Residual Effects of Biochar on Organic Carbon Fraction and Soil Properties after Three Years of Consecutive Wheat Cultivation

Abstract

The increasing pressure on agricultural soils due to intensive land use and excessive fertilization practices threatens soil quality and long-term food security. This study aimed to determine the effects of biochar application on soil carbon dynamics as well as on the chemical and biological properties of a soil cultivated with wheat for three consecutive years. Biochar, produced from woody residues via gasification, was applied at a rate of 5.0 t ha⁻¹ and incorporated into the topsoil (0–20 cm). Wheat was cultivated consecutively for three years following biochar application. Soil samples were collected from control and biochar-amended plots and analysed for mineral associated organic carbon (MAOC), particulate organic carbon (POC), bulk soil organic carbon, chemical properties, nutrient availability and microbial activity. Biochar was found to significantly increase organic carbon in all three fractions, with the greatest increase observed in POC. Biochar application did not significantly affect soil pH but reduced electrical conductivity while increasing soil organic carbon and cation exchange capacity. Exchangeable Ca, Mg and DTPA-extractable Mn contents were significantly higher in biochar-amended soils, whereas plant-available P and DTPA-extractable Cu and Zn decreased. In terms of soil biology, the amendment reduced basal respiration while increasing microbial biomass carbon. This suggests a potential for enhanced carbon stabilisation and altered microbial dynamics. These findings demonstrate that the residual effects of a single biochar application persist for several years, influencing soil carbon pools, nutrient availability and microbial activity. The contrasting responses of different nutrients emphasise the importance of optimising biochar management strategies to support long-term soil fertility and sustainable crop production.