The effects of variety and nitrogen fertiliser on protein production in oats

Five spring oats comprising two European varieties and three North American varieties were selected on the basis of differences in grain protein content (%) and grown in a field experiment with four nitrogen fertiliser treatments; (i) nil, (ii) early, (iii) late, (iv) early and late (double). Protein production (grain protein yield) and a number of its determinants including grain protein content, grain yield and yield components, the proportion of nitrogen in the grain and the ratio of grain yield: total yield (harvest index) were assessed. The adapted European varieties were higher than the North American varieties for total yield, grain yield, total protein yield, grain protein yield, harvest index and proportion of nitrogen in the grain, but lower in protein content (%) in both grain and straw. There were also varietal differences in protein production among both the European and North American varieties which were related to differences in factors such as grain weight, harvest index or the proportion of nitrogen in the grain. Nitrogen fertiliser application gave marked increases in protein production—early application primarily by increasing grain yields and late application by raising grain protein content (%). Grain protein yield was positively correlated with grain yield and all yield components, but grain protein content (%) was negatively correlated with grain yield and with all yield components except mean grain weight.