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SOLS, ECOSYSTEMES FRAGILES

INTRODUCTION

Les sols sont des milliers de vie particulière situés au point de rencontre de la roche (géosphère), des êtres vivants (biosphère) de l’air et des facteurs climatiques (atmosphère) ils fournissent aux plantes l’eau, et les éléments minéraux nécessaires à la production des matières organiques. Ils constituent ainsi un facteur fondamental de la production agricole. Face à un accroissement continu de la population mondiale, l’homme doit donc apprendre à gérer ces écosystèmes essentiels mais fragiles que sont les sols et pour cela chercher à comprendre leurs fonctionnements.
Les sols forestiers sont des systèmes naturellement équilibrés ; En effet, sauf sous les climats extrêmes, la végétation qui s’installe progressivement sur un sol forme en quelques décennies une forêt et cela en l’absence de toute intervention humaine. Cet écosystème forestier est stable, car un équilibre harmonieux s’établit entre le sol et la végétation. Dans l’écosystème forestier le prélèvement d’éléments biogènes dans le sol sont pratiquement compensés, surtout si la forêt est très ancienne par la restitution, qui résulte de la minéralisation de la litière (il y a équilibre entre le sol et la végétation (forêt) récolte une masse importante d’élément est exportée.
- Comment des interventions humaines peuvent elles perturbées, l’équilibre qui s’instaure naturellement entre un sol et sa couverture végétation ?
- Quels processus peuvent finalement, conduire à une destruction des sols ?
- Comment éviter l’épuisement des sols ?
RELATION ENTRE CARACTERISTIQUES DES SOLS ET PRODUCTION VEGETALE
Les sols servent de support, à la végétation ; leur profondeur influence la nature de l’écosystème ou les types des cultures qu’ils peuvent supporter, ils renferment les ressources en eaux et en ions minéraux des production primaires (plantes ou les plantes vertes) l’abondances de certaines constituants chimiques conditionne les espèces végétales, qui peuvent vivre sur un sol.
FORETS ECOSYSTEMES EQUILIBRES
Le sol des forêts, contient des matières organiques :
- La matière organique de couleur brune à noire provenant de la transformation de la matière organique sous l’action des êtres vivant du sol ;
- Eléments minéraux, ils constituent une réserve utilisée par les végétaux
UN PRELEVEMENT DANS LES RESERVES DU SOL
Grâce à leurs racines, les végétaux puisent dans la réserve minérale du sol les éléments biogènes, nécessaires à leur croissance :
- Les macroéléments (N, p, k, ca, Mg) c’est-à-dire, prélèves en quantité importante ;
- Oligoéléments (B (bore) Cu (cuivre) Zn, Mn (manganèse,…) indispensable à des doses, beaucoup plus faibles. Ces éléments biogènes ainsi extraits du sol, sont stockés dans les bois, les feuilles, les fruits, on appelle rhizosphère, partie du sol en contracta avec les racines.
RESTITUTION IMPORTANTE A PARTIR DE LA LITIERE
Chaque année la plus grande partie des éléments biogènes absorbée par les racines est restituée au sol, après la chute des feuilles et des branches mortes par la minéralisation de matière organique de la litière. On parle de recyclage, des éléments biogènes c’est-à-dire leur retour dans la réserve minérale.
EQUILIBRE REMARQUABLE ENTRE PRELEVEMENT ET APPORTS
La restitution par la litière, si elle est importante est toute fois inférieure au prélèvement par les racines (si la forêt est jeune et contient des nombreux arbres en période des fortes croissances) Ici il faut renforcer en mettant les engrais ou faisant une restitution supplémentaire. L’équilibre de la réserve du sol est finalement assuré grâce à des apports supplémentaires précipitation, production des nitrates à grâce à des bactéries utilisant l’Azote atmosphérique, solubilisation d’éléments provenant de la roche mère. Les faibles déficits de restitution sont ainsi aisément comblés par des mécanismes naturels. Les systèmes sol-forêt est donc un système en équilibre dynamique qui peut fonctionner pendant des millénaires sans que la réserve du sol en élément biogène ne s’épuise malgré le prélèvement réalisé par les végétaux. MERCI

English translation by community member amys

SOILS: FRAGILE ECOSYSTEMS

INTRODUCTION

Soils are specific life environments situated at the point where the rock (geosphere), living beings (biosphere) and the air and climate (atmosphere) meet. They provide plants with water and the mineral elements needed to produce organic matter. They are also a vital factor in agricultural production. Therefore, faced with a growing world population, humankind must learn to manage these essential yet fragile ecosystems, and for that we need to learn how they work.

The soils of the forest are naturally balanced systems. Except in extreme climates, the vegetation which gradually moves into a soil will form a forest within a few decades, without any human intervention. This forest ecosystem is stable because a harmonious balance is established between the soil and the vegetation. Within the forest ecosystem, the extraction of biogenic elements from the soil is compensated, especially if the forest is very old, by the mineralisation of leaf litter, which puts elements back into the soil (there is a balance between the soil and the vegetation). At harvest, a large amount of elements are exported.

- How can human interventions disturb the natural balance between the soil and its natural covering of vegetation?
- What processes may eventually lead to the destruction of the soils?
- How can we avoid exhausting the soils?

RELATIONSHIP BETWEEN SOIL CHARACTERISTICS AND PLANT PRODUCTION

Soils support vegetation; their depth influences the nature of the ecosystem and the types of cultures that they can support. They capture and hold water and mineral ion resources from primary producers (plants and greenery). The plant species that can live in a soil depend on the quantities of certain chemical constituents.

