Replacing nitrogen fertilizer by biological nitrogen fixation could lower the carbon footprint of pasture-based milk production
Pasture-based milk production using mainly nitrogen fertilizer emits more greenhouse gases than pasture-based milk production that relies mainly on fertilizing with white clover.
Researchers at University College and Teagasc research center in Ireland compared greenhouse gas emissions from the two systems using different fertilizers, using data from studies conducted at Solohead Research Farm in Ireland between 2001 and 2006.
Ten pastures with a stock rate of 2.0 − 2.5/ha with a fertilizer nitrogen input of 180 − 353kg/ha were compared with six white clover pastures with stock rate 1.75 − 2.2/ha with fertilizer nitrogen input between 80 - 99kg/ha. The carbon footprints were calculated by using Life Cycle Assessment, and the white clover-based system had 11 − 23% lower carbon footprint compared with the nitrogen fertilizer.
Average carbon footprint was 0.86-0.87 and 0.97-1.13 kg of CO2-eq/kg of energy-corrected milk, respectively. Emissions of both N2O and CO2 were lower in white clover, whereas emissions of CH4 (per kg of energy-corrected milk) were similar in both systems.
Authors: M.-J. Yan, J. Humphreys, N.M. Holden, Journal of Dairy Science, Volume 96, Issue 2 , Pages 857-865, February 2013