Nitrogen nutrition index as an in-season N diagnostic method for maize yield response to N fertilization

Authors: BOSCHE, LEONARDO - Kansas State University; GOMEZ, FEDERICO - Kansas State University; PALMERO, FRANCISCO - Kansas State University; KERNS, AIDAN - Kansas State University; HEFLEY, TREVOR - Kansas State University; Ransom, Curtis; PRASAD, P.V. VARA - Kansas State University; WOESTYNE, BRADLEY VAN DE - John Deere & Company; CIAMPITTI, IGNACIO - Kansas State University

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2025
Publication Date: 4/26/2025
Citation: Bosche, L., Gomez, F., Palmero, F., Kerns, A., Hefley, T., Ransom, C.J., Prasad, P., Woestyne, B., Ciampitti, I. 2025. Nitrogen nutrition index as an in-season N diagnostic method for maize yield response to N fertilization. Field Crops Research. 328. Article 109941. https://doi.org/10.1016/j.fcr.2025.109941
DOI: https://doi.org/10.1016/j.fcr.2025.109941

Interpretive Summary: To optimize corn growth and minimize environmental impact, managing nitrogen fertilizer is crucial. The Nitrogen Nutrition Index (NNI) is a measurement used to determine if the crop is receiving enough nitrogen. This study analyzed data from 94 field experiments conducted in eight states across the U.S. Midwest from 2014 to 2016 to understand how the relationship between NNI and crop yield changes under different weather and soil conditions. By using advanced statistical methods, researchers identified three main response types: 60% of fields showed a pattern where yield increased with more nitrogen until reaching a stable point, 27% showed a continuous increase with more nitrogen, and 13% showed no response to additional nitrogen. The study also identified three key factors that influenced these patterns: the amount of soil nitrate before planting, the evenness of rainfall during the growing season, and the amount of rainfall from mid-June to early July. Overall, this research helps farmers make better fertilizer decisions by providing a clearer understanding of the expected outcomes under different conditions. As a result, it contributes to more precise fertilizer use, better crop yields, and less environmental impact.

Technical Abstract: Assessing crop nitrogen (N) status is essential for optimizing fertilizer N inputs for maize (Zea mays L.) crop and reducing the environmental footprint of this practice. The Nitrogen Nutrition Index (NNI) offers a promising method for improved in-season N diagnosis and management. However, there is a need to identify the different types of in-season responses for the relative yield (RY) to NNI (RY-NNI) relationship to develop better management tools and identify the main drivers (weather and soil factors) governing this process. This study aimed to describe the different RY-NNI relationships and identify the main weather and soil drivers influencing these responses. We used ninety-four maize yield to fertilizer N response experiments collected using a standardized protocol from the 2014–2016'growing seasons across the United States (US) Midwestern (including eight US states). Bayesian modeling and conditional inference tree algorithm were employed to assess the different types of RY-NNI relationships and characterize key weather and soil drivers. Three distinct RY-NNI relationships were identified, 60'% of the experiments exhibited a linear-plateau response (n'='56), 27'% a linear response (n'='26), and the remaining 13'% a no response (n'='12). Pre-planting nitrate-N (NO3-N), the Shannon Diversity Index (SDI) from late vegetative (tasseling) to end of season (maturity), and the cumulative precipitation (CPP) from V9 to tasseling were key factors influencing RY-NNI responses. Together, these top three variables accounted for ~ 50'% of the total relative variable importance. These findings enhance the use of NNI as an in-season N diagnostic tool by providing insights into types of RY-NNI relationships and their drivers.