["Agribusiness, Volume 42, Issue 2, Page 460-472, Spring 2026. ", "\nABSTRACT\nAgricultural mechanization services (AMS) are important for promoting sustainable agricultural development. However, little is known about the effect of outsourcing fertilizer mechanization services (FMS) for fertilizer application to different types of service providers. This study simultaneously investigates the determinants and effect of outsourcing FMS to different types of service providers for fertilizer application in rural China. The multinomial endogenous treatment effects model that accounts for potential selection bias and endogeneity is employed to analyze cross‐sectional survey data of wheat producers. The results reveal that the likelihood of outsourcing FMS is influenced by household (gender, education, off‐farm employment, and risk attitude) and farm (farm size, land topography, soil fertility) characteristics, membership to cooperative, and the availability of AMS at village level. The treatment effect estimates suggest that outsourcing FMS can decrease fertilizer application by at least 6.6%. Outsourcing both FMS and fertilizer supply has a greater reducing effect on fertilizer application compared to only outsourcing FMS. Besides, outsourcing both FMS and fertilizer supply to organization providers has a higher effect on reducing fertilizer application and enhancing yield compared to outsourcing to individual service providers. The results have policy implications for promoting agri‐environmental sustainability in the agricultural sector.\n"]