Reduced Nitrogen Losses after Conversion of Row Crop Agriculture to Perennial Biofuel Crops
2013
Smith, Candice M. | David, Mark B. | Mitchell, Corey A. | Masters, Michael D. | Anderson-Teixeira, Kristina J. | Bernacchi, Carl J. | DeLucia, Evan H.
Current biofuel feedstock crops such as corn lead to large environmental losses of N through nitrate leaching and N₂O emissions; second-generation cellulosic crops have the potential to reduce these N losses. We measured N losses and cycling in establishing miscanthus (Miscanthus × giganteus), switchgrass (Panicum virgatum L. fertilized with 56 kg N ha⁻¹ yr⁻¹), and mixed prairie, along with a corn (Zea mays L.)–corn–soybean [Glycine max (L.) Merr.] rotation (corn fertilized at 168–202 kg N ha⁻¹). Nitrous oxide emissions, soil N mineralization, mid-profile nitrate leaching, and tile flow and nitrate concentrations were measured. Perennial crops quickly reduced nitrate leaching at a 50-cm soil depth as well as concentrations and loads from the tile systems (year 1 tile nitrate concentrations of 10–15 mg N L⁻¹ declined significantly by year 4 in all perennial crops to <0.6 mg N L⁻¹, with losses of <0.8 kg N ha⁻¹ yr⁻¹). Nitrous oxide emissions were 2.2 to 7.7 kg N ha⁻¹ yr⁻¹ in the corn–corn–soybean rotation but were <1.0 kg N ha⁻¹ yr⁻¹ by year 4 in the perennial crops. Overall N balances (atmospheric deposition + fertilization + soybean N₂ fixation – harvest, leaching losses, and N₂O emissions) were positive for corn and soybean (22 kg N ha⁻¹ yr⁻¹) as well as switchgrass (9.7 kg N ha⁻¹ yr⁻¹) but were −18 and −29 kg N ha⁻¹ yr⁻¹ for prairie and miscanthus, respectively. Our results demonstrate rapid tightening of the N cycle as perennial biofuel crops established on a rich Mollisol soil.
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