Nitrogen use efficiency in lowland rice genotypes

Nitrogen (N) is one of the most yield-limiting nutrients in lowland rice pr oduction around the world. Use of N efficient genotypes is an important com plementary strategy in improving rice yield and reducing cost of production . A greenhouse experiment was conducted at the Embrapa Rice & Beans, Santo Antonio de Goias, Brazil, with the objective to evaluate N use efficiency o f eight lowland (Oryza sativa L.) genotypes. The soil used in the experimen t was an Inceptisol and two N levels used were without N application (low l evel) and an application of 304 mg N kg(-1) of soil (high level). Grain yie ld and yield components and N uptake parameters were significantly affected by genotype and N treatments except the N uptake in shoot. On the basis of N-use efficiency (mg grain weight/mg N accumulated in shoot and grain) and grain yield at zero N, genotypes were classified as efficient and responsi ve (ER), efficient and nonresponsive (ENR), nonefficient and responsive (NE R), and nonefficient and nonresponsive (NENR). Genotypes Rio Formoso, CNA 7 550, and CNA 7556 were classified as ER, and genotypes Javae and CNA 6343 w ere classified as ENR. In the group, NER was classified genotype CNA 7857. In the group, NENR were falled genotypes CNA 8319 and CNA 8619, From a prac tical point of view, genotypes which produce high grain yield in a low leve l of N and respond well to added N are the most desirable because they are able to express their high yield potential in a wide range of N environment . Correlation analysis showed that shoot dry weight, number of panicles, nu mber of grains per panicle, grain harvest index, N uptake in shoot and grai n, N harvest index, and N use efficiency having significant positive associ ation with grain yield.