Tillage practices are critical factors for the sustainability of cropping systems by modifying the soil properties and affecting root growth. In this study we compared conventional (CT) and no tillage (NT) practices to evaluate their effects on soil structure and maize root morphology and dynamics during a two-year transition period. Pore size distribution and morphology-related parameters were analyzed with a combination of X-ray microtomography (microCT) (54–2250 μm) and mercury intrusion porosimetry (MIP) (0.0074–100 μm) within the 0–40 cm soil profile. The network model PoreXpert was applied to MIP pore distribution curves to identify subtle structural changes as affected by tillage. Root samples were collected down to 1-m depth with the core method during 2005 and 2006, 40 and 114 days after sowing, in order to quantify their mass, length and diameter. Results suggested that tillage practices affected the soil macroporosity (54–750 μm) while the micropores, detected with MIP, did not show significant differences between treatments. Conventional tillage, disrupting the macropore structure and enhancing the pore class in the range 54–250 μm, improved the soil loosening. Bulk density measurements, achieved in the last date (day 114, 2006), were negatively correlated with root growth indicators. Nevertheless, root growth was weakly affected by tillage since the soil structure did not reach a new architecture after the introduction of NT. In spite of the experiment being conducted in the short-term and the soil structure still being unpredictable, microCT analysis proved its ability to predict subtle structure changes as affected by conventional and no tillage practices.

Soil macro- and microstructure as affected by different tillage systems and their effects on maize root growth

. The characteristics of the soil macropore network determine the potential for fast transport of agrochemicals and contaminants through the soil. The objective of this study was to examine the relationships between macropore network characteristics, hydraulic properties and state variables and measures of preferential transport. Experiments were carried out under near-saturated conditions on undisturbed columns sampled from four agricultural topsoils of contrasting texture and structure. Macropore network characteristics were computed from 3-D X-ray tomography images of the soil pore system. Non-reactive solute transport experiments were carried out at five steady-state water flow rates from 2 to 12 mm h−1. The degree of preferential transport was evaluated by the normalised 5% solute arrival time and the apparent dispersivity calculated from the resulting breakthrough curves. Near-saturated hydraulic conductivities were measured on the same samples using a tension disc infiltrometer placed on top of the columns. Results showed that many of the macropore network characteristics were inter-correlated. For example, large macroporosities were associated with larger specific macropore surface areas and better local connectivity of the macropore network. Generally, an increased flow rate resulted in earlier solute breakthrough and a shifting of the arrival of peak concentration towards smaller drained volumes. Columns with smaller macroporosities, poorer local connectivity of the macropore network and smaller near-saturated hydraulic conductivities exhibited a greater degree of preferential transport. This can be explained by the fact that, with only two exceptions, global (i.e. sample scale) continuity of the macropore network was still preserved at low macroporosities. Thus, for any given flow rate, pores of larger diameter were actively conducting solute in soils of smaller near-saturated hydraulic conductivity. This was associated with larger local transport velocities and, hence, less time for equilibration between the macropores and the surrounding matrix which made the transport more preferential. Conversely, the large specific macropore surface area and well-connected macropore networks associated with columns with large macroporosities limit the degree of preferential transport because they increase the diffusive flux between macropores and the soil matrix and they increase the near-saturated hydraulic conductivity. The normalised 5% arrival times were most strongly correlated with the estimated hydraulic state variables (e.g. with the degree of saturation in the macropores R2 = 0.589), since these combine into one measure the effects of irrigation rate and the near-saturated hydraulic conductivity function, which in turn implicitly depends on the volume, size distribution, global continuity, local connectivity and tortuosity of the macropore network.

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Relations between macropore network characteristics and the degree of preferential solute transport

Long-term effects of conventional and reduced tillage on soil structure, soil ecological and soil hydraulic properties

Effect of vegetation type on microstructure of soil aggregates on the Loess Plateau, China

Impact of Long-Term Fertilization Practice on Soil Structure Evolution

Dual-scale micro-CT assessment of soil structure in a long-term fertilization experiment

Application of smoothed particle hydrodynamics (SPH) and pore morphologic model to predict saturated water conductivity from X-ray CT imaging in a silty loam Cambisol

P. Charrier

Papers

Dual-scale micro-CT assessment of soil structure in a long-term fertilization experiment

Application of smoothed particle hydrodynamics (SPH) and pore morphologic model to predict saturated water conductivity from X-ray CT imaging in a silty loam Cambisol