Investigating the effects of organic and conventional management on soil aggregate stability using X‐ray computed tomography

Abstract

Soil aggregate stability is an important measure for assessing soil structural quality. Here we compare stable and unstable soil aggregates from organically and conventionally managed soils that have similar organic matter contents to determine the role of management in aggregate stability. Aggregate stability was determined by slaking, which proved to be an accurate estimator of the rate of aggregate turnover. The results indicate that, in soil aggregates released by slaking, the organic matter is held in aggregates > 0.3 mm diameter. A relatively short aggregate turnover rate will prohibit the production of stable micro-aggregates within macro-aggregates and thus gradually reduce aggregate stability, as was observed in soils under conventional management. Data obtained by X-ray mCT suggested that intra-aggregate porosity did not significantly affect stability. We observed cracks and elongated pores connected to the surface of stable soil aggregates that can provide an escape route for entrapped air, thus reducing pressure build-up and potentially reducing slaking. Our results show that organic management has the potential to develop more stable aggregates compared with conventionally managed soils for the soil type studied. Thus, conventional soils require particular attention to management practices that increase the rate of aggregate turnover in order to reduce the production of unstable aggregates that can contribute to crusting, erosion and runoff.

Long-term Differences in Tillage and Land Use Affect Intra-aggregate Pore Heterogeneity

“…It is likely that once the macro-aggregates break into micro-aggregates, they do so along the pores >15 μm, especially along the 15 to 60 μm micro-cracks. Even though no direct relationships between aggregate pore characteristics and aggregate stability were observed previously (De Gryze et al, 2006;Papadopoulos et al, 2009), however, as pointed by Bresson and Moran (2004), such relationships might be a complex function where aggregates' physical characteristics are related to pores of some but not other sizes. Our results appear to support this notion.…”

“…Peth et al (2008) reported smaller nodal pore volumes and shorter path lengths in 5 mm aggregates from CT than from long-term grassland. Papadopoulos et al (2009) noted diff erences in pore shapes in 5 mm aggregates from conventional and organic management. We hypothesize that diff erences in the intensity of soil disturbance, frequencies of wetting/drying patterns, amounts of biomass inputs, microbial and faunal activities in soils under conventionally plowed agricultural management as compared to NT and to undisturbed nonagricultural NS land use may lead to substantial diff erences in the intra-aggregate pore characteristics, including porosity, pore size distributions, and heterogeneity in pore distribution patterns.…”

“…Fractal analysis has been used extensively and found to be eff ective in characterizing heterogeneity and complexity of the soil pore characteristics in soil micro-tomographic images (e.g., Gibson et al, 2006;Papadopoulos et al, 2008;Luo and Lin, 2009;Tarquis et al, 2009;Papadopoulos et al, 2009;Kumar et al, 2010). Fractal dimension values refl ect complexity and heterogeneity of the distribution patterns of the studied objects.…”

Application of x-ray computed tomography in the evaluation of soil porosity in soil management systems

“…The soil particles have different arrangement and structure, varying, thus, the form (ELLIOT et al, 2010;PAPADOPOULOS et al, 2009), the length (WANG et al, 2012), the width and the tortuosity (UDAWATTA et al, 2008). Therefore, the arrangement of the soil particles determines the quantity of existing pores.…”

Evaluating Soil Tillage Practices Using X-Ray Computed Tomography and Conventional Laboratory Methods

“…Consequently, several studies have documented these anthropogenic effects on soil physical properties using x-ray CT systems (Olsen and Børresen, 1997;Gantzer and Anderson, 2002;Munkholm et al, 2003;Papadopoulos et al, 2009;Garbout et al, 2013). Gantzer and Anderson (2002) indicated that important features of soil structure are the number and size of macropores, which include tillage-induced structures, wormholes, and root channels.…”