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ISMC News 17 October 2022

Announcements + Featured Paper + Featured Soil Modeller
Verra seeks applications from qualified independent modeling experts (IMEs) experienced in using process-based biogeochemical models. IMEs will be contracted to participate in the assessment of agricultural carbon projects that use biogeochemical models to estimate GHG fluxes and soil organic carbon (SOC) stock changes. Approved applicants will be added to a publicly available document on Verra’s website and may be contacted by prospective projects and/or third-party validation/verification bodies (VVBs) seeking IME support.
Verra is a globally active non-profit organization that manages the Verified Carbon Standard (VCS), the world's most widely used voluntary GHG crediting program, and other emerging sustainability standards. The most recent VCS methodology in the agriculture sector, VM0042 Methodology for Improved Agricultural Land Management, targets GHG emission reductions and removals through SOC accrual and includes an optional biogeochemical modeling component. The methodology includes a guidance module, VMD0053 Module for model calibration, validation, and uncertainty guidance, that stipulates calibration and validation procedures for biogeochemical models. It defines criteria for model application to ensure appropriateness for the cropping system and biophysical conditions occurring in each project. Adherence to VMD0053 is assessed via a model validation report (MVR) that must be assessed by a qualified IME who is contracted by the VVB responsible for the overall audit of the VM0042 project. IMEs may be individuals or organizations and must meet the minimum qualifications listed in the document “Clarifications to VM0042 Methodology for Improved Agricultural Land Management, V1.0”.
Interested parties can email Chris Ajemian ( for more information on applying to serve as an IME and apply by sending a completed application form.
Featured Paper
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Analyzing dual porosity in soil hydraulic properties using soil databases for pedotransfer function development
Current databases of soil hydraulic properties (SHPs) have typically been used to develop pedotransfer functions (PTFs) to estimate water retention [θ(h)] assuming a unimodal pore-size distribution. However, natural soils often show the presence of bimodal to multimodal pore-size distributions. Here, we used three widely spread databases for PTF development: UNsaturated SOil hydraulic DAtabase (UNSODA) 2.0, Vereecken, and European hydropedological data inventory (EU-HYDI), to analyze the presence of structural effects in both θ(h) and hydraulic conductivity [K(h)]. Only undisturbed samples were included in the analysis that contained enough datapoints for both θ(h) and K(h) properties, especially in the wet range. One-hundred ninety-two samples were suitable for our analysis, which is only 1% of the total samples in the three databases. Results showed that 65% of the samples exhibited a bimodal pore-size distribution, and bimodality was not limited to fine-textured but also coarser-textured soils. The Mualem–van Genuchten (MvG) expression for both unimodal and bimodal soils was not able to predict the observed unsaturated K. Only a joint fitting of measured θ(h) and K(h) functions provided parameter estimates that were able to describe unsaturated K for uni- and bimodal soils. In addition, we observed a negative relationship between α and n in the case of low sand content (<52%) for both unimodal and bimodal matrix domain properties, contradicting the classical notion. The ratio of α for the macropore and matrix domain was positively correlated with the fraction of macropores and sand content. We anticipate that the results will contribute to deriving PTF for structured soils and avoid unrealistic combinations of MvG parameters.
Figure 5. The relationship between van Genuchten α (cm−1) vs. n taken from literature. The superscript in the legend indicate dataset from 1Schaap and Leij (1998), 2Wösten et al. (1999), 3Puhlmann and von Wilpert (2012), and 4Botros et al. (2009). Dataset from Schaap and Leij (1998) and Wösten et al. (1999) represent mean values for the USDA textural classes. The dataset with the α value in the range of .02 and .05 and high n values are encircled by the red box. The trendline was added for the remaining dataset excluding the data in the red box
Featured Soil Modeller
Modeling microbial matter and energy flows for improved understanding of agroecosystems
Holger Pagel is an environmental engineer by training and got passionate about soils during his diploma studies at the TU Berlin (Germany) which he completed in 2007. He received his Ph.D. in agricultural sciences at the University of Hohenheim (Germany) in 2015, where he has worked as a researcher and lecturer since then. He led the interdisciplinary Young Investigator Group »Microbial Regulation of Soil Functions in Agroecosystems« (2015 – 2019). Since 2021 he has worked as a researcher on integrated trait-based modeling of carbon and energy flow in soil systems (project TraiMErgy within the priority programme 2322 »SoilSystems«, His research includes modeling and experimental work at mm scale up to the field scale related to soil organic matter turnover, the environmental fate of agrochemicals and microplastics, model-based optimal experimental design, and model-data fusion optimization. He teaches courses in environmental modeling.
- Please tell us briefly about yourself and your research interest
I am a soil system modeler who links soil physics, soil biology, and systems ecology. My focus is on understanding and predicting biogeochemical cycling, ecosystem resilience, and soil-plant interactions. I use trait-based approaches to model soil microbial communities and associated biogeochemical processes. My collaborators and I use and extend Bayesian methods for optimal experimental design and constraint-based inference. I’m excited and becoming successively involved in using hybrid modeling approaches that link process-based models with machine learning methods for improved model conditioning and prediction. Beyond modeling, I’m also interested in non-invasive and low-cost techniques for monitoring biogeophysical processes and agrochemical fate.
-  How did you first become interested in soil modeling and learn about ISMC?
My first exposure to soil modeling was using HYDRUS to simulate soil water dynamics with the Richards-Richardson equation in an undergraduate soil physics course, which was an eye-opener. During my Ph.D. I developed a process-based model that helped to understand accelerated pesticide biodegradation triggered by additional carbon supply. I don’t remember how I heard the first time about ISMC but got involved the first time during the ISMC conference 2016 in Austin/ Texas (USA).
-Can you share with us your current research focus? And, please tell us briefly how your research could contribute to ISMC Science Panel’s activities
Part of my recent research concentrates on modeling and understanding spatial controls of microbial carbon and pesticide turnover as well as on gene and enzyme-based modeling. My current research activities focus on developing an advanced bioenergetic modeling framework to predict matter and energy flows related to organic carbon turnover in soil systems (project TraiMErgy, In the CROP project (, we are developing and conditioning a trait-based rhizosphere microbiome model (PhD thesis of Ahmet Sircan). Linked to both projects I also currently refine a Bayesian method for constrained-based model conditioning that is generally applicable as a tool to integrate expert knowledge in soil and earth systems models systematically. Model approaches and methods developed in my research could contribute to ISMC activities that involve advancing the representation of microbial-mediated processes in soil models. Process-based models developed in my research could be linked with machine-learning methods and used to develop pedo-transfer functions for predicting soil microbial biomass and diversity and related degradation processes (pesticides, carbon and nitrogen cycling).
-Please tell us how can ISMC help you advance in your career?
For me, ISMC provides a platform to connect with people with complementary expertise, establish new collaborations, and discuss and share ideas to address current challenges. In this way it boosts bridging expertise and starting new research initiatives.
- What resources or skills would you recommend that early career members of ISMC should acquire? And how can ISMC help and support early career members in this regard?
Early career members of ISMC should develop a thorough understanding of soil processes, best at multiple scales. They should gain skills in estimating and evaluating parameter and prediction uncertainties. I recommend engaging in ISMC working groups to get in touch with experienced researchers and to get involved in scientific collaborations early on. ISMC can support early career members by organizing workshops/ summer schools that foster specific modeling skills and bring together early career modelers across topics and scales.



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