Distribution of soil carbon and grain yield of spring wheat under a permanent raised bed planting system in an arid area of northwest China

• We assessed tillage on TOC, POC and SMBC in the 0–90 cm soil layers.
• PRB tillage enhances TOC, POC and SMBC in the 0–10 cm soil layers.
• PRB tillage plays a role in carbon sequestration and stratification than TT.
• POC and SMBC were highly correlated with TOC.
• SMBC was the most sensitive indicator of tillage practices.

Soil organic carbon (SOC) plays a crucial role in improving soil properties and the C global cycle. Judicious tillage management can improve soil fertility and quality, and effectively reduce greenhouse gas emissions by enhancing soil carbon sequestration. An 8-year (2005–2012) field experiment was conducted in arid northwestern China to evaluate the effect of tillage practices on the distribution of total organic carbon (TOC), particulate organic carbon (POC) and microbial biomass carbon (SMBC) at 0–5, 5–10, 10–20, 20–40, 40–60 and 60–90 cm soil depths, as well as TOC stratification, TOC stocks and grain yield of spring wheat (Triticum aestivum L.). Spring wheat was grown under three tillage systems: (1) permanent raised beds–zero tillage and ride culture with controlled traffic (PRB), (2) no-tillage planting on a flat field with controlled traffic (FB) and (3) traditional tillage −conventional tillage without residue retention (TT). A tillage effect was observed on TOC, POC and SMBC, which was significantly higher in the surface soil layer (0–10 cm) in permanent raised beds (PRB) than in TT and FB. No differences in TOC or POC were encountered at 10–20, 20–40 and 60–90 cm between treatments. Below 10 cm, no differences in SMBC were observed between treatments, but TOC and POC contents at 40–60 cm were significantly higher under TT than FB, with TT > PRB > FB. PRB had the highest TOC storage in the 0–90 cm soil profile (75 Mg C ha−1) followed by FB (74 Mg C ha−1) and TT (69 Mg C ha−1). Higher TOC stratification was observed under PRB and FB than under TT. Six years of PRB increased mean grain yield by 6% and 9% compared with TT and FB, respectively. We conclude that: (1) conservation tillage with controlled traffic (PRB and FB) increased TOC, POC and SMBC concentrations (0–10 cm) and TOC stock, (2) SMBC is a sensitive indicator for reflecting the effect of agricultural management practices on TOC dynamics, and (3) PRB tillage could sustain wheat grain yields and increase carbon sequestration in arid northwestern China, such that PRB tillage is a more sustainable wheat cropping system than the TT system currently used by most farmers.