Movement of Nitrate Nitrogen in Some Grassland Soils of Southern Alberta

Abstract

AbstractThe downward movement of NO3‐N in dryland soils under native grass [Agropyron smithii Rydb., Bouteloua gracilis (HBK.) Lag., and Stipa comata Trin. & Rupr.] 6 to 8 years after N was applied at rates up to 976 kg/ha reached a depth of 180 cm. Phosphorus fertilizer did not affect NO3‐N movement. Under seeded grasses, there was no evidence of NO3‐N accumulation 2 years after a single application of N at rates up to 944 kg/ha. After repeated annual applications of N that totaled up to 3776 kg/ha over a 4‐year period, NO3‐N accumulations were found to depths of 90 to 120 cm. The depth of NO3‐N movement under bromegrass (Bromus inermis Leyss.) was similar to that under crested wheatgrass [A. cristatum (L.) Gaertn.], but more NO3‐N accumulated in the soil under the bromegrass. In irrigated soil underlaid by drains, NO3‐N leaching was greater in a loam soil over till growing a mixture of bromegrass and alfalfa (Medicago sativa L.) than in a loam soil over sandy loam‐loamy sand growing an irrigated pasture‐grass mixture [A. elongatum (Host) Beauv. and Festuca arundinacea Schreb.]. These studies indicate that, with good management, fertilizer N on grassland soils is not an important contributor to pollution in semiarid southern Alberta.