Preface: Soil biophysical contributions to hydrological processes in the vadose zone

Although significant progress has been made in our ability to characterize and quantify the soil physical environment and processes, there remains a critical gap in our understanding of interactions between the soil physical and biological realms. This was the impetus for the special symposium entitled "Soil Biophysics: A Challenging Interface" we organized for the 2005 SSSA Annual Meeting to increase awareness for the need to improve understanding of interactions between the soil physical environment, soil microorganisms, and plant roots. The symposium included research on the fate and transport of microorganisms ( microbes and viruses), control and optimization of bioremediation and phytoremediation, physical controls on microbial ecology, improved descriptions of water and nutrient uptake by roots, and rhizosphere processes. This special section includes fi ve selected articles derived from presentations at the soil biophysics symposium.