Tea Bag Index (TBI)

We developed a simple and cheap method to measure decay rate of plant material by using tea. The method consists of burying tea bags with green tea and rooibos and digging them up ca. three months later. In this period, the tea will decay, and will therefore show what will happen with normal plant material in the soil. This method was developed and tested by a team of researchers from the University of Utrecht, Umeå University, University or Reading and the Austrian Agency for Health and Food Safety Ltd.

The scientific value of this new method has already been acknowledged and experiments are currently running in countries all over the world. Many school children and other citizen scientists joined. The idea is to use this new method to collect data on decay rates from all over the world. With this data we made a global soil map, and consequently improve global climate models that use these maps.

Stepwise method description

Take one unused Lipton Green tea bag.
Take one Rooibos tea bag.

Tip:

There are many versions now of the tea: green tea: EAN 87 10908 90359 5 or the old product number, now used again for plant-based bags EAN 87 22700 05552 5; rooibos EAN 87 22700 18843 8 or 8711227514348. Using the standard tea is important for being able to compare across studies, but if you use the tea to compare within your own study, you can use whatever tea you want, as long as you use the same tea in your whole experiment and use tea with degradation resistant bags. For availability of the tea click here.
You can bury more replicates in each location. In this way, you will get a better estimate.
Our method can test the effect of different environmental variables. So you can do an experiment yourself. For instance, bury one set of tea bags at a very wet and another set at a very dry location. Or compare a forest, grassland and cropland.
Mark the tea bags on the white side of the label with a permanent black marker.

Optional: Measure the weight of the tea bag. Take a scale with at least two digits (0.01). Three digits is better. (Pharmacies or jewelers usually have such precise scales. Or buy one online.)
Bury both teabags in separate, 8 cm-deep holes, ca 15 cm apart. Keep the labels visible above the soil.

Tips:
- Mark the burial site with a stick.
- Write down the date, shading of the soil (1-5, from none to completely), impact by humans (1-5, no impact to completely impacted), vegetation type and other experimental conditions of the site.
Recover the tea bags after approximately 90 days. Well, the incubation time does not need to be exactly 3 months. In tropical climates it can be shorter (e.g. 60 days). Always write down when your experiment started and ended.
Remove adhering soil particles and dry the tea bags
- e.g. in a stove for 48h at 70°C (not warmer!).
- e.g. above the heating or a sunny place for ca. 3 or 4 days.
- Do not use water to remove the soil particles, because that can cause extra loss of material from the bag.
Take the tea out of the bag, be careful not to lose any material.
Weigh the tea (0.01 or .001 g).
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