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The science of a buried tea bag

Ed note: This is a guest post by  on a global initiative to study decomposition in diverse systems. 

Globally, about 2700 tons of carbon are stored in the soil, which is 2-3 times as much as in the atmosphere. Therefore, changes in the decomposing activities of soil organisms may have large implications for the concentration of the greenhouse gas carbon dioxide (CO2) in the atmosphere, as during decomposition, soil carbon is converted to CO2. 

Tea bags, Photo by Judith Sarneel

Therefore, there is great interest in testing the effects of climate and climate change on decomposition. Many decomposition studies have been carried out, but as each researcher chooses her own method it is difficult to compare data across studies. For example, it is difficult to filter out the effect of climate in decay curves obtained from litter incubated at 3 cm depth in Alaska vs litter from another species, buried 6 cm deep in South Africa? Furthermore, measuring decomposition is a quite laborious process. However, with the recently developed Tea Bag Index that uses tea bags as standardized litter bags, life has become much more easy, and decomposition can be measured in a standardized, highly comparable manner.

The teatime4science project aims to collect global decomposition rates and create a global soil map for decomposition. We invite you to join our project.

The Tea Bag Index experiment is easy: You take one green and one rooibos tea bag (everybody has to use the same brand). You weigh them, bury them 8 cm deep in the soil and after 3 months, you take them out, dry them and weigh them again. The weight loss will tell you how quickly plant material decomposes at the burial location.

Litter mass loss over time of Rooibos and Green tea

By using two types of tea we obtain two proxies that characterize two different phases of the decomposition process. During the first phase, all the easy material is consumed, while in the second phase, mass loss is much slower as only the more recalcitrant material is left. With the decay of easy-to-decompose green tea (green line) one can determine how much of the labile fraction of the material is decomposed and how much is stabilized, which is a proxy for the second phase of the decay model. Rooibos tea decomposes much more slowly (red line) and after three months, it is still in the first phase of decomposition, from which the initial decomposition rate (k) can be estimated.

The TBI team members: Judith, Joost, Mariet and Taru Photo by Judith Sarneel

Now we are on a mission! The mission is to get as many tea bags buried (and retrieved) as possible. So far, many researchers across the world have tested the method and we have received many positive reactions. We are in the process of running citizen scientist projects in several countries. More than 350 classes have joined the project, and each of them have had the opportunity to learn about the importance of soils and the processes that occur there.

Do you want to join? Don’t hesitate, it’s fun! Just send an email to . You can join by burying a few bags or many bags (e.g. along side your own experiments), both are very welcome!

If you want to bury a few bags, we can offer to send you tea.

If you want to buy many bags with a large geographical spread, you can apply for co-authorship of our database and its analysis paper.

You can contribute data this year and next year (2017).

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