Minirhizotron observations of the spatial distribution of the maize root system

The vertical and horizontal distribution of maize (Zea mays L.) roots was s tudied using minirhizotrons in drainage lysimeters for 3 yr. Ten minirhizot rons (60-mm o.d.) were placed horizontally at depths of 5 to 100 cm, perpen dicular to the maize row. Root density (roots cm(-2)) on minirhizotron imag es (2.43 cm(2)) was observed at leaf developmental stages 3, 6, 9, and 12 a nd at pollen shed. Root density increased to a maximum at 25-cm depth and d ecreased at greater depths. This pattern was observed in all years and at a ll developmental stages except for early in the season. The density of root s decreased with increasing distance from the plant row. Soil depth influen ced root density more than the distance from the plant row, and its pattern was more complex. Root density was influenced by an interaction between bo th factors. Significant interactions of the spatial components of root dens ity with maize developmental stage, but not with years, were Identified alt hough 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 ada pt to varying environmental conditions. Our results also indicated that the maize crop can explore soil resources only to a limited extent at early de velopmental stages, in deep soil layers, and at increasing distances from t he plant row.