Optimizing nitrogen fertilizer recommendations for field corn grown in Florida sandy soils

Nitrogen (N) is essential to maximize corn (Zea mays L.) yield; however, over- and underapplication can cause environmental concerns or yield losses. Optimizing N management is critical to balance productivity and sustainability. This study was conducted during 2022–2024 in Florida to determine corn N response. The experiment included six N rates (0–392 kg N ha⁻¹ by 78.5 increments) over 3 years, with an additional rate (471 kg N ha⁻¹) in the third year, using a randomized complete block design with four replications. Results showed that 314–471 kg N ha⁻¹ produced the highest and statistically similar aboveground biomass (21,598–23,166 kg ha⁻¹), grain yield (12,479–13,588 kg ha⁻¹), and N uptake (227–250 kg ha⁻¹). For grain N removal, (144–162 kg ha⁻¹), 392 and 471 kg N ha⁻¹ were statistically similar, while 314 kg N ha⁻¹ was significantly lower than 392 kg N ha⁻¹, indicating a threshold response beyond 314 kg N ha⁻¹. Agronomic N use efficiency and partial factor productivity were highest at 157 (58.8 kg kg⁻¹) and 78.5 (57.9 kg kg⁻¹) kg N ha⁻¹, respectively. Results suggest no agronomic advantage above the 314 kg N ha⁻¹ rate, and yield decreased at 471 kg N ha⁻¹. Response analysis indicated that 23.2 g N was required per kg of corn grain under irrigation system. The nitrogen nutrition index confirmed that moderate applications (235–314 kg N ha⁻¹) sustained crop N status, while higher rates (>392 kg N ha⁻¹) offered little to no benefit. Collectively, these results support refining N recommendations to optimize agronomic production in Florida.