BALANCED FOREST ECOSYSTEMS

Forest soils contain organic matter:
- The brown-black coloured organic matter that comes from organic matter being transformed by the action of living creatures in the soil;
- Mineral elements, which form a reserve that is used by plants.

EXTRACTION OF RESERVES IN THE SOIL

With their roots, plants are able to extract the biogenic elements they need to grow from the mineral reserves of the soil, such as:

- Macro elements (N, P, K, Ca, Mg), extracted in large quantities;
- Trace elements (such as B (boron), Cu (copper), Zn, Mn (manganese)) which are essential in far smaller doses. These biogenic elements, extracted from the soil, are stored in the wood, leaves and fruits. We give the name rhizosphere to the part of the soil in contact with the roots.

ELEMENTS RETURNED TO THE SOIL BY LEAF LITTER

Each year most of the biogenic elements absorbed through the roots are put back into the soil, after the dead leaves and branches have fallen, through the mineralisation of organic matter in the litter. We talk about the biogenic elements being recycled, meaning that they return to the mineral reserve.

REMARKABLE BALANCE BETWEEN MINERALS EXTRACTED RETURNED TO THE SOIL

The amount restored by leaf litter, though large, is still less that the amount extracted by the roots (if the forest is young and contains many trees going through strong growth periods). In this case it is essential to fortify the soil using fertiliser or by supplementing the amount of elements put into the soil. The balance of the soil’s reserve is eventually ensured thanks to supplementary provision of elements, precipitation, production of nitrates by bacteria that use atmospheric nitrogen, and dissolving elements from the bedrock. Small restoration deficits are thus easily overcome via natural mechanisms. The forest-soil system is therefore a system with a dynamic balance that can work for millennia without the soil’s biogenic element reserves running out despite extraction by plants.

THANK YOU

Comments

amys's picture

Translation

SOILS: FRAGILE ECOSYSTEMS

INTRODUCTION

Soils are specific life environments situated at the point where the rock (geosphere), living beings (biosphere) and the air and climate (atmosphere) meet. They provide plants with water and the mineral elements needed to produce organic matter. They are also a vital factor in agricultural production. Therefore, faced with a growing world population, humankind must learn to manage these essential yet fragile ecosystems, and for that we need to learn how they work.

The soils of the forest are naturally balanced systems. Except in extreme climates, the vegetation which gradually moves into a soil will form a forest within a few decades, without any human intervention. This forest ecosystem is stable because a harmonious balance is established between the soil and the vegetation. Within the forest ecosystem, the extraction of biogenic elements from the soil is compensated, especially if the forest is very old, by the mineralisation of leaf litter, which puts elements back into the soil (there is a balance between the soil and the vegetation). At harvest, a large amount of elements are exported.

- How can human interventions disturb the natural balance between the soil and its natural covering of vegetation?
- What processes may eventually lead to the destruction of the soils?
- How can we avoid exhausting the soils?

RELATIONSHIP BETWEEN SOIL CHARACTERISTICS AND PLANT PRODUCTION

Soils support vegetation; their depth influences the nature of the ecosystem and the types of cultures that they can support. They capture and hold water and mineral ion resources from primary producers (plants and greenery). The plant species that can live in a soil depend on the quantities of certain chemical constituents.

BALANCED FOREST ECOSYSTEMS

Forest soils contain organic matter:
- The brown-black coloured organic matter that comes from organic matter being transformed by the action of living creatures in the soil;
- Mineral elements, which form a reserve that is used by plants.

EXTRACTION OF RESERVES IN THE SOIL

With their roots, plants are able to extract the biogenic elements they need to grow from the mineral reserves of the soil, such as:

- Macro elements (N, P, K, Ca, Mg), extracted in large quantities;
- Trace elements (such as B (boron), Cu (copper), Zn, Mn (manganese)) which are essential in far smaller doses. These biogenic elements, extracted from the soil, are stored in the wood, leaves and fruits. We give the name rhizosphere to the part of the soil in contact with the roots.

ELEMENTS RETURNED TO THE SOIL BY LEAF LITTER

Each year most of the biogenic elements absorbed through the roots are put back into the soil, after the dead leaves and branches have fallen, through the mineralisation of organic matter in the litter. We talk about the biogenic elements being recycled, meaning that they return to the mineral reserve.

REMARKABLE BALANCE BETWEEN MINERALS EXTRACTED RETURNED TO THE SOIL

The amount restored by leaf litter, though large, is still less that the amount extracted by the roots (if the forest is young and contains many trees going through strong growth periods). In this case it is essential to fortify the soil using fertiliser or by supplementing the amount of elements put into the soil. The balance of the soil’s reserve is eventually ensured thanks to supplementary provision of elements, precipitation, production of nitrates by bacteria that use atmospheric nitrogen, and dissolving elements from the bedrock. Small restoration deficits are thus easily overcome via natural mechanisms. The forest-soil system is therefore a system with a dynamic balance that can work for millennia without the soil’s biogenic element reserves running out despite extraction by plants.

THANK YOU

amys's picture

Merci Ariane, j’ai appris

Merci Ariane, j’ai appris beaucoup en traduisant cet article! C’est vrai que, quand on pense à protéger l’environnement, on pense très rarement aux sols… je suppose qu’ils ne sont pas très beaux, comme les arbres ou les grands animaux … en anglais un des mots pour sol – « dirt » - est synonyme de « saleté » - donc les sols ne paraissent pas très attractives… mais sans eux les arbres ne pourraient pas pousser, et les animaux n’auraient pas de nourriture… Surtout avec une population mondiale croissante, l’épuisement des sols va être un des grands défis du 21ème siècle … Donc c’est bien important qu’il y ait des gens pour leur défendre.

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