Title: Does nitrogen fertilization increase pasture carbon sequestration Author
Submitted to: Extension Fact Sheets
Publication Type: Abstract Only
Publication Acceptance Date: January 6, 2012
Publication Date: January 25, 2012
Citation: Skinner, R.H. 2012. Does nitrogen fertilization increase pasture carbon sequestration [abstract]. Northeast Pasture Consortium Fact Sheets. p. 1. Interpretive Summary: An interpretive summary is not required.
Technical Abstract: Proper management of agricultural lands has the potential to increase soil C sequestration and help reduce the rate that carbon dioxide concentration is increasing in the atmosphere. Grazing lands, in particular, are thought to have a high C sequestration potential. Changes in pasture C content results from the difference between C uptake (photosynthesis and manure application) and loss (respiration and removal of harvested forage). Eddy covariance systems have continuously monitored carbon dioxide 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) the two pastures lost on average of 0.56 and 1.10 Mg C ha**-1 yr**-1, respectively. Beginning in 2008, we applied 200-250 kg N ha**-1 yr**-1 to the pasture with the greatest C loss to determine if improved fertility could increase photosynthetic C uptake and soil sequestration. Averaged over three years (2008-2010), uptake increased 20% under the high fertility regime compared to the first five years. However, respiration also increased by 16% and harvested forage yield increased by 53%. The net result was no change in the rate of C loss (1.08 Mg C ha**-1 yr**-1). However, during the same three-year period, C loss increased from 0.56 to 1.29 Mg C ha**-1 yr**-1 in the pasture that continued to receive only limited N fertilizer. It appears that increased N fertilization can improve the soil C status compared with a low-input pasture even though it might not necessarily turn the pasture into a C sink.