Relationship between Grain Crop Yield Potential and Nitrogen Response

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Abstract
The relationship between yield potential and N response in long‐term cereal production is not well known. The objective of this study was to evaluate the relationship between yield potential (yield level) and N responsiveness in long‐term winter wheat (Triticum aestivum L.) and maize (Zea mays L.) field experiments in Stillwater, OK (53 yr), Altus, OK (two trials, 45 yr each), Arlington, WI (49 yr), Shelton, NE (11 yr), Nashua, IA (32 yr), and Kanawha, IA (26 yr). Nitrogen responsiveness or the response index (RI) was determined by dividing the actual grain yield from high N rate plots by the yield from either the 0‐N fertilizer check (RI 0‐N) or medium N rate plots (RI mid‐N). Linear relationships between maximum yield, RI 0‐N, RI mid‐N, and year were thus examined. For the seven long‐term trials comprising 261 yr of site data, yield and N responsiveness were not related whether or not a medium N rate or the check plot (0‐N) was used to determine RI. Because yield level and N responsiveness are independent, and both impact N demand, using both should assist in formulating more accurate fertilizer N recommendations.

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