Humus

Summary

In classical soil science, humus is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a kind of soil organic matter. It is rich in nutrients and retains moisture in the soil. Humus is the Latin word for "earth" or "ground". In agriculture, "humus" sometimes also is used to describe mature or natural compost extracted from a woodland or other spontaneous source for use as a soil conditioner. It is also used to describe a topsoil horizon that contains organic matter (humus type, humus form, or humus profile). Humus has many nutrients that improve the health of soil, nitrogen being the most important. The ratio of carbon to nitrogen (C:N) of humus commonly ranges between eight and fifteen with the median being about twelve. It also significantly affects the bulk density of soil. Humus is amorphous and lacks the "cellular structure characteristic of plants, micro-organisms or animals". Description The primary material need

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The impact of soil temperature increase on organic matter and faunal properties in a frozen calcareous scree in the French Alps

Thomas Spiegelberger

We examine the effect of natural differences in soil temperature at two locations distant by approximately 500 m in the frozen scree of La Plagne en Chartreuse (Savoy, France). We determined humus properties, soil organisms and biologically mediated soil-forming processes in screes from a low part dominated by an open pine forest (OF, 1100 m asl) and in a top part covered by a dense pine forest (DF, 1200 m asl). Our results show a soil temperature increase of about 3.8 °C in the DF plot during June to October, but similar humus morphology at both plots. Soil pH was lower, and C/N ratio higher in the DF plot. Soil faunal composition differed between DF and OF plots for some taxa. While the abundance of the Oribatid mites was higher, abundance of Collembola was significantly lower in the DF plot. As earthworm activity was scarce at the site, Oribatid mites and Collembola presumably play an important role in the humus microstructure which was confirmed by the analysis of the humus micro-aggregation. To date, changes in the pedofaunal communities did not alter the humus form which may be explained by the complexity of biotic soil interactions and the high functional redundancy of the soil fauna.

2008

Aboveground vegetation, four belowground fauna groups and humus composition have been analyzed in order to investigate the links between autotrophic and heterotrophic communities in a Norway-spruce mountain forest in Tours-en-Savoie (France). The aboveground plant community was recorded in small patches corresponding to contrasting microhabitats. Animal communities and humus layers were sampled within the same patches. The relationships between humus profile, faunistic and floristic compositional gradients were investigated by Multiple Factor Analysis (MFA) and, for the first time in ecology, a Hierarchical Multiple Factor Analysis (HMFA) was used to interpret differences among humus layers. The analysis revealed a pattern with three main groups of microhabitats. The thorough study of separate humus layers could explain this result. The interplay of plant-animal-soil interactions is likely to drive the ecosystem toward three alternative states supporting humus traditional classification between mull-mor-moder. HMFA revealed the importance of depth to explain this contrast among humus forms, using humus layers as diagnostic tools in both inert and living components. HMFA also showed contrast between unexploited and exploited parts of the forest, but the study of soil and vegetation indicate that this contrast does not only hold in forest management but also in geomorphology. RV-coefficients among the six groups of variables showed significant fauna-fauna relationships in almost all humus layers except Actinedida. Plant-soil interactions are not as strong as expected and are even weaker when the soil in question is deep. In addition, HMFA failed to show direct interactions between plant and soil fauna but, paradoxically, HMFA does suggest that indirect plant-fauna interactions are at the focus of the ecosystem strategy that leads to the differentiation of ecological niches within the forest mosaic. (c) 2012 Elsevier GmbH. All rights reserved.

Elsevier2012

Evaluating the 'conservative' behavior of stable isotopic ratios (delta C-13, delta N-15, and delta O-18) in humic acids and their reliability as paleoenvironmental proxies along a peat sequence

Luca Bragazza

Although several studies have used bogs in order to reconstruct paleoclimatic conditions and the historical trends of pollutants, scientific literature is still rather controversial about the role of ombrotrophic bogs as reliable record of past environmental changes. Consequently, understanding whether all vegetational and climatic "information" are effectively preserved in peat deposits during humification becomes an essential aspect to be tested before using bogs as natural archives.

Elsevier2011