Long-term Effect of Biochar Application on CO$$_{2}$$ Emissions in a Fluvisol

The use of biochar (BC) improves soil properties and crop yields, as well as reduces greenhouse gas emissions. The aim of this study was to evaluate the long-term effect of BC added to soil on CO2 emissions in a Fluvisol. The study was conducted in the experimental field of Tsalapitsa village, where BC and nitrogen fertilization were applied 4, 5, and 6 years ago. The experiment started in 2019 with two doses of BC (5 and 10 t. ha–1)$ and two rates of nitrogen fertilizers (130 and 260 kg. ha–1)$. In 2023 another experiment was set up on the same field, with BC applied at 10 and 15 t. ha–1. In 2023 and 2024, greenhouse gas CO2 emissions were measured during the wheat and barley growing seasons. Following the 1—6 years of biochar application during the growing seasons significant differences in CO2 emissions at different rates of BC and time of application were noted. The higher CO2 emissions were recorded in the variants with high rate of nitrogen (N260) in combination with the two doses of BC applied 4–6 years ago (p < 0.007, p < 0.0038, p < 0.001). A positive correlation was found between CO2 emissions, total organic carbon (TOC), soil reaction, mineral nitrogen (Nmin) content, and soil moisture for 2024, also supported by results from principal component analysis (PCA). In conclusion, application rates, time of addition of BC and nitrogen fertilizers have their impact on soil CO2 emissions, but other controlling factors, such as temperature, precipitation, and soil characteristics, also played an important role.