The Effect of Crop Rotation and Soil Amendments On Soil N Bioavailability and N2O Emissions.

The majority of N₂O emissions result from bacterial denitrification and to a lesser extent nitrification, occurring in agricultural soils. Therefore, the overall N economy of a system, along with soluble C and limited O₂ are the key drivers in the release of N₂O. Crop rotations and soil amendments readily add to or deplete the soil N economy depending on the C:N ratio of the biomass returned to the field. This paper synthesizes the results of three varied studies to further elucidate the role of management on key drivers of N₂O release. Study one examined how N₂O emissions during potato production are influenced by choice of preceding crop in two-year potato rotations. There was a significant effect of preceding crop (PC) on cumulative growing season N₂O emissions from the potato crop. Preceding crops of red clover and Italian ryegrass (average of 1.7 kg N₂O-N ha^-1) produced significantly higher cumulative N₂O emissions when compared to preceding crops of corn, canola, soybean, barley and potato (average of 0.8 kg N₂O-N ha^-1). A second study on potatoes conducted by Lynch et al. (2009) using Plant Root Simulator (PRS)™-probes found that a PC containing red clover increased soil N supply rates compared to a PC containing pea-oat-vetch. This increase in PRS™–N supply rates was associated with increased N₂O emission during the five-year potato rotation. The use of by-products from biofuel processing as soil amendments and N₂O emissions during canola production was assessed by Schoenau et al. (2009). Wet distillers’ grain and thin stillage resulted in the greatest N₂O production compared with soil amendments of alfalfa powder and glycerol. PRS™–N supply rates were closely linked with these patterns of N₂O emissions. These results suggest that selection of rotation crops and soil amendments can have significant effects on N₂O emissions as affected by soil N bioavailability.