Nitrogen dynamics in a feedlot soil

the feedlot system (fl) generates a high input of sewage causing imbalances in the cycling process of nitrogen (n) as well as a potential negative impact on the environment. the objective of this study was to deepen into the dynamics of n in a fl's soil so as to provide tools to reduce its environmental impact. the study was conducted in a fl, located in balcarce county (buenos aires, argentina). soil samples were taken between november 2006 and may 2007 in a control pasture, in the fl-high (upper slope position) and fl-low (lower slope position) of the fl, and in the runoff area (ra). urease activity and concentrations of ammonium-n, nitrate-n and urea-n were evaluated in the soil up to 60 cm depth. urea-n values were always low (6 mg kg-1), due to the high urease activity measured (438 mg kg-1). ammonium-n concentration was highest in fl-low, reaching a value of 65.5 mg kg-1 at 40-60 cm soil depth. nitrate-n concentration was highest in fl-high for all depths, with a maximum concentration of 97.4 mg kg-1 in the 0-10 cm layer; at 40-60 cm depth, nitrate-n concentration in fl was 31.98 mg kg-1, higher than that in pasture (1.21 mg kg-1). there were no differences in nitrate-n concentration between pasture and ra; hence, it can be inferred that there was no transport of nitrate by surface water flow from the fl to ra. however, the potential for groundwater contamination via nitrate, a mobile soil constituent, should be studied.