Abstract

Predicting required fertilizer nitrogen (N) rates before planting a crop embodies the concept of establishing a pre-season yield goal and fertilizing for that expected yield.  The objective of this work was to evaluate the efficacy of predicting yield goals, using data from three long-term experiments.   Winter wheat (Triticum aestivum L.) grain yield data from the Magruder Plots (Stillwater, OK, 1930-present), Experiment 222 (Stillwater, OK, 1969-present) and Experiment 502 (Lahoma, OK, 1970-present) were used.  Annual preplant N rates were applied for 87, 45 and 44 years, respectively.   The Magruder Plots were established prior to the advent of modern statistics and were not replicated.  Experiment 222 and Experiment 502 employed randomized complete block experimental designs with four replications.  This work applied the concept that the average yield of the last 3 to 5 years, plus 20% could be used to establish and/or predict the ensuing years’ yield, or yield goal.   For the Magruder Plots, the ‘NPK’ (67-15-29, N-P-K) and Check (0-0-0) treatments were used.  For Experiment 222, treatments 1 and 4 (0-30-37 and 135-30-37) and in Experiment 502, treatments 2 and 7 (0-20-55 and 112-20-55) were employed to test this concept.  Preplant fertilizer sources for N, P, and K were; urea (45-0-0); triple super phosphate (0-20-0); and potassium chloride (0-0-50).  Past 3, 4, and/or 5-year wheat yield averages were not positively correlated with the ensuing season yields in all three long-term experiments, and/or for any of the treatments evaluated.  Failure of the yield goal concept to predict current-year yield levels is largely due to the unpredictable influence of environment on yield.