Contents lists available at ScienceDirect Soil & Tillage Research journal homepage: www.elsevier.com/locate/still Studying the soil pore physical resistance and resilience of a shallow volcanic ash soil subjected to pure cyclic loading José Dörner a,b, *, Rainer Horn c , Daniel Uteau d,b , Jens Rostek c , Felipe Zúñiga e,b , Stephan Peth d , Dorota Dec a,b , Heiner Fleige c a Instituto de Ingeniería Agraria y Suelos, Facultad de Ciencias Agrarias y Alimentarias, Universidad Austral de Chile, Valdivia, Chile b Centro de Investigación en Suelos Volcánicos, Universidad Austral de Chile, Chile c Institute for Plant Nutrition and Soil Science, Christian Albrechts Universität Zu Kiel, Hermann Rodewaldstr. 2, 24118 Kiel, Germany d Departament of Soil Science, University of Kassel, Kassel, Germany e Departamento de Ciencias Naturales y Tecnología, Universidad de Aysén, Eusebio Lillo 630, Coyhaique, Chile ARTICLE INFO Keywords: Soil mechanical properties Soil structure recovery Pore functions Andisols CT-Analysis ABSTRACT In the last 250 years the Aquands (depth-limited and waterlogged-volcanic ash soils) in southern Chile were exposed to an intensive land use change inducing physical degradation of these fragile soils. The aim of this work was to evaluate the effect of cyclic loading on soil structural properties and the resilience capacity after simu- lating one event of soil waterlogging as usually occurs in the field. In undisturbed soil samples, collected from two horizons (2-5 cm, Hz1 [A 1 ] and 20-23 cm, Hz2 [B s1 ]) of a Duric Histic Placaquand under secondary native forest (sNF) and naturalized grassland (NG), the precompression stress (Pc), deformation and recovery indices derived from cyclic loading tests (20, 80 and 200 kPa) were determined. The air permeability (Ka) and soil volume changes were measured during the entire test. The land use change from sNF to NG increased the rigidity of the pore system due to plastic deformation. However, the cyclic loading provokes changes in the pore system (e.g. increase in bulk density as well as decrease in wide coarse pores, which finally induce a decrease in air permeability: 1.89 to -0.17 log μm 2 and 1.03 to 0.37 log μm 2 in Hz1 of aNF and NG, respectively) even at loads lower than Pc highlighting the fragility of the soils. As the applied load increases to levels higher than Pc, the plastic deformation induces an increase in pore water pressure and mechanical strength, affecting the pore network and in turn the air permeability of the soil. After one event of ten days of waterlogging conditions, the resilience capacity of the pore system was low. CT-images show that the soil under sNF recovered apart of the deformed porosity allowing an increase in Ka (0.55 ± 0.15 log μm 2 ) after waterlogging conditions, however, no changes were identified for the soil under NG (final Ka = 0.57 ± 0.26 log μm 2 ). Therefore, both land use change and increasing loads on these fragile soils imply the loss of their resilience capacity generating a further soil settlement. 1. Introduction Volcanic ash soils constitute about 60 % of arable soils in Chile (Besoaín and Sepúlveda, 1985) and are relevant for agricultural activ- ities in the country. These soils, which can be found under a wide range of climatic ecosystems (35° - 50 °South Latitude), can be classified (according to Soil Survey Staff, 2014) as recent Andisols (e.g. Acrudoxic Hapludands), well developed Andisols (e.g. Typic Hapludands), wa- terlogged Ñadi Soils (e.g. Duric Histic Placaquands) and pleistocenic volcanic soils (Andic Palehumults). In the last 250 years these soils were exposed to an intensive land use change (Lara et al., 2012; Aguayo et al., 2009) inducing soil physical degradation (Ellies et al., 1997; Dörner et al., 2010) and erosion (Ellies, 2000). Volcanic ash soils present extreme physical properties (e.g. bulk densities lower than 0.9 Mg m -3 and very high saturated hydraulic conductivity, > 2000 cm d -1 , as presented in Ellies et al., 1997; Dörner et al., 2010, 2013). However, while the normally deep Andisols (known as Trumaos in southern Chile, soil depth > 1 m) can withstand the land use change and increasing management intensity (Dörner et al., 2011; Dec et al., 2012; Fleige et al., 2016), the negative consequences on Ñadi Soils (ÑS) can be very severe due to their shallowness (soil depth < 0.8 m) (Dörner et al., 2017). Aquands are situated in plains between moraine and glacial out- wash landscapes (Sierra, 1982), located in the central longitudinal https://doi.org/10.1016/j.still.2020.104709 Received 4 November 2019; Received in revised form 13 April 2020; Accepted 19 May 2020 ⁎ Corresponding author at: Instituto de Ingeniería Agraria y Suelos, Facultad de Ciencias Agrarias y Alimentarias, Universidad Austral de Chile, Valdivia, Chile. E-mail address: josedorner@uach.cl (J. Dörner). Soil & Tillage Research 204 (2020) 104709 0167-1987/ © 2020 Elsevier B.V. All rights reserved. T