Abstract:The summer maize yields and partial factor productivity of nitrogen (N) fertilizer (PFP N , grain yield per unit N fertilizer) on smallholder farms in China are low, and differ between farms due to complex, sub-optimal management practices. We collected data on management practices and yields from smallholder farms in three major summer maize-producing sites-Laoling, Quzhou and Xushui-in the North China Plain (NCP) for two growing seasons, during 2015-2016. Boundary line analysis and a Proc Mixed Model were used to evaluate the contribution of individual factors and their interactions. Summer maize grain yields and PFP N ranged from 6.6 t ha −1 to 14.2 t ha −1 and 15.4 kg kg −1 to 96.1 kg kg −1 , respectively, and averaged 10.5 t ha −1 and 49.1 kg kg −1 , respectively. The mean total yield gap and PFP N gap were 3.6 t ha −1 and 43.3 kg kg −1 in Laoling, 2.2 t ha −1 and 24.5 kg kg −1 in Xushui, and 2.8 t ha −1 and 41.1 kg kg −1 in Quzhou. A positive correlation was observed between the yield gap and PFP N gap; the PFP N gap could be reduced by 6.0 kg kg −1 (3.6-6.6 kg kg −1 ) by reducing the yield gap by 1 t ha −1 . The high yield and high PFP N (HH) fields had a higher plant density and lower N fertilization rate than the low yield and low PFP N (LL) fields. Our results show that multiple management factors caused the yield gap, but the relative contribution of plant density is slightly higher than that of other management practices, such as N input, the sowing date, and potassium fertilizer input. The low PFP N was mainly attributed to an over-application of N fertilizer. To enhance the sustainable production of summer maize, the production gaps should be tackled through programs that guide smallholder farmers on the adoption of optimal management practices.