Plant nitrogen status at flowering and kernel set efficiency in early- and late-sown maize crops

•We studied plant N status and kernel set efficiency (KSE) in contrasting sowing dates.•Plant N status at R1 was determined using SPAD readings in ear leaf-blade.•A boundary function analysis was performed to quantify the direct effects of plant N status on KSE.•Plant N status effect on KSE was recorded in late-sown crops at low plant growth rate (PGR).•Plant N status effect on KNP was regulated by prolificacy expression at high PGR in early-sown crops.