USE OF ACRYLIC PLASTIC AS RHIZOTRON WINDOWS

The present study determined whether soybean [Glycine max (L.) Merr. ''Corsoy''] rooting densities could be estimated reliably in Ida silt loam (fine-silty, mixed, mesic, Typic Udorthent) from the number of visible roots at the soil-acrylic plastic windows of the Ames, Iowa [USA] rhizotron. Rooting density was evaluated as a function of soil depth and distance from the plastic-soil interface in 1 compartment at the rhizotron. Fifty volumetric soil samples were collected at 10 depths and at 5 distances from the interface. Roots were washed from the Ida silt loam soil. Root length contained in the sample was estimated using a laser modification of the Rowse-Phillips root-length instrument. Rooting density was substantially greater in the 2 mm thick layers near the plastic-soil interface than in bulk soil behind it. Acrylic plastic windows apparently are satisfactory for use in root growth boxes or rhizotron compartments for phenological or for comparative experiments, but glass rhizotron windows should be used in rooting density studies.