Directional response of corn roots to physical barriers

Abstract

The primary root of corn (Zea mays L.) was studied to better understand root growth in soil containing strong structural units or coarse soil fragments. Corn seedlings were grown in rhizotrons in a growth chamber. Each rhizotron contained 5-mm wide, flat physical barriers rigidly attached to a transparent wall that served as a growth surface for the primary roots. The angle of root incidence, the length of the barrier in contact with a root, and the angle of root deflection were measured. The minimum length of the barrier which deflected a root was 0.1±0.08 mm. The angle of root deflection was primarily dependent on the angle of root incidence. Angle of deflection was also dependent on barrier length for barrier lengths less than 3.0 mm when the bulk density was 1.1 Mg/m3. At this low bulk density and for barrier length less than 3.0 mm, it was hypothesized that roots skidded along the barrier before bending. With barrier contacts greater than 3 mm, the root became essentially parallel to the barrier before deflecting downward again at its end. Increasing bulk density of the soil from 1.1 to 1.3 Mg/m3 decreased the angle of deflection. A regression equation (R2=0.848) related the angle of deflection to the angle of incidence and soil bulk density.