Effects of biochar on the acidity of a loamy clay soil under different incubation conditions

Biochar can be used to amend acidic soils, and the effectiveness of this amendment may be varied under different ventilation conditions. This study aimed to clarify the effect the incubation method (either ventilation or sealed conditions) had on the capacity of biochar to amend acidity of a typically acidic agricultural soil in hilly red soil region of southern China. Biochars pyrolyzed from the bark (PB) and the trunk (PT) of Pinus massoniana, a widely distributed tree species in the region, were prepared. Sealed treatments consisted of 100 g soil + 2 g PB (PBS), 100 g soil + 2 g PT (PTS), and 100 g soil only (CKS). Ventilated treatments were conducted correspondingly (PBV, PTV, and CKV). During the 68-day incubation, soil pH was measured periodically. Both biochars, PB and PT, amended the soil acidity significantly, e.g., increased soil pH and exchangeable cations, and decreased soil exchangeable acidity and exchangeable aluminum. After incubation, soil pH in PBS and PTS increased by 0.30 and 0.16 units, respectively, while soil pH in PBV and PTV increased by 0.25 and 0.11 units, respectively. Moreover, more positive effects on soil exchangeable acidity and nitrate nitrogen were also observed in sealed rather than in ventilated treatments. The results suggested that waste of P. massoniana can be pyrolyzed for soil acidity amendment in this region. While the effectiveness of biochar on acidity amendment of the soil can be influenced by the aeration conditions, other local environmental conditions may be involved and should also be considered when assessing soil amendments.