Effects of biochar and inorganic amendments on soil fertility, tea yield, and quality in both Pb-Cd-contaminated and acidified tea plantations

Purpose Soil amendment is an important method to improve soil ecology and crop quality. Field experiments of soil amendments were conducted to find a suitable solution to slow down soil acidification and to decrease the effect of heavy metal pollution in tea plantations.Methods A 2-year field experiment was conducted in a tea garden contamination with Pb (lead), Cd (cadmium), and soil pH below 4.5. It included five treatments with various amendments: CK (no amendment), bentonite, calcium magnesium phosphate fertilizer, biochar, and lime.Results Four soil amendments increased soil pH by 0.38-0.60, nutrient contents (available nitrogen, phosphorus, and potassium), as well as soil organic matter content. The contents of soil available Pb, Cd, and Cr (chromium) also decreased significantly (p < 0.05). Tea yield increased significantly by 15.13-40.89%, as tea polyphenols, free amino acids, caffeine, and water extract increased by 2.06-11.68%, 2.48-46.51%, 6.97-22.40%, and 5.46-33.76%, respectively. In addition, Pb in tea treated with biochar was decreased significantly by 61.28%. The Cd and Cr in tea treated with bentonite, calcium magnesium phosphate fertilizer, and lime decreased significantly by 15.93-41.15%, 25.27-31.87%, while As (arsenic) decreased by 9.82-18.05% (p > 0.05), respectively.Conclusion Four soil amendments could promote the rebalancing of soil nutrients and raise the soil pH in the acidified tea plantations. The accumulation of heavy metals in tea was reduced, and the yield of tea increased. Biochar has a better effect on improving the soil of acidified tea plantations, while its molecular mechanism of promoting tea tree growth should be focused on research.