Use of Acrylic Plastic as Rhizotron Windows 1

Reliable cotton ( Gossypium hirsutum L.) rooting densities (cm roots/cm 3 soil) for bulk soil have been estimated previously from the number of visible roots in sandy soil immediately behind glass 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 rhizotron. Rooting density was evaluated as a function of soil depth and distance from the plastic‐soil interface in one compartment at the rhizotron. Fifty volumetric soil samples were collected at ten depths and at five 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.