Objective  Reducing application of controlled-release fertilizers can effectively increase soil nitrogen (N) levels, reduce N input, and reduce environmental pollution. Therefore, the reducing application amount of controlled-release fertilizers to regulate soil N levels and maintain summer maize yield is of great significance for guiding scientific fertilization.

  Method  Five treatments were set up for no N fertilizer (N0), 100% regular urea (FP), 80% regular urea (LFP), 100% formulated controlled-release fertilizer (CRF) and 80% formulated controlled-release fertilizer (LCRF). Soil NH₄⁺-N, NO₃⁻-N, enzyme activities and yield were determined in these treatments.

  Result  The results showed that the mixed application of common urea and controlled-release N fertilizer could not only meet the nutrient requirements in the early growth period of summer maize, but also significantly increase the contents of NH₄⁺-N and NO₃⁻-N in the soil during the later growth period of summer maize, and significantly increase the activities of nitrate reductase and urease in the soil. At the jointing stage, flowering stage and maturity stage, the soil nitrate reductase activities in the CRF treatment increased by 72.9%, 40.9% and 58.8%, respectively, and the soil urease activities increased by 24.6%, 95.9% and 29.2%, respectively, compared with the FP treatment. The 20% reduction of formula controlled-release fertilizer treatment could still maintain the N level in the late growth stage of summer maize. And the LCRF treatment increased the NH₄⁺-N and NO₃⁻-N contents in the mature stage soil by 8.8% and 13.9% compared with the FP treatment. The activities of nitrate reductase and urease activities in the LCRF treatment were higher than those of FP treatment in each growth period, which met the requirements of maize growth and improved fertilizer utilization rate.

  Conclusion  In summary, the formulated controlled-release fertilizer can not only realize the one-time fertilization to meet the N fertilizer demand of the summer corn growing season, but also effectively improve the N fertilizer utilization efficiency, so as to realize the weight-loss and high-efficiency production of summer maize.