The smell of wet earth is unmistakable and awakens something in all human beings. But why do we like that smell so much? Probably because it is more than a perfume: it is the aroma of the **diversity of “active” soils**, with **organic matter, fertile and full of life**.
This smell, that of a **biologically healthy soil**, is the result of **geosmin**, a compound produced by certain bacteria. Even with our limited **olfactory sensitivity**, we could perceive its aroma if a single spoonful of geosmin dissolved in 200 Olympic swimming pools.
## The importance of diversity in healthy soils
Although we often imagine them as simple handfuls of **inert soil**, healthy soils are home to millions of organisms. Just a few grams of soil can contain a **great biodiversity**, including fungi, bacteria, animals, plants, and more. In fact, soils host more than half of all the planet’s species.
The interaction between these organisms, their **waste, and soil minerals** results in organic matter, the material that supports the multiple **benefits of soil** for people.
Organic matter allows plants to grow and provide us with food, as well as providing structure to the soil and **regulating water flows**, facilitating rain infiltration and preventing rivers from drying up during **dry seasons**.
Furthermore, organic matter contains more carbon than the atmosphere and all the world’s vegetation combined. Therefore, forming new organic matter is a **key strategy to combat climate change**.
The **carbon from the atmosphere** that organic matter incorporates into the soil can be trapped there for hundreds or thousands of years, mitigating climate change. However, if that organic matter is lost, its carbon is released into the air, contributing to climate change.
Since the beginnings of agriculture, around 12,000 years ago, **human activity** has often negatively affected soils and their organic matter. Currently, the organic matter of the soil in almost every corner of the planet has decreased as a result of **deforestation**, the expansion of farmland, agricultural practices, and urban developments.
These transformations have led to the loss of approximately 116 billion tons of carbon from the soil globally, an amount equivalent to the **carbon dioxide emissions** produced by the entire world over 10 years.
## Strategies to recover organic matter
Latin America is not an exception to this pattern. In the region, **losses of organic matter** ranging from 5 to 15% on average have been recorded. However, natural areas that were transformed for **intensive agricultural or livestock production** show more drastic losses, ranging from 40 to 75%. This is the case, for example, in the Mata Atlántica and certain areas of the Cerrado and Amazon of Brazil, the Chaco and Pampas of Argentina (and Paraguay and Uruguay, respectively), or the Andean and Orinoco regions in Colombia.
But how can we recover lost organic matter? To answer this question, we must first understand how it is formed. Until a few years ago, we believed that organic matter was mainly composed of very complex substances.
Today we know that it is composed of both **simple substances**, which decompose quickly (such as soft leaves and fine roots), and **complex substances**, which decompose slowly (such as hard 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**, remaining trapped for millennia. Thus, simple substances provide nutrients and stability in the short and long term. On the other hand, complex substances, not trapped in soil minerals, decompose within years or decades, providing **nutrients and soil structure** in the medium term.
To recover lost organic matter and have healthy and fertile soils, we need to incorporate diverse materials into the soil, both slow and fast decomposing. This implies a change in some **agricultural management paradigms** and, in particular, rethinking agriculture where one or a few crops predominate. Until just a couple of centuries ago, farmers cultivated multiple species in their plots.
Since the mid-20th century, most production has been specialized in **monocultures** (cultivation of a single species, such as soybean, wheat, or corn). This agricultural model seeks **greater efficiency and profitability**, but in doing so, it consumes much more organic matter (and its nutrients) from the soils than it incorporates. As a result, many soils have become unable to produce food or can only do so by using fertilizers, herbicides, and other inputs, as they have lost the organic matter that made them **fertile and stable**.
## Traditional practices applied to soil
In response to this issue, in recent decades traditional practices have been recovered and revalued by integrating them into modern science. This is the case of **agroecology**, **agroforestry**, and the **use of cover crops**. These practices allow soils to receive leaf litter and roots from different species, feeding more abundant and diverse soil organism communities, forming diverse organic matter.
These practices also protect soils from erosion and insolation by keeping them covered with vegetation, and thus also protect them from the challenges of climate change, primarily extreme **temperatures, rains, and droughts**.
For example, in the Colombian Amazon, the integrated cultivation of cocoa with fruit trees and native forest species not only maintains more fertile soils but can also be used as a strategy to improve up to 40% multiple functions of degraded pasture soils.
In the mountainous systems of Latin America in general, agroforestry, in addition to conserving soil organic matter, contributes to the **conservation of biodiversity of animals and plants** in the region and, at the same time, helps sustain the livelihoods of local producers. Even in the region of the Pampean grasslands of southern Latin America, where monocultures such as soybeans predominate, the incorporation of **cover crops** such as oats would begin to recover the loss of organic matter caused by monocultures.
Soils are the silent foundation of our societies and define our cultures. Their fertility feeds us, and their stability protects us. More than a resource, soils are a reflection of **our relationship with nature**. Understanding their functioning, especially the essential role of organic matter and the organisms that make it up, is key to **rethinking how we manage ecosystems**. Only then will we ensure that soils remain a source of diversity, life, and well-being for future generations.
*Authors: Natalia Pérez-Harguindeguy and Franco Fernández-Catinot/Latinoamérica21*
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