Mechanisms of soil acidification under leguminous fast growing tree plantations in the humid tropics and its prediction

本研究以印度尼西亚南苏门答腊省的马占相思人工林为研究对象，探讨在湿润热带地区建立豆科速生树种人工林引起土壤酸化的可能性及其机理，并建立酸化预测方法。1)在较大面积的多点土壤调查的基础上，用经验的方法说明退化的水芹草地向相思人工林的转化导致了明显的土壤酸化，土壤养分转运到生长的乔木生物量所导致的土壤交换性盐基离子的减少是酸化的主要原因。此外，还表明含可变电荷特性矿物的湿润热带土壤的有效阳离子交换量可能会随着土壤酸化而下降，并可能进一步加速土壤…。L进一步酸化2)以重粘性土和轻粘性土上的7年生相思林为材料，通过破坏性测定，建立了异速生长公式，并测定了各器官的养分浓度。基于这些信息，在假定养分只通过降水输入的情况下，估算了树木通过采收输出的养分，并模拟了可能的补种-采收轮作次数。3)对凋落物(Ao层，0层)中凋落物、穿透雨、树干径流和水分在凋落物层(Ao层，0层)中的迁移和分解释放的养分和溶解有机质进行了为期3年的监测，结果表明，各相关参数在旱季和湿季之间表现出明显的季节性，大部分是相互关联的。4)根据离子平衡和物质平衡建立了土壤酸化预测模型，并利用野外观测数据预测了三个轮次土壤的变化。模型的模拟结果表明，土壤酸化可能出现快速而显著的变化，但模型仍有不足之处。较少

This study was conducted in the Acacia mangium plantation in the Province of South Sumatra, Indonesia for the purpose of elucidating the possibility of soil acidification caused by establishment of leguminous fast growing tree plantation in the humid tropics and its mechanism, and to develop the methodology to predict the acidification. The progresses obtained are the followings.1)Based on the multipoint soil survey covering relatively large area, we illustrated in an empirical way that conversion of degraded Imperata grassland into Acacia tree plantation causes obvious soil acidification, and the decline in exchangeable base cations in soils resulted from nutrients trans location from soil to growing tree biomass is the major cause of the acidification. Furthermore, it was indicated that effective cation exchange capacity of the humid tropical soils containing minerals of variable charge characteristics might decline with soils acidification, and it may possibly accelerate further soi … More l acidification.2)For the two 7-year-old Acacia stands respectively on a heavy clay soil and a light clay soil, allometry formulas were developed by destructive measurements, and nutrients concentrations were determined for every organ of trees. Based on these information, nutrients export through tree harvest was estimated, and possible number of replanting-harvest rotation was simulated on a supposition that nutrients is input only through precipitation. The results of simulation suggested that Ca and K will become deficient in near future and its magnitude is different by the soil characteristics especially clay content.3)Nutrients transported by litterfall, throughfall, stemflow and water percolation through litter layers (Ao horizon, 0 horizon), and nutrients and dissolved organic matter released from litter decomposition were monitored for 3 years at the permanent plot, and the results showed every related parameters display obvious seasonality between drier and wetter seasons mostly in conjunction with each other.4)A model to predict the soil acidification was formulated based on ion balance and mass balance, and soil change during a period of three rotations was predicted by using data collected by field observation. The simulation output by the model indicated possible rapid and significant soil acidification, however also it became clear that the model still have weakness to be improved. Less