Genotypic differences for grain yield and nitrogen utilization in Indica and Japonica rice under Mediterranean conditions

The identification of the factors that determine grain yield and nitrogen utilization in rice production systems is necessary to optimize their productivity and reduce the pollution risk for the environment. A field study was conducted to analyze the various component traits that cause variation in grain yield, grain nitrogen yield and nitrogen utilization efficiency (NUE) of direct water-seeded Indica and Japonica rice, using yield and yield component analysis. Five rice cultivars, Olympiada and L-202 (Indica type) and Ispaniki A', Melas and Dion (Japonica type), with contrasting traits were grown in a silty loam soil (Aquie Xerofluvents) in 1999 and 2000. Grain yield ranged from 6045 (Melas) to 83 10 kg/ha (Olympiada). More than 50% of the total variation in grain yield among cultivars was explained by the variation in panicles per square meter, suggesting the importance of tillering ability of a given cultivar in obtaining high yields. The relative contribution of grains per particle was moderate (35.2% in 1999 and 34.1% in 2000), while that of grain weight the lowest. Grain yield was significantly correlated with N concentration in vegetative parts at anthesis. NUE for biomass accumulation during grain filling period was generally similar or lower compared to that during vegetative period. Indica cultivars had lower NUE for biomass accumulation and higher nitrogen utilization efficiency for grain yield (NUEg) compared to Japonica cultivars, mainly due to the higher NHI. For a reliable comparison among cultivars, the agronomic traits of each cultivar should be taken into account. Short and late maturing cultivars had significantly higher NUEg than the tall and early or mid-season cultivars, respectively. NUEg was negatively correlated with grain and straw N concentration at maturity, suggesting that low grain or straw N concentrations may be indications of higher NUEg (C) 2603 Elsevier Science B.V. All rights reserved.