Plants have been one of the main enemies of our crops for a long time, especially in intensive farming, which has already used all the available technology and techniques to fight against them. However, Mesopotamians already used them to assess lands as fertility indicators.
When we talk about crops, we talk about changing nature to meet our needs. But, in order to control nature, first you must obey it. We need to understand that nature is ruled by some laws. If we understand how nature works, we will understand better our crops and the soil on which they are.
Soil is a natural creation resulting from the action of weather and microorganisms on the parent material or parent rock, located on the soil surface for hundreds of years. Organic farming considers the soil as a living thing which is the basis of fertility, and therefore, of our production. It is an ecosystem made of millions of organisms and, depending on our actions, we can improve it or make it worse.
Nowadays, we know that plants exude a huge amount of sugars through their roots in order to feed microorganisms which, in turn, will provide the plant with minerals. Besides, the plant selects the microorganisms that it needs depending on the mineral that it needs at any given moment. It is a millions-of-years relationship that we are just trying to understand. In any case, this hidden world under our feet is still unknown, only a very small fraction of soil microorganisms is known (2/3%).
Soil is very important, but its management from our part will make us move towards a better or worse fertility. We need to understand what it is, how it works, who lives there, how it is organised… because it is clear that the health of our soil will also be the health of our plants. And bioindicator plants will be a diagnostic tool of this health.
A fertile and biologically active soil works first with a water infiltration that feeds groundwater which, in turn, will serve as a water storage that will be available for plants when the dry season comes. There are some provisions of minerals through both, organic waste and parent material. There are some aerobic and anaerobic microorganisms (bacteria and fungi). These minerals can be stored in a clay-humic complex or change complex (fine particles of clay and humus) – the great nutrients storage in the soil –
Unfortunately, despite the years needed for soil formation, it can be destroyed in a very short time. It is the reality of soils in Europe and in the modern world, whose amount of organic matter has been reduced to half of its content. We remember that the organic matter content is what tells us whether the soil is fertile or not. And, unfortunately, it is a non-renewable resource, at least not on a human scale.
The vast majority of agricultural lands have leaching problems (the structure is lost), they also have runoff problems because there are crusts on the surface, they are unprotected, and water flows across the surface instead of infiltrating (the steeper the slope, the larger the amount of water flowing); they have erosion problems, problems related to organic matter humification (because it fossilizes, it is not available for microorganisms, either because of a lack of nitrogen when humifying, or because the weather conditions when humifying did not allow it), and physical barriers caused by the same machinery that we use to work and which blocks the minerals release. The porosity needed and wanted for the soil to have is lost.
All this soil degradation is originally caused when we destroy a forest (the spontaneous vegetation of an area) to work it as a crop. Biodiversity declines drastically (both, aerial and edaphic) and the loss of fertility, compaction, erosion, and the soil lack of capacity to carry out its basic functions, among others, storing and purifying water, begins. Desertification can be a journey without return in many cases that we must avoid (examples of this desertification is North Africa, which was considered as the breadbasket of Rome and Los Monegros, an area with holm oaks forests).
This mineral degradation also has an impact on our food and, as a result, on our health too, with micronutrients deficiencies in a large proportion (%) of the world’s population.
Therefore, the other side of the coin is to treat plants as allies. Plants have many uses and functions in our agricultural ecosystems. One of them is to prevent erosion. When the soil is covered, their roots facilitate water infiltration and prevent runoff. They facilitate the cycling of nutrients that they absorb through their roots and that they emit through their leaves, which otherwise we would be forced to provide with our work. Plants also provide organic matter which will decompose and produce carbon, and therefore, will also increase water storage capacity. This, in its aerial part, brings us biodiversity which, in turn, has an effect on soil biodiversity.
There are many benefits, regarding the biological aspects and the formation of humus, biodiversity, at an environmental level, regarding erosion, water cycling, water storage, regulation of temperature… among others. What we need to see is how we manage it so that it does not interfere in our work. However, what is clear is that maybe they are not weeds, as it was believed until recently.
Plants serve as a tool to diagnose a particular situation in our crop. Most of the diagnosis that we make today from observing the bioindicator plants of a given plot give us a desertification result. We go to the desert or we come from it and go to a better place. Depending on the diagnosis and the practices that we do, we will have to understand which is our situation, which is its context (in what direction it is going).
The diagnosis method based on bioindicator plants was developed by Gérard Ducerf (botanist and farmer), who asked himself why a plant grows here and not there. He has devoted his life to this research, and he has published, among other works, L’encyclopédie des Plantes bio-indicatrices alimentaires et médicinales (“The Encyclopaedia of Bioindicator, Edible and Medicinal Plants”), with 3 volumes.
Seeds do not germinate just like that, there must be the right conditions so that they can grow. The soil seed bank is a resource that nature has to revegetate itself quickly when a disaster strikes. 1 m3 of soil can contain from 4000 to 20000 different seeds that can be stored and preserved at least between 10 and 30 years. What breaks this latency? Different factors are involved, such as light, soil structure, soil geology, aerobic and an aerobic life, the farming practices suffered by that soil and compatibility. Each species has its latency break specific code of conditions. For this reason, identifying the species will help us understand what happens in our soil in that particular moment. The diagnosis method considers the different species that we identify, the density and the covering rate, among other things.
Therefore, it is a way to check the health status of our crops and the soil on which they are planted.

Thank you, Neus Vinyals, from the Era Association, for having let us attend the workshop about soil diagnosis from bioindicator plants (Diagnosis del Sòl a partir de les Plantes Bioindicadores) organised by the Montsant Designation of Origin (DO Montsant) on 28th April.