Biogenic and physicogenic aggregates: formation pathways, assessment techniques, and influence on soil properties

Abstract

The soil particles can be gathered through physical and/or chemical processes in association with the biological activity, leading to the formation of aggregates. Soil aggregates has several functions in the soil, increasing macroporosity and water circulation -consequently reducing soil erosion and mechanical resistance to root growth, contributing to greater fixation of plants to the soil and absorption of water and nutrients, and protection of intra-aggregate organic matter. The aggregates were initially classified morphologically and in terms of their stability. In recent years, another way of evaluating aggregates, regarding their formation or origin pathway, has gained prominence in the studies conducted in Brazil. As for their origin, the aggregates can be classified morphologically as physicogenic, biogenic, or intermediate. This manuscript presents the techniques used to sample aggregates, the morphological patterns for their distinction observed in different soil classes and management types, and the chemical and physical properties. Additionally, we present analyses that are not commonly used to evaluate aggregates but which have the potential to be used as tools for a better understanding of their origin and to evaluate their modifications when subject to different types of management. In practical terms, identifying the aggregate origin and determining the related attributes allows recognizing the effect of vegetation/soil/management on soil aggregate forming agents, mainly roots and soil fauna, which reflects soil quality. For future studies, and especially to determine the importance of biogenic aggregation in improving edaphic properties, we suggest the use of micromorphology, near-infrared spectroscopy, X-ray computed tomography, clay dispersion analyses in addition with chemical, physical, and biological analysis. This approach can contribute to the identification of other patterns related to pedogenesis and the pathways of aggregate formation.

Stability, labile organic carbon, and glomalin of biogenic aggregates in sandy soils under management systems in the subtropical region of Brazil

“…The aggregates retained in the two intervals of 9.7> Ø ≥8.0 and 8.0> Ø ≥4.0 were selected for the study. The aggregates obtained in each interval were examined under binocular magnification and manually separated according to their origin or route of formation, according to the morphological patterns established by Bullock et al (1985) using the protocol adapted by Pulleman et al (2005) and validated by the studies gathered in Pereira et al (2021).…”

“…Aggregates and their stability influence a wide range of soil properties, including carbon stabilization, porosity, water infiltration and aeration, compaction and densification, water retention, hydraulic conductivity, and the ability to resist erosion (Cheng et al, 2015). Many researchers (Six et al, 2000(Six et al, , 2004Bronick and Lal, 2005;Briedis et al, 2012;Tivet et al, 2013;Melo et al, 2019aMelo et al, , 2021Lavelle et al, 2020;Pereira et al, 2021) consider aggregate stability as a reflection of soil structure and, consequently, of edaphic quality in general because it depends on an integrated balance between chemical, physical, and biological factors. A better understanding of the balance and interactions between these factors can improve our understanding of soil restoration and/ or recovery, and thus the ability of soils to perform services ranging from food production to services of an ecosystemic nature (Lavelle et al, 2020).…”

“…Some studies have evaluated the existence of a third class of aggregates (the intermediates) and their influence on soil properties (Pulleman et al, 2005;Batista et al, 2013;Ferreira et al, 2020). However, a specific origin or formation pathway has not yet been identified for this aggregate class (Pereira et al, 2021) because it commonly encompasses aggregates that cannot be classified as biogenic or physicogenic. For the more established aggregate classes, physical, chemical, and biological analyses are often performed to understand the contribution of the aggregation pathways to soil properties.…”

“…For the more established aggregate classes, physical, chemical, and biological analyses are often performed to understand the contribution of the aggregation pathways to soil properties. In addition to compiling studies that have reported improvements in soil attributes due to biogenic aggregation, Pereira et al (2021) also suggested the use of other methods or indicators that can be applied to evaluate soil structure and/ or aggregates.…”

Alterações na qualidade do solo induzidas pelo uso de ativador da microbiota em áreas cultivadas com soja e milho

“…Portanto, o estímulo da atividade dos microrganismos nativos do solo gerado por um ativador da microbiota, ao longo do tempo, poderia promover alterações nas propriedades físicas do solo indiretamente. Isto por meio da formação de agregados e bioporos (Vogel et al, 2022), através da exsudação de substâncias cimentantes ou pelo próprio desenvolvimento das hifas de fungos que aproximam as partículas de solo (Pereira et al, 2021). No entanto, os resultados deste estudo demonstraram que não houve efeito da aplicação do ativador da microbiota nos atributos físicos do solo nessa primeira safra.…”