Investigation of time dependent development of soil structure and formation of macropore networks as affected by various precrop species

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 75 cm) and cultivation periods (1, 2 and 3 years). Furthermore, morphological (air-filled porosity theta(a), pore surface area) and geometrical (pore diameter, connectivity, continuity, tortuosity tau) 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 (theta(a)) was measured in the laboratory for the same cylinders and compared to the results derived by image analysis. Air-capacity was highest for alfalfa (3 years, 75 cm). Tortuosity (tau) ranged between 1.3 and 4.38, while alfalfa (3 years) 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 r 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.