氮素施肥对西南桦无性系早期生长的影响

目的]通过造林试验研究西南桦无性系早期生长对氮素施肥的响应,揭示西南桦幼林氮素需求规律及无性系间差异。方法]以4个西南桦无性系作为试验材料,设置0、50、150、250、400、550、700 g·株^-1 7个处理,开展氮素(尿素)施肥试验,调查保存率、生长(树高、胸径、枝下高和冠幅)、干形(径高比、树干通直度及主干分叉情况)等性状,分析这些性状在施肥处理间、无性系间的差异及二者的交互作用。结果]造林后第5年,对于4个参试无性系而言,其保存率随施氮量的增加无明显变化规律,树高、胸径和冠幅整体上呈现"增加-稳定-减少"的变化趋势,径高比、树干通直度和主干分叉情况亦渐趋优良,但各施肥处理间差异并不显著(P>0.05)。各无性系间生长和干形均差异显著,无性系C3的各性状总体上表现最优,其保存率、树高、胸径、枝下高、冠幅、主干分叉及通直度比最差的无性系C2分别高34%、42%、32%、16%、25%、22%和19%,氮肥和无性系的交互作用不显著。结论]综上所述,施氮肥并不影响西南桦无性系造林后早期生长和干形质量,无性系间生长和干形差异显著,其中,无性系C3的生长和干形表现最佳。

Effects of Nitrogen Fertilization on Early Growth of Betula alnoides Clones

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.