Everything you wanted to know about soils, the basis of the crops that sustain our civilization


The soil is the sustenance of life and development. Its protection and conservation begin with the recognition and appreciation of its importance, reflected in its multiple functions, such as water infiltration, carbon capture, and the possibility of maintaining biogeochemical cycles, as well as being the habitat for immense biodiversity and, of course, for being the basis of the crops that sustain our civilization.

In this text, the soil is recognized as an element directly related to watershed logic, linked to the cumulative impacts of human activities along with the stream system (sediments, pollutants, and nutrients) that affect the quality and quantity of water, the adaptive capacity of ecosystems and the quality of life of their inhabitants. Therefore, it will end with a reflection and compilation of key elements and challenges to build the foundations for soil conservation.

Understanding the relevance of soil as life support is the first condition for its effective protection at different scales and areas, with the idea that this will translate into living, productive and resilient soils in an environment with greater pressures and increasing vulnerability to climate change. This understanding begins with knowing what soil is and how it is formed, as well as recognizing it as a finite resource that is depleting, which implies that its loss and degradation are not reversible in the course of a human lifetime.

What is soil?

Soil is a natural, dynamic, highly variable body that serves as a medium for plant growth. It consists of elements and compounds of mineral and organic nature and living organisms. It is the result of the interaction between climate and living organisms, which produce effects on the parent rock or parent material, a process that is conditioned by topography and time.

Soil is a living and complex system open to multiple interactions, from different spatial and temporal scales. The importance, quality, and functionality of soil as a natural and dynamic body derives from its role as a meeting place (interface) between rocks (lithosphere), air (atmosphere), water (hydrosphere), and living organisms (biosphere), as well as from human management.

Soils are home to at least a quarter of the world's biodiversity, are key to the carbon cycle, help us mitigate and adapt to climate change, play an important role in water management, and improve resilience to floods and droughts. José Graziano da Silva, Director-General of The Food and Agriculture Organization of the United Nations (FAO).

The soil is a system made up of the three states or phases of matter: solid, liquid, and gas. The solid phase of the soil is made up of:

The organic components, which originate from plant remains and animal residues, have a key influence on soil properties through biological fertility - stimulating biological activity by providing energy and nutrients for microorganisms -, physical fertility - improving aeration, infiltration and moisture retention - and chemical fertility - increasing the availability and reserve of nutrients for plants.

The inorganic or mineral components, which are made up of particles of different sizes and nature, from large rock fragments to tiny particles.

The liquid phase of the soil consists mainly of water and substances in solution or homogeneous mixtures (such as nitrates), or in suspension or heterogeneous mixtures (such as clays).

The gaseous phase is composed of the so-called soil atmosphere, composed mainly of elements and compounds such as nitrogen (N2), oxygen (O2), and carbon dioxide (CO2). These gases are found mainly between the pores and spaces that form in the soil.

Soils are of crucial importance for society and ecosystem functioning because of the benefits they provide through their functions. Among the functions performed by soils are:

To be a medium for plant growth. A plant obtains from the soil physical support, air, water, nutrients, temperature regulation, and protection from toxic substances. In this way, soils are the basis for the provision of biomass.

Be a regulator of water supply through infiltration, retention, and purification of water, improving its quality and quantity, as well as resistance to flooding.

Serve as a natural recycling and carbon storage system. Soils have the capacity to assimilate large quantities of organic residues and transform them into fertile soil (humus). This makes mineral nutrients available for use by plants, animals, and soil microorganisms.

Being a modifier of the atmosphere. Soils also respire, that is, they absorb and release oxygen, carbon dioxide, and other gases. Such gases exchanged between the soil and the atmosphere, have a significant influence on the composition of the atmosphere. For example, soils can absorb and contain large amounts of carbon, which helps to significantly mitigate the concentration of greenhouse gases.

Being habitat for organisms. A fistful of soil can be a habitat for millions of organisms, belonging to thousands of species, including predators, prey, producers, consumers, and parasites are likely to be found integrating the food chain. the trophic or food chain.

Being a medium for engineering and construction. Soils are one of the most widely used materials for construction.

How is soil formed?

The process of soil formation begins with the disintegration of the parent rock or parent material, which is exposed on the surface of the earth's crust, from the physical and chemical breakdown caused by rainfall, wind, exposure to the sun, and the mechanical-biological activity of plant roots, as well as by the action of bacteria and lichens.

