New directions for the Tea Bag Index: Alternative teabags and concepts can advance citizen science

Since its first publication in 2013, the Tea Bag Index (TBI) has attained widespread ecological application, generating scientific data on stabilization and turnover of organic matter in soils. As a result of manufacturing changes (net structure, net material, tea varieties) in the past years, a critical examination of alternative tea bag products is necessary. The present study for the first time generated decomposition data on a wide range of potential alternative tea brands (four brands tested) and varieties (rooibos [RB], green [GT], black [BT], and peppermint tea [PM]). They were tested in both a laboratory and a field experiment lasting 90 days. Under controlled laboratory conditions GT, BT, and PM corresponded well to the kinetic assumptions of an asymptote model of the TBI, but RB did not. In the field experiment, the tea mass remaining after 90 days was determined for all tea bags across different land uses (arable land, grassland, and forest). BT imitated the decomposition behavior of Lipton's original GT even better than any of the GT tested. The finer structure of Lipton's new tea bag nets did not negatively affect the precision of resultant remaining masses and thus can be recommended for future studies. In conclusion, alternative tea bags should be explored across brands as well as varieties. Based on our findings, we proposed an update of the TBI, which is based on the readily feasible modeling of the decomposition curve. Crucial is the combined consideration of both multiple tea varieties and incubation intervals of different durations.