Abstract:

N is yet the most important and largest input required in rice production although over use of N causes so many environment problems. N use efficiency is varied in different rice genotypes. Therefore it is necessary to identify the physiological mechanism of N absorption and utilization in different rice genotypes in order to increase N use efficiency through rice cultivar improvement. In this research, field experiment with 225 kg ha^-1 N fertilizer application and twelve rice genotypes (6 N-efficient and 6 N-low-efficient ) selected from 120 rice cultivars grown in Yangzhou during 2004 and 2005 were carried out in 2006 on the farm of Yangzhou University, Jiangsu province, China. Relationship between N use efficiency and indexes of rice N accumulation and translocation was analyzed. At the three growth stages including critical stage of productive tillering, heading, and maturing, the amount of N accumulation of N-efficient rice was obviously higher than that of N-low-efficient genotypes while at the stage of elongating, there was no significant difference in N accumulation between the two rice genotypes. In order to analyze the N accumulation progress of rice genotypes with different N use efficiency, the growth was also divided into four phases including from transplanting to critical stage of productive tillering, from critical stage of productive tillering to elongating, from elongating to heading and from heading to maturing. Results revealed that the amount of N accumulation of N-efficient genotypes was significantly higher than that of N-low-efficient genotypes during all growth phases except the phase from critical stage of productive tillering to elongating, at which the amount of N accumulation of N-efficient genotypes was significantly lower than that of N-low-efficient genotypes. The percentage in N accumulation of N-efficient genotypes was higher than that of N-low-efficient genotypes during the growth phases from elongating to heading and from heading to maturing while it showed the reversed trend during the phases from transplanting to critical stage of productive tillering and from the critical stage of productive tillering to elongating. The amount and the efficiency of N translocation before heading were obviously higher in N-efficient genotypes than those in N-low-efficient genotypes. On the contrary, the contribution rate of transferred N to the total N of rice grain at maturity was significantly lower in N-efficient genotypes than that in N-low-efficient genotypes. For N efficient genotypes, the amount of N accumulation before the critical stage of productive tillering was modest. And during the phase from the critical stage of productive tillering to heading, its N accumulation of usefulness was large while the N accumulation of uselessness was few. Therefore, till the stage of rice heading, the amount of N accumulation of N-efficient genotypes was obviously higher than that of N-low-efficient genotypes. And the amount and the efficiency of N translocation before heading of N-efficient genotypes were also higher than that of N-low-efficient genotypes. Because of the strong ability of N accumulation of N-efficient genotypes after heading, its contribution rate of transferred N to the total N of rice grain at maturity was relatively lower than that of N-low-efficient genotypes before heading.

Key words:

Rice, N use efficiency, N accumulation, N translocation, Correlation