Cultivar Difference in the Response of Root System to Nitrogen Application in Rice Plant

Abstract

This study was conducted to examine whether the root system development in rice plant under different nitrogen (N) application regimes is related to adaptability for heavy manuring (AHM) of the cultivar. Four rice cultivars that differ in AHM were grown in plastic pots (25 cm in diameter, 30 cm in depth), under three N levels, which were equivalent to 5 kg-N/1000 m² (5 N plot), 10 kg-N/1000m² (10 N plot) and 30 kg-N/1000 m² (30 N plot). The plants were harvested 33 days after sowing and at heading stage. In the 33-day-old plants, growth of root system was inhibited with increasing N application, apart from the production of the nodal roots, which was promoted. Although the root responses differed with the cultivars, the differences were not related to those of AHM. On the other hand, in the heading-stage plants, the total number and length of nodal root axes per plant increased. But again, notable differences among the cultivars were not recognized. In contrast, different responses to N application according to AHM of the cultivars was found in lateral root development. The cultivars with AHM showed a substantial increase in total lateral root length per plant at 30 N plot as compared with those in 5 N and 10 N plots, whereas the lateral root growth of the cultivars with high AHM remained relatively unchanged under the different N levels.