Maize potential yields and yield gaps in the changing climate of northeast China

Northeast China (NEC) is not only one of the major agricultural production areas in China, but it is also the most susceptible to climate variability. This led us to investigate the impact of climate change on maize potential yield and yield gaps in this region, where maize accounts for about 30% of the nation's production. The APSIM-Maize model was calibrated and validated for maize phenology and yields. The validated model was then used to estimate potential yields, rain-fed potential yields, and yield gaps for assessing the climate impacts on maize productivity in NEC. During maize growing seasons from 1981 to 2010, the analysis indicates a warming trend all across NEC, whereas the trends in solar radiation and total precipitation tended to decrease. When the same hybrid was specified in APSIM for all years, a simulated increase of maximum temperature resulted in a negative impact on both potential yield and rain-fed potential yield. A simulated increase in minimum temperature produced no significant changes in potential or rain-fed potential yield. However, the increase of minimum temperature was shown to result in a positive impact on the on-farm yield, consistent with our finding that farmers adopted longer season hybrids for which the increase in minimum temperature provided better conditions for germination, emergence, and grain filling during night time. The gap between potential and rain-fed potential yields was shown to be larger at locations with lower seasonal precipitation (<500 similar to mm). Our results indicate that regions with the largest yield gaps between rain-fed potential and on-farm yields were located in the southeast of NEC. Within NEC, on-farm maize yields were, on average, only 51% of the potential yields, indicating a large exploitable yield gap, which provides an opportunity to significantly increase production by effective irrigation, fertilization, herbicide, and planting density in NEC.