Assessing in-season N response and recovery of maize from mild N stress

Efficient nitrogen (N) management in maize ( Zea mays L.) is critical to achieving high yields. However, N overapplication remains widespread, driven by concerns over potential yield losses. Understanding tolerance of maize to early-season N deficiencies is essential for developing effective in-season strategies. This study evaluated different in-season N fertilization strategies and their effects on crop growth rate (CGR), leaf area index (LAI), and plant N status (via chlorophyll meter) throughout the season. The study also assessed the impact on yield and yield components to determine recovery ability from temporary N deficiencies. Two field trials were conducted in Kansas, United States, during 2023 and 2024 under irrigated conditions. Treatments comprised N rates ranging from 0 to 180 kg ha −1 applied at planting or split between planting (90 kg N ha −1 ) and V6, V10, or V14 (30–90 kg N ha −1 ). Nitrogen deficiencies during vegetative growth reduced CGR and kernel number, but plant N status recovered even with N applied as late as V14. Kernel weight was positively associated with CGR during grain filling, highlighting the importance of crop N status to maximize kernel development and yield. The NSI was more responsive than LAI to N fertilization timing. Results showed that maize can tolerate early-season N deficiencies without yield penalties if plant N status is corrected timely, under the tested yield levels. These findings underscore the importance of implementing timely in-season N strategies to mitigate N stress and promote balanced productivity and sustainability. • Nitrogen (N) stress during vegetative period reduced crop growth rate. • N timing had greater impact on N sufficiency index (NSI) than on leaf area index. • Maize can recover from early-season N stress if N status is timely adjusted. • Delayed N applications up to V14 recovered plant N status without yield penalties. • Timely in-season N fertilization is crucial for optimizing kernel number and yield.