There is overwhelming evidence for the long-term persistence of biochar in soil. However, the partitioning of biochar into light and heavy carbon (C) fractions and microbial biomass C (MBC), and the dynamics of C use efficiency (CUE_E: net incorporation of biochar into MBC per unit of biochar-C consumed, including microbial death and recycling of biochar-derived microbial metabolites) in planted soil systems are poorly understood. A ¹³C-labelled wood biochar (δ¹³C: −36.7‰) was incorporated into topsoil (0–10 cm) in an Arenosol, Cambisol and Ferralsol under C₃ dominated temperate pastures (δ¹³C: −25 to −27‰). The partitioning of biochar-C into the various soil C pools and CUE_E were measured at 4, 8 and 12 months. The results showed that 8.6–28.2% of the biochar-C in the top soils was distributed to the heavy fraction (HF) within 4 months, which increased to 11.0–33.3% at 8 and 12 months. Biochar-C recovery in the HF was the highest in the Ferralsol (cf. Arenosol and Cambisol), possibly due to greater interaction of biochar and biochar-derived microbial metabolites with soil minerals. Biochar significantly increased MBC across the three soils. Biochar-derived MBC ranged from 22 to 93 mg C kg⁻¹ soil over time (Arenosol < Cambisol < Ferralsol), representing 11–20% of the total MBC pool. Biochar CUE_E was 0.20–0.27 at 4 months, which decreased over time, possibly due to lowering of biochar-C availability to microbes. Further, although biochar-derived MBC was higher, biochar CUE_E was lower in the Ferralsol (cf. Arenosol and Cambisol), likely supported by higher microbial respiration and turnover, and lower recycling of microbial metabolites via greater organo-mineral interaction. Here, the study advanced our understanding of key C cycling processes, such as CUE_E and the temporal fate of biochar-derived C in an organomineral fraction with relevance for biochar sequestration in contrasting soils under planted field conditions.

Item Type:	Refereed Article
Keywords:	pyrogenic carbon, carbon use efficiency, biochar, mineralisation, stabilisation
Research Division:	Environmental Sciences
Research Group:	Soil Sciences
Research Field:	Carbon Sequestration Science
Objective Division:	Animal Production and Animal Primary Products
Objective Group:	Pasture, Browse and Fodder Crops
Objective Field:	Sown Pastures (excl. Lucerne)
Author:	Boersma, M (Dr Mark Boersma)
ID Code:	122311
Year Published:	2018
Deposited By:	Tasmanian Institute of Agriculture
Deposited On:	2017-11-09
Last Modified:	2018-01-05
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