Long-term effects of biochar on soil carbon storage and its fractions in a tropical soil

Biochar is a climate-smart solution to combat climate change by sequestering carbon (C). However, little is known about long term effects of biochar in tropical conditions. The objective of this study was to evaluate the long-term effects of biochar on soil C storage and its distributions between particulate organic carbon (POC) and mineral-associated organic carbon (MAOC). Soil samples at 0–10, 10–20, and 20–30 cm were collected in Uruçuí, Piauí, Brazil, 10 years after application of the following doses of biochar: 0 (T0), 4 (T4), 8 (T8), and 16 (T16) Mg ha⁻¹. A native forest (NF) was sampled as a reference. The total C content and fractions (POC and MAOC) were determined using an elemental analyzer; stocks were calculated and subjected to ANOVA and Tukey's test (p < 0.05). Increased biochar doses resulted in 27-42% increases in C stocks at 0-30 cm compared to no application (T0). In this layer, the highest dose (T16) stored 38.2 Mg C ha⁻¹, and was statistically equal to NF (38.8 Mg C ha⁻¹). MAOC stocks in the soil increased by 23%-36% at doses T8 and T16, respectively, compared to T0. Regarding POC stocks, the initial 20 cm showed the largest increases, with 84% increases in soil POC stocks at doses T8 and T16 compared to T0. We conclude that biochar application is an efficient strategy for increasing C stocks and quality in tropical soils, promoting its stabilization in the MAOC fraction and C levels similar to those found in native forests.