Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski], a cool-season introduced bunchgrass, offers producers an alternative to crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schultes] for spring and fall grazing in the Northern Great Plains. Tetraploid Russian wildrye with improved seedling establishment may offer even greater potential for seasonal grazing. This study investigates how the concentrations of some nutritive quality components in leaf, stem, and inflorescence tissue of diploid and tetraploid Russian wildrye were affected by growing season water (50 and 150% of average precipitation) and fertilizer (10 and 134 kg N ha⁻¹). Plants were sampled at vegetative, boot, anthesis, and anthesis plus 10-day stages of maturity in 1994, 1995, and 1996. Tetraploid plants had slightly (P < 0.05) less crude protein (CP) in leaf, stem and inflorescence tissue than diploid plants. Plants grown at the 50% water treatment had higher CP and in vitro dry matter digestibility (IVDMD), and lower acid detergent fiber (ADF) and neutral detergent fiber (NDF) in leaf and inflorescence tissue, while in stem tissue only CP was affected by the growing season water treatment. Nitrogen fertilizer resulted in greater CP and IVDMD and lower ADF and NDF in all 3 plant tissues. Maturity affects were consistent over leaf, stem and inflorescence tissue, with CP and IVDMD declining and ADF and NDF increasing as plants matured. There were some differences in nutritive quality components between diploid and tetraploid plants, but overall their qualities were comparable and quite good. Crude protein at all stages of maturity in leaf and inflorescence tissue would have been adequate for most classes of beef cattle, while stem tissue CP would have only been adequate for lower producing animals.