Soil resistance and resilience to mechanical stresses for three differently managed sandy loam soils

To improve our understanding of how clay-organic carbon dynamics affect soil aggregate strength and physical resilience, we selected three nearby soils (MFC, Mixed Forage Cropping; MCC, Mixed Cash Cropping; CCC, Cereal Cash Cropping) with identical clay content and increasing contents of organic carbon (CCC<MCC<MFC). The objective was to assess the resistance and resilience of the three soils to compaction using air permeability (k(a)), void ratio (e) and air-filled porosity (E) as functional indicators and to characterise aggregate stability, strength and friability. Aggregate tensile strength measurements were done at -1000 hPa and in the air dried state. Soil cores were subjected to uniaxial confined compression (200 kPa) followed by a period of natural recovery and wet-dry or freeze-thaw cycles. The MFC soil displayed greater tensile strength, specific rupture energy and friability at both soil-water potentials than the MCC and CCC soils possibly due to higher biotic binding of soil particles by the greater organic carbon content. The water dispersible clay was negatively correlated with the level of clay saturation by organic carbon. The resistance of the soils to compaction, quantified by both the compression index and a proposed functional index, was significantly greater for the MFC soil compared to the other two soils. The change in compression index with initial void ratio was significantly less for the MFC than the other soils. Plastic reorganisation of the soil particles immediately after compaction, prior to removal of the load, was greatest for the high organic soil Physical resilience after natural recovery followed the organic carbon gradient (MFC>MCC>CCC). After wet-dry cycles, the MFC soil showed a significantly greater resilience for all three indicators (k(a), e and epsilon). Resilience (k(a), and e) after freeze-thaw cycles was significantly lower for the CCC soil than the MFC and MCC soils. A significant positive correlation between resistance and resilience was observed for k(a) and e but not for epsilon. Resilience to compaction was found to be independent of the soil properties monitored. (C) 2012 Elsevier B.V. All rights reserved.