Biochar, Organic Fertilizer, and Bio-Organic Fertilizer Improve Soil Fertility and Tea Quality

Tea, the world’s second most traded commodity, significantly impacts the economies of producing countries. However, prolonged cultivation leads to soil degradation, particularly through acidification and the depletion of essential nutrients, which adversely affects tea quality. This study investigates the effects of biomass materials—biochar, organic fertilizer, and bio-organic fertilizer—on both tea quality and soil properties. The results revealed that all biomass treatments improved the catechin quality index (CQI) of tea, with bio-organic fertilizer (BOF) yielding the highest CQI at 629.41, followed closely by biochar (624.16) and organic fertilizer (581.34). Soil analysis indicated that biochar increased soil pH from 4.53 to 5.54, total carbon by 194.6% (from 12.61 g kg−1 to 24.42 g kg−1), and nitrogen levels by 11.7% (from 14.91 mg kg−1 to 16.17 mg kg−1), while reducing soluble salts significantly. Furthermore, biomass treatments enhanced enzyme activities, with urease and acid phosphatase increasing by up to 136.6% and 149.5%, respectively. Correlation analysis revealed significant positive relationships, with tea amino acid content correlating with soil total nitrogen (r = 0.62, p < 0.05) and tea polyphenols positively correlating with available potassium (r = 0.60, p < 0.05). This study demonstrates that integrating biomass materials into tea cultivation not only enhances tea quality but also contributes to soil health, supporting sustainable tea garden management practices.