Manure applied to irrigated land may potentially contaminate groundwater with NO3-N. An 8-yr field experiment was conducted in southern Alberta, Canada, to determine the effects of different rates of manure on NO3-N accumulation in two irrigated soil types and NO3-N leaching to shallow groundwater. An annual cereal silage was grown at each site and irrigation was based on soil moisture depletion. Treatments included a control, nitrogen fertilizer (NF) at 180 kg N ha(-1) yr(-1), and four rates of cattle (Bos taurus) manure (20, 40, 60, and 120 Mg ha(-1) yr(-1), wet-weight basis). Annual manure applications for 8 yr resulted in NO3-N accumulation in the soil profile at both sites. For every megagram of total N added from manure, NO3-N in the 0- to 1.5-m layer increased by about 50 kg ha(-1) at the coarse-textured (CT) site and by about 100 kg ha(-1) at the medium-textured (MT) site. Silage yield for all of the manure treatments was similar to yield for the NF treatment after the first 3 to 4 yr of annual manure applications. The greatest manure rate and NF treatments significantly increased NO3-N concentrations in groundwater at the CT site. Groundwater NO3-N concentrations were not adversely affected by manure or NF applications at the MT site. An annual cattle manure application rate of 20 Mg ha(-1) provided sufficient N for irrigated cereal silage production and minimized NO3-N leaching in a medium-textured soil.