Frequently Asked Questions

Soil is the thin layer of material on the Earth’s surface. It is a natural resource consisting of weathered and organic materials, air and water. As it is the medium in which plants establish themselves and grow, the most widely recognized function of soil is its support for food production. Soil provides nutrients and water that are absorbed through plant roots and contribute to the regulation of water and atmospheric gases and therefore play an important role in climate regulation.

As a dynamic natural system, soils are made up of the following components: inorganic mineral particles (sand, silt and clay, gravel, stones and rock), organic matter, air, water and living organisms. The specific contribution of these different components to the soil system has a prominent effect on soil functions and depends on soil type, and its related forming factors.  Man-made materials may also form part of the soil.

There are many different factors that come together to create soils, and the process can take thousands of years to reach an equilibrium. The main soil forming factors are: climate, topography, parent material, time and biological factors (plants, animals, micro-organisms and humans). Different combinations and intensities of soil forming factors lead to different soil types.

Soil is considered a non-renewable resource because it does not renew itself at a sufficient rate in the human time frame. Indeed, one centimetre of soil can take hundreds to thousands of years to form from parent rock. 

Soils are a key enabling resource for human well-being, central to the creation of a host of products and essential ecosystem services:

• Soils are the basis for the production of food, fibers, fuel and medicinal products.
• Soils absorb, store, alter, purify and release water, both for plant growth and water supply.
• Soils interact with the atmosphere through absorption and emission of gases (e.g. carbon dioxide, methane, water vapour) and dust;
• Soils make up the greatest pool of terrestrial organic carbon (over double the organic carbon stored in vegetation).
• Soils regulate carbon, oxygen and plant nutrient cycles (N, P, K, Ca, Mg, etc.)
• Soil is the habitat of several animals and organisms such as bacteria and fungi and thus sustain biological activity, diversity and productivity.
• Soil is the habitat for seed dispersion and dissemination of the gene pool.
• Soils buffer, filter and moderate the hydrological cycle.
• Soils are the platform for urban settlement and are used as materials for construction.

Soil is where food begins! It is estimated that 95% of our food is directly and indirectly produced on our soils. Therefore, food availability relies on soils. Healthy and good quality food can only be produced if our soils are healthy. A healthy living soil is a crucial ally to food security and nutrition.

Based on the different soil properties, there are an infinite number of possible combinations that can be grouped and classified in major soil types/classes. However in the spirit of giving a short and practical answer, the following soil types are illustrated: (1) Soils with organic layers; (2) Soils showing strong human influence; (3) Soils with limitations to root growth; (4) Soils distinguished by their special iron and aluminium chemistry; (5) Soils with a dark and humus rich topsoil; (6) Soils with accumulation of soluble salts; (7) Soils with a subsoil enriched in clay; (8) Soils with little or no development and (9) Soils that are permanently flooded.  

Soils are classified on the basis of a combination of soil properties that are considered indicative of the way they have been formed. The quantity and the depth at which soil characteristics such as organic matter, clay, iron  and soluble salt content occur are some of the factors that are used to define the major soil classes. There are two internationally accepted soil classification systems, the World Reference Base (IUSS) and the Soil Taxonomy (USDA). Many countries have also developed their own national soil classification systems with the aim of organizing their national soil knowledge in the form of soil classes.

Studies report that approximately 33% of our soils are facing moderate to severe degradation. The current rate of soil degradation threatens the capacity to meet the needs of future generations, unless we reverse this trend through a concerted effort towards the sustainable management of soils.

Soil degradation is the reduction in the capacity of soil to provide ecosystem goods and services and ensure its functions over a period of time for the beneficiaries of these. Soil degradation manifests itself in various forms, such as: soil erosion, soil salinization, nutrient depletion, loss of soil biodiversity, soil pollution, soil compaction, loss organic matter, soil sealing and others.

Soil health is the capacity of soil to function as a living system. Healthy soils maintain a diverse community of soil organisms that help to control plant disease, insect and weed pests, and form beneficial symbiotic associations with plant roots. Healthy soils recycle essential plant nutrients, improve soil structure with positive repercussions for soil water and nutrient holding capacity, and ultimately improve crop production. A healthy soil does not pollute the environment; rather, it contributes to mitigate climate change by maintaining or increasing its organic carbon content.

