Objectives In response to the challenges of indistinct nutrient requirements, low fertilizer efficiency, and subpar forage quality in the silage maize production system within the saline-alkali region of the agro-pastoral transitional belt in the northern Loess Plateau, this study investigates the impact of various nitrogen fertilizer forms and application levels on the nutrient demands and nutritional quality of silage maize. The objective is to provide scientific guidance for the efficient, high-yielding, and environmentally sustainable development of forage production in this area.

Method This study was conducted in Donghuiyao Village, Yingxian County, Shuozhou City, Shanxi Province, from 2022 to 2023, where a two-year field experiment was carried out. The tested silage maize variety was Dajingjiu 26. Using a split-plot experimental design, the main treatments included two types of nitrogen fertilizers: calcium ammonium nitrate (N) and urea (U), with four nitrogen application levels as sub-treatments (90, 180, 270, and 360 kg/hm²), along with a control group with no nitrogen application (CK). In total, nine treatments were studied to investigate the impact of different types of nitrogen fertilizer and application levels on silage maize yield, nitrogen uptake, and forage quality.

Result The dry matter accumulation, yield, and nitrogen accumulation of silage maize under the ammonium calcium nitrate (N) and urea (U) treatments showed a trend of initially increasing and then decreasing with higher nitrogen fertilizer application, reaching their highest values at an application rate of 270 kg/hm². By fitting a quadratic function to nitrogen application and silage maize yield, the optimal nitrogen application rates for urea and calcium ammonium nitrate were found to be 293.5 and 283.1 kg/hm², respectively, resulting in the highest yields of 80.37 and 90.95 t/hm². As nitrogen application increased, the acid detergent fiber and neutral detergent fiber content in silage maize gradually decreased. The relative forage value and total digestible nutrient content of silage maize showed an increasing trend, followed by stabilization with increasing nitrogen application. Type of fertilizer significantly influenced the dry matter accumulation, yield, and nitrogen accumulation of silage maize. Calcium ammonium nitrate application led to an increase in dry matter accumulation by 2.55% to 18.05%, nitrogen accumulation by 5.44% to 12.24%, and silage maize yield by 0.04% to 18.05% compared to urea application. Except for the total digestible nutrient content in 2022, the fertilizer type had no significant effect on acid detergent fiber, neutral detergent fiber, relative forage value, or total digestible nutrient content.

Conclusion Compared with urea, calcium ammonium nitrate improves the nitrogen use efficiency of silage maize, leading to increased yields and higher economic returns. Therefore, in the saline-alkali areas of the agro-pastoral transitional zone near Yanmen Pass, the application of 283.1 kg/hm² of ammonium calcium nitrate can synergistically enhance yield, nitrogen utilization efficiency, forage quality, and the overall forage value of silage maize. This approach represents an effective nitrogen fertilizer management strategy for optimizing high-yield silage maize production in this region.