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

Soil physical conditions play an important role in determining the env ironment in which biological processes take place. These conditions ca n be defined at different spatial and temporal scales. For the main fi eld site of the Dutch Programme on Soil Ecology of Arable Farming Syst ems 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 differen t arable farming systems are studied. The field water balance is studi ed by monitoring soil physical conditions in the field, characterizing the hydraulic properties, modeling the water balance of the unsaturat ed zone, and calculating time-depth curves of parcels of water. The so il physical conditions of the plots with a different arable farming sy stem were similar, except for an integrated system with minimum tillag e. No relevant hydrological differences between the soil physical char acteristics of the plots could be demonstrated. In all plots the groun dwater level often came close to the soil surface, even in the growing season. These wet conditions are favorable for denitrification. The d istance from a drain is an important factor determining the soil physi cal conditions in the topsoil under wet conditions, due to the curved phreatic surface. The water balance simulation results were not in goo d agreement with measured pressure heads. However, by using time-depth curves a good impression of the flow of water and the convective tran sport of solutes could be obtained.