Nitrous Oxide Emissions in Potato Production Are Influenced by Choice of Preceding Crop.

In humid regions, the majority of anthropogenic N₂O emissions result from bacterial denitrification occurring in agricultural soils. N₂O emissions resulting from denitrification are principally controlled by soil aeration and by the availability of soil nitrate and carbon.  However, the influence of crop rotation on these parameters, and consequently their influence on N₂O emissions, is poorly understood. This study examined how N₂O emissions during potato production are influenced by choice of preceding crop in two-year potato rotations through their effect on soil carbon and nitrate availability and soil aeration. Preceding crops grown in 2007 were corn, canola, soybean, Italian ryegrass, potatoes, barley and red clover. In 2008, all plots were planted to Russet Burbank potatoes, each receiving the recommended rate of 193 kg N ha^-1. N₂O and CO₂ fluxes were measured weekly in the hill and the furrow using the non-flow-through, non-steady state vented and insulated chamber method. Presented here are preliminary results from potatoes grown in 2008. Preceding crop was found to have a significant effect on N₂O and CO₂ emissions. Cumulative growing season N₂O emissions were higher for potatoes grown after preceding crops of red clover and Italian ryegrass (average of 1.34 kg N₂O-N ha^-1) compared with potatoes grown after all other preceding crops (average of 0.40 kg N₂O-N ha^-1). The effect of preceding crop on N₂O emissions may reflect differences in soil carbon availability. For example, cumulative growing season CO₂ emissions, a measure of soil respiration, explained 36% of the variability in the cumulative growing season N₂O emissions. Similarly both N₂O and CO₂ emissions were found to be significantly higher from the hill compared with the furrow regardless of preceding crop. These preliminary results suggest that the selection of rotation crop in two-year potato rotations can have a significant effect on N₂O emissions.