![]() ![]() The velocity of development of such profile is determined by climatiological and other local conditions, but one can estimate it to a period of at least 100 years. In some types of soil a soil profile (see figure) is formed due to relocation of minerals and organic material. By roots and fauna activity the top layer is mixed and aired. When weathering processes are sustained the soil layer become bigger, so that larger weeds and trees can grow.Īn important factor for soil development is the increase in the number of species and individuals of soil animals. Organic matter is further demineralized and when water passes it drains some of the components to deeper layers. When nutrients are liberated from these remains they boost the microbiological development. When plants die away their remains are added to the already present soil particles. Secretion products have a favorableeffect on the development of the microflora and microfauna in the rhizosphere (the space around the roots). Plant roots further penetrate in these cracks, and enhance on their turn the fragmentation process. In these cracks bit by bit a raw soil is formed, in which pioneer plants can survive. When mechanical weathering takes place the rock crumbles off under influence of weather and climate: Cracks in hard rocks increase in number and size due to freezing of water, leading to expansion and application of pressure, alternated with thawing of ice. Acidification results in fragmentation of solid rock or sediments. ![]() Many of the above-mentioned organisms also produce organic acids. These protons (H +) play an important role in dissolving the rock, especially limestone. The increase in amount of chemo-organotrophic organisms is proportional to the amount of plant growth.Ĭarbon dioxide that is produced by the respiration of chemo-organotrophic organisms, is transformed by the soil to bicarbonate and protons according to: They take up light enenrgy to produce organic matter (they are autotrophic) which on its turn stimulates the growth of chemo-organotrophic organisms (organisms which are partly or completely dependant of organic compounds), like bacteria and fungi. Under dry conditions the organisms can become dormant (quiescent), so that they can survive the unfavorable drought period. The population of those organims expands when water is present. When chemical weathering happens the rock dissolves or changes in chemical composition of the rock occurs under influence of organisms or substances: Any bedrock or exposed rock will be colonized by algae, lichens or mosses. In these webpages we will only focus on the second type. Roughly speaking two types of soils can be diistinguished: 1) Organic soil determined by accumulation ofmaterial in swamps of peat and 2) Mineral soils arisen from weathering of rocks (minerals). Soil development regards the complex interactions between earth material (bedrock, rocks, clay, sand), the topography (= the location of certain elements in the landscape), the climate and living organimsms. These layers are mostly in the deeper part of the profile. G: G indicates the permanent non-aerate or poorly aerate parts of the soil, characterized by the blue-gray color of ironsulfide (FeS = pyrite). G: g indicates the layers where iron, sedimented under anaerobe conditions, became oxidized later to ironoxide or rost Hypothetical soil profiles with example of codes for horizons.Ġ: Litter layer of not or little decomposed plant materialĪ1: Upper layer, dark in color, very rich in humusĪ2: Mineral layer relatively poor in clay material, iron, aluminium or all three due to leachingī1: Gradual transition layer from A2 to B2ī3: Gradual transition from B2 to a C-horizon.Ĭ: Unconsolidated earth material. oxygen of importance for the respiration of roots). liquid phase (water and the therein dissolved nutrients).free phase (minerals and organic material, among which living organisms).Three phases can be distinguished in a soil: These changes results in the formation of vertical layering: so-called soil profiles and soil horizons (zone of soil profile that can be discriminated due to its color and other morphological characteristics from other zones). This surface layer is distinct form the rocks or sediments in the deeper layers, since its composition is subject to changes under influence of physical, chemical, biological and anthropogenic factors. The term Soil indicates approximately the upper layer of the ground in which the life of plants, animals and man takes place. ![]()
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