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United States Department of Agriculture

Agricultural Research Service

Research Project: IDENTIFYING AND MANIPULATING DETERMINANTS OF PHOTOSYNTHATE PRODUCTION AND PARTITIONING Title: Reduced nitrogen losses following conversion of row crop agriculture to perennial biofuel crops

Authors
item Smith, Candice -
item David, Mark -
item Mitchell, Corey -
item Masters, Michael -
item Anderson-Teixiera, Krista -
item Bernacchi, Carl
item Delucia, Evan -

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 31, 2012
Publication Date: January 2, 2013
Citation: Smith, C.M., David, M.B., Mitchell, C.A., Masters, M.D., Anderson-Teixiera, K.J., Bernacchi, C.J., DeLucia, E.H. 2013. Reduced nitrogen losses following conversion of row crop agriculture to perennial biofuel crops. Journal of Environmental Quality. 42:219-228.

Interpretive Summary: Nitrogen is a large input to agricultural ecosystems and major losses to the environment are caused by leaching of nitrogen into streams and through the release of nitrous oxide to the atmosphere. Nitrate leaching is responsible for low water quality including the hypoxic zones where agricultural runoff enters the ocean and nitrous oxide is one of the three major greenhouse gases that are responsible for the warming of earth’s climate system. In terms of its overall contribution to warming it is more potent than carbon dioxide and methane, but it is much less abundant than these other gases thus making it responsible for less than 10 percent of global warming. However, it is the single largest pollutant from agriculture. The conversion of land use from row agriculture to a perennial grasses to use as feedstocks for bio-ethanol production can potentially reduce these N loses because they rely on less fertilizer and internally recycle nutrients. We measured N losses and cycling in establishing perennial biofuel crops, Miscanthus, Switchgrass, and prairie, in central Illinois. We found that perennial grasses quickly reduced nitrate leaching and runoff from drainage tile systems. A lag in miscanthus establishment demonstrated that lack of plant uptake leads to large losses of nitrate, even without fertilization. Nitrous oxide emissions were much higher in corn and soybean than in the perennial crops, even with fertilization of switchgrass. 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 24 kg N ha-1 yr-1 for prairie and miscanthus, respectively. The N exported from prairie and miscanthus could be from 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.

Technical Abstract: Current 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. Our objective was to measure N losses and cycling in establishing perennial biofuel crops in central Illinois. Miscanthus (Miscanthus x giganteus), switchgrass (Panicum virgatum L. fertilized with 56 kg N ha-1 yr-1), and mixed prairie were established on typical row crop fields [Mollisols, formerly in corn (Zea mays L.), soybean (Glycine max L.), and alfalfa (Medicago sativa L.)] 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). Initial soil C and N pools were determined to 1 m. Soil N mineralization using buried soil-bags, nitrate leaching at 50 cm using resin lysimeters, and tile flow and nitrate concentrations to determine overall nitrate losses to a nearby stream were measured. Nitrous oxide emissions were measured using vented static chambers. Harvested biomass N was determined 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 leads to large losses of nitrate, even without fertilization. Nitrous oxide emissions were 2.6 to 7.6 kg N ha-1 yr-1 in corn and soybean, but were < 1.5 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 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 24 kg N ha-1 yr-1 for prairie and miscanthus, respectively. The N exported from prairie and miscanthus could be from 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.

Last Modified: 12/19/2014
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