Background and aims <p>Effective nitrogen (N) management in maize is challenging under low plant density, where the process of tillering enhances plant plasticity. Although the N nutrition index (NNI) is widely used to assess N status of several crops, including high-density maize (<i>Zea mays</i> L.) crops, the relationship between NNI and grain yield of tillered and de-tillered maize crops remains unclear. This study evaluated whether NNI at the blister stage (R₂) of low-density maize crops predicts grain yield of a hybrid prone to tillering.</p> Methods <p>Four irrigated field experiments (Exp) were conducted across different growing seasons using a maize hybrid prone to tillering. Treatments combined low plant densities [D4: 4 pl m⁻², D2: 2 pl m⁻², with an additional tiller removal treatment to D2, D2(–T) in Exp1 and Exp2 and D3: 3 pl m⁻² in Exp3 and Exp4] and soil N availabilities at sowing [60 (N60) and 220&#xa0;kg N ha⁻¹(N220) in Exp1 and Exp2 and 370&#xa0;kg N ha⁻¹ (N370) in Exp3 and Exp4].</p> Results <p>For crops, main shoots, and tillers, N dilution during the growth cycle was less pronounced under moderate and high N availability than under low N availability. Crop NNI increased with higher N availability, and NNI at R₂ explained a large proportion of the grain yield variability in low-density maize crops (R² = 0.64).</p> Conclusions <p>The NNI adequately characterized the N status of tillered and de-tillered maize crops. Our results provide a better understanding of N management in low-density maize crops, particularly those prone to tillering.</p>