Nitrous oxide emissions are greater in silt loam soils with a legacy of manure application than without

Soil carbon (C) content, often found at elevated levels in manured soils, can play a critical role in regulating nitrous oxide emissions. Nitrate availability and oxygen status are the other primary drivers of emissions, yet the interaction of these three variables and the dynamics of the denitrification process are inadequately known. Emissions of N₂O and N₂ were measured from two New York State soils that were historically managed either with regular cattle manure applications (M) or without manure (NM). For 168 h, repacked soil cores were maintained at 80 % water-filled pore space after the application of 0, 50, 100, and 200 kg ha^?1 of labeled K¹⁵NO₃. Significant differences were found in the N₂O emission profiles between the two treatments with a simultaneous increasing trend in emissions with higher fertilizer applications. The M soil produced 53-, 15.5-, and 8.6-fold increases in N₂O emissions over the NM soil at the 50-, 100-, and 200-kg ha^?1 N rates, respectively. Additionally, the mean ratio of nitrous oxide to total denitrification (N₂O/(N₂O + N₂)) was higher for M soil. It increased to values of 0.17, 0.25, and 0.43 for fertilizer rates of 50, 100, and 200 kg ha^?1, respectively, in contrast to ratios in the NM soil of 0.01, 0.03, and 0.14.