313-1 Nitrogen Fertilization Increases Pasture Canopy Photosynthesis and Ecosystem Respiration.



Wednesday, October 19, 2011
Henry Gonzalez Convention Center, Hall C, Street Level

R. Howard Skinner, USDA-ARS, University Park, PA
Proper management of agricultural lands has the potential to increase soil C sequestration and help reduce the rate that CO2 concentration is increasing in the atmosphere. Grazing lands, in particular, are thought to have a high C sequestration potential. Eddy covariance systems have continuously monitored CO2 flux from two low-input temperate pastures since January 2003. These pastures received only limited fertilizer inputs and as a consequence had relatively low productivity. Averaged over the first five years of C flux measurements (2003-2007) net ecosystem exchange (NEE) on one pasture was 69 g CO2 m-2 yr-1 (positive values indicate a net loss of CO2 to the atmosphere, whereas negative values indicate net ecosystem uptake). Beginning in 2008, we applied 200-250 kg N ha-1 yr-1 to one of the two pastures to determine if improved fertility could increase gross primary productivity (GPP) but also to determine if concurrent increases in ecosystem respiration (Re) would offset the gains in GPP. Gross primary productivity averaged over three years (2008-2010) increased 20% under the higher fertility regime compared to the first five years, but Re also increased by 16%. The net result was to change NEE from a net source to a net sink of -118 g CO2 m-2 yr-1. It appears that increased N fertilization of previous low-input pastures can improve soil C sequestration despite the concurrent increase in Re.
See more from this Division: ASA Section: Environmental Quality
See more from this Session: Management Impact On GHG Emissions and Soil C Sequestration: III