Humus-balancing methods are simple tools for the assessment of interactions between agricultural land use and soil organic matter (SOM). Aside from this commonality, approaches for humus balancing differ considerably with regard to their specific aim, scope, and methodical approach. The term "humus balance" covers both simple models to quantify SOM change in arable soils, or soil organic C (SOC) change in particular, and models that refer to the optimization of soil productivity in arable soils by calculating organic-fertilizer demand, without quantifying SOM or SOC change. This situation naturally has caused much discussion and misunderstandings. Against this background, the aim of this review is to systematically explore the different methodical approaches to humus balancing in order to contribute to a more sophisticated discussion of this model family, its opportunities, and limitations. As humus balancing has long history as well as special actual relevance in Germany, and, lately Switzerland, we focus on these countries and discuss the different approaches that are presently available and applied there. We argue that humus balances can be roughly categorized into "ecological" and "agronomical" approaches based on their specific concepts and methodology. Ecological humus balances comprise a strong link to quantitative SOM change, while humus balances of the agronomical family refer to the maintenance of soil productivity without a quantitative link to SOM change. Lately, some models have been presented that link the two concepts. However, we identify that humus-balancing methods often are insufficiently validated, partly because the validation of agronomical humus balances is not easily possible without a very comprehensive field-experimental basis. Further, the comparability of different approaches even within the two concept families is low at present, indicating the need for a comparative model evaluation for a proper assessment of the methods.

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The dry anaerobic batch digestion process is an organic waste treatment technology most appropriate for the treatment of stackable (non‐free‐flowing) dry organic waste materials. The effect of the process fluid percolation and substrate permeability on methane production of organic household waste was investigated in anaerobic dry digestion trials at pilot scale. The container system consisted of two percolation digesters and a fixed‐bed methane digester. The experimental results indicate that material compaction occurs during the digestion process and can have a negative effect on substrate permeability. Structure material addition reduced material compaction and as a result increased the substrate permeability.

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