Soil organic matter relationships with the geotechnical-hydrological parameters, mineralogy and vegetation cover of hill
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ORIGINAL PAPER
Soil organic matter relationships with the geotechnical-hydrological parameters, mineralogy and vegetation cover of hillslope deposits in Tuscany (Italy) Elena Benedetta Masi 1
&
Gabriele Bicocchi 1,2 & Filippo Catani 1
Received: 3 May 2019 / Accepted: 24 April 2020 # The Author(s) 2020
Abstract Soil organic matter (SOM) represents a main fraction of superficial soil characterized by a mechanical-hydrological behaviour different from that of the inorganic fractions. In this study, a method to measure the SOM content was applied to 27 selected sites in Tuscany (central Italy) characterized by the presence of soil types common in the region: cambisols and regosols. The method included the contribution from root fragments, which is a fraction often neglected or underestimated in measurements, in the overall estimate of the SOM content. The retrieved SOM contents were analysed considering the vegetation cover at the sites and the selected attributes of geological interest, such as geotechnical parameters and the mineralogical composition of the soils. The SOM normalized to the bulk samples ranges between 1.8 and 8.9% by weight, with the highest values of the SOM content being associated with vegetation cover classes of forest and woodlands without shrubs. The SOM values showed close relationships with the abundance of the finer fractions (silt and clay) of the soil samples, and considering the relations with geotechnical properties, moderate correlations were found with the plasticity index, unit weight and effective friction angle, overall demonstrating the importance of considering SOM when the geotechnical and hydrological properties of soils are evaluated. Keywords Organic matter . Grain size . Soil mechanics . Vegetation cover . Geotechnical parameters
Introduction Soil organic matter (SOM) is the fraction of soil consisting of plant and animal fragments at different stages of decomposition (Brady and Weil 1999). It has a fundamental role in the global carbon cycle, acting both as a C sink and source in the pedosphere in response to land use and climate changes. The structural, dimensional and chemical characteristics of SOM affect soil properties such as the soil structure, erodibility, water infiltration rate and holding capacity (Schulte 1995; Ding et al. 2002; Krull et al. 2004). It is known that the presence of organic matter in soil affects its engineering behaviour. However, a major part of the research on the influence of
* Elena Benedetta Masi [email protected] 1
Department of Earth Sciences, University of Florence, Via G. La Pira 4, 50121 Florence, Italy
2
Institute of Geosciences and Earth Resources, CNR – National Research Council of Italy, Via G. La Pira 4, 50121 Florence, Italy
organic matter has been carried out on highly organic soils, and relatively little is known about the mechanicalhydrological effects of low organic matter contents on soil behaviour. In relatively poor organic soil, increasing the organic matter content increases the optimum moisture conten
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