DEVELOPMENT CHANGES RELATED TO NITROGEN-USE EFFICIENCY IN RICE

With limited new land available for rice (Oryza sativa L.) production in Asia and the need to conserve fossil energy, technologies giving maximum grain yield per unit of available nitrogen applied should be explored. In this study we examine factors associated with the development of 33 lines of rice known to differ in N-use efficiency. Among these lines, tiller number, which reached a maximum in all duration groups about 50 days after transplanting, was not a useful index of N-use efficiency. Patterns and rate of N uptake were similar among duration groups up to harvest of short-duration lines. The longer period for N accumulation available to long-duration lines did not enhance values, though six of the most N-efficient lines were of medium duration and four were of long duration. Translocation of nitrogenous compounds and other dry matter from leaf to spikelets as reflected by the (leaf weight) / (dry matter) ratio and loss of leaf N between panicle initiation and harvest as a fraction of maximum leaf N were also well correlated with N-use efficiency.