Changes in Check Plot Yields over Time in Three Long-Term Winter Wheat Experiments

Long-term trials conducted by Oklahoma State University convey relevant information on the changes of yield over time. These changes might be due to different factors such as weather, soil organic matter or available nutrients. In long-term experiments, yield of the check plot (no fertilizer) can reveal added information about the environment when studied alone. Long-term trials can be used to evaluate trends that cannot be understood over short periods. Three long-term experiments (Experiment 502, Experiment 222 and Magruder Plots) were used to evaluate changes in check plot yields over time in continuous winter wheat. These changes were expected to provide a better understanding of fertilizer N response and yield potential. Check plots and nitrogen fertilized plots had similar variability over the years, with coefficient of variations (CVs) for both near 30%. Overall means for the check plot (Magruder Plots, Experiment 222 and Experiment 502) were 1072, 1078 and 1674 kg ha(-1),respectively. The unpredictable variability in grain yields from year to year in both fertilized and unfertilized plots was further documented and that highlights the need for mid-season determination of fertilizer nitrogen rates. Unpredictable variability is thus expected and should be internalized at the outset of every planting season.