A comparison of root characteristics in relation to nutrient and water stress in two maize hybrids

Root responses of maize (Zea mays L.) to limited nutrients and water availability were evaluated in two highly productive full-season hybrids, DK585 and Santos (Dekalb - Monsanto), in laboratory, pot and field tests. In the laboratory, under optimal nutrient and water supply, seedlings of DK585 had higher growth ( leaves and roots). Under nitrate or sulphate deprivation, DK585 showed better ability in adapting its root/shoot ratio to stress conditions, whereas Santos showed less plastic behaviour. This morphological trait of DK585 was associated with higher sulphate and constitutive nitrate influxes. In pot trials ( plants with four to five leaves), DK585 maintained a high transpiration level to very low values ( around 0.2) of FTSW ( fraction of transpirable soil water), whereas Santos showed a higher response to soil drying. The latter reduced the rate of transpiration starting from a FTSW of about 0.6. In the open field ( trial in 2000, Legnaro, NE Italy), in conditions of fluctuating combined water and nitrogen stress, DK585 at flowering reached greater root length density (RLD) than Santos in deep layers (50-100-cm interval depth) of positions further from the plant. However, in these conditions, the yield of DK585 was found to be only slightly higher than that of Santos (8.88 vs. 8.49 t ha(-1) d. w.). An overall evaluation of the two hybrids indicates the more conservative strategy towards limited water and nutrient resources in Santos, and a greater tendency towards stress avoidance in DK585.