DRY MATTER PRODUCTION AND NITROGEN ACCUMULATION IN NO-TILL WINTER WHEAT
Norstar winter wheat (Triticum aestivum L.) was examined in 11 trials with the objective of determining the pattern of dry matter and nitrogen (N) accumulation in dryland stubbled-in winter wheat grown in Saskatchewan. In all 4 yr of this study, replicated no-till field trials were supplemented with 0, 34, 67 and 100 kg N ha−1 applied as ammonium nitrate (34-0-0) in early spring. A fifth treatment of 200 kg N ha−1 was evaluated in the final year of trials. Plant samples were collected at 2-wk intervals. Early season N uptake was more rapid than dry matter accumulation and 89% of the total N, compared to 70% of the total dry matter, was present at anthesis (Zadoks growth stages 60–68). Poor soil moisture availability limited N uptake after anthesis. Consequently, N uptake during the growing season was best described by a quadratic equation, Nitrogen yield = −29.1 + 3.02 Z − 0.018 Z2, where Z represents the Zadoks growth stage. Nitrogen concentrations of the stems and leaves decreased during the growing season while the N concentration of spikes varied among trials. Nitrogen fertilization often produced large increases in tissue N concentration at the beginning of the growing season. These differences decreased with time and by the end of the season tissue N concentrations were usually similar for all N rates. In general, when residual soil N levels were low to intermediate and rainfall was adequate, N fertilization increased dry matter yield, plant N yield, grain yield and grain protein yield. Nitrogen fertilization increased plant N concentration, plant N yield, grain protein concentration and grain protein yield when soil N reserves were intermediate to high and rainfall was adequate.Key words: Nitrogen uptake, wheat (winter), nitrogen response, tissue nitrogen, grain protein, environment