A new technique for placement of radioactive solutions in root studies and a study of root growth of Paspalum commersonii

A new technique is described for placement of radioactive solutions for studies on root growth. This technique involves placement of a perforated ring of polythene tubing at a predetermined depth with an access tube leading to the soil surface. Cylinders of 16 gauge galvanised iron and of different diameters are used for placement of polythene rings. Soil is excavated from outside the cylinder as it is forced to the required depth ; the polythene is placed in position and soil back-filled over it as the cylinder is withdrawn, thus leaving an undisturbed core of soil of the same diameter as the cylinder to the depth of placement. Radioactive solution introduced through the access tube from an automatic burette is distributed evenly in the soil by percolation from the perforated polythene ring. Rate of root growth of single plants through the undisturbed soil can be determined from measurement of radioactivity in plant leaves at various intervals of time. The technique was tested using radioactive phosphate (32P) as tracer and Paspalm commersonii Lam. as the test species. Root growth both vertically and laterally was measured. The advantages of this technique compared with others at present in use are : 1. Non-disturbance of the soil through which root growth is being measured. 2. Repeated applications of radioactive solution without disturbance of the system may be made in long-term studies. 3. Soil contamination by 32P solution above the point of placement is eliminated. The technique is well suited for studies on root growth and activity of single plants, or for competition studies.