Carbon Sequestration and Nitrous Oxide Emissions in Dairy Forage Rotations and Alternative Land Uses

Forages, especially silage corn and alfalfa, are commonly grown in the northeastern US and fed to confined dairy cattle. Alternative land uses in the region are grazed pasture and the production of perennial grass biomass for cellulosic ethanol production. However, little information on either soil carbon sequestration potential or greenhouse gas emissions is available for these systems. As part of the USDA-ARS GraceNet project, a long-term study comparing soil C accumulation and nitrous oxide emissions from a silage corn/soybean/alfalfa rotation; grazed orchard grass/white clover and six species mix pasture; and switchgrass and reed canarygrass was established in central Pennsylvania in 2004. To date, measurable difference in soil C accumulations have not been observed. Overall nitrous oxide emissions have been relatively low and are frequently below detection, but substantial emissions have been observed with all vegetation types when soils are wet. Nitrous oxide emissions have tended to be greatest from alfalfa and grazed pasture (when emissions from the points of cattle urine deposition are considered). Nitrous oxide emissions from corn plots have been lower than expected, possibly because most N fertilizer is applied after plants are growing.