Minirhizotron observations of the spatial distribution of the maize root system

The vertical and horizontal distribution of maize (Zea mays L.) roots was studied using minirhizotrons in drainage lysimeters for 3 yr. Ten minirhizotrons (60-mm o.d.) were placed horizontally at depths of 5 to 100 cm, perpendicular to the maize row. Root density (roots cm(-2)) on minirhizotron images (2.43 cm(2)) was observed at leaf developmental stages 3, 6, 9, and 12 and at pollen shed. Root density increased to a maximum at 25-cm depth and decreased at greater depths. This pattern was observed in all years and at all developmental stages except for early in the season. The density of roots decreased with increasing distance from the plant row. Soil depth influenced root density more than the distance from the plant row, and its pattern was more complex. Root density was influenced by an interaction between both factors. Significant interactions of the spatial components of root density with maize developmental stage, but not with years, were Identified although years strongly influenced maize leaf area. These results suggest that there is a basic pattern of maize root distribution in the soil, which is modified, but not fundamentally changed, by the ability of the roots to adapt to varying environmental conditions. Our results also indicated that the maize crop can explore soil resources only to a limited extent at early developmental stages, in deep soil layers, and at increasing distances from the plant row.