MACROSCOPIC SOIL PHYSICAL PROCESSES CONSIDERED WITHIN AN AGRONOMICAL AND A SOIL BIOLOGICAL CONTEXT

Soil physical conditions play an important role in determining the environment in which biological processes take place. These conditions can be defined at different spatial and temporal scales. For the main field site of the Dutch Programme on Soil Ecology of Arable Farming Systems it is demonstrated that a macroscopic soil physical approach gives useful information, also for processes on the micro-scale. The field site is described in a historical context, and new plots with different arable farming systems are studied. The field water balance is studied by monitoring soil physical conditions in the field, characterizing the hydraulic properties, modeling the water balance of the unsaturated zone, and calculating time-depth curves of parcels of water. The soil physical conditions of the plots with a different arable farming system were similar, except for an integrated system with minimum tillage. No relevant hydrological differences between the soil physical characteristics of the plots could be demonstrated. In all plots the groundwater level often came close to the soil surface, even in the growing season. These wet conditions are favorable for denitrification. The distance from a drain is an important factor determining the soil physical conditions in the topsoil under wet conditions, due to the curved phreatic surface. The water balance simulation results were not in good agreement with measured pressure heads. However, by using time-depth curves a good impression of the flow of water and the convective transport of solutes could be obtained.