Aluminum chemistry of nonallophanic Andosols

本研究的目的是通过考察铝在铝腐殖菌络合物主导的土壤中的溶解度和释放率，扩大先前关于铝化学的研究。铝在pH范围3-5的溶解度关系是在30天的平衡研究中确定的。用10^<-3> M醋酸缓冲液调节pH值为3.5、4.0和4.5，用焦磷酸钠、草酸和KCl溶液预处理土壤样品，使用搅拌式流动反应容器测量铝的释放率。非allophanic Andosol样品的pAl - pH斜率为2.0-2.4，溶解度明显低于普通Al(OH)_3相。土壤样品显示出非常快的铝释放速率。提取液的pH和离子强度对铝的释放速率有很大影响。焦磷酸盐处理使铝的释放率降低到非常低的水平，表明铝腐殖质复合体是溶解铝的主要来源。一些非钾化土壤表明，氯化钾处理后的残留物的铝释放率和铝释放总量大于或几乎与未处理的土壤样品相同。因此，在以腐殖质络合物为主的土壤中，1M kcl可提取Al的量并不总是反映可交换Al的量。本研究和文献表明，kcl可萃取Al的量与有机络合Al的量密切相关。这些数据表明，非allophanic andosol中铝的动力学很大程度上受Al离子与腐殖质交换的影响。

The aim of this study is to expand upon previous investigations about aluminum chemistry by examining aluminum solubility and release rates in soils dominated by Alhumus complexes. Aluminum solubility relationships over the pH range 3-5 were determined in a 30-d equilibration study. Aluminum release rates were measured using a stirred, flow-through reaction vessel with 10^<-3> M acetate buffer adjusted to pH 3.5, 4.0 and 4.5 for pretreated soil samples with Na-pyrophosphate, acid oxalate and KCl solutions.The nonallophanic Andosol samples displayed pAl versus pH slopes of 2.0-2.4 and solubilities considerably lower than those of common Al(OH)_3 phases. The soil samples showed very rapid Al release rates. The Al release rates were greatly dependent on the pH and ion strength of extracting solution. Pyrophosphate treatment reduced Al release rates to very low levels indicating that Al-humus complexes were the primary source of dissolved Al.Some non-allophanic soils showed that the aluminum release rates and the total amount of Al released from KCl-treated residues were greater than or nearly identical with those of non-treated soil samples. Thus, the amount of 1M KCl-extractable Al does not always reflect the amount of exchangeable Al in soils dominated by Al-humus complexes.This study and the literature showed that the amount of KCl-extractable Al is closely related to the amount of organically complexed Al. These data indicates that the dynamics of aluminum in nonallophanic Andosols is largely influenced by the exchange of Al ions with humic substances.