Abstract
Soil structure refers to the spatial arrangement of primary soil particles and pores, and is known to influence a variety of soil functions including carbon sequestration and water holding capacity. At present, research in this field is often divided, focusing either on pores where pore networks are investigated in undisturbed soil or on solids where isolated soil aggregates are commonly studied. The choice of approach depends on the needs and traditions in different disciplines of soil science. While there is much debate regarding how well these viewpoints relate to each other, there have been only marginal research efforts undertaken to compare them quantitatively. In this study, we presented and evaluated methods to identify 3-D subunits in X-ray images of eight undisturbed soil samples that we interpreted as macroaggregates, and compared these to to results from drop-shatter tests. Here, we exploited the cohesive forces of water that induces shrinkage cracks under drying. Despite promising trends, comparisons between image and drop-shatter test derived aggregate properties remained inconclusive. Nevertheless, our results encourage further investigations on larger sample sets and different observation scales. The here presented and discussed aggregate delineation methods illustrate an approach to harmonize soil structure characterization in terms of both pore-networks and soil aggregation. For example, respective extended approaches may be developed to evaluate the locations of microaggregates within macroaggregates.
Highlights
The term soil structure, similar to that of soil architecture, refers to the morphology and topology of soil pores and solids (Rabot et al, 2018)
We focused on soil samples of several centimetre diameter and exploited tensile forces that occur in drying soils with sufficient amounts of shrinking and swelling clay minerals
To examine how pore networks influence the frag mentation of the soil we investigated correlations between mea sures of soil aggregate sizes and morphological properties of the pore network of the respective intact soil samples
Summary
The term soil structure, similar to that of soil architecture, refers to the morphology and topology of soil pores and solids (Rabot et al, 2018). The second point of view describes soil structure by the arrangement of individual mineral and organic primary particles as well as different levels of aggregations (Tisdall and Oades, 1982). According to the Soil Science Society of America (SSSA, 1997), an aggregate is defined as “a group of primary soil particles that cohere to each other more strongly than to other surrounding particles”. To avoid confusion and following the SSSA, we define a soil aggregate as any aggregation of soil primary particles, regardless of size, that is held together by any kind of cohesive force, be it of biotic origin or not
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