| To investigate the effects of combined application of cake fertilizer and poly-γ-glutamic acid (γ-PGA) on crop yield and soil water\|nitrogen regulation, and to determine an appropriate application rate, a field plot experiment was conducted in 2024 and 2025 using maize as the test crop. A split-plot design was employed, with three cake fertilizer application rates, namely B1 (900 kg·hm-2, low), B2 (1 100 kg·hm-2, medium), and B3 (1 300 kg·hm-2, high), and three γ-PGA application rates, namely R1 (200 kg·hm-2), R2 (400 kg·hm-2), and R3 (600 kg·hm-2), resulting in a total of nine treatments. The effects of different combined application treatments on maize yield, as well as the distribution and utilization of soil water and nitrogen, were evaluated. The results showed that (1) the combined application of cake fertilizer and γ-PGA had significant synergistic or inhibitory effects on soil water and nitrogen regulation (P<0.05). Under the low cake fertilizer rate, an appropriate γ-PGA application exerted a synergistic promoting effect, whereas under the high cake fertilizer rate, it showed an antagonistic inhibitory effect, especially in the 0\|20 cm soil layer. Under the B1 treatment, soil moisture content at the seedling stage in 2024 was significantly increased by 31.58% in B1R2 compared with B1R1. In 2025, soil moisture content at the seedling and jointing stages in B1R3 increased by 10.17% and 8.75%, respectively, compared with B1R1. In 2024, soil total nitrogen content in B1R3 was 15.49% and 47.34% higher than that in B1R1 at the seedling and filling stages, respectively, while in 2025, soil total nitrogen content at the seedling stage increased by 8.90%. In contrast, under the B3 treatment, especially in 2024, soil moisture content and total nitrogen content at the jointing stage in B3R3 were reduced by 46.42% and 70.15%, respectively, compared with B3R1. (2) Under the B1 treatment, soil water use efficiency, nitrogen use efficiency, and maize yield increased with increasing γ-PGA application during 2024-2025. In 2024, compared with B1R1, soil water use efficiency, nitrogen use efficiency, and maize yield in B1R3 increased by 10.00%, 8.44%, and 8.43%, respectively; in 2025, the corresponding increases were 4.66%, 6.91%, and 6.82%, respectively, indicating a significant synergistic effect. However, under the B2 and B3 treatments, soil water and nitrogen use efficiency as well as maize yield decreased with increasing γ-PGA application. In 2024, compared with B3R1, soil water use efficiency, nitrogen use efficiency, and maize yield in B3R3 decreased by 19.67%, 21.34%, and 21.35%, respectively; in 2025, the corresponding decreases were 5.57%, 8.27%, and 8.21%, respectively, indicating a significant antagonistic effect. (3) Based on the entropy weight-TOPSIS method integrating maize yield, water and nitrogen use efficiency, and economic benefit, the B2R1 treatment achieved the highest comprehensive score. Overall, the combined application of 1 100 kg·hm-2 cake fertilizer and 200 kg·hm-2 γ-PGA was identified as the optimal fertilization strategy for improving soil nutrient distribution and enhancing water and nitrogen use efficiency as well as maize yield. |