A model ensemble approach to determine the humus building efficiency of organic amendments in incubation experiments

Abstract

Organic amendments are important to sustain soil organic matter (SOM) and soil functions in agricultural soils. Information about the contribution of organic amendments to SOM can be derived from incubation experiments. In this study, data from 72 incubated organic amendments including plant residues, digestates and manure were analysed. The incubation data was compiled from three experimental setups with varying incubation times, soils and incubation temperatures, in which CO2 release was measured continuously. The analysis of the incubation data was performed with an approach relying on conceptual parts of C‐TOOL, CCB, Century, ICBM, RothC and Yasso which are all well‐approved first‐order carbon models that differ in structure and abstraction level. All models are an approximation of reality, whereby each model differs in understanding of the processes involved in soil carbon dynamics. To accumulate the advantages from each model a model ensemble was performed for each substrate. With the ability of each carbon model to compute the distribution of carbon into specific SOM pools a new approach for evaluating organic amendments in terms of humus building efficiency is presented that, depends on the weighted model fit of each ensemble member. Depending on the organic substrate added to the soil, the time course of CO2 release in the incubation studies was predicted with different accuracy by the individual model concepts. Averaging the output of the individual models leads to more robust prediction of SOM dynamics. The EHUM value is easy to interpret and the results are in accordance with the literature.

Novel Methodology for the Assessment of Organic Carbon Stocks in German Arable Soils

“…Our approach is definitely a step in the direction of a more quantitative interpretation if these units can now be expressed in terms of C rep . This establishes a link to quantitative SOC modeling and allows the quantification of the balance elements from incubation experiments [36,37]. The application of this C rep -based scale to the dataset from Bad Lauchstädt is not a final validation, but provides reasonable results that open new prospects for a more sensible assessment of SOC stock together with soil management.…”

Transfer of carbon incubation parameters to model the SOC and SON dynamics of a field trial with energy crops applying digestates as organic fertilizers

“…Gasser et al (2021) demonstrated in a model ensemble approach amongst other models, the application of the CCB to incubation data. In this context, k 10 and k 12 were fitted to the mineralization of 72 different organic substrates.…”

“…The values for k fom and η (k 10 & k 12 ) for the plant residues were also obtained from Gasser et al (2021), whereby the analysed incubation experiments were conducted for fine and coarse roots separately. Owing to the different mineralization behaviour of coarse roots (relatively fast) and fine root (relatively stable) (Gasser et al, 2021), k fom and η were weighted according to their ratio, derived from Höcker (2017) (see Table A1 in Appendix 3). For green rye, no incubation data were available; therefore, the incubation data of winter wheat were used instead.…”

“…Especially, new or seldom applied organic amendments cannot be explored within field experiments to their fullest extent. A plausible method to study the quality of organic substrates is the modelling of incubation, as shown by Gasser et al (2021). The authors used the carbon turnover concepts of six mechanistic models to model the C dynamics of 72 incubated substrates.…”

“…The hypothesis that the results from incubation experiments can be used to model the turnover of organic substrates on field scale is proposed. To validate this hypothesis, a result dataset from an incubation study (Gasser et al, 2021) is used to parameterize the CCB model accordingly and applied on a field experiment where the same organic materials that were studied during incubation are applied as organic amendments. The data of incubated roots and stubbles are used to parameterize the residues used to model the field trial.…”