不同连栽代次桉树人工林的养分循环

Nutrient Cycle of Eucalyptus Plantations with Different Continuous-Planting Rotations

研究结果表明，养分的归还量和吸收量均以１代林最大，其它依次为２代林＞３代林＞４代林。随代次增加，枯落物归还量在总归还量中的比例增加。从总吸收量看，Ｎ、Ｃａ两元素占比例较高，有随代次增加而增加的趋势。随代次增加，５种营养元素总生物循环率增高，代数越高养分的消耗率越低。从养分移出量估计，各代次林分干材部分所占的养分存留量为１／３。“全树利用”及其短轮伐期经营制度是导致林地养分衰竭和生产力下降的主要原因。

The nutrient uptake and return of the Eucalyptus plantations was found highest inthe 1st rotation, followed by the 2nd>the 3rd>the 4th. Nutrient return from litter increasedin the total nutrient return with continuous-planting rotation (CPR). The Ca and N elementswere higher in the nutrients absorbed and tended to increase with CPR. The total biocyclerate of all elements investigated increased with the CPR, and the nutrient consumption decreased with the CPR. It was estimated that the trunks of the trees in the plantations withvarious CPR contained only 1/3 of the total nutrients when calculated with the removal ofthe nutrients. It is believed that all tree utilization and short rotation system were main factors responsible for nutrient depletion and productivity decline of the stand sites.