No Variation in Critical Nitrogen Curves of Modern Maize Hybrids Differing in Maturity Group Grown Under Contrasting Environmental Conditions

Silage maize (Zea mays L.) is a key crop in the European livestock and bioenergy sectors, and nitrogen (N) fertilisation is a critical management factor associated with N losses. With ongoing climatic changes, later-maturing hybrids can be grown in northern latitudes. Critical N (N_crit) dilution curves describe the relationship between plant biomass and minimum N concentration to achieve maximum growth, providing a benchmark for diagnosing N status. Therefore, it is essential to test if adapted N_crit dilution curves are needed in order to improve N fertilisation management. This study aimed to (1) analyse potential differences in N_crit curves of contrasting hybrids and of varying regional conditions and (2) calculate the N nutrition index (NNI). Data collection was conducted in a 2-year field experiment under rainfed conditions in three regions of Germany, evaluating three maize hybrids differing in maturity group at six mineral N input levels. Aboveground forage mass and plant N concentration were determined at five to six sampling dates during the crop cycle. Forage mass increased with N input and differed in response to regional conditions caused by drought conditions during the second year, but not in response to hybrids. N_crit function parameters and NNI did not differ amongst hybrids and regions, making N_crit and NNI a tool to improve N efficiency, regardless of the maturity group used, even as changing patterns emerge due to climate change.