Increasing and Sustaining Productivity of Tropical Eucalypt Plantations Over Multiple Rotations

Summary

Eucalypt plantations in India are an important source of fiber for paper making and fuel for local villagers. Large areas of land have supported eucalypt plantations for several rotations, and productivity has generally been declining through successive rotations. In 1997, we initiated a project to examine site management options as a way to improve the productivity of these sites. We established a large experimental infrastructure at each of four sites in Kerala, consisting of up to five separate fully randomized block experiments at each site, examining interrotation management options (organic matter manipulation, N and P fertilizer input, legume cover cropping, weed control). Two of the sites were typical lowland plantations with Eucalytus tereticornis, and the other two sites were typical upland plantations with Eucalytus grandis. Following treatments, we monitored plantation productivity and impacts on soil and nutrient cycling for one full rotation (6.5 years). We found it is possible to increase the volume growth of E. grandis by up to 48%, and E. tereticornis by up to 268% through a combination of optimum site practices (mostly weed control and nutrient addition), but productivity responses are dependent on site-specific factors. Key outcomes of this research are presented, with special reference to application in the broader context of tropical eucalypt plantations.     

不同树龄橡胶林土壤微生物生物量碳的垂直分布特性

采用时空替代法,选取4,12,19,24,29 a橡胶林,研究不同树龄土壤微生物生物量碳含量的分布特征及其与有机碳含量的比值、以及与土壤养分含量的相关关系。结果表明:4,12,19,24,29 a橡胶林不同土层微生物生物量碳含量在28.87～138.71mg/kg之间,随土层深度的增加明显下降;土壤微生物生物量碳含量和有机碳的比值在0.66%～2.10%之间,土壤碳处于积累状态;土壤微生物生物量碳含量与有机碳、全氮、全磷含量有显著的相关性,相关系数R>72%。     

桂西南两种桉树人工幼林生物量、营养元素积累量及其分布特征

对广西宁明县相似立地条件下1年生尾巨桉(DH32-29)和雷林1号桉幼林的生物量和5种营养元素(N、P、K、Ca 和 Mg)积累量及其分配特征进行了研究。结果表明：1年生尾巨桉和雷林1号人工幼林林分生物量分别为13.70和12.06 t·hm–2,不同器官生物量均以树干最大,树叶或树根最小。两种桉树不同器官中营养元素含量均以树叶最高,其次是树皮、树枝和树根,树干最低,林木不同器官中营养元素含量均以 N 最高,其次是 K 和 Ca,Mg 和 P最低。1年生尾巨桉幼林营养元素积累量为124.84 kg·hm–2,略低于雷林1号桉幼林(132.76 kg·hm–2),5种营养元素积累量在尾巨桉人工林的分配为树叶＞树枝＞干皮＞干材＞树根,在雷林1号桉的分配为树枝＞树叶＞干材＞干皮＞树根。尾巨桉幼林营养元素利用效率略高于雷林1号桉幼林。