T-shirt experiment: How well regenerative farming practices improve the soil microbial activity

Key points:

  • The activity and diversity of soil microbes can be measured using simple and inexpensive methods, such as the T-shirt degradation test.
  • Terra Nostra Foundation, together with partners, decided to use the T-shirt degradation test to check the impact of regenerative practices on the activity of soil microbes.
  • The BIOTREX95 analysis revealed differences in microbial activity and diversity between conventional and regenerative fields.
  • After three months in the soil, the rate of decomposition of the T-shirts was in line with the results of the BIOTREX analysis.
Although soil microbes cannot be seen with the naked eye, the results of their work in the soil are clearly visible. Microbes carry out soil processes that are essential to agriculture, such as nutrient cycling, decomposition of organic matter, carbon sequestration, and stimulation of plant growth. Without active and diverse microbes, crop production is, to put it mildly, not very efficient. But to improve their performance, you need a way to measure it.
If you are just starting to explore the potential of microbes hidden in the soil, you probably look for a simple method that does not require special equipment. One of the most popular methods is the T-shirt degradation test. It’s a simple and inexpensive way to assess soil microbial activity and decomposition rates. All you need is a clean, 100% cotton T-shirt and a shovel to bury it in the soil. After a few weeks, the T-shirt is dug up and its condition examined. The method is based on the idea that soil microbes play a vital role in breaking down organic matter, including the cotton fibres from the T-shirt. The more active the microbial community, the faster the T-shirt will decompose.
In 2023, the Terra Nostra foundation in cooperation with Top Farms Group Wielkopolska and the FarmTech laboratory, decided to put the T-shirt experiment into practice. In March 2023, they buried cotton T-shirts in five selected locations in Poland, including fields where so-called regenerative practices are used (use of organic fertilisers, limiting mineral fertilisers, using simplified cultivation, introducing cover crops into crop rotation). The aim was to study the impact of different farming practices on soil microbial activity and decomposition potential. Regenerative practices are known to stimulate soil microbes and have overall positive impact on soil health, so they expected the T-shirt to be much more decomposed after few weeks in this field. To verify the results of the T-shirt test, they also performed BIOTREX95 analysis (which utilises 95 different compounds to assess metabolic activity and diversity of soil microbes) and chemical analysis of soil samples before and after the T-shirts were dug up. This allowed to confirm the accuracy of the test results.
The chemical analysis revealed no significant differences between the two fields. However, BIOTREX95 results were able to distinguish the fields by their microbial decomposition capacity. The microbial performance score on the conventional field was low, at 755,850. This indicates that soil processes relying on microbes are not very efficient. As a result, we would expect the decomposition rate of this field to be rather low. On the other hand, the microbial performance score of regenerative field was higher, at 906,743. This means that we would expect soil processes to be more efficient than the conventional field.
Now, were the results of the T-shirt test in line with the findings? The team admits that digging up the T-shirts after three months was much harder than they expected. But the hard work was rewarded, as the T-shirts degradation aligned with the results of BIOTREX95 analysis. On the regenerative field, the T-shirt had almost completely decomposed. They spent a lot of time searching for the T-shirt residues left in the soil. The job was much easier on the conventional field, as the T-shirt maintained its integrity, but it still had a few holes in it. For more information on the results of the experiment, have a look at the BIOREACTION conference website where the results were presented.

In summary, the T-shirt test proved to be a simple and inexpensive way to qualitatively assess activity of soil microbes. However, it has some limitations. Firstly, you need a lot of patience to wait few months for the results. Secondly, you have to spend a lot more time and energy burying the T-shirts and then digging them up than you do taking samples of the soil for laboratory testing. Also, if the decomposition rate of the soil is high, it may be quite difficult to find the remains of the T-shirt. Finally, it only provides approximate estimates, and comparing results over time and across different fields is challenging. For professional use, where thorough and quantitative results are essential, it is better to use advanced and reliable methods such as BIOTREX.