Biochar application method influences root growth of tea (Camellia sinensis L.) by altering soil biochemical properties

Although the application of biochar increases crop productivity and soil fertility, the effects of different biochar application methods on tea plant growth and soil nutrient status remain unclear. In this study, we conducted a root chamber experiment to assess the effects of various biochar application methods on root growth in tea plants and edaphic factors. Four treatments were included: T1) No biochar, T2) Homogenized biochar, T3) Localized biochar, and T4) Strip biochar. Biochar application generally resulted in higher macronutrient contents in tea plants, with 114–371%, 196–1167%, and 327–960% increases in nitrogen (N), phosphorus (P), and potassium (K), respectively. Biochar application also increased the soil pH by 18.7–22.5% compared to the control. T2 treatment increased the leaf and root biomasses by 80.9% and 262.2%, respectively, compared to the control, and the total carbon and soil nutrient [i.e., total N, inorganic N, available P, and available K, calcium (Ca), and magnesium (Mg)] contents were significantly higher than in the control. Variation in root growth was significantly explained by soil properties, including microbial biomass carbon, Ca, Mg, and total N (P < 0.05), with contributions of 47.9%, 15.6%, 17.6%, and 4.7%, respectively. These results suggest that biochar application in acidic soils would increase tea plant productivity and soil nutrient contents. Overall, homogenized biochar application led to optimal tea plant growth and soil fertility.