Assessing changes in potential yields and yield gaps of summer maize in the North China Plain

In recent years, China's crop production growth rate has decreased. This has provoked questions on whether the grain yields have reached their potential. Taking the North China Plain (NCP) as the study area, this study first simulated the potential yield of an irrigated maize crop with the WOFOST model, using daily weather data for 1960-2017. The yield gap was quantified for 1998-2017, and finally, the total potential maize production was estimated. The results indicate that during 1960-2017, the average potential yield for the region varied annually from 9.5 to 13.5 t ha(-1), showing an obvious downward trend at a rate of 37.6 kg ha(-1) per year. The long-term mean potential yield at all 327 counties ranged from 9.9 to 13.7 t ha(-1), increasing from south to north. The annual maize yield gap was between an average of 2.7-6.0 t ha(-1) (29.0%-51.3%) of the potential yield for the NCP during 1998-2017. At county-level, the yield gap varied between 1.9 and 7.8 t ha(-1) and exceeded 5.0 t ha(-1) for 99 counties (30.3% of all counties). Attainable yields can be increased by 0.1-5.2 t ha(-1) at county-level, and by 2.2 t ha(-1) for the whole NCP, implying that the maize production has the potential to increase with 20.8 Mt. To increase maize production, the focus areas should be the southcentral NCP, which have a larger yield gap during 2012-2017.