Bélanger, G., Rochette, P., Chantigny, M., Ziadi, N., Angers, D., Charbonneau, E., Pellerin, D. and Liang, C. 2015. Nitrogen availability from dairy cow dung and urine applied to forage grasses in eastern Canada. Can. J. Plant Sci. 95: 55-65. Nitrogen availability from dung and urine excreted by dairy cows has been studied extensively but few studies have been conducted in areas with short growing seasons and cold winters. We assessed N availability from dairy cow urine and dung applied to forage grasses under the cool conditions of eastern Canada, with a focus on soil- and plant-based indicators. The experiment was conducted with timothy (Phleum pratense L.)-dominated swards on two soil types (clay, sandy loam) with three periods of application (mid-September, early June, early July) and four treatments: Control, Dung (1.75 kg fresh weight m^-2), Diluted urine (U-50; 50 g N m^-2), and Urine (U-100; 100 g N m^-2) from lactating cows. Dry matter (DM) yield and N concentration were measured from several successive clippings. Ion exchange membranes (IEM) and crop N nutrition index (NNI) were used, respectively, as soil-based and plant-based indicators of N availability. Relative cumulative DM yields, calculated as cumulative DM yield over all clippings for a given treatment divided by maximum cumulative DM yield among the four treatments, increased from Control (clay: 31 - 69%; sandy loam: 21-63%) to Dung (clay: 39-84%; sandy loam: 46-86%) and U-50 (clay: 81-83%; sandy loam: 78-100%). Relative values of cumulative N uptake were close to those of DM yields. The percentage of applied N taken up by the crop from all clippings was greater with urine (8-28%) than with dung (3-12%) on both soil types. Nitrogen from dung and urine was available to timothy at all periods of application, but urine N availability was greater than that of dung N. Nitrogen exposure, calculated as cumulative mineral N on IEMs, and NNI were both related to relative DM yield (R²>0.61; P<0.001), confirming their capacity to assess N availability to forage grasses receiving dung and urine excreted by dairy cows.