With an increasing population and changing diet structure, summer maize is increasingly becoming an important energy crop in China. However, traditional farmer practices for maize production are inefficient and unsustainable. To ensure food security and sustainable development of summer maize production in China, an improved, more sustainable farmer management system is needed. Establishing this system requires a comprehensive understanding of the limitations of current farming practice and the

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... ways it could be improved. In our study, 235 plots from three villages in the North China Plain (NCP) were monitored. Maize production on farms was evaluated; our results showed that the maize yield and nitrogen partial factor productivity (PFP N ) were variable on smallholder farms at 6.6-13.7 t ha -1 and 15.4-88.7 kg kg -1 , respectively. Traditional farming practices also have a large environmental impact (nitrogen surplus: -64.2-323.78 kg ha -1 ). Key yield components were identified by agronomic diagnosis. Grain yield depend heavily on grain numbers per hectare rather than on the 1 000-grain weight. A set of improved management practices (IP) for maize production was designed by employing a boundary line (BL) approach and tested on farms. Results showed that the IP could increase yield by 18.4% and PFP N by 31.1%, compared with traditional farmer practices (FP), and reduce the nitrogen (N) surplus by 57.9 kg ha -1 . However, in terms of IP effect, there was a large heterogeneity among different smallholder farmers' fields, meaning that, precise technologies were needed in different sites especially for N fertilizer management. Our results are valuable for policymakers and smallholder farmers for meeting the objectives of green development in agricultural production.