Corncob-derived biochar decelerates mineralization of native and added organic matter (AOM) in organic matter depleted alkaline soil

The understanding of the carbon (C) and nitrogen (N) mineralization is essential to mitigate the climate change and improve the soil quality for agricultural sustainability. An incubation study was carried out to investigate the effects of corncob-derived biochar with and without the corncob residues, as added organic matter (AOM), on C and N mineralization in an organic C deficient alkaline soil. The study used biochar produced from corncobs by pyrolysing the biomass at 400 degrees C and consisted of four treatments: unamended control soil, soil +2% biochar (45 tons ha(-1)), soil +2% corncob residue (45 tons ha-1) and soil +1% corncob residue +1% biochar (22.5 tons ha(-1) each of biochar and residue). Soil C mineralization was quantified by measuring soil respiration periodically throughout the experiment over the 54 d incubation period. Soils were analyzed for microbial biomass C (MBC), water extractable organic C (WEOC) and N mineralization. We also calculated microbial metabolic quotient (qCO(2)), net C mineralization (NCM), net CO2 efflux and priming effect values. The results revealed that only a very little fraction of biochar was respired whereas a high proportion of corncob was decomposed. Biochar addition suppressed decomposition of native and AOM by 16.31% and 30.13% respectively through negative priming effect (-40.01%). Compared to the corncob residue alone, addition of biochar with corncob residue significantly increased MBC but decreased WEOC, qCO(2), NCM and net CO2 efflux. Moreover, residue significantly increased the net CO2 efflux, NCM and qCO(2) and, at the same time, decreased net N mineralization. Extractable NH4+-N, NO3--N and mineral-N contents were the highest in the biochar and biochar + residue treatments. In addition, biochar alone and in combination with residue resulted in higher negative net N mineralization/immobilization. Enhanced MBC contents and reduced qCO(2) indicated efficient C utilization by microorganisms. The results of this study conclude that biochar could decrease C mineralization but enhanced microbial C use efficiency and, therefore, offer an important management strategy to improve C sequestration in nutrient and organic C deficient alkaline soil. The results also imply that the amendment of corncob residue with biochar had a potential to reduce the rate of the soil N leaching and N2O emission by N immobilization and sorption to biochar. (C) 2017 Elsevier B.V. All rights reserved.