As a crucial staple crop in agricultural production, maize is extensively cultivated worldwide and plays a pivotal role in ensuring global food security. However, the significant deficiency of essential amino acids (EAA) and conditionally essential amino acids (CEAA), such as lysine (Lys), tryptophan (Trp), methionine (Met), and cysteine (Cys), leads to an imbalance of amino acids in the grain. This study investigates the regulatory mechanism of sulfur (S) application for regulating the amino acid balance of maize grains. The results demonstrate that S application has substantial effects on both the maize yield and nutritional quality. The S application resulted in an increase in maize yield by simultaneously enhancing the grain number per ear (GN) and 100-grain weight (GW), while S application elevated protein concentration through the augmentation of Cys concentration in maize grains. Furthermore, the Cys in grains optimizes the amino acid balance by regulating the ratio of other amino acids, thereby enhancing the nutritional quality of maize while ensuring a steady increase in protein concentration, simultaneously. Overall, the S application at 60–90 kg ha⁻¹ synergistically improved both the yield and nutritional quality of maize, meeting the requirements for sustainable development in maize production. The findings offer a novel theoretical foundation and nutrient management approach for achieving high-yield and superior-quality maize production.

Simultaneous achievement of high yield and excellent quality in rice is essential for food security and human health. The coordinated application of nitrogen (N) and sulfur (S) can effectively increase the grain yield (GY) and grain protein concentration (GPC) of rice. A two-season field experiment was conducted to investigate the synergistic effects of combined N and S application on the GY and GPC of rice. This study employed four N rates (0, 120, 180, and 240 kg ha⁻¹, designated as N0, N1, N2, and N3, respectively) and four S rates (0, 30, 45, and 60 kg ha⁻¹, designated as S0, S1, S2, and S3, respectively) using two rice cultivars: Jiujiuxiang (JJX) and Jiuxiangyou (JXY). The experimental results demonstrate that N and S exert significant effects on the GY and GPC of rice, with notable interactive effects between these two nutrient elements. The synergistic fertilization of N and S enhanced the GY by improving rice plant photosynthesis and dry matter accumulation while increasing GPC through elevated cysteine concentration in grains. Compared to the unfertilized treatment, the GY of the JJX cultivar showed increases of 68.3–143.2% (Season I) and 59.4–133.4% (Season II) under combined N and S applications, while the GY of the JXY cultivar increased by 53.2–144.1% (Season I) and 66.0–192.9% (Season II). Similarly, the GPC of the JJX cultivar showed increases of 7.5–43.4% (Season I) and 5.7–43.9% (Season II) under combined N and S applications, while the GPC of the JXY cultivar increased by 13.1–66.7% (Season I) and 13.3–61.0% (Season II). Overall, whether on the JJX or JXY cultivars, the application of 180 kg ha⁻¹ of N combined with 45 kg ha⁻¹ of S (i.e., the N2S2 treatment) synergistically enhances GY and GPC in rice. The synergistic fertilization of N and S synergistically enhances both rice yield and nutritional quality by regulating plant growth dynamics, which meet the requirements for healthy and sustainable development in rice production systems.