Objectives Soil acidification and low phosphorus (P) availability are major constraints to maize production in the red soil region of southern China. This study aimed to investigate the effects of long-term different fertilization treatments on nutrient uptake and leaf metabolism in maize and to elucidate the mechanisms underlying yield improvement.

Methods A long-term field fertilization experiment established in 1986 on upland red soil was used, including three treatments: no fertilizer (CK), chemical NPK fertilizers (NPK), chemical NPK fertilizer combined with organic fertilizer (NPKM). Shoot biomass, straw dry weight, grain yield, and leaf contents of macronutrients and secondary nutrients were determined. Leaf metabolites were profiled using gas chromatography–mass spectrometry (GC-MS). Differential metabolites were identified using the criteria of VIP>1 and P<0.05. Metabolic pathways were annotated using the KEGG database. Correlations between leaf nutrient contents and differential metabolites were further assessed.

Results Compared with CK and NPK, the NPKM treatment significantly increased shoot biomass, straw dry weight, grain yield, and leaf P content by 99.6% and 83.3%, respectively. Long-term fertilization significantly modulated leaf metabolic profile. A total of 56, 86, and 62 differential metabolites were identified in the NPK vs CK, NPKM vs CK, and NPKM vs NPK comparisons, respectively. Among them, 17, 14, and 8 metabolites were specifically up-regulated, while 4, 7, and 12 metabolites were specifically down-regulated in the respective comparisons. KEGG pathway analysis indicated that these metabolites were mainly enriched in pathways related to amino acid metabolism and protein biosynthesis, carbon and energy metabolism, and redox regulation and antioxidant defense. Correlation analysis further showed that, in the NPK vs CK comparison, the specific differential metabolites were mainly significantly associated with leaf N, K, and S contents but weakly correlated with leaf P content. In contrast, in NPKM vs CK and NPKM vs NPK comparisons, these metabolites exhibited strong correlations with leaf P content, but relatively weak correlations with other nutrient contents. Long-term application of chemical fertilizer alone promoted K uptake and strengthened N- and S-related metabolism in maize leaves. Long-term application of organic fertilizer improved soil conditions and enhanced P associated metabolism regulation, with leaf P content being significantly positively correlated with the contents of multiple organic oxygen compounds. Furthermore, organic fertilizer treatment reduced the levels of stress responsive metabolites such as γ-aminobutyric acid (GABA).

Conclusions Long-term organic fertilization promotes P uptake in maize leaves, enhances amino acid metabolism and protein biosynthesis, improves energy metabolism, and alleviates oxidative stress, thereby achieving high and stable maize productivity in the red soil region of southern China. These results provide scientific support for rational maize fertilization management in this region.