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Methodology for Evaluating Nitrogen Utilization Efficiency by Rice Genotypes

Dep. of Agronomy, Int. Rice Res. Inst. (IRRI), P.O. Box 933, Manila, Philippines
Dep. of Land, Air and Water Resources, Univ. of California, Davis, CA 95616

^* Corresponding author.

Low prices for rice (Oryza sativa L.) have placed farmers all over the world in a cost-price squeeze. There is an urgent need for cultivars and production technology that will help increase yield at lower monetary costs. A method is proposed for evaluating N utilization efficiency among rice genotypes by various combinations of plant parameters, and to rank their performance in the field. From field experiments on an Andaqueptic Haplaquoll soil in six consecutive seasons, a ranking procedure was devised that does not require the use of isotopically labeled fertilizer, which makes it less expensive and more widely applicable than a similar procedure described previously. The criteria for ranking genotypes were based on differences in several plant parameters in six seasons, in three of which 33 genotypes were grown and in three when 24 genotypes were grown. Statistically significant differences among genotypes were found in 52 out of a possible 60 instances involving five selected parameters over six seasons in nonfertilized and fertilized plots. From among these five parameters, grain yield (Y) and panicle weight per total N uptake (WP/N_t) were selected by analysis of data for 12 genotypes common to all six seasons of the experiment. Genotypes such as IR21912-56-3-1-2-2 and IR15323-78-1-3-1 had consistently high rankings with and without fertilizer N and in both wet and dry seasons. Growth duration of genotypes was a factor in the differences among genotypes. Most of the high-ranking genotypes were of medium or long duration. A satisfactory evaluation of N utilization efficiency can be obtained without the use of isotopically labeled fertilizer. Advanced breeding lines can be routinely screened for their N utilization efficiency, a valuable trait of rice for resource-poor farmers.

Received for publication July 24, 1987.

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