Optimize nitrogen application rate and planting density to improve the yield and quality of silage maize in China

Objectives The yield of silage corn in China shows an increasing trend from south to north, while there is a negative correlation between yield and quality. This study aims to coordinate the nitrogen (N) fertilizer application rate and planting density of silage corn (Zea mays L.) and establish an optimized cultivation and nutrient management model that synergistically enhances both yield and quality.

Methods Using the keywords “silage corn” or “forage corn” “yield” and “quality”, a total of 106 articles published from 2004 to 2024 were retrieved from the China National Knowledge Infrastructure (CNKI). This yielded 1343 sets of yield data and 295 to 765 sets of quality data. From these, 152 complete samples containing data on nitrogen application rate, planting density, yield, and six quality indicators were selected for analysis. By entropy weighting method, the weight coefficients of the quality indicators—starch, relative feed value, crude fat, crude protein, acid detergent fiber, and neutral detergent fiber—were quantified as 28.2%, 17.0%, 16.6%, 16.2%, 12.6%, and 9.5%, respectively, to calculate the comprehensive quality score for each sample. Furthermore, the NSGA-Ⅱ multi-objective optimization algorithm was employed to maximize both yield and comprehensive quality score, thereby determining the optimal combination of nitrogen fertilizer application rate and planting density. Based on this, the sample yields were divided into low, medium, and high categories using the 25% and 75% quantiles, and recommendation intervals were determined by ±5% of the mean of the corresponding optimal solutions for each category, with differentiated management suggestions proposed.

Results Yield increased with increasing nitrogen application rate and planting density (R² values of 0.17 and 0.13, respectively). The comprehensive quality score exhibited a significant quadratic relationship with nitrogen application rate (R²=0.31) and decreased with increasing planting density (R²=0.13). The NSGA-Ⅱ optimization results indicated that the N application rates in the Pareto optimal solutions were concentrated in 246−296 kg/hm², with planting densities ranging from 6.75×10⁴ to 10.50 ×10⁴ plants/hm². Based on these findings, a management plan was proposed: for fields with low yield potential, nitrogen application rates of 262−292 kg/hm² and densities of 6.80×10⁴ −7.52×10⁴ plants/hm² were recommended; for fields with medium yield potential, nitrogen application rates of 257−284 kg/hm² and densities of 7.98×10⁴−8.82×10⁴ plants/hm² were recommended; for fields with high yield potential, nitrogen application rates of 248−275 kg/hm² and densities of 9.41×10⁴ −10.40×10⁴ plants/hm² were suggested.

Conclusions Yield demonstrated a notable upward trend as the N application rate increased, whereas comprehensive quality displayed a significant parabolic relationship with N application rate. Planting density had a comparatively minor effect on yield but exerted a certain negative influence on nutritional quality. Taking into account the yield potential of farmland, the following recommendations are made: for fields with low yield potential, nitrogen application rates ranging from 262 to 292 kg/hm² and densities between 6.80×10⁴ and 7.52×10⁴ plants/hm² are advised; for fields with medium yield potential, nitrogen application rates of 257−284 kg/hm² and densities of 7.98×10⁴−8.82×10⁴ plants/hm² are recommended; for fields with high yield potential, it is suggested to reduce nitrogen application rates to the range of 248−275 kg/hm² and increase planting densities to 9.41×10⁴ −10.40×10⁴ plants/hm².