Perennial crop in annual crop-based rotation enhances soil organic carbon storage

Perennial cropping in annual crop-based rotations promotes soil organic C (SOC) storage. However, SOC gain rate with the inclusion of perennial crops is not adequately examined. We evaluated Canadian publications on SOC storage impacted by the inclusion of perennial crops in annual crop-based rotations. In temperate regions of Eastern Canada, there was 20.9 ± 4.4 Mg C ha −1 or 32.4 ± 8% more SOC storage in perennial rotations compared to annual, in the top 34 ± 3 cm soil over a mean period of 31.4 ± 2.6 years. However, in subhumid and semiarid regions of Western Canada, perennial rotations gained only 5.5 ± 0.7 Mg C ha −1 or 17.7 ± 2.3% in the top 20.8 ± 1.0 cm soil over a mean period of 27.5 ± 2.4 years. On a per year basis, perennially cropped rotations gained 710 ± 135 kg C ha −1  year −1 in the temperate region, and 100 ± 50 kg C ha −1  year −1 on the Canadian prairies. In temperate regions, continuous and discrete perennial cropping had similar SOC change rate, while in subhumid and semiarid regions, the rates significantly differed (250 vs. −10 kg C ha −1  year −1 ), likely due to yield variation in perennial crop and soil-disturbance effects on SOC storage. The findings revealed regional variations in the SOC gain rate when perennial crops are integrated into annual crop-based rotations. Our findings can refine national and regional SOC models, improving estimates of SOC change for annual–perennial crop conversion.