Over time, an undisturbed layer of greenstone will often become covered with reddish brown Munsell color 2. They determined that the greatest impact to the land occurred in the eighteenth and nineteenth centuries, mainly from more primitive farming methods that plowed the earth more deeply than modern surface farming. What we commonly refer to as color is actually a combination of three visual measurements — chroma saturation , value light reflection , and hue wavelength dominant.
Soil color is an excellent indicator of soil structure and components, as well as characteristics of wetness and drainage. The color of soil can also reveal a lot about geological history, weather changes, and environmental factors, even before soil sample analysis.
Red, yellow, or brown tints to soil indicate the presence of iron oxide. Gracheva, R. Formation of soil diversity in the mountainous tropics and subtropics: Rocks, time, and erosion. On particle size distribution of purple soil and its chemical composition in southern Sichuan basin.
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Shouqin Zhong designed and performed the experiments, analyzed the data, wrote the paper, and prepared the figures and tables. Zhen Han performed the experiments and contributed reagents, materials, and analysis tools. Jing Du performed the experiments and reviewed drafts of the paper. En Ci performed the experiments and reviewed drafts of the paper.
Jiupai Ni contributed reagents, materials, and analysis tools and reviewed drafts of the paper. Deti Xie contributed reagents, materials, and analysis tools and reviewed drafts of the paper. Chaofu Wei conceived and designed the experiments and reviewed drafts of the paper.
As the corresponding author, he provided professional guidance on the writing. Correspondence to Chaofu Wei. Reprints and Permissions. Relationships between the lithology of purple rocks and the pedogenesis of purple soils in the Sichuan Basin, China. Sci Rep 9, Download citation. Received : 10 May Accepted : 29 August Published : 13 September Anyone you share the following link with will be able to read this content:. Sorry, a shareable link is not currently available for this article.
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Introduction Geological processes create conditions for soil development 1 , 2 , 3. Figure 1. Location of the study area. Full size image. Results Variations in paleoenvironments during the mesozoic era in the sichuan basin The parent material of purple soil is purple sedimentary rock of the Mesozoic Erathem. Figure 2. Schematic diagram of the Jurassic palaeoenvironment of the Sichuan Basin.
Figure 3. Schematic diagram of the Cretaceous palaeoenvironment of the Sichuan Basin. Table 1 The particle size distribution of the purple rocks. Full size table. Figure 4. Figure 5. Table 3 Calcium carbonate contents and pH values of the purple rocks. Table 4 Organic matter and nutrient contents of the purple rocks. Table 5 The particle size distribution of the purple soils from various purple rocks. Table 7 Calcium carbonate contents and pH values of the purple soils.
Table 8 Organic matter and nutrient contents of the purple soils. Discussion Obvious inheritance from parent rocks The purple soils, whether natural or agriculturally modified in hilly or mountainous areas, developed from the purple sedimentary rocks that were deposited and diagenetically altered in the Sichuan Basin in the Jurassic and Cretaceous periods and are characterized by obvious characteristics, such as their inherited color, particle size distribution, mineralogy, chemical composition, pH value, OM content and nutrient content.
Rapid physical weathering and pedogenetic processes Under natural conditions, it takes a long time for soils to develop on sandy rocks, limestone, and granite. Slow chemical pedogenetic process The purple soil formation is characterized by the simultaneous eluviation of base exchangeable ions in soils and their compensation via the weathering of purple rocks.
Conclusion This study was conducted in the Sichuan Basin, which is mainly covered by Triassic to Cretaceous red and purple rock series. Data Availability The original data can be obtained from the authors upon reasonable request.
References 1. Article Google Scholar 4. Article Google Scholar 5. Article Google Scholar Google Scholar View author publications. Ethics declarations Competing Interests The authors declare no competing interests. Supplementary information. Dataset 1. About this article. Cite this article Zhong, S. Copy to clipboard. One of the properties most commonly used by soil scientists to describe and classify soil horizons is color.
