Soil total carbon and nitrogen under long‐term perennial bioenergy crops receiving various nitrogen fertilization rates

Perennial crops may sequester greater soil carbon (C) and nitrogen (N) than annual crops due to higher root biomass production, but the potential of long‐term cultivation of perennial bioenergy crops receiving various N fertilization rates in sequestering C and N needs further exploration. Soil samples (0–120 cm) collected from 2009 to 2019 under perennial bioenergy crops receiving various N fertilization rates and an annual crop were analyzed for soil total C (STC) and N (STN) in the US northern Great Plains. Perennial bioenergy crops were intermediate wheatgrass (IW, Thinopyrum intermedium [Host] Barkworth and Dewey), smooth bromegrass (SB, Bromus inermis L.), and switchgrass (SG, Panicum virgatum L.); N fertilization rates were 0, 28, 56, and 84 kg N ha⁻¹, and annual crop was spring wheat (WH, Triticum aestivum, L.). The STC increased, but STN decreased by soil depth, regardless of treatments and years. At 0–120 cm, IW sequestered C at 10.6 Mg C ha⁻¹ year⁻¹ compared with 5.4–6.8 Mg C ha⁻¹ year⁻¹ for SB and SG from 2009 to 2019. Nitrogen fertilization rate had limited effect on STC and STN. At 0–30 cm, STC was 2.0–5.4 Mg C ha⁻¹ greater and STN 0.10–0.24 Mg N ha⁻¹ greater with perennial bioenergy crops than WH. Long‐term cultivation of IW can sequester more C in the soil to a greater depth than SB and SG and perennial bioenergy crops can sequester more C and N at the surface layer than an annual crop in the semiarid region of the US northern Great Plains.