连栽对杨树人工林林木生长的影响

通过野外调查和室内试验，研究苏北杨树产区相似立地条件下，不同种植代次的杨树人工林树高、胸径、材积和其叶片N、P、K3种营养元素含量的变化特征。结果表明，4年生林树高、胸径和材积从第三代开始出现明显下降，第二代4年生林生长较快，第三代林生长势与第一代大致相同。随栽植代数增加，7年生、10年生林树高、胸径、材积生长呈下降趋势，7年生林的树高、胸径、材积生长量受连栽的影响存在显著差异。不同年生林叶片营养元素受代次增加的影响未显示一定的规律性。

Effects of Continual Cropping Poplar on Plant Growth

In the North of Jiangsu Province,characteristics of the tree growth of poplar(I-69 and I-72) with the same site index but different continual cropping generations and different ages were studies through field investigations and indoor experiments.The results were as follows: With the increasing continual cropping,the height,D.B.H.and volume of the 4-year-old poplar began to decrease significantly from the third generation,but the second generation grew better than the first and the third ones.With the increase continual cropping,the height,D.B.H.and volume of 7-year-old and 10-year-old poplar declined and the difference between different generations were significant.The effects of increasing continual cropping on the nutrition of the leaves of different generations of poplar didn't demonstrate certain regularities,however,it effected on the contents of N,P and K of the poplar leaves.