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-Hoh enheim, root growth of one experimental and nine commercial maize cult ivars was studied. According to the core method, roots of all cultivar s penetrated the soil down to a depth of 150 cm indicating that no dif ferences in maximum rooting depth existed. However, significant differ ences 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. Di fferences between cultivars in root growth as identified by the core m ethod could be confirmed by minirhizotron observations only at early s tages of plant development. Quantitative comparisons between both meth ods showed that minirhizotron observations resulted in (a) an underest imation 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 pr ofile depth were excluded from analysis, significant positive relation ships between ln RLD in soil cores and RD assessed with the minirhizot rons were calculated for different stages of plant development. Howeve r, the slope of the regression lines varied considerably between calib ration dates indicating that one calibration is not sufficient to esti mate RLD from minirhizotron observations.