Integrated Nutrient Management refers to the maintenance of soil fertility and plant nutrient supply at an optimum level for sustaining the desired productivity. This is achieved by optimizing the benefits from all possible sources of organic, inorganic, biological and sustainable recyclable waste components in an integrated manner, to prevent environmental impacts from nutrient outflows.

Fertilizers enrich soils content of micro- and macronutrients. However, overuse of fertilizers can result in soil and water contamination.

Soil contamination implies that the concentration of a substance (e.g. nutrient, pesticide, organic chemical, acidic or saline compound, or trace elements) in soil is higher than would naturally occur (See also soil pollution).

Sustainable management of soil resources contributes effectively to the mitigation of: 1) climate change through carbon sequestration and reduction of GHG emissions; and 2) desertification processes. It is imperative to promote sustainable soil management practices for climate change mitigation and adaptation, and resilience to changing weather patterns and extremes. Protection and management of organic carbon-rich soils and the identification of zones that are either highly vulnerable to degradation or poorly resilient is of particular concern.

Soil pollution refers to the presence of substances at concentrations above threshold levels where they become harmful to living organisms (See also soil contamination). Soils break down pollutants and limit groundwater and surface water pollution. Indeed, soils hamper pollutants leaching into the groundwater and limit their transport to surface waters. 

Nutrients in soil are recycled through the decomposition of organic matter coming from plant or animal sources. Soil microorganisms break down the organic matter and make the nutrients available to living organisms. 

The ability of a soil to store water is called soil water retention capacity and it is related to  the particle-size distribution. The particle-size distribution is also related to the ability of a soil to act as a filter. Indeed, the finer the soil particles, the higher the ability of the soil to trap pollutants and prevent them from leaching into the groundwater. 

Yes, it is true. There are billions of microorganisms such as bacteria, fungi, and protozoans in the soil, as well as thousands of insects, mites and worms. 

Soils provide a key set of fundamental ecosystem services that are crucial for our well-being. Despite their crucial role, soils have been taken for granted for a long time. Considering that human pressures on soils are reaching critical limits that jeopardize our future, there is an urgent need to raise awareness on the importance of this strategic resource.

To protect planet’s soil resources it is important to:

• Prevent and reverse soil degradation
• Practise sustainable soil management
• Prevent soil pollution
• Avoid sealing the soil
• Combat climate change
• Shrink your carbon footprint
• Preserve and increase vegetation cover
• Stop food waste
• Spread the word about the importance of soils

Soils and soil organisms provide a multitude of ecosystem services, including waste breakdown, release of nutrients, enhancement of soil structure and biodegradation of pesticides and other chemicals; in addition, they act as a sink for greenhouse gas emissions and fight pests and soil-borne plant pathogens, benefiting human and animal health including digestion and immunity. It is therefore important to maintain the genetic and species diversity of soil organisms for the continued provision of these functions.

Soils support plant growth by providing anchorage, sufficient oxygen, moisture and nutrients. Additionally, soil protects roots from drastic fluctuations in temperature by buffering temperature modification.

There is a very direct link between soil health and human health as 95% of the food we consume comes from soils. Micronutrient malnutrition is a major factor affecting the health and wellbeing of people throughout the world, especially in developing countries. Over two billion people suffer from micronutrient deficiencies, in particular vitamin A, iodine, iron and zinc, among others. Current food systems are being increasingly challenged to provide adequate, safe, diversified and nutrient-rich food for all, that contribute to healthy diets.

Food grown on nutrient-impoverished soils contributes to systemic human (protein-energy) malnutrition because of the lack of important micronutrients in the human diet such as iron, lithium, magnesium, zinc, copper and iodine. Soil health and its fertility have a direct influence on the nutrient content of food crops. The available levels of micronutrients in soils are a primary factor in determining micronutrient content of crops. If the necessary micronutrients are not present in the soil, this impacts directly on the food system by failing to deliver adequate amounts of micro­nutrients to meet human requirements. This is especially true for trace elements that are essential nutrients for humans but are not known to be essential for plant growth, such as selenium and iodine. There is evidence about the relation between deficiencies of zinc, selenium and iodine in humans and related deficiencies of those microelements in soils.

From a different angle, plants not only absorb nutrients and water from the soil but they also up-take other harmful substances present in a plant-available form in the soil solution such as heavy metals and pollutants, which can harm both humans and animals, and accumulate in the food chain.