Blog article - Dirk Paessler, Jens Hammes, Ralf Steffens, Ingrid Smet - 21.1.2024 - V1.0

Abstract

In our endeavor to measure the climate relevant effects of rock weathering in agriculture we have been setting up several field and greenhouse experiments over the last three years. During this work we started experimenting with low cost electronic sensors in 2022 with the goal to monitor the soil gas CO₂ concentration (pCO₂) in our enhanced rock weathering (ERW) experiments, mainly in lysimeters in fields and greenhouses. 

In this article we document our latest sensor design which gives us reasonably good pCO₂ measurements as well as the steps that got us to this design. We furthermore share a preview of our pCO₂ data and compare these with the CDR estimates we recently derived from soil leachate alkalinity measurements.

So far, we haven’t observed a good match between these two parameters which likely indicates that leachate alkalinity and soil pCO2 data alone do not suffice to understand all carbon related processes in the soil. Our main observation is that whether or not the soil pCO2 changes after rock dust amendment, and if it does whether it increases or decreases, seems to mostly depend on the soil type rather than the type of rock dust. This could explain why studies where only one or two soil types are tested result in very different conclusions. 

In our main experiment with 4 soils and 4 types of rock dust the majority of soil-rock variations tends to move towards an increase in soil pCO₂ although only a few of them are significantly different from their control. In our secondary experiment where the same rock dust was applied to 7 different soils, we see almost the opposite as now 5 out of 7 variations are significantly different from their control, showing 2/3 increase/decrease of the soil pCO2. We will continue monitoring soil pCO2 to see how these trends might evolve over time and whether a correlation between soil water alkalinity and soil pCO₂ still emerges.

Despite giving away the ending already, we hope this story is still an entertaining and interesting read. Follow us through the jungle of building scientific instruments from scratch and trying to make them work in greenhouse as well as in outdoor settings.

Note 1: What you are about to read is a hopefully entertaining mashup of a photo album of our prototyping experiences along with the reasoning of why we do this and an overview of the data we have generated so far. This is not a scientific article, although we certainly strive to do serious scientific work at all times. 

Note 2: According to feedback from scientists we are doing something unusual with our pCO₂ based approach - which is intentional. Only if one does things differently will he or she be able to achieve different results. We all know the challenge of measuring the carbon dioxide removal effects of enhanced rock weathering at scale in agriculture has not yet been solved. Our goal is to uncover new potential MRV approaches using novel concepts. Measuring the pCO₂ is one of the things that might help, but nobody knows yet if this will actually be a solution, or even a part of it. Although we don’t actually measure the CDR, the pCO₂ metrics might at least help to understand the carbon fluxes and balances inside our experiments which could bring us one step closer to MRV. In essence, we will either fail completely - as predicted by some of these scientists - or we will find some surprising new insights. We are ready for both outcomes, let’s enjoy the journey anyway. 

Download the full paper

Here is the download of the paper (pdf, 22 pages, 6 MB, V1.0, Jan 1st 2024).

DOI is coming soon.

Please send feedback to info@carbon-drawdown.de!