Nitrogen Redistribution Characteristics of Oilseed Rape (Brassica napusL.). Varieties with Different Nitrogen-Use Efficiencies during Later Growth Period

To determine the relationship between nitrogen (N) redistribution of oilseed rape (Brassica napus L.) varieties and N-use efficiency during later growth stages, the differences in N-use efficiency between two varieties (X-36 and X-50) were studied using the 15N labeling method with sand culture under complete nutrient solution conditions. Results showed that X-36 had greater grain yield not because of greater N uptake but because of greater grain yield per unit N in the plant and N-harvesting index. The average proportion of N in the two varieties that was redistributed from the vegetative organs to the grain was 65.1%. The redistribution amount and the proportion of N absorbed at the stem elongation stage and redistributed into the grain of two varieties were the greatest; the least were amounts absorbed at the siliquing stage. The high-N-use-efficiency variety (X-36), when compared with the low-N-use-efficiency variety (X-50), had slower redistribution speed of N before the siliquing stage, which then became faster after the siliquing stage. The amount of N redistributed to the grains and its proportion were larger, whereas those toward the silique husk were smaller. The amount of N loss from the plant and its proportion were smaller, and the velocity of N loss was also slower. This explains why varieties with high N efficiency have high N-harvesting index. At the later growth stages, N redistribution in the vegetative organs will significantly affect N-use efficiency.