PRESSURIZED-WALL MINIRHIZOTRON FOR FIELD OBSERVATION OF ROOT-GROWTH DYNAMICS

Data derived from minirhizotrons, tubes installed in the field for observation of root growth, can suffer from particular conditions at the interface between tube and soil. These include the interface being excessively tight-leading to under observation of roots-or to gaps between wall and soil-leading to visibility problems and over-proliferation of roots at the wall. Details are presented for a minirhizotron designed to overcome these problems by use of flexible and constantly pressurized outer walls. The 0.5-mm thick, clear polyvinyl outer wall is concentric with and sealed to an inner wall of extruded acrylic. Air pressure of 10 to 20 kPa is maintained between inner and outer walls. The system appears to have yielded data of a comparable or better quality than other described rhizotron-type devices and is recommended for usage by workers with soils that present problems to minirhizotron usage.