Looking for soil structure

Ever since mankind has started to dig up the earth for planting, we are concerned with soil structure. For a long time digging the soil and breaking it into pieces was the only way to get insight into its architecture. Many valuable things were learned by this way: how the stability of the structure depends on the constituents, which soils are accessible for roots. To study the soil constituents in detail and in their natural ensemble has only begun about 90 years ago with the establishment of micromorphology. Thus, describing the soil by looking at its pieces has a 100 times longer history.

The new endeavor started with looking at the solid constituents of soil. The arrangement gave a new insight on processes, and enabled to describe the development of minerals, the activity of soil fauna and the diffusion of substances. It was in a rather descriptive manner that the light of microscope was shed on the soil structure.

With the introduction of X ray CT a new chapter was opened. Now it became possible to generate sufficient data for a quantitative analysis of the soil space. And with that the study of a new aspect of soil structure became feasible: the description of the pore space. Most of the functions of soil architecture are directly related to the pore space, thus a quantitative tool to describe this feature was required to understand the influence of pore space architecture on soil functions. The possibility to quantify pore space has meanwhile gotten a new tool: a standardized quantitative evaluation routine together with a comprehensive and growing library of evaluated soil structure images.

Here we are. We have to go on. To study dynamics of structural development is still tedious and can only be achieved by getting small glimpses at points in time.

New techniques occur. As is X ray CT for pore space, imaging techniques for the composition and arrangement of the solid phase evolve. They will give rise for new quantitative descriptions of soil forming processes.

Yet all this insight has to be digested and put into meaningful concepts. To profit from the wealth of information on pore space dynamics we have to implement models that can deal with a dynamic pore space. For soil hydraulics such a model is in development. It shows a clear dependency of the soil’s properties on the structure. With this, the importance of soil structure forming and preserving in agricultural management can be stressed.