Comparison of Nitrous Oxide Emissions and Soil Carbon Sequestration with a Dairy Forage Rotation, Biomass Crops, and Grazed Pasture.

Production of harvested forages to feed confined dairy cattle is an important land use in the northeastern US, but cattle grazing and biofuel biomass production provide two alternative land uses with the potential for greater soil carbon sequestration and lower nitrous oxide emissions. An experiment was established in 2004 in central Pennsylvania to compare nitrous oxide emissions and soil carbon accumulations among a corn/soybean/alfalfa rotation, biomass crops (switchgrass and reedcanary grass), and a grazed pasture (red clover/orchard grass or six species mix).  Organic carbon has increased in the upper 5 cm of soil under reedcanary grass and pasture but has changed little under other crops.  Soil organic carbon content below 5 cm has either remained stable or decreased slightly with time.   Nitrous oxide emissions have generally been low for all land uses and appear to be more strongly influenced by soil moisture than land use and associated differences in nitrogen fertilization.  Data accumulated to date suggest that the biomass crops and grazing have a moderate potential to increase soil organic carbon compared to the corn/soybean/alfalfa rotation.  However, the alternative land uses did not provide a reduction in nitrous oxide emissions relative to the crop rotation, possibly because the use of split nitrogen applications resulted in lower than expected emissions from the rotation.