Soil formation is determined by factors (parent rock or parent material, climate, living organisms, geomorphology or relief, and time) and processes at various temporal and spatial scales. These soil-forming factors vary across the landscape and over time and, together with human action or influence through land management, determine the direction, speed, and duration of the processes that originate or form the soil.

Soil profiles

A soil profile is the vertical slice of the ground that allows the study of the life history of the soil through a series of horizontal layers (called horizons). These layers are differentiated by changes in color, structure - or arrangement of soil particles into aggregates under different forms - and texture - or the relative percentage of mineral particles according to their size. Horizons are the result of the input of matter and energy into the soil surface by the action of the forming factors and their subsequent transformation.

Mexico has almost all the soil types that exist in the world due to the diversity of the landscape and climates, which allow the development of very diverse soils and determine a great natural richness.

Soils and organic matter

Among all the components of soils, organic matter is the one that determines their quality. The decomposition of leaves, stems, fruits, and flowers, carried out by microorganisms, fungi, and bacteria residing in the soil, gives rise to organic compounds that allow soils to recover the nutrient levels required by crops. The quantity, diversity, and activity of soil fauna and microorganisms are directly related to organic matter, which has a great influence on the physical and chemical properties of soils.

The soil's resistance to possible impacts (such as the use of agricultural machinery or raindrops) is increased by the organic matter content, increasing the infiltration rate, the soil's water availability, and its resistance to erosion. It also improves the dynamics and availability of the main plant nutrients, which contributes to better yields in agricultural crops.

Importance of soil biodiversity

Biodiversity is necessary to maintain the fundamental functions of the ecosystem, its structure, and processes. Soil biodiversity depends on the type of climate, mineral soil, and type of vegetation. In one gram of soil, there can be more than a hundred million bacteria, hundreds of protozoa, fungi, and several dozen roundworms called nematodes. In one square meter, there can be hundreds of arthropods (woodlice, spiders, centipedes, millipedes, and other insects) and dozens of earthworms. Furthermore, most plants have their roots and deposit their seeds in the soil (seed bank).

Soil organisms form complex food webs, beginning and ending with bacteria and fungi, capable of decomposing any organic material. The diversity of organisms maintains the functions and resilience (ability to recover from disturbance) of the soil. Many of the problems of soil biodiversity conservation are associated with the lack of recognition of its importance for agricultural production, so it is necessary to promote training and education on this subject.

Soil degradation

The degradation of the soil affects its state of health, which is reflected in a decrease in the capacity of the ecosystem to provide goods and services. About half of the surface of Mexico (45.2 percent) has soils affected by some type of degradation, the main causes being the change of land use towards agriculture and livestock use with overgrazing, each with 17.5 percent of the surface. Deforestation is the third cause of soil degradation with 7.4 percent of the surface.

There are two processes that can be identified in the degradation of soils: The erosion or displacement of its material, caused by water or air. The deterioration of its quality, due to physical, chemical, and biological processes. Soil degradation takes various forms from the origin of the processes that generate it, be they chemical, physical, or biological.

Soil chemical degradation is closely associated with the intensification of agriculture, which leads to a reduction in soil fertility through the loss of nutrients. Other factors leading to chemical degradation are contamination and salinization. The former, in many cases, is due to the presence of foreign substances in the soil from urban solid waste dumps, spills, industrial waste, and the deposit of acidifying compounds on the surface. The second is the accumulation of salts in the soil, occurring mainly in areas with naturally saline soils. In Mexico, 34 million hectares (17.9 percent of the national territory) present this type of chemical degradation.

Physical degradation manifests itself in compaction and erosion processes. One form of physical degradation refers fundamentally to the loss of the soil's capacity to absorb and store water through compaction, hardening (crusting), which in many cases is generated by heavy agricultural machinery or covering (urbanization). In Mexico, an estimated 10.84 million hectares (6 percent of the country's surface) are physically degraded.

Soil erosion, as a degradation process, refers to the loss of soil from the surface layer by the action of water or wind:

Water erosion is the detachment of soil particles by the action of water (impact of raindrops and runoff), which leaves it unprotected and alters its infiltration capacity, and reduces its fertility. 11.8 percent of the country's surface (22.7 million hectares) shows this type of erosion.

Wind erosion is generated by the action of the wind, in mainly arid or semi-arid areas, detaching and lifting soil particles. 9.5 percent of the country's surface (18.1 million hectares) presents this type of erosion.

