What dismantling an EW greenhouse experiment looks like

In preparation of the next experiment we have dismantled most of our 2023/2024 greenhouse experiment with 400 lysimeter pots over recent weeks. 80 pots have been preserved to run for a 3rd and 4th year. While taking apart the other 320 pots we have secured hundreds of samples that will be sent to various labs now, so we can find out what the data from the soils will tell us about the weathering processes over the last 2 years.

We are now preparing the next experiment, and it will be much bigger! Stay tuned.

“Killing” most of our pots

First we marked the pots with colored stickers (“stays”/”goes”), then we went to work. 320 pots with 15 kg of soil means we had to handle almost 5 tons of soil. We did many runs to the dumping grounds.

Many pots were taken apart and analyzed before dumping. We documented their status with photographs (can you see the worms’ tunnels?) and we took many many soil samples. This is a dirty job!

During the process we realized we made an unfortunate decision last summer: Some of the pots had been taken out of the irrigation cycle already last summer and had dried fully in the greenhouse since. Which made them hard as concrete and it was tough to the get the pCO₂ sensors out, before we could dump the soil properly. Now our soil pCO₂ sensors are ready for reuse in the next experiment:

We had been using two different models/builds of CO₂ sensors. Most of the second models did not survive. When we took them apart we found out why: The foam material we had used to hold the sensor in place had acted like a sponge and the sensors’ electronics died due to water.

Tea bags with rock dust

Every pot had a small tea bag with 5 gram of the amended rock dust buried in the soil. By preserving these bags we can now look at the rock grains, analyze changes in grain size distribution or BET surface area or find out if some “coating” has occured that might slow weathering.

Soil samples!

Ultimately, getting our hands on soil samples, was the most important part of the dismantling process. We couldn’t take soil samples earlier during the 24 months experiment because taking e.g. 100 g out of a 12-15 kg pot by poking a hole into it would have potentially changed the hydrology and as such the weathering processes.

We homogenized the soils (manually!) for different vertical layers and now these samples are sent to several labs around the planet for analysis. We are REALLY looking forward to finding out what these soil analyses will tell us about the weathering, this data will complement the extensive leachate water data, biomass data and gas data that we have already collected.

Gras/biomass samples

Over the 2 years we have collected and filed more than 5.000 biomass samples, individually packed and marked for each pot and for each cutting event. A few are already being analyzed, but most of them are waiting for a lab! If you know somebody who wants to get into this, let us know.

Waiting for the next experiment

Now the greenhouse is ready for the next set of experiments, and we will even double our greenhouse space for the 2025/2026 experiment. The new buckets are already waiting!