Differences In Japonica Rice Productivity And Nitrogen Use Efficiency Between The Main Varieties Released In Different Times In Jianghuai Area

Rice is the first major food crop, about60%of the world population take rice as their staple food. Japonica Rice is the major cultivated rice subspecies in China, accounting for over25.5%of the total rice growing area. Jianghuai area is the most important base of Japanica rice cropping region in China since the alteration of rice cropping from Indica rice to Japanica rice in1990s. To study the improvement trends of rice productivity and N use efficiency in Jianghuai area will be enoumus of benefits to rice variety breeding in China. To learn the improvement trends of crop productivity and N fertilizer use efficiency of the main cultivars released in different times can provide important references not only to the comprehensive evaluation of crop production but also to new vairaty breeding and cultivation technique study for higher-yield with hiher-effciency. Therefore, on field experiment was conducted with three N treatment levels and two cropping densities in2007-2008. Our objectives were to learn the improvement trends of rice productivity and N use efficiency in Jianghuai area.(1) Rice grain yield under three N levels increased significantly along with years. The average yield of1950s was lower than those of1960s-1970s,1980s-1990s, and2000s by21.79%,14.91%, and27.09%, respectively. The changes in yield trait as following:Grain per-spike and the seedsetting rate increased obviously with years but the spike number and spike length decreasing significantly. There was no significant difference in1000-grain weight between varities. As N application and cropping density rising, rice yields all increased obviously mainly due to the higher spike number. The yield effect of cultivars released after1980s were significantly higher than1950s under low density and high N level. The yield responses of cultivars released before1980s were more sensitive by density levels. The maximum yield of each time was under high N and high density level. N application levels, cultivars and cropping density were the key factors to determine rice grian yield, grain per-spike and spike number.N×cultivar had certain impacts on grain yield, grain per-spike and1000-grain weight. The interactive effects of factors (N×density, density×cultivar, N×density×cultivar) had little impacts on yield and yield traits.(2) Rice plant height and aboveground biomass under the three N application levels decreased significantly with cultivar improvement times. The aboveground biomass of1950s was higher than those of1960s-1970s,1980s-1990s and2000s by6.78%,35.37%, and20.99%respectively.The harvest index showed decreasing trends as far as the post-anthesis accumulating rate of dry matter along with times. Rice aboveground biomass in4times all increased obviously with N application and cropping density rising. The yield effect of cultivars released after1980s were obviously higher than1950s under high N level.The response of aboveground biomass of variety released in1950s was more sensitive than those in other times by density level. The harvest index and the dry matter accumulation showed decreased trends as N application increasing. N fertilizer and cultivar, cultivar were the key factors to determine rice aboveground biomass, harvest index and dry matter accumulation. Density and density×cultivary also had obvious impacts on aboveground biomass and dry matter accumulation.(3)Along with years, rice biomass N accumulation showed decreasing at first, and then increasing obviously. Grain N accumulation increased obviously under medium (high) N application level. Post-anthesis nitrogen accumulatin rate, nitrogen translocation rate, NHI, NUE and PEP showed increasing trends with cultivar improvement. The NUE of1950s was lower than those of1960s-1970s,1980s-1990s and2000s by13.48%,17.92%and36.38%, respectively.Under different densities, aboveground biomass and grain N accumulations increased with N application increment, but the NHI, NUE and PEP decreased obviously. Under low density level, nitrogen translocation rate showed a decreasing trend as N application increasing. Under different N application levels, nitrogen accumulations in aboveground biomass and grain increased with density increasing. The responses of N production efficiency and NUE of rice cultivars released in4times were insensitive. N fertilizer was an important factor that had impacts on N accumulation amount and PEP, which contributed above36%of all the indices. The contribution of cultivar to the post-anthesis N accumulatin rate, NHI and NUE above53%of all the indices. The planting density also had obvious impacts on N accumulation amount and NUE.