A distinction must be made between geological erosion and anthropogenic or accelerated erosion. Geological erosion is a natural and inevitable process that takes place slowly in geological times, without the action of man, and is so slow that it goes unnoticed and contributes in a certain way to the formation of the relief itself and the weathering of rocks. 

Human beings have been involved in accelerated erosion, destroying protective vegetation by introducing other uses to the soil and thus breaking the natural balance, promoting the erosive action of water and wind, especially on sloping terrain, using inadequate cultivation systems and tools, cutting down forests and/or burning vegetation, building infrastructure, etc.

The impacts of erosion are manifested on-site and off-site. On-site, productivity is gradually lost and fertility is rapidly depleted, with economic and social repercussions. Off-site, the impacts are manifested in reduced water quality in the bodies where soil particles are deposited and in the siltation or reduction of the useful life of hydraulic infrastructures, such as dams.

The costs of soil erosion at both sites are high. At the plot level, a cost between US$38 and US$54 per hectare has been estimated; however, the costs outside the plot, throughout the watershed, are much higher and involve a larger population, making this phenomenon a public problem.

It is estimated that in Mexico the average soil loss is 2.76 tons/hectare/year. Water erosion is estimated at 365 million tons per year, of which 113 million tons remain in bodies of water, while 252 million tons are discharged into the sea.

Biological degradation of the soil is caused by the loss of organic matter, as well as by the reduction of fauna (bacteria, fungi, insects, small mammals), which implies a reduced capacity to support life.

In sum, various factors cause soil degradation. Some of them are environmental: there are erodible soils, that is, more prone to erosion due to their characteristics (chemical, physical and biological), the conditions of the relief, the intensity of rainfall, and the vegetation cover.

However, most of the time these degradation processes are caused by inappropriate uses of the territory, such as fertilization with chemical fertilizers, the existence of agricultural land on steep slopes, deforestation, and changes in land use, which in many times they are fostered by public policy and market pressure. It also happens that the decision to carry out various actions in the field is permeated by social, cultural, and economic conditions.

What is the soil quality and soil conservation?

Soil quality is the ability of soil to function within the limits of a natural or managed ecosystem, to sustain plant or animal productivity, to improve air and water quality, and to sustain human health. A quality soil has the capacity to:

Promote the productivity of the system without losing its physical, chemical, and biological properties (sustainable biological productivity).

Mitigate environmental pollutants and pathogens (environmental quality).

Promote the health of plants, animals and humans.

Being the basic substrate for plants, which captures, retains, and emits water and is an effective environmental filter.

The concept of soil quality is a broad concept that considers the relationship of this dynamic natural body with its environment to provide ecosystem services, that is, benefits that ecosystems give us in terms of provision of goods, regulation and support of physical processes, chemical and biological and a cultural basis for societies.

Soil conservation has, then, as its purpose the maintenance and recovery of its quality. And to achieve this, it is necessary to consider soil degradation as a social problem, based on the type of management and cultural, social, and economic factors that determine the decision to conserve or degrade them. According to the approach of integral management of hydrographic basins, it is an alternative to determine in a participatory way and at various scales, integral actions that contribute to the conservation of such a fundamental resource.

Soil conservation comprises a series of practices within the framework of production systems, which must respond to the identification of the causes of the social and environmental factors of degradation. For this, it is necessary to understand the problem from its origins, such as social conflicts, land tenure, institutional arrangements and public policies past or present, market pressures, migration processes and land abandonment, changes of production systems and others that indicate the trigger for land management decisions and degradation.

Once these problems are identified, it will be essential to know the perception of the owners of the land in a participatory way and reconcile the scientific vision with the local one, and from there to build a common vision of soil conservation. Soil conservation encompasses three types of practices: agronomic, vegetative, and mechanical or structural.

Agronomic practices seek to reduce the impact of agricultural and/or livestock activities on soil quality through modifications in agricultural or livestock methods. Intensive tillage and the use of agrochemicals diminish the natural vegetation cover and deplete the soils and their ability to recover. With these practices, the soil's moisture capacity and resistance to loss through erosion are increased.

Vegetative practices are those that incorporate vegetation, improving productive capacity, increasing biodiversity, organic matter content, and reducing soil loss. These types of practices are very important to protect the soil from the interception of raindrops and wind by trees, shrubs, or grasses.

Mechanical or structural practices are those works that are carried out with agricultural implements and tools, and consist of earthworks to reduce surface runoff and erosion on sloping land. Each of them should be chosen according to the type of soil and the value of the land to be protected, as they are expensive.

