Assessing the heterogeneity and persistence of farmers' maize yield performance across the North China Plain

The gap between yield potential and average farmers' yield measures the capacity for yield improvement with current technology. The North China Plain (NCP) is a major maize producing region of China, and improving maize yield of NCP is essential to food security of the country. Some previous studies have found a substantial maize yield gap in this region (similar to 100% of average yields), whereas others have reported much smaller gaps. This study used remote sensing estimated yield at 30-m resolution to quantify county level yield distributions, and then used these distributions to calculate yield gaps and the persistence level of yield for 76 counties in NCP. The average yield was 8.66 t/ha across county years, and the averaged county-level yield gap, as measured by the difference between the top 10 percentile of yields and the average yield of each county, was 0.76 t/ha, or 8.7% of the average yield. When measured as the difference between maximum and average yields in each county, the estimated gap increased to an average of 31%. We also evaluated the persistence level of farmers' yield performance, as an indicator of how much gap might be reduced by propagating agronomic practices of the highest yielding farmers. The average of yield gap persistence was 25.9% of the average yield gap, or 2.3% of average yield with a range from 0.4% to 5.3% across counties. The distance to major rivers was identified as one factor with a significant effect on yield. Nevertheless, there was tremendous spatial heterogeneity in yield persistence level across NCP, and further analysis within individual counties is required to better prioritize means to shrink the yield gap. (C) 2017 Elsevier B.V. All rights reserved.