Abstract
Soil acidification affects the growth of tea plants and induces magnesium loss, which further reduces tea quality. In this study, magnesium-modified biochar was developed from discarded tea plant branches, via potting test to evaluate the effect on the red loam soil, and to study the quality of tea in acidified tea gardens. Four treatments were set up as control (no biochar added, CK), conventional magnesium fertilizer treatment (FC), tea plant branch biochar treatment (BC) and magnesium-modified biochar with acetic acid (BCY) respectively. Our results showed that soil pH was significantly increased by 0.3 and 0.42 units in BC and BCY treatments respectively, conventional magnesium fertilizer, biochar, and magnesium-modified biochar treatments could significantly increase soil organic matter, alkaline-dissolved nitrogen, effective phosphorus, quick-acting potassium, and exchanged calcium and magnesium content in acidified tea plantations. Compared with CK treatment, both conventional magnesium fertilizer treatment and biochar treatment could increase the root dry weight and tea plant height to some extent; the SPAD values of tea fresh leaves of BC and BCY treatments were significantly higher than those of CK and FC treatments by 17.6, 37.6 and 6.4, 26.4, respectively; and the increase in accumulation of nitrogen, phosphorus, potassium, calcium, and magnesium in tea leaves of FC, BC, and BCY treatments compared with that of CK was 2.49~8.04 g·kg-1, 0.19~0.49 g·kg-1, 0.30~3.27 g·kg-1, 0.26~0.50 g·kg-1, and 0.15~1.45 g·kg-1; and SPAD value, tea polyphenols, water leachate, caffeine, and amino acid contents of tea leaves in BC and BCY treatments were significantly higher than CK treatment (P < 0.05). Our study showed that magnesium-modified biochar improved the quality of tea significantly via enhancing the pH, organic matter and nutrient content of soil, increasing the uptake of nitrogen, phosphorus, potassium, calcium and magnesium in the tea plant, and ascending photosynthesis, The best results were obtained with magnesium chloride modified biochar (BCL) treatment. This study plays a guiding role for the improvement and nutrient supplementation of acidified soil in tea plantations and promotes the healthy development of tea plantation soil..