An instrumentation and a tracer technique has been employed for the investigation of root bioactivity in plants with injected
75Se in a study carried out under field conditions. The investigation was based on a previously developed instrumentation and
on findings that 75Se is preferably transferred within the root system to the active tissues of the injected plants. The root bioactivity was
investigated in corn and sunflower as subjected to different fertilization and irrigation treatments. The pattern of root
bioactivity varied with crop, time and treatment applied. The technique showed to be reliable and easy-to-use and the detection
equipment scanned the radioactivity along the soil profile with good accuracy. The described method has proved to be a useful
tool to study under field conditions the root response to variations in moisture and nutrient status in the soil.