Are the benefits of yield responses to nitrogen fertilizer application in the bioenergy crop Miscanthus giganteu s offset by increased soil emissions of nitrous oxide?

• Published in: Global change biology. Bioenergy Vol. 7; no. 1; pp. 145 - 152
• Main Authors: Roth, Brendan, Finnan, John M, Jones, Mike B, Burke, James I, Williams, Michael L
• Format: Journal Article
• Language: English
• Published: 01.01.2015
• Subjects: Miscanthus
• ISSN: 1757-1693; 1757-1707
• DOI: 10.1111/gcbb.12125

A field trial was carried out on a 15 year old Miscanthus stand, subject to nitrogen fertilizer treatments of 0, 63 and 125 kg-N ha super(-1), measuring N sub(2)O emissions, as well as annual crop yield over a full year. N sub(2)O emission intensity (N sub(2)O emissions calculated as a function of above-ground biomass) was significantly affected by fertilizer application, with values of 52.2 and 59.4 g N sub(2)O-N t super(-1) observed at 63 and 125 kg-N ha super(-1), respectively, compared to 31.3 g N sub(2)O-N t super(-1) in the zero fertilizer control. A life cycle analyses approach was applied to calculate the increase in yield required to offset N sub(2)O emissions from Miscanthus through fossil fuel substitution in the fuel chain. For the conditions observed during the field trial yield increases of 0.33 and 0.39 t ha super(-1) were found to be required to offset N sub(2)O emissions from the 63 kg-N ha super(-1) treatment, when replacing peat and coal, respectively, while increases of 0.71 and 0.83 t ha super(-1) were required for the 125 kg-N ha super(-1) treatment, for each fuel. These values are considerably less than the mean above-ground biomass yield increases observed here of 1.57 and 2.79 t ha super(-1) at fertilization rates 63 and 125 kg-N ha super(-1) respectively. Extending this analysis to include a range of fertilizer application rates and N sub(2)O emission factors found increases in yield necessary to offset soil N sub(2)O emissions ranging from 0.26 to 2.54 t ha super(-1). These relatively low yield increase requirements indicate that where nitrogen fertilizer application improves yield, the benefits of such a response will not be offset by soil N sub(2)O emissions.