Organic carbon and particle size distribution of aggregates from chernozem under arable land and shelterbelt

The particle size distribution (PSD) and the content of organic carbon (Corg) in dry and water-stable aggregates were determined in the upper layer of chernozem under arable land and shelterbelt. In water-stable aggregates, the Corg content is 1.2-1.5 times higher than in dry sieving aggregates. Dry sieving and water-stable aggregates of arable chernozem consist of particles identical in terms of the PSD. And in the chernozem under the shelterbelt the content of physical clay increases with a decrease in the size of the aggregate in water-stable aggregates isolated from the fraction of dry sieving < 1 mm.

Initial aggregate formation: Disentangling the effects of soil texture, OM properties and microbial community using artificial model soils

&lt;p&gt;The interaction between mineral particles and organic matter (OM) is an important and complex process in the course of soil structure formation. For a better understanding it is necessary to disentangle the texture-dependent interplay of individual OM types and mineral particles. We developed an experimental set-up to study early aggregate formation within a controlled lab environment. Artificial soil microcosms with a mineral mixture resembling arable soils of three different textures (clay loam, loam and sandy loam) were used in a short-term, 30-day incubation experiment under constant water-tension. OM was added individually either as plant litter (POM) of two different sizes (0.63-2 mm and &lt; 63 &amp;#181;m, respectively) or bacterial necromass (Bacillus subtilis). The mechanisms of soil structure formation were investigated by isolating water-stable aggregates after the incubation, analyzing their mechanical stability and organic carbon allocation, and measuring the specific surface area and OM covers of the mineral surface, microbial activity, and community structure.&lt;/p&gt;&lt;p&gt;The dry mixing process and incubation of the mineral mixtures led to particle-particle interactions and fine particle coatings of the sand grains as shown by a reduction of the specific surface area. The OM input of all types caused between 3 to 17% of the mineral surfaces to be covered by OM, with larger covered areas in the clay-rich mixtures. The added OM was quickly accessed and degraded by microbes, as shown by the peak in CO&lt;sub&gt;2&lt;/sub&gt;-release within the first 10 days of the incubation. The POM of both sizes induced the predominant formation of water-stable macroaggregates (0.63-30 mm) with a mass contribution of 72 to 91% (irrespective of texture) and fostered the development of a microbial community with a high relative abundance of fungi. The bacterial necromass induced the formation of macroaggregates, but also microaggregates (63-200 &amp;#181;m), while the microbial community was dominated by bacteria. The mechanical stability analysis showed that very small forces &lt; 4 N were sufficient for aggregate failure and breakdown to 80% of the original aggregate size.&lt;/p&gt;&lt;p&gt;We propose that the microbial degradation of all OM types leads to small, distinct OM clusters consisting of OM substrate, microbes, and extracellular polymeric substances. These interact with mineral particles, resulting in the cross-linking of particles and formation of water-stable aggregates in all textures. The OM can thereby act both as microbial substrate and as structural building block. The initially formed aggregates are a loosely connected scaffold with a very low mechanical stability. Differences in the developed microbial community may lead to additional stabilization mechanisms, like fungal hyphae enmeshing and stabilizing larger aggregates also in sandy texture.&lt;/p&gt;

Comparison of water-stable aggregates on different soil types and land-uses in a Portuguese Mediterranean catchment

&lt;p&gt;Erosion is one of the main soil threats in the Mediterranean region, leading to degradation and desertification of several areas. Water stable aggregates (WSA) is a rate of the extent to which soil aggregates resist falling apart when wetted and hit by rain drops, indicating also the resistence of soil to compaction and soil quality status. This study aims to determine the WSA in differrent soils, characterized by distinct land-uses and soil types. This work is part of Ribeira dos Cov&amp;#245;es catchment research, in the suburbs of Coimbra, the largest city of central Portugal, where research dealing with soil and hydrological properties has been developed for long time. WSA were investigated for agricultural and forest soils, on both sandstone and limestone. Soil surface samples (0-10cm) were collected in December 2020, and analysed through wet sieving method which quantifies the amount of water-stable soil aggregates fractions. &lt;br&gt;&lt;br&gt;Not surprisingly, the results showed that forest soils contain a much higher proportion of water-stable soil aggregates of larger fractions than agricultural soil, where the smaller fractions prevailed. Similar results have been also reported in previous studies and found during our previous research at Praha-Suchdol locality (Housle), in Czech Republic. The fraction distribution of WSA in sandstone and limestone was comparable for forest soils. In case of agricultural soils, distribution of WSA was slightly different. WSA are a relevant part of soil surface layer, with important impacts on other soil properties (e.g. soil moisture, hydrophobicity, infiltration), thus affecting the rainfall-runoff-erosion processes, previously investigated in the study area. Further research will be developed to better assess WSA differences between distinct forest types, given the relevance of vegetation species for example on hydrophobicity and WSA dynamics. A better understanding of WSA in different soil types will be useful to support improved soil management and mitigate land degradation.&lt;/p&gt;