Effects of aged and fresh biochars on soil acidity under different incubation conditions

• Biochar aging declines ameliorating effect of biochar on soil acidity in short-term.
• Effects of incubation conditions on soil acidity amendment using biochar are few.
• Local forestry wastes biochar can be used to amend soil acidity in study region.

Biochar has positive effects as a soil acidity amendment which is a global concern. However, few studies have been reported on the effect of aged biochar on soil acidity. Incubation methods with different ventilation conditions may induce different effects on soil acidity amendment using biochar. This study analyzed the effects of fresh and aged biochars on soil acidity amendment with different incubation methods. Samples of typical acidic soil (plinthudults) and fresh Pinus massoniana bark were collected from the hilly red soil region of southern China and used to create biochar (PB) with the oxygen-limited pyrolysis method at 450 °C. A 4-month-aged PB (PBa) which was produced by a natural forest fire was collected from the same area as that of biochar PB. A 69 days incubation experiment was conducted using an improved incubation method. The treatments comprised 100 g soil + 2 g PBa (PBA), 100 g soil + 2 g PB (ventilated incubation, PBV), 100 g soil + 2 g PB (sealed incubation, PBS) and 100 g soil only incubated under ventilated (CKV) and sealed (CKS) conditions. Soil pH was measured periodically. Soil exchangeable base cations, exchangeable acidity, exchangeable aluminum (Al3+) and cation exchange capacity (CEC) were measured after incubation. Throughout the incubation period, PB and PBa positively enhanced soil pH (P < 0.05), with PB exhibiting more remarkable effects. A similar effect was also observed for soil exchangeable Al3+ and exchangeable acidity. After incubation, soil pH values of PBV (5.05 ± 0.02) and PBS (4.99 ± 0.03) were than the value of PBA (4.98 ± 0.03), with nonsignificant differences (P > 0.05) between values in PBV and PBS. PB addition improved soil exchangeable base cations and base saturation compared to PBa addition. Soil CEC levels in PBA, PBV, and PBS were not significantly different from those in CKV and CKS, but CEC in PBV and PBS were significantly higher than the CEC in PBA. All parameters in PBV were not significantly different from the parameters in PBS. Biochar PB can be used to amend soil acidity, but the efficiency declines to a certain extent if biochar PB has undergone a short-term aging before being added to soils. The different ventilation conditions had little influence on soil acidity amendment using biochar.