Blog Post

As part of the FENIX project, several experimental sites have been selected across Europe to evaluate the potential of biochar-digestate mixtures as soil improvers. In our previous blog, we took you to our Spanish soils to share our findings from the land there. Now, this week, we want to take you to across the Mediterranean to Greece.

The Greek test site is located at the ELGO experimental farm in Thermi, near Thessaloniki, where the FENIX soil improver will be tested on cereal crops under semi-arid conditions and in homogeneous soils.

 

 

Nutrient Predicaments and How Biochar Can Help

Initial soil characterization shows that the Greek cereal soils have severe nutrient depletion. These soils have been found to have a basic pH and relatively low nutrient availability. Phosphorus levels were also found to be deficient, which hinders crop productivity. Nutrient depletion is a common challenge in cereal-based agricultural plots. Oftentimes, potassium is removed through crop harvest and exceeds fertilizer inputs, leading to long-term soil impoverishment.

Despite these nutrient limitations, measurements of enzyme activity and soil respiration indicate that the Greek cereal soils exhibit relatively high biological activity compared with our other project sites, with the highest induced respiration values measured here. This high level of biological activity suggests that the soils still have an active microbial community that could be responsive to our biochar-digestate mixture.

Recent research suggests that biochar can help by contributing to the slow release of potassium while also reducing nutrient losses through leaching. At the same time, potassium availability in soils depends on complex interactions influenced by soil moisture and calcium, magnesium, and sodium levels. Our potassium enriched biochar will help improve understanding of these processes under field conditions.

This is evident in the results obtained during the pot experimentation conducted by ELGO in Greece to evaluate the performance of different biochar-digestate mixtures under controlled conditions. According to the observed effects, the digestate is the main carrier of readily available macro- and micronutrients, while biochar plays a complementary role by moderating pH and increasing nutrient retention. Based on the results of these pot tests, the selected biochar-digestates formulations were applied in the field in December 2025. We are now waiting for the next harvest to assess the synergistic interactions arising from the mixture.

Comparing Soils Across the FENIX Sites

Preliminary analysis comparing all FENIX sites shows interesting similarities between soils under very different agricultural systems. Multivariate analysis grouped the Greek cereal soils together with avocado soils in southern Spain, indicating comparable soil characteristics despite differences in climate and cropping systems.

These findings reveal the importance of evaluating soil improvers across a wide range of environmental conditions, which ultimately helps us understand how soils respond in heterogeneous contexts.

Looking Ahead

As field trials progress, the results obtained in Greece during the soil characterisation and pot testing will contribute to a better understanding of how biochar-digestate mixtures can improve soil fertility, enhance nutrient availability, and support sustainable cereal production across Europe. We expect our first results to arrive in July 2026, and we look forward to sharing them.

By: M. Romero
February 2026