on monocultures. Until just a couple of centuries ago, farmers cultivated multiple species in their fields. Since the mid-20th century, however, most production has specialized in monocultures (single-species crops like soy, wheat, or corn). This model aims for greater efficiency and profitability but depletes soils of much more organic matter (and nutrients) than it replenishes. As a result, many soils have lost their ability to produce food or can only do so with the help of fertilizers, herbicides, and other inputs, having lost the organic matter that made them fertile and stable.
In response to this issue, traditional practices have been revived and integrated with modern science in recent decades. This includes agroecology, agroforestry, and the use of cover crops. These practices allow soils to receive litter and roots from various species, fostering more abundant and diverse soil organism communities, which, in turn, generate diverse organic matter. They also protect soils from erosion and excessive sun exposure by keeping them covered with vegetation—offering protection against climate change, particularly in the face of extreme temperatures, rainfall, and droughts.
For example, in the Colombian Amazon, cacao cultivation integrated with fruit trees and native forest species not only maintains more fertile soils but can also improve the functioning of degraded pastureland soils by up to 40%. In Latin America’s mountainous regions, agroforestry not only conserves soil organic matter but also helps preserve biodiversity and supports the livelihoods of local farmers. Even in the grassland regions of southern Latin America, where monocultures like soy dominate, incorporating cover crops such as oats could help begin recovering the organic matter lost due to monocultures.
Soils are the silent foundation of our societies and shape our cultures. Their fertility nourishes us, and their stability protects us. More than just a resource, soils reflect our relationship with nature. Understanding their function—especially the essential role of organic matter and the organisms that form it—is key to rethinking how we manage ecosystems. Only by doing so can we ensure that soils continue to be a source of life and well-being for future generations.
*Machine translation proofread by Janaína da Silva.
Autor
Biologist and PhD in Biological Sciences from the National University of Córdoba. Professor of Biogeography at the FCEFyN of the UNC and CONICET researcher at IMBIV.
Biologist from the National University of Córdoba. PhD candidate in Biological Sciences at the Multidisciplinary Institute of Plant Biology (UNC-CONICET), where he is a member of the Ecosystems, Diversity and Sustainability group.
