Revisiting the relationship between nitrogen nutrition index and yield across major species

Abstract

Crop nitrogen (N) fertilization diagnoses via the N nutrition index (NNI)-yield relationship have been tested forseveral crop species, but a cross-species comparison of that relationship has not been performed yet. This studyaimed to perform a cross-species comparison of the relationship between NNI and yield with emphasis on theyield sensitivity to N deficiency, slope of the models. Additionally, we conducted an evaluation to determine thebest NNI sampling moment to predict relative yield, with focus on major grain crops. Based on a recently publishedglobal dataset to parametrize critical dilution curves, we calculated integrated NNI, instantaneous NNI,relative yield, and relative shoot biomass for annual ryegrass, tall fescue, maize, potato, rice, and wheat. Weobtained 238 observations to fit integrated NNI-relative yield linear mixed-effects models and 1606 observationsto fit instantaneous NNI-relative yield models. Subsequently, we performed a sensitivity analysis to determinethe best NNI sampling moment to predict relative yield, with focus on major grain crops (maize, rice, and wheat).Our results show that there was low inter-species variation of sensitivity to N deficiency, i.e., the slope of therelationship between relative yield and integrated NNI. For grain crops, instantaneous NNI around anthesisdemonstrated a better predictive capability for relative yield, outperforming other vegetative stages. This findingcontributed to improving the understanding of the association between relative yield and NNI with implicationsfor breeding programs, nutrient management practices, and crop modelling. Most importantly, this study is acontribution to improving the N nutrition diagnosis for several crop species, by using an integral, comparativeapproach.