COMPARATIVE GROWTH ANALYSIS OF UPLAND RICE AND MAIZE GROWN UNDER DIFFERENT SOIL-MOISTURE CONDITIONS

The growth of upland rice [Oryza sativa] a species with a relatively large waterlogging tolerance capacity, and maize [Zea mays], a species with a relatively large drought tolerance capacity, under waterlogged, moderate soil moisture and drought conditions were investigated from seeding to heading stage by means of growth analysis. Upland rice showed more vigorous growth in terms of dry matter production and RGR [relative growth rate] under waterlogged conditions than drought conditions, and a reverse trend was evident in maize. Analyzing RGR into its components, NAR [net assimilation rate] with an additive effect of LAR [leaf area ratio] principally determined RGR in upland rice, while NAR showed a clear correspondence with RGR in maize. Nitrogen (N) concentration in leaf blades of both species showed considerably close relationship with NAR and thus RGR. The difference of the ratios of N content in leaf blades of a plant to the number of roots, which were considered to express the root activity, also well corresponded with those in NAR and RGR for both species. Furthermore, intimate relationships between RGR of roots and NAR were also found. These facts indicate that the distinct growth responses which upland rice and maize showed under waterlogged and drought conditions well reflected the capacity of waterlogging and drought tolerances of each species; and the responses largely depended on the activity and the growth of roots exhibited under those different soil moisture conditions.