Objectives In Yunnan’s Erhai Lake Basin, maize growing season coincides with the rainy season, conventional fertilization leads to heavy nitrogen leaching and causes serious non-point source pollution. By means of the existing drip irrigation infrastructure, we tried daily fertigation scheme characterized by low-dose water and fertilizer amount during the heavy rainfall period.

Methods Field experiments were conducted over three consecutive seasons in the Erhai Lake Basin from 2023 to 2024, using sweet maize as the test material. In the first and second seasons, the controls were set at the traditional nitrogen application rate of 400 kg/hm² with 5 top - dressing practices. The treatments involved reduced nitrogen fertilizer rates under 17 and 30 fertilization practices, respectively, and the optimal nitrogen application rate range was proposed. In the third season, the optimal nitrogen application rate range was further refined according to the daily N absorption of maize, and fertigation was automatically triggered when the light intensity was greater than 10,000 lux. The fertilization frequency was recorded, and investigations were carried out on sweet maize yield, nitrogen uptake dynamics, nitrogen use efficiency, and residual mineral nitrogen in the 0−60 cm soil layer.

Results In the first season, there were no significant differences in maize yield under nitrogen application rates ranging from 200 to 400 kg/hm². The nitrogen uptake process of sweet maize conformed to the Logistic model, with a peak nitrogen uptake occurring 35−53 days after emergence, a daily uptake rate of 3.38−4.03 kg/(hm²·d), and a total nitrogen removal of 142−152 kg/hm² over the entire growth period. In the second season, the N application rate was reduced to 180 kg/hm², and the fertilization frequency was increased to 30 times, resulting in a comparable maize yield to the controls, but a 60% reduction in N losses and a 1.2 - fold increase in the apparent nitrogen use efficiency. In the third season, the 180 kg/hm² of N fertilizer was evenly divided into the daily requirement and applied with a minimum water volume of 4.5 m³/hm² every day, except on rainy days, and a total of 35 fertigation events were recorded. The scheme significantly enhanced maize dry matter accumulation, yield, and N use efficiency while reducing nitrogen losses. Comprehensive effect analysis revealed that the highest comprehensive score was achieved at a nitrogen application rate of 120 kg/hm² under a scenario where the weights of yield and environment were at 1∶1.

Conclusion The optimal nitrogen application rate for sweet maize in the Erhai Lake rainy season is 120−180 kg/hm². Sweet maize exhibits a distinct Logistic cumulative pattern of nitrogen absorption, with the peak absorption period concentrated between 35 and 53 days, reaching a rate of 3.38−4.03 kg/(hm²·d), accounting for over 70% of the total nitrogen uptake during the entire growth period. By reducing the nitrogen application rate from the traditional 400 kg/hm² to 120−180 kg/hm² and utilizing automatic, small-dose, high-frequency drip irrigation triggered by light radiation intensity, the inorganic nitrogen content in the 0−20 cm surface soil can be significantly increased while maintaining yield. This approach notably improves nitrogen use efficiency, reduces apparent nitrogen loss, and represents the optimal nitrogen management technique for sweet maize in Yunnan, balancing both yield and environmental benefits.