Proceedings of the 2022 Mississippi Water Resources Conference

Year: 2022 Authors: Carter K.S., Beatrice A., Varco J.J., Dygert A., Brown S., Pittman Jr. C.U., Mlsna T.

Biochar can directly hold cations in soil because of the negative charge that exists on its surfaces. Besides, improving soil cation exchange capacity, the negative charges on biochar surfaces can buffer acid soil by protonation and deprotonation mechanisms. Moreover, biochar can ameliorate soil acidity due to the presence of oxide, carbonate and hydroxide of its basic cations (Ca, Na, K, and Mg). Both biochar surface functional groups and basic cations concentrations can be altered by modification with chemical agents (Chemerys, 2017; Godwin et al., 2019), which could affect its soil pH buffering capacity. However, information concerning the impact of modified biochar application on soil pH buffering capacity is still scanty. This study investigated the pH buffering capacity of acid soil amended with three P-enriched modified Douglas fir biochars and compared this to amendment with untreated Douglas fir biochar. These three P-enriched biochars, designated CCPP, CAPP and MSPP, were prepared by treating Douglas fir biochar respectively, with: 1) anhydrous calcium chloride (CaCl₂) and potassium phosphate monobasic (KH₂PO₄), 2) calcium carbonate (CaCO₃) and diammonium phosphate {(NH₄)₂HPO₄} and 3) aqueous solution of magnesium sulfate (MgSO₄), potassium hydroxide (KOH) and potassium phosphate monobasic (KH₂PO₄). The acid soil was then treated with biochar samples in biochar: soil ratios of 0%, 10%, 30%, and 50% (w/w), followed incubation for 30 days at room temperature with soil moisture levels maintained at 80% field capacity. The soil-biochar mixtures were titrated with 0.1 M aqueous HCl solutions and the resultant pH values determined. The amount of H+ added to soil-biochar mixture was plotted against pH. The pH buffering capacities of the soil and the soil-biochar mixtures were obtained from the graph's slope. The soil pH buffering abilities were largely dependent on the added biochar's alkalinity and ash contents.