Nitrous oxide emissions from denitrification and the partitioning of gaseous losses as affected by nitrate and carbon addition and soil aeration

National inventories of N 2 O emissions from agricultural situations are being developed; however, the factors controlling such emissions may vary with soil and environmental conditions and management practices. This study determined the relative importance of soil aeration, as measured by water-filled pore space (WFPS), NO 3 − addition, C addition and C source on the amount and partitioning of gaseous N losses from denitrification from an arable soil in Atlantic Canada. Denitrification (N 2 O + N 2 ) and N 2 O emissions were measured on repacked soil cores using acetylene inhibition.The N 2 O:(N 2 O + N 2 ) ratio was frequently 0.7 or higher, indicating that most emissions occurred as N 2 O. N 2 O emissions and denitrification were negligible at a WFPS of 0.45 m 3 m -3 , and high at WFPS of 0.75 m 3 m -3 , regardless of NO 3 − or C addition treatments. At a WFPS of 0.60 m 3 m -3 , N 2 O emissions and denitrification were low and were increased by both NO 3 − and C addition treatments. Carbon source was investigated by amendment with glucose, red clover or barley straw. Based on the quantity of soil respiration per unit of C added in the amendment, C in the red clover and barley straw was estimated to be 48 and 28% as available as glucose C. When corrected for C availability, cumulative N 2 O emissions averaged 0.010, 0.011 and 0.002 mg N kg -1 soil, and cumulative denitrification averaged 0.014, 0.014 and 0.003 mg N kg -1 soil, for each 1.0 mg C kg -1 soil of available C added as glucose, red clover or barley straw, respectively. NO 3 − addition had no effect on denitrification, but increased N 2 O emissions, especially where C availability was high. The amount of denitrification was controlled primarily by soil O 2 supply, as controlled by WFPS and C availability. The N 2 O:(N 2 O + N 2 ) ratio was generally high in cases where the supply of O 2 or NO 3 − was sufficient to meet the demand for terminal electron acceptors.