The effect of ionic strength variation and anion competition on the development of nitrate accumulations in variable charge subsoils
The effect of ionic strength variation and anion competition on the development of nitrate accumulations in variable charge subsoils
复制标题
离子强度变化和阴离子竞争对可变电荷底土中硝酸盐积累发展的影响
DOI：
10.1071/sr04036
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发表时间：
2005
期刊：
影响因子：
1.6
通讯作者：
N. Menzies
中科院分区：
文献类型：
--
作者：
M. Donn;N. Menzies
氮肥的淋溶导致了约翰斯通河流域深层土壤（>5米深）中硝酸盐（NO3）的积累。本文概述了这些NO3积累形成和维持的化学机制。这是通过一系列的列实验，旨在调查NO3淋溶有关的土壤电荷化学和阴离子交换网站的竞争。可变电荷矿物的存在导致了这些配置文件中的正表面电荷的形成。土壤溶液离子强度的增加伴随着肥料淋溶前沿的作用，以增加正（和负）电荷密度，从而为NO3提供吸附位点。土壤溶液离子强度的降低发生在肥料脉冲移动经过剖面中的一个点之后，由于雨水的稀释。然后，硝酸盐从交换中释放回土壤溶液中，从而缓冲土壤溶液离子强度的降低。由于在本实验中NO3在整个剖面中被吸附，因此不能有效地解释现场发生的情况。硫酸盐（SO4）剖面分布的以前的观察表明，大的SO4积累在上部剖面可能会影响NO3的分布，通过竞争吸附位点。随后的实验调查SO4添加对NO3浸出的影响表明，NO3吸附是最小的上部配置文件。NO3的吸附确实发生了，尽管仅在SO4占有率低的剖面区域，即在较低的剖面中。因此，NO3积累的形成取决于可变电荷矿物学，电荷密度随土壤溶液离子强度的变化，以及SO4竞争吸附位点的影响。
The leaching of N fertilisers has led to the formation of nitrate (NO3) accumulations in deep subsoils (>5 m depth) of the Johnstone River catchment. This paper outlines the chemical mechanism by which these NO3 accumulations are formed and maintained. This was achieved via a series of column experiments designed to investigate NO3 leaching in relation to the soil charge chemistry and the competition of anions for exchange sites. The presence of variable charge minerals has led to the formation positive surface charge within these profiles. An increase in the soil solution ionic strength accompanying the fertiliser leaching front acts to increase the positive (and negative) charge density, thus providing adsorption sites for NO3. A decrease in the soil solution ionic strength occurs after the fertiliser pulse moves past a point in the profile, due to dilution with incoming rainwater. Nitrate is then released from the exchange back into the soil solution, thus buffering the decrease in the soil solution ionic strength. Since NO3 was adsorbed throughout the profile in this experiment it does not effectively explain the situation occurring in the field. Previous observations of the sulfate (SO4) profile distribution indicated that large SO4 accumulations in the upper profile may influence the NO3 distribution through competition for adsorption sites. A subsequent experiment investigating the effect of SO4 additions on NO3 leaching showed that NO3 adsorption was minimal in the upper profile. Adsorption of NO3 did occur, though only in the region of the profile where SO4 occupancy was low, i.e. in the lower profile. Therefore, the formation of the NO3 accumulations is dependent on the variable charge mineralogy, the variation of charge density with soil solution ionic strength, and the effects of SO4 competition for adsorption sites.