OVERWINTER NITRATE LOSS AND DENITRIFICATION POTENTIAL OF CULTIVATED SOILS IN ALBERTA

Studies comparing overwinter field losses of NO3-N and denitrification potential using laboratory methods were conducted on the dominant soil Great Groups in Alberta. Recovery in spring of N-15-labelled NO3-N incorporated into the 0-15 cm depth during winter was lower in the Solod, Black and Gray Luvisolic soils in northern and central Alberta (3 30%) compared to the Dark Brown, Brown and Thin Black soils in southern Alberta (68-95%). The northern and central Alberta sites retained a melting snowpack as thawing of top soil began. Nitrate loss was measured in the laboratory on the (0-15 cm samples from 8 soils amended with 150 mg N kg-1 as KNO3. After 7 days incubation, losses ranged from 62 to 90 mg of added NO3-N kg-1 (i.e. 8.9 12.9 mg N kg-1 d-1). In an additional experiment, cumulative emissions of N2O ranged from 19 to 58 mg N kg-1 after 48 h incubation (i.e. 9.5-29.5 mg N kg-1 d-1). A Brown, Black and Gray Luvisol soil amended with 100 mg N kg-1 as KNO, was used to compare two laboratory methods of measuring denitrification potential. Nitrate loss after 3 days ranged from 53 to 60 mg N kg-1 using a method developed in our laboratory compared to 2-17 mg N kg-1 using a published method. The laboratory losses of NO,-N did not correlate with losses in the field. These findings suggest that denitrification in the field was controlled by climatic rather than inherent soil chemical or biological variables.