Foliar Supplementation with NPK Stimulates Carbon Metabolism and Improves Water Use Efficiency and Off-Season Maize Crop Yield

Maize production in Brazil is concentrated in the off-season, after soybean harvest. Reduced water availability can compromise maize growth and productivity. Foliar fertilization may improve crop development and yield, although evidence on simultaneous application of macronutrients remains limited. This study evaluated the effects of foliar nitrogen–phosphorus–potassium (NPK) formulations application on off-season maize physiology and grain yield. We compared foliar NPK application with an untreated control over two growing seasons. Leaf nutritional status, photosynthetic enzymes (ribulose-1,5-bisphosphate carboxylase/oxygenase [Rubisco] and phosphoenolpyruvate carboxylase [PEPcase]), gas exchange, oxidative stress indicators (H2O2 and MDA), antioxidant enzymes (superoxide dismutase [SOD] and catalase [CAT]), protein and sugar concentrations, yield components, and grain yield were evaluated. Foliar NPK application improved maize nutritional status and photosynthetic performance Rubisco activity, gas exchange, water use efficiency (WUE) in 2020, and protein and sugar concentrations. Foliar NPK reduced hydrogen peroxide (H2O2) accumulation and lipid peroxidation, measured as malondialdehyde (MDA) in both seasons, accompanied by lower antioxidant enzyme activities, suggesting reduced oxidative pressure and antioxidant demand. Grain yield increased by 0.72 Mg ha−1 (11.5%) and 0.64 Mg ha−1 (12.0%) in the first and second seasons, respectively, compared with untreated maize. NPK improved physiological performance and grain yield of off-season maize, supporting its use as a complementary practice.