Perennial Biofuel Crops Reduce Nitrogen Losses During Establishment in Central Illinois.

First generation biofuel feedstock crops such as corn lead to large environmental losses of N through nitrate leaching and N₂O emissions, and require large inputs of N fertilizer. Second generation cellulosic crops have the potential to reduce these N losses, and provide even greater biomass for conversion to fuel or combustion. For this study, we examined nitrogen cycling in establishing perennial biofuel crops in central Illinois. Miscanthus, switchgrass (fertilized with 56 kg N ha^-1 yr^-1), and mixed prairie were established on typical row crop fields (Mollisols, formerly in corn, soybeans, and alfalfa) in a randomized complete block design with five replicates (one 4 ha plot with individual tile drainage systems, and four 0.7 ha plots), along with a corn-corn-soybean rotation (corn fertilized at 168 to 202 kg N ha^-1). Most measurements were conducted during the first four years of establishment and growth. Initial soil C and N pools were determined to 1 m and soil N mineralization was measured using buried soil-bags. Nitrate leaching was measured using resin lysimeters (50 cm) and tile flow, and nitrate concentrations. Nitrous oxide emissions were measured using vented static chambers and harvested biomass N was also measured for each crop. We found that perennial crops quickly reduced nitrate leaching at 50 cm as well as concentrations and loads from the tile systems (year 1 tile nitrate concentrations of 10 to 15 mg N L^-1 declined by year 4 in all three perennial crops to < 0.6 mg N L^-1, and loads of < 0.8 kg N ha^-1 yr^-1). A lag in Miscanthus establishment demonstrated that lack of plant uptake can lead to large losses of nitrate, even without fertilization. Nitrous oxides emissions were 2.6 to 7.6 kg N ha^-1 yr^-1 in the corn-corn-soybean rotation, but were < 1 kg N ha^-1 yr^-1 by year 4 in the perennial crops, even with fertilization of switchgrass. Overall N balances (atmospheric deposition + fertilization + soybean N₂ fixation – harvest + leaching + N₂O emissions) were near zero for corn and soybeans as well as switchgrass, but were about -30 kg N ha^-1 yr^-1 for prairie and Miscanthus. This N could be due to N₂ fixation or soil organic N, and needs further study. Our results demonstrate the rapid tightening of the N cycle as perennial biofuel crops establish on a rich Mollisol soil.