Root development of maize (Zea mays L.) as observed with minirhizotrons in lysimeters

Knowledge of root growth patterns is relevant for agronomic management practices, The growth of maize roots (Zea mays L.) was studied by means of minirhizotrons in lysimeters, Ten minirhizotrons (60-mm outer diameter) were plated horizontally at soil depths between 5 and 100 cm, perpendicular to the maize row. The root density (roots cm-2) on images (2.43 cm(2)) was observed at weekly intervals, During the growing season, the root density increased to a maximum and then decreased, a pattern observed in 3 yr and at all depths and positions relative to the plant row. Growing degree days, compared with chronological time, did not improve the description of temporal root growth patterns. Maximum root density did not occur at the same time as pollen shed, in contrast to maximum leaf area, At shallow depths, the maximum root density was observed at the same time as pollen sited, while at a depth of 100 cm, the maximum root density occurred 2 wk after pollen shed. The maximum root density was observed about 10 d after pollen shed at most positions relative to the plant row. In conclusion, the maximum root density and hence resource uptake capacity of the root system was reached with some delay in relation to the vegetative development of the crop.