Boletín de la Sociedad Geológica Mexicana Volumen 71, núm. 1, 2019, p. 11- 20 http://dx.doi.org/10.18268/BSGM2019v71n1a2

A micromorphological analysis for quantifying structure descriptors in a young constructed Technosol 

Françoise Watteau¹, Nouhou Salifou Jangorzo^1,2, Christophe Schwartz¹

¹ Laboratoire Sols et Environnement, UL-INRA UMR 1120, Vandœuvre-lès-Nancy, 54518, France.

² Université Dan Dicko Dankoulodo de Maradi, Maradi, BP 465 ADS, Niger.

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Abstract

Evaluating soil structure dynamics is a major challenge when analysing or modelling pedogenesis. Constructed Technosols are considered, by definition, to be good candidates for pedogenetic studies, insofar as their initial characteristics and implementation conditions are controlled. Thus, we developed an approach based on image analysis of soil microstructures in order to specify the structure dynamics of a constructed Technosol. We described and quantified porosity and aggregation descriptors on a microscale (1) from pictures of mesocosms performed during 14 months, using an innovative automatic high-resolution image-acquisition device (Soilinsight^®), and (2) from thin sections sampled in situ in a 1 ha field experiment at t0 and t2 (17 months). Plant root system architecture of Lupinus albus and the behavior of introduced earthworms (Lumbricus castaneus) were described using the Soilinsight^® device. After 14 months, the pore surface was 10 times greater in the presence of plants and macrofauna than in the control samples. Although the biological activity promoted the genesis of aggregates, their dynamics were irregular. In fact, the proportion of aggregates varied depending on both root age and worm action. In situ, the soil was progressively compacted due to a significant decrease in the number of >2000 µm pores. In the same way, three aggregate descriptors—number, area and shape—were selected as the most significant indicators of soil aggregation evolution during the early stages of pedogenesis. In conclusion, this approach, based on the quantification of microstructure parameters, did indeed allow the description and monitoring of 2D soil structure dynamics in both field and mesocosms conditions. Completed with 3D soil structure data, this micromorphological analysis could advantageously contribute to the impact of climatic and biological agents modelling on a structural evolution of Technosols during initial pedogenesis.

Key words: micropedology, biological activity, structure dynamics, image analysis, Soilinsight^®