9. LONG-TERM FIELD EFFECTS OF FRESH AND AGED BIOCHAR ON SOIL MICROBIAL COMMUNITY STRUCTURE

Abstract

Understanding how soil microbial communities respond to biochar over time is essential for predicting its long-term effects on soil health and nutrient cycling. However, evidence from long-term field studies or repeated applications remains limited. This study examined how microbial communities involved in carbon and nitrogen processes differ between short-term and long-term wood biochar amendments in subtropical grassland soils (rhodic ferralsol). Four field treatments were compared: (i) NPK only (B0), (ii) newly applied biochar in 2019 (B1), (iii) biochar applied in 2010 (B9), and (iv) biochar applied in 2010 with reapplication in 2019 (B9 + 1). Using 16S rRNA gene sequencing, we found that recently applied biochar enhanced bacterial diversity and the abundance of carbon- and nitrogen-transforming taxa, whereas decade-old biochar supported more phototrophic communities, likely linked to higher dissolved organic carbon levels. Variations in microbial composition were primarily driven by soil pH, dissolved organic carbon, and total nitrogen. Notably, reapplication of biochar after long-term use (B9 + 1) did not alter microbial diversity, suggesting that the soil microbial community had stabilized to biochar-derived carbon inputs. These findings highlight that microbial responses to biochar evolve, underscoring the importance of long-term field observations to guide sustainable biochar management in subtropical soils.