Effect of crop residue biochar on soil acidity amelioration in strongly acidic tea garden soils

Strongly acidic soil (e.g. p H  < 5.0) is detrimental to tea productivity and quality. Wheat, rice and peanut biochar produced at low temperature (max 300 °C) and differing in alkalinity content were incorporated into X uan‐cheng ( U ltisol; initial p H soil/water = 1/2.5 4.12) and Y ing‐tan soil ( U ltisol; initial pH soil/water = 1/2.5 4.75) at 10 and 20 g/kg (w/w) to quantify their liming effect and evaluate their effectiveness for acidity amelioration of tea garden soils. After a 65‐day incubation at 25 °C, biochar application significantly ( P  <   0.05) increased soil p H and exchangeable cations and reduced A l saturation of both tea soils. Association of H + ions with biochar and decarboxylation processes was likely to be the main factor neutralizing soil acidity. Further, biochar application reduced acidity production from the N cycle. Significant ( P  <   0.05) increases in exchangeable cations and reductions in exchangeable acidity and Al saturation were observed as the rate of biochar increased, but there were no further effects on soil p H . The lack of change in soil p H at the higher biochar rate may be due to the displacement of exchangeable acidity and the high buffering capacity of biochar, thereby retarding a further liming effect. Hence, a significant linear correlation between reduced exchangeable acidity and alkalinity balance was found in biochar‐amended soils ( P  <   0.05). Low‐temperature biochar of crop residues is suggested as a potential amendment to ameliorate acidic tea garden soils.