Increase in cation exchange capacity by the action of maize rhizosphere on Mg or Fe biotite-rich rocks

ABSTRACT The weathering of some silicate minerals in crushed rocks may occur in a few days of cropping and generate different physicochemical properties, with potential benefits to tropical soils. This study aimed to investigate the infuence of maize (Zea mays L.) rhizosphere on the weathering products and on the cation exchange capacity of Mg-biotite from biotite schist and Fe-biotite from biotite syenite. An experiment was carried out in pots, so that plants and crushed rock materials could be evaluated during seven successive growth cycles. The nutrients iron and potassium were taken up from biotite schist and biotite syenite during cropping. The weathering of both biotites promoted by the rhizosphere caused mineralogical changes. The most expressive change in the X-ray diffraction patterns occurred in the < 53 µm particle size fraction; however, the 53-300 µm fractions also changed. The alteration in the Mg-biotite, which has a lower Fe/Mg relation in octahedral sites than the Fe-biotite, was responsible for the most expressive cation exchange capacity increase in the fractions < 300 µm. However, the Fe-biotite weathering process, which presents a higher Fe/Mg relation in octahedral sites, did not increase the cation exchange capacity.

摘要 破碎岩石中的部分硅酸盐矿物可在作物栽培数日内发生风化，生成具有不同理化特性的产物，对热带土壤具备潜在应用价值。本研究旨在探究玉米（Zea mays L.）根际对黑云母片岩（biotite schist）中的镁质黑云母（Mg-biotite）以及黑云母正长岩（biotite syenite）中的铁质黑云母（Fe-biotite）的风化产物与阳离子交换量（cation exchange capacity）的影响。实验采用盆栽方式，可在7个连续的作物生长周期内对植株与破碎岩石材料开展评估分析。栽培过程中，作物可从黑云母片岩与黑云母正长岩中吸收铁、钾养分。根际促发的两种黑云母风化过程均引发了矿物学层面的变化。粒径小于53 μm的粒级组分在X射线衍射（X-ray diffraction）图谱中呈现出最为显著的变化；不过53~300 μm的粒级组分同样发生了改变。相较于铁质黑云母，镁质黑云母的八面体位点具有更低的Fe/Mg比值，其结构改造是导致粒径<300 μm粒级组分阳离子交换量显著提升的核心原因。然而，八面体位点Fe/Mg比值更高的铁质黑云母风化过程，并未使其阳离子交换量得到提升。