Characterizing and Classifying Variability in Corn Yield Response to Nitrogen Fertilization on Subfield and Field Scales

Marked spatial and temporal variability in yield response to N fertilizer observed in individual yield response trials creates a high degree of uncertainty when estimating economic optimum rates (EORs) of N for a group of trials and when extrapolating these rates from one location to another. A survey was conducted to characterize and classify variability in yield response to N on subfield and field scales. Fertilizer N was applied at five rates (56, 84, 112, 140, and 168 kg N ha −1 ) in many (6–12) replicated strips within three 18‐ to 24‐ha no‐till fields during two corn ( Zea mays L.) growing seasons. Yield responses or yield differences between two adjacent strips were measured in 22 to 25 grid cells ha −1 within each field. Cumulative probability distributions (CPDs) were used to estimate the probability that a given N rate produces a yield response less or equal to a specified quantity. The yield responses were classified into potential categories with different N fertilizer requirements using apparent soil electrical conductivity (EC a ), digital soil map units, and relative elevation. Analysis indicated that the classifications explained <3% variability in yield response to N applied in the near‐optimal range, where probabilities of receiving positive and negative marginal returns were the same. Presenting probabilities of yield response observed at different ranges of N fertilization may provide the basis for assessing the uncertainty associated with the variable effects of weather and variable supply of N when assessing economic risk and benefits of N fertilization in large‐scale on‐farm studies.