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，eighty eight and one hundred and twenty two conventional indica rice cultivars were solution-cultured in 2001 and 2002, respectively. Leaf area index, dry matter weight (including root system), nitrogen content of rice plant, yield and its components were measured. The tested rice cultivars were clustered 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 yield and yield components. Results were as follows: (1) Difference of NUEg in the cultivars used in this study were very large, the ratio of the maximal NUEg to the minimum NUEg in 2001 and 2002 were 344% and 425%, respectively. The average NUEg of 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 were 24.33, 31.61, 35.83, 39.06, 43.51, 50.00 g grain·g^-1 N in 2002, respectively. The result of experiments in two years showed the same tendency. (2) As NUEg increased, yield level of conventional indica rice cultivars significantly increased. Polynomial regression analysis showed that yield level was significantly influenced by total nitrogen uptake (including root system) and NUEg which indicated that higher yield level can be reached by improving nitrogen uptake and NUEg of conventional indica rice cultivars. (3) The cultivars with high NUEg were higher in panicle number, sink potential, grain setting percentage, grain yield per unit leaf area and harvest index, but lower in leaf area index. The relationships between spikelet number per panicle, 1000-grain-weight, biomass and NUEg were not significant.

Key words: Conventional indica rice, Cultivars, Nitrogen use efficiency for grain output, Yield, Leaf area index