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item Samonte, Stanley Omar P
item Wilson, Lloyd
item Medley, James
item Pinson, Shannon
item Mcclung, Anna
item Mcclung, Anna
item Lales, Joveno

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2004
Publication Date: 1/1/2006
Citation: Samonte, S.B., Wilson, L.T., Medley, J., Pinson, S.R., McClung, A.M., Lales, J. 2006. Nitrogen utilization efficiency: relationships with grain yield, grain protein and yield-related traits in rice. Agronomy Journal 98:168-176.

Interpretive Summary: Rice plants require nitrogen during their vegetative and reproductive growth phases. This is made available to the plant through soil mineralization and/or application of nitrogen fertilizer. Excessive application of nitrogen fertilizer can result in pollution problems in irrigation water or because of runoff. Development of rice cultivars that use nitrogen efficiently will reduce the need for excessive inputs of nitrogen, will save production costs for farmers and will benefit farmers in developing countries who do not have access to fertilizer inputs. This study evaluated fifteen genotypes that had been selected from a common population to be diverse for several factors associated with grain yield. These genotypes were evaluated for nitrogen uptake, nitrogen utilization efficiency, nitrogen translocation ratio, and grain protein content. All of these factors were found to be positively correlated with grain yield. This indicates that breeders can select for genotypes that are efficient in nitrogen utilization and have elevated levels of grain protein without sacrificing grain yield.

Technical Abstract: Rice (Oryza sativa L.) breeders have historically not included nitrogen utilization efficiency (NUE) as a selection criterion in breeding for cultivars, even though it has economic and ecological implications. This study examined the significance and magnitude of variation in N content, NUE, N translocation ratio (NTR), and grain protein concentration among diverse rice genotypes. Fifteen rice genotypes were studied representing the combinations of low and high levels of four yield-related traits ' maximum number of tillers, grain mass, panicle node number, and panicle mass. These genotypes included 'Lemont', 'Teqing' and 13 advance recombinant inbred genotypes obtained from a Lemont x Teqing cross. Field data were obtained from experiments conducted during two cropping seasons. Plant samples were analyzed for N concentration. There was significant variation in N content, NUE, NTR, and grain protein concentration among genotypes. The genotype NUE means ranged from 25.3 to 63.9 g grain per g N in a m-2 of plants (g grain g-1 N), with the top four NUE values ranging from 56.6 to 63.9 g grain g-1N. The genotype NTR means ranged from 0.264 to 0.643 g grain N g-1 N, while the genotype grain protein concentrations ranged from 43.0 to 74.8 g protein kg-1 grain. Nitrogen content and NUE were not significantly correlated with each other, and they had significant positive direct effects on grain yield. Grain yield was positively correlated with NUE, N content, and NTR, which was correlated with grain protein concentration. Plant breeders could use these significant correlations to their advantage in breeding for rice cultivars that not only produce high yield but also utilize N efficiently and produce grain with a higher protein concentration