Abstract: To investigate the synergistic regulatory effects of different types of humic acid combined with optimized fertilization on crop yield, a fixed-site field experiment with a winter wheat（Triticum aestivum L.）-summer maize（Zea mays L.） rotation was conducted from 2022 to 2024 in the fluvo-aquic soil area of Xinxiang County, Henan Province. Five treatments were established, including conventional fertilization (T1), optimized fertilization (T2), and optimized fertilization combined with micro-activated humic acid (T3), humic acid organic material (T4), or potassium humate (T5), respectively. The results showed that wheat yield over the two years was higher under the T3 and T4 treatments than under other treatments, while maize yield was higher under the T5 treatment. The two-year average results indicated that the T3 and T4 treatments were most effective in increasing wheat spike number. The T5 treatment resulted in higher maize kernel number per ear and 1000-kernel weight compared to other treatments, showing stable and optimal performance. High yield in wheat mainly relied on the increase in spike number, whereas achieving high yield in maize required the synergistic optimization of key traits such as ear number, kernels per row, and ear length, indicating differences in yield formation mechanisms between the two crops. In conclusion, the combined application of optimized fertilization with humic acid synergistically achieved fertilizer reduction along with increased yield and efficiency. The optimal combination for wheat was optimized fertilization with micro-activated humic acid or humic acid organic material, while for maize, it was optimized fertilization with potassium humate.

Key words: humic acid, optimized fertilization, wheat-maize rotation, combined application, yield, components