Since the main purpose of these practices is to reduce runoff, the implementation of any of them must be preceded by precise calculations of average annual and maximum runoff. It is also necessary to consider that the construction of ditches involves significant excavations that remove soil, causing impacts on soil formation and carbon loss. These practices should be carried out in a timely manner on the property and always accompanied by agronomic and vegetative practices, which protect the soil from erosion while promoting its formation and improving its quality.

The most important thing in soil conservation is that the practices are incorporated into the production systems and that, therefore, they are accepted and appropriate by the owners of the land, they are adapted to the social environment, and not the other way around, and they consider the land fitness. Without this premise, the only thing that would be achieved is the construction of subsidized and temporary practices.

Another key element is the strengthening of capacities from the training, education, and communication of management practices and models, which allow the conservation of soils from this perspective of appropriation by the owners of the land, based on a knowledge of the benefits of its conservation.

Watershed management and soil conservation

Soil conservation is closely related to land management. In a hydrographic basin - defined by its watershed and a single outlet for runoff, a logic of accumulation of impacts from human activities develops, including sediments, pollutants and / or nutrients, along its functional zones, which are mentioned then:

The upper basin or head, where erosive processes occur mainly.

The middle basin or transition zone, where both erosive phenomena and sediment transport occur.

The lower basin or emission zone, where sediment transport is the most important phenomenon.

Understanding the characteristics and properties of the soils in a basin and their relationship with water, vegetation cover, and human intervention, is necessary to build a common vision from recognizing the suitability of the territory and maintaining or improving the benefits they give us. soils as the basis of the functionality of a basin.

The integrated watershed management approach in soil conservation is conducive to guiding orderly management of the territory, which results in living and productive soils and a reduction of impacts throughout the watershed, as a strategy also to adapt in a context of vulnerability to climate change.

Reflections and challenges for soil conservation

Soils are the sustenance of our ecosystems, of crops, and of our history and culture. However, they are under increasing pressure due to the intensification and competition of their use for agriculture, forestry, livestock and the growth of cities, noting the reduction of yields, the abandonment of production units due to the deterioration of fertility, the increase in sugars and pollution problems in water bodies.

Climate change, the growth of cities, and the increase in the demand for food are elements that determine major challenges that require effective actions for soil conservation from all actors and sectors. These actions need to be prioritized and harmonized in the face of the problem that in Mexico half of the soils are degraded, which generates a social problem that begins in the plot and accumulates throughout the hydrographic basins, affecting large areas and millions of people.

Some key elements in the challenge of influencing soil conservation in Mexico are:

Promote participatory processes for soil conservation

Soil conservation actions, as a means of recovering their functions and quality, must be identified and appropriate by the community itself, based on a clear and precise diagnosis of the causes of degradation. In principle, erosion prevention actions should be prioritized.

In present degradation processes, interventions should be aimed at reducing them. In both cases, it is important to consider that the conservation processes can take several years or decades. For this reason, technical support and economic incentives for conservation must be adjusted to these temporary periods under the growing participation of landowners.

Implement soil information systems

Updating data and periodically knowing the degree of soil degradation, the pressure variables in each region or basin, and the actions for their conservation are fundamental as a product of a robust information system since what is not known can not be protected. Soil conservation and its promotion must start from a detailed knowledge of the problem and its causes at various scales, in order to influence effectively.

Develop and implement effective education, training, and communication programs and projects for soil conservation

It is essential to generate and promote systematic, significant, long-term educational processes, in different modalities and areas, which are reflected in a greater appreciation of our soils and in greater individual and collective participation in their conservation.

Harmonize agricultural, urban, and environmental policies to halt and reverse soil degradation

The design of public policies to address land degradation and its impact on the quality of life must be based on the recognition that this is a social and public problem. Likewise, they must be congruent and harmonious and be aligned in their incentives to address the problem from its causes, with the synergic support of regulatory instruments and the promotion of various sectors.

Promoting integrated watershed management as a model for soil conservation

The integrated watershed management approach is useful for planning and implementing participatory soil conservation actions, linked to a logic of cumulative impacts that are clearly identified in the degradation of soils in a watershed.

Conserving the soils of the watersheds comes from each one of us, from our determined participation in the community and from our field, to propose and implement actions. This article intends for you to be a promoter of soil conservation, as soon as you recognize its importance as a fundamental natural resource for life and development.

Source: Ministry of the Environment and Natural Resources