Acidification of soil in Alberta by nitrogen fertilizers applied to bromegrass

Abstract

The objective was to determine the effect of rate and source of N on the amount and depth of soil acidification. The N fertilizers were broadcast on established bromegrass (Bromus inermis Leyss) stands in the fall or spring of each year in six field experiments. Soil samples were taken after N fertilizer had been applied over a period of 5 to 16 years. There was a significant reduction in soil pH due to N fertilizer in all experiments, but primarily in the 0–15 cm layer. When the 0–15 cm layer was sampled by 5 cm increments, the N fertilizer effects on soil pH were much more pronounced in the 0–5 cm depth than the lower depths, and N fertilizer had no effect on soil pH in the 10–15 cm depth. The acidity and extractable Al in soil increased with increasing N rate. The average annual rate of depression in soil pH in the 0-5 cm layer ranged from 0.09 to 0.16 with 112 kg N ha−1 rate. The amount and depth of depression in soil pH was greatest with ammonium sulphate, followed by ammonium nitrate, with a small effect by urea and no reduction from calcium nitrate. In conclusion, these results indicated that long-term application of fertilizer N to bromegrass may require liming to counteract the acidifying effect of N fertilizer.