Exploring the Impact of Biochar-Dolomite Application at Different Pyrolysis Temperatures on Acid Sulfate Soil Properties

The use of biochar as a soil amendment for acid soil, particularly acid sulfate soil, has garnered significant interest due to its capacity to improve soil properties, which is further accentuated when combined with dolomite. However, the extent to which the magnitude and direction of this effect vary with biochar produced at different pyrolysis temperatures remains uncertain. We conducted an incubation by mixing soil with dolomite and biochar types derived from Melastoma malabathricum (MMBC) and Dicranopteris linearis (DLBC) at three temperatures (300, 500, and 700°C). The incorporation of dolomite with both biochar types led to significant improvements in soil pH, available P, available Fe, exchangeable K, and exchangeable Ca compared to soil amended with dolomite only. These enhancements were likely attributed to the release of alkalinity, which further raised soil pH, as well as the direct dissolution of P, K, and Ca from the biochar. Moreover, the reduced Fe availability was likely due to the complexation of Fe onto surface functional groups of biochar. Furthermore, these improvements surpassed the effect of the initial feedstock and became increasingly pronounced with higher pyrolysis temperatures. However, an antagonistic effect of dolomite and biochar co-incorporation was observed, particularly in the relative reduction of soil exchangeable Mg with both biochar types, and a decrease in the soil available N with MMBC produced at 300 and 500°C compared to dolomite addition alone, which could be due to the adsorption of Mg and N onto biochar surface. The results indicate that concurrent application of dolomite and biochar can change the acid sulfate soil properties to varying magnitudes and in different directions, largely regulated by the characteristics of biochar as well as the probable interplay with dolomite. Consequently, selecting the appropriate biochar that aligns with the desired soil properties is crucial in managing dolomite-treated acid sulfate soil.