Soil Description and Taxonomy

Supplementary materials

Soil description and taxonomy

For those who are not familiar with soil description and taxonomy, the manuals used to describe and classify the soil understudy are freely available at the following addresses:

Keys to Soil Taxonomy, Twelfth Edition (2014) http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey/class/?cid=nrcs142p2_053580

Field Book for Describing and Sampling Soils, version 3.0 http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/research/guide/?cid=nrcs142p2_054184

Mineralogical analysis

The mineralogical assemblage was qualitatively determined on the basis of the peak position using the Brindley and Brown (1980) and Dixon and Schulze (2002) databases. For quantitative estimations, the area of the peaks was calculated by multiplying peak height by the width at half- height. For each sample, a quantitative estimate was obtained for quartz and calcite. The quartz content was assessed following the internal standard addition procedure (Brindley, 1961). Based on this method, relatively pure quartz grains were recovered after the repeated digestion in H2SO4 of quartz specimens from the 3Bwb horizon. The digestion residue contained mainly quartz, with small amounts of plagioclases that were manually removed under an optical microscope. Known quantities of this “purified” quartz were added to the samples, and their contribution was quantified by subtracting the 0.333-0.335 nm peak area of specimens with no quartz addition from the area of the same peak of specimens with quartz additions. By calculating the gain in peak-area per unit of quartz mass, the relative peak-area of the natural specimens was converted to a mass basis. The calcite content was determined by the dissolution method of Bundy and Bremner (1972). The difference between 100% and the sum of quartz and calcite percentages was attributed to the x-ray recognizable minerals on the basis of the area of their primary reflections: peaks from 0.318 to

0.324 nm were ascribed to plagioclases, the peak at 7.59-7.62 nm was attributed to gypsum (whose presence was also assessed via BaCl2 test), and the peak at 0.996-1.009 nm was assigned to micas.

Clay minerals were recognized after the specimens were saturated with Mg and K, solvated with glycerol and heated at 550°C.

References

Brindley GW (1961) Quantitative Analysis of Clay Mixtures. In: Brown G (ed) The X-ray

Identification and Crystal Structures of Clay Minerals. Mineralogical Society, London, pp. 489–

Brindley GW, Brown G (1980) Crystal structures of clay minerals and their identification.

Mineralogical Society Monograph No. 5. Mineralogical Society, London.

Bundy LG, Bremner JM (1972) A simple titrimetric method for determination of inorganic carbon

in soils. Soil Sci Soc Am Proc 36: 273–275.

Dixon JB, Schulze SG (2002) Soil mineralogy with environmental applications. Number 7 in the

Soil Science Society of America Book Series, Soil Science Society of America Inc., Madison.