Abstract:

To investigate the phosphorus leaching capacity of pepper straw biochar in different regions, biochar were prepared from pepper straw in different regions (Taikang County of Henan Province, Xinjian District of Nanchang City, Dingxi City of Gansu Province and Bijie City of Guizhou Province) using two pyrolysis temperatures (400℃ and 700℃). The concentrations of four phosphorus fractions (H₂O-P, NaHCO₃-P, NaOH-P and HCl-P) in the biochars were extracted by distilled water, 0.5 mol/L sodium bicarbonate, 0.1 mol/L sodium hydroxide and 1 mol/L hydrochloric acid, respectively. Additionally, the kinetic dissolution experiments of phosphorus from biochars and the effect of pH on phosphorous leaching were carried out in the study. The results indicated that the content of H₂O-P was the highest among the four fractions of phosphorus in biochars and NaHCO₃-P was the lowest. The content of H₂O-P in the biochar prepared at 400℃ in Guizhou was the highest, reaching 7.89 mg/g. The content of NaHCO₃-P in the biochar prepared at 700℃ in Henan was the lowest, which was only 0.13 mg/g. The higher the temperature of carbonization, the lower the concentration of phosphorus dissolution in biochar. The biochar prepared at 400℃ in Guizhou had the strongest phosphorus dissolution ability, and the maximum dissolution amount was 1.58 mg/g at 10 min. The higher the initial pH of the solution, the lower the leaching of phosphorus from the biochar. When the initial pH 2.0, the maximum phosphorus leaching rate was achieved, the dissolved concentration of the biochar prepared at 400℃ in Guizhou was 3.21 mg/g. Our finding would provide a reference for the use of biochar to improve soil nutrients by enhancing phosphorus availability.

Key words: pepper straw biochar, phosphorus fractions, phosphorus dissolution, initial pH