Effect of supplementary foliar fertilization on maize: A ¹⁵ N tracer study

Abstract

Supplementary foliar nitrogen (N) fertilization at low rates has been explored as an alternative strategy to supply N to field crops when soil application is impractical. However, its effects on maize ( Zea mays L.) yield and fertilizer N recovery remain poorly understood. We conducted a 2‐year field experiment in Brazil, using ¹⁵ N‐labeled urea applied to maize leaves at four low rates (0, 650, 1300, and 1950 g N ha ⁻¹ ) and two growth stages (six‐leaf, V6; and tassel emergence, VT). Overall, 55% of the foliar‐applied N was recovered in the maize plant, with ¹⁵ N mainly allocated to grain (36% of applied N) and shoot (18%). Foliar N application did not increase grain yield or total plant N accumulation in either year. Yields averaged 10.5 Mg ha ⁻¹ in a year with adequate rainfall and 5.3 Mg ha ⁻¹ under drought, with no yield differences among foliar N treatments. In the drier season, foliar‐applied N showed greater recovery in grain, indicating enhanced translocation under N stress conditions. The additional N from low‐rate foliar sprays did not improve maize yield when applied from early to late vegetative stages, suggesting that such small supplemental N applications are insufficient to overcome soil N limitations or further boost yield in well‐fertilized maize. These findings contribute to understanding the fate of foliar‐applied N in maize and indicate that low‐rate foliar N is recovered mainly in grain but has a negligible yield effect.