A study was made of those morphological and physical soil properties considered to govern root development.A deep and wide-branched root system was shown only to develop in a soil containing a permanent heterogeneous pore system, formed by biological activity in the profile. Therefore a distinction was made between biogenic structures having a relatively heterogeneous pore-size distribution and physicogenic and geogenic structures with a more homogeneous one.To demonstrate the effect of differences in management on soil structure in originally similar profiles, three types of land use were compared. Use as arable land proved to give rise to the formation of compacted surface soils with physicogenic structures. Here, mechanical forces leading to degeneration of structure were not compensated by biological regeneration. The same soil under horticulture was, however, shown to have a high biological activity, through added organic manure, and to yield very porous surface soils.Land, used as pasture, proved to have intermediate properties in this regard. Only with sufficient drainage this favourable biological effect was found. Methods, developed to study the occurrence of biopores, were applied in some small soil surveys. It was suggested to include the biopore concept in both soil suitability and classification studies.