The degree of root-soil contact was evaluated from thin sections for maize grown in pots with soil aggregates packed at three bulk densities. Root-soil contact was found to increase with bulk density of the soil. For soils with a porosity of 60, 51 and 44% (v/v), the average fraction of root-soil contact was 60, 72 and 87%, respectively. The frequency distribution of nearest-neighbour distances from points in a void to the nearest point of the soil matrix was measured. This was then used for a statistical test of a null hypothesis of random positioning of roots in voids. Where roots grew in larger pores or voids the degree of root-soil contact was greater than expected for random positioning of roots. Possible mechanisms of the observed preference of roots for proximity to the soil, and higher root-soil contact are discussed.

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A number of efficient and diverse mathematical methods have been used to model electromagnetic wave propagation. Each of these methods possesses a set of key elements which eases its understanding. However, the modelling of the propagation in concrete becomes impossible without modelling its electrical properties. In addition to experimental measurements; material theoretical and empirical models can be useful to investigate the behaviour of concrete's electrical properties with respect to frequency, moisture content (MC) or other factors. These models can be used in different fields of civil engineering such as (1) electromagnetic compatibility which predicts the shielding effectiveness (SE) of a concrete structure against external electromagnetic waves and (2) in non-destructive testing to predict the radar wave reflected on a concrete slab. This paper presents a comparison between the Jonscher model and the Debye models which is suitable to represent the dielectric properties of concrete, although dielectric and conduction losses are taken into consideration in these models. The Jonscher model gives values of permittivity, SE and radar wave reflected in a very good agreement with those given by experimental measurements and this for different MCs. Compared with other models, the Jonscher model is very effective and is the most appropriate to represent the electric properties of concrete.

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