On-Farm Strip Trials to Improve Nitrogen Recommendations.

Evaluation and improvement are two important components of adaptive nutrient management programs for continuous refinement of nitrogen recommendations and management practices for corn (Zea mays L.). Replicated on-farm strip trials are an effective method to evaluate and demonstrate improved practices to reduce uncertainty in N recommendations. Eighty-seven replicated on-farm strip trials with two to five nitrogen rates in five years in Ohio and Indiana, and 35 trials in seven years in Pennsylvania were conducted to quantify the risk to corn yields from decreasing or increasing nitrogen rates.We documented field-level management practices such as form, timing, and rate of nitrogen, tillage, previous crops, manure application history,  and other factors such as soil type for evaluation of within field-level yield variability. Bayesian analyses of hierarchical models will be used to estimate predictive probabilities of yield response to reductions or increases in nitrogen for an individual field. Posterior distributions will be used to identify and quantify the effects of the within field- and field-level critical management practices that could improve current nitrogen recommendation.