Controlled-release urea optimizes the pathway to yield increase via post-anthesis carbon-nitrogen coordination in maize

The precise regulation of nitrogen supply after flowering for maize can be achieved by blending urea and controlled-release urea (CCU) one-off application. However, the dynamic optimization driving source-sink allocation and mechanisms underlying synergistic carbon–nitrogen regulation remain poorly understood. We investigated the physiological and molecular mechanisms underlying carbon and nitrogen metabolism in maize under various controlled-release urea (CRU) and conventional urea treatments. The experiment included five fertilization treatments: CK (no nitrogen) and four treatments at 180 kg N ha ^− 1 : U (all Urea-N), C1 (CRU-N: Urea-N = 1:2), C2 (CRU-N: Urea-N = 2:1), and C3 (all CRU-N). Physiological traits were measured, and integrated leaf transcriptomic and metabolomic analyses were conducted. Compared with urea treatment, CCU (C2 treatment) boosted maize yield by up to 18.3–22.8%, synergistically enhancing nitrogen components (N content and soluble protein), carbon metabolites (C content and soluble sugar), and total dry matter. Notably, total dry matter was positively correlated with C/N ratio. CCU optimized carbon–nitrogen allocation by simultaneously increasing grain nitrogen reserves (soluble protein and free amino acids) and carbon storage (non-structural carbohydrates). Integrated transcriptomic and metabolomic analysis revealed CCU-mediated metabolic shifts, activating aromatic amino acid biosynthesis and glyoxylate and dicarboxylate metabolism. Multi-omics integration identified GLT1 and IDH3 as pivotal regulatory factors, whose expression levels showed significantly correlated with alanine, homocitric acid, and dry matter accumulation, thereby linking the crosslink between the TCA cycle and nitrogen assimilation to yield formation. These findings demonstrate that CCU drives the priority distribution of assimilation products to grains through the synergistic regulation of slow nitrogen release and carbon-nitrogen metabolism. This study provides insights into the regulation of maize metabolism and offers guidance for the efficient utilization of nitrogen under one-off application of nitrogen.