Overwinter nitrate loss and denitrification potential of cultivated soils in Alberta

Abstract

Studies comparing overwinter field losses of NO 3-N and denitrification potential using laboratory methods were conducted on the dominant soil Great Groups in Alberta. Recovery in spring of 15N-labelled NO 3-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 150mg N kg −1 as KNO 3. After 7 days incubation, losses ranged from 62 to 90 mg of added NO 3-N kg −1 (i.e. 8.9–12.9 mg N kg −1 d −1). In an additional experiment, cumulative emissions of N 2O 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 100mg N kg −1 as KNO 3 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 3-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.