Determination of a critical nitrogen dilution curve and nitrogen nutrition index for maize in Western Nile Delta of Egypt

Critical nitrogen (N) dilution curves are valuable tools for diagnosing N deficiency and managing its levels in plants. The objectives of this study were to establish a critical N dilution curve for maize in Egypt's West Delta region, assess the potential of using it to compute the N nutrition index (NNI) and compare this curve with existing curves for maize in other regions. The experiment was carried out across four site years (2020-2021), with seven N fertilization rates (0-360 kg N ha(-1)) used to induce variability in plant growth. Aboveground shoot biomass (W; Mg DM [dry matter] ha(-1)) and N concentration (N-c; g kg(-1) DM) were determined on five sampling dates during the growing season. A critical N dilution curve (Nc=43.022 W-0.51) was developed, which differed moderately from those reported in France, Germany, and China. The NNI computed from this curve recognized both limited and non-limited N nutrition conditions. The findings of progressing NNI suggest that the period between V9 (9th leaf collar fully unfolded) and V12 is critical and that a sufficient supply of N fertilizer is essential. Furthermore, the NNI derived from an independent dataset, utilizing the N-c established in this study, exhibited a strong relationship with the relative grain yield. The relationship was characterized by a linear plateau function, which accounted for 74% of the observed variance. The results of this study will offer dependable guidance for detecting N levels in maize and customizing the application of precision N fertilizers to enhance yield and use efficiency.