Soil is the living part of the earth's crust. When the parent rock (the oldest part of the earth's crust) degrades (notably because of the climate), it is then enriched by various organic inputs (fauna, flora, micro-organisms) as it decomposes. This phenomenon thus allows the development of a large number of living organisms (bacteria, fungi, invertebrates, plants or even certain mammals) which will themselves fulfil various functions necessary to maintain life on earth.
In this sense, women and men are also highly dependent on the soil, as it is the basis for all food production. Representing approximately 6.4% of the earth's surface, cultivable soils are therefore a rare resource that must be preserved because their over-exploitation can have irreversible consequences over several decades.
However, today, cultivable soils are increasingly threatened by multiple physical, chemical and biological degradations that have a direct impact on agricultural yields.
But what are the practices that contribute to the degradation of soil structure and how can they be avoided without reducing agricultural yields?
Catégories dominantes de couverture des sols. Source : https://www.fao.org/3/cb7654fr/cb7654fr.pdf
What is healthy soil?
Soils are home to 25% of the planet's biodiversity. It contains micro-organisms (bacteria, fungi, etc.) and a highly developed fauna (from mites to moles). These living beings take part in the food chain that allows the decomposition of organic matter. From the latter comes the presence of nutrients that are essential for plant growth. A healthy soil is therefore above all a living ecosystem that ensures long-term plant growth. There are several layers: vegetation (living or decomposing plant matter), humus (rich in decomposed organic matter, contains vital plant nutrients) and a mineral-rich topsoil (whose composition is modified by crops over the years), followed by a subsoil and bedrock.
The health of the soil is characterised by its ability to absorb water, as water supports all soil life. For this absorption to take place, it is important that the soil is porous and allows water to infiltrate deeply. This porosity is the result of the presence of organisms (such as earthworms) that decompose the material and hollow out the pores. Pesticides, by directly attacking the micro-organisms, stop this phenomenon and prevent water from hydrating and vitalizing the whole soil.
Healthy soils also ensure the functioning of the terrestrial carbon cycle. All the surface layers of the soil constitute the planet's carbon reservoirs, the most important after the oceans. Plants absorb gases from the atmosphere, including carbon dioxide, and release oxygen. This is called the process of photosynthesis. Another part will be released. Conversely, the more artificial or unvegetated the soil is, the less capacity it has to store CO2, which disrupts the carbon cycle.
Les supers pouvoir des sols. Source : https://www.adaptation-changement-climatique.gouv.fr/thematiques/sols
What causes soil depletion?
Soil is considered impoverished or degraded when it is unable to support a crop, maintain environmental quality and promote plant and animal health. This is the case, for example, when it no longer provides the nutrients necessary for plant growth or when it can no longer retain and filter water. In other words, soil is degraded when it can no longer provide the ecosystem services of provisioning, regulation and socio-cultural services.
There are natural factors (erosion, floods, drought) that contribute to soil impoverishment, but the main causes of soil degradation are anthropogenic (intensive agriculture, deforestation, overgrazing, pollution or urbanisation). Agricultural intensification (increased productivity, mechanisation, reparcelling, overgrazing and deforestation) since the Green Revolution of the 1950s has led to a continuous process of soil impoverishment. Even if this model has enabled populations to escape the risk of famine after the war, it has now reached its limits (29% of degraded soils are due to agriculture).
Focus on 4 of the main factors of soil impoverishment:
Soil erosion, whether water or wind, is one of the major causes of soil degradation. It is the process by which water or wind loosen and carry away soil particles. The damage caused is sometimes severe, the soil is cut into and cultivation becomes impossible. Even if this phenomenon is natural, it is often amplified by intensive agriculture which compacts the soil and prevents water from infiltrating, thus creating runoff phenomena.
Livestock farming can also have harmful consequences on the soil. Uncontrolled grazing can prevent vegetation from regenerating. Even when there is no overgrazing, poor consideration of natural parameters can also lead to soil impoverishment. For example, sloping ground requires more attention to the renewal of vegetation and therefore more careful grazing.
In addition, the trampling of livestock and the use of heavy mechanical equipment are responsible for soil compaction which is harmful to biodiversity. When the soil settles, porosity decreases and air and water circulate less well. This has many biological consequences: a decrease in wildlife and a lack of nutrients for plants. In Europe, the surface area of compacted land is estimated at 4% of all land.
Finally, chemical pollution (nitrate, phosphate, pesticides) of the soil also contributes to its degradation. The excessive use of agrochemicals to increase production yields is causing a loss of biodiversity. As a result of runoff and drainage, the freshwater and food we consume can become contaminated and dangerous.
Conservation agriculture, a solution to all the challenges?
After the Second World War, agriculture intensified its model by choosing to develop monoculture in order to pursue productivity and profitability. Today, the agricultural sector is faced with new constraints such as the reduction and depletion of arable land and new challenges (climate change). At the same time, it must continue to feed a growing population. The new challenge is to continue to produce while reducing the ecological footprint of the activity and preserving natural resources for future generations.
The pursuit of this objective can no longer be done according to the same model of conventional agriculture which leaves the soil bare during part of the crop, causing runoff, erosion and loss of biodiversity.
In order to fight against soil impoverishment, many farming methods are constantly being tested, improved and worked on. Among them is conservation agriculture.
This is a cultivation system that favours the maintenance of permanent soil cover. The benefits of this technique include
- Minimise the natural causes of soil impoverishment (erosion, run-off)
- Enhance biodiversity and natural biological processes above and below the soil surface.
Where there is permanent soil cover, there is a clear increase in water and nutrient use efficiency and a significant improvement in crop production. This method prevents soil depletion and the regeneration of degraded land.
Conservation agriculture advocates minimal use of mechanical equipment to limit compaction. In addition, this method often goes hand in hand with optimal application of agrochemicals and plant nutrients so that they do not interfere with or disrupt biological processes.
Conservation agriculture facilitates good agronomy through well-targeted interventions over time and improves overall land management for rainfed and irrigated production. Complemented by other good practices (use of quality seeds), conservation agriculture provides a basis for sustainable intensification of agricultural production. It opens up important possibilities for integrating crop-livestock or tree and pasture into agricultural landscapes.
In most cases, this method of farming allows for the conservation of soil properties. However, there are situations where the soil is so depleted that it is no longer a question of conservation but of regeneration in order to recreate a quality soil that is suitable for agriculture.
This is the mission that Sand to Green has set itself: to rehabilitate desert soils in order to develop agricultural plantations that will feed the women and men of tomorrow.
This is the mission that Sand to Green has set itself: to rehabilitate desert soils in order to develop agricultural plantations that will feed the women and men of tomorrow.