Objective To examine the response of early growth of Betula alnoides Buch.-Ham. ex D. Don to nitrogen application and reveal the differences in the nitrogen requirement among clones.

Method Four clones of Betula alnoides were used as materials in the nitrogen fertilization (urea) experiment with seven nitrogen treatments (0, 50, 150, 250, 400, 550 and 700 g urea per seedling), and the indicators such as survival rate, growth (tree height, DBH, height to crown base and crown width) and stem form (DBH/H ratio, axis persistence and stem straightness) were investigated, respectively. This study is to determine the differences in these traits among nitrogen fertilization treatments, clones and their interactions.

Result The survival rate showed no obvious change, while the tree height, DBH and crown width displayed an “increase-stabilize-decrease” trend with the increase of nitrogen application amount for all the four clones in five years after planting. Moreover, the DBH/H ratio, axis persistence and stem straightness also tended to be better with the increasing nitrogen application. However the differences between nitrogen fertilizer treatments did not reach a significant level (P>0.05). There were significant differences among clones in the growth and stem form traits. The clone C3 showed the greatest performance, whose survival rate, tree height, DBH, height to crown base, crown width, axis persistence and stem straightness were 34%, 42%, 32%, 16%, 25%, 22% and 19% higher than those of clone C2, respectively. The interaction between nitrogen fertilization and clone was not significant.

Conclusion Nitrogen fertilization would not affect the early afforestation growth and stem form quality of Betula alnoides. The clone C3 showed the best growth and wood quality.