AbstractPercent crude protein and yield of protein information from oat fertilizer trials was collected from twelve sites, including eight soil types and two drainage classifications.Nitrogen was responsible for increases in crude protein content of the grain grown on all soil types studied. Phosphorus and potassium generally reduced the crude protein content of grain, although there were some slight increases recorded. Imperfectly drained soils produced grain of higher crude protein content than well drained soils.Nitrogen, and to a lesser extent phosphorus, was necessary for maximum yield of protein on the well drained soils. Nitrogen alone on the imperfectly drained soils gave maximum protein yields. Potassium had little effect on the yield of protein on either drainage system. Significant seasonal differences in yield of protein were recorded. Higher yields of protein were found on the well drained soils than on the imperfectly drained soils.Yield of grain and yield of protein were highly correlated (r = + .93). Thus, yield information alone is capable of predicting 86% of the variability of yield of protein.