Contents lists available at ScienceDirect Soil & Tillage Research journal homepage: www.elsevier.com/locate/still Soil load support capacity increases with time without soil mobilization as a result of age-hardening phenomenon Moacir Tuzzin de Moraes a, ⁎ , Felipe Bonini da Luz b , Henrique Debiasi c , Julio Cezar Franchini c , Vanderlei Rodrigues da Silva b a University of Sao Paulo, 13416-000, Piracicaba, SP, Brazil b Federal University of Santa Maria, 98400-000, Frederico Westphalen, RS, Brazil c Embrapa Soja, PO Box 231, 86001-970, Londrina, PR, Brazil ARTICLE INFO Keywords: Preconsolidation pressure No-tillage system Soil structure ABSTRACT Soil compaction is a result of soil compression, and this efect depends on the pressure applied and the soil structure. Nevertheless, studies regarding the efects of long-term tillage systems on strengthening of particle bonds are scarce. Thus, we aimed to study the soil bond strengthening due to the age-hardening phenomenon using the soil load support capacity model of an Oxisol managed under diferent tillage systems in Southern Brazil. Soil samples were collected from three soil layers (0.0–0.10 m; 0.10–0.20 m and 0.20–0.30 m) and fve soil tillage systems of conventional tillage; minimum tillage with chiselling performed every year or every three years; and no-tillage for 11 or 24 years. Age-hardening was investigated using the soil load support capacity model. Soil cores were equilibrated at four matric potentials (−6, −33, −100 and −500 kPa) and submitted to uniaxial compression tests to obtain preconsolidation pressure. The soil load support capacity models were afected by the tillage systems. The long-term no-tillage presented the highest soil load support capacity for the same bulk density and water content in all layers, demonstrating greater resistance to additional compaction. Higher preconsolidation pressure values in long-term no-tillage at the same soil bulk density and water content were attributed to the age-hardening phenomena, which increased the number and strength of bonds among soil particles, leading to higher soil cohesion. Longer time under no-tillage improves the soil structure and soil load support capacity. Thus, soil mobilization strongly afected the soil structure by breaking particle bonds leading to the greater compaction. 1. Introduction Soil load support capacity has been known as a tool to evaluate soil structure and management in mechanized areas (Keller and Lamandé, 2010). This parameter is determined from the precompression stress (σ p ), which indicates the maximum load pressure applicable to the soil without additional compaction (Dias Junior and Pierce, 1995), and it has been used as a soil physical quality indicator (Imhof et al., 2016). Soil load support capacity is afected by several soil attributes, e.g., organic matter content, texture, type and concentration of iron oxides (Mazurana et al., 2017), water content (Tang et al., 2009), bulk density (Assouline, 2002), porosity (Veiga et al., 2007), structure (Veenhof and McBride, 1996), and especially the cohesion and adhesion forces among soil particles (Horn, 2004). However, soil load support capacity has rarely been related to soil strengthening resulting from the age- hardening process (Moraes et al., 2017). Age-hardening is described as the process through which soil strength increases spontaneously over time after soil disturbance by the greater bonding and cementation among soil particles (Dexter et al., 1988; Moraes et al., 2017; Utomo and Dexter, 1981). Two diferent mechanisms are involved in the age-hardening called type A and type B (Dexter et al., 1988; Moraes et al., 2017). Type A age-hardening occurs when new bonds are formed by the rearrangement of soil particles into new positions of minimum free energy. In the type B mechanism, ex- isting bonds among soil particles become stronger. Additionally, the critical water content for the type B mechanism increases as a function of the soil organic carbon content (Utomo and Dexter, 1981). Most soil properties associated with σ p and hence, with soil load support capacity, are infuenced by cropping and soil tillage systems (Moraes et al., 2017; Ortigara et al., 2015; Pires et al., 2017). https://doi.org/10.1016/j.still.2018.09.009 Received 20 February 2018; Received in revised form 6 August 2018; Accepted 18 September 2018 ⁎ Corresponding author. E-mail addresses: moacir.tuzzin@gmail.com (M.T.d. Moraes), boninisolos@gmail.com (F.B.d. Luz), henrique.debiasi@embrapa.br (H. Debiasi), julio.franchini@embrapa.br (J.C. Franchini), vanderlei@ufsm.br (V.R.d. Silva). Soil & Tillage Research 186 (2019) 128–134 Available online 24 October 2018 0167-1987/ © 2018 Elsevier B.V. All rights reserved. T