Color is a physical property of soils that allows us to know some of its most important characteristics, such as mineral composition, age and soil processes chemical alteration, carbonate accumulation, the presence of humified organic matter, etc.
The presence of water in the soil profile during long periods of time also affects soil color as a result of changes in the oxidation rate. Similarly, together with other physical properties, color helps us to differentiate between types of horizons of the same profile or different soil profiles. Red to greysh green colors in a soil profile as a consequence of redox processes.
The substances resulting from decomposition of the organic matter are oxidized and acquire a dark coloration. On the other hand, some of these substances can be combined with mineral substances present in the soil as a consequence of mineralization of organic materials or chemical alteration of clays such as iron oxides.
After physical and chemical alterations, organic and inorganic materials contribute to soil color in different ways and proportions and, as a result, color is a product of co-working soil processes and environmental conditions.
Soil color is related to soil processes, and is used as a diagnostic criteria for soil classification. In the WRB , for example, soil color is used as a criteria for classifying diagnostic horizons albic , anthric, fulvic, hortic, hydragric, melanic, mollic , plaggic, sombric, spodic , terric, umbric and voronic horizons must meet certain color parameters , diagnostic properties albeluvic tonguing , aridic properties , gleyic and stagnic color patterns , and diagnostic materials limnic and sulphidic materials , and is used for supporting field indentification in many cases.
Soil scientist Dr. Agricultural soils, for example, often have a color slightly influenced by organic matter, since the contribution of organic residues is much lower than in the case of forest soils. Thus, in this case, the distinction between organic and mineral horizons is much weaker, having to rely on other properties such as texture or structure. Dark and grey colors in a peaty soil in the Andean highland Ecuador. Credit: Matin Mergili. Dark or black.
Dark colors are usually due to the presence of organic matter, so that the darker the surface horizon more organic matter content is assumed this is not an exact and one-to-one correspondence. It is characteristic of the surface horizon, but can be found in other exceptional cases in Podzols, under acid conditions, transformed organic residues accumulate in the spodic horizon. Chernozems are mainly in a band that includes Croatia, northern Serbia, northern Bulgaria, southern Romania, Ukraine and Russia Europe and Asia and Canada America , where climatic conditions favor the accumulation of humus.
Dark surface horizon mollic horizon in eastern Spain. Credit: Jorge Mataix-Solera. Clear or white. Usually due to the presence of calcium and magnesium carbonates, gypsum or other more soluble salts. Carbonates may show continuous or discontinuous patterns: nodules, fine powder or films on soil aggregates pseudomycelia. Soluble salts such as NaCl, may form a surface white crust or be present in the soil matrix in a diffuse form.
Carbonates and soluble salts may be present in the parent material or accumulate in soil due to the arid climate or other processes. In other cases, light color is due to a relatively high proportion of sand quartz crystals , either in the whole soil or in profile horizons that have suffered extensive washing under very humid climate.
Light color in a cacium carbonate-rich soil southeastern Spain. White salt crust Mexico. The red color is usually a result of alteration of clay minerals, so it usually occurs in the argillic horizons.
Weathered clay minerals release aluminium and iron oxides such as hematite Fe2O3. This process is favored in hot climates with a long and intense dry season, as the Mediterranean climate. Reddish colors indicate good drainage and aeration of the soil, allowing the existence of oxidizing conditions to form oxides. Olive-cropped red soil Andalusia, Spain.
Yellowish or orange colors may be due to the presence of goethite, FeO OH , and bound to the clay and organic matter. Therefore, although composition is similar to some red soils, we know that these soils were formed under conditions of increased moisture availability red soil.
Gleyic color pattern. This color pattern is due to the presence of ferrous and ferric compounds. These colors are characteristic of Gleysols, developed under alternating reducing and oxidizing conditions. The mottled or marbled is presented as groups of spots of red, yellow and gray colors. This property appears in soils or horizons that are waterlogged for at least one part of the year.
Sometimes it may be due to the activity of plant roots living in ponding. Wet soil Egypt.
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