Optimal N fertilizer management method for improving maize lodging resistance and yields by combining controlled-release urea and normal urea

Despite being an efficient nitrogen (N) management method, the effects of controlled-release urea combined with normal urea (CRUNU) on stem and root lodging and yield in maize have been rarely reported. Therefore, we conducted a field trial for three years between 2020 and 2022 using two N fertilizer types (CRUNU and normal urea (NU)) and three N application levels (low: 135 kg N ha–1; medium: 180 kg N ha–1; and high: 225 kg N ha–1) to evaluate their effects on stem and root lodging and the yield in maize, and the factors involved. The results showed that, compared with NU, CRUNU reduced the stem and root lodging rate under the three N application rates, and all were lowest under the medium N application rate. The decreased stem and root lodging rate was mainly attributed to the improved the synchronization of nitrogen supply and demand, reduced population traits (plant height, ear height, and center of gravity height), improved morphological traits (length and mass density) for the basal second, third, and fourth internodes (I2, I3, and I4), increased mechanical properties (stem breaking strength and rind penetration strength), greater stem lodging resistance index (SLRI), enhanced chemical compositions (lignin and its related synthetase activities, cellulose, and hemicellulose) in I2, I3, and I4, and increases in the stem bending strength, root average diameter, and vertical root-pulling resistance under CRUNU. In addition, the SLRI values for different internodes followed the order of: I2 > I3 > I4, thereby indicating that I2 and I3 played important roles in stem lodging resistance. Furthermore, compared with NU, the maize grain yield increased by 1.27–44.83% under CRUNU with the three N application rates. In particular, there was no significant difference in the grain yield between the high and medium N application rates under CRUNU. In conclusion, CRUNU combined with N application at a rate of 180 kg ha–1 may be a superior N fertilizer management method.