Effect of N Fertilizer Levels on the Differences of Yield,N Uptake and Utilization in Japonica Rice with Different Breeding Time

A field experiment with 12 Japonica rices selected of different breeding(two breeding time)time was carried out on the farm of Yangzhou University,Jiangsu province,China.The effects of different N levels including 0,225,300 kg/ha N on rice grain yield,dry matter production,N accumulation and utilization efficiency were analyzed.Results showed that,rice yield increased with the selection time replacement and the performance of yield with two times was different with N application rate increasing.Yield of 83.3% varieties selected early increased with N application rate increasing,while a half of contemporary varieties having higher yield level at 225 kg/ha N level.It indicated that varieties selected early responded more sensitive to N fertilizer than contemporary varieties.Among agronomic traits,plant height and panicle length decreased,grain setting density increased with selection time replacement.Dry matter accumulation,N uptake and utilization efficiency of contemporary varieties were higher than those of varieties selected early.Correlation analysis showed that the relationship between rice yield and dry matter and N accumulation at heading,maturing but jointing stages were significant or highly significant positively.N utilization efficiency was positive significantly correlated with yield,negative with plant height and panicle length,It indicated that rice yield,N uptake and utilization efficiency increased,plant height tended to dwarf type and panicle type evolution from sparse dense to type with the selection breeding time changed.