Biochar Derived from Black Liquor as a Soil Amendment: Effects on Soil Quality, Growth Parameters, Chlorophyll and Mineral Content of Barley

This study investigated the application of biochar obtained from black liquor, a residue generated during the Kraft pulping process in the paper industry, as a sustainable soil amendment in barley (Hordeum vulgare L.) cultivation. The biochar was produced through controlled pyrolysis at 450 °C and subsequently characterized with respect to elemental composition, porosity, specific surface area, and chemical stability, confirming its suitability for agricultural use. The experiment comprised three treatments: unamended soil (control), soil supplemented with 3% biochar, and soil fertilized with NPK, all conducted under controlled growth conditions. The results showed that biochar significantly improved key soil fertility indicators, increasing cation exchange capacity from 11 to 19 cmol(+)/kg and soil organic matter from 2.1% to 2.6%. Mineral nitrogen availability increased from 7.0 mg/kg to 10.5 mg/kg in the biochar treatment compared with the control. At the plant level, biochar enhanced early barley growth, with plant height increasing from 25 cm to 27 cm and chlorophyll content rising from 32.35 SPAD units to 39 SPAD units. Although NPK fertilization produced slightly higher immediate growth responses, biochar contributed to improved soil chemical properties and nutrient retention. Overall, the results suggest that black liquor-derived biochar shows potential as a complementary soil amendment under controlled conditions.