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

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.