Nitrogen Fertilization of No‐Till Winter Wheat and Rye. II. Influence on Grain Protein

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Abstract
No‐till seeding into standing stubble immediately after harvest of the previous crop (‘stubbling‐in’) has been employed to successfully produce winter wheat (Triticum aestivum L.) and rye (Secale cereale L.) on the western Canadian prairies. Soil N deficiencies, which result in low grain protein concentrations, are often associated with stubbled‐in winter cereals. In the present study, the effect of N fertilization on protein concentration and protein yield of stubbled‐in winter wheat and rye was evaluated in 40 field trials conducted over a wide range of soil types and environmental conditions in Saskatchewan, Canada. Grain protein concentrations exhibited sigmoidal responses to N fertilization with minimums of 98.8 and 93.0 and maximums that varied from 130 to 231 and 107 to 177 g protein kg−1 dry grain for wheat and rye, respectively. The Gompertz equation was employed to describe the relationship between protein concentration and total available N, providing an average reduction in sums of squares, due to the model, of 96 and 97% for wheat and rye, respectively. Grain protein yield response to N fertilizer was described by an inverse polynomial function that provided an average reduction in sums of squares, due to the model, of 99% for both wheat and rye. Although grain protein concentration was significantly higher for winter wheat in most trials, winter rye demonstrated a greater N use efficiency for grain production. Higher grain yields for rye compensated for lower protein concentrations, and at equal N rates rye produced as much or more protein per hectare than wheat in all comparable trials except two.