Varietal Differences of Rice (Oryza sativa L.) Growth to Low Nitrogen Supply

Appropriate and effective nitrogen (N) use is an important factor to realize the sustainable rice production and to avoid environmental pollution. In this study, the low N conditions were induced by two different treatments; the restricted supply of N fertilizer by soil culture and the sudden depression of N by water culture. The growth responses of eight varieties of indica rice to low N supply were analyzed using fundamental growth parameters and specific nitrogen utilization rate (NUR) . The relative growth rate (RGR) was generally higher in the local varieties than improved varieties in both experiments. The net assimilation rate (NAR) showed a close correlation with RGR, whereas the specific leaf area and leaf weight ratio did not. A highly positive correlation was found between RGR and NUR. Among the local varieties, Pokkali showed the highest RGR, NAR and NUR in both experiments. These results indicated that under low N supply, the growth rates of the local varieties were higher than those of the improved varieties due to their higher NAR and NUR.