Organic Matter Stabilization in Two Semiarid Tropical Soils: Size, Density, and Magnetic Separations
Organic Matter Stabilization in Two Semiarid Tropical Soils: Size, Density, and Magnetic Separations
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DOI：
10.2136/sssaj1998.03615995006200050015x
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发表时间：
1998-09
影响因子：
2.9
通讯作者：
C. Shang;H. Tiessen
中科院分区：
文献类型：
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作者：
C. Shang;H. Tiessen
许多热带土壤中的土壤有机质 (SOM) 不如温带土壤稳定，部分原因是热带地区分解过程较快，但也可能是由于有机矿物质稳定机制不同。我们使用粒度、密度和磁力分离研究了两种半干旱热带土壤（Oxisol 和 Alfisol）表面层中 SOM 的矿物组合。使用化学萃取和 X 射线衍射检查分级材料的无机相。与沙子部分相关的有机物质占土壤碳的 21% 至 30%，大部分为粗粒、漂浮物质。这种粗物质在阿尔菲索尔中更为丰富。两种土壤的有机碳的一半与淤泥大小的部分有关，其中含有很大一部分耐超声处理的微团聚体。粉粒大小的聚集体中的碳主要通过与结晶性差的氧化物结合以及与结晶性氧化物和粘土的聚集来稳定。通过连续的超声处理从淤泥尺寸的微团聚体中释放出的轻质碳（<1.8 g cm -3 ）占两种土壤总碳的23%。 <1.8 g cm -3 部分中的SOM似乎比具有相似密度和等效尺寸的温带土壤部分中的有机物质更年轻并且分解更少。在粘土中，C 集中在中等磁化率的部分，而主要是结晶良好的 Fe 的高磁性部分和非磁性部分都缺乏 C。该研究指出了铁氧化物的粒径和结晶度以及氧化物、有机质和其他矿物质之间的微聚集在稳定热带土壤有机质方面的重要作用。
Soil organic matter (SOM) in many tropical soils is less stable than that of temperate soils, in part due to faster decomposition processes in the tropics, but possibly also due to different mechanisms of organomineral stabilization. We studied the mineral associations of SOM in the surface horizons of two semiarid tropical soils (an Oxisol and an Alfisol) using particle-size, density, and magnetic separations. The inorganic phases of fractionated materials were examined using chemical extraction and x-ray diffraction. Organic matter associated with the sand fraction accounted for 21 to 30% of soil C, mostly as coarse, floating material. This coarse material was more abundant in the Alfisol. One-half the organic C of both soils was associated with the silt-sized fraction, which contained a substantial portion of microaggregates resistant to sonication. Carbon in silt-sized aggregates was mainly stabilized by association with poorly crystalline oxides and by aggregation with crystalline oxides and clays. The C as light matter (<1.8 g cm -3 ) liberated from silt-size microaggregates by successive sonication treatments accounted for 23% of total soil C for both soils. The SOM in the <1.8 g cm -3 fraction seemed younger and less decomposed than the organic materials in the temperate soil fractions with similar density and equivalent sizes. In clays, C was concentrated in fractions of intermediate magnetic susceptibility, whereas both the highly magnetic fraction of predominantly well-crystallized Fe and the nonmagnetic fraction were C poor. The study points to the important role of particle size and crystallinity of Fe oxides and of microaggregation between oxides, organic matter, and other minerals in stabilizing tropical soil organic matter.