Sorption of Atmospheric Ammonia by Soil and Perennial Grass Downwind From Two Large Cattle Feedlots
2006
Livestock manure in feedlots releases ammonia (NH₃), which can be sorbed by nearby soil and plants. Ammonia sorption by soil and its effects on soil and perennial grass N contents downwind from two large cattle feedlots in Alberta, Canada were investigated from June to October 2002. Atmospheric NH₃ sorption was measured weekly by exposing air-dried soil at sampling points downwind along 1700-m transects. The amount of NH₃ sorbed by soil was 2.60 to 3.16 kg N ha⁻¹ wk⁻¹ near the source, declining to about 0.25 kg N ha⁻¹ wk⁻¹ 1700 m downwind, reflecting diminishing atmospheric NH₃ concentrations. Ammonia sorption at a control site away from NH₃ sources was much lower: 0.085 kg N ha⁻¹ wk⁻¹ Based on these rates, about 19% of emitted NH₃ is sorbed by soil within 1700 m downwind of feedlots. Field soil and grass samples from the transect lines were analyzed for total N (TN) and KCl-extractable N content (soil only). Nitrate N content in field soil followed a trend similar to that of atmospheric NH₃ sorption. Soil TN contents, because of high background levels, showed no clear pattern. The TN content of grass, downwind of the newer feedlot, followed a pattern similar to that of NH₃ sorption; downwind of the older feedlot, grass TN was correlated to soil TN. Our results suggest that atmospheric NH₃ from livestock operations can contribute N to local soil and vegetation, and may need to be considered when determining fertilizer rates and assessing environmental impact.
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