Effects of Nitrogen Rate on Silage Maize Yield in China: A Meta-Analysis

Silage maize is an important forage crop in China and globally. Applied nitrogen (N) is crucial for increasing the harvest yield (aboveground dry matter) of silage maize. However, there is a lack of information on how nitrogen rate affects the harvest yield of silage maize in different planting regions and under different climatic and soil conditions in China. A meta-analysis was conducted to quantify and evaluate the effects of N rate on the harvest yield and N fertilizer contribution rate of silage maize in China and different planting regions in the country based on research published from 2000 to 2025. The effects of mean annual temperature, annual precipitation, soil properties, planting density, and cultivar used on the maize yield response were also investigated via subgroup analysis. The means of the N rate, harvest yield, and N contribution rate for silage maize in China were 211 kg ha−1, 20,117 kg ha−1, and 27%, respectively. In the southwest hilly and mountainous region, silage maize exhibited the highest harvest yield-change rate (55.41%) under a N rate of >0–100 kg ha−1. In Northern China, the Huang-Huai Plain region, and the southern hilly region, the maximum harvest-yield-change rates for silage maize (31.42%, 54.11%, and 42.66%) were observed at a N rate of >200–300 kg ha−1. In northwest inland China, the maximum harvest-yield-change rate (50.76%) of silage maize occurred at a N rate of >300 kg ha−1. Furthermore, the aggregated boosted tree algorithm was adopted to quantify the relative contribution of N rate, annual mean temperature, annual precipitation, soil pH, soil organic matter, soil type and texture, cultivar selected, and planting density to the harvest yield and N contribution rate of silage maize. Soil type made the greatest contribution to the yield of silage maize in China, accounting for 41.36%, followed by cultivar (40.28%) and planting density (5.97%), and the total contribution of the three factors reached 87.61%. Soil type exhibited the highest contribution (26.35%) to the N contribution rate of silage maize in China, followed by cultivar (22.36%) and planting density (15.11%). The combined contribution of the three factors was 63.82%. Based on the dual criteria of maximizing harvest yield and the N contribution rate, the optimal N rates found for silage maize were 173–300, 110–200, 311–395, 168–270, and 92–270 kg ha−1 for Northern China, the Huang-Huai Plain region, northwest inland China, the southern hilly region, and the southwest hilly and mountainous region, respectively. Meanwhile, in Northern China, the Huang-Huai Plain region, northwest inland China, the southern hilly region, and the southwest hilly and mountainous region, the increase in the yield of silage maize at harvest reached its maximum, and the corresponding silage maize cultivars were Yayu 8, Baimaya, Xinyu 9, Aoyu 5102, and Yuqingyu 3, respectively. This study provides reasonable guidance on suitable N rates for improving the yield and N contribution rate of silage maize in China and various other planting regions.