Abstract:

Improving nitrogen use efficiency in crops is of great importance both in crop production and environmental protection. Genetically improving crop varieties so as to make full use of the potentials in nitrogen uptake and utilization has been considered as one of the most economical and effective ways to enhance nitrogen use efficiency in crops. Nitrogen use efficiency depends on the ability of nitrogen uptake and utilization in rice plant. Many studies have shown that there exist genotypic differences in nitrogen use efficiency for biomass and grain production in rice. Yet, little information in the characteristics of yield components, biomass production and allocation, nitrogen uptake and allocation and structure of root system in rice varieties with higher nitrogen use efficiency has been reported. In this study, 88 and 122 conventional indica rice cultivars were solution-cultured in 2001 and 2002, respectively. Dry matter weight (including root system, stem and sheath, leaves, ear), nitrogen content of different organs was measured. The tested rice cultivars were classified into 6 types (i.e. A, B, C, D, E and F, A was lowest, F was highest) based on their nitrogen use efficiency for grain output (NUEg) level by the MinSSw method, to study their characteristics of dry matter accumulation and distribution. Results ware as follows: (1) Difference of NUEg of the cultivars used in this study was very large, the averages of NUEg for A, B, C, D, E and F were 20.51, 31.04, 35.64, 39.46, 43.55 and 50.92 g grain·g-1N in 2001, and 24.33, 31.61, 35.83, 39.06, 43.51, 50.00 g grain·g-1N in 2002, respectively; (2) Difference of biomass among cultivars of different types was not significant, while dry matter accumulation of the cultivars with high NUEg level was small at heading stage, its dry matter production after heading was large and the ratio of that to biomass was high; (3) Difference between cultivars of different types in the ratio of dry root weight to dry matter weight per plant (DMWP)and the ratio of dry stem and sheath weight to DMWP was not significant at heading stage, while those at mature stage in the cultivars with high NUEg level was lower; (4) The smaller the ratio of dry leaf weight to DMWP, the longer the ratio of dry panicle weight to DMWP in the cultivars with high NUEg level at heading stage and maturing stageble.

Key words: Conventional indica rice, Cultivars, Nitrogen use efficiency for grain output, Dry matter accumulation, Dry matter distribution