Cover crop effects on nitrous oxide emission from a manure-treated Mollisol

Abstract

Agriculture contributes 40–60% of the total annual N 2O emissions to the atmosphere. Development of management practices to reduce these emissions would have a significant impact on greenhouse gas levels. Non-leguminous cover crops are efficient scavengers of residual soil NO 3, thereby reducing leaching losses. However, the effect of a grass cover crop on N 2O emissions from soil receiving liquid swine manure has not been evaluated. This study investigated: (i) the temporal patterns of N 2O emissions following addition of swine manure slurry in a laboratory setting under fluctuating soil moisture regimes; (ii) assessed the potential of a rye ( Secale cereale L.) cover crop to decrease N 2O emissions under these conditions; and (iii) quantified field N 2O emissions in response to either spring applied urea ammonium nitrate (UAN) or different rates of fall-applied liquid swine manure, in the presence or absence of a rye/oat winter cover crop. Laboratory experiments investigating cover crop effects N 2O emissions were performed in a controlled environment chamber programmed for a 14 h light period, 18 °C day temperature, and 15 °C night temperature. Treatments with or without a living rye cover crop were treated with either: (i) no manure; (ii) a phosphorus-based manure application rate (low manure): or (iii) a nitrogen-based manure application rate (high manure). We observed a significant reduction in N 2O emissions in the presence of the rye cover crop. Field experiments were performed on a fine-loamy soil in Central Iowa from October 12, 2005 to October 2, 2006. We observed no significant effect of the cover crop on cumulative N 2O emissions in the field. The primary factor influencing N 2O emission was N application rate, regardless of form or timing. The response of N 2O emission to N additions was non-linear, with progressively more N 2O emitted with increasing N application. These results indicate that while cover crops have the potential to reduce N 2O emissions, N application rate may be the overriding factor.