Karamanos, R., Hanson, K. and Stevenson, F. C. 2014. Nitrogen form, time and rate of application, and nitrification inhibitor effects on crop production. Can. J. Plant Sci. 94: 425-432. Nitrogen management options for anhydrous ammonia (NH₃) and urea were compared in a barley-wheat-canola-wheat cropping sequence (2007-2010) at Watrous and Lake Lenore, SK. The treatment design included a factorial arrangement of N fertilizer form (NH₃ versus urea), nitrification inhibitor application, time of N application (mid-September, mid- to late October, and spring) and four N fertilizer rates (0, 40, 80 and 120 kg ha^-1). Anhydrous ammonia applications at 40 kg N ha^-1 in 2008 (fall) and in 2010 (all times of application) resulted in wheat yield reductions relative to the same applications for urea. For wheat years, yield was reduced for both fall versus spring N fertilizer applications, when no nitrification inhibitor was applied and the inclusion of nitrification inhibitor maintained wheat yield at similar levels across all times of N fertilizer applications, regardless of form. Protein concentration was approximately 2 g kg^-1 greater with urea compared with NH₃ at both sites in 2008 and only at Watrous in 2010. Also, early versus late fall N fertilizer applications consistently increased N concentration of grain only for the 40 and/or 80 kg N ha^-1 rates. Effects of nitrification inhibitor on N concentration were not frequent and appeared to be minimal. Urea had greater agronomic efficiency (AE) than NH₃ at the lower N fertilizer rates. The nitrification inhibitor had a positive effect on wheat AE only for early fall N fertilizer applications. It can be concluded that for maximum yields NH₃ or urea will be suitable if applied at rates of 80 kg N ha^-1 and greater. If N fertilizer is applied at 40 kg N ha^-1, especially in fall without inhibitor, urea is better. In terms of protein concentration for wheat, urea seemed to better than NH₃ and fall was better than spring application.