•XRCT and endoscopy as new approach to investigate biopore characteristics.•Highly advantageous characterization of structural elements (blockages, linings).•Observation of dynamic development of ...pore network after introduction of earthworms in microcosms.•Rate of colonization of existing biopores by earthworms is higher than rate of newly formed pores.•Favorable effects on the nutrient contents of the biopore walls as result of fresh earthworm cast.
Bioporosity in subsoils is strongly influenced by either deep rooting taproots or earthworms, which can affect important properties for plant growth provided by soils. The open question of this study was, in how far the combination of X-ray computed tomography (XRCT) and endoscopy may support the analysis of soil bioporosity and the effects induced by earthworm activity. The hypothesis were that earthworms can re-open, close and re-connect pores as well as change the biopore wall properties (by leaving coatings at the wall) and that with a combination of XRCT and endoscopy much more detailed information about those changes can be observed. Soil monoliths were collected from a Haplic Luvisol (developed from loess) at the experimental station Klein Altendorf (University of Bonn, Germany). The microcosms were then prepared under laboratory conditions in terms of temperature, soil temperature gradient, relative humidity, illumination, watering and fertilizer. The microcosms were examined before cultivation and incubation, and re-examined after one-month earthworm incubation (Lumbricus terrestris L.), three months wheat growth period and shoot harvesting. XRCT and endoscopy were used to qualitatively and quantitatively analyze the soil microcosms. After the incubation with earthworms, physical properties like porosity and accessible surface area of biopores have changed with respect to the original state. Coatings at the biopore walls resulted in smaller pore diameters of large biopores with a diameter >0.5cm, while some of them have previously been pores with diameters <0.5cm. Contrary to this, biopores with a diameter <0.5cm were increased after earthworms, i.e. widened due earthworm passage. It was found that earthworms may have disconnected lateral pores that reach into the bulk soil from the vertical biopores by pore wall coatings. After incubation, biopores lined with fresh earthworm coatings in the monolith increased from 30% to 80%, which may indicate that earthworms potentially have a considerable influence on biopore properties and therefore the physical, chemical and microbiological environment which roots are exposed to in biopores.
A well developed macropore network is advantageous in terms of transport processes regarding gas and water, as well as nutrient acquisition and root growth of crops. X-ray computed tomography ...provides a non-destructive method to visualize and quantify three-dimensional pore networks. Geometrical and morphological parameters of the complex pore system such as connectivity, tortuosity, porosity and pore surface area would be very useful for modeling and simulation of transport and exchange processes by providing quantitative data on relevant soil structural features and their modification by soil management.
The scope of this study was to analyze and quantify the development of soil structure in the subsoil depending on three different precrop species (alfalfa A, chicory C and fescue F), at three depths (45, 60 and 75cm) and cultivation periods (1, 2 and 3 years). Furthermore, morphological (air-filled porosity θa, pore surface area) and geometrical (pore diameter, connectivity, continuity, tortuosity τ) parameters were gathered with X-ray CT and image analysis. From an experimental field trial (Germany) with a Haplic Luvisol as soil type samples were taken and investigated. Air-capacity (θa) was measured in the laboratory for the same cylinders and compared to the results derived by image analysis.
Air-capacity was highest for alfalfa (3years, 75cm). Tortuosity (τ) ranged between 1.3 and 4.38, while alfalfa (3years) showed the highest value, which indicated structural development due to crack formation by enhanced root water uptake. Thus, an increase in accessible surface may improve water and nutrient supply for plants, whereas the high τ values may assume that oxygen supply is limited. It was found that the interaction of gas-diffusivity and the calculated parameters should be further investigated in terms of limitations to plant growth.
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