Nitrogen Distribution And Yield And Quality Of Rice As Related To Nitrogen Application Time By ～(15)N Tracing In Cold Region

Under cold climate condition in north China, we studied the effects of nitrogen fertilizer application time on yield and quality of rice, analyzed the relationship between nitrogen uptake and yield and quality of rice using two representative rice varieties in this region with 15N tracing pot culture. The main results obtained are as following:1.The results of 15N tracing showed that the fertilizer-N uptake in rice plant and grain of two varieties increased with the advance of growth stage. There was a definite relationship between nitrogen uptake and rice yield. Nitrogen application at later stage is beneficial for the increase of nitrogen utilization efficiency. The nitrogen accumulated in rice grain mainly comes from soil, instead of coming from fertilizer. In vegetative growth stage, the shoots of rice uptakes more fertilizer -N than in later growth stage.2. The effect of nitrogen application time on effective spike formation of multiple-spike variety (Dongnong V10) was significant, but for the big-spike variety (Dongnong V7), this effect was not significant. There is a good relationship between effective spike and yield, therefore, increasing effective spike through application of tilling and spike fertilizer is the main approach for high yield of multiple-spike variety.3. The effects of nitrogen application time on seed rates and 1000-grain weight of two rice varieties were completely different. Seed rate is the leading factor of big-spike rice (V7), whereas 1000-grain weight is the leading factor of multiple -spike rice (V10).4. The effects of nitrogen application time on distribution of dry matter of two rice varieties were not the same. For V7, the difference among treatments was not significant, but for V10, the difference in dry matter distribution was significant. In general, the dry matter weight of shoots seems similar, but the distribution between straw and grain was quite different.5. The effect of nitrogen application time on the yield of all treatments for both varieties was significant. For VI, the highest yield was from base fertilizer, and for V10, the highest yield occurred in the treatment of base + tillering fertilization.6. In general, nitrogen application at later growth stage resulted in higher protein content and lower amylose content.