The (Bio)Chemistry of Soil Humus and Humic Substances: Why Is the “New View” Still Considered Novel After More Than 80 Years?

Abstract

Three years ago, a novel "soil continuum model" was proposed, in which soil organic matter was suggested to be of heterogeneous composition and to consist of a continuum of organic fragments of all sizes. A search of the literature reveals that this model is identical to several similar conceptualizations proposed about 15 years ago, and that it corresponds closely with the description of humic substances given in Waksman's (1936) remarkably thorough book on the topic, which also emphasized the intimate connections existing between humic substances and soil microorganisms. Several historical reasons, reviewed in this Perspective article, may explain why Waksman's viewpoint might still be considered novel more than 80 years later. Here we argue that the key reason for the agonizingly slow rate of progress in the field is linked to the extreme compartmentalization of research and education in soil science, which has been organized along distinct subdisciplines, with the result that interdisciplinary efforts that are desperately needed to understand the dynamics of soil humic substances are very hard to launch. To meet growing demands on soils we have to understand the mechanisms that underpin their many functions. To gain this understanding and finally make badly needed progress, we must reorganize funding and educational efforts to support exploration of "Waksman's frontier," which includes the microscale where the microbial, physical and biochemical processes governing organic matter turnover occur.

Conceptualizing soil organic matter into particulate and mineral‐associated forms to address global change in the 21st century

“…Humic substances have been the subject of much scrutiny. Recognition that they were artificial by‐products of extraction and inaccurate proxies for naturally occurring SOM began to emerge as early as the 1840s (see references to Mulder and Eggertz in Baveye & Wander, ; Waksman, ), and they have more recently been dismissed by much of the SOM community (Lehmann & Kleber, ). In place of harsh chemical separations, physical methods of separation based on size and/or density have gained favor.…”

Interactions between Humic Substances and Microorganisms and Their Implications for Nature-like Bioremediation Technologies

“…One of them sees HSs as aggregates of low-molecular-weight compounds [ 41 , 42 , 43 ]. The debate on the structure of HSs is not over yet [ 40 , 44 , 45 ]. It is generally accepted that HSs are composed mainly of aromatic, aliphatic, phenolic, quinonic, and N-derived components, which are covalently bound through C–C, C–O–C, and N–C bonds.…”

Editorial: Elucidating Microbial Processes in Soils and Sediments: Microscale Measurements and Modeling

“…They highlighted that when different methods are being integrated, one needs to consider an "appropriate spatial scale" to understand the factors that regulate the distribution of microbial communities in soils. It is hoped that these type of interdisciplinary efforts will not only help us understand better what controls the activity of microorganisms in soils, but will also enable us to (finally) make progress on the intimately linked topic of the dynamics of humic substances (e.g., Baveye and Wander, 2019).…”