ROOT-GROWTH OF MAIZE CULTIVARS UNDER FIELD CONDITIONS AS STUDIED BY THE CORE AND MINIRHIZOTRON METHOD AND RELATIONSHIPS TO SHOOT GROWTH

In a 2-year field study conducted on a Gleyic Luvisol in Stuttgart-Hohenheim, root growth of one experimental and nine commercial maize cultivars was studied. According to the core method, roots of all cultivars penetrated the soil down to a depth of 150 cm indicating that no differences in maximum rooting depth existed. However, significant differences among the cultivars were found in root-length densities (RLD) at silking in 1987 (1988) the ranges being 3.07 - 4.41 (2.88 - 4.43), 1.21 - 2.14 (1.14 - 1.75), 0.24 - 0.68 (0.24 - 0.56), and 0.05 - 0.12 (0.05 - 0.13) cm cm-3 in the various 30 cm layers down to 120 cm depth. In both years of the study vegetative yield was positively correlated with RLD in the 60 - 90 cm layer, whereas relationships between shoot traits and total root length were not consistent between the years. Differences between cultivars in root growth as identified by the core method could be confirmed by minirhizotron observations only at early stages of plant development. Quantitative comparisons between both methods showed that minirhizotron observations resulted in (a) an underestimation of root density (RD) in the topsoil and (b) the description of a linear decline of RD with depth below 30 cm whereas RLD in the soil cores decreased exponentially with depth. When RD at 7.5 and 15 cm profile depth were excluded from analysis, significant positive relationships between ln RLD in soil cores and RD assessed with the minirhizotrons were calculated for different stages of plant development. However, the slope of the regression lines varied considerably between calibration dates indicating that one calibration is not sufficient to estimate RLD from minirhizotron observations.