Differences and Correlations in Grain Yield,N Uptake and Utilization between Medium-Maturing Indica and Japonica Rice under Different N Fertilizer Levels

Nitrogen(N) is a very important nutrition element in improving rice yield.Study on the relationship between N absorption and grain yield is necessary to optimize their productivity and reduce environment pollution risk.In this research,a field experiment with 10 medium-maturing medium indica rice(138–143 d) cultivars and 10 medium-maturing medium japonica rice(136–145 d) cultivars was carried out in 2006 and 2007 on the farm of Yangzhou University,Jiangsu province,China.The effects of different N levels including 0,150,225,and 300 kg ha-1 N on rice grain yield and the N absorption and utilization of plant at different growth stages were analyzed.Results showed that,with the increase of N application,grain yield of Japonica rice in-creased continuously while yield of indica rice get the highest under the N level of 225 kg ha-1 and then declined under the N level of 300 kg ha-1.Grain yield of indica rice was higher than that of Japonica rice under four N levels,which was resulting from the large number of panicles and 1000-grain weight in indica rice with 22.45% and 7.514% higher than those in Japonica rice respectively.N accumulations of indica rice in elongation,heading and maturing stages were 24.26%,3.14%,and 6.45% higher than those of japonica rice,respectively.And N uptake rates of indica rice from transplanting to elongation,from elongation to heading and from heading to maturing were 38.07%,16.05%,and 23.22% higher than those of japonica rice respectively.Correlation analysis indicated that there existed significant or highly significant positive correlations between yield and indices of N uptake and utilization,which also illustrated that the higher yield of Indica rice was from the intensive N absorption of its plant.