Priming effect of bamboo (Phyllostanchys edulis Carriere) biochar application in a soil amended with legume

Biochar application to soils can mitigate carbon dioxide (CO2) by increasing soil carbon (C) sink, but also causes increased CO2 released from soils through priming effects of soil organic carbon (SOC). However, priming effects of biochar application on SOC are complex, showing inconsistent results, and further complicated when applied with other substrates such as organic amendment (OA). Incubation experiments were conducted using Typic Durudand with bamboo (Phyllostanchys edulis Carriere) biochar (400 degrees C) and OA (crotalaria) applied individually, simultaneously or with biochar applied 5 weeks prior to OA application. After 56 d of incubation, cumulative CO2 released from soils with no amendments (control), biochar only (BC), OA only (OA), simultaneous (BC+OA), and differently timed (BCP+OA) applications reached 313, 326, 1270, 1535 and 1311mg CO(2)kg(-1), respectively. The OA application distinctly increased CO2 released from the soils due to its decomposition. The OA decomposition rates were comparable with OA and BC+OA, while those with BCP+OA were lower than those with other treatments during early incubation. Net CO2 (CO2-(treatment) - CO2-control) from soils with BC, OA, BC+OA and BCP+OA yielded 13, 957, 1222 and 998mg CO(2)kg(-1), respectively. Primed CO2-BC of 13mg CO(2)kg(-1) was equivalent to 4.2% of priming effect relative to CO2-control. Primed CO2-BC+OA [net CO2-BC+OA - (net CO2-BC + net CO2-OA)] and primed CO2-BCP+OA were 252 and 28mg CO(2)kg(-1), equivalent to 26% and 2.9% of priming effects relative to sum of net CO2-BC + net CO2-OA, respectively. The priming effect with BC was negligible likely because of limited amounts of biochar labile C to induce co-metabolism, while BC+OA showed a modest priming effect most likely as a result of co-metabolism induced by additional mineralization of presumably SOC and/or biochar, because the OA decomposition rates were not affected by biochar application. The priming effect with BCP+OA was comparable to that with BC likely due to changes in soil properties caused by biochar application prior to OA, likely from slowed decomposition rates of OA.