Greenhouse gas emissions under perennial bioenergy crops with various nitrogen fertilization rates

Little information exists about greenhouse gas (GHG) emissions under perennial bioenergy crops (PBCs) with various N fertilization rates. Our objectives were to evaluate the effect of PBCs receiving various N fertilization rates on N₂O and CH₄ emissions, GHG balance (GHGB), and yield-scaled GHGB (YSGB) and compare them with an annual crop from 2012-2013 to 2013-2014 in the northern Great Plains. The PBCs were intermediate wheatgrass (IW, Thinopyrum intermedium [Host] Barkworth and Dewey), smooth bromegrass (SB, Bromus inermis L.), and switchgrass (SG, Panicum virgatum L.), and N fertilization rates were 0, 28, 56, and 84 kg N ha^-1. The annual crop was spring wheat (WH, Triticum aestivum L.) with 80 kg N ha^-1. The N₂O flux peaked immediately after planting, fertilization, intense precipitation (>15 mm), and snowmelt. Cumulative N₂O flux was greater for SG than IW and SB with 56 kg N ha^-1 in 2012-2013 and with 28-84 kg N ha^-1 in 2013-2014. The CH₄ flux was not affected by treatments. Carbon sequestration rate at 0-30 cm from 2009 to 2019 was greater for IW than other PBCs. The GHGB and YSGB were greater for SG and SB than IW with almost all N fertilization rates in both years. Comparing PBCs and an annual crop, cumulative N₂O flux, GHGB, and YSGB were greater for SG than IW, SB, or WH in 2013-2014. The IW can reduce GHG emissions per unit area and per unit crop yield compared to other PBCs and WH.