Soil organic matter relationships with the geotechnical-hydrological parameters, mineralogy and vegetation cover of hillslope deposits in Tuscany (Italy)

Elena Benedetta Masi,Gabriele Bicocchi,Filippo Catani

doi:10.1007/s10064-020-01819-6

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.

Highlights

Soil organic matter (SOM) is the fraction of soil consisting of plant and animal fragments at different stages of decomposition (Brady and Weil 1999)
Even if soil organic matter (SOM) has very different features in terms of weight and physical-chemical behaviour compared with inorganic components, the evaluation of SOM is not a very common practice in soil characterization for geotechnical purposes
The method we adopted in this study to measure the SOM contents allows us to measure an important fraction of the SOM that is usually lost during the analysis, i.e. the root fragments

Summary

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. As SOM mainly derives from growing in situ plants and residues of previous root systems (Bernoux et al 1998; Malkawi et al 1999), the measure of SOM could provide indications about root density and its spatial variations in soils, which is essential information to properly consider the influence of the belowground part of vegetation (the roots system) on slope stability

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Conclusion