UNCIEP, Instituto de Ecología y Ciencias Ambientales, Facultad de Ciencias, Universidad de República, Iguá 4225, CP 11.400, Montevideo, Uruguay.
Sci Total Environ. 2012 Nov 1;438:549-57. doi: 10.1016/j.scitotenv.2012.08.075. Epub 2012 Oct 10.
The current change in land use of grassland in the temperate region of South America is a process associated with the worldwide expansion of annual crops and afforestation with fast growing exotic species. This last cultivation has particularly been the subject of numerous studies showing its negative effects on soil (acidification, loss of organic matter and base cations, among others). However its effects on the mineral fraction are not yet known, as it is generally considered as one of the slowest responses to changes. This stimulated the present study in order to assess whether the composition of clay minerals could be altered together with some of the physicochemical parameters affected by afforestation. This study compares the mineralogical composition of clays by X-ray diffraction (XRD) in a grassland soil (Argiudolls) under natural coverage and under Eucalyptus grandis cultivation implanted 25 years ago in a sector of the same grassland. The tendency of some physicochemical parameters, common to other studies was also compared. XRD results showed, as a most noticeable difference in A(11) and A(12) subhorizons (~20 cm) under eucalyptus, the fall of the 10Å spectrum minerals (illite-like minerals), which are the main reservoir of K in the soil. Meanwhile, the physicochemical parameters showed significant changes (p<0.01) to highly significant ones under eucalyptus, particularly in these subhorizons, where on average soil organic matter decreased by 43%; K(+) by 34%; Ca(2+) by 44%, while the pH dropped to this level by half a point. Our results show that the exportation of some nutrients is not compensated due to the turnover of organic forestry debris; the process of soil acidification was not directly associated with the redistribution of cations, but with an incipient podzolization process; the loss of potassium together with soil acidification, leads to a drastic change in clay mineralogy, which would be irreversible.
目前，南美洲温带地区草原的土地利用变化是一个与全球范围内一年生作物的扩张和速生外来树种造林相关的过程。后一种栽培方式尤其成为了大量研究的主题，这些研究表明其对土壤具有负面影响（酸化、有机质和碱基阳离子流失等）。然而，其对矿物组分的影响尚不清楚，因为一般认为它是对变化反应最慢的因素之一。这激发了本研究，以评估粘土矿物的组成是否会随着造林而发生变化，以及一些受造林影响的理化参数。本研究通过 X 射线衍射（XRD）比较了天然覆盖下的草原土壤（Argiudolls）和 25 年前在同一草原的一个区域种植的桉树（Eucalyptus grandis）下的粘土矿物的矿物组成。还比较了其他研究中常见的一些理化参数的趋势。XRD 结果表明，桉树种植下 A(11)和 A(12)亚层（~20 厘米）最明显的差异是 10Å 谱矿物（类伊利石矿物）的下降，这些矿物是土壤中钾的主要储备。同时，理化参数显示在桉树种植下发生了显著变化（p<0.01），甚至是高度显著变化，特别是在这些亚层中，土壤有机质平均减少了 43%；K(+)减少了 34%；Ca(2+)减少了 44%，而 pH 值下降了半点。我们的结果表明，由于有机林业废弃物的周转，一些养分的输出没有得到补偿；土壤酸化过程与阳离子的再分配没有直接关系，而是与初始的灰化过程有关；钾的流失与土壤酸化一起导致了粘土矿物学的急剧变化，这将是不可逆转的。
