Spatio-temporal changes and influencing factors of grain yield based on spatial smoothing method in dryland farming regions

As water constraints become increasingly severe in Northern China, it is of great significance to study the grain yield pattern and its driving factors in dryland farming regions. Based on the county-level grain statistics from 1995 to 2015, combined with land use raster data and other materials, we studied the spatial pattern and process of grain yield in dryland farming regions of the Northeast and North China Plain using spatial smoothing methods. In addition, the natural and socio-economic driving factors of grain yield in different agricultural regions were investigated. Our results showed that: (1) In the past 20 years, the grain yield increased steadily and high production area expanded gradually in the dryland farming regions of Northeast and North China Plain, with obvious spatial agglomeration characteristics. And the total grain yield in the plain of North China dryland farming regions was higher than that in dryland farming regions of the Northeast China Plain. (2) The main increase rate of grain yield exhibited a medium speed, followed by slow speed, high speed increase, and absolute reduction in production. And increase rate of the grain yield in the dryland farming regions of the Northeast China Plain was higher than that in the North China Plain. (3) The per unit area yield of grain in the dryland farming regions of Northeast China Plain was higher than that of the North China Plain. And after the spatial smoothing processing, the pixel frequency of per unit area yield of grain generally exhibited a Gaussian distribution, which is consistent with the objective laws. The peak value of histogram pixel gradually moved to the right, and the per unit yield grid showed a gradual decentralization trend over time, indicating that the regional yield gap increases with the overall improvement of cultivated land productivity. (4) The mean annual temperature among the natural factors had the highest correlation with the per unit area yield of grain of the agricultural regions in Yan-Taihang mountain foothill plain. The annual precipitation and confluence capacity exhibited the highest correlation with the per unit area yield of grain of the agricultural regions in Ji-Lu-Yu low-lying plain. The soil type showed the highest correlation with the per unit area yield of grain of the agricultural regions in Songnen-Sanjiang plain. (5) The correlation analysis of per unit area yield of grain with socio-economic factors showed that grain production was gradually shifting from labor-intensive to technology-intensive. And the application of agricultural machinery obviously contributed to the study area, especially to the Northeast dryland farming regions of China. The application of chemical fertilizers had always played a significant role in improving grain production in the study region. And irrigation conditions played a critical role in ensuring grain production in the dryland farming regions of North China Plain. In summary, the results of our study are helpful for the research of spatial-temporal pattern of grain yield, and can provide references for the maintenance of high yield, stable yield and cultivated land conservation in different agricultural areas.